534 
FXUS63 KUNR 122317
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
517 PM MDT TUE MAY 12 2015

.SHORT TERM...THIS EVENING THROUGH WEDNESDAY NIGHT
ISSUED AT 224 PM MDT TUE MAY 12 2015

20Z SURFACE ANALYSIS HAD MEANDERING FRONTAL BOUNDARY FROM CENTRAL
ID INTO NORTHWEST SD. BREEZY SOUTHERLY WINDS ACROSS CWA WITH
DECENT GRADIENT IN RESPONSE TO PRESSURE FALLS/WARM AIR ADVECTION.
WATER VAPOUR HAD RIDGE BUILDING INTO THE NORTHERN PLAINS WITH
SOUTHWEST FLOW OVER THE SOUTHWEST US. LOOKS LIKE A WEAK SHORTWAVE
OVER SOUTH CENTRAL WY WILL MOVE ACROSS NORTHERN PORTIONS OF THE
CWA TONIGHT. IT WILL INTERACT WITH 20-40KT LOW LEVEL JET ON THE SD
PLAINS...MODEST 700-850MB THETA-E ADVECTION...AND WEAK MUCAPE TO
BRING A FEW -SHRA/-TSRA ACROSS MAINLY NORTHERN PORTIONS OF THE CWA
VERY LATE THIS AFTERNOON THROUGH THE OVERNIGHT HOURS. TEMPERATURES
WILL BE NEAR GUIDANCE.

WEDNESDAY...FRONTAL BOUNDARY MOVES VERY LITTLE WITH ANOTHER WEAK 
WAVE MOVING ACROSS CWA AS UPPER RIDGE SHIFTS EAST AND UPPER FLOW 
BECOMES SOUTHWESTERLY. MODELS MAY BE OVERDOING MOISTURE ALONG 
FRONTAL BOUNDARY...BUT IT APPEARS 0.5-1KJ/KG SBCAPE WILL DEVELOP BY 
AFTERNOON WITH SBCIN DROPPING BELOW 50J/KG WEST OF RAPID CITY. 
INTERACTION OF TERRAIN AND BOUNDARY SHOULD BE SUFFICIENT FOR TSRA 
LATER IN THE DAY. 0-6KM SHEAR SUFFICIENT FOR AN ISOLATED/SEVERE 
STORM ACROSS NORTHEAST WY/FAR WESTERN SD. LARGE HAIL WOULD BE MAIN 
THREAT. TEMPERATURES WILL BE NEAR GUIDANCE.

WEDNESDAY NIGHT...FRONTAL BOUNDARY SHIFTS EAST SOME AND BECOMES 
NORTHEAST/SOUTHWEST ORIENTED. SOUTHWEST FLOW ALOFT WILL SUPPLY WEAK 
DISTURBANCES AND 20-35KT 800MB FLOW WILL BRING SUSTAINED THETA-E 
ADVECTION. SOME -SHRA/-TSRA EXPECTED. ACTIVE STORMS WOULD OCCUR 
EARLY IN THE EVENING AND WEAKEN BY SUNSET.

.LONG TERM...THURSDAY THROUGH TUESDAY
ISSUED AT 224 PM MDT TUE MAY 12 2015

THE REGION WILL BE UNDER ACTIVE SOUTHWEST FLOW FOR THE END OF THE
WEEK INTO THE WEEKEND...WITH DAILY CHANCES FOR RAIN SHOWERS AND
SOME THUNDERSTORMS. A STRONG UPPER LOW OVER THE WEST COAST WILL
EJECT SOME ENERGY INTO THE AREA FRIDAY. MODELS ARE SHOWING ABOUT
2000 J/KG SBCAPE COLLOCATED WITH 40-50 KTS 0-6KM SHEAR ACROSS THE
SOUTHERN CWA...AND SO THERE IS A SLIGHT RISK OF SEVERE
THUNDERSTORMS FRIDAY. UPPER LOW WILL THEN MOVE ACROSS THE ROCKIES
INTO THE PLAINS THIS WEEKEND...BRINGING THE BEST CHANCES FOR
ADDITIONAL RAINFALL. MODELS ARE INDICATING AROUND A HALF INCH OF
QPF BY THE END OF THE WEEK...WITH AN ADDITIONAL INCH OR TWO DURING
THE WEEKEND. AS FAR AS TEMPERATURES GO...MORE SPRING LIKE READINGS
ARE EXPECTED FROM MID WEEK THROUGH THE WEEKEND. A SHOT OF COLD AIR
WILL BRIEFLY MOVE INTO THE AREA SUNDAY NIGHT...AND SO THERE MAY BE
SOME LIGHT SNOW SHOWERS THEN...BUT THE MAJORITY OF THE PRECIPITATION
WILL REMAIN RAIN.

&&

.AVIATION...FOR THE 00Z TAFS THROUGH 00Z WEDNESDAY EVENING
ISSUED AT 513 PM MDT TUE MAY 12 2015

GUSTY SOUTHERLY WINDS ACROSS SOUTH CENTRAL SD WILL DIMINISH EARLY THIS
EVENING. ISOLD-SCT -SHRA AND A FEW THUNDERSTORMS ARE EXPECTED OVER
NORTHEASTERN WYOMING AND FAR WESTERN SOUTH DAKOTA THIS EVENING AND
OVERNIGHT. GENERALLY VFR CONDITIONS ARE EXPECTED THROUGH
WEDNESDAY MORNING...ALTHOUGH THERE MAY BE SOME LOCAL MFVR CIGS
WITH ANY SHOWERS AND THUNDERSTORMS. MODELS ARE IN DISAGREEMENT ON
THE POSSIBLE DEVELOPMENT OF FOG ACROSS NERN WY...NWRN SD AND AREAS
NEAR THE BLACK HILLS. HAVE INCLUDED SOME MVFR STRATUS TO TREND THE
CIGS DOWNWARD FOR NOW.

&&

.HYDROLOGY...
ISSUED AT 224 PM MDT TUE MAY 12 2015

RUNOFF FROM RAIN AND MELTING SNOW IS CAUSING RISES IN THE LEVEL
OF THE WHITE RIVER BETWEEN INTERIOR AND OACOMA. A FLOOD WARNING
REMAINS IN EFFECT FOR THAT AREA AS MINOR TO MODERATE FLOODING IS
FORECAST TO DEVELOP. HAVE BEEN WATCHING UPSTREAM GAGES TO THE
NE/SD LINE...AND BOTH INTERIOR AND THE STATE LINE SEEM TO BE
CRESTING FOR NOW...SO DO NOT PLAN ON ISSUING ANOTHER WARNING FOR
UPSTREAM LOCATIONS AT THIS TIME. HOWEVER...WILL CONTINUE TO KEEP A
CLOSE EYE ON RIVERS WITH ADDITIONAL RAIN EXPECTED BY THE END OF
THE WEEK INTO THE WEEKEND. THERE ARE DAILY CHANCES FOR SHOWERS
AND THUNDERSTORMS THROUGH THE END OF THE WEEK...WITH SEVERE STORMS
POSSIBLE ON FRIDAY...AND GREATER CHANCES OF RAIN FOR THE WEEKEND.

&&

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

$$

SHORT TERM...HELGESON
LONG TERM...POJORLIE
AVIATION...10
HYDROLOGY...POJORLIE