Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
432 PM CST Sat Nov 28 2015
Short term...(this evening through sunday)
issued at 337 PM CST Sat Nov 28 2015
Very quiet in the short term as high pressure slowly moves off to
the east with east-southeast winds developing in advance of the
large storm system that will affect the upper Midwest/northern
plains Mon/Tue. Similar temperatures tonight as light winds and
radiational cooling allow for temperatures to drop rapidly after sunset.
Morning lows will be coolest where recent snow fell. Clouds will
begin to increase Sunday in advance of the next storm...this may
allow for temperatures to be a degree or two cooler than today.
Long term...(sunday night through saturday)
issued at 337 PM CST Sat Nov 28 2015
Sunday night through Tuesday...significant snowfall event expected
starting late Sunday night into Monday morning in far southwestern
portions of the area...spreading eastward Monday through
Tuesday...potentially delivering significant snowfall amounts for
much of the weather forecast office mpx County warning forecast area.
A large longwave trough moving onshore the western Continental U.S. Coast will
deepen into an expansive cutoff low over the central rockies by
Monday morning. It will then steadily move into the Central Plains by
midday Monday...helping to organize a surface low pressure system over the
middle Mississippi River valley. The upper low will then move
northeast into Iowa/Minnesota Monday night on its way to the central Great
Lakes by midday Wednesday. The surface low will then move NE in conjunction
with the upper low with a similar speed...allowing for a well-
developed and tilted deep low pressure system with plenty of
moisture...duration and cold air to produce significant snowfall
for central-southern Minnesota into western WI Monday through Tuesday. With respect
to moisture...model precipitable waters are in the 0.50-0.75 inch area which is
well above normal for this area and time of year.
Latest model runs have given a slight northward and eastward shift
with the heaviest snow and this is also reflected in the latest
wpc thinking...in terms of both probabilistic and deterministic
forecasts...so have mimicked that thinking for the local forecasts
here. In fact...the 00z and 12z European model (ecmwf) end up as drier and offset
outliers compared to a variety of other models...and going this
Route produces a wide swath of 7-10 inches for much of the weather forecast office mpx
County warning forecast area...particularly central-southern Minnesota...with lesser amounts going to
the north and east...including western WI. Given the high moisture amounts
along with the prolonged duration of snowfall...have opted to
slightly drop temperatures by a 1-2 degrees for highs on Monday which will
keep a more solid snow p-type rather than any mixture with
-ip/-ra. This then also spells slightly higher snowfall amounts.
Therefore...in collab with surrounding offices...have opted to get
the message out with a Winter Storm Watch for much of central-
southern Minnesota with this forecast pkg...advertising the potential for
7-10 inches for Monday through Tuesday. There is still some
variation that may occur but given the good amount model
agreement...the particular event parameters involved and with this
event starting out the week...confidence was high enough to go
with the watch at this point. Later forecast shifts will evaluate
the need to go further north and/or east with the watch to cover the
later development of snow outside the normal issuance period of a
Look for the snow to commence over southwestern Minnesota during the day on
Monday and gradually spread eastward over the County warning forecast area during the
day...potentially getting heavier as the day progresses. Difficult
to say at this time if there will be any 1 inch/hour rates but given the
strong height falls and deep moisture involved...it cannot be
ruled out. In addition...with min temperatures only dropping to the middle-
upper 20s Monday night before rising to the low-middle 30s on Tuesday before
the event ends...this snowfall will be more of the heavy wet type
rather than a light fluffy snow.
All this being said...all are urged to stay tuned to the latest
forecasts and updates on this potentially significant snow storm.
Wednesday through Saturday...a much more tranquil period can be
expected for the latter portion of the week into next weekend as
upper level ridging combined with surface high pressure will dominate
the weather. This will lead to a prolonged drying out and mostly
clear period but with a slight warming trend in temperatures.
What will temper the warming and keep temperatures slightly below model
projections will be the snow cover. Some of the snow may well
evaporate with the plenty of sunshine expected but this will also
keep temperatures in the middle-upper 30s instead of rising into the lower 40s.
Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1120 am CST Sat Nov 28 2015
No aviation concerns over the next 24 hours with VFR conds and light
SW to S winds.
Kmsp...no aviation concerns with light SW wind...becoming southeast/east
under 6 kts Sunday afternoon.
/Outlook for kmsp/
Monday...VFR becoming IFR or lower in snow/+sn late. Winds east-northeast 10 kts.
Tuesday...IFR in snow early. Poss VFR late. Winds NE becoming northwest 10-15 kts.
Wednesday...VFR. Winds northwest-west-northwest 5-10 kts.
Minnesota...Winter Storm Watch from Monday morning through Tuesday afternoon