Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 221727
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1127 AM MDT FRI MAY 22 2015

.UPDATE...
ISSUED AT 940 AM MDT FRI MAY 22 2015

LATEST SAT IMAGES SHOW THE LEADING SHORTWAVE ALONG WITH THE
ASSOCIATED THICK CLOUD COVER AND PRECIPITATION MOVING NORTHWARD
INTO NEBRASKA LATE THIS MORNING. THE PRECIPITATION WILL HAVE TO
OVERCOME WEAKENING FORCING AS IT MOVES NORTHWARD BUT IT STILL
LOOKS LIKE RAIN SHOWERS WILL BE LIKELY ALONG THE SD/NEB BORDER
THIS AFTERNOON. THERE IS A CHANCE OF SHOWERS AND POSSIBLY A FEW
THUNDERSTORMS OVER NORTHEASTERN WYOMING THIS AFTN WHERE WEAK CAPE
DEVELOPS TODAY. THERE IS ALSO A CHANCE OF SHOWERS OVER THE BLACK
HILLS AND THE REST OF SOUTHWESTERN AND SOUTH CENTRAL SOUTH DAKOTA.
THE CHANCE OF SHOWERS DECREASES QUICKLY NORTH OF THOSE AREAS THIS
AFTN.

&&

.SHORT TERM...TODAY THROUGH SATURDAY NIGHT
ISSUED AT 327 AM MDT FRI MAY 22 2015

THE LARGE UPPER LOW OVER THE SWRN CONUS...PER WATER VAPOR
IMAGERY...WILL BE THE MAIN PLAYER FOR OUR WEATHER THROUGH THE
WEEKEND. LATEST OBS SHOWED A 100-KT 300-MB JET STREAK ROUNDING THE
BASE OF THE UPPER LOW...JUST SOUTHWEST OF CA. IN ADDITION...AN
UPPER LOW TO THE SOUTHEAST OF THE HUDSON BAY WILL HELP MAINTAIN A
CONFLUENT ZONE OVER THE NERN CWA...WHICH WILL HELP LIMIT THE NWD
EXTENT OF SHOWERS THROUGH TNGT.

FOR TODAY...A LEAD SHORT-WAVE TROUGH OVER SERN CO EARLY THIS MRNG
WILL MOVE TO NEAR KCDR BY 24Z. AS IT MOVES NORTH IT WILL ENCOUNTER
THE CONFLUENT UPPER FLOW AND GRADUALLY SHEAR OUT...WITH FORCING
DIMINISHING W/TIME PER THE WEAKENING Q-VECTOR CONVERGENCE. THUS...
WILL KEEP POPS CONFINED MOSTLY TO THE SWRN CWA. IN ADDITION...CAPE
WILL BE MARGINAL FOR TSTMS EXCEPT FOR PARTS OF NERN WY.

FOR TNGT...THE LEAD SHORT-WAVE TROUGH WILL SHEAR OUT AS IT MOVES
SLOWLY NORTH ACROSS THE CWA. FORCING WILL BE WEAK WITH THE BEST Q-
VECTOR CONVERGENCE GOING EAST OF THE CWA. AS A RESULT...ONLY EXPECT
SCT SHRA OVER SRN SECTIONS OF THE AREA...WITH LIMITED PCPN AMOUNTS.

ON SATURDAY...SOUTHWEST FLOW ALOFT WILL STRENGTHEN AS THE HUDSON BAY
AREA LOW MOVES SOUTHEAST AND THE SWRN CONUS LOW MOVES TO THE FOUR-
CORNERS AREA. ANOTHER SHORT-WAVE TROUGH WILL APPROACH THE CWA DURING
THE DAY...WITH INCREASING PWATS AND SBCAPES OF 500-750 J/KG...MAINLY
OVER THE SRN HALF OF THE AREA. AS A RESULT...EXPECT SCT SHRA/TSRA
ACROSS THE CWA. THE SEVERE POTENTIAL WILL BE LOW BECAUSE OF THE
LIMITED BUOYANCY AND MODEST MIDLEVEL LAPSE RATES.

ON SATURDAY NIGHT THE MODELS AGREE ON BRINGING A STRONGER SHORT-WAVE
TROUGH ACROSS THE AREA WITH NOTABLE DIFFERENTIAL CVA AND Q-VECTOR
CONVERGENCE IN THE 500-300MB LAYER...ALONG WITH LOW-LEVEL FGEN. THIS
SHOULD LEAD TO A GOOD ROUND OF PCPN THAT WILL PERSIST AFTER 12Z SUN.
WILL KEEP THE ESF GOING FOR THE HEAVY RAIN POTENTIAL.

.LONG TERM...SUNDAY THROUGH THURSDAY
ISSUED AT 327 AM MDT FRI MAY 22 2015

UPPER LEVEL LOW LIFTS OUT OF THE WESTERN TROF AND CROSSES THE
NORTHERN PLAINS ON SUNDAY...BRINGING WIDESPREAD PRECIPITATION TO
THE AREA. BEST PRECIP CHANCES ON SUNDAY WILL BE ACROSS NORTHEAST
WYOMING...ACROSS THE BLACK HILLS...AND INTO NORTHWEST SOUTH
DAKOTA...WHERE A QUARTER TO ONE HALF INCH OF RAINFALL IS POSSIBLE.

THIS SYSTEM WILL GRADUALLY EXIT THE REGION ON MONDAY...BUT PRECIP
CHANCES WILL CONTINUE THROUGH THE WEEK AS AN ACTIVE UPPER-LEVEL
PATTERN CONTINUES. TEMPERATURES WILL CONTINUE TO BE BELOW AVERAGE
OVER THE WEEKEND...WITH A GRADUAL WARMING TREND TO NEAR AVERAGE
TEMPERATURES BY THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...FOR THE 18Z TAFS THROUGH 18Z SATURDAY
ISSUED AT 1127 AM MDT FRI MAY 22 2015

SCATTERED SHOWERS AND AREAS OF MVFR CONDITIONS WILL SLOWLY PUSH
NORTH INTO SOUTHERN PORTIONS OF NORTHEAST WY...SOUTHWEST SD...AND
THE BLACK HILLS THIS AFTERNOON. OTHERWISE...VFR CONDITIONS ARE
EXPECTED ELSEWHERE THROUGH THE AFTERNOON. SCATTERED SHOWERS WILL
CONTINUE TONIGHT INTO SATURDAY MORNING...MOSTLY ACROSS NORTHEAST
WY...THE BLACK HILLS...AND SOUTHERN SD...WITH MVFR/IFR CONDITIONS
DEVELOPING ACROSS MUCH OF NORTHEAST WY AND WESTERN SD OVERNIGHT.

&&

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

$$

UPDATE...10
SHORT TERM...BUNKERS
LONG TERM...15
AVIATION...26


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