Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 200906
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
306 AM MDT SUN APR 20 2014

.SHORT TERM...TODAY THROUGH MONDAY NIGHT
ISSUED AT 305 AM MDT SUN APR 20 2014

CURRENT SURFACE ANALYSIS SHOWS WEAK HIGH PRESSURE OVER THE
CENTRAL AND EASTERN DAKOTAS. AN AREA OF LOW PRESSURE IS LOCATED
OVER SOUTHERN AB...WITH WEAK COLD FRONT STRETCHING SOUTH-SOUTHWEST
ACROSS WESTERN MT INTO EASTERN ID. LEE TROF STRETCHES SOUTHEAST
INTO EASTERN WY. UPPER LEVEL ANALYSIS SHOWS WEAK RIDGING OVER THE
NORTHERN HIGH PLAINS...WITH SHORTWAVE TROF MOVING QUICKLY EAST
ACROSS THE NORTHERN ROCKIES. SKIES ARE MAINLY CLEAR ACROSS THE
AREA WITH TEMPS MOSTLY IN THE MID 30S TO MID 40S. WINDS ARE SOUTH
TO SOUTHEAST ACROSS MOST OF THE AREA NOW.

WARM AND MAINLY DRY WX WILL CONTINUE FOR TODAY AND INTO EARLY THIS
WEEK AS NEAR ZONAL FLOW ALOFT PERSISTS. FOR TODAY...SKIES WILL BE
MOSTLY SUNNY IN GENERAL...ESPECIALLY THROUGH THE MIDDAY HOURS.
CLOUDS WILL INCREASE SOME IN THE AFTERNOON AS THE COLD FRONT
ARRIVES...ESPECIALLY ACROSS SOUTHERN AREAS. HIGHS WILL MOSTLY BE IN
THE 70S...WITH 60S OVER THE BLACK HILLS AND PORTIONS OF NORTHEAST
WY. THE FRONT WILL MAKE ITS WAY INTO WESTERN PORTIONS OF THE CWA BY
18Z AND ACROSS THE REST OF THE CWA DURING THE AFTERNOON AND EARLY
EVENING. BRISK NORTHWESTERLY WINDS WILL DEVELOP ACROSS THE PLAINS
BEHIND THE FRONT THIS AFTERNOON AND EVENING.

AHEAD OF THE FRONT...SOUTHERLY WINDS WILL HELP TO BRING INCREASING
LOW LEVEL MOISTURE THROUGH THE DAY...ESPECIALLY TO THE EAST OF THE
BLACK HILLS...WHERE DEWPOINTS SHOULD RISE INTO THE 40S THIS
AFTERNOON. THIS MOISTURE...COMBINED WITH STRONG WARMING AND STEEP
LAPSE RATES THIS AFTERNOON...WILL HELP TO PRODUCE CAPE VALUES LIKELY
EXCEEDING 500 J/KG OVER SOUTH CENTRAL SD BY LATE IN THE DAY. THE
FRONT WILL ARRIVE IN THIS AREA LATE IN THE DAY...WITH AT LEAST
ISOLATED SHOWERS AND STORMS EXPECTED TO DEVELOP LATE IN THE
AFTERNOON AND EARLY EVENING. A STRONGER STORM OR TWO LOOKS POSSIBLE
WITH GUSTY WINDS AND AT LEAST THE POTENTIAL FOR SMALL HAIL. ANY
ACTIVITY SHOULD PUSH EAST OF SOUTH CENTRAL SD BY LATE EVENING.

AS TODAYS WEATHER WILL BE SIMILAR TO WHAT HAPPENED FRIDAY...MONDAY
WILL BE MUCH LIKE YESTERDAY...WITH MOSTLY SUNNY SKIES...MILD
TEMPERATURES...AND RELATIVELY LIGHT WINDS. NORTHWESTERLY WINDS CAN
BE EXPECTED TO THE NORTH AND EAST OF THE BLACK HILLS...WITH WINDS
TURNING SOUTHERLY OVER NORTHEAST WY AND THE BLACK HILLS. HIGHS WILL
BE IN THE 60S AND LOWER 70S. LOWS MONDAY NIGHT WILL GENERALLY BE IN
THE MID 30S TO MID 40S...WITH SOUTH TO SOUTHEAST WINDS DEVELOPING
OVER THE ENTIRE AREA.

&&

.LONG TERM...TUESDAY THROUGH SATURDAY
ISSUED AT 305 AM MDT SUN APR 20 2014

MODELS ARE IN PRETTY GOOD AGREEMENT FOR MEDIUM RANGE. AN UPPER
LEVEL TROUGH ENTERING THE NORTHWEST US COAST EARLY TUESDAY WILL
MOVE ACROSS THE ROCKIES INTO THE NORTHERN PLAINS BY THURSDAY
MORNING.

AHEAD OF IT ON TUESDAY...LOW PRESSURE WILL DEVELOP OVER MT WITH WELL
DEFINED PRESSURE FALLS AND SUBSEQUENT WINDY SOUTHERLY RETURN FLOW.
LOW MOVES INTO SOUTHEAST MT WITH TROUGH PIVOTING NORTHEAST INTO
NORTHEAST WY/WESTERN SD. A FEW -TSRA MAY DEVELOP ALONG/AHEAD OF THIS
BOUNDARY. 0-6KM SHEAR SUFFICIENT FOR STRONG STORMS...BUT MOISTURE
AVAILABILITY IN QUESTION GIVEN AMOUNT OF MIXING AS TEMPERATURES
CLIMB WELL INTO THE 70S.

WEDNESDAY...INITIAL LOW PRESSURE MOVES EAST OF CWA AS SECONDARY LOW
DEVELOPS OVER MT/SK BORDER AS UPPER LOW WRAPS UP OVER THE SAME AREA.
THIS WILL PUSH DRIER AIR INTO CWA EARLY...BUT MOISTURE WILL RETURN
LATER IN THE DAY/NIGHT AS WRAP AROUND SHIFTS SOUTH FROM MT/ND.
TEMPERATURES WILL BE QUITE WARM GIVEN FORECAST SOUNDINGS WITH WEAK
INSTABILITY SUPPORTIVE OF DIURNAL -TSRA. AS PRECIPITATION TRENDS TO
-SHRA WEDNESDAY NIGHT...A FEW -SHSN POSSIBLE IN THE HIGHER
ELEVATIONS GIVEN WET BULB PROFILES.

THURSDAY...UPPER/SURFACE LOW SHIFTS EAST INTO THE UPPER MIDWEST
LEAVING BACKWASH PRECIPITATION ACROSS THE CWA AS WELL AS A RATHER
TIGHT PRESSURE GRADIENT. HAVE PAINTED VERY WINDY CONDITIONS...BUT
COULD EASILY BE IN THE STRONG CATEGORY GIVEN CYCLONIC FLOW/COLD AIR
ADVECTION. COLD ENOUGH FOR -SHRASN THURSDAY NIGHT...EVEN ON THE
PLAINS OF NORTHEAST WY/NORTHWEST SD. TEMPERATURES WILL BE NOTICEABLY
COLDER.

FOR FRIDAY...LULL IN THE WEATHER EXPECTED AS UPPER LEVEL RIDGE POKES
INTO THE CWA. LOOKING AHEAD TO NEXT WEEKEND...GFS/ECMWF BRING
ANOTHER STORM SYSTEM/UPPER LOW INTO THE AREA...BUT THIS TIME MOVING
IT FROM THE CENTRAL ROCKIES INTO THE CENTRAL PLAINS. MODELS HAVE
TRENDED WETTER WITH THIS SYSTEM...BUT TOO FAR OUT TO ASCERTAIN
EFFECT ON SENSIBLE WEATHER. WILL HAVE NORMAL CHANCE POPS IN THERE
FOR NOW.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z MONDAY MORNING
ISSUED AT 305 AM MDT SUN APR 20 2014

A WEAK COLD FRONT WILL PASS THROUGH THE AREA TODAY. AHEAD OF
IT...SOUTHERLY WINDS ARE EXPECTED. BEHIND IT...WINDS WILL SHIFT TO
A NORTHERLY DIRECTION AND BECOME GUSTY AT TIMES. ISOLATED -TSRA
ARE POSSIBLE OVER SOUTH CENTRAL SD LATE THIS AFTERNOON/EARLY THIS
EVENING WITH LOCAL MVFR VSBYS/GUSTY WINDS. OTHERWISE...VFR
CONDITIONS ARE EXPECTED THROUGH TONIGHT.

&&

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

$$

SHORT TERM...26
LONG TERM...HELGESON
AVIATION...HELGESON





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