Update 12/27/15 - Look for a New Battle of Air Masses and Jets to Commence at the Week's Open to Top off an Exceptionally Warm December!

 Update - 12/2715 

Freezing Rain and Strong Easterly Winds to Cause Problems in Areas with the Longest Periods of Freezing Rain Monday Afternoon into Early Night

Very little change to original analysis: 
If anything I am even more definite on the freezing rain and associated problems along with the strong gusty easterly winds which will accompany the battle of the systems mentioned below. Look for mixed precipitation to over spread Southeast Lower Michigan from south to north during the afternoon on Monday. Most of the freezing precipitation from this system should be in the form of sleet then freezing rain as a thicker warm wedge of air surges north quickly on the southern jet over the colder, relatively drier Polar air. Freezing rain will become rain during the evening into night from south to north with time.

Strong high pressure in excess of 1040+ MB will but-up against the deep but slowly weakening low pressure over the middle Mississippi and cause a decent period of freezing rain. Most of the region, especially away from the Southeast corner has the biggest risk of ice build-ups up to around .2" with some "hold-out freezing or below temperature areas" from Detroit suburbs northward of around .2" - to as much as .4 - .5" of ice possible. This along with strong easterly winds of 20 to 30 mph with gusts to near 40 will bring the risk of icy roads and falling weaker tree limbs and power outages where conditions hold on the longest before the changeover. Temperatures hovering from upper 20s to lower 30s early in the event will gradually rise into the lower to mid 30s by evening.

Original Post 12/26/15

Earlier in the month, I sent out a blog about how the second half of the month would see a resurgence of the battle of the two distinct air masses that would dominate our winter weather. I stated it would not all be about El Nino this winter and from time to time, an impressive battle would brew between the Pacific energized El Nino jet stream and the Polar/Arctic jet stream. All indications are a new battle will commence in style early this upcoming week but first; lets look at this exceptional December...

Thus far this December has held true to form for an El Nino December with unseasonably warm weather, so much so, it should be at the top of the warmest Decembers on record at all three sites; Detroit, Flint and Saginaw! Even though cooler weather is expected this upcoming week; it shouldn't be enough to knock Detroit's standing out of first place while both Flint and Saginaw are more than safe.

In our analogue section for this winter; December had the best chance at being above normal and notably so - but admittedly, not ranking in first place. In the December analogues, there were three distinct very mild Decembers; 1877 - 38.1, 1940 - 35.6 and 1982 - 37.3. Overall; early in the game, the Winter of 1940-41 seemed to be the best analogue fit for the entire winter but with the two very strong El Nino's of 1982-83 and 1997-98 contending for very close seconds. In winter of '97-98, which arguably has had a very good showing for similar Pacific "goings-on" this past summer into early winter, its December locally though was not all warm as this years - nor the other three mentioned. December of '97 had an average temperature of just 32.2 (didn't even make the top 20 warmest Decembers). The exceptional warmth occurred later in that Winter of '97-98.

Top 20 Coldest/Warmest Decembers in Southeast Lower Michigan
Rank Detroit Area* Flint Bishop** Saginaw Area***
Coldest Warmest Coldest Warmest Coldest Warmest
Temp Year Temp Year Temp Year Temp Year Temp Year Temp Year
1 17.8 1876 42.2 2015 16.1 1989 42.42015 16.2 1989 40.62015
2 18.0 1989 40.6 1881 16.6 2000 37.2 1982 17.2 2000 35.3 1923
3 19.2 2000 39.3 1889 17.4 1976 36.8 1923 18.8 1983 34.5 1982

The second half of December has not all been tranquil and nice as our former air mass battle that occurred last week; brought an outbreak of severe weather over the Midwest and South - and a very rare tornado in Southeast Lower Michigan near the border of Canton and Plymouth. Never had a tornado been reported in Michigan during the month of December - a very rare bird indeed! This severe weather outbreak across the country was preceded by record warmth over the Midwest and East. Detroit broke an very old record high from 1893 /56/ with a 58 on the 23rd...while Flint topped the 60 mark with a 61 for both the 23rd/24th. Its previous records occurred in 1982 (an analogue) with 55 and 56 respectively. Other warm records occurred during the month and can be found here.

Now on to our new battle...

This time around an intense low pressure center over Texas expected to produce a news worthy blizzard over portions of eastern New Mexico and western Texas (see map) overnight into Sunday.

Dawn Sunday 12/2715

The deep low will track north northeast aided by a strong jet streak over the south which came aboard from the Pacific. Note the 135K jet feeding into the storm at 250 MB at that time.

As the low approaches, the cold dome of high pressure will glide across Southern Canada. Timing of these systems, along with cold air in place after being advected in Sunday by the high pressure will determine what sort of mess  (snow, sleet and freezing rain) will be on the docket for Monday and Monday evening. in addition; ground temperatures are unusually warm for late December which only complicates matters. At this time, the risk of mixed precipitation will be the greatest at the onset of the approach of the low later Monday.

The surge of moisture remains robust even with the cold, dry air and subsidence advected in by the 1040+ high pressure - a fairly impressive strength. And thus, our battle commences locally between the deep low moving north northeast toward
western Illinois/eastern Iowa and large Polar high to our northeast in Canada. this will also create strong easterly winds across the region. One thing noted at this time is the remarkable agreement with various models on positioning and affects of the aforementioned systems.

It's interesting and passing to note, a few days ago this storm was progged to move more northeast into the Ohio Valley, which would have put Southeast Lower Michigan in heavy snow and/or a possible ice storm. That solution remains more transitory at this time as the air masses and jets have become bettered sampled. That is not to say Southeast Lower Michigan is out of the woods for mixed precipitation and possible icing, just not extent that was telegraphed a few days ago. This system appears to have enough wind at its sail to surge far enough northward to drag milder air back over the region.

At this time; the best chance for mixed precipitation runs from Monday afternoon into mid evening; the map below /Mon, early eve/ shows the classic mixed precipitation of snow, sleet and freezing rain set up when the clash of air masses takes hold over a the region. Picture warm, moist air being pushed northward aloft while colder, around freezing or below air remains trapped below near the ground. If a stand-off develops, an extended period of mixed precipitation, including destructive freezing rain as it accumulates on surfaces. The warm air is expected to win the battle and therefore, an extended period of freezing rain is not anticipated. However, the situation will be watched as new guidance and actual events unfold.

In any event, look for a mix of precipitation to move into the region later Monday into Monday evening with icing to affect mainly "exposed in the air items" as opposed to warmer ground surface areas, including roadways. Temperatures should hover in the lower to mid 30s for a time until the low pressure and jet streak has enough "umph" to push aside the cold residual affects of the high pressure. Any mixed precipitation accumulation is expected to be limited and transitory over extreme Southeast Lower Michigan with a slower change over time as one moves into Detroit's northern suburbs and points north and northeast toward Saginaw and the Thumb. At this time I look for ice to accumulate any where from a trace over the extreme southern regions to up around a 1/4" possible further north before any changeover to rain.

Various model solutions for Mon eve:

 Any important updates will be forthcoming for this holiday period.

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

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