Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
1128 PM CST Friday Dec 6 2013
issued at 940 PM CST Friday Dec 6 2013
Temperatures are on track this evening...dropping into the teens
and approaching 20 below in many places over central Minnesota. Wind
chills have fallen into the 20s to low 30s below in these
areas...and think as temperatures continue to fall into the -20s wind
chills will easily reach wind chill warning criteria. Further
south and east...Wind Chill Advisory criteria is being reached but
think lows will remain a bit milder to keep wind chills from
reaching -35 on a widespread basis. Thus...the current headline
configuration looks good.
Did decrease temperatures in some locations...otherwise the previous
forecast is on track.
Short term...(this evening through saturday)
issued at 345 PM CST Friday Dec 6 2013
1052 mb Arctic high centered over southern Alberta this afternoon will
slowly fill into a 1040 mb high by the time it reaches southern Wisconsin
Saturday evening. This means two things for the short term...
continued bitter cold and little in the way of cloud cover. For
forecast lows tonight and highs tomorrow...favored the forecast
toward the much cooler met and European model (ecmwf) MOS guidance based on how
temperatures have performed...or under performed really this
afternoon /see a high of -7 at axn today/. This resulted in taking
about 2-5 degrees off the forecast temperatures tonight and Saturday. Now
have lows of 20 to 25 below across central Minnesota and when adding in west-northwest
winds of 5-10 miles per hour...we are now getting forecast apparent
temperatures of 35 to 45 below zero across west central and most of
central Minnesota. As a result...have upgraded the advisory across the northwest
quarter or so of the County Warning Area to a wind chill warning. Other change to
the wind chill headlines was to extend all headlines out to noon on
Saturday...as the cooling of the temperatures tomorrow resulted in apparent
temperatures of -25 lingering a bit longer than previously forecast. As for
tomorrow...925 mb temperatures will be a bit colder than what we have seen
today...so it should be a few degrees cooler that what we saw today.
Will be a tough go for the Minnesota portion of the County Warning Area with snow cover to
see highs get above zero.
Long term...(saturday night through friday)
issued at 345 PM CST Friday Dec 6 2013
Shortwave energy currently off the coast of Washington/or on the western
edge of the long wave trough spanning the western and central
Continental U.S. Will be the focus for a snow event Sunday into early Monday
morning /the only significant precipitation event over the next 7 days/.
The NAM/sref solution remains the farthest north and stronger with
the surface low expected to track a state or two to our south
Sunday and Sunday night. The 06.12z GFS/ec did come in a little
higher with the quantitative precipitation forecast across Iowa...but they still have less than 0.20"
across the forecast area. The big concern is the deep dendrite
growth zone and expected high snow ratios. The Omega and forcing
isn't overly impressive...but we will quickly saturate the column
with respect to ice and we have about 8000-10000 feet of good
dendrite growing temperatures. We think snow ratios should be near 25:1.
We increased snow totals by 1-2 inches and bumped the probability of precipitation to 100%
across the eastern half of the forecast area for Sunday evening.
The key to the northern NAM forecast seems tied to the development
of precipitation farther north with an early weaker band of fgen...which
in turn develops more latent heating and pulls the system farther
north and strengthens it. This certainly appears like at least an
advisory-type event with 3-5" possible in the southeast forecast
area. A strong unidirectional wind profile on Monday suggest we
will have plenty of surface gusts up near 30 kts and the
potential for good blowing and drifting of all that high ratio
snow that falls the previous day. Snow will end late Sunday night
with cold air persisting into early next week. Models do hint at
some moderation after midweek next week as upper flow flattens
somewhat allowing near surface flow from the west as opposed to
the Arctic. Precipitation chances into next week appear rather
minimal with systems passing to just to the north or remaining
west and south of the area by late in the forecast cycle...light
snow with the clipper system Monday-Tuesday is possible however. In terms
of temperatures...the weekend continues to be very cold will
Arctic high pressure hanging tough and wind chill headlines will
be needed through early next week...especially with another Arctic
boundary expected with more of a weak clipper system on Tuesday.
Aviation...(for the 06z tafs through 06z Saturday night)
issued at 1121 PM CST Friday Dec 6 2013
Almost VFR conds through the next 24 hours with winds generally from
the west-northwest around 10 kts...becoming more SW/S Saturday evening. Clouds
will begin to thicken and lower after 00z/8 with some -sn possible
in krwf by 3-6z.
VFR conds through 6z/8 with winds west-northwest around 10 kts...becoming SW/S by
00z...then southeast/east-southeast after 6z/8. Clouds will begin to increase and lower
after 6z...with some -sn possible by the end of the taf period.
/Outlook for kmsp/
Sun...becoming MVFR/IFR with snow by afternoon. Winds east-southeast at 5-10kts.
Monday...MVFR/-sn ending early...then VFR. Winds west at 15g25kts.
Tuesday...VFR. Winds west-northwest 15g25kts.
Minnesota...Wind Chill Advisory until noon CST Saturday for mnz045-052-053-
Wind chill warning until noon CST Saturday for mnz041>044-
WI...Wind Chill Advisory until noon CST Saturday for wiz014>016-