1/29/13

Arctic Front to Slam into the Region Late Wednesday!

Mother Nature will put the kabosh on yet another prelude to spring as the air mass that froze us just last weekend; aggressively comes back home to roost. After snow, sleet, freezing rain, heavy rains and thunderstorms; Mom Nature will leave us where she found us...in the deep freeze; a flash deep freeze!

The Arctic cold will slam into the region late Wednesday and change any rain showers to light snow and snow showers. Latest indications now indicate enough moisture and energy will remain on the backside of the front (as waves of low pressure move along it) to generate a light accumulation of snow Wednesday night into Thursday. This, along with sharply falling temperatures from the 50s to near 60 early in the day to the 30s by the evening and teens on Thursday morning, will result in residual water on untreated roads and walkways to flash freeze causing slippery driving and walking conditions. Undoubtedly; "walking like a penguin conditions" will become common-place Wednesday night into Thursday. 

Overnight into Wednesday: 

In the meantime; Hang on, 'cause it's gonna be a bumpy ride!

It not hard to see with a 250 MB /35000 Ft/ jet core where our spring warmth is coming from on the second map below; note the strong sub-tropical wind max across northern Mexico and Texas arched northeastward into the Lakes! Meanwhile; the foreboding of Arctic air is just beginning to get entrained into this mammoth system over the Pacific Northwest aloft.

On the third map; the surface reflection of this strong jet is in the form of a stationary from draped from Michigan, south southwest into a deepening storm/low pressure center over Illinois. As the jet core races northeast it will accelerate the front as an Arctic cold front Wednesday. Ahead of the front, a line of strong to some severe thunderstorms area expected overnight well northeast into the Mid- Mississippi and Ohio Valleys (see insert first map; severe wx outlook for the overnight hours).

While the bulk of the severe weather should remain south of Southeast Lower Michigan, some thunderstorms and strong shifting winds are likely as the apex of the instability moves across the region overnight and then again; as the Arctic front roars through during Wednesday afternoon and evening. Gusts of winds during these periods may be as high as 35 - 50 mph considering the winds just aloft. With the instability and convective nature of the beast; it is quite possible some of that wind will make it to the surface; irrespective of a shallow stable lower layer! Extra-ordinary forceful winds of near hurricane speeds /75 mph/ are projected to cross the region aloft /5000ft/ toward sunrise. Hang on; that 12Z weather balloon release at DTX should track out like a bat out of hell as she lifts north - northeast into the jet!  LOL
      
With the rest of the snow melt and still mainly frozen ground; the heavy showers and scattered thunderstorms will continue lowland flooding into Wednesday before the freeze.


                                                                 SVR WX OUTLOOK OVERNGHT-WEDNESDAY MORNING





By Wednesday evening (fourth map); the balmy air for January will be rudely shunted eastward and Mom Nature reminds us what season it truly is! A second re-enforce of Arctic air (fifth map) will be overspreading the region.



 Look for below normal temperatures and periods of snow showers Thursday into into Sunday. Highs will be in the teens and 20s; while lows fall into the single digits to teens.


Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian




1/27/13

After a Cold Week; a Volatile Week Containing Freezing Rain, Possible Thunderstorms, Record Warmth and More Snow!

After a period of rather cold and stable weather; things across Southeast Lower Michigan are about to become very volatile and changeable. The cold Arctic air that's encased the region the past week will be rudely shunted out of the region early in the week. The cold won't leave quietly however; as I look for snow, freezing rain and possible sleet...a mix of precipitation...to overspread the region overnight into Monday morning. Initially; snow accumulations from around an inch to as much as two to four inches will occur across the region...with the highest amounts over the northern and northeast half of the region.



While a light glaze (trace to three tenths of an inch in coldest areas) is likely over much of the region initially; atmospheric conditions are not conducive for a major ice event for a number of reasons. First; the positioning of the Arctic high pressure that feeding the cold air into the region is east southeast of Southeast Michigan over the Mid-Atlantic rather than north or northeast. Second; The surge of the warmer air aloft (and lowering to the surface) will be rather predominant with much of the region climbing above freezing from the wee morning hours to the forenoon hours of Monday from southwest to northeast.  Third; It's rather dry aloft and some of the initial precipitation will be "eaten-up" through evaporation. All in all; still not the best of nights to be out and about across Southeast Lower Michigan.

After that initial mess; milder air will infiltrate the region Monday, eating away our snow cover with the warmer air, light rain and drizzle. With the milder air over the frozen ground, this it will be conducive for fog formation. A stronger push of warmer air will give us a prelude to spring Tuesday into Tuesday night as temperatures surge through the 50s to possibly as warm as around 60 at some locations. Keep in mind records for the time period are in the mid to upper 50s.

This spring-like, possible record warmth won't last long however, as a sharp cold front will be approaching the region Wednesday morning. This is liable to touch off some heavy showers and a few thunderstorms as the air becomes marginally unstable. The sharply colder air will spill over the region during Wednesday and changeover any residual moisture to snow. Depending on the changeover time, the intensity of a wave (low pressure) slated to form along the cold front and available moisture, some accumulating snow is possible from the midday to the evening hours of Wednesday.

Stay tuned for updates to this prediction of rather radical changes in the temperatures and weather the next several days. In addition; as things become more certian, I will include more maps for the most notable weather.

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian


1/26/13

THE 35TH ANNIVERSARY OF THE GREAT BLIZZARD OF 1978!

"A GREAT STORM IS UPON MICHIGAN"
THE GREAT BLIZZARD OF 1978!

Written by: William R. Deedler, Weather Historian - Southeast Lower MI

As with the huge snowstorm of December 1974 another even more powerful (in terms of intensity/extent) storm is of strong interest to all meteorologists who have studied winter storms in the Great Lakes. This storm is also of interest and remembrance to many longtime residents of the Great Lakes, the Upper Ohio Valley and Ontario, Canada who had to deal with winter's full fury late in January of 1978. In addition, the storm certainly casts many memories for those of us who were on duty and worked during the storm...while being in awe of the development and subsequent immense strength of this great monster. With the 25th anniversary of this Great Blizzard at hand, it is worth taking a step back in time to re-live this monumental example of nature's fury.

While there are several contenders for the worst blizzard ever to hit the Great Lakes in relatively modern times (since 1870 when records began in Detroit), the immense and intense Blizzard of January 26-27th 1978 must rank at or near the top along with the Great White Hurricane of 1913 with its similar track and powerfulness.

The incredible Blizzard of January 26-27th, 1978 evolved out of a winter that was infamous for cold and storms. The Winter of 1977-78 thus far had been one the coldest, since records began, in many areas from the Rockies eastward to the Appalachians. Mammoth blizzards occurred late in January and early February from the Midwest to the East Coast as strong Arctic plunges dove south into the country and met up with the warmer winds from the deep south. The winter of 1977-78 was similar to its predecessor (1976-77) in terms of cold. The main difference between the two winters, however, came in February. In 1977, temperatures moderated rapidly during February, while in 1978, the cold actually worsened - with several locations reporting their coldest recorded February to date. The Winter of 1977-78 is written down in the record books as Detroit's seventh coldest winter, Flint's fifth coldest and Saginaw's sixth. West of the Rockies, it was a different story as a dominant upper ridge of high pressure provided a relatively mild winter, with some stations even reporting one of their warmest winters on record.

The Great Storm

Since there were some forecasted variances of the intensity and track of the storm, and considering the primitive model of the day (LFM - Limited Fine Mesh), forecasters did an admirable job in forecasting one of the most severe winter storms ever to hit the Great Lakes Region.

A Winter Storm Watch was posted as early as Tuesday night, the 24th, for the southern half of the Lower Peninsula for Wednesday Night into Thursday. Gale Warnings for the Great Lakes were hoisted the following Wednesday morning, along with the Watch. A weaker system had moved through the region earlier during the day on Tuesday and already dropped some snow on the region (a Winter Storm Watch had been issued for this system as well, earlier on Monday, the 23rd). After Tuesday's snow, the headline on the Special Weather Statement that was issued by the NWS Tuesday evening read as follows: "Another Winter Storm Threatens Lower Michigan" and thus, a second Winter Storm Watch was officially posted.

Meanwhile, the ingredients of what would later prove to be a truly fascinating yet vicious winter storm were coming together from different parts of the country. As with the "White Hurricane of 1913," the massive storm actually began as two smaller but distinct storms. A strong low pressure with an attending arctic air mass was entering the Northern Plains by way of Northern Minnesota on Tuesday evening (24th). At the same time, another developing low pressure system was taking shape over the eastern Texas/Louisiana area.

The phasing of two distinct jet streams aloft proved to be the key as to the subsequent strength and massive extent of the storm. A very strong and energetic Arctic impulse surged almost due south and plowed the Arctic front through the Northern Plains late on the 24th. At the same time, another very strong upper wind impulse surged south through southern Arizona. These two jet streaks made up the larger North American jet stream as a huge upper ridge of high pressure along the West Coast of the U.S. diverted the powerful Pacific Jet north into Northern Canada. This northern jet (containing a wind max of 110 knots) then dove due south, like on a giant roller coaster, across the western U.S. as the second, subtropical jet (with an even stronger wind max of 130 knots) surged across southwestern states. On Wednesday (25th), a deepening area of low pressure made its way east across the Gulf States into Georgia by evening (surface | 500mb). Meanwhile, across the north, the Arctic front barreled east across the Upper Midwest into the Western Lakes by Wednesday evening.

Earlier that Wednesday morning, the Winter Storm Watch for Southeast Lower Michigan was changed to a Heavy Snow Warning, while a Travelers Advisory was issued for Western and Northern Lower Peninsula. Later, at the issuance of the evening forecast, the entire Lower Peninsula was upgraded to a Heavy Snow Warning. Meanwhile, a rapid deepening of the surface low over the southeast portion of the country also commenced on Wednesday evening. As the low intensified over Alabama and Georgia, Atlanta registered its lowest barometric pressure ever late on the 25th. At the same time, further north in Michigan, snow was falling over much of the Lower Peninsula. In and around the Ann Arbor and Metro Detroit, the snow mixed with or changed to light rain Wednesday night as slightly warmer air surged northwest 500mb chart, 00z January 26th, 1978; click to enlarge into that area ahead of the deepening storm. While the storm was organizing in the lower levels of the atmosphere over Georgia, the Subtropical and Arctic jet aloft began to merge and phase over the Southeast part of the country. This merging of jet streaks contained a wind max of 150 knots which helped induce a rapid intensification of the Georgia Low as it surged northward into West Virginia early on the 26th. Record low barometric pressures were set all along its path as an ominous track (trough) began to materialize toward the Eastern Great Lakes.

Bands of heavier snow spread north into much of Southern Lower Michigan during the very early morning hours of the 26th. Rain continued to fall, however, over the extreme southeast corner of Lower Michigan. At 1 AM EST, rain was observed at Detroit Metro Airport with the temperature comfortably above freezing at 36 degrees. Further north at Flint, however, sleet and freezing rain were falling as the temperature hovered around freezing. Air pressure tendencies were noted as falling rapidly /PRESFR/ and continued that way for several hours (in fact, several stations in this storms path had to re-adjust their barographs for station pressures traces that were BELOW initial chart scale).
The aforementioned Arctic cold front that was across the Western Great Lakes advanced steadily east into Lower Michigan as the main southern low underwent explosive deepening (this low's central pressure fell 40 millibars in 24 hours)! The central pressure was recorded at 28.28 inches as it tracked north across eastern Ohio, just west of Cleveland, at 7AM EST. As the low moved out over Lake Erie, the Arctic cold front over Southeast Lower Michigan was pulled sharply east into it's mammoth cyclonic circulation. Any residual rain over Southeast Lower Michigan quickly changed to heavy snow and blowing snow during the pre- dawn hours of the 26th. As the Arctic front plowed through the Cleveland area, the wind gusted to an incredible 82 mph! As the Arctic air flooded the Cleveland area, the temperature dropped from a relatively balmy 44 degrees at 4AM EST to a bitterly cold 7 degrees by 1000 AM EST.

Blizzard Warnings were hoisted across much of the Great Lakes and Upper Ohio Valley Region by daybreak Thursday. The center of the huge storm (surface | 500mb) continued to trek north northwest across Southwest Ontario (roughly between Chatham and London) while Detroit measured its lowest pressure reading at 28.34 inches at 650 AM EST. The incredibly deep center made its way north along the St. Clair River with Sarnia ON reporting the lowest pressure on land at 28.21 inches. Not only was the depth of this mammoth storm's center very impressive, so too was the extent of low pressure from its center. Even locations that were far removed from the storm's center also reported record low pressures. Stations such as Cincinnati OH, Rochester NY and Toronto ON and even as far east as Wilmington N.C., all recorded record low pressure readings from this monster. In fact, at Toronto, where records go back as far back as 1840, the lowest pressure reading of 28.40 inches broke the old record of 28.57 inches by 0.17 inches. In addition, dozens of other cities, with records going back a century, also recorded their lowest pressure reading of all time or, for at least the month of January. This massively intense storm was responsible for strong wind gusts as far away from the center as Boston /72 MPH/ and Chesapeake Bay Bridge /90 MPH/ with even damaging winds reported as far south as Tallahassee FL.

As the Arctic air circulated throughout the storm while it made its way over Lake Huron, the lowest pressure was reached around 950 millibars or a hurricane-like 28.05 inches! "A Great Storm is Upon Michigan" read the headline of the 800 AM EST Special Weather Statement issued by the National Weather Service Forecast Office in Ann Arbor that Thursday /26th/ morning. Heavy snow and blizzard conditions were extensive as wind gusts in excess of 35 mph whipped the snow into huge drifts across much of Southeast Lower Michigan. Other areas of Eastern Michigan, Indiana and Ohio reported near hurricane-force winds, heavy snow and temperatures hovering between zero and 10 above, resulting in extreme blizzard conditions. These conditions later expanded further east into Pennsylvania and West Virginia and prevailed into the night (26-27th) across much of the Eastern Great Lakes, Southern Ontario and the Upper Ohio Valley. With the storm generating copious amounts of snow and very strong winds, whiteout conditions were widespread. All land and air traffic came to a stand still in the affected regions. Several major roads were closed for at least two to three days, if not longer, while clean up got underway. Numerous NWS employees were stranded at work, home, or on the road somewhere between the two. Several employees worked double shifts into at least Friday (some longer) because of the impassable roads with others simply unable to get to work.
The Blizzard Warnings were allowed to die across Michigan during the forenoon hours of Friday, the 27th. Record 24 hour snowfall totals from the storm included, 16.1 inches at Grand Rapids, 15.4 inches at Houghton Lake and 12.2 at Dayton, OH. Snowfalls for the entire storm (25-27th) included a whopping 30.0 inches at Muskegon (some of which was Lake Michigan enhanced), 19.3 inches at Lansing and 19.2 at Grand Rapids. Snowfalls were less over Southeast Lower Michigan (mainly because of the rain that fell for a period) and included 9.9 inches at Flint and 8.2 inches at Detroit.
The following is a quote from the summary written about the storm by Meteorologist in Charge, C.R. Snider on January 30th, 1978 at the National Weather Service Ann Arbor:
"The most extensive and very nearly the most severe blizzard in Michigan history raged throughout Thursday January 26, 1978 and into part of Friday January 27. About 20 people died as a direct or indirect result of the storm, most due to heart attacks or traffic accidents. At least one person died of exposure in a stranded automobile. Many were hospitalized for exposure, mostly from homes that lost power and heat. About 100,000 cars were abandoned on Michigan highways, most of them in the southeast part of the state."
The employees of the National Weather Service Forecast Office in Ann Arbor had just set up shop at the new quarters at the Ann Arbor Federal Building a WEEK before the storm hit. The forecast staff had transferred from the Detroit Metropolitan Airport Office while the observing and radar staff remained at the airport. The majority of employees still lived in and around the metro Detroit area and all major roads between Detroit and Ann Arbor were blocked for approximately 18 hours due to the storm. Several employees put forth efforts beyond the call of duty, stated Mr. Snider in his storm report.

Yet, as mentioned earlier, the Winter was not yet over by any means as the month of February (after the storm) was brutally cold across much of country. The below normal temperature departures of February 1978 were strikingly similar to that of January 1978 (and in some places, February was actually colder). The average temperature for Detroit that winter came in at just 20.5 degrees /normal 27.1/ which again, made it the seventh coldest winter on record. Snowfall totaled a hefty 61.7 inches which made the winter of 1977-78 the eighth snowiest winter on record at Detroit. Flint's average temperature of 19.1 degrees made it the fifth coldest winter on record, but Flint received less snow than Detroit with 50.6 inches /19th snowiest/. Saginaw's winter average temperature of 17.9 degrees made it the sixth coldest winter on record and was accompanied by 55.6 inches of snow, making it the just the 20th snowiest winter.

1/18/13

Coldest Air of the Season Thus Far Due Next Week

The cold air spoken about on a few previous blogs will engulf the region by Sunday and hold over the region into at least mid week. An Alberta Clipper will surge east-southeast across the northern Lakes late Saturday and bring a brief burst of milder air before the Arctic air BLASTS the Great Lakes late Saturday into Sunday. By Monday evening; the Arctic express will be fully revved-up from the Arctic south-southeast thru Canada down into the Great Lakes and East.



Look for the Clipper to surge the Arctic front thru the region Saturday evening after a rather, breezy mild Saturday with temperatures rising into the 40s across Southeast Lower Michigan. Normal highs for mid-late January are in the upper 20s to lower 30s across the region.


By Tuesday evening; a broad, expansive Arctic high pressure will be sprawled over the Midwest to the East Coast bringing the core of the Arctic cold to the States. Much of the area is snow-free; so while temperatures originating in the Polar region will be below normal, they will moderate a bit over the snow-less region. Coldest of days; Monday into Wednesday will see highs struggle to rise to between 10 and 20, while lows fall to around zero to around 10 above.




After the surge of Arctic air passes; we will turn our attention to a developing low pressure system late in the week which will bring the threat of snow as it moves toward the southern Great Lakes.




Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian





1/15/13

World and National 2012 Weather Review

It was another warm year across the globe but even warmer conditions, relative to average were noted across the U.S. where it was the warmest year in the 1895 - 2012 time-frame (see national overview). Several eventful storms took place in addition to the warmth; see map and links below for some interesting reading.



State of the Climate: National Overview  Annual 2012

State of the Climate: Global Analysis  Annual 2012

Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian


 

1/9/13

Update 1/14 - Does Sudden Warming High Up in the Stratosphere Over the Arctic Foretell Much Colder Weather is in the Offing for Southeast Lower Michigan?

Update 1/14-
It was prudent on my part to offer cautious reasoning on the conflicting guidance on a substantial cold outbreak for this week back on 1/9. Some models were too hasty in bringing the brunt of cold air up in Canada southward into the Lakes. I summed up the blog with the following statement:

While colder weather should arrive after our "January Thaw" don't break out the extreme cold gear just yet!  This is something to watch for the next week or so, to see if the models change their consensus thinking and surge colder air into our neck of the woods!

It was a potent January thaw followed by colder, more seasonal temperatures that arrived for this week. For the near term; look for near seasonal temperatures for the rest of this week (1/14-19) with normal variability but briefly colder weather about Thursday. That being said; the coldest of air that remains locked-up in Canada now looks like it will finally get a more southward push late next weekend (1/19-20) on the heels of an Alberta Clipper/Saskatchewan Screamer type of storm.  More on that bugger later this week!
 
_____________________________________________________________________

1/9/2013
Over the past several years, meteorologists have studied the weather and climate high over the Polar Region. It's been noted when a sudden, sharp warming occurred high up in the stratosphere over the Polar region, it foretold of a change in the subsequent weather at the lower levels of the atmosphere... a sharp, notable COLD change to those areas affected.

A fascinating paper appeared in the Quarterly Journal of the Royal Meteorological Society entitled The association between stratospheric weak polar vortex events and cold air outbreaks in the Northern Hemisphere by Erik W Kolstad, Tarjei Breiteig and Adam A. Scaife. Basically 51 winters were researched to discover the relationship between the sudden stratospheric warming and subsequent cold outbreaks. Over eastern North America it was found it occurred about 50% or more of the time at peak phase.

This phenomenon, sudden stratospheric warming /SSW/ has occurred in the Arctic region during the past week or so (see chart below as of 1/7/12). The stratosphere is located roughly between 6 miles and 30 miles above the ground. After this occurs, many times in the past it forced cold air to build in the lower layers of the atmosphere. After the pooling of the frigin air (yes I know it says frigin rather than frigid - a mistake I chose to keep - a little levity there ;-) generally 10 to 14 days later, the cold air drives south but where it will go presents bigger problems. The exact location(s) of this cold or Arctic outbreak depends largely on the upper air jet stream at the time and other influences. Stratospheric warming events do lead to temperature drops in the Arctic, they don't necessarily have to have a core effect on the Great Lakes and Southeast Lower Michigan. Again, note the big warming on the chart!




Therefore; this is definitely an initial alert for the possibility of much colder temperatures in the offing BUT more must follow. Another tool that I've posted many times in previous articles/papers at the NWS and now here in my blog, is the projection of the Arctic and North Atlantic Oscillations. 

More often than not; when the Arctic Oscillation and larger encompassing North Atlantic Oscillation show a decline (or become negative) in the forecast, colder air is likely to invade the U.S. So step two, is to examine that data.

The projected AO and NAO is extremely erratic in the next 7-14 days. More so in the latest runs so NO assurance the coldest of air will be delivered here. While both show a general trend down or negative; the NAO has a few members that are completely opposite while the projection of the AO is extremely unstable! One of the widest ranges I've observed over the years, ranging from a +3 to a -6!





Taking a jaunt over the our friendly experimental NAO/AO projection page of Kyle MacRitchie at Albany (mentioned in earlier blog) for more clarification pretty much tells the same story.


While again, the NAO is projected to go negative, the extent of that negativity becomes more questionable because of the ensemble variance. Likewise and to a larger extent, so does the AO projection, below. Note as you get further out into February; it is very variable with the negative outlook. Why does it become less variable way out? I would imagine because the model has returned more to climate averages and thus; projects near average in March and early April. In any event in the near term; the NAO/AO are at odds as to the extent or magnitude of the trough expected to develop over eastern Canada and the States.



Another ensemble to take a gander at is the NCEP ENSEMBLE GFS 500H mean which shows the animated projected 500 MB flow for the next 360 hours over North America. Important; note the link I posted here started from Jan 9th's data and subsequent runs after are likely to vary as updated. To account for that, I also posted some of the maps in the Jan 9th time lapse.


NCEP Ensemble 500 mb Mean Z


NCEP Ensemble 500 mb Mean Z



NCEP Ensemble 500 mb Mean Z


 NCEP Ensemble 500 mb Mean Z

So; Does what happens in Canada, stay in Canada?

As you can see; it is very cold up in eastern and central Canada but the brunt of the cold at the 500 MB (Jet Stream) level, stays mainly up in Canada on this run. Ok, most of the data I've presented has been of GFS origin; what about the latest European?

At 120 hr, they look pretty similar:

Height 500 hPa ECMWF Mon 14.01.2013 12 GMT

At the 192H below; the Euro shows extreme low or cold heights up over James Bay but note the "bowling ball" is fairly contained (meaning the coldest of air stays up in Canada).

Height 500 hPa ECMWF Thu 17.01.2013 12 GMT

At the 240H; the Euro moves the "ball" east and it moderates significantly!


Height 500 hPa ECMWF Sat 19.01.2013 12 GMT

While colder weather should arrive after our "January Thaw" don't break out the extreme cold gear just yet!  This is something to watch for the next week or so, to see if the models change their consensus thinking and surge colder air into our neck of the woods!


Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian





1/2/13

December 2012 in the Top 10 Warmest Decembers; What Happened To Analogue Projected Cold December?

Back in late November, I wrote a blog on this winter's analogue years and what the predominate call was for DecemberClearly the predominant below normal trend called for by the analogues for December was wrong as one can see below it was the opposite; December ended up in the ten warmest Decembers on record at all three climate sites.

Top 20 Coldest/Warmest Decembers in Southeast Lower Michigan
 
RankDetroit Area*Flint Bishop**Saginaw Area***
ColdestWarmestColdestWarmestColdestWarmest
TempYearTempYearTempYearTempYearTempYearTempYear
117.8187640.6188116.1198937.2198216.2198935.31923
218.0198939.2188916.6200036.8192317.2200034.51982
319.2200038.1187717.4197635.4200618.8198334.42006
420.8198337.7192317.8195835.4196518.9197634.21931
521.5197637.4200620.1198334.7193119.0195834.12012
621.8191737.3198220.5194434.1200119.1191733.52001
721.8188037.2193120.8196333.6194119.5191933.41941
822.2198536.3191821.3198533.5201220.1196333.11936
922.4195835.9201221.7196033.4198421.0192433.02011
1022.5190335.9196522.2194533.3201121.3194433.01965
1122.8187835.8200122.4195032.8193921.5196032.41911
1223.0190935.6189122.9196232.4197121.6198532.31994
1323.1191935.5201123.0199532.3199822.0198032.21913
1423.2192435.5194123.1194232.2198722.0191432.01998
1523.3191035.4199423.2192432.1200322.2196232.01918
1623.8196335.3199823.9193732.1197922.2190331.51959
1723.8191434.8195624.0192632.0199422.4192631.41987
1823.9188634.6195924.3201031.7195922.5195031.41952
1924.7194534.3191324.3200531.7195222.5194531.41920
2024.8194434.1195724.4198031.5195622.5194231.21912



DETROIT...DECEMBER 2012
DY
MAX
MIN
AVG
DEP
DAY
1
57
37
47
12
2
57
50
54
19
3
63
47
55
21
4
63
41
52
18
5
43
29
36
2
6
40
27
34
1
7
43
36
40
7
8
42
35
39
7
9
40
35
38
6
10
42
33
38
6
11
36
26
31
0
12
43
24
34
3
13
44
24
34
3
14
48
29
39
9
15
46
32
39
9
16
53
45
49
19
17
45
39
42
13
18
43
34
39
10
19
40
34
37
8
20
46
35
41
12
21
35
30
33
5
22
35
27
31
3
23
38
21
30
2
24
35
24
30
2
25
33
22
28
0
26
32
27
30
3
27
32
17
25
-2
28
30
13
22
-5
29
31
22
27
0
30
30
15
23
-4
31
36
14
25
-1


So what happened? Why did much of the month turn out so mild and the projected pattern so wrong? It really wasn't until the last week or so of December that our temperatures settle down to "normal to slightly below" (see Detroit's December climatic temperature data above).

Oh, the cold pattern was in fact there; in Canada. Much of Canada and Northeast Pacific was cold during December as the cold Polar/Arctic air remained bottled-up north of the border and out over the Pacific Ocean. Ok then; why did it stay there and not blast down like so many other analogue years? An examination of the jet stream or 500 MB pattern holds the key here.

Let's analyze the monthly upper wind pattern for December 2012.

Added>>>Check out this animated 500 MB map. Set to December 2012, start at 00Z on the 1st, 20 day length at 12 hour intervals and let it roll! You will see that the majority of the 20 day animation is ruled by the nearly continuous upper low propagation out of Alaska southeastward. Only around the 9th thru the 11th is there a break with a full lat trough over the U.S. Note at the very end on the 21st, the deep trough that dives into the Midwest and through the Lakes.

While more subtle way up at 18,000 ft (map above), the areas of lower mean heights are reflected from Alaska southward out of the Pacific. Several times during the month, the cold air that pooled over the Arctic and headed south into Alaska spread southward (in the form of an upper low pressure) and plopped down over the northeast Pacific Ocean. Meanwhile; what air that did come into the country; modified over the ocean and spread east over a weak ridge of high pressure situated over the Mountain states before shooting off to the east across the Midwest, Great Lakes and East (white arrow). The remaining air over the northeast Pacific pushed up into western Canada and met with the main Polar/Arctic jet and continued east southeast across southern Canada. Until a change late in the month; much of the Midwest, Great Lakes and Ohio Valley was in "no-man's land" (which leads us to our vector wind map below).


This vector wind flow map shows the wind in vectors at 500 MB (18,000 ft). It also shows where the wind flow was stronger THIS December (the anomaly) compared to the past 30 year average. It is easy to see where the jet streak prevailed. The main core of wind vector (relative to normal or average) shot across the Aleutians (large red arrow) southeastward across the northeast Pacific, down across California (while weakening) and then spread out across the western and northern U.S. into central Canada. Another anomaly reflects the upper low out over the western Atlantic. Note the very light, almost nondescript wind over the Great Lakes. Our next map below, shows where the anomalous low and high heights that were found relative to normal.


It is seen clearly here where the 500 MB heights were well below normal and well above (relative to the 30 year average) while reflecting the below and above normal temperatures aloft. One last map on this December below; we'll look at is the 850 MB mean which shows closer to the earth (5,000ft) the mean heights. No doubt here, the below normal heights (compared to average) extended Alaska, across western Canada and into the west and south-central portions of the U.S. Above to well above normal heights at 850 MB show up well over north and eastern Canada.


Ok, that was December's upper wind pattern compared to average. Now; let's look at the analogue  500 MB mean wind flow from the Winter Outlook for the month of December. Note the difference, the BIG difference in the trough over eastern Canada and the second trough just poking south from Alaska.

The trough over Alaska and points south into the northeast Pacific Ocean (below) was much stronger and deeper this past December (reflected by the below normal heights). In other words; much of the cold that was headed for the eastern Canadian trough was diverted southeast over the northeast Pacific Ocean and then modified; in sort of a pseudo El Nino pattern, or more zonal pattern across the States. The cold air that flooded at times southeast from Alaska and the Arctic (shown by the upper low and arrow) was modified and then was somewhat "exhausted" as it tracked southeast over the ocean and phased with the Pacific jet. That is shown in all the maps whether it be the 500 MB heights, wind vectors or 850 MB heights. At the same time; the trough over eastern Canada contracted and pivoted northward and thus; pulled the coldest of air northward along with it.



Ok; then what happened the last week of December? Temperatures finally fell to normal to slightly below normal into early January. Looking at the following three maps during late December; note the deep trough pivoting out of the Desert SW and into the Midwest and Great Lakes while phasing with the eastern Canadian trough. Meanwhile; a newly formed ridge of high pressure develops and strengthens over Alaska and the northeast Pacific. This pattern is just the opposite from the one(s) depicted above that was seen much of December. In response to this change; the colder Arctic air that's been bottled over much of Canada surges south into the U.S.! This distinct change in the December pattern was culminated by our snowstorm on the 26th.







Epilogue:
So now what? Basically our pattern expected to develop earlier in December is now here...albeit three weeks late. Remember what I stated in the December analogue outlook blog?

"In regard to the above mentioned trends of winter; very rarely do you see these trends distributed nice and neatly in each winter month. On the other side of the coin; trends usually don't come all wrapped up nicely in individual monthly sequences; whether it be colder, warmer; snowier or snow-less than average. Many, many times prevailing trends of the month tend to overlap before or after the month. Meteorological oscillation patterns tend to prevail in a two to three week dominance. Therefore; when we look at composites for monthly sequences during the analogue years they a reflecting only the anomaly for the particular month not the dominant trend."

The first three weeks of December were ruled and dominated by a very mild pattern caused by the meteorological variables (and more) I stated above. We are now into the more seasonable pattern expected, with normal to below normal temperatures. Latest model trends indicate a continuation of the cold until a moderating trend starting this weekend (Jan 5th->) into next week. Another plunge of Arctic cold is suggested later the following weekend (12-13th time-frame). Welcome to winter and stay tuned!

Oh, BTW... three of our analogue winters DID start out with a mild or above normal December...all three had a cold or below normal January (but ya didn't hear that from me). ;-)


Making weather fun while we all learn,
Bill Deedler -SEMI_WeatherHistorian