Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1151 am CST Wednesday Dec 4 2013
issued at 934 am CST Wednesday Dec 4 2013
Through today...models and current radar coverage indicate a
slight southeast shift and more intense forcing for today. Fn
vector convergence best lines up through the west and northwest
metropolitan toward just east of Mille Lacs Lake. Went ahead and upped
quantitative precipitation forecast and hence snowfall totals for this area...where 7 to 11" will
be common with isolated amounts near Mille Lacs of one foot of
snow by tonight.
12z radiosonde observation at mpx indicated 850mb temperature of 0c...which is being
handled well by the rap. The 850mb 0c line has shifted just south
and east of msp...with sleet and freezing rain being reported in
Goodhue and Dakota counties. So...trimmed snowfall totals slightly
across south and southeast metropolitan. Very tight snowfall gradient is
likely through Scott and far south eastern Hennepin...Ramsey and
Short term...(today and tonight)
issued at 339 am CST Wednesday Dec 4 2013
Only minor adjustments to ongoing headlines for this event. Will
hold onto the dense fog advisory in the far southeast corner of the
area...although this may be cancelled early. The winter weather
headlines still look good for the snow expected across the region.
May be a tight gradient across the southeast County Warning Area.
Local radar mosaic showing a nice band of moderate snow lifting
northeast over the central portion of the area now. This will impact
the morning commute with a couple of inches possible by middle morning
over the east central Minnesota into west central Wisconsin.
Followed a GFS/European model (ecmwf) blend overall...although all deterministic
models are in fair agreement overall. The 00z European model (ecmwf) and Gem are
very similar which has been the case throughout most of the model
runs unable to now. They remain the slowest of the models...so will
linger some high probability of precipitation into the evening across the northern portion
of the area as the system lifts northeast and deepens. There will
likely be a mix of precipitation/rain/sleet and snow over a portion
of west central Wisconsin through the day. The snow will
transition to the mix by noon as the surface low deepens off to the
east of the area. The heavier snow/higher quantitative precipitation forecast is displaced
a bit between models...but still looks like the best placement will
remain over central Minnesota...shifting northeast into northwest
Wisconsin by afternoon.
Lingering light snow and increasing gusty winds will develop behind the
system this afternoon and into Thursday. As the Arctic air filters
in in the wake of the surface low...we should see some gusts
approach at least 30 kts over the southwest portion of the County Warning Area.
This will develop considerable blowing and drifting snow into
tonight. Will have to monitor the possibility of near blizzard
conditions if the winds coincide with any significant falling snow.
Long term...(thursday through tuesday)
issued at 339 am CST Wednesday Dec 4 2013
The winter storm will have winded down by daybreak
Thursday...and with the exception of scattered lingering
flurries...the snowfall should be over. A very tight surface
pressure gradient in the wake of the trough will yield blustery
west/northwest winds and resultant areas of blowing snow.
Temperatures will struggle to warm under the influence of low level
cold air advection...and highs are expected to top out from around
5 above /west central MN/...to 10 above /east and south central
MN/...to between 10 and 15 /west central WI/. The brisk winds and
very cold temperatures will combine to yield daytime wind chill
values between 10 below and 20 below on Thursday. Furthermore...lows on
Thursday night will drop to between zero and 10 below...and while
winds will be weaker...overnight wind chills will likely plummet
to between 15 below and 30 below by daybreak Friday.
Cold and dry high pressure dominates the region through the
weekend...although 850mb flow shifts to more of a
south/southwesterly direction on Sunday. This should allow for a
moderation from Saturday highs in the 5 below to 5 above range to
Sunday highs in the 5 above to 15 above range. The low level flow
transition will be accompanied by the arrival of weak shortwave
energy...and therefore snowfall chances from Saturday night into
Monday. There are still some notable timing/strength/placement differences
between the GFS and European model (ecmwf)...but it looks like a decent potential
for a quick shot of accumulating snowfall.
Next week continues to feature reinforcing shots of Arctic air
into the upper Midwest...with temperatures running around 15 to
30 degrees below normal for early December.
Aviation...(for the 18z tafs through 18z Thursday afternoon)
issued at 1150 am CST Wednesday Dec 4 2013
Low level warm layer with temperatures a little above 0 degree c is
progressing slowly east of the Twin Cities per the kmpx dual
polarization products. This would suggest more of a snow scenario
for kmsp with a mix of freezing rain and sleet for krnh into middle
afternoon. The profile is warm enough for all rain at Keau through
early afternoon as well with a mix late afternoon with some snow
this evening. Kaxn...kstc and krwf all cold enough for all snow.
Ceilings for the most part this afternoon below 1k with ceilings
increasing to 1k-2k from SW to NE as the storm lifts out this
evening. One big concern in the wake of the synoptic snow will be
the increase in west-northwest winds this evening that will persist into
Thursday morning. This should produce blowing and drifting snow
for kaxn...krwf and kstc which may result temporary white-out
conditions. Northwest winds from 20 to 25 knots forecast with gusts near
30 knots. Ie...vlifr conditions possible. This is something future
taf issuance/S can focus on.
Kmsp...the airfield is going to be on the edge of mixed precipitation for
a few hours this afternoon before the thermal profile turns cold
enough for all snow. This will leave a few hours in the middle to
late afternoon for accumulating snow before winds switch to the
west and the better forcing for snow moves northeast. Increasing
west-northwest winds this evening from 15 to 20 knots with gusts around 25
/Outlook for kmsp/
Thursday night...VFR. West wind 5-15 knots.
Friday...MVFR ceilings possible. West wind 5-15 knots.
Friday night...VFR. West wind less than 10 knots.
Sat...VFR. Variable wind 5 knots or less.
Minnesota...Winter Weather Advisory until 6 am CST Thursday for mnz069-070-
Winter Storm Warning until 6 am CST Thursday for mnz041>045-
Dense fog advisory until noon CST today for mnz092-093.
WI...Winter Weather Advisory until 6 am CST Thursday for wiz024>028.
Winter Storm Warning until 6 am CST Thursday for wiz014>016-023.