Scientific Forecaster Discussion
Area forecast discussion
National Weather Service La Crosse WI
1146 PM CDT Thursday Oct 8 2015
Short term...(tonight through sunday)
issued at 224 PM CDT Thursday Oct 8 2015
High impact weather potential: watching cloud trends later tonight
into Friday...along with the potential for some drizzle/fog for
northeastern counties. Otherwise...no widespread hazardous weather
is foreseen into the weekend...though very warm and breezy
conditions by Sunday will likely lead to some fire weather concerns.
Rather classic October "roller coaster" weather is set to continue
through the weekend (and beyond)...as broad upper troughing in place
across the middle/upper miss valley on Friday is replaced by quickly
building heights through the weekend...in advance of quite the sharp
upper trough axis working through the northern rockies (our issue by
monday). Farther down low...low pressure departing into the northern
Great Lakes this evening will yield to a large area of high pressure
slowly working through the region into Saturday...before our local
area falls in the stronger return flow axis by Sunday...setting up
potentially quite the really warm day.
From a weather perspective...sharp sub-800mb cooling beneath
residual warmth aloft into tonight is as classic a setup for stratus
expansion as one can get...and confidence remains high in lower
clouds encompassing much of the area through the night. Do have some
concerns we may get into a drizzle situation across mainly the far
northeast County Warning Area (chimney counties) given a period of better cyclonic
flow and a Lake Superior connection...with forecast radiosonde observations indicative
of a sharp moisture increase just above the inversion coupled with
ample shear for drizzle production. However...sharper drying and a
well-mixed boundary layer below 900mb does give ME pause as that may
offset that moisture component. In either case...will really have to
watch cloud evolution on Friday as have a feeling we may deal with
pesky stratus longer than guidance forecasts given the expansiveness of
current upstream low cloud deck. That of course may have a big
influence on temperatures for Friday...with high res 2-meter temperatures
suggestive we may be stuck more in the 50s than lower 60s.
Regardless...looking like a nice warmup by Saturday with increased
mixing into building thermal ridging from the west. Should be a
breezy day with a tightening gradient and said mixing...with gusts
pushing 30 knots for the higher spots across southwest Minnesota.
However...the bigger story still looks to be warmth by Sunday with a
corridor of 20-23c 925mb temperatures sliding overhead. Mixing depth could
be better (it is nearly middle October after all)...so we won't get to
realize all of that potential...but still foresee readings well into
the 70s and lower 80s...likely just shy of current records for the
11th. For reference...those are 86 for La Crosse (1928) and 82 for
Rochester (1930 and 1934). Overall...simply a fantastic stretch of
Long term...(sunday night through thursday)
issued at 224 PM CDT Thursday Oct 8 2015
Typical October weather continues right on into much of next
week...with a little something for just about every weather fan
(sorry snow fans...we have to wait on that stuff for a while yet).
As alluded to above...sharp upper troughing looks to make a run at
US on Monday...punting a strong cold front through the area.
Was quite surprised the past few days at the extreme dryness in GFS
runs with the passage of this system...as strong upward forcing
should drive at least a chance for some showers with its passage...
even in the face of limited pre-frontal moisture return. 08.00z runs
of the Gem/European model (ecmwf) have reversed this trend somewhat but feel that at
least a small chance for showers is warranted along the front...
simply given such a strong push of low/middle level frontogenesis. It
may ultimately be that some lighter precipitation starts to take shape
across the County Warning Area but really takes off just to our east as the upper
wave intercepts better moisture return. Otherwise...high pressure
and quite seasonable conditions look to prevail Tuesday Onward into
late week...with temperatures generally a couple of degrees above average
each day though with seasonably cool overnights given relatively
light winds and expected clear skies with high pressure nearby.
Aviation...(for the 06z tafs through 06z Friday night)
issued at 1146 PM CDT Thursday Oct 8 2015
Some drizzle has formed this evening that briefly allows the
ceilings to drop to IFR and at times produces a little bit of a
visibility restriction. Appears this is tied to a weak secondary
short wave trough coming across the area and the 09.00z NAM and
09.03z rap indicate the lift from this wave should be just about
done with so do not plan to show any drizzle for either site.
Satellite continues to show an expansive area of MVFR clouds over
all but the northeast section of Minnesota. The NAM indicates this
moisture field to hold on for much of Friday morning so will
continue the trend of keeping the clouds in place. Once these
scatter out...it will be VFR for the rest of the period with high
pressure over the region.