Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 311151
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
651 AM CDT SUN MAY 31 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 315 AM CDT SUN MAY 31 2015

COOL HIGH PRESSURE NOSING IN FROM THE GREAT LAKES TONIGHT...WITH A
FAIRLY STRONG DRY WEDGE FROM 5000-8000 FT AGL IN PLACE ACROSS THE
AREA. WEAKLY NORTHWEST FLOW ALOFT SHOWING A COMPACT WAVE PUSHING
INTO THE WESTERN DAKOTAS...AND THIS FEATURE WILL CLIP ALONG FAIRLY
QUICKLY THROUGH THE DAY. SO FAR...AREA OF RAINFALL HAS BEEN TREKKING
THROUGH THE WESTERN DAKOTAS...WITH EVEN A STRAY CLOUD TO GROUND
LIGHTNING INDICATION...BUT SYSTEM WILL QUICKLY BEGIN TO ENCOUNTER
DRIER AND MORE STABLE AIRMASS PUSHING EASTWARD. EXPECT THAT TRENDS
SHOWN IN HRRR AND RAP WILL CAPTURE THE FLAVOR OF THE SHORT RANGE
FORECAST...IN THAT INITIALLY TOGETHER SYSTEM IN TERMS OF FRONTAL AND
JET DYNAMICS WILL BECOME DISJOINTED AS UPPER LEVEL WAVE CLIPS
RAPIDLY SOUTHEAST...AND LIFT FORCING BECOMES MORE ONE DIMENSIONAL IN
TERMS OF WEAK ISENTROPIC UPGLIDE AS THE MID LEVEL FRONT MOVES EAST
AND SLOWS UP LATER TODAY AND TONIGHT.  SCENARIO SHOULD PLAY OUT
WHERE SCATTERED LIGHT PRECIPITATION WILL PUSH INTO THE CWA VERY LATE
MORNING FROM THE WEST/NORTHWEST...STRUGGLES TO MOVE EASTWARD AS
UPPER WAVE OUTRUNS THE MID LEVEL LIFT FOCUS...AND SEE A SLOW
PROGRESSION EASTWARD OF A GRADUALLY DISSIPATING PRECIPITATION AREA.
VIRTUALLY NO INDICATION OF INSTABILITY THIS FAR EAST FROM ANY
LEVEL...SO HAVE KEPT PRECIPITATION CLEAR OF THUNDER MENTION.
HOWEVER...BY LATER NIGHT...LINGERING MID LEVEL BOUNDARY ACROSS
SOUTHEAST SOUTH DAKOTA...AS WELL AS THE INCREASING LOW LEVEL JET AND
MOISTURE TRANSPORT...COULD SPARK A FEW MORE SHOWERS ACROSS SOUTHEAST
SOUTH DAKOTA...AND PERHAPS A RUMBLE OF THUNDER TOWARD THE JAMES
VALLEY.

OTHERWISE...SOME STRATUS ADVECTING WESTWARD INTO THE EASTERN CWA
EARLY THIS MORNING...AND SEVERAL HIGH RESOLUTION MODELS SUGGEST THIS
PROCESS WILL CONTINUE THIS MORNING...BUILDING NORTHWARD THROUGH
SOUTHWEST MINNESOTA...AND SPREADING THROUGH THE I29 CORRIDOR...BUT
EVENTUALLY WILL BE MASKED BY INCREASE IN HIGHER CLOUDS IN ADVANCE OF
UPSTREAM WAVE. WITH ABUNDANCE OF CLOUDS...AND EVEN A SCATTERED
NATURE TO LIGHT PRECIPITATION TODAY...EXPECT TEMPS TO STRUGGLE A BIT
TO REACH POTENTIAL MOST AREAS...MEANING 60S FOR MOST. PERSISTENT
SOUTHEAST WINDS TONIGHT ALONG WITH CLOUDS SHOULD MAKE FOR A MILDER
NIGHT IN THE UPPER 40S TO LOWER 50S.

.LONG TERM...(MONDAY THROUGH SATURDAY)
ISSUED AT 315 AM CDT SUN MAY 31 2015

A RATHER MESSY PATTERN SETTING UP FOR THE MEDIUM AND EXTENDED RANGE
FORECASTS...WITH SEVERAL CHANCES FOR THUNDERSTORMS AS WE MOVE
THROUGH THE MIDDLE AND END OF NEXT WEEK.

THE EARLY PORTIONS OF THE FORECAST...MONDAY...MONDAY NIGHT...AND
TUESDAY CONTINUE TO REMAIN QUIET.  WEAK ISENTROPIC LIFT INTERACTING
WITH MID-LVL MOISTURE STRUNG OUT ACROSS THE CWA WILL KEEP A FEW
SHOWERS PERCOLATING ACROSS THE JAMES RIVER VALLEY MONDAY MORNING.
HOWEVER...INCREASING EML AND A LACK OF ANY APPRECIABLE FORCING
MECHANISM SHOULD PREVENT ANY AFTERNOON CONVECTION INTO MONDAY
NIGHT.

A FEW SHOWERS MAY AGAIN TRY TO MOVE EASTWARD MONDAY NIGHT INTO
TUESDAY MORNING...LIKELY REMNANTS FROM CONVECTION OVER THE WESTERN
PLAINS MONDAY EVENING. THE OTHER NOTICABLE THING WILL BE SHARP
SOUTHERLY FLOW DEVELOPING BY TUESDAY MORNING.  A FAIRLY
UNIDIRECTIONAL MERIDIONAL FLOW SHOULD PROMOTE RATHER GUSTY WINDS
TUESDAY AFTERNOON...HAVE BUMPED UP WIND SPEEDS SLIGHTLY.  THE
SOUTHERLY FLOW WILL INCREASE SFC MOISTURE INTO THE AREA...AND SHOULD
BEGIN TO POOL ACROSS THE WESTERN DAKOTAS ALONG A NORTH-SOUTH
ORIENTED SFC BOUNDARY. WE SHOULD SEE CONVECTION FORM ALONG THIS
BOUNDARY TUESDAY EVENING AS SHORTWAVE ENERGY EJECTS INTO THE PLAINS.
WHILE SHEAR REMAINS ON THE LOW SIDE (15-30 KTS)...INSTABILITY SHOULD
PROMOTE A FEW STRONG TO SVR STORM CLUSTERS WEST OF THE AREA.
POTENTIAL FOR A WIND DRIVEN NOCTURNAL MCS SEEMS PLAUSIBLE GIVEN THE
INCREASING 700:500 MB WESTERLY FLOW...AND INCREASING NOCTURNAL
LLJ...BUT THE TRACK WOULD BE VERY QUESTIONABLE. SOUNDINGS ALSO
INDICATE A RATHER WARM EML AOA 12C AT 700 MB TUESDAY EVENING AT
CHAMBERLAIN.

REMNANT CONVECTION WILL SLIDE THROUGH THE AREA WEDNESDAY
MORNING...LEAVING CONSIDERABLE QUESTIONS ON SVR CHANCES ON WEDNESDAY
AFTN/EVE. BEST FOCUS FOR LATE DAY REDEVELOPMENT WOULD BE ALONG
SFC BOUNDARY JUST WEST OF THE CWA. AGAIN...HARD TO PINPOINT SVR
RISK GIVEN POOR SHEAR...BUT POTENTIAL INSTABILITY WOULD SUGGEST AN
ELEVATED RISK AT MINIMUM. OF MORE UNCERTAINTY WILL BE THE DRASTIC
INCREASE IN HUMIDITY...WITH DEW POINTS PUSHING THE MID/UPR 60S
GIVEN DEEP SOUTHERLY FLOW.

AS WE MOVE THROUGH THE END OF WEEK AND INTO NEXT WEEKEND...MORE
UNCERTAINTY DEVELOPS AND REALLY DIFFICULT TO TAKE ANY MODEL AT FACE
VALUE GIVEN CONVECTIVE CONTAMINATION. APPEARS THAT WE WILL AT LEAST
HAVE ADDITIONAL CONVECTION CHANCES AND A MARGINAL SVR WX RISK ON
THURSDAY AND FRIDAY AS THE FLOW REMAINS SOUTHWESTERLY AND POTENTIAL
DESTABILIZATION REMAINS MODEST. THE WEEKEND FORECAST IS VERY MUCH UP
IN THE AIR.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING)
ISSUED AT 651 AM CDT SUN MAY 31 2015

SMALL AREA OF STRATUS ACROSS SOUTHWEST MINNESOTA AND NORTHWEST
IOWA WILL CONTINUE TO ADVECT WITH PREVAILING GRADIENT TO THE WEST
AND NORTHWEST THROUGH THE MORNING. HIGHEST PROBABILITY REMAINS
THAT ANY CLOUDINESS IMPACTING KSUX AND KFSD TAF SITES WILL BE JUST
INTO THE VFR RANGE. OTHERWISE...UPPER LEVEL SYSTEM BUILDING INTO
THE WESTERN PLAINS WILL MOVE QUICKLY PAST TODAY. DECENT COVERAGE
OF LIGHT PRECIPITATION THUS FAR IN THE WESTERN PLAINS. BEST THREAT
FOR SOME PERIOD OF LIGHT RAINFALL WILL OCCUR TOWARD MIDDAY AND
EARLY AFTERNOON FOR KHON...BUT SHOULD REMAIN VFR DURING TIME OF
ANY PRECIPITATION. HOWEVER...BATTLE WITH DRIER AIR AND UPPER
DYNAMICS OUTRACING THE LOWER TO MID LEVEL FRONTAL SUPPORT KEEPS
MENTION OF ANY PRECIPITATION FOR KFSD OR KSUX BELOW THRESHOLD FOR
THE TIME. LOW LEVEL SOUTH TO SOUTHEAST WINDS COULD RETURN SOME
LOWER CLOUDINESS TOWARD KSUX TOWARD END OF PERIOD...AND FOR NOW
HAVE HINTED TOWARD LOWER END OF VFR RANGE.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...DUX
AVIATION...CHAPMAN


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