Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 251152
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
652 AM CDT FRI JUL 25 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 358 AM CDT FRI JUL 25 2014

AFTER EARLY MORNING WEAK FORCING FOR LINGERING CONVECTION IN THE
EXTREME NORTH/EAST WITH CONTINUED VEERING OF 45-55KT LOW LEVEL
JET...WILL BE SETTLING IN TODAY TO ENVIRONMENT WITH EXTREME WARMTH
ALOFT. WEAK AREA OF SURFACE LOW PRESSURE JUST APPROACHING THE FAR
WESTERN CWA AT 08Z AND ACCOMPANYING BOUNDARY WILL WORK SLOWLY
EASTWARD THROUGH THE CWA TODAY. A CONSIDERABLE SOURCE OF LOWER LEVEL
MOISTURE IN PLACE WITH SOUTHERLY FLOW IN ADVANCE OF FRONTAL
BOUNDARY...AND THE STRENGTH OF INVERSION IN PLACE...SO DEWPOINTS ARE
LIKELY TO PUSH INTO THE LOWER 70S FOR AT LEAST THE EASTERN HALF OF
THE CWA. CAP WILL BE TOO STRONG FOR ANY DEVELOPMENT ALONG THE
ADVANCING BOUNDARY. HOWEVER...DO HAVE SOME CONCERN FOR POTENTIAL
STRATUS DEVELOPMENT AHEAD OF BOUNDARY ONCE INITIATION OF DAYTIME
HEATING OCCURS. SHOULD NOT BE A BULK OF DAY AFFAIR FOR ANYONE
WITH ENOUGH WESTERLY COMPONENT ALONG WITH THE FRONTAL PUSH TO LIMIT
AREA AND COVERAGE...AT LEAST TO A POINT TO ANTICIPATE BUT A MINOR
IMPACT ON POTENTIAL HIGH TEMPERATURES. SHOULD HAVE ENOUGH SUNSHINE
TO GET MID 80S TO LOWER 90S ACROSS THE AREA...WARMEST THROUGH THE
MISSOURI VALLEY. HEAT INDEX DOES ACTUALLY APPROACH 100 IN THE LOWER
MISSOURI VALLEY BY EARLY TO MID AFTERNOON COURTESY OF THE LINGERING
HIGHER DEWPOINTS.

FURTHER NORTH AND WEST...WHERE A BETTER NORTHERLY FLOW DEVELOPS
BEHIND THE FRONT...RAW MODEL SOLUTIONS ARE A BIT BETTER OVERALL ON
SHOWING THE DRYING POTENTIAL WORKING IN BEHIND THE FRONT THIS
AFTERNOON. THIS DRYING WILL EVENTUALLY PUSH IN ALONG WITH THE
STRONGER NORTHERLY FLOW AREA THROUGH THE DAY...BUT SHOULD LOSE A
FAIR CHUNK OF MOMENTUM GOING INTO THE EVENING...LEAVING SOMEWHAT
BETTER LOW LEVEL MOISTURE LINGERING TOWARD THE SOUTHERN CWA IN THE
EVENING AND OVERNIGHT. SOME CONSIDERATION TO MENTIONING A LITTLE FOG
IN THE LOWER MISSOURI VALLEY...BUT MORE LIKELY TO REMAIN FAIRLY
LIGHT.

BY LATER TONIGHT...WILL START TO SEE INFLUENCE OF STRONG UPPER WAVE
CURRENTLY IN SOUTHERN ALBERTA...AS MODESTLY STRONG JET STREAK MOVES
OUT INTO THE NORTHERN PLAINS. WILL SEE DEVELOPMENT OF SOME WEAKER
RETURN FLOW AND MID LEVEL THETA E ADVECTION/FRONTAL FORCING AS RIGHT
ENTRANCE REGION PROGRESSES TOWARD AREA. THIS TYPE OF FRONTAL FORCING
OFTEN OCCURS AT A PACE SOMEWHAT FASTER THAN MODELS SUGGEST...BUT
WILL ALSO HAVE IMPACT OF DRYING OF LOWER TO MID LEVELS PUSHING INTO
AREA FROM THE NORTH/NORTHEAST OVERNIGHT TO SLOW UP PRECIP THREAT.
ARW SUBSET OF THE SREF ARE HIGHLY IN FAVOR OF DEVELOPING
PRECIPITATION...BUT FAIL TO SEE WHAT DEVELOPMENT WOULD BE QUITE AS
FAR NORTH AS MANY OTHER SOLUTIONS...WITH MID LEVEL FLOW A BIT NORTH
OF ZONAL...AND ANY HIGH PLAINS INITIATION DURING THE NIGHT MORE
LIKELY TO WANDER A BIT SOUTH OF DUE EAST GIVEN THE LARGER SCALE FLOW.
FOR NOW...WILL MAINLY HIT SOUTHWEST THIRD OF THE CWA WITH MODERATE
CHANCE PRECIPITATION MENTION...MAINLY 09-12Z WINDOW.  GIVEN JUST A
BIT MORE INFLUENCE ON THE LOWER LEVEL WIND FIELDS...COULD EASILY
INDUCE JUST A BIT MORE CROSS FRONTAL FLOW AND INCREASE PRECIPITATION
THREAT.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 358 AM CDT FRI JUL 25 2014

CONVECTION FROM FRIDAY NIGHT IS EXPECTED TO CONTINUE TO MOVE EAST
ON SATURDAY MORNING ASSOCIATED WITH A WEAK UPPER LEVEL WAVE MOVING
ACROSS SOUTHERN SOUTH DAKOTA AND NORTHERN NEBRASKA. THE QUESTION
IS HOW MUCH INSTABILITY WILL EXIST IN THE MISSOURI VALLEY. THE GFS
AND NAM STRUGGLE TO PRODUCE ANY APPRECIABLE INSTABILITY ABOVE THE
BOUNDARY LAYER BUT THE WRF-ARW MEMBERS OF THE SREF HAVE INSTABILITY
EXCEEDING 1000 J/KG IN SOME CASES...AND THIS IS ACCOMPANIED BY
EFFECTIVE SHEAR OF 30 TO 40 KTS. THUS COULD SEE SOME STORM
ORGANIZATION THAT MAY SUPPORT ISOLATED SEVERE HAIL DURING THE
MORNING. BUT THIS IS REALLY CONTINGENT ON GETTING ENOUGH
INSTABILITY TO ENHANCE UPDRAFTS. FOR THAT REASON WILL ONLY MENTION
NONSEVERE HAIL IN THE HWO AT THIS TIME FOR SATURDAY MORNING. THIS
AREA OF STORMS WILL SHIFT SOUTH AND EAST OF THE AREA BY SATURDAY
AFTERNOON. THEN THE STRONG COLD FRONT WILL MOVE ACROSS THE AREA
SATURDAY AFTERNOON AND EVENING. THE SYNOPTIC SCALE FORCING FAVORS
SUBSIDENCE BUT WITH A BOUNDARY MOVING SOUTH AND SOME BOUNDARY
LAYER MOISTURE AM RELUCTANT TO REMOVE POPS FOR SATURDAY AFTERNOON
AHEAD OF THE FRONT SO CONTINUED WITH 20 TO 30 POPS OVER MOST AREAS
EAST OF THE JAMES RIVER. TEMPERATURES ARE VERY DEPENDENT UPON
CLOUD COVER. NEAR THE COLD FRONT MOVING IN ON SATURDAY
AFTERNOON...IT WILL BE VERY WELL MIXED AND IF THERE IS FULL
SUN...IT IS CERTAINLY POSSIBLE HIGHS COULD REACH THE UPPER 80S AND
LOWER 90S IN MOST LOCATIONS. THE REAL QUESTION IS THE EFFECT OF
THE MORNING CONVECTION AND HOW LONG CLOUDS PERSIST INTO THE
AFTERNOON. THE UPPER LEVEL FLOW WOULD TEND TO KEEP MOST OF THE
ANVIL CIRRUS MOVING EAST WHICH MEANS AN INCREASING LIKELIHOOD OF
PARTLY TO MOSTLY SUNNY SKIES AS ONE GOES NORTH OF INTERSTATE 90.
ALONG THE MISSOURI RIVER...CLOUDS MAY PERSIST INTO AFTERNOON WHICH
COULD KEEP HIGHS IN THE LOW TO MID 80S. SO THIS IS A RATHER LOW
CONFIDENCE TEMPERATURE WITH FORECAST HIGHS IN THE MID TO UPPER
80S.

CONVECTION WILL MOVE EAST OF THE AREA AND THE BOUNDARY WILL MOVE
THROUGH SATURDAY NIGHT. DRIER AND COOLER AIR WILL MOVE INTO THE
AREA SATURDAY NIGHT AND SUNDAY. WINDS SHOULD PICK UP LATE SATURDAY
NIGHT AND ARE LIKELY TO GUST OVER 30 MPH ON SUNDAY AS THE
ATMOSPHERE BECOME WELL MIXED. THERE IS STRONG SYNOPTIC SCALE
SUBSIDENCE OVER THE AREA ON SUNDAY SO HAVE REMOVED THE CHANCE FOR
LIGHT SHOWERS IN SW MN BUT DO STILL EXPECT SOME CAPPED
STRATOCUMULUS TO FORM DURING THE AFTERNOON. AS THE HIGH MOVES OVER
ON SUNDAY NIGHT...THESE CLOUDS SHOULD SLOWLY DISSIPATE AND WINDS
DECREASE. HIGHS ON SUNDAY WILL GENERALLY BE IN THE 70S WITH LOWER
80S IN THE MISSOURI VALLEY. LOWS ON SATURDAY NIGHT WILL BE IN THE
UPPER 50S AND LOWER 60S...WITH 50S EXPECTED ON SUNDAY NIGHT.

IN THE EXTENDED...MONDAY THROUGH THURSDAY...THE AREA WILL BE IN
NORTHWEST FLOW ALOFT WITH A STRONG TROUGH OVER THE EASTERN US AND
A STRONG RIDGE OVER THE WESTERN US. THIS PLACES A LARGE AREA OF
HIGH PRESSURE OVER THE PLAINS THROUGH THE PERIOD. THE GFS TRIES TO
MOVE THIS HIGH EAST MORE QUICKLY THAN THE ECMWF AND CANADIAN GEM
AND BRING MOISTURE AND EVEN A CHANCE OF SHOWERS INTO THE AREA BY
LATE TUESDAY. BUT GIVEN THE RELATIVE STABILITY OF THIS PATTERN
SEE NO REASON WHY THE HIGH WILL BE IN ANY HURRY TO MOVE INTO THE
GREAT LAKES. THEREFORE FOLLOWED CLOSER TO THE ECMWF AND GEM. THIS
MEANS DRY WEATHER...PARTLY TO MOSTLY SUNNY SKIES...AND RELATIVELY
LIGHT WINDS EXPECTED ACROSS THE AREA THROUGH WEDNESDAY. DEW POINTS
WILL ALSO BE LOW FOR JULY...GENERALLY IN THE 50S. DID KEEP HIGHS
CLOSER TO THE ECMWF/CANADIAN WITH MID TO UPPER 70S ALONG AND EAST
OF I29 AND UPPER 70S TO LOWER 80S WEST OF I-29. DID BRING A LOW
CHANCE OF THUNDERSTORMS IN FOR THURSDAY BUT MOISTURE REMAINS
LIMITED. THE HIGH WILL BEGIN TO MOVE EAST SO HIGHS WILL APPROACH
OR EXCEED 80 IN MOST LOCATIONS ON THURSDAY.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 651 AM CDT FRI JUL 25 2014

BIGGEST CHALLENGE OF THE TAF PERIOD IS THE DETERMINATION IF ANY
MVFR TO IFR CEILINGS WILL DEVELOP THIS MORNING. CURRENTLY WATCHING
AN AREA OF VFR STRATOCUMULUS FORM BETWEEN KSUX AND KFSD EASTWARD...
IN OUTFLOW FROM EARLIER THUNDERSTORMS. PRESENCE OF THESE CLOUDS
WILL DIMINISH LATER CHANCES FOR A LOWER DEVELOPMENT...BUT KFSD AND
KSUX WILL BE RIGHT ON THE EDGE. EXPECT THAT ONCE GET MORE DIURNAL
HEATING...WILL FIND AREA OF LOWER STRATOCUMULUS DEVELOPMENT
BETWEEN THESE CLOUDS AND THE LOCATION OF FRONTAL ZONE WORKING
SLOWLY EASTWARD. ALSO POTENTIAL FOR A LITTLE POSTFRONTAL CUMULUS
AROUND KHON BY MIDDAY.  WITH DRYING PUSH LOSING ITS PUNCH TOWARD
THE SOUTHEAST CWA...POSSIBLE THAT LATER TONIGHT COULD GET SOME
MVFR VISIBILITIES IN FOG.

&&

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

$$

SHORT TERM...CHAPMAN
LONG TERM...SCHUMACHER
AVIATION...CHAPMAN






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