Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 271646
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1046 AM MDT WED AUG 27 2014

.UPDATE...
ISSUED AT 1012 AM MDT WED AUG 27 2014

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER FAR NORTHEAST
CO...WITH A NEARLY STATIONARY FRONTAL BOUNDARY FROM WESTERN WY TO
NORTHEAST KS. UPPER LEVEL ANALYSIS SHOWS LOW PRESSURE OVER EASTERN
UT...WITH TROF COVERING THE ROCKIES AND MUCH OF THE HIGH PLAINS.
SKIES ARE VARIABLY CLOUDY ACROSS THE AREA...WITH AREAS OF FOG
LIFTING OVER EASTERN PORTIONS OF THE CWA. REGIONAL RADARS SHOW
MOST OF THE SHOWER AND THUNDERSTORM ACTIVITY IN TWO AREAS. THE
MAIN AREA IS OVER SOUTHERN AND CENTRAL WY...MOVING NORTH-
NORTHWESTWARD AROUND THE UPPER LOW. ANOTHER AREA OF LIGHTER
ACTIVITY IS LOCATED OVER CENTRAL NEB INTO PORTIONS OF SOUTHEAST
SD...MOVING NORTH-NORTHEAST. OUR AREA IS DRY AT THE MOMENT...BUT
SHOWERS AND STORMS WILL MOVE IN FROM THE SOUTH AND ALSO DEVELOP
AS THE UPPER LOW MOVES ACROSS SOUTHERN WY/NORTHERN CO THIS
AFTERNOON AND EVENING...ESPECIALLY OVER THE BLACK HILLS AND
SOUTHERN PORTIONS OF THE CWA. THERE SHOULD BE A FAIRLY SHARP
CUT-OFF TO THE COVERAGE OF SHOWERS... LIKELY SOMEWHERE NEAR OR
JUST NORTH OF THE I-90 CORRIDOR. THE THREAT FOR SEVERE STORMS
REMAINS LOW WITH MAIN AREA OF INSTABILITY STAYING SOUTH OF THE
AREA.

HAVE MADE A MINOR UPDATE TO THE FORECAST...MAINLY TO LOWER POPS
ACROSS THE AREA THIS MORNING AND RAISE THEM OVER THE BLACK HILLS
THIS AFTERNOON. ALSO MADE SOME ADJUSTMENTS TO CLOUD COVER FOR THE
NEXT FEW HOURS. TEMP FORECAST FOR TODAY LOOKS GOOD AT THE MOMENT...
BUT MAY HAVE TO TWEAK THEM A BIT LATER ON...DEPENDING ON CLOUD
AND SHOWER COVERAGE.

&&

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
ISSUED AT 251 AM MDT WED AUG 27 2014

LATEST WATER VAPOR IMAGERY SHOWS AN AREA OF LOW PRESSURE OVER
NEVADA/UTAH WITH A NORTHERN STREAM TROUGH EXTENDING FROM CENTRAL
CANADA INTO THE NORTHERN PLAINS. THE NORTHERN STREAM TROF WILL
QUICKLY MOVE EASTWARD AS THE CUTOFF LOW SLOWLY PROPAGATES INTO THE
CENTRAL ROCKIES. SOUTHWESTERLY FLOW CONTINUES OVER THE
CENTRAL/NORTHERN PLAINS.

FOR TODAY THE BEST FORCING REMAINS SOUTH OF THE CWA. BEST CHANCES
OF PRECIP THROUGH THURSDAY WILL BE ACROSS THE FAR SOUTHERN PORTIONS
OF THE FORECAST AREA AS A SERIES OF WAVES CROSS THE COLORADO/NEBRASKA
AREA. MODELS ARE VARYING WITH TIMING OF WAVES AND HOW FAR NORTH
THE PRECIP WILL EXTEND WITHIN THE CWA. EITHER WAY QPF AMOUNTS WILL
BE LIMITED...EXCEPT WITH THE POSSIBILITY OF SOME STRONGER STORMS
CROSSING AREAS NEAR THE NEBRASKA BORDER. HIGH TEMPERATURES TODAY
WILL ONCE AGAIN BE BELOW AVERAGE DUE TO CLOUD COVER. AS THE UPPER
LOW MOVES THROUGH NEBRASKA/KANSAS...PRECIP CHANCES WILL DIMINISH
ACROSS THE AREA WITH DRY CONDITIONS BY THURSDAY AFTERNOON/EVENING.

&&

.LONG TERM...FRIDAY THROUGH TUESDAY
ISSUED AT 251 AM MDT WED AUG 27 2014

PROGRESSIVE NORTHERN STREAM FLOW WILL CONTINUE THROUGH THE
PERIOD. TWO MAIN SYSTEMS EXPECTED TO AFFECT THE REGION IN THE
PERIOD...A WEAK NORTHERN STREAM TROUGH FRIDAY...AND A MORE ROBUST
LONGWAVE UPPER TROUGH SAT NIGHT INTO MONDAY. FORECAST MODELS IN
GOOD AGREEMENT PER WAVE AMPLITUDE AND TRACK. HOWEVER...SOME
SUBSTANTIAL DIFFERENCES BEGIN TO EMERGE IN THE SUNDAY NIGHT INTO
MONDAY PERIOD BETWEEN THE ECMWF AND GFS...MAINLY THE HANDLING OF
THE NW CONUS SOUTHERN PERIPHERY EJECTING IMPULSE. THE ECMWF HAS A
SOUTHERN BIAS TO THE SYSTEM WITH THE BULK OF LSA PASSING THROUGH
THE FA AS OPPOSED TO A MORE NORTHERN TRACK IN THE GFS...WHICH IS
ALSO FASTER. THE ECMWF SOLUTION WOULD SUPPORT BETTER CHANCES FOR
RAIN IN THE FA HOWEVER MOISTURE LIMITATIONS MAY PRECLUDE ANY
PRECIP TOTALS THEN.

RETAINED PREV POPS FOR FRIDAY AFTERNOON...WITH A SLIGHT UPTICK AND
EXPANSION OF SLIGHT MENTION. FORECAST MODELS CONTINUE TO INDICATE A
SFC TROUGH STALLING ACROSS THE SW HALF FRIDAY...WITH A PASSING UPPER
LEVEL IMPULSE. SUFFICIENT LL MOISTURE ND RESULTING CAPE WOULD BE
CONDUCIVE FOR CONVECTION IN THE AFTERNOON...ESP OVER THE BLACK
HILLS. OTHERWISE...A MORE IMPRESSIVE UPPER LEVEL TROUGH WILL PUSH
OUT OF THE NE PAC AND INTO THE NORTHERN PLAINS...SUPPORTING
INCREASING LSA SAT NIGHT THROUGH SUNDAY NIGHT. BETTER SFC CYCLONE
DEVELOPMENT LOOKS TO REMAIN WELL EAST OF THE REGION...SUPPORTING
MORE ELEVATED/CONVECTIVE CHANCES BEHIND THE SFC TROUGH RATHER THAN
WIDESPREAD DEFORMATION RAINS. HENCE...KEPT POPS IN THE SLIGHT TO
LOW CHANCE CAT FOR NOW...ESP AS DEEPER MOISTURE WILL SHIFT QUICKLY
EAST OUT OF THE REGION. KEPT MOST OF THE REGION DRY MONDAY THROUGH
TUES...WITH UPPER LEVEL RIDGING COMMENCING AND DRY PROFILES.

SEASONAL TEMPS EXPECTED IN MOST OF THE PERIOD...WITH BELOW NORMAL
TEMPS /5-10 DEGREES/ EXPECTED MONDAY AND PERHAPS TUES BEHIND
SUNDAY/S COLD FRONT...ESP NW AREAS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY)
ISSUED AT 1042 AM MDT WED AUG 27 2014

SCATTERED SHRA/TSRA EXPECTED ACROSS SOUTHERN HALF OF AREA THROUGH
TONIGHT. LOCAL MVFR CIGS/VSBYS EXPECTED WITH THE HEAVIER
PRECIPITATION. AREAS ST/BR ALSO EXPECTED THROUGH THE PERIOD
ALONG/SOUTH OF A LINE FROM KPHP TO KCUT...ALTHOUGH FINAL NORTHERN
EDGE OF ST/BR WILL BE LARGELY DEPENDENT ON HOW FAR NORTH
PRECIPITATION DEVELOPS. NORTHERN HALF OF CWA SHOULD REMAIN LARGE
VFR THROUGH THE PERIOD.

&&

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

$$

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



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