Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 220912
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
412 AM CDT FRI APR 22 2016

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 412 AM CDT FRI APR 22 2016

THE REAL CHALLENGE TODAY WILL BE THE EXPANDING STRATUS FIELD ACROSS
PARTS OF NORTHWEST IOWA AND SOUTHWEST MINNESOTA. WHILE IT HAS THUS
FAR REMAIN JUST EAST OF FSD AND SUX...STILL A DECENT CHANCE THAT IT
COULD EXPAND FURTHER TO THE WEST...ESPECIALLY AROUND SUX. EXPECT THE
STRATUS TO LINGER THROUGH MID TO LATE MORNING IN PARTS OF NORTHWEST
IOWA AND SOUTHWEST MINNESOTA...BEFORE GIVING WAY TO A SUNNY
DAY.STARTING TO GET A LITTLE WORRIED HOWEVER WITH A LOW LEVEL WIND
FIELD TURNING TO THE NORTHEAST AND EAST THROUGH THE DAY THAT THIS
STRATUS WILL BE DIFFICULT TO SHAKE. WINDS WILL BE LIGHT ACROSS THE
AREA AND WITH PLENTY OF SUNSHINE HIGHS IN THE 60S WILL FEEL PRETTY
NICE.

BY TONIGHT THE RIDGE OF HIGH PRESSURE WILL MOVE EAST OF THE AREA
ALLOWING A SOUTH TO SOUTHEAST WIND TO DEVELOP. LOWS WILL BE MILDEST
IN CENTRAL SOUTH DAKOTA WHERE WINDS WILL INCREASE QUICKEST WHILE THE
COOLER READINGS WILL BE IN THE LOW SPOTS ACROSS NORTHWEST IOWA WHERE
WINDS WILL LIKELY REMAIN AT ABOUT 6 OR 7 MPH OR LESS THROUGH MOST OF
THE NIGHT. EXPECT LOWS TO RANGE FROM THE LOWER 50S IN CENTRAL SOUTH
DAKOTA TO THE MID 40S IN NORTHWEST IOWA.


.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 412 AM CDT FRI APR 22 2016

SOUTHERLY FLOW INCREASES ON SATURDAY AS AN INTENSIFYING AREA OF LOW
PRESSURE APPROACHES FROM THE WEST.  WITH THE GULF OPENING UP...THERE
IS SOME QUESTION AS TO HOW QUICKLY MOISTURE RETURNS ACROSS THE
AREA.MODELS SUGGEST 20-30 KNOTS OF SOUTHERLY FLOW THROUGH A DEEP
PORTION OF THE ATMOSPHERE...AND WITH A LITTLE EASTERLY COMPONENT
SHOULD KEEP SPEEDS BELOW ADVISORY LEVEL. THE NAM IS THE MOST
AGGRESSIVE WITH THE MOISTURE...AND ACTUALLY BECOMES UNSTABLE WITH
SATURATION AROUND 800 MB BY SUNDAY MORNING.  THE OPERATIONAL RUN OF
THE NAM IS CLOSE TO 2000 J/KG OF CAPE...WHILE OTHER MEMBERS OF THE
SREF ARE MUCH MORE STABLE.  WITH THE OPERATIONAL RUN OF THE NAM
BEING AN OUTLIER AND THE GFS REMAINING STABLE...IS A TOUGH CALL AND
LEFT LOW POPS IN. BEST CHANCES FOR STORMS ON SUNDAY APPEAR TO BE IN
THE EAST AHEAD OF THE TROUGH.

AS THE TROUGH MOVES THROUGH...MUCH COOLER MORE STABLE AIR IS
EXPECTED TO MOVE IN.  MODEL SOUNDINGS SUGGEST STRATUS
POTENTIAL...AND MAY SQUEEZE OUT SOME DRIZZLE. DROPPED MENTION OF
POPS AT THIS POINT ACROSS THE SOUTH...AND MAY NEED TO DO THE SAME
THING IN THE NORTH AS ATMOSPHERE APPEARS TO BE QUITE STABLE.  FOR
NOW...DROPPED POPS JUST TO A SLIGHT CHANCE.

DROPPED MENTION OF POPS ON MONDAY NIGHT AS FORECAST AREA IS IN
BETWEEN SYSTEMS.  NEXT SYSTEM MOVES INTO THE CENTRAL PORTIONS OF THE
PLAINS.  TOUGH CALL ON HIGHS ON TUESDAY...AS WE WILL LIKELY BE
SHROUDED IN CLOUDS WITH INCREASING EASTERLY FLOW.  REAL QUESTION AS
TO HOW FAR NORTH THE WARM FRONT WILL WORK THROUGHOUT THE DAY.  FOR
NOW...DECREASED HIGHS A FEW DEGREES ACROSS THE NORTH WHERE THE WARM
FRONT IS UNLIKELY TO REACH.

THEREAFTER...DIFFICULT FORECAST AS MODELS ARE UNSURE HOW MUCH COLD
AIR WILL COME DOWN. JUST THE GFS AND ECMWF ARE OFF NEARLY 10C AT 925
HPA.  FOR NOW...STUCK FAIRLY CLOSE TO CONSENSUS...WHICH IS NEARLY
ISOTHERMAL IN THE EC WORLD.

SURFACE RIDGE IS EXPECTED TO BUILD INTO THE REGION LATE WEEK... BUT
APPEARS AS THOUGH CLOUDS WILL ACCOMPANY THE RIDGE...MAKING
TEMPERATURES TRICKY.  FOR NOW...STUCK CLOSE TO CONSENSUS BUT COULD
BE STUBBORN TO WARM.


&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1041 PM CDT THU APR 21 2016

06Z TAFS ARE LIKELY GOING TO REFLECT VFR CONDITIONS WITH A COUPLE
OF CAVEATS. FIRST...STILL A LITTLE CONCERNED ABOUT PATCHY FOG
DEVELOPMENT IN THE JAMES RIVER VALLEY LATE TONIGHT AND EARLY
FRIDAY...RIGHT ALONG A SURFACE RIDGE AXIS WHICH WILL GIVE VERY
LIGHT WINDS IN THAT AREA. THEREFORE HEDGED WITH SOME MVFR TYPE FOG
FOR KHON...BUT AT THIS TIME DO NOT HAVE ENOUGH CONFIDENCE TO GO
ANY WORSE THEN THAT SINCE THE FOG MAY NOT FORM AT ALL. SECOND...
THERE ARE SOME INDICATIONS FROM THE LATEST NAM AND HRRR FIELDS
THAT THERE WILL BE ABUNDANT HUMIDITY IN THE VERY LOW LEVELS JUST
ABOVE THE SURFACE LATE TONIGHT THROUGH MID FRIDAY MORNING AT KSUX.
THE GROUND IS QUITE WET IN THAT AREA...SO IT MAY BE AN ARTIFACT OF
GROUND MOISTURE. BUT FOR A HEADS UP...DECIDED TO INCLUDE A
SCATTERED DECK AT 800 FEET JUST IN CASE SOME LOWER STRATUS FORMS
JUST BEFORE SUNRISE AND LINGERS INTO MID MORNING AT KSUX.

OTHERWISE CURRENTLY...UPPER END IFR TO MVFR STRATUS IS MOVING
SOUTHWARD ACROSS PARTS OF SOUTHWEST MN AND NORTHWEST IA. AT THIS
TIME...THE TRAJECTORY OF THESE CLOUDS SUGGEST THAT THEY WILL STAY
TOO FAR EAST TO IMPACT KSUX OR KFSD...BUT ESPECIALLY AT KSUX...IT
WILL BE CLOSE FOR A FEW HOURS.


&&

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

$$

SHORT TERM...08
LONG TERM...BT
AVIATION...MJ



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