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