Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 212348
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
548 PM MDT THU MAY 21 2015

.SHORT TERM...THIS EVENING THROUGH FRIDAY NIGHT
ISSUED AT 225 PM MDT THU MAY 21 2015

CURRENT UPPER ANALYSIS SHOWS A HIGH AMPLITUDE RIDGE OVER THE GREAT
PLAINS WITH AN UPPER LOW MOVING ONSHORE THE CALIFORNIA COAST.
SOUTHEASTERLY UPSLOPE SFC FLOW OVER THE GREAT PLAINS IS COMBINING
WITH MID/HIGH LEVEL MOISTURE TO THE EAST OF THE UPPER LOW/TROUGH
TO PRODUCE SHOWERS OVER MUCH OF THE ROCKIES THIS AFTN.

FOR TNGT...SOUTHEASTERLY SFC FLOW WILL CONTINUE OVER THE FORECAST
AREA WITH A SLIGHT STRENGTHENING OF THE 850-MB WINDS AS THE
BOUNDARY LAYER DECOUPLES THIS EVENING. A SHORT-WAVE TROUGH WILL
EJECT NORTHEASTWARD FROM THE UPPER LOW AND WILL CROSS COLORADO
TONIGHT. MOISTURE AND LIFT WILL REMAIN CONFINED MOSTLY TO THE
SOUTHWEST OF THE CWA THROUGH 12Z. 850-MB TEMPS OF 8-10C AND
BOUNDARY LAYER FLOW SHOULD KEEP TEMPERATURES TOO WARM FOR ANY
FROST DEVELOPMENT ON THE PLAINS OVERNIGHT.

ON FRIDAY/FRIDAY NIGHT...THE SHORT-WAVE TROUGH WILL SLOWLY CROSS
THE NEB PANHANDLE...WITH NORTHWARD PROGRESS BEING SLOWED BY AN UPPER-
LEVEL NW-SE ORIENTED CONFLUENT ZONE. A NARROW ZONE OF
MOISTURE/LIFT WILL FAVOR THE HIGHEST POPS ACROSS THE SRN CWA.
INSTABILITY IS EXPECTED TO BE WEAK...SO HAVE KEPT THE THUNDER
POTENTIAL CLOSEST TO THE BOUNDARY OVER NERN WYOMING ON FRIDAY
AFTN/EVE. ON FRIDAY NIGHT...THE SHORT- WAVE TROUGH WILL MOVE
NORTHEASTWARD ACROSS THE FORECAST AREA. SOME ISENTROPIC LIFT IS
PRESENT IN THE LOW-MID LEVELS...BUT THE WAVE WILL ENCOUNTER DRY
AIR TO THE NORTH...SO WILL KEEP ONLY LOW POPS OVER THE NORTHERN
CWA...HIGHEST POPS ACROSS THE SOUTH.

.LONG TERM...SATURDAY THROUGH THURSDAY
ISSUED AT 225 PM MDT THU MAY 21 2015

MEDIUM RANGE MODELS ARE IN GOOD AGREEMENT ON UNSETTLED
WEATHER THROUGH THE HOLIDAY WEEKEND AS UPPER LEVEL SYSTEM SLOWLY
TRACKS ACROSS THE CENTRAL ROCKIES INTO THE NORTHERN PLAINS. WITH THE
LEFT EXIT REGION OF THE UPPER JET MOVING OVER THE CWA...IT STILL
LOOKS LIKE THE HEAVIER AND MORE WIDESPREAD RAINFALL WILL BE LATE
SATURDAY INTO SUNDAY. BEST INSTABILITY AND SHEAR FOR STRONGER STORMS
WILL BE FROM SOUTHWEST INTO CENTRAL SD ON SATURDAY...SHIFTING
EASTWARD FOR SUNDAY. MODELS DIFFER ON THE LOCATION OF THE HEAVIER
PRECIP BUT ARE GENERALLY SHOWING 0.5 TO 1.5 INCHES BY SUNDAY
NIGHT...WITH SOME LOCALLY HIGHER AMOUNTS POSSIBLE.

THIS SYSTEM WILL GRADUALLY EXIT THE REGION MONDAY...BUT PRECIP
CHANCES WILL CONTINUE THROUGH THE WEEK AS THE ACTIVE PATTERN
CONTINUES. TEMPERATURES WILL CONTINUE TO BE BELOW AVERAGE OVER THE
WEEKEND...WITH A GRADUAL WARMING TREND TO NEAR AVERAGE TEMPERATURES
BY THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z FRIDAY EVENING)
ISSUED AT 545 PM MDT THU MAY 21 2015

3000-5000FT AGL CIGS SPREADING INTO NORTHEAST WYOMING/SOUTHWEST
SOUTH DAKOTA THIS EVENING...WILL CONTINUE TO MOVE NORTHWARD
OVERNIGHT. MVFR CIGS EXPECTED AROUND THE BLACK HILLS.
SHOWERS/THUNDERSTORMS ON TAP FOR FRIDAY...WITH MVFR/LCL IFR
CONDITIONS.

&&

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

$$

SHORT TERM...10
LONG TERM...POJORLIE
AVIATION...7



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