Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 151006
AFDUNR

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

.SHORT TERM...TODAY THROUGH THURSDAY NIGHT
ISSUED AT 405 AM MDT WED APR 15 2015

WATER VAPOR IMAGERY SHOWS LARGE CUT OFF LOW ACROSS THE GREAT
BASIN...AND STRONG RIDGING OVER THE MIDWEST. DEEP SOUTHERLY FLOW
CONTINUES ACROSS THE CWA AHEAD OF THE UPPER LOW/TROUGH. SURFACE
ANALYSIS SHOWS LOW PRESSURE EXTENDING FROM THE ND/MT BORDER TO THE
BLACK HILLS INTO SE WY ALONG THE FRONTAL BOUNDARY. TEMPS IN NE WY
HAVE DROPPED INTO THE LOW 40S WHILE TEMPS ARE IN THE 50S OVER WRN
SD...EVEN LOW 60S IN SOME SPOTS. REGIONAL RADAR BAND OF RAIN/SNOW
ACROSS CNTRL MT INTO THE BIG HORNS AREA. WINDS HAVE BEEN BREEZY
OVERNIGHT...BUT HAVE REMAINED UNDER ADVISORY CRITERIA FOR THE MOST
PART. WILL CANCEL THE WIND ADVISORY WITH THE MORNING FORECAST
PACKAGE.

MODELS CONSISTENCY HAS STILL BEEN LACKING EVEN NOW...BUT THERE IS
SOME HINTING AT REACHING A BETTER AGREEMENT AMONG THE DIFFERENT
OUTPUTS. MODELS ARE SHOWING THE UPPER LOW WRAPPING UP AND DRIFTING
SOUTHWARD ACROSS THE GREAT BASIN INTO THE FOUR CORNERS REGION. AS
THIS HAPPENS...THE SURFACE LOW WILL REDEVELOP ACROSS THE CENTRAL
PLAINS. THE COLD FRONT PUSHING INTO THE AREA WILL STALL...WITH A
WIDE RANGE OF MAX TEMPS TODAY. HIGHS WILL BE IN THE UPPER 30S TO
UPPER 40S ACROSS NE WY...TO THE UPPER 50S TO UPPER 60S OVER THE WRN
SD PLAINS. PRECIP WILL MOVE IN FROM THE WEST THIS MORNING INTO NE
WY...WITH SOME MIX WITH SNOW POSSIBLE. RAIN IS THEN EXPECTED TO MOVE
INTO THE BLACK HILLS AREA LATER THIS AFTERNOON.

MODELS ARE SHOWING A SHORTWAVE PUSHING INTO THE CWA FROM THE S/SE
WITHIN THE INVERTED TROUGH TONIGHT...AND THIS SEEMS TO BE THE FOCUS
FOR PRECIP DEVELOPMENT. RAIN WILL DEVELOP THIS EVENING ACROSS SW
SD/BLKHLS THIS EVENING...AND MOVE N/NW INTO NE WY AND PERHAPS INTO
PARTS OF NW SD. MODELS ARE SUGGESTING A STRONG BAND OF PRECIP
CROSSING THE AREA. WITH THE FRONT STILL STRADDLING THE CWA...NE
WY/BLKHLS WILL HAVE BETTER CHANCES OF THIS RAIN OR RAIN/SNOW MIX
CHANGING TO ALL SNOW LATE THIS EVENING OR EARLY THU MORNING.
FORECAST SNOW AMOUNTS FROM THE SOLUTIONS ARE VARYING WIDELY...FROM A
COUPLE INCHES TO WELL OVER A FOOT. THINK THE LOWER END OF THE RANGE
IS MORE BELIEVABLE CONSIDERING WARM GROUND TEMPS AND THE SLOW
COOLING OF THE LOW LEVELS OVERNIGHT TONIGHT. WILL GO WITH 1 TO 4
INCH WORDING...BUT GIVEN THE LACK OF CONFIDENCE THAT REMAINS WITH
SNOW AMOUNTS...THE DAY SHIFT WILL HAVE TO REEVALUATE THE SITUATION
WITH THE 12Z RUNS.

THE UPPER LOW WILL CONTINUE ITS SLOW DRIFT ACROSS THE FOUR CORNERS
THURSDAY...BUT NOW MODELS ARE SHOWING A NORTHWARD WOBBLE TO ITS
TRACK. THIS KEEPS PRECIP ACROSS THE SOUTHERN PORTIONS OF THE CWA
THROUGH THURSDAY AND THU NIGHT. HAVE INCREASED POPS TO CHANCE OVER
THESE AREAS TO REFLECT THIS. OTHERWISE LOOKS LIKE MOST OTHER AREAS
WILL STAY DRY. TEMPS WILL RANGE FROM THE 40S OVER NE WY TO THE
MID/UPPER 50S OVER CNTRL SD.

.LONG TERM...FRIDAY THROUGH TUESDAY
ISSUED AT 405 AM MDT WED APR 15 2015

THERE IS A BIT OF A CHANGE IN THE MODEL SOLUTIONS FOR THIS
FORECAST. 00Z RUNS OF BOTH THE GFS AND ECMWF SHOW THE FOUR CORNERS
LOW PRESSURE SYSTEM BEGINNING TO MOVE NORTHEASTWARD INTO THE
PLAINS AS THE SYSTEM PHASES WITH ANOTHER UPPER TROUGH ASSOCIATED
WITH A LOW PRESSURE SYSTEM CROSSING THE CANADIAN PRAIRIE
PROVINCES. THE MORE NORTHWARD MOVEMENT OF THE SOUTHERN LOW WILL
PUSH A CHANCE OF SHOWERS INTO THE SOUTHERN PARTS OF THE FORECAST
AREA...MAINLY SOUTH OF I-90 ON FRIDAY AND FRIDAY NIGHT WITH LOW
POPS OVER MUCH OF THE AREA ON SATURDAY AND A BETTER CHANCE OF
SHOWERS ON SATURDAY NIGHT AS THE UPPER TROUGH AND ASSOCIATED SFC
COLD FRONT SWEEPS ACROSS THE NORTHERN PLAINS. THERE WILL BE A
LINGERING SLIGHT CHANCE OF SHOWERS ON SUNDAY DUE TO CYCLONIC FLOW
AROUND THE UPPER TROUGH AND INSTABILITY DUE TO THE COLDER AIR
FLOWING IN AT THE SFC AND ALOFT. DRY WEATHER AND NEAR AVERAGE
TEMPERATURES ARE THEN EXPECTED FOR SUNDAY THROUGH WEDNESDAY AS AN
UPPER TROUGH BUILDS TO THE WEST OF THE FORECAST AREA.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z THURSDAY MORNING
ISSUED AT 405 AM MDT WED APR 15 2015

FLIGHT CONDITIONS WILL DETERIORATE THIS MORNING TO MVFR WITH
AREAS OF IFR CIGS ACROSS NERN WY AND INTO PORTIONS OF FAR WRN SD
INCLUDING THE BLKHLS AS -RA DEVELOPS. THE POOR CONDITIONS WILL
CONTINUE THROUGH THE DAY TODAY. MVFR/LCL IFR CONDITIONS WILL
INCREASE IN COVERAGE OVER THE REST OF WESTERN AND CENTRAL SOUTH
DAKOTA THIS EVENING WITH AREAS OF RAIN AND SNOW OVERNIGHT.

&&

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

$$

SHORT TERM...13
LONG TERM...10
AVIATION...10



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