Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 281703
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1103 AM MDT THU AUG 28 2014

.UPDATE...
ISSUED AT 950 AM MDT THU AUG 28 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER CENTRAL NEB...
WITH INVERTED TROF STRETCHING NORTHWARD ACROSS CENTRAL SD. HIGH
PRESSURE IS IN PLACE OVER THE CENTRAL ROCKIES. UPPER LEVEL
ANALYSIS SHOWS LOW NOW OVER WESTERN NEB...SLOWLY MOVING EAST-
SOUTHEAST. KUDX RADAR SHOWS ISOLATED TO SCATTERED SHOWERS FROM
CENTRAL SD TO FAR SOUTHWEST SD. THERE ARE A FEW LIGHTNING STRIKES
FROM TIME TO TIME WITH THE ACTIVITY OVER SOUTH CENTRAL SD. SKIES
RANGE FROM MOSTLY SUNNY OVER NORTHEAST WY TO MAINLY CLOUDY EAST OF
THE BLACK HILLS. TEMPS ARE IN THE 60S AND LOWER 70S WITH LIGHT AND
VARIABLE WINDS.

SHOWER AND THUNDERSTORM ACTIVITY WILL LINGER OVER MUCH OF
SOUTHWESTERN INTO CENTRAL SD INTO THE AFTERNOON...WITH A GRADUAL
EASTWARD SHIFT THROUGH THE AFTERNOON. MAY NEED TO ADD SOME POPS
FOR THE EARLY EVENING ACROSS SOUTH CENTRAL SD IF THE EASTWARD
TREND SLOWS DOWN A BIT. CLOUDS WILL ALSO GRADUALLY DECREASE FROM
WEST TO EAST ACROSS THE AREA THROUGH THE EVENING. HIGH TEMPS MIGHT
BE A BIT TOO HIGH IN SOME AREAS...BUT WILL SEE HOW QUICKLY THEY
RISE OVER THE NEXT 2 OR 3 HOURS BEFORE MAKING ANYMORE ADJUSTMENTS.
UPDATED FORECAST HAS BEEN SENT TO MAKE SHORT TERM CHANGES TO
POPS...CLOUD COVER...AND WIND.

&&

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 302 AM MDT THU AUG 28 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER SASKATCHEWAN...WITH
A FRONTAL BOUNDARY EXTENDING THROUGH EASTERN MONTANA AND CENTRAL
WYOMING. UPPER LEVEL ANALYSIS SHOWS MAIN LOW PRESSURE AREA OVER NRN
COLORADO/SRN WYOMING WITH A TROF COVERING THE ROCKIES AND HIGH
PLAINS. LATEST RADAR IMAGERY SHOWS SHOWERS CONTINUING TO ROTATE AND
LIFT NORTH ACROSS THE SD PLAINS. A LITTLE EMBEDDED CONVECTION IS ALSO
OCCURRING IN SOUTH CENTRAL SD.

AS THE UPPER LOW MOVES SLOWLY EAST INTO THE CENTRAL HIGH PLAINS...
SHOWER/THUNDERSTORM ACTIVITY WILL QUICKLY DECREASE FROM WEST TO
EAST...WITH SHOWERS/STORMS CONTINUING ACROSS MUCH OF SOUTH CENTRAL
SOUTH DAKOTA. WITH A LOT OF LOW LEVEL MOISTURE AROUND...EXPECT
AREAS OF FOG TO LINGER INTO THE MORNING HOURS ACROSS MOST OF THE
WRN SD PLAINS. BY THIS AFTERNOON...DIURNAL HEATING AND LINGERING
INSTABILITY COULD PRODUCE A TERRAIN INDUCED SHOWER/STORM OVER THE
BLACK HILLS. THUS LEFT ISOLD POPS IN THE FORECAST. TEMPS TODAY
WILL BE WARMER WITH DECREASING CLOUDS...ESPECIALLY ACROSS THE NRN
AND WRN AREAS.

FOR TONIGHT...CLOUDS WILL CONTINUE TO GRADUALLY DECREASE FROM
NORTHWEST TO SOUTHEAST...WITH MOSTLY CLEAR SKIES OVERNIGHT. THIS
COMBINED WITH LIGHT WINDS AND SURFACE HIGH PRESSURE TO THE
WEST...DECIDED TO ADD SOME FOG FOR THE SD PLAINS. TEMPS WILL BE
NEAR NORMAL.

ON FRIDAY...SHORTWAVE TROF MOVES RAPIDLY ACROSS MT/ND PUSHING A WEAK
COOL FRONT INTO WESTERN SD. FORECAST SOUNDINGS SUPPORT 250-500J/KG
MLCAPE...WITH SUFFICIENT LOW LEVEL MOISTURE/CAPE/SHEAR FOR STORMS.
MOST OF THE 500-700MB MOISTURE REMAINS NORTH OF THE CWA...HOWEVER
COULD SEE SCATTERED STORMS WITH AN ISOLATED STRONG STORM ACROSS
NORTHWEST HALF OF CWA. TEMPERATURES ON FRIDAY WILL BE A LITTLE
COOLER THAN TODAY IN THE NW...BUT MOST AREAS WILL SEE WARMER
TEMPERATURES.

&&

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 302 AM MDT THU AUG 28 2014

PROGRESSIVE NORTHERN STREAM FLOW WILL CONTINUE THROUGH THE PERIOD
WITH A LONG WAVE UPPER LEVEL TROUGH ON TRACK TO ADVECT THROUGH THE
REGION SAT-SUN...WITH A WEAKER SHORTWAVE IMPULSE POSSIBLE MONDAY.
TROUGH RELOADING OVER THE NE PAC TUE-WED FAVORED IN ECMWF/GFS
SOLUTIONS...WHICH WOULD SUPPORT MEAN RIDGING OVER THE NORTHERN
PLAINS WITH DRY AND WARMER CONDITIONS. MAIN FORECAST TREND IS A
QUICKER ARRIVAL OF THE EXPECTED LONG WAVE TROUGH SAT...WITH PRECIP
CHANCES INCREASING SAT AFTERNOON WESTERN THIRD. OTHERWISE...THE
REMAINDER OF THE FORECAST IS ON TRACK ATTM.

UPPER LEVEL TROUGH WILL PUSH OUT OF THE NE PAC AND INTO THE NORTHERN
PLAINS...SUPPORTING INCREASING LSA SAT THROUGH SUNDAY. LEE SIDE SFC
TROUGH WILL WILL INTERACT WITH THE APPROACHING UPPER WAVE SUPPORTING
A FOCUS FOR SHRA/TS ACTIVITY OVER THE WESTERN FA BY SAT AFTERNOON.
LL SE FLOW AHEAD OF THIS SYSTEM WITH MOIST UPPER LEVEL SW FLOW WILL
SUPPORT INCREASING PW OVER THE REGION...WITH PLENTY OF MOISTURE
BEING AVAILABLE WITH THIS SYSTEM. SOME MODEL INDICATION FOR
SUFFICIENT DEEP LAYER SHEAR AND CAPE OVER THE FAR NW ZONES...ESP NW
SD BY SAT EVENING...SUPPORTING A POSSIBLE SEVERE THREAT THERE.
SOMETHING TO WATCH. HAVE ADJUSTED POPS UP SAT AFTERNOON AND SAT
EVENING...WITH THE PRIMARY SOUTHERN PERIPHERY IMPULSE EXPECTED TO
SHIFT NE ACROSS THE NW FA. TRAILING SFC TROUGH WITH SUFFICIENT LSA
SHOULD SUPPORT A GOOD CHANCE OF SHRA/TS NW THIRD...WITH MORE
SCT/ISOLD ACTIVITY ACROSS THE REMAINDER OF THE FA. UPPER LEVEL COLD
POOL WILL SUPPORT STEEP LL LAPSE RATES OVER THE FA SUNDAY WITH
RESIDUAL LL MOISTURE IN PLACE. DIURNAL HEATING COUPLED WITH BH/NE WY
TERRAIN INFLUENCES SHOULD SUPPORT SCT TO ISOLD SHRA/TS SW HALF OF
THE FA. BUMPED POPS UP OVER THE BH. OTHERWISE...ONE MORE WEAKER
WESTERLY FLOW IMPULSE STILL INDICATED IN FORECAST MODELS
MONDAY...POSSIBLY SUPPORTING A FEW SHRA/TS...ALTHOUGH UPPER LEVEL
SUPPORT LOOKS MARGINAL ATTM...ESP WITH DRY PROFILES. DRY CONDS
EXPECTED TUE-WED WITH MEAN DEEP LAYER RIDGING.

SEASONAL TEMPS EXPECTED IN MOST OF THE PERIOD...WITH BELOW NORMAL
TEMPS /5-10 DEGREES/ EXPECTED SUNDAY THROUGH MONDAY...ESP NW AREAS.
THE WARMEST DAY IN PERIOD LOOKS TO BE SAT...ESP ON THE SD PLAINS.
ALTHOUGH THERE IS SOME INDICATION FOR WARM CONDITIONS NEXT WED GIVEN
SW WAA FLOW AHEAD OF THE NEXT POTENTIAL EJECTING NE PAC UPPER
TROUGH.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 1059 AM MDT THU AUG 28 2014

-SHRA/ISOLATED -TSRA EAST OF A LINE FROM KMGB TO KCUT WILL
CONTINUE TO SLIDE EAST THIS AFTERNOON...EXITING THE AREA
COMPLETELY EARLY THIS EVENING. AREAS IFR CIGS/VSBYS ASSOCIATED
WITH THE PRECIPITATION AND ST/BR WILL SHIFT EAST ALSO. BEHIND
THESE FEATURES...VFR CONDITIONS ARE EXPECTED THROUGH FRIDAY
MORNING. THE EXCEPTION WILL BE ON THE SD PLAINS LATER TONIGHT
WHERE LOCAL MVFR VSBYS DUE TO BR MAY OCCUR.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...NONE.
&&

$$

UPDATE...26
SHORT TERM...MLS
LONG TERM...JC
AVIATION...HELGESON



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