Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 011455
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
855 AM MDT TUE SEP 1 2015

.UPDATE...
ISSUED AT 844 AM MDT TUE SEP 1 2015

HAVE MADE A FEW ADJUSTMENTS TO THE FORECAST BASED ON LATEST OBSERVATIONS
AND MODEL DATA.
1...LATEST SATELLITE OBSERVATIONS SHOW THE FOG IN
BUTTE AND MEADE COUNTIES HAS BEEN SLOW TO ERODE THIS MORNING. HAVE
UPDATED GRIDS TO INCLUDE PATCHY FOG UP TO 18Z.
2...SHOWERS AND THUNDERSTORMS HAVE BEEN SLOW TO MOVE OUT OF
MELLETTE...TODD...AND TRIPP COUNTIES. THE SHORT TERM HIGH
RESOLUTION MODELS HAVE MOST OF THE PRECIPITATION EXITING OUR CWA
BY 18Z...AND HAVE REFLECTED THAT IN OUR GRIDS.
3...THIS MORNINGS SOUNDING AT UNR HAD A MAX TEMPERATURE OF 94
DEGREES...AND WITH MAINLY CLEAR SKIES AND DECENT MIXING EXPECTED
TODAY...HAVE ADJUSTED TEMPERATURES UP A COUPLE OF DEGREES FROM THE
PREVIOUS FORECAST ACROSS MOST OF NORTHEAST WYOMING AND WESTERN
SOUTH DAKOTA.

&&

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
ISSUED AT 202 AM MDT TUE SEP 1 2015

08Z SFC ANALYSIS SHOWS HIGH PRESSURE OVER THE EASTERN
DAKOTAS/MINNESOTA WITH A SFC TROUGH DEVELOPING FROM NORTHWESTERN
MONTANA INTO CENTRAL WYOMING. WEAK UPPER FORCING AND SOME
850-700 MB FRONTOGENESIS MAY ALLOW A FEW SHOWERS OR POSSIBLY A
THUNDERSTORM TO CLIP TRIPP CO IN SOUTH CENTRAL SOUTH DAKOTA EARLY
THIS MORNING.

THE SURFACE HIGH WILL CONTINUE TO MOVE OFF TO THE EAST TODAY AND
THE DEEPENING SFC TROUGH WILL MOVE EASTWARD INTO FAR WESTERN SOUTH
DAKOTA. SOUTHERLY FLOW TO THE EAST OF THE TROUGH WILL BRING LOW
LEVEL MOISTURE INTO CENTRAL AND WESTERN SOUTH DAKOTA. VERY DRY
CONDITIONS WILL DEVELOP TO THE WEST OF THE TROUGH OVER NERN WY AND
FAR WRN SD DUE TO SUBSIDENCE ASSOCIATED WITH WESTERLY DOWNSLOPE
FLOW. HIGH TEMPERATURES ON THE PLAINS WILL MAINLY BE IN THE 90S
TODAY...WITH THE MIN RH FALLING TO AROUND 12 PERCENT OVER
NORTHEASTERN WYOMING AND TO 25 TO 30 PERCENT OVER PARTS OF WESTERN
AND CENTRAL SOUTH DAKOTA. AT THIS TIME IT LOOKS LIKE THE CAPPING
INVERSION DUE TO THE WARM AIR ALOFT WILL KEEP ANY SHOWERS OR
THUNDERSTORMS FROM FORMING THIS AFTN/EVE. THE CAP WILL BE WEAKEST
OVER SOUTH CENTRAL SOUTH DAKOTA SO AN ISOLATED THUNDERSTORM MAY BE
POSSIBLE THERE DURING THE LATE AFTN IF THE INSTABILITY ENDS UP
BEING SLIGHTLY STRONGER THAN CURRENTLY EXPECTED.

WEDNESDAY WILL BE VERY WARM WITH THE SFC TROUGH DEEPENING OVER
EASTERN MT/WY AND THE WESTERN DAKOTAS. VERY DRY AIR IS EXPECTED
AGAIN TO THE WEST OF THE TROUGH AND SOUTHWESTERLY WINDS WILL
BECOME BREEZY...OVER PARTS OF NORTHEASTERN WYOMING. DRY WEATHER IS
EXPECTED AGAIN ON WEDNESDAY.

.LONG TERM...THURSDAY THROUGH MONDAY
ISSUED AT 202 AM MDT TUE SEP 1 2015

STRONG UPPER TROUGH WILL DEVELOP ACROSS THE PAC NW THU
TOWARD THE END OF THE WEEK. SWRLY FLOW WILL STRENGTHEN ACROSS THE
REGION AHEAD OF THE TROUGH WITH SEVERAL EMBEDDED WAVES. A STATIONARY
FRONTAL BOUNDARY WILL SIT ACROSS NW ND/ERN MT. CONVECTION WILL
DEVELOP ACROSS THE NRN PLAINS LATE FRIDAY AND MAINLY INTO SATURDAY
AS THE UPPER TROUGH CUTS OFF AND CROSSES THE NRN ROCKIES INTO THE
NRN PLAINS SAT INTO SUN. COOLER AND DRIER AIR WILL PUSH INTO THE
AREA ON THE BACKSIDE OF THE LOW SUN/MON. WEAK RIDGING WILL DEVELOP
EARLY NEXT WEEK WITH NEAR TO SLIGHTLY BELOW AVERAGE TEMPS.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 202 AM MDT TUE SEP 1 2015

VFR CONDITIONS WILL CONTINUE TODAY AND TONIGHT.


&&

.FIRE WEATHER...
ISSUED AT 202 AM MDT TUE SEP 1 2015

DRY AND BREEZY CONDITIONS WILL DEVELOP ACROSS PARTS OF NERN WY
WEDNESDAY AHEAD OF A DEEPENING TROUGH OF LOW PRESSURE OVER MT.
DEWPOINTS OVER NORTHEASTERN WYOMING SHOULD DROP TO AROUND 35F
WITH RH DROPPING TO 10-15 PERCENT. NAM FORECAST SOUNDINGS INDICATE
WINDS OF 25-30KT MIXING DOWN FROM ALOFT. WILL KEEP THE FIRE
WEATHER WATCH FOR SRN CAMPBELL COUNTY ON WEDNESDAY.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...FIRE WEATHER WATCH FROM WEDNESDAY MORNING THROUGH WEDNESDAY
     EVENING FOR WYZ259.

&&

$$

UPDATE...MCKEMY
SHORT TERM...10
LONG TERM...13
AVIATION...13
FIRE WEATHER...10



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