000
FXUS63 KUNR 170518
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1118 PM MDT THU MAY 16 2013

.UPDATE...
ISSUED AT 847 PM MDT THU MAY 16 2013

A COUPLE OF CONVECTIVE COMPLEXES ACROSS THE CWFA THIS EVE...ONE
MOVING THROUGH SCNTRL SD AND THE OTHER PUSHING INTO THE BLKHLS.
SVR THREAT FOR THE REST OF THE EVENING RATHER MINIMAL. BOTH OF
THESE COMPLEXES WILL CONTINUE PUSHING EWD...WITH MOST ACTIVITY
ENDING ACROSS THE CWFA BY OR SHORTLY AFT MIDNIGHT. HAVE ADJUSTED
POPS/CLOUD COVER TO ACCOUNT FOR ONGOING ACTIVITY. FOG CHANCES
STILL INTACT ALONG THE EAST SLOPES OF THE BLKHLS AND ADJACENT
PLAINS LATE TONIGHT GIVEN RATHER LOW TEMP/DP SPREADS AND
CONTINUED ELY BL FLOW OVERNIGHT.

UPDATE ISSUED AT 516 PM MDT THU MAY 16 2013

HAVE RAISED POPS OVER SWRN SD FOR THE NEXT FEW HOURS THIS EVE
BASED ON CLUSTER OF STORMS EXTENDING FROM NEWCASTLE TO CUSTER TO
ARDMORE. HAVE ALSO LOWERED POPS A BIT FOR NWRN SD BASED ON LACK OF
RETURNS THAT AREA.

&&

.SHORT TERM...THIS EVENING THROUGH FRIDAY NIGHT
ISSUED AT 134 PM MDT THU MAY 16 2013

19Z SURFACE ANALYSIS HAD LOW OVER CENTRAL WY WITH OLD FRONTAL
BOUNDARY EXTENDING FROM LOW ACROSS NE. WATER VAPOR SHOWED SEVERAL
SHORTWAVES OF INTEREST. STRONGEST WAVE OVER NORTH CENTRAL
NE...WHICH CAUSED CLUSTER OF TSRA ACROSS SOUTH CENTRAL SD. SYSTEM
IS MOVING EAST OF CWA. ANOTHER WAVE OVER NORTHEAST CO...AND THIS
WAVE SHOULD PASS SOUTH/EAST OF AREA TONIGHT. MAIN WAVE OF INTEREST
ENTERING WESTERN WY. ATMOSPHERE AHEAD OF WAVE CHARACTERIZED BY
100-500J/KG MUCAPE AND WEAK SBCIN. AS WAVE ROLLS ACROSS THE AREA
THROUGH THIS EVENING...EXPECT AN INCREASE IN TSRA COVERAGE AND
HAVE PAINTED HIGHER SCATTERED POPS IN THE NORTH WHERE BEST LIFT IS
CONCENTRATED. SHEAR IS MARGINAL FOR ORGANIZED STORMS...BUT A STORM
OR TWO MAY PRODUCE SOME HAIL/GUSTY WINDS. ACTIVITY WILL DIE DOWN
OVERNIGHT AS OLD FRONTAL BOUNDARY LIFTS NORTH INTO FAR SOUTHERN SD
AND UPPER RIDGE REBUILDS BEHIND SHORTWAVE. EASTERLY UPSLOPE FLOW
AHEAD WARM FRONT COMBINED WITH EXPECTED MOISTURE AND BOUNDARY
LAYER COOLING MAY RESULT IN SOME PATCHY FOG/ST LATE ON THE EASTERN
SLOPES OF THE BLACK HILLS. TEMPERATURES WILL BE NEAR GUIDANCE.

FRIDAY...HEIGHTS BUILD OVER THE NORTHERN PLAINS AS UPPER RIDGE
AMPLIFIES AND UPPER TROUGH MOVES INTO THE ROCKIES. CENTRAL WY LOW
WILL SLIDE INTO THE NE PANHANDLE WITH WARM FRONT INTO CENTRAL SD.
OBJECTIVE MODEL GUIDANCE SHOWS SHORTWAVE ENERGY WILL BE
LACKING...BUT GIVEN SOUTHWEST FLOW ALOFT SUSPECT SOME SORT OF WAVE
WILL MOVE TOWARD THE CWA LATE IN THE DAY. ALONG/NORTH OF WARM FRONT
1-2KJ/KG SBCAPE DEVELOPS DUE TO DIURNAL HEATING...MOISTURE POOLING
NEAR WARM FRONT...AND PLUME OF STEEP MID-LEVEL LAPSE RATES SPREADING
OVER WESTERN SD. 20M/S 0-6KM BULK SHEAR WILL BE PRESENT OVER THE
NORTH...SUPPORTIVE OF SUPERCELLS AS 45KT 500MB JET STREAK PASSES
THROUGH WY/WESTERN ND. IF CONVECTION CAN BECOME ORGANIZED UNDER
RISING HEIGHT REGIME...SEVERE THUNDERSTORMS WILL BE POSSIBLE.
ACTIVITY WILL WANE AGAIN FRIDAY NIGHT WITH LOSS OF SOLAR INSOLATION.
TEMPERATURES NEAR GUIDANCE.

&&

.LONG TERM...SATURDAY THROUGH THURSDAY
ISSUED AT 134 PM MDT THU MAY 16 2013

DEEP UPPER TROF CROSSES THE WESTERN CONUS OVER THE WEEKEND...WITH
UPPER LOW EVENTUALLY CUTTING OFF OVER THE NORTHERN PLAINS. 12Z
GFS/ECMWF/GEM IN DECENT AGREEMENT WITH UPPER LOW CUTTING OFF OVER
CENTRAL SOUTH DAKOTA MONDAY. PATTERN WOULD FAVOR DECENT RAINFALL
AMOUNTS ACROSS THE FORECAST AREA.

SOUTHWEST FLOW ALOFT ACROSS THE AREA ON SATURDAY WITH SHORTWAVE
EJECTING FROM WESTERN CONUS TROF. WARM FRONT LIFTS NORTHWARD INTO
SOUTH DAKOTA. SOME DIFFERENCES WITH POSITION OF WARM FRONT AS
GFS/ECMWF TAKE IT FURTHER NORTH THAN THE NAM. LOCATION OF WARM FRONT
WILL HAVE BIG IMPACT ON HIGHS SATURDAY. INSTABILITY/SHEAR WILL BE
SUFFICIENT FOR SEVERE THUNDERSTORMS SATURDAY
AFTERNOON/EVENING...ESPECIALLY ACROSS CENTRAL SOUTH DAKOTA.

WIDESPREAD SHOWERS AND THUNDERSTORMS ARE EXPECTED FOR SUNDAY/MONDAY
AS THE UPPER LOW CUTS OFF. POSITION OF UPPER LOW AS IT CUTS OFF WILL
DETERMINE THE LOCATION OF HEAVIEST RAINFALL. SHOWERS AND A FEW
THUNDERSTORMS WILL LINGER ACROSS THE AREA TUESDAY AS THE UPPER LOW
MOVES SLOWLY EAST. UPPER RIDGE BUILDS ACROSS THE NORTHERN PLAINS FOR
THE END OF THE EXTENDED PERIOD IN RESPONSE TO NEXT UPPER TROF MOVING
INTO THE PACIFIC NORTHWEST.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z FRIDAY NIGHT)
ISSUED AT 1111 PM MDT THU MAY 16 2013

ISOLD TSTMS WILL CONTINUE ACROSS SCNTRL SD BEFORE PUSHING EAST OF
THE AREA BY 08Z...WITH BRIEF MVFR VSBY POSSIBLE. EASTERLY LO LEVEL FLOW
WILL LEAD TO IFR STRATUS OVER PARTS OF THE SD PLAINS AFT
MIDNIGHT...WITH SOME IFR/LIFR VSBYS IN FOG FOR AREAS ALONG THE
EAST SLOPES OF THE BLKHLS/ADJACENT PLAINS. ADDITIONAL TSTM
ACTIVITY EXPECTED FRIDAY AFTERNOON.

&&

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

$$

UPDATE...JOHNSON
SHORT TERM...HELGESON
LONG TERM...7
AVIATION...JOHNSON