WINTER 2000-2001 UPDATE FOR SOUTHEAST LOWER MICHIGAN

The winter of 2000-2001 thus far has been quite variable since setting in by late November.  The extremely harsh and stormy beginning with copious amounts of snow and at times, brutal cold, calmed to a mild and almost uneventful mid-winter period until recently.

So, now what?  Historically, what does the remainder of the winter hold for Southeast Lower Michigan?   Before looking ahead, let's briefly reflect back and quote sections of the winter outlook originally released October 18th, 2000.  (For the entire write-up: http://www.crh.noaa.gov/dtx/wntr200001.php )

"Nearly all of the fall-winter periods analyzed indicated large monthly (sometimes weekly) fluctuations in temperatures but with a decided preference toward a colder winter than the past few winters.  Since there is such a range in average temperatures with past neutral  winters,' near normal temperatures' is the 'average' call here.  Past Neutral winters did, however, indicate some notable cold outbreaks with below zero temperatures

As a rule, these Neutral winters made an appearance earlier than the past few winters with late November to early December the optimum time (or around Thanksgiving into the first two weeks of December).  This was the time of the first significant snows (a couple of inches or better).  The majority of winters indicated a rather snowy (or above normal snow) beginning (mainly December into early January) with a notable mild spell mid-late winter (example: January thaw), before a snowy end. As far as "recent" winters, this proposed scenario recalls some winters in the 1970s and 80s.

So summarizing, temperatures are expected to average in the normal range but with considerable fluctuations, while snowfall should range around normal to above."


Latest analysis of Pacific Ocean sea surface temperatures indicate that the weak La Nina pattern has returned (sea surface temperatures have cooled) and replaced the Neutral pattern prevalent  earlier this winter.  This change in the Pacific Ocean temperature pattern may indeed influence the Pacific air currents and alter the weather patterns expected the rest of the winter.  Meanwhile, cold Arctic air continues to pool and recharge over the Arctic and most of Canada, much like earlier this winter.  However, unlike early this winter, the Pacific Jet Stream has remained strong enough to keep most true Arctic air invasions north of the US/Canadian border from January into early February.  As mentioned above in the original outlook, this pattern was noted in the majority of the previous winters examined and was expected to appear by mid-winter.  The fact that this La Nina pattern resurfaced at the same time has just added one more intriguing  piece to this weather puzzle. Also, the latest indications suggest that the weak La Nina pattern will prevail into spring. In the Neutral winters studied, after the aforementioned lull in storm activity and relatively mild weather experienced in mid-winter, the storm track once again became more active.  And, while those storm tracks were similar to early winter, the overall weather was not as harsh. In other words, these winters were basically "front-end" loaded with the worst of the winter weather early.  Still, as the majority of these winters faded, the area was dealt a busier storm track than during mid-winter, which produced snow, mixed precipitation and rain at times. In addition, the last of the Polar blasts were interspersed with warm winds from the south. This set up the area for the fluctuating temperatures, mentioned above, into  early spring (which is more the norm in these parts, anyway).

It should be noted, however, since the weak La Nina pattern has resurfaced, winter's ending is not as focused as its trends were for the beginning and middle. In any event, the above-mentioned scenarios were dominant. Interestingly, the spring seasons that followed these winters were quite variable as far as temperatures and precipitation.  Despite this, though, a  few weak trends were still noted.  There was a slightly better than even money chance the spring would start out cooler than normal, but a much better chance it would end warmer than normal. More specifically,  March's temperatures leaned toward normal or below, April's were a mixed bag and most of May's were above normal.  There was really no definitive trend noted as far as precipitation.

Deedler
(2/19/01)



 


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