Scientific Forecaster Discussion
fxus63 kmpx 151158
Area forecast discussion
National Weather Service Twin Cities/Chanhassen Minnesota
558 am CST Fri Dec 15 2017
Short term...(today and tonight)
issued at 349 am CST Fri Dec 15 2017
Biggest concern during the short term is timing in precip and
amounts with a warm frontal band of snow that is expected to impact
areas mostly north of I-94 this evening.
Water vapor imagery this morning shows energy working into British
Columbia that is finally starting to break down the western ridge
that has been in place for the better of the past week. This ridge
axis will slide southeast and flatten out through the short term,
but Theta-E advection on the nose of the ridge will provide US with
the forcing for a light snow event this evening and more so
overnight. Main change seen with guidance overnight is this band is
coming in a little slower and a little farther southwest. The two
camps we have are with the European model (ecmwf) and cams, which have the heaviest
quantitative precipitation forecast (all of 0.10-0.15") falling from Brainerd down toward Chippewa
Falls, while the NAM/GFS/Canadian have it more from Bemidji down
toward Hayward. Right now, we still have a 1-2" forecast along and
northeast of a Little Falls to Chippewa Falls line, which is closer
to the European model (ecmwf)/cam solution. Top end potential with this band is 3".
As for timing, even though there are placement differences, there is
pretty good agreement on the timing, which has it coming through a
few hours later than what we had going and updated the pop forecast
to reflect a blend of the cams for timing. Looks like the heaviest
snow will not start moving in until after midnight and will linger
into Saturday morning for western WI.
For temperatures, stayed with a blended forecast, which nicely
accounted for the slowing of this system and its associated warm
front. We will again see a pretty strong temperature gradient across
the mpx cwa, with highs in southwest Minnesota getting into the upper 30s,
while out around Ladysmith stays in the upper teens. The warmest
925-50mb temps we will see during the short term will actually move
in overnight, so this warm air advection combined with continued cloud cover will
result in near steady temperatures tonight, with lows likely
staying within 5 degrees of this afternoons highs.
Long term...(saturday through thursday)
issued at 349 am CST Fri Dec 15 2017
Overall a relatively benign long term forecast period is in store
for the area...at least until the end of next week.
After precipitation comes to an end on Saturday, we are displaced
from any sort of shortwave forcing through the rest of the
weekend, although clouds will linger through Sunday.
On Monday a northern stream wave dips into the north central
conus, with shortwave energy sagging into central Minnesota. Light
rain/snow look possible north of I-94, but nothing of any
significance. Temperatures to start the week look fairly mild with
westerly flow dominating. Highs look to range from the lower 30s
to possibly even lower 40s in southwest Minnesota from Monday through
By Thursday the forecast gets quite interesting. There is pretty
good agreement amongst the medium-range models that a weather
system most closely resembling the "colorado low" archetype will
push across the central Continental U.S. To the Great Lakes. However, there
is a large amount of forecast spread and uncertainty regarding the
extent of the amplification of the western trough, and resultant
track of the surface low. This could mean the difference between
no snow and 8 inches of snow for a given point in the forecast
area on Thursday. Therefore, it's way too early to start getting
overly excited (or worried) about a significant event for our
area, but it certainly bears a close watching, especially for
those who have travel plans.
Aviation...(for the 12z tafs through 12z Saturday morning)
issued at 558 am CST Fri Dec 15 2017
Although it may be hard to believe when looking at current
conditions, the lavs depiction of msp and WI terminals going VFR
late this morning into the afternoon has support from rap/NAM
soundings, so followed this trend. Band of snow in eastern nodak
will build southeast through the morning and will eventually bring
light snow to most terminals by the afternoon. Heaviest snow, with
IFR vis and accums up around an inch will be coming to WI
terminals, with the heaviest snow expected after midnight.
Kmsp...we look to get a brief break in the endless flurries
through the morning, before the frontal band sets up this
afternoon, bringing back the occasional bouts of flurries. In all
of this though, it is looking increasing likely that we will see
a brief period of more persistent snow between 21z and 03z when we
may see IFR vis in snow at times. Followed the idea of the lav
and most other models in cigs going VFR for a time today, though
it is not a given this will be the case
/outlook for kmsp/
Sat...MVFR. Wind east 5 kts.
Sun...chc mrng MVFR. Wind northwest 5 kts.
Mon...VFR. Wind SW 10-15 kts.