Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 120427
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1127 PM CDT THU SEP 11 2014

.SHORT TERM...(THIS EVENING THROUGH FRIDAY)
ISSUED AT 327 PM CDT THU SEP 11 2014

MODELS HAVE COME INTO MUCH BETTER AGREEMENT ON FRONTOGENETIC BAND
OF COLD RAIN DEVELOPING IN SOUTH CENTRAL SOUTH DAKOTA AS UPPER
WAVE TO THE WEST SHIFTS EAST. THIS BAND IS EXPECTED TO SHIFT EAST
ALONG AND SOUTH OF THE MISSOURI RIVER VALLEY THROUGH THE OVERNIGHT
INTO NORTHWEST IOWA. HAVE INCREASED POPS ALONG THE SOUTH
DAKOTA/NEBRASKA BORDER INTO NORTHWEST IOWA INTO THE CATEGORICAL
RANGE...WITH FAIRLY STEEP DROP OFF TOWARDS I-90 AS DRY AIR
CONTINUES TO FEED IN FROM THE NORTH. HAVE KEPT LOWS ABOVE GUIDANCE
VALUES...AND CLOUD COVER SHOULD LIMIT THE AMOUNT OF RADIATIVE
COOLING.

BAND OF PRECIPITATION IS EXPECTED TO SHIFT EAST OF THE FORECAST AREA
IN THE MORNING...HOWEVER...FORECAST SOUNDING SHOW STEEP MID LEVEL
LAPSE RATES THAT WILL AT LEAST SUPPORT SELF DESTRUCTIVE SUNSHINE...
IF NOT BONAFIDE SHOWERS ACROSS THE AREA. LAPSE RATES DECREASE
SLIGHTLY THROUGHOUT THE DAY FROM WEST TO EAST...SO HAVE CHANCE OF
SHOWERS SHIFTING EAST THROUGHOUT THE DAY. WITH RELATIVELY MIXY
CONDITIONS...EXPECT TEMPERATURES TO WARM INTO THE MID 50...ONLY 20
DEGREES BELOW NORMAL.

.LONG TERM...(FRIDAY NIGHT THROUGH THURSDAY)
ISSUED AT 327 PM CDT THU SEP 11 2014

SURFACE RIDGE OF HIGH PRESSURE FINALLY NUDGES OFF TO THE EAST
FRIDAY NIGHT WHICH WILL GIVE OUR AREA A RETURN FLOW OF SOUTHERLY
AIR. STILL LOOKS AS THOUGH OUR SOUTHEAST ZONES ARE THE MOST IN
DANGER OF GETTING A LIGHT FROST...GENERALLY ALONG AND EAST OF A
SIOUX CITY TO WINDOM MN LINE...DUE TO THE SURFACE FLOW BEING
EXTREMELY LIGHT. CONVERSELY...BELIEVE THAT OUR WESTERN ZONES ARE
TOO COOL. MANY GUIDANCE VALUES SHOW VERY CHILLY AIR CONSIDERING
THAT THE SOUTHERLY FLOW WILL BE INCREASING A BIT OVERNIGHT. MANY
GUIDANCE VALUES ARE NOT MUCH MILDER THAN OUR EASTERN ZONES WHICH
DOES NOT MAKE ANY SENSE TO ME. THEREFORE BLENDED SOME MILD ECMWF
LOWS INTO THE CONSENSUS NUMBERS TO MODERATE THE LOWS ALONG AND
WEST OF THE JAMES RIVER.

SATURDAY...TEMPERATURES FINALLY MODERATE SOME...TO 10 TO 15
DEGREES BELOW NORMAL. MIXING TEMPERATURES TO AROUND 850MB YIELDS A
LOT OF HIGHS IN THE 60 TO 65 DEGREE RANGE. DOUBT MIXING WILL BE
HIGHER THAN THAT WITH A SOUTHERLY FLOW...BUT SKIES WILL BE SUNNY
TO PARTLY CLOUDY AS A BAND OF WARM AIR ADVECTION MID CLOUDS MOVES
WESTWARD ACROSS OUR FORECAST AREA.

THE NEXT WAVE TO MOVE ACROSS OUR REGION WILL BE SUNDAY AFTERNOON
AND SUNDAY NIGHT. QG FORCING SHOWS MUCH OF THE DYNAMICS ASSOCIATED
WITH THE UPPER PORTION OF THE WAVE TO BE NORTH OF OUR AREA.
HOWEVER THERE IS ENOUGH CONVERGENCE AND MOISTURE IN THE MID LEVELS
TO NOW WARRANT LOW POPS FROM I 90 SOUTHWARD ON SUNDAY...WITH
STRONGER CHANCE POPS IN MUCH OF OUR EAST AND SOUTH SUNDAY NIGHT
WHEN THE MOISTURE PROFILE DEEPENS MORE. SUNDAYS TEMPERATURES WILL
CONTINUE TO CRAWL BACK TO VALUES CLOSER TO NORMAL...BUT STILL A
GOOD TEN DEGREES BELOW NORMAL WITH MID TO UPPER 60S COMMON.

IN THE EXTENDED PORTION OF THE FORECAST...THE DETERMINISTIC MODELS
ARE IN GOOD AGREEMENT IN SHOWING A BROAD NORTHWEST FLOW ALOFT
THROUGH MID WEEK...WITH UPPER RIDGING OVER THE PLAINS BY DAY 7
THURSDAY. IN GENERAL...THERE WILL LIKELY BE A WARMING TREND WITH
MOST HIGHS SEASONABLY MUCH MORE REASONABLE WITH NO THREAT FOR
FROSTY TEMPERATURES AT NIGHT. AS OF THIS TIME...THERE IS NOT A LOT
TO KEY ON PRECIPITATION WISE EITHER.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1122 PM CDT THU SEP 11 2014

MAINLY VFR CEILINGS ARE EXPECTED TO PERSIST THROUGH THE PERIOD.
BAND OF LIGHT RAIN WILL CONTINUE TO TRACK ALONG THE MISSOURI RIVER
VALLEY...WITH SCATTERED SHOWERS POSSIBLY REACHING AS FAR NORTH AS
INTERSTATE 29. COULD SEE SOME TEMPORARY MVFR VISIBILITY AND CEILINGS
WITH THIS ACTIVITY...WHICH WILL SLOWLY SHIFT EASTWARD THROUGH
AROUND MID MORNING THURSDAY. OVERCAST LOW END VFR CEILINGS WILL
BECOME SCATTERED LATE FRIDAY MORNING...HOWEVER AGAIN...THERE MAY
SOME SOME BRIEF LOWERING TO MVFR WITH ISOLATED RAIN SHOWERS AGAIN
POSSIBLE LATE MORNING INTO THE AFTERNOON. NORTHERLY WINDS WILL BE
AROUND 10 KT OR LESS. MORE WIDESPREAD CLEARING WILL FINALLY ARRIVE
AROUND SUNSET FRIDAY.

&&

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

$$

SHORT TERM...
LONG TERM...MJ
AVIATION...



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