Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 240926
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
326 AM MDT THU APR 24 2014

.SHORT TERM...TODAY THROUGH FRIDAY NIGHT
ISSUED AT 325 AM MDT THU APR 24 2014

CURRENT SURFACE ANALYSIS SHOWS COLD FRONT JUST TO THE EAST OF THE
FORECAST AREA...WITH LOW PRESSURE LOCATED ALONG THE FRONT ACROSS
KS AND TO THE NORTH NEAR THE UPPER LEVEL CIRCULATION OVER SOUTHERN
SK. UPPER LEVEL ANALYSIS SHOWS TROF STRETCHING SOUTHWARD FROM SK
ACROSS THE HIGH PLAINS. RIDGE IS MOVING EAST ACROSS THE PACIFIC
NW. SKIES ARE MOSTLY CLEAR ACROSS WESTERN PORTIONS OF THE
CWA...WITH SOME MID AND HIGH CLOUDS LINGERING TO THE EAST OF THE
BLACK HILLS INTO CENTRAL SD. TEMPS ARE IN THE 30S OVER NORTHEAST
WY AND FAR WESTERN SD...WITH 40S TOWARD CENTRAL SD. WINDS ARE
MOSTLY FROM THE WEST TO NORTHWEST AT 5 TO 15 MPH.

EVEN WITH SOME COOLER AIR ACROSS THE AREA...TEMPS WILL REMAIN ABOVE
AVERAGE LATE THIS WEEK. AS MAIN UPPER LEVEL SYSTEM PASSES TO THE
NORTH OF THE AREA...DRIER WEST TO NORTHWEST FLOW WILL PERSIST FOR A
COUPLE MORE DAYS BEFORE A WET AND COOLER STRETCH OF WEATHER DEVELOPS
OVER THE WEEKEND.

FOR TODAY...SKIES WILL BE MOSTLY SUNNY...WITH SOME INCREASE IN
CLOUDS OVER WESTERN AREAS DURING THE AFTERNOON. SURFACE LOW OVER
SOUTHERN SK WILL PASS TO THE NORTH OF THE REGION TODAY...BUT FAIRLY
TIGHT PRESSURE GRADIENT OVER THE NORTHERN PLAINS WILL RESULT IN
BREEZY TO WINDY WEST TO NORTHWEST WINDS ACROSS MUCH OF THE WESTERN
AND SOUTH CENTRAL SD PLAINS LATE THIS MORNING AND AFTERNOON. DEEP
BOUNDARY LAYER MIXING WILL ALLOW TEMPS TO MAX OUT IN THE 60S
ACROSS THE PLAINS...WITH SOME 50S ACROSS THE HIGHER BLACK HILLS.
TEMPS OVER SOUTH CENTRAL SD WILL APPROACH 70 DEGREES THIS
AFTERNOON. HUMIDITIES WILL BE RATHER LOW THIS AFTERNOON ACROSS
THE AREA...WITH THE LOWEST VALUES FORECAST OVER SOUTH CENTRAL SD.
SOME FIRE WEATHER HEADLINES WILL BE ISSUED...SEE THE DISCUSSION
BELOW. SKIES WILL BE PARTLY CLOUDY TONIGHT WITH DECREASING WINDS
AND LOWS IN THE 30S TO AROUND 40 DEGREES.

THE RIDGE TO THE WEST WILL MOVE OVER THE AREA ON FRIDAY...WITH SOUTH
TO SOUTHEAST WINDS DEVELOPING FROM WEST TO EAST DURING THE DAY.
SLIGHTLY WARMER AIR WILL ADVECT IN...WITH HIGHS IN THE MID 60S TO MID
70S. CLOUDS WILL INCREASE...ESPECIALLY LATE IN THE DAY...AS
SOUTHWEST FLOW ALOFT DEVELOPS BEHIND EXITING RIDGE. SHORTWAVE
ENERGY WILL CLIP NORTHERN AND WESTERN PORTIONS OF THE AREA FRIDAY
NIGHT...BRINGING A CHANCE FOR LIGHT RAIN SHOWERS FROM NORTHEAST
WY INTO NORTHWESTERN SD. THE BETTER CHANCES LOOK TO BE TOWARD FAR
NORTHWESTERN SD OVERNIGHT.

&&

.LONG TERM...SATURDAY THROUGH WEDNESDAY
ISSUED AT 325 AM MDT THU APR 24 2014

SW FLOW ALOFT WILL INCREASE AS STRONG UPPER TROF WORKS INTO THE
ROCKIES...WITH SFC LOW DEVELOPING OVER ERN CO. STRONG ELY BL
TRANSPORT WILL RESULT IN MOISTENING LOW LEVELS AND A CHANCE FOR
TSTMS DURING THE AFTN ESPECIALLY ACROSS OUR WRN ZONES AS UPPER
LEVEL ENERGY ROTATES NEWD AND LAPSE RATES STEEPEN. TEMPS SHOULD BE
RATHER MILD WITH THERMAL RIDGE STILL IN PLACE. PCPN CHANCES THEN
INCREASE DRAMATICALLY BY SUNDAY INTO MONDAY AS UPPER LOW FORMS
OVER THE CNTRL ROCKIES AND DEEPENS AT IT MOVES EWD INTO THE
PLAINS. LATEST 00Z MODEL RUNS HAVE TRENDED THE UPPER LOW BACK A
BIT FURTHER NORTH...WHILE ALSO CONTINUING THE TREND OF SLOWING THE
SYSTEM DOWN. REGARDLESS OF THE EXACT EVENTUAL POSITION OF THE
UPPER LOW...WDSPRD PCPN WILL BE FOUND ACROSS OUR CWFA BEGINNING
SATURDAY NITE AND CONTINUING INTO MONDAY...WITH MANY AREAS
RECEIVING AN INCH OR MORE QPF. AND IF THE LOW DOES STALL A BIT AS
SOME GUIDANCE IS ADVERTISING...PCPN COULD CONTINUE INTO MIDWEEK.
THERMAL PROFILES DO SUGGEST A MAINLY RAIN EVENT AT LOWER
ELEVATIONS...WITH SOME SNOW ACROSS HIGHER ELEVATIONS IN NERN WY
AND THE BLKHLS. IF SNOW LEVELS DO LOWER ON THE PLAINS...IT WOULD
LIKELY NOT BE UNTIL MONDAY OR TUESDAY AS COLDER AIR FINALLY WRAPS
INTO THE SYSTEM.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z FRIDAY MORNING
ISSUED AT 325 AM MDT THU APR 24 2014

VFR CONDITIONS EXPECTED NEXT 24 HOURS. GUSTY WEST TO NORTHWEST
WINDS WILL SPREAD ACROSS THE AREA THIS MORNING AND CONTINUE
THROUGH THE AFTERNOON.

&&

.FIRE WEATHER...
ISSUED AT 325 AM MDT THU APR 24 2014

A LOW PRESSURE SYSTEM TO THE NORTH OF THE AREA WILL BRING GUSTY
WINDS AND DRY AIR TO THE AREA TODAY. WEST TO NORTHWEST WINDS OF 15
TO 25 MPH...WITH HIGHER GUSTS...CAN BE EXPECTED FROM NORTHWEST
INTO SOUTH CENTRAL SD. THE DRY AIR AND MILD TEMPERATURES WILL
ALLOW RELATIVE HUMIDITIES TO DROP TO NEAR 15 PERCENT ACROSS SOUTH
CENTRAL SOUTH DAKOTA...WITH MINIMUM VALUES AROUND 20 PERCENT
ELSEWHERE. THE COMBINATION OF WIND AND LOW HUMIDITY WILL LIKELY
RESULT IN A PERIOD OF CRITICAL FIRE WEATHER CONDITIONS DURING THE
AFTERNOON OVER SOUTH CENTRAL SD. HAVE DECIDED TO ISSUE A RED FLAG
WARNING FOR SD FIRE ZONE 265 FOR THIS AFTERNOON. THE GRASSLAND
FIRE DANGER INDEX WILL BE IN THE EXTREME CATEGORY ACROSS MOST OF
THE WESTERN AND SOUTH CENTRAL SD PLAINS. CONDITIONS WILL IMPROVE
BY EARLY EVENING.

&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...RED FLAG WARNING FROM NOON TODAY TO 6 PM MDT THIS EVENING FOR
     SDZ265.

WY...NONE.
&&

$$

SHORT TERM...26
LONG TERM...JOHNSON
AVIATION...JOHNSON
FIRE WEATHER...26





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