Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 270529
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1129 PM CST Mon Jan 26 2015

.UPDATE:
Issued at 933 PM CST Mon Jan 26 2015

Low level clouds will continue to advect southeastward through IL
and portions of eastern MO for the rest of tonight. Although the
coldest air was over the eastern/northeastern portion of our
forecast area, the low level cloud cover was keeping surface
temperatures from falling much. The temperatures across portions of
eastern MO where these low level clouds have moved in have
actually risen slightly during the past few hours. It appears that
any drizzle/freezing drizzle or flurries, associated with weak
lift due to weak northwest flow shortwaves dropping southeastward
through WI and IL, will remain east of our forecast area for the
rest of tonight.

GKS
&&

.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 during 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.

2%

.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.

2%
&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1128 PM CST Mon Jan 26 2015

Surface low continues to make slow progress southeast away from
forecast area. Winds behind system are from the northwest to
north. As for clouds, back edge remains along and east of
Mississippi River. Currently VFR cigs, but models and some sites
upstream are MVFR. For now have MVFR cigs moving into KUIN by 07z
and into metro area by 10z. Then as surface ridge builds in clouds
to scatter out from north to south. KUIN to scatter out by 15z
Tuesday while metro area will be around 01z Wednesday. In the
meantime, KCOU to remain clear with just a few sc through the
forecast period. By late afternoon/early evening, winds to veer
to the east.

Specifics for KSTL:
Surface low continues to make slow progress southeast away from
forecast area. Winds behind system are from the northwest to
north. As for clouds, back edge remains along and east of
Mississippi River. Currently VFR cigs, but models and some sites
upstream are MVFR. For now have MVFR cigs moving into metro area
by 10z. Then as surface ridge builds in clouds to scatter out around
01z Wednesday and winds veer to the east.

Byrd
&&

.LSX WATCHES/WARNINGS/ADVISORIES:
MO...NONE.
IL...NONE.
&&

$$
WFO LSX




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