Winter 2013-14 Outlook for Southeast Lower Michigan
William R Deedler; Southeast Michigan Weather Historian
This being my 17th year of issuing season outlooks reminds me of how quickly the time has past, how variable and many times exciting the winters have been but most of all, how enthusiastic I still become at the challenges forecasting the upcoming season.
This upcoming season looks to be a more exciting season than the past few (especially 2012-13). The winter of 2012-13 was a boring, slow season with hopes of snowstorms for snow lovers dashed frequently. And, while the Winter of 2012-13 started in that same vein, it did make up for the slow start with an active late season. On to the Winter of 2013-14...
While the analysis of my winter analogues show mainly below normal (very similar to our recent summer analogues), it is felt the coldest of analogues are too cold and thus, skewing the average down some. However, at the same time, some of the cold outbreaks seen this winter will rival some of the outbreaks seen in recent milder winters leading to a normal to above normal amount of below zero days.
Snowfall and Rainfall:
Broad Scale Discussion
The Pacific Decadal Oscillation
The Winter 2013-14 Analogues
In one of the strongest below normal signals I've seen in the 17 years of Outlooks; you'd think it'd be a slam dunk but not always. Granted most of the time when a temperature trend was even close to this strong, it turned out to be in the right direction. I can recall a few winters however, where that backfired and the minority ruled. One thing that has me concerned is there were no normal temperature winters in the Detroit sample. The two past trends were cold or mild..no normal or average. More often than not this tells me either a cold trough dominated or very infrequently, a flat ridge (or zonal flow) prevailed. I can't go against a cold signal this strong and dominant nor from what I'm seeing this fall, therefore below normal it is. Best below normal chances would be at Detroit but that's only because of the inflated heat island norms.
As far as timing, while on the whole all months averaged below normal, scattered about each month's column were a few above normal Decembers, Januaries and Februaries. December had the second best chance for an above normal average after the many below normals prevailing. The Decembers that were on the milder side were followed by some brutally cold Januaries and/or Februaries. There also a strong likelihood of a few mild periods or thaws during the winter given the upper air pattern expected (see in Upper Air/Storm Track section) and the scattering of mild analogue months. Of course, timing will be the issue for milder weather but there is enough of evidence to indicate breaks in the dominant cold. This variance would also be supportive of an amplified upper wind pattern that would be at least, somewhat progressive.
Now this trend result, the analogues are not so kindly instructive with snowfall amounts ranging from well below normal to well above. In the Detroit sample alone; two of our snowiest winters are matched against several "snow-less"! What to do? Well let's attack this first from what we do see...and that's trend and location.
First off; The analogues are suggesting a back-end loaded winter as far as snowfall with averages hinting toward an above normal February & March. In fact; there were some hefty snowfalls in some Januaries, Februaries and Marches with even some notable late season snows in April and even May...let's hope not! On the flip side; in many other analogues there were seasons with light to very light amounts of snow. Given this mixed snow amounts picture and averages falling in the normal to below normal category, I'm inclined to go overall normal (locally above) to below snowfalls for the snow season.
Secondly; Best snowfall averages (highest) this season focuses on the southern sections of the region. This would include areas along and south of 1-69...or mainly from the Flint and Port huron areas south throuh Ann Arbor and Metro Detroit to the Ohio border. See below for estimates...
Overall, I look for a wider range of snowfalls this winter across the region. Generally normal (to locally above) snowfalls are possible over the southern sections of Southeast Lower Michigan (generally along and south I-69); while normal to below normal snowfalls can be expected across the northern areas of Southeast Lower Michigan including the Saginaw Valley and areas well away from Lake Huron. This would be primarily a result of prevailing storm tracks passing over and to the south of the region. This is a difficult call since if dominant storm tracks were to travel just a bit further north, then heaviest snow would also be further north into northern areas. At this time though, recent patterns and analogue data suggest heavier snow chances are more to the south and updates will be issued if needed.
Snowfall should average near to locally above normal (or near the statistical normal to locally 8" above of the normal) across the south half of the region; and widespread normal to 8” below the statistical norm across the northern sections. (Keeping in mind that the range considered in the normal category is 6”+/- of the statistical normal value - located on the bottom of analogue data).
Upper Air and Resulting Storm Tracks
After a positive NAO/AO and resultant ridging dominated the eastern half of the country during the Winter of 2011-12 and then again, early in the Winter of 2012-13; there was a distinct change in the upper pattern since mid Winter of 2012-13. A more neutral to negative NAO/AO phase took hold at that time and has prevailed since, resulting in more troughing over the eastern half of North America. I look for this to prevail during the up coming winter which would encourage blocking in the upper air pattern and thus, aid in delivering colder air to the region.
Using my analogue winters upper air reanalyzed patterns and comparing it to recent trends leaves me with this conclusion; a predominantly neutral to negative NAO/AO for the Winter of 2013-14. In Fig- 5a below, there is little doubt of the prevailing cold upper level trough extending from the Arctic south over the Eastern half of North America
In Fig 5b; here will see the dominant upper air jet streams to be key players in the upcoming winter based on past and present observations.
It's very interesting to note, that this experimental NOA/AO projection also supports the analogue set for the winter.
Projected Prevailing Storm Tracks
First off; lets look at the anomalies (departure from normal) of the upper air patterns averaged out for the analogue winters and see if there are similar patterns noted at the present time. In Fig - 6a, one of the first items noticed is the strong above normal heights extending from western Alaska southwest out over the northern Pacific and over Greenland; both representing dominant upper air high pressure or ridging. The other notable feature is the broad troughing extending from Canada southward into the northern half of U.S.
Expected Prevailing Storm Tracks for the Winter of 2013-14
Three main storm tracks are expected to cross the United Stated this winter.
-The first in order of precedence is the Alberta Clipper type systems bringing the Arctic
air crossing the southern prairie lands of Canada and northern Plains of the US into the
Great Lakes and East.
-The second in precedence involves several main tracks; The clippers that travel further
south into the Midwest and Ohio Valley and intensify over the Mid Atlantic region. The
British Columbia/Pacific Northwest impulses that drive south-southeast into the US
heartland and Southern Plains (Kansas/Texas Hookers-Panhandle Lows) on there way to
the Great Lakes. Also; The Pacific Ocean driven impulses which ride over the Rockies and
also energize Southern Plains low centers.
-The third storm tracks in order of precedence; the Ohio Valley Low taking shape over
Arkansas/southern Missouri and deepening as it moves toward the eastern Great
Lakes and finally, the Gulf Low that moves into the Ohio Valley/Lakes or up the East
Winter Temperature Analogue Composite Map: Dec - Feb
Winter Precipitation Analogue Composite Map: Dec - Mar (March included for possible better snowfall representation - especially in normally snowfall regions).
Look for storm and cold alerts during the winter along with updates and possible changes.
Bill Deedler -SEMI_WeatherHistorian