Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 230830
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
330 AM CDT SAT AUG 23 2014

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 328 AM CDT SAT AUG 23 2014

WELL ADVERTISED SHORTWAVE HAVE MOVED INTO THE CENTRAL HIGH PLAINS
EARLY THIS MORNING AND IS LIFTING NORTH NORTHEAST INTO CENTRAL
NEBRASKA. SURFACE HIGH PRESSURE HAS DEEPENED IN WESTERN KANSAS AND
IS TAKING A SIMILAR TRACK. ALL MODELS...INCLUDING THE HIGH
RESOLUTION MODELS ARE NOT DOING WELL WITH THE TIMING AND TRACK OF
THE MCV THIS MORNING. MODELS ARE LARGELY UNDERESTIMATING
PRECIPITATION AMOUNTS AND TRACK THROUGH OUR SOUTHEASTERN COUNTIES
WITH THE NOSE OF THE LOW LEVEL JET CONTINUE TO FIRE ADDITIONAL
THUNDERSTORM CELLS ALONG THE EASTERN FRINGE. ADDITIONALLY...THE
OVERALL TIMING OF PRECIPITATION IS TOO SLOW.

WITH THE SHORTWAVE AND SURFACE LOW LIFTING NORTH NORTHEAST...THE
BEST FORCING AND DYNAMICS WILL MOVE THROUGH THE CENTRAL DAKOTAS
TODAY...WHICH WILL KEEP THE BEST AFTERNOON PRECIPITATION CHANCES
ACROSS OUR NORTHWESTERN HALF AFTER THE INITIAL MCV MOVES THROUGH THE
REGION THIS MORNING. MUCH OF NORTHWEST IOWA MAY REMAIN DRY THIS
AFTERNOON BEFORE A MORE EASTWARD COMPONENT OF THE SYSTEM BEGINS
MOVING PRECIPITATION BACK INTO OUR EASTERN FORECAST AREA LATE
AFTERNOON INTO THE EVENING. SHOWER AND THUNDERSTORM CHANCES FINALLY
BEGIN TO TAPER OFF FROM SOUTHWEST TO NORTHEAST LATE EVENING THROUGH
THE OVERNIGHT HOURS AS A COLD FRONT DROPS INTO OUR WESTERN FORECAST
AREA.

WITH PWAT VALUES AS HIGH AS 1.85...HEAVY RAINFALL WILL CONTINUE TO
BE THE MAIN CONCERN WITH THIS SYSTEM. THINK THAT LOCALLY UP TO 2 OR
3 INCHES OF STORM TOTAL RAINFALL WILL BE POSSIBLE...ESPECIALLY
ACROSS OUR WESTERN COUNTIES. FLASH FLOODING THREAT WILL LIKELY BE
MAINLY IN URBAN AREAS RATHER THAN A WIDESPREAD THREAT WITH DECENT
STORM MOTION EXPECTED. COULD SEE SOME TRAINING...BUT AGAIN THIS
WOULD BE MORE A ISOLATED THREAT...SO WILL NOT ISSUE A FLASH FLOOD
WATCH AT THIS TIME - HOWEVER THIS CONCERN WILL NEED TO BE CLOSELY
MONITORED.

WITH A DECENT LLJ AND INSTABILITY SEEN WITH THE ONGOING
MCV...MARGINAL SEVERE CONDITIONS ARE NOT OUT OF THE QUESTION BUT AS
THIS FEATURE SLOWLY WEAKENS...THE PROBABILITY IS SLIM. IN THE WAKE
OF THE MCV LATE MORNING AND INTO THIS EVENING...MARGINAL SHEAR AND
STRONG INSTABILITY AS TEMPERATURES WARM BACK INTO THE 80S WITH
DEWPOINTS IN THE LOW TO MID 70S...COULD SPELL A BETTER SEVERE
THUNDERSTORM THREAT ACROSS THE FORECAST AREA. A FEW ISOLATED SEVERE
STORMS WITH LARGE HAIL TO PING PONG SIZE AND GUSTS TO 65 MPH WILL BE
POSSIBLE.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 328 AM CDT SAT AUG 23 2014

FOCUS IN THE EXTENDED IS MAINLY ON PRECIPITATION CHANCES WITH
ACTIVE PATTERN CONTINUING. REDUCED POP MENTION ON SUNDAY AS THE CAP
APPEARS TO BE ADEQUATELY STRONG ENOUGH TO SUPPRESS CONVECTION ACROSS
THE REGION.  WITH STRONG HEATING THROUGHOUT THE DAY...WILL
DESTABILIZE ESPECIALLY AHEAD OF THE FRONT...BUT WITH WEAK
CONVERGENCE ALONG THE FRONT LIMITED POP MENTION TO AFTER 00Z MAINLY
ALONG AND EAST OF HIGHWAY 60 WHERE THE ADDITION OF A STRENGTHENING
LOW LEVEL JET MAY BE JUST ENOUGH TO IGNITE SOME ISOLATED CONVECTION.

HAVE ADDITIONAL CHANCES OF CONVECTION ON MONDAY WITH BAND OF WARM
AIR/THETA E ADVECTION LIFTING NORTH. THIS FEATURE IS ASSOCIATED WITH
A WARM FRONT ASSOCIATED WITH A DEVELOPING LOW PRESSURE CENTER TO THE
SOUTH AND WEST.  LOW LEVEL JET IS EXPECTED TO DEVELOP ACROSS THE
PLAINS ON MONDAY NIGHT...AND WITH GOOD CONVERGENCE ALONG THE
ELEVATED BOUNDARY...RAISED POPS IN THE SOUTH TO JUST SHY OF
CATEGORICAL.  WITH UNCERTAINTY ON HOW FAR NORTH THE BOUNDARY WILL
LIFT...HAVE A FAIRLY TIGHT GRADIENT IN POPS ACROSS THE FORECAST
AREA. TUESDAY INTO TUESDAY NIGHT APPEARS TO BE FAIRLY WET RIGHT NOW
WITH SLOW MOVING WEAK TROUGH APPROACHING FROM THE WEST AND A SERIES
OF SHORT WAVES TRAINING OVER THE AREA IN SOUTHWEST FLOW ALOFT.
WHILE PRECIPITABLE WATER INCREASES NEAR THIS BOUNDARY...BELIEVE THE
NEAR 2 INCH VALUES ARE DUE TO MODEL CONVECTIVE FEEDBACK...AND
ENVIRONMENTAL VALUES WILL BE CLOSER TO 1.5-1.75 INCHES. DESPITE THE
REDUCTION IN PRECIPITABLE WATER...STILL THE POTENTIAL FOR FLOODING
AS THE BOUNDARY IS EXPECTED TO STALL WITH THE POTENTIAL FOR TRAINING
OF STORMS.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT)
ISSUED AT 1149 PM CDT FRI AUG 22 2014

PRIMARY AVIATION CONCERN THROUGH THIS TAF PERIOD WILL BE POTENTIAL
FOR CONVECTION...AND ASSOCIATED MVFR-IFR CEILINGS/VISIBILITY...
MAINLY EXPECTED TO AFFECT SD PORTIONS OF THE FORECAST AREA. MORE
WIDESPREAD CONVECTION OVER NEBRASKA WILL LIFT INTO SOUTH DAKOTA
THROUGH THE OVERNIGHT HOURS AND INTO SATURDAY MORNING. PERIODIC
RESTRICTIONS IN VISIBILITY AND CEILINGS WILL BE LIKELY AS THIS
ACTIVITY MOVES THROUGH.

PERIOD OF MVFR-LOCALLY IFR STRATUS MAY FOLLOW CONVECTION SATURDAY
MORNING...IMPROVING TO VFR AS WARM FRONT APPROACHES FROM THE SOUTH.
ADDITIONAL CONVECTIVE DEVELOPMENT POSSIBLE WITH THE WARM FRONT
SATURDAY AFTERNOON. NORTHWEST PORTIONS OF THE FORECAST AREA APPEAR
TO BE MORE FAVORED FOR THIS AFTERNOON DEVELOPMENT...AND HAVE ADDED
MENTION INTO KHON FOR THE MID-LATE AFTERNOON. CAPPING INVERSION MAY
LIMIT DEVELOPMENT FARTHER SOUTHEAST AND HAVE KEPT AFTERNOON/EVENING
THUNDER OUT OF KFSD/KSUX AT THIS TIME.


&&

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

$$

SHORT TERM...
LONG TERM...
AVIATION...JH






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