Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 160236
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
836 PM MDT WED APR 15 2015

.UPDATE...
ISSUED AT 830 PM MDT WED APR 15 2015

LARGE BATCH OF CONVECTION IS SHIFTING FROM THE NEB PANHANDLE INTO
SWRN SD...SO HAVE UPPED POPS FOR THAT AREA WHILE INTRODUCING
ISOLD TSTMS. BEST INSTABILITY...THOUGH...REMAINS SOUTH OF OUR
CWFA. THE OTHER CHANGE TO THE FCST WAS TO REMOVE SNOW FROM THE
FCST FROM THE SD PLAINS AND MOST FOOTHILL LOCATIONS (INCLUDING
RAPID CITY) AS TEMP PROFILES WILL REMAIN TOO WARM OVERNIGHT. REST
OF FCST LARGELY UNCHANGED.

&&

.SHORT TERM...THIS EVENING THROUGH THURSDAY NIGHT
ISSUED AT 222 PM MDT WED APR 15 2015

STRONG UPPER LOW IS CIRCULATING OVER UTAH...PUSHING
CLOUDS...RAIN...AND SNOW INTO NORTHEASTERN WYOMING. COLD FRONT IS
SLOWLY MOVING EASTWARD. TEMPS BEHIND THE FRONT ARE GENERALLY IN
THE 40S...AND TEMPS AHEAD OF THE FRONT RISING INTO THE UPPER 60S
AND LOWER 70S WITH BREEZY SOUTHERLY WINDS.

GFS IS IN BETTER AGREEMENT WITH THE OTHER MODELS TODAY WITH THE
TRACK OF THE LOW PRESSURE SYSTEM. CLOSED LOW WILL SHIFT SOUTH OVER
THE FOUR CORNERS REGION TONIGHT...CONTINUING TO PUSH MOISTURE INTO
WY AND SD. AREAS OF BEST FRONTOGENESIS AND ISENTROPIC LIFT SET UP
OVERNIGHT ACROSS NORTHEAST WY INTO SOUTHWEST SD. WARMER TEMPS IN
SOUTHWEST SD SHOULD KEEP MOST PRECIP THERE RAIN...BUT A FEW INCHES
OF SNOW ARE EXPECTED ACROSS PORTIONS OF NORTHEAST WYOMING. GFS AND
NAM AGREE ON PLACEMENT OF HIGHEST SNOW AMOUNTS ACROSS SOUTHERN
CAMPBELL COUNTY...AND BOTH HAVE UP TO A FOOT OF SNOW IN THAT AREA.
HOWEVER...CONSIDERING THESE MODELS HAVE 1-3 INCHES OF SNOW THERE
THROUGH TODAY AND WEBCAMS INDICATE ONLY A TRACE HAS FALLEN WITH WARM
SURFACE TEMPS AND MELTING...BELIEVE THESE MODELS ARE OVERESTIMATING
SNOW AMOUNTS. SIDING MORE WITH SREF AND WPC...WHICH ARE CONSISTENT
WITH THE PREDICTION OF 1-4 INCHES ACROSS NORTHEASTERN WYOMING AND
THE BLACK HILLS...WITH THE HIGHER AMOUNTS ACROSS SOUTHERN CAMPBELL
COUNTY. BREEZY WINDS ACROSS CAMPBELL COUNTY MAY CREATE SOME BLOWING
SNOW ISSUES AS WELL...AND SO WILL ISSUE A WINTER WEATHER ADVISORY
FOR SOUTHERN CAMPBELL COUNTY. FROUDE NUMBER SHOWS SOME POTENTIAL
UPSLOPING OVER THE NORTHERN HILLS BUT NOTHING TOO SIGNIFICANT...SO
HAVE 1-2 INCHES THERE. MOST AREAS FARTHER EAST SHOULD SEE MOSTLY
RAIN...AND SOME WEAK INSTABILITY MAY ALLOW FOR SOME ISOLATED
THUNDERSTORMS.

PRECIP WILL GRADUALLY SHIFT SOUTHEASTWARD ON THURSDAY AS HIGH
PRESSURE PUSHES INTO THE NORTHERN PLAINS. UPPER LOW WILL BEGIN
TRACKING NORTHEASTWARD...AND AS PRECIP CONTINUES TO WRAP AROUND THE
LOW...RAIN/SNOW WILL BE PUSHED BACK INTO SD THURSDAY NIGHT FROM THE
SOUTH.

LOWS TONIGHT WILL BE IN THE 30S ACROSS THE WESTERN CWA AND LOWER 40S
OVER CENTRAL SD. HIGHS THURSDAY WILL RANGE FROM NEAR 40 ACROSS
PORTIONS OF NORTHEAST WY AND THE BLACK HILLS...TO THE LOWER 60S IN
SOUTH CENTRAL SD.

.LONG TERM...FRIDAY THROUGH WEDNESDAY
ISSUED AT 222 PM MDT WED APR 15 2015

MODELS IN DECENT AGREEMENT FRIDAY WITH CUT OFF LOW OVER
COLORADO...WITH STEADY STREAM OF MOISTURE SURGING NORTHWARD THROUGH
THE CENTRAL/SOUTHERN PLAINS. JET STREAK ROTATING AROUND EAST SIDE OF
UPPER LOW FRIDAY AFTERNOON RESULTS IN AREA OF UPPER LEVEL DIVERGENCE
ACROSS WESTERN NEBRASKA INTO SOUTHWEST/SOUTH CENTRAL SOUTH DAKOTA.
THERE WILL BE A SHARP CUTOFF ON NORTHERN EDGE OF PRECIPITATION.
MODELS BEGIN TO DIVERGE SOME FOR SATURDAY AS NORTHERN STREAM TROF
MOVES ACROSS THE NORTHERN ROCKIES. GEM/ECMWF BULLISH WITH HEAVIER
PRECIPITATION LIFTING INTO SOUTHWEST/CENTRAL SOUTH DAKOTA SATURDAY.
ECMWF/GFS THEN PULLS PRECIPITATION EAST OF THE FORECAST AREA EARLY
SUNDAY...WHILE GEM IS MUCH SLOWER. WITH A LOT OF UNCERTAINTY IN
THE INTERACTION OF NORTHERN STREAM TROF AND EJECTING UPPER
LOW...ONLY MINOR ADJUSTMENTS MADE TO OVERALL MODEL BLEND. WITH
RECENT MODEL TRENDS...THERE IS INCREASING CHANCE OF PRECIPITATION
LATE FRIDAY/SATURDAY. LARGE UPPER LOW SETS UP JUST NORTH OF THE
GREAT LAKES EARLY NEXT WEEK. THIS WILL RESULT IN COOLER NORTHWEST
FLOW ACROSS THE NORTHERN PLAINS.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z THURSDAY EVENING)
ISSUED AT 436 PM MDT WED APR 15 2015

WDSPRD IFR/LIFR CONDITIONS IN RAIN/SNOW WILL CONTINUE INTO
THURSDAY MORNING ACROSS NERN WY AND THE BLKHLS. CONDITIONS WILL
SLOWLY DETERIORATE TONIGHT ACROSS WRN/CNTRL SD AS RAIN
INCREASES...WITH WDSPRD IFR CIGS BY MRNG. SLOW IMPROVEMENT
EXPECTED THURSDAY AFTERNOON.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
WY...WINTER WEATHER ADVISORY UNTIL 9 AM MDT THURSDAY FOR WYZ055.

&&

$$

UPDATE...JOHNSON
SHORT TERM...POJORLIE
LONG TERM...7
AVIATION...JOHNSON


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