Area Forecast Discussion
Issued by NWS St. Louis, MO

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FXUS63 KLSX 280456
AFDLSX

Area Forecast Discussion...Updated Aviation
National Weather Service Saint Louis MO
1156 PM CDT Thu Jul 27 2017

.SHORT TERM...  (Through Late Friday Afternoon)
Issued at 313 PM CDT Thu Jul 27 2017

Latest GOES-16 imagery showed a MCV moving southeast near the
Missouri/Arkansas line.  A cold front extends from near Champaign to
south of Kansas City and the atmosphere remains unstable ahead of it
despite the cloudiness with MLCAPES between 500-1000 J/kg.  Regional
radars are still showing scattered showers and a few thunderstorms
ahead of the front.  Expect this trend to continue the next few
hours as the front moves south and eventually through the CWA by mid
evening.  The clouds will linger around, at least along and south of
I-70, into Friday morning before drier air finally moves into the
area.  Partly to mostly sunny skies are still expected on Friday
with north winds as both the GFS/NAM shows a high moving into the
Great Lakes.

Went above MOS guidance tonight where I expect clouds to linger.
Once the clouds clear tomorrow, should have enough sun and mixing to
850mb to go at or above MOS guidance.

Britt

.LONG TERM...  (Friday Night through Next Thursday)
Issued at 313 PM CDT Thu Jul 27 2017

Seasonably cool and less humid weather is expected Friday night
through early next week. Mid/upper level ridge is expected to move
westward from the central Plains to the Great Basin by early next
week with a downstream trough carving out along the eastern seaboard
of the CONUS. At lower levels, anomalously strong anticyclone will
remain nearly stationary across the Upper Midwest to Great Lakes,
helping to provide cool, dry northeasterly flow across the bi-state
area. This area of high pressure will slowly slide ESE toward the
Ohio Valley and weaken by midweek. Some agreement on some kind of
cold frontal passage mid-late next week, but differences in timing.
This front is expected to bring the next chance of precipitation to
the area.

Coolest conditions in the extended will likely be this weekend with
850-hPa temperatures only in the +10 to +15C range. Highs on
Saturday and Sunday are forecast only to be in the low to mid 80s,
with lows Sunday morning ranging from the mid 50s to near 60
degrees.

Gosselin

&&

.AVIATION...  (For the 06z TAFs through 06z Friday Night)
Issued at 1151 PM CDT Thu Jul 27 2017

Challenging cloud forecast for tonight as low-level moisture
continues to linger near a front moving through the area. Latest
trends suggest MVFR cigs may not last quite as long as previously
thought, due to drier air working in from the north. However,
expect MVFR cigs to develop over the next couple of hours in the
St. Louis metro sites (with a light shower not out of the
question), and last into the early morning hours. Then, drier air
infiltrating from the northwest should help raise cigs to VFR
through the rest of Friday. UIN/COU should remain VFR through the
period. Winds through the period will be generally out of the
north.

SPECIFICS FOR KSTL:
Still a challenging ceiling forecast tonight due to lingering low-
level moisture near a passing cold front. Upstream obs still
suggest enough low-level moisture persists for a period of
potentially MVFR cigs (and perhaps even a light shower) through
the early morning hours. Skies should then rise to VFR as drier
air works in behind the front. Winds through the period will
generally be out of the north.

KD

&&

.LSX WATCHES/WARNINGS/ADVISORIES...
MO...None.
IL...None.
&&

$$

WFO LSX


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