Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 240837
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
237 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 12Z TAFS THROUGH 12Z WEDNESDAY MORNING
ISSUED AT 236 AM MDT TUE MAR 24 2015

AN UPPER LEVEL DISTURBANCE AND COLD FRONT WILL SLOWLY
CROSS THE REGION TODAY. SCATTERED TO NUMEROUS SHOWERS ARE EXPECTED
THIS MORNING FROM FAR NORTHEAST WYOMING INTO NORTHWEST SD...WITH
ISOLATED TO SCATTERED SHOWERS ELSEWHERE. SOME SNOW SHOWERS ARE
POSSIBLE OVER THE HIGHER BLACK HILLS. AREAS OF MVFR CONDITIONS CAN
BE EXPECTED THIS MORNING...MAINLY FROM NORTHEAST WY INTO NORTHWEST
SD. AS COLD FRONT MOVES THROUGH THE AREA THIS MORNING... WINDS WILL
TURN NORTHWESTERLY AND INCREASE...WITH THE STRONGEST WINDS OVER
NORTHWEST SD. GUSTS TO AROUND 40 KTS CAN BE EXPECTED THERE DURING
THE DAYTIME HOURS.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY FROM 6 AM THIS MORNING TO 5 PM MDT THIS AFTERNOON
     FOR SDZ001-002-012-013.

WY...NONE.
&&

$$

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






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