Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 251603
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1003 AM MDT SAT APR 25 2015

.UPDATE...
ISSUED AT 1003 AM MDT SAT APR 25 2015

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER NORTHEAST
WY...WITH FRONTAL BOUNDARY EXTENDING ACROSS PORTIONS OF NORTHEAST
WY INTO SOUTHWEST SD AND WESTERN NEB. UPPER LEVEL ANALYSIS SHOWS
AN AREA OF LOW PRESSURE OVER NORTHWEST MO...WITH SHORTWAVE RIDGE
OVER THE NORTHERN PLAINS AND TROF ALONG THE WEST COAST. SOUTHWEST
FLOW EXTENDS FROM THE GREAT BASIN REGION INTO WESTERN PORTIONS OF
THE HIGH PLAINS. SKIES ARE MAINLY CLOUDY ACROSS MUCH OF THE
CWA...BUT A NARROW AREA OF CLEAR TO PARTLY CLOUDY SKIES IS IN
PLACE OVER THE BLACK HILLS AND FAR SOUTHWEST SD FOR THE TIME BEING.
EXTENSIVE AREA OF STRATUS HAS BACKED WESTWARD INTO THE EASTERN
SLOPES OF THE BLACK HILLS...WITH AREAS OF FOG STILL LINGERING...
THOUGH VISIBILITIES ARE SLOWLY IMPROVING. REGIONAL RADARS SHOW
MOST OF THE SHOWER ACTIVITY RIGHT NOW IS OVER NORTH CENTRAL
WY...EXTENDING NORTHWARD INTO MT...WITH A FEW LIGHT SHOWERS
OVER PORTIONS OF SOUTH CENTRAL SD. TEMPS AT 15Z RANGED FROM THE
40S TO AROUND 50 DEGREES OVER THE SD PLAINS...TO 50S OVER A GOOD
CHUNK OF NORTHEAST WY AND THE BLACK HILLS.

CLOUDS WILL HANG AROUND OR FILL IN ACROSS THE AREA INTO THE
AFTERNOON. SHOWERS AND THUNDERSTORMS ARE EXPECTED TO DEVELOP OVER
NORTHEAST WY AND THE BLACK HILLS BY EARLY AFTERNOON...WHERE
ATMOSPHERE WILL DESTABILIZE THE EARLIEST. WATER VAPOR IMAGERY
SHOWS A SHORTWAVE OVER SOUTH CENTRAL WY...MOVING NORTHEASTWARD...
THAT WILL HELP TO FUEL DEVELOPMENT THIS AFTERNOON. BEST CHANCES
STILL LOOK TO BE ACROSS FAR NORTHEAST WY AND FAR WESTERN SD THIS
AFTERNOON AND EVENING. THERE COULD BE ENOUGH INSTABILITY GENERATED
TO GET A STRONGER STORM OR TWO WITH SMALL HAIL THIS AFTERNOON...
MAINLY OVER SOUTHWEST SD.

HAVE UPDATED TO LOWER HIGHS A FEW DEGREES ACROSS MUCH OF THE WESTERN
SD PLAINS...WHERE LOW CLOUDS SHOULD KEEP TEMPS DOWN. ONLY MINOR
ADJUSTMENTS MADE TO POPS...MOSTLY TO LOWER THEM A BIT AND PUSH
OFF THE TIMING TO LATER THIS AFTERNOON ACROSS AREAS TO THE NORTH
AND EAST OF THE BLACK HILLS. OTHER TWEAKS WERE MADE TO SKY
COVER..DEW POINTS...AND RH.

&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 243 AM MDT SAT APR 25 2015

UPPER LEVEL ANALYSIS HAS WEAK RIDGING OVER THE NORTHERN PLAINS
WITH CLOSED LOW UNDER THE RIDGE IN SOUTHERN NEBRASKA. ADDITIONAL
CLOSED LOW IS SPINNING OVER VANCOUVER ISLAND WITH TROF EXTENDING
SOUTH ALONG THE WEST COAST. SKIES ARE CLEAR TO MOSTLY CLOUDY
ACROSS NORTHEAST WYOMING AND WESTERN SOUTH DAKOTA WITH A FEW RAIN
SHOWERS OVER SOUTH CENTRAL SOUTH DAKOTA. AT THE SURFACE...LOW
PRESSURE IS LOCATED ACROSS NORTH CENTRAL WYOMING WITH A FRONTAL
BOUNDARY EXTENDING INTO NEBRASKA. WEAK HIGH PRESSURE RIDGE EXTENDS
NORTH FROM THE BLACK HILLS AREA. TEMPERATURES AT 3 AM ARE MAINLY
IN THE 40S...WITH SOME 50S ACROSS FAR SOUTH CENTRAL SOUTH DAKOTA.
WINDS ARE LIGHT.

FOR TODAY...UPPER LEVEL RIDGING WILL SHIFT EAST WITH UPPER FLOW
BECOMING SOUTHWESTERLY ACROSS THE NORTHERN PLAINS. LOW PRESSURE IN
WYOMING WILL LIFT NORTHEAST AND ELONGATE INTO AN INVERTED TROF
ALONG THE MONTANA/WYOMING/DAKOTAS STATE LINES BY LATE IN THE DAY.
THIS SURFACE BOUNDARY WILL BE THE FOCUS FOR SHOWERS AND
THUNDERSTORMS THIS AFTERNOON THROUGH SUNDAY AS UPPER LEVEL
DISTURBANCES LIFT OUT OF THE WESTERN TROF AND CROSS THE FORECAST
AREA. AS TEMPERATURES WARM INTO THE 50S AND 60S TODAY...SHOWERS
AND THUNDERSTORMS WILL DEVELOP ACROSS NORTHEAST WYOMING AND THE
BLACK HILLS. BEST INSTABILITY WILL BE OVER THE BLACK HILLS AND
SOUTHWEST SOUTH DAKOTA WHERE A FEW STRONGER STORMS WILL BE
POSSIBLE THIS AFTERNOON.

TONIGHT...SURFACE BOUNDARY REMAINS NEARLY STATIONARY WITH SHOWERS
AND THUNDERSTORMS PERSISTING AS WEAK UPPER LEVEL ENERGY CONTINUES
TO CROSS THE AREA. THUNDERSTORM CHANCES DIMINISH DURING THE
EVENING AS INSTABILITY DECREASES...BUT SHOWER ACTIVITY WILL
PERSIST THROUGH MUCH OF THE NIGHT. PRECIPITATION AMOUNTS THROUGH
TONIGHT FOR PARTS OF NORTHEAST WYOMING AND FAR WESTERN SOUTH
DAKOTA LOOK TO BE IN THE QUARTER INCH TO HALF AN INCH RANGE. LOW
TEMPERATURES WILL FALL INTO THE UPPER 30S TO MID 40S.

SUNDAY...WESTERN UPPER TROF SHIFTS EAST AND DEVELOPS A CLOSED LOW
OVER THE FOUR CORNERS REGION. ADDITIONAL UPPER LEVEL ENERGY
CONTINUES TO LIFT OUT OF THE TROF AND CROSS THE NORTHERN PLAINS.
INVERTED SURFACE TROF ALSO REMAINS OVER THE AREA WITH RAIN SHOWER
ACTIVITY CONTINUING ACROSS NORTHEAST WYOMING AND WESTERN PORTIONS
OF SOUTH DAKOTA. AN ADDITIONAL QUARTER INCH TO HALF AN INCH LOOKS
LIKELY FOR THESE AREAS. WITH THE CLOUD COVER AND PERSISTENT
PRECIPITATION...HIGH TEMPERATURES WILL STRUGGLE INTO THE UPPER 40S
TO LOWER 50S. FURTHER EAST ACROSS THE CENTRAL SOUTH DAKOTA PLAINS
WHERE PRECIP CHANCES ARE LESS...TEMPS WILL BE CLOSER TO 60. LOW
TEMPERATURES SUNDAY NIGHT WILL FALL INTO THE 30S TO MID 40S. NEAR
FREEZING TEMPERATURES ARE EXPECTED ACROSS THE HIGHER ELEVATIONS OF
THE BLACK HILLS...WHERE AN INCH OR TWO OF SNOWFALL WILL BE
POSSIBLE LATE SUNDAY NIGHT.

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 243 AM MDT SAT APR 25 2015

AFOREMENTIONED UPPER CLOSED-LOW WILL BE WELL SOUTH OF THE CWA BY
MONDAY...BUT NORTHERN STREAM TROUGH WILL MOVE THROUGH THE NORTHERN
PLAINS BRINGING ONCE LAST CHANCE OF PRECIPITATION.

UPPER LEVEL RIDGE THEN BUILDS INTO THE AREA FOR MUCH OF NEXT WEEK.
AS THE RIDGE SHIFTS EAST OF THE AREA LATE IN THE WEEK...SOUTHWEST
FLOW WILL DEVELOP WITH WEAK SHORTWAVES FROM TIME TO TIME. LEE TROUGH
EXPECTED...WHICH WILL BE THE FOCUS FOR ANY DIURNAL SHRA/TSRA
ACTIVITY STARTING THURSDAY AFTERNOON...ESPECIALLY WHERE THE TROUGH
INTERSECTS THE HIGHER TERRAIN. TEMPERATURES WILL BE QUITE WARM BY
THE END OF THE WEEK.

&&

.AVIATION...FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT
ISSUED AT 243 AM MDT SAT APR 25 2015

EASTERLY FLOW AHEAD OF A STORM SYSTEM THIS MORNING WILL PROMOTE
MVFR/IFR ST DEVELOPMENT WITH POSSIBLE IFR VSBYS DUE TO BR OVER THE
HIGHER TERRAIN. CONDITIONS WILL IMPROVE SOME THIS AFTERNOON DUE TO
DIURNAL EFFECTS. SHRA/ISOLATED TSRA WILL DEVELOP THIS
AFTERNOON...PERSISTING THROUGH TONIGHT. AREAS IFR CIGS/VSBYS
EXPECTED WITH THE RATHER WIDESPREAD PRECIPITATION TONIGHT.


&&

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

$$

UPDATE...26
SHORT TERM...15
LONG TERM...HELGESON
AVIATION...HELGESON



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