Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 271147
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
547 AM CST Thu Nov 27 2014

.SHORT TERM: (Today through Saturday)
Issued at 356 AM CST Thu Nov 27 2014

Clipper system is now well southeast of the CWFA, and only a few
lingering flurries remain.  Expect any lingering precip to end by
12Z this morning and for the rest of the day to be cold and dry.
Some uncertainty on sky condition today as stratus over Iowa is
clearing fairly slowly from northwest to southeast.  Short range NAM
and RAP 925mb RH field has a decent handle on the clouds at this
time, so have used a combination of these guidance products and
satellite observations to try and time gradual clearing today.
Canadian airmass over eastern Dakotas at this time will drift
southeast today and will provide the area with unseasonably cold
air.  Cannot argue with MOS high temps in the mid-upper 20s to mid
30s across the area due to this cold high pressure system`s
influence.

Models continue to advertise a general pattern shift Friday into the
weekend with mid-upper level flow becoming more zonal.  This will
allow warmer air to flow back into the area as the storm track
shifts north.  Temperatures will moderate on Friday as the flow
shifts to the south-southwest on the western side of the Canadian
high which will have settled in over the Eastern CONUS. Expect
temperatures on Friday to be at least 10 to 15 degrees warmer than
today.  Boundary layer moisture will also be on the increase, and
low level RH progs for Friday night/Saturday morning are showing
very moist conditions across the area by 12Z Saturday from about
900mb down to the surface.  Have therefore increased cloud cover on
Saturday morning with some gradual clearing during the afternoon.
Models continue to spit out light QPF Saturday, but am still
skeptical due to the models` tendency to develop precipitation in
strong moisture return situations even with lifting mechanisms
aren`t present.  Indeed, in this case model soundings are showing a
strong subsidence inversion in the low levels and positive values of
omega in the moist layer which would tend to lend credence to a dry
(tho cloudy/mostly cloudy) forecast for Saturday.  Am still sticking
with above normal temperatures Saturday, though due to expected
cloud cover have backed off a little bit from warmest MOS guidance.

Carney

.LONG TERM:  (Sunday through Wednesday)
Issued at 423 AM CST Thu Nov 27 2014

Sunday continues to look pretty mild over the majority of the area,
with the possible exception of northeast Missouri and west central
Illinois.  Timing differences between the faster GFS and slower
ECMWF could mean the difference between a chilly day up north and a
day with highs between 10 and 15 degrees above normal.  Leaned
toward the warmer solution this morning since the upstream shortwave
which will drive the front south is well back over Montana in the
ECMWF, and the GFS solution keeps the teeth of the shortwave up
north across the Upper Midwest.  Would like to point out that this
could easily be wrong.

Cold front should be through the area by Monday morning according to
both the ECMWF and GFS with a 1040mb high building into the
Midwest.  Confidence in the extended forecast beyond Monday is
pretty low as there seems to be little agreement between the GFS and
ECMWF.  GFS hangs on to quasi-zonal flow aloft through Wednesday
which is mild and potentially a little wet.  ECMWF develops a
full-latitude longwave trof over the eastern 1/2 of the CONUS which
would be drier and colder.  Stuck with the ensemble blend of
guidance which tended toward a warmer and wetter solution for this
forecast cycle.

Carney

&&

.AVIATION:  (For the 12z TAFs through 12z Friday Morning)
Issued at 545 AM CST Thu Nov 27 2014

At 1130z, ragged back edge of MVFR cloud deck extends from just
east of KALO, to near KCSQ, to around KFNB, and is working
southeast at about 20kts. This rate of movment suggests erosion of
MVFR cigs at UIN and COU around midday and in the STL metro by
mid afternoon, which dovetails fairly well with RUC 925mb RH
trends. There is a large hole in this MVFR deck is over central
and parts of S IL, but it appears to be working SE so any impacts
of this feature will miss our TAF sites. Once the low clouds clear
VFR conditions will prevail for the remainder of the forecast
period, with any additional clouds aoa 8kft overnight and into
Friday morning.

Specifics for KSTL: Bases of MVFR cigs will slowly increase as we
head through the morning and early afternoon, with this low cloud
deck finally scattering out around 22z. Once the lower deck
erodes, occasional mid level cloudiness (with bases aoa 8kft) can
expected for the remainder of the forecast period.

Truett

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     32  26  50  39 /   0   0   0   0
Quincy          24  20  45  36 /   0   0   0   0
Columbia        32  25  54  40 /   0   0   0   0
Jefferson City  33  26  56  41 /   0   0   0   0
Salem           30  23  45  37 /   5   0   0   5
Farmington      35  24  49  39 /   0   0   0   0

&&

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

$$

WFO LSX






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