Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 250927
AFDLSX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ST LOUIS MO
327 AM CST Tue Nov 25 2014

.SHORT TERM: (Today through Wednesday Night)
Issued at 325 AM CST Tue Nov 25 2014

West-northwest flow will continue through most of the day today
as a weak surface ridge tries to move into the Mississippi Valley.
Short range guidance is indicating that the clouds currently over
northeast Missouri and west central Illinois should clear out
during the morning. Expect temperatures to rise into 35-40 degree
range across most of the area under a partly to mostly sunny sky
today.

Meanwhile, shortwave upstream over Alberta will dive down into the
longwave trof over the central CONUS.  The surface clipper is now
forecast to dive southeast through the Missouri Valley tonight and
early Wednesday morning.  Guidance seems to be in pretty good
agreement that the surface low will be near Kirksville at around 18Z
Wednesday.  Low will continue off to the southeast into Kentucky
Wednesday night.  Mid-level shortwave energy combined with weak to
moderate frontogenetical forcing and even some upper level
divergence on the left exit region of an upper level jet streak will
combine to produce a band of precip which will affect areas
primarily along and east of the low track.  This will encompass most
if not all of our CWFA on Wednesday.  BUFKIT soundings from the NAM
and GFS do support mostly snow during the morning, with a potential
for mix of snow and/or rain in the afternoon.  Expect surface
temperatures to be near or just above freezing at the initial
outset with slowly rising temperatures through the day.  Current
thinking is that accumulations will be an inch or less, but this
could change quite a bit if the low shifts its track either to the
west or to the east.  Some lingering sprinkles or light snow will
likely continue over eastern areas during the evening, drying out
overnight with lows dipping back into the 20s.

Carney

.LONG TERM:  (Tuesday through Next Monday)
Issued at 304 PM CST Mon Nov 24 2014

(Tuesday through Thursday)

Latest models runs indicate the clipper that will move across
the area on Wednesday will be slightly deeper than previous runs
with slightly more QPF.  Have increased PoPs, particularly on
Wednesday, when the NAM and GFS show swath of decent ascent moving
across the CWA during the morning hours.  Precipitation type should
be mainly snow Tuesday night into Wednesday morning before low
level  temperatures warm during the afternoon.  Should be enough
moisture with this clipper for some minor snow accumulations over
northeast Missouri and west central Illinois.  Then the system will
quickly move out of the area leaving Wednesday night and Thursday
dry.

Stayed close to reasonable MOS guidance for temperatures which will
be below normal through Thursday.

(Friday through Monday)

GFS and ECMWF agree that upper pattern will be zonal through the
extended period with an upper trough approaching the area from the
west by next Monday.  Even with the current agreement with the upper
pattern and no big systems moving across the area, timing of weak
troughs can be difficult with zonal flow so there is some
uncertainty with this forecast. Then there is good agreement in both
models that a cold front will move southeast across the area on
Sunday night, though with zonal flow staying over the area the
coldest air will not move into the area. Both models are showing
some precipitation developing along this front over the area on
Sunday and Monday.  Still looks like low level flow will be
southwestly on Friday and Saturday with 850mb temperatures near +10C
on both models on Saturday.  This supports above normal temperatures
both days.

Britt

&&

.AVIATION:  (For the 06z TAFs through 06z Tuesday Night)
Issued at 1047 PM CST Mon Nov 24 2014

Low level clouds continue to rotate southeastward through
northeast MO and west central IL this evening, southwest of the
deep surface low just northeast of the Great Lakes region. These
clouds may remain just east northeast of COU late tonight, but
will continue to drop southeastward through UIN and may also move
through the St Louis metro area. There will be at least a brief
period of MVFR cloud heights in UIN, and also possibly in the St
Louis metro area as well. These low level clouds should completely
shift east of UIN and the St Louis metro area Tuesday morning.
W-nwly surface winds will weaken and lose the gustiness late
tonight as the surface pressure gradient relaxes. The surface wind
will back around to a swly direction Tuesday afternoon at UIN and
COU as the surface ridge axis shifts southeast of these taf
sites, and become light in the St Louis metro area Tuesday
evening.

Specifics for KSTL: Low level clouds across northern MO may advect
southeastward into STL late tonight with a brief period of MVFR
cigs possible. These clouds will shift east of STL by Tuesday
morning. W-nwly surface wind will weaken to around 8 kts late
tonight, then become light early Tuesday evening.

GKS

&&

.PRELIMINARY POINT TEMPS/POPS:
Saint Louis     38  29  41  29 /   5   5  70  20
Quincy          35  27  37  23 /   5  10  60  10
Columbia        39  30  40  25 /   0  30  50   5
Jefferson City  40  30  42  27 /   0  20  50   5
Salem           37  27  39  30 /   5   0  60  20
Farmington      40  27  43  29 /   0   5  50  10

&&

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

$$

WFO LSX





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