Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 241737
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1137 AM MDT TUE MAR 24 2015

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
ISSUED AT 236 AM MDT TUE MAR 24 2015

UNSETTLED WNW FLOW WILL PREVAIL IN THE PERIOD. DEPARTING UPPER
WAVE AND ASSOCIATED SFC CYCLONE/TROUGH WILL SUPPORT RAIN OVER THE
NW HALF OF THE FA THIS MORNING WITH DRYING THIS AFTERNOON MOST
PLACES. BACKSIDE COLD FRONT WILL SHIFT SE INTO THE FA THIS
EVENING...WITH SIG LL COOLING EXPECTED. LL BAROCLINIC ZONE WILL
STALL JUST TO THE WEST OF THE FA WITH NW FLOW UPPER LEVEL IMPULSES
ADVECTING SE ALONG THIS FEATURE. FGEN RESPONSES AND ASSOCIATED
STEEP MID LEVEL LAPSE RATES COMBINED WITH PAC MOISTURE WILL BE
SUFFICIENT TO SUPPORT PRECIP WITH EACH IMPULSE. WARMEST DAY IN THE
PERIOD WILL BE TODAY...WITH MUCH COOLER CONDS ON TRACK FOR WED AS
STRONGER NEGATIVE HEIGHT ANOMALY SHIFTS SE INTO THE EASTERN HALF
OF THE CONUS...A TYPICAL PATTERN FOR THE LAST SEVERAL MONTHS.

TODAY...UPPER IMPULSE AND ASSOCIATED BACKSIDE DEFORMATION ZONE WILL
SHIFT EAST ACROSS THE NW HALF OF THE FA...WITH RAIN EXPECTED THERE
THIS MORNING. SYSTEM DRY SLOT WILL ADVECT OVER THE REMAINDER OF THE
FA. WIDESPREAD RAINS WILL END OVER NW SD THIS MORNING WITH MOST
PLACES EXPECTED TO BE DRY THIS AFTERNOON. FORECAST MODELS DO
INDICATE VERY STEEP LL LAPSE RATES. HOWEVER...LL MOISTURE WILL BE
HIGHLY LIMITED. HENCE OPTED FOR ONLY A VERY LOW POP MENTION ACROSS
THE ENTIRE FA THIS AFTERNOON PER DIURNAL HEATING AND ASSOCIATED
INSTABILITY. PRESSURE RISE COUPLET TIMED WITH DIURNAL HEATING AND
FAST LL FLOW WILL SUPPORT WINDY CONDS ACROSS FAR NW SD. DYNAMICALLY
FORCED WINDS WILL ENSUE THIS MORNING...WITH DIURNAL MIXING
SUPPORTING STRONG GUSTY WINDS INTO THE AFTERNOON. WILL ISSUE A WIND
ADV FOR THE FAR NW SD ZONES THROUGH THIS AFTERNOON.

TONIGHT...SFC COLD FRONT WILL SHIFT INTO THE FA...WITH THIS LL
BAROCLINIC ZONE STALLING TO THE WEST OF THE FA. ANOTHER WEAKER
IMPULSE WILL ADVECT SE ALONG THIS FEATURE SUPPORTING AN ELEVATED
FGEN RESPONSE OVER THE SW THIRD OF THE FA. THIS LOOKS TO SUPPORT A
RAIN/SNOW MIX THERE...BEST CHANCES OVER NE WY WHERE HIGH CHANCES
WERE RETAINED. SOME UNCERTAINTY PER THE TRACK/STRENGTH OF THIS
SYSTEM REMAINS...WITH THE POTENTIAL FOR SNOW ACCUMS OVER NE AND THE
WESTERN BLACK HILLS TONIGHT IF THIS SYSTEM ENDS UP BEING STRONGER.

WED...WEAK IMPULSES WILL CONTINUE TO AFFECT MAINLY THE WESTERN THIRD
OF THE FA WITH ANOTHER SYSTEM EXPECTED LATE WED AFTERNOON INTO WED
NIGHT. THEN NAM REMAINS THE MOST AGGRESSIVE PER WAA AND THE
RESULTING FGEN RESPONSE ACROSS SE MT AND NE WY/NW SD. IF THE NAM
SOLUTION WERE TO VERIFY...A NARROW BAND OF DECENT SNOW ACCUMS WOULD
BE POSSIBLE IN THESE LOCATIONS STARTING LATE WED NIGHT GIVEN
POTENTIAL INSTABILITY PER STEEP LAPSE RATES IN THE DGZ. CERTAINLY
SOMETHING TO KEEP AN EYE ON. OTHERWISE...COOL CONDS EXPECTED WITH
MOST LOCATIONS SEEING 20S FOR LOWS.

.LONG TERM...THURSDAY THROUGH MONDAY
ISSUED AT 236 AM MDT TUE MAR 24 2015

UNSETTLED NORTHWEST FLOW ALOFT ON THURSDAY WILL BRING ANOTHER
UPPER LEVEL DISTURBANCE ACROSS THE CWA DURING THE DAY. THERE WILL
BE A GOOD CHANCE FOR RAIN AND SNOW SHOWERS ACROSS MUCH OF THE
CWA...ESPECIALLY OVER THE BLACK HILLS AREA. SOME LIGHT SNOW
ACCUMULATIONS ARE LIKELY OVER AT LEAST THE BLACK HILLS AND THE
BEAR LODGE MTS. CONDITIONS WILL BEGIN TO IMPROVE THURSDAY NIGHT
AND ESPECIALLY ON FRIDAY AS A RIDGE BUILDS OVER THE WESTERN CONUS
AND SLOWLY MOVES EAST INTO THE ROCKIES. TEMPERATURES WILL BE WELL
ABOVE AVERAGE AGAIN BY SATURDAY.

SOME TIMING ISSUES RIGHT NOW WITH THE NEXT UPPER LEVEL DISTURBANCE
AND COLD FRONT THAT WILL APPROACH THE REGION SOMETIME LATE SATURDAY
OR SATURDAY NIGHT. WILL KEEP SOME LOW POPS ACROSS MOSTLY WESTERN
PORTIONS OF THE CWA AS IT SLIDES THROUGH. SOME COOLER AIR WILL PUSH
IN FOR THE SECOND HALF OF THE WEEKEND...BUT WELL ABOVE AVERAGE
TEMPERATURES ARE STILL EXPECTED INTO EARLY NEXT WEEK.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY)
ISSUED AT 1136 AM MDT TUE MAR 24 2015

STRONG NORTHWEST WINDS ACROSS THE WESTERN SD PLAINS WILL
GRADUALLY DECREASE INTO THE EVENING BUT REMAIN BREEZY THROUGH WED
MORNING. RAIN SHOWERS WILL DEVELOP ACROSS NE WY...THE BLKHLS
AREA...AND SW SD THIS AFTERNOON AND TONIGHT...CHANGING TO SNOW
SHOWERS OVERNIGHT. MVFR CONDITIONS ARE EXPECTED WITH THESE
SHOWERS...LOCALIZED AREAS OF IFR CONDITIONS ESPECIALLY IN THE
BLKHLS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY UNTIL 5 PM MDT THIS AFTERNOON FOR SDZ001-002-012-
     013.

WY...NONE.
&&

$$

SHORT TERM...JC
LONG TERM...26
AVIATION...13






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