Area Forecast Discussion
Issued by NWS Sioux Falls, SD

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000
FXUS63 KFSD 042328
AFDFSD

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SIOUX FALLS SD
628 PM CDT SAT JUL 4 2015

.SHORT TERM...(THIS EVENING THROUGH SUNDAY)
ISSUED AT 235 PM CDT SAT JUL 4 2015

SMOKE FROM CANADIAN FIRES APPEARS ON VISUAL IMAGERY TO BE GETTING
PUSHED EAST/NORTHEAST OF THE AREA DUE TO THE INCREASING FLOW AT LOW
AND MID LEVELS. IN ANY EVENT I WILL KEEP MENTION OUT OF THE PUBLIC
GRIDS AS I DID EARLIER IN THE TAFS. AS FOR THUNDERSTORMS...COVERAGE
IS STILL LOOKING WEAK FOR TONIGHT AND PROBABLY RESTRICTED TO THE
WESTERN PART OF THE CWA AND DURING THE EVENING HOURS. THIS SEEMS NOT
SO MUCH DUE TO THE LACK OF HEATING IN THIS REALM OF NIGHTTIME
CONVECTION...BUT MORE FROM WEAKENING THERMAL SUPPORT FOR INITIATION
AND SUPPORT AS INSTABILITY SLOWLY INCREASES FROM THE WEST. WILL KEEP
THE CHANCE LOW AND MAINLY FAR WEST.

ONE THING THE INCREASING LOW LEVEL MOISTURE AND STEADY LOW LEVEL
FLOW WILL DO IS HOLD UP TEMPERATURES TONIGHT WITH LOWS IN THE MID TO
UPPER 60S.

SUNDAY DAYTIME LOOKS LIKE THE COLD FRONT HOLDING NORTHWEST OF THE
AREA AND THUNDERSTORM DEVELOPMENT...IF ANY...BEING RESTRICTED TO
LATE IN THE DAY IN THE CAPPED AIR MASS AHEAD OF THE FRONT. WILL
ALLOW THE CHANCE TO INCREASE SIGNIFICANTLY LATE IN THE AFTERNOON
FROM THE NORTHWEST LEADING UP TO WIDESPREAD STORMS AT NIGHT...BUT
MOST OF THE DAY EVEN NORTHWEST...AND ALL OF IT TO THE SOUTHEAST...
SHOULD BE DRY BREEZY AND PRETTY WARM WITH HEATING NOT RESTRICTED TOO
MUCH BY SOME CLOUD INCREASE FROM THE NORTHWEST LATE. HAVE RAISED
WIND SPEEDS A NOTCH OR TWO FURTHER INTO THE BREEZY CATEGORY FROM
MODEL BLENDS GIVEN THE HEALTHIER WINDS NOT TOO FAR UP ON BUFKIT
SOUNDINGS. HIGH TEMPERATURES LOOK LIKE UPPER 80S EAST TO LOWER 90S
WEST.

.LONG TERM...(SUNDAY NIGHT THROUGH SATURDAY)
ISSUED AT 235 PM CDT SAT JUL 4 2015

THUNDERSTORM CHANCES SUNDAY NIGHT INTO MONDAY REMAIN THE BIGGEST
CONCERN IN THE MEDIUM RANGE...AS PATTERN PERSISTENCE CONTINUES IN
THE REMAINING PORTION OF THE FORECAST.

HIGH-RES MODELS CONTINUE TO SLOW THE PROGRESSION OF SHORTWAVE
ENERGY AND ASSOCIATED FRONTAL BOUNDARY SUNDAY EVENING...WITH
NAM/GFS SOUNDINGS INDICATING A STOUT CAP HOLDING INTO THE EARLY
EVENING HOURS FOR MOST AREAS. CONVECTION SHOULD BEGIN TO BLOSSOM
ALONG A FRONTAL BOUNDARY NEAR THE ND/SD/MN BORDERS BY 21Z...AS A
SHORTWAVE TRACKING OVER NORTHERN ND/MN BEINGS TO SLIDE EAST. OVER
SOUTHWESTERN AND WESTERN SD...A SECOND SHORTWAVE LIFTING THROUGH
THE NEBRASKA PANHANDLE WILL IGNITE A SEPARATE AREA OF CONVECTION
LATE IN THE AFTERNOON. EVENTUALLY THESE WAVES WILL BEGIN TO PHASE
TOGETHER...BRINGING STRONG UPR DIVERGENCE INTO THE AREA AND LIKELY
LEADING TO CONVECTING ZIPPING THROUGH CENTRAL SD ALONG THE FRONT
IN THE EVENING. THIS CONVECTION WILL TAKE A BIT OF TIME TO TRACK
INTO THE AREA...BUT SHOULD ENTER THE CWA BY 03Z. MODERATE TO
STRONG INSTABILITY...NEARLY 4K J/KG MLCAPE FROM NAM BUFR SOUNDINGS
AND 3K J/KG FROM GFE...COMBINED WITH INCREASING MID- UPR LVL SHEAR
APPROACHING 30-40 KNOTS...WILL PROMOTE A LARGE HAIL RISK
ESPECIALLY WITH INITIAL DEVELOPMENT. LLVL LAPSE RATES AND DCAPE
VALUES ARE ALSO RATHER IMPRESSIVE...ALSO OWING TO A DAMAGING WIND
RISK. THE OVERALL PROGRESSION OF STORMS MAY LEAD TO MORE OF A
DAMAGING WIND THREAT AS STORMS BEGIN TO COALESCE INTO THE LATE
EVENING HOURS AND SLIDE THROUGH EASTERN SD AND MN AS THE LLJ
INCREASES. THE SEVERE THREAT MAY LINGER WELL INTO THE NIGHT...AS
SOUNDINGS SHOW SUBSTANCIAL MUCAPE AND ONLY A MARGINALLY DECOUPLED
BOUNDARY LAYER.

AS THE NIGHT PROGRESSES ON...THE RISK OF ELEVATED RAINFALL AND FLASH
FLOODING INCREASES.  PWAT VALUES APPROACH 1.75 INCHES OR
HIGHER...WHICH BASED ON ABR CLIMATOLOGY...IS APPROACHING THE MAX
VALUES RECORDED FOR JULY 5TH. THE OTHER CONCERNING FACTOR IS THE
BOUNDARY PARALLEL FLOW THAT DEVELOPS AS CONVECTION SLIDES
SOUTHEAST OVERNIGHT...SETTING THE STAGE FOR POTENTIAL TRAINING OF
STORMS...ESPECIALLY NORTH OF I-90. LATER SHIFTS MAY NEED TO
CONSIDER A FLASH FLOOD WATCH.

CONVECTION WILL FINALLY CLEAR THE CWA BY MONDAY MORNING...LEAVING
COOLER AND MORE STABLE AIR IN THE REGION THROUGH MIDWEEK.  BEYOND
WEDNESDAY...MODEL VARIANCE DOES BEGIN TO INCREASE...AS A
PROGRESSIVE MID-LVL PATTERN PERSISTS. THE NEXT POTENTIAL RAIN
CHANCES ARRIVE ON WEDNESDAY INTO THURSDAY...AS UPR TROUGHING
SWINGS THROUGH THE NORTHERN PLAINS. AGAIN...DEEP MOISTURE IS
LIMITED...SO POPS REMAIN ON THE LOWER END DUE TO ANTICIPATED
COVERAGE.

BY THE END OF NEXT WEEK...WE MAY BEGIN TO ESTABLISH A WARMER FLOW
REGIME...SUGGESTIVE OF ABOVE NORMAL TEMPERATURES AND DIURNAL
THUNDERSTORM CHANCES. THIS REMAINS A VERY LOW CONFIDENCE PORTION OF
THE FORECAST.


&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z SUNDAY EVENING)
ISSUED AT 628 PM CDT SAT JUL 4 2015

VFR CONDITIONS WILL DOMINATE THROUGH THIS TAF PERIOD...THOUGH MAY
STILL SEE SPOTTY MVFR VISIBILITY EAST OF I-29 THIS EVENING DUE TO
LINGERING SMOKE. WILL BE WATCHING FOR ISOLATED STORM THREAT WEST OF
THE JAMES RIVER THIS EVENING...AND AGAIN POSSIBLY LATE TONIGHT IN
AREAS WEST OF I-29...BUT EXPECTED ISOLATED COVERAGE AND LIMITED
CONFIDENCE IN DEVELOPMENT PRECLUDE MENTION IN THE TAFS. STORM THREAT
MAY BEGIN IN FAR NORTHWEST AREAS AGAIN TOWARD THE END OF THIS TAF
PERIOD...BUT MORE LIKELY HOLDING OFF UNTIL AFTER 05/00Z.

&&

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

$$

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


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