Second Half of Winter ~ Same as the First?

The actual temperature trend of the winter has unfolded as suggested by preferred Winter Analogues (see table below and clips from original outlook). Basically after the warm fall  (especially November), research suggested a change in the trend would commence in December. A sharper contrast in the warm pattern was projected with a pattern change to more seasonal weather. Colder temperatures more typical for early winter were in the offing as December unfolded.

 

In my opening Winter 2024-25 Outlook headline; I questioned "Another milder winter in store, is this becoming a habit - or is it?" mainly because last winter (2023-24) was like a perpetual fall in Michigan or basically, like a "Kentuckian Winter".  In addition; many of our previous winters have been predominately mild with just a few weeks to month of real cold winter weather. Original Winter 2024-25 Outlook.

 

Best thing to do is to compare what has transpired the past few months, compare it to analogues and trends, also look at hemispheric patterns from previous similar analogue winters and patterns locally. We've got at least 3 analogues that fit the bill, but which one(s) if any, will pan out into April?

 

First, lets check the temperature/precipitation pattern for the first half of the cold season...  

Dec Temp/Pcpn: Both temperatures and precipitation showed the beginning of the winter milder and wetter with 3.27" recorded. However; colder spells came more frequently with the monthly average coming in mainly below normal until just after Christmas when a burst of warmer weather boosted the average 2.0 degrees above.

Jan Temp/Pcpn: a complete reversal in both temperature and precipitation came to fruition with both below normal. With an average temperature of 23.0, the average departure came in just shy of 3.0 degrees /-2.8/ below normal.

 

Colder snaps did indeed start in December but they were offset enough with warmer spells mainly late in the month. While November's average temperature was nearly +7.0 degrees above normal; December's dropped to just +2.0 degrees above normal with January's average falling -3.0 degrees below normal - quite a dramatic turn-around (a departure turn-around of 10 degrees). The colder trend is easily seen and verified.

 

Interestingly, this did reflect all of the analogues overall trend change from the warmer fall into the colder first part of Winter. When just looking at each individual month below or above temperatures, averages were projected to fall closer to below. The analogues strongly suggested the trend of colder weather coming in the first half of the winter starting sometime in December. Later, as the winter to spring evolved, it became more mixed again with averages actually reverted back to above normal mainly because of a few recent warmer winters.

 

Snowfall thus far this winter has been low and nearly half below the normal snowfall through the end of January.

 

 SNOWFALL (IN)                                                              
                                                              NORM      DEP
  MONTH TO DATE JAN   8.9           14.0        -5.1       
  SINCE DEC 1                 12.5           22.9      -10.4      

  SEASON                         14.3           24.8      -10.5              
 

First, lets look at the projected snow averages for the winter -which actually have averaged lighter than normal - when all (and preferred analogue winters) are  considered. By the end of January 2025 thus far, only 14.1" at DTW has fallen which is just under 10" below average by the end of January (see official stats from DTW). On average about 2 feet of snow can be expected by this time.                             

Winter 2024-25 Analogue Snowfalls
DETROIT	SEA TOT	SEASON
SEASON	44.4	1
1942-43	16.6	1
1952-53	49.2	2
1964-65	50.6	1
1966-67	35.4	2
1970-71	51.8	2
1983-84	27.6	3
1995-96	36.3	4
2005-06	37.9	5
	Ave 38.2
	Norm 45.0
	Dep - 6.8

Checking out the preferred Winter Analogues below snowfall amounts below; obviously one would ask, why is 1942-43 since we didn't have anywhere near 18.4" of snow in January? Obviously, snowstorms (when they do come) don't usually come all neatly packed in a particular month. What we are looking for here is the previous analogue trends before mid-end of the winter. Thus, that 18.4" of snow could come during the second half of the snow season (Feb-Mar) and would still suffice for a trend seen for a snowier middle to end of the season.

Basically; heaviest snowfalls in two of the analogue seasons (1942-43 and 1964-65) came middle to end of the season. In the case of the Winter of 1970-71, the seasonal snowfall was lighter than normal and was distributed throughout the season.

So according to the preferred analogues that have verified in trend; the normal to below snowfall seen in all the winters (38.2"/-6.2) still holds sway. Temperatures become more variable later winter into spring relative to normal. Some analogues remained cold while others moderate and actually warm to above normal. The over preferred analogues thus far through February /Dec-Feb/ keep temperatures ending normal to below for the winter.

A	DETROIT	T	E	M	P	S		P
N	SEASON	DEC	JAN	FEB	WNT AVE	WINTER	NAO/SC	SEASON
A	1942-43-n **	25.6	21.7	28.0	25.1	1	N/SC--	1942-43
O	1964-65-a **	30.4	25.5	26.6	27.5	1	N-/SC	1964-65
U	1970-71-n **	29.0	20.7	27.4	25.7	2	N-/SC++	1970-71
	DETROIT	S	N	O	W	F	A	L	L
W	SEASON	OCT	NOV	DEC	JAN	FEB	MAR	APR	SEA TOT
E	1942-43	T	4.4	9.2	18.4	2.7	2.9	6.8	44.4
K	1964-65	T	2.6	8.4	7.1	15.8	12.9	2.4	49.2
L	1970-71	0.0	1.7	9.8	8.7	5.9	8.7	0.6	35.4

Model Outlook into February: another moderation to warming of the stratosphere has been projected and continues with an actual split and lowering of the polar vortex(s) further south over the mid latitudes in some areas (the States and Europe). This occurs occasionally and can produce unseasonably cold, arctic/polar air to drain into the mid-latitudes - the exact areas and intensity in the surface jet stream remains questionable. Sometimes the lower atmospheric engages this delivery; sometimes not so much and models have a difficult time in forecasting this change and where.  This is what is seen thus far through the mid February time-frame. A notable drop in the NAO and AO and the stratospheric moderation or warming which at this point is forecast. This will encourage more of a stormy period and fluctuations of temperatures; so stay tuned.

 

 

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

 

JANUARY 2025 IS PROVING TO END UP A COLDER THAN NORMAL MONTH AS NEGATIVE DEPARTURES GROW!

The switch from unseasonably warm month in November (and resulting fall) to a mixed cold and mild December to a colder than on average first half of January. The worst is yet to come as us meteorologists look at the waves of Arctic cold projected possibly into the end of the month. This jives well with the Stratospheric moderation-warming at 30-10mb mentioned here days ago.

While cold looks more & more likely with brief moderations between, no clear-cut storm system has been ginned-up by models with any certainly. More light snow is expected this weekend as temperatures moderate to the lower 30s (a veritable heat-wave) before plummeting back down into the deep bone-chilling, wind-chilling cold later in the weekend into next week! Later in the month into early February is beginning to look interesting but as for the next couple of weeks…

 

This was written Tue afternoon /14th/ by extended forecasters in Maryland and still looks good…

 

Prognostic Discussions

Valid: Jan 20 - 24, 2025 (6-10 Day Outlook)

Valid: Jan 22 - 28, 2025 (8-14 Day Outlook)

Issued: Jan 14, 2025

 

Prognostic Discussion for 6 to 10 and 8 to 14 day outlooks

NWS Climate Prediction Center College Park, MD

300 PM EST Tue January 14 2025

 

6-10 DAY OUTLOOK FOR JAN 20 - 24 2025

A highly amplified 500-hPa height pattern is forecast across the forecast domain during the 6-10 day period, with ridging over western North America and strong troughing downstream east of the Rockies. The 0z ECENS and CMCE are quicker to lift the troughing out in the East by day-10 while the 0z GEFS maintains stronger negative height anomalies. The manual height blend indicates above-normal heights west of the Rockies and extending northward through Alaska. A +210 meter positive height anomaly center is noted just to the west of British Columbia. Below normal heights are predicted for most of the CONUS east of the Rockies, with the strongest negative anomalies (-150 meters) to the north of the Great Lakes.

 

A major Arctic air outbreak is forecast to be ongoing across the central and eastern CONUS at the start of the period. The 0z ECENS and GEFS indicate widespread daily temperature anomalies exceeding -20 deg F on days 6 and 7,corresponding with subzero temperatures across the Northern and Central Plains, Midwest, and possibly into the Interior Northeast, and minimum temperatures in the 20s deg F possibly reaching the Gulf of Mexico coast. The re-forecast and uncalibrated tools all support elevated probabilities for below-normal temperatures across nearly all of the CONUS, with the highest chances (greater than 80 percent) across the Southern Plains and much of the East. Probabilities for below-normal temperatures are reduced across the Northern Plains due to the possibility of quickly moderating temperatures as the trough lifts out, with the ECENS depicting a flip to above-normal temperatures at the end of the period.

 

Below is the CFS run (1/13/12Z) from the same period starting at Wed 1/15/25 @ 48hs. Surges of Arctic air backed by large, High Pressures /blue H's/ stacked up across the North Pole into northern Canada sliding SE from the far north

 

 

Next we'll look at which analogues actually accurately projected the first half of the winter's trend /Dec-Jan/ and what happened then - and what is more likely to occur for the winter period Feb-Mar '2025.

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

 

 

With The First Week of a New Year Comes a Change in the Weather

The first official month of the Winter 2024-25 season brought a notable change in the prevailing unseasonably warm fall weather. For the most part; the month of December contained equal amounts of below normal temperatures and above until the end; when a quick mild spell boosted the monthly average to above normal at 33.3/+2.0. All in all; December was a fairly "snowless"  month with below average snowfall at 3.6" /normal  8.9"/ through the 31st but with above normal precipitation with 3.27". Thus far; only half our normal amount of snow has fallen this winter with 5.4" /Norm -10.8"/

The outlook for January 2025 keeps the declining temperature trend in vogue for now with a predominantly colder than normal January in store for the early - mid month period. Latest indications are a gradual stratospheric warming trend (not official SSW) far aloft over Siberia toward the North Pole will help elongate the Polar Vortex (and some of the brutal cold at the surface) and push it south (blue/purple) into the mid latitudes, including North America with some moderation. Coldest air at the surface would concentrate over the eastern two-thirds of the nation and deep into the south!

 

Projected 500 MB upper air pattern for all of January shows the elongated trough over eastern Canada into the eastern U.S.

 

With the ridging/upper high pressure building over the eastern Pacific and western U.S at times and blocking in Greenland, this will enable the delivery of Polar/Arctic air south into the U.S.

Low pressure will move along the Polar front early in the new week but at this time it appears much of the snow will stay south in the Ohio Valley. Models have had a terrible time with this system varying from a snowstorm for the southern Great Lakes to nothing, keeping it south. The dynamics and upper air pattern won't be sampled better until Friday. Any significant changes will be blogged.

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