Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 041132
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
632 AM CDT MON MAY 4 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 400 AM CDT MON MAY 4 2015

CHALLENGING FORECAST LOOKS TO BEGIN WITH CHALLENGING SHORT TERM.
OVERNIGHT...HAVE SEEN THE STRONG SURFACE FRONTAL BOUNDARY SETTLE
INTO FAR SOUTHERN PORTIONS OF THE REGION...AS MUCH DRIER AIR HAS
INVADED FROM THE NORTH BEHIND THE BOUNDARY.  SEVERAL CONTRADICTING
FACTORS TO THE SHORT TERM PRECIPITATION FORECAST.  FIRST...VERY FEW
SOLUTIONS HAVE AMPLE HANDLE ON THE DRY AIR INTRUSION AT LOWEST
LEVELS...WITH DEWPOINTS INTO THE UPPER 20S AND 30S OVER ALL BUT THE
EXTREME SOUTHEAST CWA. SECOND...THE DEGREE OF ELEVATED INSTABILITY
ACROSS THE FAR SOUTHERN CWA IS LACKING IN SHORT TERM HIGH RESOLUTION
MODELS...WHICH IS EVIDENT GIVEN RECENT UPTAKE IN SCATTERED BANDED
CONVECTION FROM THE LOWER MISSOURI VALLEY EASTWARD ACROSS NORTHWEST
IOWA FORCED IN BROAD JET ENTRANCE REGION. THIRD...DEALING WITH
TYPICAL BATTLE OF LOWER VERSUS HIGHER RESOLUTION MODELS. LARGE SCALE
SYNOPTIC TREND IS FOR LOWER LEVEL BAROCLINIC ZONE TO SETTLE FURTHER
SOUTHWARD OVER LAST COUPLE OF MODEL RUNS. HOWEVER...SOME QUESTION AS
TO HOW MUCH FURTHER THE MID LEVEL BOUNDARY WILL SETTLE GIVEN THE
PROXIMITY OF UPPER LEVEL JET ENTRANCE REGION PASSING ACROSS THE AREA
TODAY.  HIGHER RESOLUTION MODELS GENERALLY MUCH MORE AGGRESSIVE WITH
NORTHWARD SPREAD OF PRECIPITATION. HOWEVER...SHOULD MAKE NOTE THAT
TREND IN RAP HAS BEEN TO ALLOW LESS AND LESS THREAT TO SOUTHERN CWA
THROUGH THE DAY.

EARLY ON THIS MORNING...SHOULD SEE A GRADUAL DECREASE IN THE
SCATTERED SHOWERS AND ISOLATED THUNDERSTORMS OVER THE FAR SOUTH
EARLY THIS MORNING AS THE WAVE CONTINUES TO SHEAR AWAY. WILL SEE
RIDGING BEGIN TO REESTABLISH PRESENCE...BUT BATTLE A SMALL WAVE
WANDERING FROM KANSAS TOWARD EASTERN NEBRASKA LATER IN THE DAY.
CONVECTION SHOULD BREAK OUT CLOSER TO THIS FEATURE AND THE DEEPER
SYNOPTIC BOUNDARY...EXPANDING AND TRENDING TOWARD A MORE EASTWARD
MOTION WITH TIME ALONG BAROCLINIC ZONE EXPANDING TOWARD THE SIOUX
CITY AREA LATE DAY. GRADUALLY...THIS WAVE PULLS EASTWARD AND MAY SEE
MOST EXPANSIVE COVERAGE BRUSH THROUGH THE SOUTHERN CWA DURING THE
EVENING HOURS...THEN PROGRESS TOWARD A MORE SCATTERED COVERAGE AS
MID LEVEL WAVE AND ISENTROPIC ASCENT PUSHES NORTHWARD WITH DEEPENING
SOUTHERLY FLOW. OVERALL...WILL BE LOOKING FOR THUNDER COVERAGE TO BE
SMALL FRACTION OF THE OVERALL PRECIPITATION...WITH BEST THREAT
THROUGH THE SOUTHEAST HALF OF THE CWA OVERNIGHT. NO SEVERE STORMS
ARE EXPECTED WITH MINIMAL ELEVATED INSTABILITY AND GENERALLY WEAK
MID LEVEL FLOW.

TEMPWISE...WILL SET UP FOR FAIRLY DECENT EASTERLY MIXING WITH DRY
AIR...DESPITE A DECENT AMOUNT OF CLOUDINESS MOST LOCATIONS THROUGH
THE DAY. HIGHS SHOULD BE MAINLY UPPER 60S TO LOWER 70S...ON THE WARM
SIDE OF MIXING POTENTIAL DUE TO THE DRY AIR. INCREASING MOISTURE
TONIGHT FROM SOUTH TO NORTH WILL DEFINE LOWS UNDER THICKER
CLOUDS...MID 40S NORTH TO LOWER TO MID 50S SOUTH.

.LONG TERM...(TUESDAY THROUGH SUNDAY)
ISSUED AT 400 AM CDT MON MAY 4 2015

A RATHER MESSY MEDIUM AND EXTENDED FORECAST IS IN STORE FOR THE
REGION THIS WEEK AND INTO NEXT WEEKEND. THE LONG WAVE PATTERN WILL
BE DOMINATED BY LONG WAVE RIDGING ACROSS THE CONUS THIS WEEK...WITH
SEVERAL TROUGHS LIFTING THROUGH THE PLAINS.  THE MAIN WEATHER
FEATURE THROUGH WEDNESDAY/THURSDAY WILL BE A BROAD UPPER LOW
CURRENTLY OVER THE SOUTHWESTERN UNITED STATES THAT IS EXPECTED TO
SLIDE ALONG THE WESTERN PERIPHERY OF THE RIDGE. BY TUESDAY...THIS
TROUGH WILL BEGIN TO NUDGE THE LOW-LVL BAROCLINIC ZONE
NORTHWARD...WITH BROAD ISENTROPIC LIFT BRINING A CHANCE FOR SHOWERS
TO THE AREA ON TUESDAY. THE PRIMARY CONCERN WILL BE JUST HOW
WIDESPREAD THIS ACTIVITY WILL BE...AS SHORTWAVE ENERGY MOVING
THROUGH LATER TONIGHT SLIDES EAST OF THE AREA ON TUESDAY...ONLY TO
BE REPLACED BY SHORTWAVE RIDGING.  AND ADDITIONAL FACTOR IS THE
DEGREE OF DRY AIR REMAINING IN THE SUB-700 MB LAYER. WITH THE LIFT
BROAD IN NATURE...AND MOISTURE LIMITED TO A DEGREE...QPF THROUGH
TUESDAY NIGHT SHOULD BE FAIRLY LOW.

THEN A STRONGER PORTION OF THE AFOREMENTIONED UPPER TROUGH WILL
BEGIN TO LIFT INTO THE PLAINS ON WEDNESDAY. MODELS ALL IN GOOD
AGREEMENT THAT REMNANT CONVECTION FROM TUESDAY NIGHT ON THE WESTERN
PLAINS WILL LIFT INTO THE LOCAL AREA DURING THE DAY ON WEDNESDAY
WITH BROAD AND STRONG ISENTROPIC LIFT ASSISTING IN THE DEVELOPMENT
OF ADDITIONAL SHOWER AND EMBEDDED THUNDERSTORM ACTIVITY THROUGH THE
DAY. MOISTURE TRANSPORT RATHER IMPRESSIVE...BRINGING PWAT VALUES
AROUND 1.5 INCHES INTO THE AREA.  HOWEVER...A DISTINCT LACK OF
INSTABILITY IS ASSOCIATED WITH THIS PRECIPITATION FOR MUCH OF
WEDNESDAY...AND THIS SHOULD KEEP QPF DOWN.

DEPENDING ON THE SPEED OF PRECIPITATION WEDNESDAY MORNING...WILL
NEED TO WATCH FOR THE POTENTIAL OF CLOUDS SCATTERING LATER IN THE
AFTERNOON. A SECONDARY ROUND OF CONVECTION WILL LIKELY DEVELOP ALONG
INVERTED TROUGH OR DRYLINE ACROSS WESTERN NEBRASKA/KANSAS LATE
WEDNESDAY AFTERNOON. ONCE FORMED...IT WILL LIFT NORTHEAST WITH THE
SHORTWAVE WEDNESDAY NIGHT.  MUCAPE VALUES COULD CLIMB AS HIGH AS 500-
1000 J/KG WEDNESDAY EVENING AND SHEAR WILL BE ON THE
INCREASE...MAINLY SOUTH AND WEST OF THE JAMES RIVER.  THAT
SAID...FEEL THE GENERAL RISK OF SVR STORMS IS LOW...BUT COULD SEE
MARGINAL OUTLOOK SLIDE A BIT FURTHER NORTH. I WOULD ANTICIPATE
QUITE A BIT OF THUNDER AS THIS ACTIVITY LIFTS THROUGH THE AREA
INTO THURSDAY MORNING.

FEEL MOST OF THURSDAY WILL BE DRY...AS UPPER FORCING LIFTS
NORTHEAST.  THE UPPER TROUGH COULD LEAVE AN ELONGATED BOUNDARY
ACROSS THE SOUTHERN ZONES BY THURSDAY AFTERNOON.  MODELS STILL VARY
SIGNIFICANTLY WITH THIS FRONT...BUT A DECENT BUILDUP OF INSTABILITY
ALONG AND SOUTH OF IT COULD BE TAPPED INTO SHOULD A WEAK WAVE LIFT
NORTHWARD IN THE SWLY FLOW ALOFT. SHEAR CONTINUES TO BE
MARGINAL...BUT COULD SUPPORT A SEVERE STORM.

FRIDAY MAY BE THE DRIEST DAY OF THE EXTENDED...AS MODELS ARE IN
REASONABLE AGREEMENT FORMING A DEEP TROUGH OVER THE WESTERN THIRD
OF THE CONUS. BEYOND FRIDAY...BEGINNING TO LOOK RATHER WET ACROSS
MANY AREAS AS THIS UPPER TROUGH BEGINS TO LIFT INTO THE PLAINS AND
EVENTUALLY GREAT LAKES.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING)
ISSUED AT 631 AM CDT MON MAY 4 2015

MAIN CONCERN FOR THIS PERIOD IS POTENTIAL AND TIMING DEVELOPMENT
OF ELEVATED CONVECTION FOR KFSD AND KSUX. STRONG WAVE WILL MOVE
FROM KANSAS TO EASTERN NEBRASKA BY LATE AFTERNOON. ELEVATED
CONVECTION WILL SPREAD NORTH AND EAST TODAY...EXPECTED TO SPREAD
LATE AFTERNOON INTO SIOUX CITY. OVERALL ELEVATED INSTABILITY IS
FAIRLY WEAK...SO STUCK WITH MENTION OF SHOWERS WITH PEAK MENTION
BETWEEN 00Z AND 04Z. THERE WILL STILL BE A THREAT FOR ADDITIONAL
SHOWERS AND PERHAPS A RUMBLE OF THUNDER EVEN AFTER 04Z FOR KSUX...
BUT SHOULD DIMINISH TO A MORE SCATTERED THREAT LATER INTO THE
NIGHT. FOR KHON...THREAT APPEARS MINIMAL LATE IN PERIOD AND HAVE
NOT INCLUDED IN TAF.

&&

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

$$

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



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