Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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897
FXUS63 KFSD 151726
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
1226 PM CDT FRI MAY 15 2015

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 412 AM CDT FRI MAY 15 2015

ACTIVE WEATHER EXPECTED TODAY MAINLY ALONG AND WEST OF THE JAMES
RIVER. WITH THE LOW LEVEL FLOW TURNING EAST TO SOUTHEAST THROUGH THE
DAY AND THE LOW LEVEL JET IN THE CENTRAL HIGH PLAINS EARLY THIS
MORNING EXPECTED TO LIFT NORTHWARD...MOISTURE WILL BE ON THE
INCREASE. EXPECT UPPER 50S AND LOWER 60S DEWPOINTS TO SPREAD INTO
THE SOUTHERN AND WESTERN CWA BY MIDDAY WHILE BROAD LIFT ASSOCIATED
WITH MID LEVEL THETA-E ADVECTION...ALSO SHIFTS NORTHWARD. ALREADY
SEEING A LINE OF THUNDERSTORMS FIRING ALONG THIS MODEST AREA OF LIFT
IN WESTERN NEBRASKA. HIGH RES GUIDANCE SUGGESTS THAT THIS CONVECTION
MAY CLIP OUR SOUTH CENTRAL SD COUNTIES AROUND MIDDAY SO HAVE SLOWED
THE ARRIVAL OF POPS IN THIS AREA BY A FEW HOURS.

THIS AFTERNOON...INCREASED INSTABILITY ACROSS OUR SOUTHERN AND
WESTERN COUNTIES SHOULD PRODUCE CAPE VALUES OF AROUND 1000 TO 1500
J/KG AS SURFACE TEMPERATURES WARM INTO THE 70S. ADDITIONALLY...MID
LEVEL LAPSE RATES AND VEERING SHEAR PROFILES INCREASE AS THE
AFTERNOON AND EVENING PROGRESSES. WITH THE STRONGER SHEAR AND
INSTABILITY COINCIDING WITH THE ARRIVAL OF DEVELOPING LOW PRESSURE
OVER THE HIGH PLAINS AND AN ATTENDANT WARM FRONT...MID TO LATE
AFTERNOON AND EVENING STRONG TO SEVERE STORMS ARE POSSIBLE WITH THE
MAIN AREA OF INTEREST ALONG AND WEST OF THE JAMES RIVER. THE MAIN
THREATS WILL BE HAIL TO PING PONG BALL SIZE AND GUSTS TO 70 MPH.
WHILE THE THREAT FOR TORNADOES ARE LOW...CANNOT RULE OUT AN ISOLATED
TORNADO ALONG THE WARM FRONTAL BOUNDARY MID/LATE AFTERNOON THROUGH
MID EVENING...DEPENDING ON HOW FAR NORTH THIS BOUNDARY ADVANCES
THROUGH SUNSET.

OVERALL SEVERE THREAT WILL DIMINISH AROUND MIDNIGHT
TONIGHT...HOWEVER SHOWERS AND THUNDERSTORMS WILL CONTINUE TO LIFT
NORTHEAST ACROSS THE REMAINDER OF THE FORECAST AREA THROUGH THE
OVERNIGHT HOURS. LOWS TONIGHT WILL BE IN THE UPPER 50S TO LOWER 60S.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 412 AM CDT FRI MAY 15 2015

THERE IS A NOTABLE CONTRAST IN THE WAY AND TIMING OF BRINGING THE
STRONG MAIN WAVE AND UPPER LOW TO AND ACROSS THE AREA BETWEEN THE
NAM AND GFS. THE NAM IS MOSTLY DISCARDED THOUGH THE EC WHICH SEEMS
TO HAVE A GOOD SOLUTION LEANS SLIGHTLY TO THE NAM SPEED.

IN ANY EVENT SHOWER AND STORM ACTIVITY IS EXPECTED TO BE AT A
MINIMUM DURING THE DAY SATURDAY WITH THE WARM FRONT HAVING PASSED
NORTH...THE MAIN WAVE STILL TO THE SOUTH...AND EVEN A DEGREE OF H8
CAA OVER THE AREA ALONG WITH MEAGER SHEAR. AT THIS POINT HAVE KEPT
IN A SLIGHT CHANCE FOR MOST OF SATURDAY AND STARTED TO BRING UP POPS
LATE SATURDAY AFTERNOON BUT WOULD NOT BE SURPRISED TO SEE THE AREA
EXPERIENCE A GENERALLY DRY DAYTIME. THE THREAT INCREASES QUICKLY
SATURDAY EVENING WITH SOME NIGHTTIME SEVERE THREAT AS THE STRONG
MAIN SYSTEM COMES NORTH INTO THE AREA. SHEAR AND INSTABILITY ISSUES
PARTLY ASSOCIATED WITH THE LATE TIMING APPEARS TO BE THAT REASON FOR
A SLIGHT DOWNGRADE OF THE SPC SEVERE THREAT FOR WHAT IS NOW DAY 2
AND THIS SEEMS REASONABLE. DECENT COVERAGE OF SHOWERS AND STORMS
DURING THE NIGHT STILL LOOKS LIKE A GOOD BET THOUGH.

TEMPERATURES SHOULD GET WELL UP INTO THE 70S SATURDAY GIVEN AT LEAST
SOME LIKELY SUNSHINE...BUT SOME MARGINAL COOLING BEHIND THE WARM
FRONT SHOULD PREVENT ANY 80S. SATURDAY SHOULD BE WINDY FROM THE
SOUTH BUT NOT UP TO WIND ADVISORY LEVELS.

SUNDAY AS THE UPPER LOW PASSES NORTH OF THE AREA...THE SHOWER AND
STORM THREAT WILL BEGIN TO DO LIKEWISE. WINDS WILL TURN STEADILY
FROM S TO SW AND EVENTUALLY TO W/NW AND COOLER AIR WILL BEGIN TO
ARRIVE. A FEW LIGHT SHOWERS WILL LINGER SUNDAY NIGHT. MONDAY IS
EXPECTED TO BE DRY...COOL,,,AND BREEZY ESPECIALLY EAST.

HIGH PRESSURE PUSHING INTO THE AREA MONDAY NIGHT SHOULD BRING A FROST
FREEZE THREAT...MAINLY NORTH. TUESDAY THROUGH THURSDAY LOOKS LIKE A
COOL REGIME CONTINUING AND THE THREAT OF RAIN ASSOCIATED WITH A
THERMAL RIBBON TO THE SOUTH...THOUGH THE WEAKNESS OF THE UPPER
SUPPORT AND RESULTANT TIMING DIFFICULTIES THROWS SOME DOUBT ONTO
THE DETAILS. NO BIG STORMS IN ANY EVENT AT LEAST UNTIL AFTER THE
FORECAST PERIOD AS ANOTHER SOUTHWESTERN WAVE APPROACHES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 1222 PM CDT FRI MAY 15 2015

SCATTERED SHOWERS AND THUNDERSTORMS ARE EXPECTED TO CONTINUE INTO
THE AFTERNOON HOURS AS ELEVATED INSTABILITY LIFTS NORTHWARD AND
LIFT REMAINS ABUNDANT. GENERALLY...VFR CONDITIONS SHOULD
PREVAIL...OUTSIDE OF VERY OCCASIONAL LOWERING FROM PASSING SHOWERS.

VERY TRICKY FORECAST INTO THE OVERNIGHT AND DAYTIME HOURS OF
SATURDAY. MODEL CONSENSUS CONTINUES TO POINT TO LINGERING SHOWERS
IN THE EARLY EVENING AS STRONGER AND MORE WIDESPREAD CONVECTION
BLOSSOMS OVER WESTERN NE/SD. SHOULD AN ORGANIZED STORM CLUSTER
DEVELOP...FLOW VECTORS WOULD TAKE THIS ACTIVITY EASTWARD INTO THE
CWA AFTER MIDNIGHT.

WITH ABUNDANT MOISTURE AND AN INCREASING LLJ...WOULD ALSO
ANTICIPATE REDEVELOPMENT OF MVFR TO IFR STRATUS INTO SATURDAY
MORNING.

&&

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

$$

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



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