NZUS99 KLSX 280957
WRKAFD

Thursday through Friday night

The entire fcst prd will feature aoa normal temps.

Strong jet streak will continue to dig an Ern US trough as it moves
off the E Coast Fri. This will put the FA in NW flow to start the
prd but will be back to zonal flow by the end of the week. CAA will
be in full swing on Thu with strong NW winds. Fcst sounding indicate
the area will mix to near 850 mb on Thu. This will accomplish two
things. One...winds will be quite gusty...on the order of 30-40 mph.
Two: mixing that deep means highs have the potential to be warmer
than the current fcst suggests. Normally this time of year...we
would be much colder with a 1040+mb high building into the region
but this air mass is of Pacific origin so it is relatively mild. The
mix down chart suggests with 850 mb temps of -6C to -8C across the
area corresponds to high temps in the 40s...which is what the going
fcst is advertising...though wouldn't be surprised if some locations
across cntrl and SE MO top out in the lower 50s. Winds will diminish
some overnight but will still remain elevated and gusty due the
pressure gradient remain fairly tight. This will keep overnight
temps from dropping off as much as they normally otherwise would.
Friday temps should be similar to Thursdays as the SFC ridge moves
from the sthrn Plains E along the Gulf Coast. This puts the entire
fcst area in return flow by Friday evng. Cntrl MO may very well
reach 50 degrees again since they will have sthrly winds most of the
day. Our IL counties E of the STL metro area will be the coolest as
that area will be closer to the heart of the coldest air assoc with
the high and will be the last to get sthrly winds. Due to the
increasing shtly flow overnight Friday night...lows will not drop
off that much and are expected to remain at or above freezing across
the CWA.

Saturday through Tuesday

This prd will begin with zonal flow but will transition to SW flow
over the wknd. This is shaping up to be an active stretch. There is
still a fair amount of model spread through the wknd. There will be
a series of short waves that get ejected from a complex split flow
trough structure across the Wrn US. Strength and timing of these
features will drive the sensible wx at the SFC. The first short wave
to affect the region will drop SE out of Canada and is actually the
feature that shifts the flow from NW to zonal. This feature will
drive an assoc SFC low from the nthrn Plains to SE Canada over the
wknd which will drag a cold front into the CWA Sat PM. The models
dvlps WAA precip in advance of the upper level energy...but confines
it mostly to SE MO and sthrn IL. Guidance continues to trend the
bulk of this precip SE and now keeps the majority of it out of the
FA. The highest PoPs with this wave will be across SE MO Sat. The
GFS features a sthrn stream vort max that passes just S of the CWA
on Sun with little impacts to the local area. The more significant
trough ejects ejects Mon. The timing of this feature is similar
between the GFS and ECMWF but the structure of the actual short wave
is not. The GFS has a sthrn stream vort max that tracks from the
sthrn Plains into the Deep S while the Euro has more of a phased
solution. Therefore the GFS keeps most of the precip S of the FA
once again while the Euro lifts a SFC low right across the FA with
widespread precip across the CWA. Due due such wide disparity...have
maintained chance PoPs Sun night and Mon. In the wake of Monday's
energy the Euro goes back to zonal flow whereas the GFS digs a deep
trough a across the cntrl CONUS and dvlps a significant SFC low that
takes a track that puts accumulating snow across the nthrn portion
of the CWA. The Euro does not have this solution. And this is the
first GFS run to depict this scenario so...introduced slight chance
PoPs.