Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 171630
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1030 AM MDT FRI APR 17 2015

.UPDATE...
ISSUED AT 1022 AM MDT FRI APR 17 2015

UPPER LOW CONTINUES TO CHURN OVER THE FOUR CORNERS REGION WITH
BANDS OF LIGHT RAIN MOVING NORTHWEST THROUGH NEBRASKA AND JUST
EDGING INTO FAR SOUTHWEST SOUTH DAKOTA. EXPECT THESE BANDS OF
LIGHT RAIN TO CONTINUE TO MOVE INTO FAR SOUTHERN PORTIONS OF SOUTH
DAKOTA WITH RAIN EVENTUALLY MOVING NORTH TO THE INTERSTATE 90
CORRIDOR BY LATE THIS AFTERNOON.

MADE MINOR ADJUSTMENTS TO THE PROGRESSION OF RAIN NORTHWARD -
SLOWING IT DOWN...AND REMOVED MENTION OF ISOLATED THUNDER THROUGH
LATE AFTERNOON...AS IT LOOKS LIKE LAPSE RATES AND AVAILABLE ENERGY
ARE MEAGER AT BEST. BETTER CHANCES FOR THUNDER ACROSS NORTHEAST
WYOMING AND SOUTHERN SOUTH DAKOTA SATURDAY AFTERNOON.

REMAINDER OF FORECAST IN GOOD SHAPE. UPDATES ARE OUT.

&&

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
ISSUED AT 352 AM MDT FRI APR 17 2015

CURRENT SURFACE ANALYSIS SHOWS LOW PRESSURE OVER THE OKLAHOMA
PANHANDLE AREA RIGHT NOW...WITH WEAK HIGH PRESSURE OVER EASTERN MT
INTO WESTERN ND. UPPER LEVEL ANALYSIS SHOWS LARGE LOW PRESSURE
SYSTEM CENTERED OVER THE FOUR CORNERS AREA...WITH STRONG JET
WRAPPING AROUND THE SOUTHERN AND EASTERN SIDES OF THE LOW. CLOUD
SHIELD TO THE NORTH AND EAST OF THE SYSTEM IS PUSHING NORTHWARD
INTO SOUTHERN PARTS OF THE CWA...BUT DRYING UP AS IT MOVES INTO
VERY DRY AIRMASS OVER NORTHERN PORTIONS OF THE NORTHERN PLAINS
RIGHT NOW. REGIONAL RADARS SHOWING SHOWERS MOVING WEST-NORTHWEST
ACROSS MUCH OF WESTERN NEB INTO SOUTHEAST WY...WITH DRY CONDITIONS
PREVAILING ACROSS OUR CWA AT THE MOMENT. TEMPS CURRENTLY RANGE
FROM THE LOW TO MID 30S ACROSS PORTIONS OF NORTHEAST WY...THE
BLACK HILLS...AND FAR NORTHWEST SD...TO THE UPPER 40S ACROSS SOUTH
CENTRAL SD. WINDS ARE VARIABLE AT LESS THAN 10 MPH.

THE SYSTEM OVER THE FOUR CORNERS AREA EARLY THIS MORNING WILL MOVE
SLOWLY NORTHEASTWARD ACROSS SOUTHERN AND EASTERN CO OVER THE NEXT
COUPLE OF DAYS AND THEN ACCELERATE EASTWARD ACROSS THE CENTRAL
PLAINS SATURDAY NIGHT INTO SUNDAY. THE EXACT TRACK AND TIMING OF THE
SYSTEM IS STILL UNCERTAIN AT THIS POINT AND WILL ULTIMATELY HELP
DETERMINE HOW MUCH PCPN WE GET ACROSS THE AREA...ESPECIALLY NORTHERN
AND WESTERN PORTIONS OF THE CWA...WHERE AMOUNTS OF VERY LITTLE TO A
HALF INCH OR MORE ARE POSSIBLE DEPENDING ON THE TRACK. ALL THE 00Z
SHORT RANGE MODELS SHOW MOST OR ALL OF THE CWA RECEIVING AT LEAST A
LITTLE BIT OF RAINFALL...WITH THE HIGHEST AMOUNTS GENERALLY OVER FAR
SOUTHWEST INTO SOUTH CENTRAL SD. THE 00Z GFS SHOWS THE HEAVIEST PCPN
FURTHER EAST TOWARD CENTRAL SD...WHILE THE OTHER MODELS GENERALLY
HAVE IT OVER FAR SOUTHWEST/SOUTHERN SD. WILL LEAN THE FORECAST MORE
TOWARD THE CONSENSUS AT THIS POINT AND KEEP HEAVIER PCPN AMOUNTS
OVER FAR SOUTHERN SD. FORECAST CONFIDENCE IS HIGHEST RIGHT NOW ON
SOUTHERN PORTIONS OF THE CWA RECEIVING THE MOST RAINFALL...AS WELL
AS THE BEST CHANCES FOR RAINFALL ACROSS THE CWA BEING LATER TONIGHT
INTO SATURDAY EVENING. PROJECTED RAINFALL AMOUNTS ACROSS THE CWA
WILL MOSTLY BE IN THE 0.25 TO 0.75 INCH RANGE...WITH LESSER AMOUNTS
LIKELY OVER FAR NORTHWESTERN PORTIONS OF THE CWA AND POSSIBLY AN
INCH OR MORE OVER FAR SOUTHWEST INTO SOUTH CENTRAL SD.
HOWEVER...WOULD TEND TO LEAN MORE TOWARD THE LIGHTER AMOUNTS FOR
MOST AREAS AS HAS BEEN THE CASE FOR SYSTEMS OF LATE.

FOR TODAY...SKIES WILL STAY MOSTLY CLOUDY ACROSS FAR SOUTHERN
PORTIONS OF THE CWA...WITH CLOUDS GRADUALLY INCREASING TO THE NORTH.
WITH MORE SUNSHINE...TEMPS THIS AFTERNOON WILL BE HIGHEST OVER FAR
NORTHERN AND EASTERN PORTIONS OF THE CWA...WITH HIGHS RANGING FROM
THE 50S OVER THE BLACK HILLS AND FAR SOUTHWEST SD TO THE MID TO
UPPER 60S OVER FAR NORTHWEST INTO CENTRAL SD. WINDS WILL BECOME EAST
TO NORTHEAST IN MOST AREAS BY THE AFTERNOON. CHANCES FOR SHOWERS
WILL MAINLY BE CONFINED TO SOUTHERN SD TODAY...WITH THE BEST CHANCES
IN THE AFTERNOON. CAN NOT RULE OUT A THUNDERSTORM OR TWO ACROSS
SOUTHERN AREAS AS WELL THIS AFTERNOON.

AS THE UPPER LOW MOVES ACROSS CO TONIGHT AND SATURDAY...LOW LEVEL
MOISTURE AND UPPER LEVEL ENERGY WILL EXPAND NORTHWARD INTO THE
NORTHERN PLAINS...ESPECIALLY LATER TONIGHT AND SATURDAY. SHOWERS AND
ISOLATED THUNDERSTORMS CAN BE EXPECTED ACROSS THE AREA. THE MOST
WIDESPREAD COVERAGE OF SHOWERS SHOULD BE ON SATURDAY...SO WILL GO
WITH LIKELY POPS ACROSS MOST OF THE CWA. WITH THE LOW STAYING FAR
ENOUGH SOUTH OF THE CWA...TEMPS WILL STAY WARM ENOUGH FOR MOSTLY
RAIN ACROSS EVEN THE BLACK HILLS...BUT COULD SEE A MIX OVER THE
HIGHEST ELEVATIONS...MAINLY LATE TONIGHT/EARLY SATURDAY AND THEN
SATURDAY NIGHT WHEN THE SYSTEM EXITS. A COLD FRONT WILL TRACK ACROSS
THE CWA LATE SATURDAY AND SATURDAY NIGHT...HELPING TO PUSH THE
SYSTEM OUT OF THE REGION...BUT WILL BRING GUSTY WINDS ACROSS THE
AREA INTO SUNDAY.

.LONG TERM...SUNDAY THROUGH THURSDAY
ISSUED AT 352 AM MDT FRI APR 17 2015

BLOCKED FLOW TO DEVELOP OVER THE WESTERN ATLANTIC AND
EASTERN NOAM...WHICH WILL SET THE STAGE FOR WESTERN NOAM RIDING AND
POTENTIAL REX TYPE BLOCKING OVER THE WESTERN CONUS. THIS WILL
SUPPORT A LOW CONFIDENCE FLOW REGIME AS FORECAST MODELS WILL
CONTINUALLY ADJUST TO THE LATEST OBS GIVEN TYPICAL POOR MODEL
PERFORMANCE IN THESE PATTERNS. GENERALLY DRY CONDS CAN BE EXPECTED
GIVEN THE REGION/S PROXY TO THE EASTERN NOAM UPPER TROUGH. A WEAK
SIGNAL FOR PRECIP DOES REMAIN TOWARD THE END OF THE PERIOD WHEN
FORECAST MODELS TRY TO ADVECT A WANDERING UPPER TROUGH EAST.
HOWEVER...AS ALREADY STATED...LOW CONFIDENCE PER FLOW DETAILS LENDS
ONLY A 20 POP AT BEST...WITH DRY THE LIKELY SCENARIO GIVEN THE
PATTERN. GIVEN STRONG INFLUENCE EXPECTED OF THE EVENTUAL EASTERN
CONUS UPPER LOW...EXPECT TEMPS TO BE NEAR OR SLIGHTLY BELOW SEASONAL
NORMS IN THE MAJORITY OF THE PERIOD.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SATURDAY MORNING)
ISSUED AT 538 AM MDT FRI APR 17 2015

VFR CONDS WILL PREVAIL MOST PLACES IN THE PERIOD. A SLOW MOVING
UPPER LOW WILL SLIDE NE AND BRING MVFR CONDS IN RAIN TO MAINLY
EXTREME SW SD TODAY. MVFR CONDS WILL SPREAD NORTH
TONIGHT...AFFECTING THE RAP TERMINAL BY LATE IN THE PERIOD...WITH
SCT IFR CIGS POSSIBLE IN THE BLACK HILLS.


&&

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

$$

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



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