Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 210051
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
651 PM MDT WED AUG 20 2014

.UPDATE...
ISSUED AT 647 PM MDT WED AUG 20 2014

00Z SURFACE ANALYSIS HAD LOW NEAR KPIR WITH BOUNDARY INTO CENTRAL
ND...WHICH HAS BEEN THE FOCUS FOR TSRA THIS EVENING. SHORTWAVE
OVER NORTHWEST SD/SOUTHWEST ND PER WATER VAPOUR. AIR STABILIZING
BEHIND LOW ON THE SD PLAINS...CONSISTENT WITH 00Z KUNR SOUNDING.
SEVERE TSRA SHOULD STAY NORTHEAST OF CWA REST OF THIS EVENING AND
HAVE DROPPED WATCH FOR CWA. CLEARED POPS IN THE WEST THROUGH
ABOUT 06Z GIVEN RADAR/SATELLITE TRENDS. ADDITIONAL SHORTWAVE
ENERGY MAY BRING SOME OVERNIGHT TSRA TO WESTERN AREAS OVERNIGHT
WITH WEAK MUCAPE PRESENT.

&&

.SHORT TERM...THIS EVENING THROUGH THURSDAY NIGHT
ISSUED AT 315 PM MDT WED AUG 20 2014

CURRENT SURFACE ANALYSIS SHOWS WEAK LOW PRESSURE OVER WESTERN
SD...WITH WARM FRONT EXTENDING SOUTHEAST THROUGH EASTERN NEB AND A
SURFACE TROF EXTENDING NORTH INTO ND. A COLD FRONT ALSO EXTENDS
ACROSS NORTHERN MT. UPPER LEVEL ANALYSIS SHOWS A LOW OVER THE
NORTHERN GREAT LAKES REGION...WITH HIGH PRESSURE OVER THE SOUTHERN
PLAINS. A LARGE SCALE TROF NOW COVERS MUCH OF THE WESTERN CONUS.
SOUTHWEST FLOW IN PLACE OVER THE HIGH PLAINS CONTINUES TO BRING
UNSETTLED WEATHER TO THE AREA. KUDX RADAR SHOWS SCATTERED SHOWERS
AND STORMS DEVELOPING OVER NORTHWEST AND WEST CENTRAL SD ALONG THE
SURFACE TROF. TEMPS ARE IN THE 80S AND LOWER 90S ACROSS THE
PLAINS...WITH SOME 70S OVER THE HIGHER BLACK HILLS.

UNSETTLED WEATHER WILL CONTINUE THROUGH THE SHORT TERM PERIOD AS A
SERIES OF UPPER LEVEL DISTURBANCES CROSS THE REGION IN SOUTHWEST
FLOW. THE EXACT TIMING OF THE DISTURBANCES IS STILL UNCERTAIN...
ESPECIALLY FURTHER OUT IN TIME. TEMPERATURES WILL REMAIN NEAR TO
ABOVE AVERAGE THROUGH THURSDAY...WITH A GRADUAL COOLDOWN LATE IN THE
WEEK AS THE WESTERN TROF SHIFTS SLOWLY EAST.

FOR LATE TODAY AND INTO TONIGHT...THE BEST CHANCES FOR SHOWERS AND
THUNDERSTORMS WILL BE TO THE EAST AND NORTHEAST OF THE BLACK
HILLS...ESPECIALLY THROUGH THE EARLY EVENING. THE SLIGHT RISK FOR
SEVERE STORMS REMAINS NEAR AND EAST OF A LINE FROM LEMMON TO PHILIP
TO MARTIN...WHERE THE BEST INSTABILITY AND SHEAR WILL BE THROUGH
EARLY EVENING. THE LOW WILL GRADUALLY MOVE EAST OF THE AREA LATER
TONIGHT...TAKING SHOWERS WITH IT. FURTHER WEST...ANOTHER DISTURBANCE
WILL MOVE INTO NORTHEAST WY AND THE BLACK HILLS AREA OVERNIGHT. HAVE
ADDED SLIGHT CHANCES FOR SHOWERS AND POSSIBLY A THUNDERSTORM FOR
LATE TONIGHT INTO THURSDAY MORNING FOR A GOOD PORTION OF THE CWA.
LOWS WILL BE IN THE MID 50S TO MID 60S...WARMEST OVER SOUTH CENTRAL
SD.

SOUTHWEST FLOW REMAINS OVER THE AREA ON THURSDAY...WITH THE NEXT
SYSTEM MOVING INTO THE AREA DURING THE AFTERNOON OR EVENING. THE
VARIOUS MEDIUM RANGE MODELS DIFFER SOME ON TIMING...WITH THE NAM AND
ECMWF SEVERAL HOURS FASTER THAN THE GFS. WILL KEEP WITH THE QUICKER
TIMING FOR NOW AND DID NOT MAKE MUCH IN THE WAY OF ADJUSTMENTS TO
THE GOING POP CHANCES. HIGHS ON THURSDAY WILL BE IN THE 80S AND
LOWER 90S ACROSS THE PLAINS...WITH SOME 70S OVER THE HIGHER BLACK
HILLS. THE THREAT FOR SEVERE STORMS LOOKS MINIMAL...WITH
RELATIVELY CAPE VALUES OVER MOST OF NORTHEAST WY AND WESTERN SD
LATE IN THE DAY...UNDER 1000 J/KG. THE BEST CHANCES FOR PCPN
THURSDAY NIGHT WILL GENERALLY BE OVER NORTHWESTERN SD.

&&

.LONG TERM...FRIDAY THROUGH WEDNESDAY
ISSUED AT 315 PM MDT WED AUG 20 2014

LARGE UPPER TROF WILL WORK THROUGH THE ROCKIES FRIDAY AND
SATURDAY...THEN PUSH INTO THE PLAINS SUNDAY THROUGH EARLY NEXT WEEK.
THIS WILL BRING THE BEST CHANCES FOR PRECIP FRI THROUGH SAT NIGHT.
TEMPS WILL GRADUALLY COOL THROUGH THE WEEKEND...WITH SUNDAY LIKELY
BEING THE COOLEST DAY IN THE EXTENDED WITH TEMPS IN THE 60S TO LOWER
70S OVER MOST AREAS. TEMPS WILL THEN SLOWLY MODERATE EARLY NEXT WEEK
BUT STILL REMAIN WELL BELOW AVERAGE. PCPN CHANCES WILL CONTINUE
THROUGH MOST OF THE EXTENDED PERIOD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 513 PM MDT WED AUG 20 2014

ISOLATED/SCATTERED TSRA ARE EXPECTED OVER NORTHWEST SD THIS
EVENING WITH LOCAL IFR CIGS/VSBYS. VFR CONDITIONS WILL THEN
PREVAIL THROUGH THURSDAY AFTERNOON. ISOLATED TSRA ARE POSSIBLE
TONIGHT...WITH SLIGHTLY BETTER CHANCES THURSDAY AFTERNOON OVER ALL
OF NORTHEAST WY/WESTERN SD.

&&

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

$$

UPDATE...HELGESON
SHORT TERM...26
LONG TERM...13
AVIATION...HELGESON



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