Area Forecast Discussion
Issued by NWS St. Louis, MO

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000
FXUS63 KLSX 301730
AFDLSX

AREA FORECAST DISCUSSION...UPDATED AVIATION
NATIONAL WEATHER SERVICE ST LOUIS MO
1230 PM CDT SUN AUG 30 2015

.SHORT TERM:  (THROUGH LATE THIS AFTERNOON)
ISSUED AT 345 AM CDT SUN AUG 30 2015

WITH SOME BREAKS IN THE CLOUD COVER, LIGHT WINDS AND PLENTY OF LOW
LEVEL MOISTURE, FOG HAS DEVELOPED ALONG AND NORTH OF WEAKENING
FRONTAL BOUNDARY. DENSE FOG IS NOT WIDESPREAD ENOUGH IN OUR AREA TO
WARRANT A HEADLINE AT THIS TIME, THOUGH WILL HAVE AREAS OF FOG
MENTIONED IN FORECAST FOR THIS MORNING THROUGH 14Z. OTHERWISE,
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS STILL POSSIBLE OVER
SOUTH HALF OF FORECAST AREA DUE TO LINGERING WEAK FRONTAL BOUNDARY.
AS FOR HIGH TEMPS TODAY, LOW TO MID 80S EXPECTED DESPITE PARTLY TO
MOSTLY CLOUDY SKIES.

BYRD

.LONG TERM:  (TONIGHT THROUGH SATURDAY)
ISSUED AT 345 AM CDT SUN AUG 30 2015

SHOWERS AND THUNDERSTORMS THAT DO DEVELOP THIS AFTERNOON SHOULD
DIMINISH HEADING INTO THE EVENING HOURS, BUT WITH UPPER LEVEL SHEAR
AXIS LINGERING OVER SOUTHEAST MISSOURI AND SOUTHERN ILLINOIS WILL
CONTINUE SLIGHT CHANCE POPS THROUGHOUT THE NIGHT OVER SOUTHEAST
SECTIONS OF THE CWA.

PRIMARY FORECAST QUESTION FOR MONDAY AND POSSIBLY EVEN INTO TUESDAY
IS WHAT IF ANY IMPACT THE AFOREMENTIONED SHEAR AXIS WILL HAVE ON THE
THUNDERSTORM THREAT IN OUR FA.  THERE IS GENERAL CONSENSUS THAT THIS
FEATURE WILL TAKE UP RESIDENCE FROM THE LOWER OHIO VALLEY INTO AR
DURING THE EARLY PART OF THE WORK WEEK...BUT THE EXACT LOCATION
DOES VARY FROM MODEL TO MODEL. MOS POPS FROM 00Z OPERATIONAL
NAM/GFS RUNS BOTH SUGGEST POPS AOB 10% OVER SE SECTIONS OF THE
CWA, ALTHOUGH 00Z OPERATIONAL ECMWF POPS ARE SLIGHTLY HIGHER THAN
THIS. FOR NOW HAVE DECIDED TO MAINTAIN A DRY FORECAST FOR
MONDAY (AND TUESDAY)...AND WILL LET DAY SHIFT TAKE ANOTHER LOOK
AT THIS THREAT.

MODELS REMAIN IN GOOD AGREEMENT THAT UPPER LEVEL RIDGE WILL BE
EXPANDING FROM THE PLAINS INTO THE MID-MISSISSIPPI VALLEY AS WE
HEAD THROUGH THE UPCOMING WEEK. THIS SHOULD SHIFT SHEAR AXIS SOUTH
OF THE FA WITH TIME...WHILE ANY UPPER LEVEL DYNAMICS WILL REMAIN
WELL NORTH AND NORTHWEST OF OUR AREA IN BAND OF WESTERLIES THAT
WILL STRETCH FROM THE PACIFIC NORTHWEST INTO SOUTH CENTRAL CANADA.
THIS SHOULD MEAN DRY AND TRANQUIL EARLY SEPTEMBER WEATHER FOR THE
CWA...WITH THE RETURN OF SUMMERTIME HEAT AND HUMIDITY. DEWPOINTS
HAVE ALREADY REBOUNDED TO SUMMERY LEVELS OVER THE PAST TWO
DAYS...AND IT APPEARS THAT TEMPERATURES WILL BE FOLLOWING THIS
TREND AS THE EASTWARD EXPANSION OF THE UPPER RIDGE PUSHES 850MB
TEMPS INTO THE 18-20C RANGE. THIS SHOULD EASILY SUPPORT HIGHS
AROUND THE 90 DEGREE MARK ACROSS THE ENTIRE FA IN THE TUESDAY-
SATURDAY TIME FRAME.

TRUETT

&&

.AVIATION:  (FOR THE 18Z TAFS THROUGH 18Z MONDAY AFTERNOON)
ISSUED AT 1220 PM CDT SUN AUG 30 2015

ISOD TO WIDELY SCT TSRA ARE POSSIBLE AGAIN THIS AFTERNOON INTO
EARLY EVE. BEST CHANCES ARE S OF STL/SUS/CPS AND WILL THEREFORE
KEEP TAFS DRY FOR NOW. OTHERWISE...EXPECT CLOUDS TO CLEAR OUT
TONIGHT AND REDEVELOPMENT OF FG AT UIN AND SOME LIGHT FG AT COU
BEFORE THE SFC BOUNDARY LIFTS NWD. WINDS WILL BECOME SLY MON
MORNING WITH SCT CU.

&&

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

$$

WFO LSX


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