Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 262151

351 PM CST Mon Jan 26 2015

.SHORT TERM: (Tonight through Friday Night)
Issued at 349 PM CST Mon Jan 26 2015

NW flow is expected to continue thru Tue across the ern CONUS while
a ridge extends along the Rockies. Main flow is across the Pacific
NW while a cut off low continues to spin off the sthrn CA/Baja
Coast. The closed low gets absorbed into the mean flow on Tue and
flattens the ridge Tue night/Wed. Upper heights across the mid-MS
Vly begin rising Tuesday night as a low amplitude ridge builds into
the area for Wed ahead of the energy, which is the remnants of the
closed low, approaches the region late Wed night into Thu mrng. All
this while a separate nthrn stream short wave follows closely behind
for Thu aftn/Thu evng. These two features will effectively reinforce
the east Coast trough towards the end of the wk.

At the sfc, weak low/clipper that produced the light snow across
IL today will quickly exit to the SE this evng. Not much CAA
behind this system despite NWrly winds. Temps are in the 50s and
60s in the air behind this system across the Plains today. Sfc
ridge passes to the NE of the FA overnight allowing winds to
become S/SSE by Tue mrng. New SFC low dvlps in the lee side trough
on Tue in response to energy topping the ridge and tracks ENE to
near KEOK by 6Z Thu. This puts the CWA in the warm sector on Wed.
The 850 mb thermal ridge noses into the FA drng the aftn with
temps ranging 8-12C, though soundings suggest we will not realize
that potential, only mixing to near 925mb. Guidance indicates that
most of the precip will remain north of the low track, so have
just slight chance PoPs across the nthrn and ern portions of the
CWA for late Wed night into Thu mrng. The low moves into the Ern
Grt Lks Thu with the CAA on the backside of the storm returning
temps closer to normal for the end of the wk. Another short wave
comes onshore along the West Coast Wed night/Thu. This system is
expected to be a player in a potential wknd storm system.

There will likely be a significant E/W temp gradient across the CWA
on Tue due to potential cloud cover along and east of the MS R on
Tue and a better thermal profile with deeper mixing across cntrl MO
on Wed. Temp gradient relaxes for Thu and Fri under CAA. Used a
blend of MOS guidance along and east of the MS R on Tue due to
expected cloud cover. Didn`t use the cooler MET guidance exclusively
as it has had a cool bias recently. Went closer to the warmer MAV
across cntrl MO on Tue. Went aoa guidance on Wed due the synoptic
set up but didn`t get carried away due to the limited mixing.


.LONG TERM: (Saturday through Next Monday)
Issued at 349 PM CST Mon Jan 26 2015

The trough that moves onshore late in the wk cuts off over the
wknd and slowly drifts south along the Baja peninsula. Meanwhile,
another short wave drops out of Canada in the mean flow with
height falls continuing into Sun until the trough axis passes Sun
aftn/evng. GFS and ECMWF both have precip mvng into the area late
Sat and continuing into Sun but differ significantly in the
details. The GFS has a decent sfc low tracking from the nthrn
Plains into the Grt Lks while the ECMWF has a weaker low mvng from
the sthrn Plains into the SE. Guidance has been anything but
consistent with this system having it one run and then not on the
next so do not have a great deal of confidence in any solution
attm. With colder air in place, the system bears watching.



.AVIATION:  (For the 18z TAFs through 18z Tuesday Afternoon)
Issued at 1135 AM CST Mon Jan 26 2015

Upper level disturbance moving southeast through the Midwest is
producing spotty areas of light snow across parts of west central
and southwest Illinois. KUIN had about 10-20 minutes of light snow
which dropped vsby to IFR very briefly. Brief periods of IFR will
be possible through the early afternoon as this area of snow moves
southeast, but for the most part MVFR ceilings will prevail along
and east of the Mississippi this afternoon with unrestricted
visibilities. Expect VFR conditions to prevail over central
Missouri at least into early evening. Should see a clearing trend
this afternoon at least up to the Mississippi river, but then
guidance brings another round of MVFR clouds down across the area
this evening. MVFR ceilings will likely hang across the area
through most if not all of Tuesday morning.

Specifics for KSTL:

MVFR ceilings will be scattering at Lambert over the next hour or
two, and VFR flight conditions are expected to prevail after that
until evening. There may be a few snow flurries in the area
through 19-20Z as well, but do not expect snow heavy enough to
affect flight conditions.  Guidance brings another area of MVFR
ceilings down from Iowa along the Mississippi during the mid to
late evening hours. Looks like ceilings could fall below 2,000ft
for a short period overnight tonight, but confidence is not high
in that at this time. Ceilings between 2,000-3,000ft are expected
to prevail through Tuesday.





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