Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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272
FXUS63 KFSD 201816
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
116 PM CDT WED MAY 20 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 350 AM CDT WED MAY 20 2015

THIS FAIRLY WEAK RAIN SYSTEM IS WELL BEHAVED...OR PERHAPS ONE SHOULD
SAY THAT APPLIES TO THE MODEL FORECASTS. THE LIGHT RAIN PATTERN
CONTINUES TO EVOLVE AS EXPECTED...WITH THE WILD CARD AROUND THE
NORTHERN EDGE BEING THE EFFECT OF DRIER AIR BELOW MID LEVELS
AFFECTING WHEN AND WHERE RAIN REACHES THE SURFACE. THE FSD AREA IS
RIGHT IN THE POP GRADIENT ALTHOUGH NOT MUCH WILL FALL IF IT DOES
RAIN HERE. THE PEAK OF THE NORTHWARD EXTENT OF THE RAIN AND THE
SYSTEM ITSELF OVER OUR AREA APPEARS TO BE EARLY THIS MORNING AROUND
13-14Z. THE RAIN WILL THEN DECREASE FROM THE WEST AND
NORTHWEST...APPEARING TO HOLD STEADY ON THE NORTHERN EDGE FOR A BIT
LONGER. IN ANY EVENT BY NOON THE DECREASE WILL BE IN FULL SWING AND
THE RAIN SHOULD BE DONE WITH BY THE END OF THE AFTERNOON. BESIDES
THE SYSTEM MOVING OFF TO THE EAST...IT WILL ALSO BE WEAKENING AND
THUS DO NOT SEE A STUBBORN LINGERING RAIN INTO THE EARLY EVENING
SOUTHEAST.

HIGH TEMPERATURES NATURALLY ENOUGH WILL BE WARMEST IN THE FAR NORTH
WHERE THERE WILL BE SOME SOLAR HEATING. LOWS 50S SOUTHWEST TO LOWER
60S NORTHEAST SHOULD BE GOOD FOR HIGHS.

THE CLOUD THINNING AND DECREASE STARTING THIS AFTERNOON WILL BE IN
FULL SWING THIS EVENING AS IT ACCELERATES IN RESPONSE TO THE INCOMING
NORTHERLY UPPER FLOW WHICH WILL HELP BRING DRYING. SKIES WILL CLEAR
AND TEMPERATURES WILL DROP TO COOL BUT NOT FROSTY LEVELS.

WINDS TODAY AND TONIGHT WILL RANGE FROM LIGHT AND VARIABLE TO
NORTHERLY...WITH A TREND TO STILL FAIRLY LIGHT WESTERLY TONIGHT.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 350 AM CDT WED MAY 20 2015

RIDGING SURFACE AND ALOFT WILL BRING DRY CONDITIONS TO THE AREA
THURSDAY THROUGH FRIDAY. MOSTLY CLEAR SKIES ASIDE FROM A BIT OF
AFTERNOON/EARLY EVENING CU IN OUR EAST THURSDAY IN AREA OF SHALLOW
INSTABILITY...THEN GRADUAL INCREASE IN MID-HIGH CLOUDS THROUGH THE
DAY FRIDAY AS SHORTWAVE APPROACHES FROM THE SOUTHWEST. WITH THE
SURFACE RIDGE STILL DOMINANT OVER THE MID-MISSISSIPPI VALLEY EARLY
IN THE WEEKEND...LOW LEVEL MOISTURE RETURN TO OUR AREA IS LACKING
AND MODELS IN FAIRLY GOOD AGREEMENT SLOWING DOWN EASTWARD PUSH OF
SHOWERS WITH THIS LEAD WAVE FRIDAY NIGHT INTO SATURDAY. WILL STILL
CARRY POPS THROUGHOUT THE AREA BY SATURDAY...BUT HAVE SLOWED DOWN
TIMING A BIT.

UNFORTUNATELY STILL VERY LITTLE AGREEMENT AMONG THE LONGER RANGE
MODELS IN FINER DETAILS OF THE WESTERN CONUS TROUGH AS IT EVOLVES
EASTWARD INTO THE NORTHERN PLAINS THROUGH THE HOLIDAY WEEKEND. THIS
LEADING TO LOWER CONFIDENCE FORECAST WITH REGARD TO PRECIP TIMING AS
WELL AS TEMPERATURES FOR THE LATTER HALF OF THE WEEKEND SATURDAY
NIGHT THROUGH MEMORIAL DAY. WITH GULF BEGINNING TO OPEN UP BY LATE
SATURDAY...SEEMS REASONABLE TO CONTINUE FOCUS OF HIGHEST POPS IN THE
SATURDAY NIGHT PERIOD...THOUGH LATEST 20/00Z ECMWF TRENDING A BIT
DRIER IN EASTERN PARTS OF THE AREA EVEN INTO SUNDAY MORNING AS A
LINGERING LOW LEVEL BOUNDARY IN THE CENTRAL/SOUTHERN PLAINS HOLDS UP
THE MOISTURE RETURN...SO WILL HAVE TO WATCH FOR SUPPORT OF THIS
TREND IN FUTURE RUNS.

GENERALLY LOOKS LIKE WE SHOULD WORK TOWARD A DRIER PERIOD MONDAY
NIGHT INTO TUESDAY...BUT STILL LARGE DISCREPANCIES AMONG THE MODELS
AT THIS RANGE...SO DIFFICULT TO COMPLETELY PULL POPS FROM ANY ONE
PERIOD. WARMING TREND FROM CURRENT COOL SPELL ALSO APPEARS TO BE ON
TRACK...THOUGH HIGHS MAINLY MID 60S-LOWER 70S STILL THE BEST BET
THROUGH THE HOLIDAY WEEKEND. OUTLIER GFS DOES TRY TO SPREAD WARMER
AIR ACROSS THE REGION SUNDAY...BUT BEST AGREEMENT ON RETURN TO NEAR
OR ABOVE NORMAL TEMPERATURES LOOKS TO BE TUESDAY.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1252 PM CDT WED MAY 20 2015

MVFR CEILINGS WILL EXIT THE FAR SOUTHERN CWA EARLY IN THE
PERIOD...THEN VFR THROUGHT THE REMAINING TIME.

&&

.FSD WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
IA...NONE.
NE...NONE.
&&

$$

SHORT TERM...
LONG TERM...JH
AVIATION...08



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