National Weather Service Weather Forecast Office

• Home
• Site Map
• News
• Organization
• Search for: NWS All NOAA 

000
FXUS63 KFSD 171940
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
240 PM CDT FRI MAY 17 2013

.UPDATE...
ISSUED AT 1050 AM CDT FRI MAY 17 2013

NO MAJOR CHANGES TO THE FORECAST THROUGH THE AFTERNOON. CLOUDS
DECREASING A BIT MORE THAN ANTICIPATED SO BRINGING IN A LITTLE
MORE SUNSHINE FOR THE DAY. DID INCREASE CLOUD COVER MORE QUICKLY
THIS EVENING IN CENTRAL SD AS CONVECTION FAIRLY LIKELY TO FIRE
BETWEEN ABOUT 23Z AND 3Z JUST TO THE WEST AND SOUTHWEST OF THE
CWA. ALL HIGH RESOLUTION MODELS AS WELL AS THE NAM AND GEM SUPPORT
CONVECTIVE INITIATION FROM SOMEWHERE BETWEEN ABOUT CHADRON AND
VALENTINE NEBRASKA NORTH TOWARDS PIERRE DURING THIS TIME. EXPECT
THIS ACTIVITY TO MOVE NORTHEAST THROUGH THE EVENING THEN POSSIBLY
TRACK THROUGH THE FAR WESTERN AND NORTHERN CWA OVERNIGHT. MAY NEED
TO ADD SOME SMALL POPS INTO AREAS ALONG AND NORTH OF INTERSTATE 90
AS UPPER LEVEL SUPPORT SWINGS THROUGH AND WITH A LITTLE ELEVATED
INSTABILITY COULD SEE SOME SPOTTY SHOWERS OR THUNDERSTORMS
DEVELOP. SEVERE THUNDERSTORMS VERY UNLIKELY BUT A FEW COULD GET
CLOSE AROUND THE CHAMBERLAIN AREA THIS EVENING. CAPE VALUES LIKELY
AROUND 1500 J/KG WITH ONLY MARGINAL EFFECTIVE SHEAR BUT STILL
ENOUGH TO SUPPORT A WIND OR HAIL THREAT.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 453 AM CDT FRI MAY 17 2013

MAIN ACTION FROM THE EVENING AND EARLIER OVERNIGHT HAS SHIFTED EAST
OF THE AREA WITH DYNAMICS OF MAIN WAVE PUSHING ACROSS MINNESOTA AND
IOWA. CONVECTIVELY REINFORCED FRONTAL BOUNDARY LIES JUST SOUTH OF
THE AREA ACROSS EASTERN NEBRASKA. HOWEVER...A VERY NICE COHERENT
CYCLONICALLY WRAPPED CORE OF RETURNS NOTED MOVING ACROSS THE WESTERN
CWA BETWEEN I 90 AND THE MISSOURI RIVER...ASSOCIATED WITH AN MCV
FROM EARLIER HIGH PLAINS CONVECTION. TWO THINGS WORKING AGAINST THIS
PRECIP ARE THE INCREASING VEERING OF LOW LEVEL JET AWAY FROM SLOW
MOVING AREA OF PRECIPITATION...AND ALSO THE LARGE SCALE FORCING
BECOMING MORE HOSTILE WITH HEIGHTS BEGINNING TO BUILD ALOFT. LIKELY
TO SEE OVERALL COVERAGE WITH THIS CORE DECREASE HEADING INTO THE
EARLY MORNING HOURS AS IT SHIFTS EAST...BUT HOW QUICKLY THIS OCCURS
IS THE QUESTION. WOULD THINK AT LEAST SOME OF THIS WOULD LIMP INTO
THE FSD AREA AFTER 12Z...WITH SOME INDICATION THAT BROADER AREA MAY
REDEVELOP FOR A SHORT TIME AHEAD OF THIS FEATURE FROM SOUTHWEST
MINNESOTA INTO FAR NORTHERN IOWA. CHANCES FOR PRECIP SHOULD REALLY
DIMINISH AFTER 15Z...AND DESPITE A MARGINALLY UNSTABLE AIRMASS
ALOFT...KEPT MENTION OF THUNDER AT LEAST A CATEGORY OR TWO UNDER
EXPECTED PRECIP COVERAGE. FOR MUCH OF THE AFTERNOON...EXPECT VERY
LITTLE TO OCCUR AS WARM FRONT CONTINUES TO PUSH NORTHWARD...WITH
HEIGHTS BUILDING/TEMPS WARMING ALOFT.

WHILE SOME LINGERING CLOUDS AND DEVELOPMENT OF CAPPED CUMULUS FIELD
WILL BE A DISTINCT ISSUE FOR NORTHERN/EASTERN CWA...IS FAIRLY LIKELY
THAT THE FAR SOUTHWEST WILL BREAK INTO A GREATER DEGREE OF SUNSHINE
TODAY.  WINDS WILL MAINTAIN TOO MUCH OF A SOUTH OR SOUTHEAST
COMPONENT TO EXPECT TEMPS TO FULLY RACE ABOVE GUIDANCE...BUT PURE
MIXING OF RAW MODEL OFF SURFACE TEMPS WOULD SUGGEST UPPER 80S A GOOD
BET FOR THE SOUTHWEST...SLIDING TOWARD MORE UPPER 70S TO LOWER 80S
FROM EAST CENTRAL SD THROUGH SOUTHWEST MINNESOTA.

WILL KEEP A SMALL POP IN OUR FAR NORTH...MAINLY ALONG THE HIGHWAY 14
CORRIDOR THIS EVENING...WITH SURFACE BOUNDARY EXPECTED TO BE IN THAT
VICINITY AS SUBTLE WAVE IS FORECAST TO LIFT INTO CENTRAL SD. SOME
UNCERTAINTY REGARDING LOCATION OF THE LOW LEVEL BOUNDARY BY THIS
EVENING...AND ANY CHANGE IN LOCATION WOULD IMPACT THE EVENING POPS.
WAVE AND ASSOCIATED LOW LEVEL WARM ADVECTION EXPECTED TO SHIFT NORTH
OF THE AREA AFTER 06Z...AND THUS TAPER POPS OFF THROUGH THE LATTER
HALF OF THE NIGHT. SHOULD BE A MILD NIGHT WITH LOWS IN THE LOWER 60S
MOST AREAS.

.LONG TERM...(SATURDAY THROUGH THURSDAY)
ISSUED AT 453 AM CDT FRI MAY 17 2013

MAIN FOCUS IN THE LONGER TERM IS CONVECTIVE DEVELOPMENT/ASSOCIATED
SEVERE THREAT OVER THE WEEKEND AS WESTERN CONUS TROUGH PUSHES OUT
INTO THE PLAINS. EXPECT MOST OF SATURDAY TO BE CAPPED OFF...WITH
SURFACE BOUNDARY EXTENDING FROM WESTERN NEBRASKA THROUGH CENTRAL
SOUTH DAKOTA...AND THEN NORTHEAST INTO FAR SOUTHEAST NORTH DAKOTA.
OUR FORECAST AREA WELL INTO THE WARM SECTOR AND FORECAST SOUNDINGS
SUGGEST STRONG CAP IN PLACE THAT SHOULD INHIBIT DEVELOPMENT WITHOUT
ASSISTANCE FROM DYNAMIC FORCING. WILL KEEP A SLIGHT CHANCE IN OUR
FAR WEST IN THE AFTERNOON...BUT PREFER 17/00Z GFS AND 16/12Z ECMWF
PLACEMENT OF INITIAL DEVELOPMENT MAINLY WEST OF OUR AREA NEAR THE
BOUNDARY THROUGH THE LATE AFTERNOON. WITHIN THE WARM SECTOR...WILL
SEE A HOT/HUMID DAY WITH HIGHS IN THE MID-UPPER 80S AND AFTERNOON
DEW POINTS IN THE LOWER TO MID 60S.

ACTIVITY SHOULD QUICKLY DEVELOP INTO OUR WEST SATURDAY EVENING AS
MID-UPPER WAVE LIFTS INTO CENTRAL SOUTH DAKOTA AND AIDS IN BREAKING
THE STRONG CAP. DEEP LAYER SHEAR SOMEWHAT MARGINAL INITIALLY THIS FAR
EAST ALTHOUGH STRONG DYNAMIC LIFT ALONG WITH STEEP MID LEVEL LAPSE
RATES AND INSTABILITY IN THE 2000-3000 J/KG RANGE SUPPORTIVE OF A
SIGNIFICANT HAIL THREAT WITH INITIAL DEVELOPMENT ACROSS FAR WESTERN
CWA SATURDAY EVENING. ISOLATED TORNADO THREAT AS WELL...BUT THINK
THIS WILL BE TIED MORE CLOSELY TO THE BOUNDARY...WITH WIND THREAT
INCREASING AS THE STORMS MOVE EAST THROUGH SOUTHEAST SOUTH DAKOTA IN
THE LATE EVENING.

SUNDAY LESS CLEAR AS WILL BE DEPENDENT ON EVOLUTION OF ACTIVITY LATE
SATURDAY NIGHT/SUNDAY MORNING. CURRENT EXPECTATION WOULD SEE STORMS
PUSH EAST OF THE AREA EARLY SUNDAY MORNING...WITH PARTIAL CLEARING IN
THE EAST BY MIDDAY AS MID LEVEL DRY SLOT MOVES IN EAST OF UPPER LOW
AS IT BEGINS TO CLOSE OFF OVER CENTRAL PORTIONS OF SOUTH DAKOTA AND
NEBRASKA. WILL HANG ONTO CHANCE POPS IN MOST AREAS SUNDAY MORNING
GIVEN GREAT DEAL OF UNCERTAINTY IN THIS EVOLUTION. WAVE SWINGING
THROUGH THE BASE OF THE CLOSED LOW SHOULD THEN BRING INCREASING
THREAT OF DEVELOPMENT THROUGH THE AFTERNOON...WITH GFS INDICATING
POTENTIAL FOR ANOTHER ROUND OF SEVERE STORMS IN OUR CENTRAL/EASTERN
CWA...WITH WEAK CAP TOPPED BY STEEP LAPSE RATES/STRONG INSTABILITY
AND SLIGHTLY BETTER DEEP LAYER SHEAR THAN IN OUR WEST ON SATURDAY.
OTHER MODELS NOT QUITE AS BULLISH ON INSTABILITY ACROSS THE EAST
SUNDAY AFTERNOON...THOUGH STILL PLENTY OF DYNAMICS WITH UPPER LEVEL
SUPPORT TO ASSIST DEVELOPMENT AND AT LEAST ISOLATED SEVERE THREAT.

CLOSED UPPER LOW SLOW TO SHIFT EAST OF THE AREA...KEEPING DECENT
CHANCE OF SHOWERS AROUND THROUGH TUESDAY NIGHT BEFORE INFLUENCE
BEGINS TO WEAKEN. MID-UPPER LEVEL RIDGING SHOULD BRING DRIER WEATHER
TO THE AREA BY WEDNESDAY NIGHT/THURSDAY...THOUGH TEMPERATURES WILL BE
ON THE COOL SIDE OF NORMAL MIDWEEK WITH HIGHS MAINLY IN THE 60S.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SATURDAY AFTERNOON)
ISSUED AT 238 PM CDT FRI MAY 17 2013

VFR THROUGH THE PERIOD WITH THE MAIN CONCERN THUNDERSTORM CHANCES.
EXPECT THUNDERSTORMS TO DEVELOP IN CENTRAL PARTS OF NEBRASKA AND
SOUTH DAKOTA AND SHIFT NORTHEAST OVERNIGHT. KHON WILL SEE THE
BETTER CHANCE FOR THUNDERSTORMS...ESPECIALLY FROM ABOUT 3Z THROUGH
7Z...WHILE KFSD MAY CATCH A PASSING SHOWER LATER IN THE NIGHT.
LITTLE IF ANY THUNDERSTORM ACTIVITY IS EXPECTED FROM 13Z THROUGH
18Z SATURDAY WITH BETTER CHANCE LATE AFTERNOON AND OVERNIGHT
SATURDAY.

&&

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

$$

UPDATE...08
SHORT TERM...CHAPMAN/
LONG TERM...
AVIATION...08