000
FXUS63 KUNR 210151
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
751 PM MDT MON MAY 20 2013

.UPDATE...
ISSUED AT 747 PM MDT MON MAY 20 2013

LATEST SFC ANALYSIS SHOWS THE LOW PRESSURE CENTER OVER NERN
SD/SERN ND WITH A TIGHT SFC PRESSURE GRADIENT TO THE WEST OF THE
LOW...RESULTING IN GUSTY NORTHWEST WINDS OVER THE FORECAST AREA.
WINDS HAVE DROPPED TO SLIGHTLY BELOW ADVISORY CRITERIA BUT
ANALYSIS SHOWS ANOTHER SURFACE TROUGH ROTATING AROUND THE WEST
SIDE OF THE LOW THAT WILL TIGHTEN THE SFC PRESSURE GRADIENT AGAIN
AND RAISE THE WIND SPEED AGAIN LATER THIS EVENING. THEREFORE WILL
KEEP THE WIND ADVISORY IN EFFECT OVER NWRN SD AND ON THE PLAINS
EAST OF THE BLACK HILLS.

&&

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 158 PM MDT MON MAY 20 2013

19Z SURFACE ANALYSIS HAD LOW OVER THE SD/NE/MN BORDER. TIGHT
PRESSURE GRADIENT ASSOCIATED WITH LOW BRINGING WINDY WEATHER TO
THE CWA THIS AFTERNOON. UPPER LOW STACKED ON TOP OF SURFACE
LOW...WHICH IS PINWHEELING SEVERAL EMBEDDED SHORTWAVES THROUGH THE
CWA UNDER STRONG CYCLONIC FLOW ALOFT. REGIONAL RADARS SHOW MANY
BATCHES OF SHRA TO MOVE THROUGH THE AREA TONIGHT...SO HIGH POPS
CONTINUE TO BE WARRANTED. FORECAST SOUNDINGS SUGGEST WIND WILL
TAPER SOME THIS EVENING...BUT LIKELY STAY IN THE MARGINAL WIND
ADVISORY AREA OVERNIGHT. WET BULB ZERO DROPS TO AROUND 7KFT MSL
LATER TONIGHT...SO WOULD NOT BE SURPRISED TO SEE SOME SNOW OVER
THE HIGHER ELEVATIONS OF THE BLACK HILLS WHERE UPSLOPE-ENHANCED
PRECIPITATION...FROUDE NUMBER ABOVE 1 WITH 0-2KM AGL
SATURATION...WILL FALL. TEMPERATURES NEAR GUIDANCE.

TUESDAY...STACKED UPPER LOW BEGINS TO MOVE EAST WITH PRECIPITATION
BECOMING LESS WIDESPREAD OVER THE CWA. HOWEVER...STEEP LOW LEVEL
LAPSE RATES...CYCLONIC FLOW ALOFT...AND IMPULSES ROTATING AROUND THE
LOW WILL RESULT IN NUMEROUS SHOWERS. A BIT OF SNOW POSSIBLE IN THE
MORNING OVER THE HIGHER ELEVATION OF THE BLACK HILLS. FROUDE NUMBER
DROPS BELOW 1 BY AFTERNOON...SO UPSLOPE ENHANCEMENT WILL SLACKEN.
LATEST GUIDANCE SHOWS TOP OF BOUNDARY LAYER WIND SPEEDS DROPPING TO
20-25KTS BY AFTERNOON AND THUS WE SHOULD SEE WIND SPEEDS SLOWLY
DECLINE. WILL END WIND ADVISORY AT 18Z. CONDITIONS WILL IMPROVE
MORESO TUESDAY NIGHT AS MOISTURE BEGINS TO DIMINISH AND FORCING
SHIFTS EAST. TEMPERATURES NEAR GUIDANCE.

&&

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 158 PM MDT MON MAY 20 2013

THE STORM SYSTEM WILL CONTINUE TO SLOWLY MOVE EAST OF THE REGION
ON WEDNESDAY...WITH ONLY ISOLATED TO SCATTERED SHOWERS
EXPECTED...MAINLY IN THE MORNING OVER NORTHERN AND EASTERN
PORTIONS OF THE CWA. WEAK RIDGING DEVELOPS BEHIND THE EXITING
SYSTEM ALLOWING TEMPERATURES TO RETURN TO NORMAL. MOST AREAS WILL
BE DRY ON WEDNESDAY NIGHT...BUT DID KEEP SLIGHT CHANCE OF POPS
OVER CAMPBELL COUNTY WY SINCE A SHOWER OR TWO COULD REACH THE AREA
AS IT COMES OFF THE BIGHORNS. WITH RETURN FLOW WEDNESDAY NIGHT AND
THURSDAY...EXPECT GUSTY SOUTHEASTERLY WINDS ACROSS THE CWA. THUS
INCREASED WIND SPEEDS FOR THIS PERIOD FROM THE PREVIOUS FORECAST.

THE RIDGE AXIS PUSHES EAST BY FRIDAY...RESULTING IN SOUTHWEST FLOW
ALOFT FOR THE REST OF THE EXTENDED AS AN UPPER LOW STALLS ACROSS THE
PACIFIC NORTHWEST. LOW LEVEL MOISTURE WILL INCREASE...ALLOWING FOR A
DAILY CHANCE FOR SHOWERS AND THUNDERSTORMS. THIS COULD BE AN ACTIVE
PERIOD FOR SEVERE WEATHER...ESPECIALLY FOR THE BLACK HILLS AND
EASTWARD ACROSS THE SD PLAINS...BUT WILL DEPEND ON THE TIMING OF THE
DISTURBANCES. MODELS ARE IN FAIRLY GOOD AGREEMENT KEEPING THIS
PATTERN IN PLACE FOR THE CWA THROUGH THE END OF THE MONTH.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 512 PM MDT MON MAY 20 2013

SCATERED RAIN SHOWERS WILL CONTINUE TONIGHT AND TUESDAY...WITH MVFR/IFR
CONDITIONS PERSISTING ACROSS MOST OF THE AREA. A MORE STEADY RAIN
IS EXPECTED TO CONTINUE ACROSS THE FAVORED UPSLOPE AREAS OF THE
NORTHERN BLACK HILLS AND INTO PORTIONS OF WESTERN SOUTH DAKOTA.
GUSTY NORTHWEST WINDS WILL CONTINUE THROUGH THE PERIOD.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...WIND ADVISORY UNTIL NOON MDT TUESDAY FOR SDZ001-002-012-013-026-
     030-031-072-073.

WY...NONE.
&&

$$

UPDATE...10
SHORT TERM...HELGESON
LONG TERM...MLS
AVIATION...10