000
FXUS63 KUNR 250836
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
236 AM MDT SAT MAY 25 2013

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 233 AM MDT SAT MAY 25 2013

08Z SURFACE ANALYSIS HAD LOW OVER EASTERN CO WITH BOUNDARY/LEE
TROUGH INTO CENTRAL MT. WARM FRONT EXTENDED FROM THE LOW INTO
NORTHEAST NE...LIKELY WHERE THE CONVECTION OVER NORTHERN NE IS
BEING FOCUSED. WATER VAPOUR SHOWED UPPER RIDGE EAST OF THE AREA
WITH SOUTHWEST FLOW ALOFT FROM CA INTO THE DAKOTAS. EMBEDDED
SHORTWAVES NOTED...WITH THE ONE MOST LIKELY TO AFFECT TODAY/S
WEATHER OVER UT.

TODAY/TONIGHT...UPPER AIR PATTERN CHANGES LITTLE AS SHORTWAVE ENERGY
WORKS INTO WY/WESTERN SD THIS AFTERNOON. LEE TROUGH DEEPENS AHEAD OF
SHORTWAVE WITH GRADIENT/ISALLOBARIC FORCING RESULTING IN
BREEZY/WINDY SOUTHEAST WINDS OVER THE CWA EAST OF THE BOUNDARY. TD/S
WELL INTO THE 50S TO PERHAPS LOWER 60S WILL POOL ALONG WARM FRONT AS
IT SLOWLY LIFTS NORTH DURING THE DAY. MLCAPE INCREASES TO AT LEAST
2KJ/KG WITH 0-6KM BULK SHEAR RISING TO 20-25M/S. HODOGRAPHS NORTH OF
WARM FRONT FROM SOUTHEAST MT INTO CENTRAL SD DEVELOP PRONOUNCED LOW
LEVEL CURVATURE. AS UT SHORTWAVE MOVES THROUGH CWA...EXPECT SEVERE
THUNDERSTORMS TO ERUPT...INITIALLY OVER THE CONVERGENCE REGION ON
THE NORTH SIDE OF THE BLACK HILLS. A FEW SUPERCELLS AT FIRST...BUT
THEN STORMS SHOULD MERGE INTO A LARGE SCALE COMPLEX LIKELY TURNING
INTO A SQUALL LINE/MCS OVER FAR EASTERN REACHES OF THE CWA
TONIGHT...ESPECIALLY AS LOW LEVEL JET KICKS IN. VERY LARGE HAIL IS
EXPECTED WITH THE STRONGEST SUPERCELLS. ISOLATED TORNADOES MAY OCCUR
GIVEN FORECAST SOUNDINGS/HODOGRAPHS. THREAT WILL THEN TURN TOWARD
DAMAGING WINDS LATER THIS EVENING. LOCAL WRF AS WELL AS SOME
CONVECTIVE ALLOWING MODELS SUPPORT THIS SCENARIO. PRECIPITABLE
WATERS WILL BE 100-150 PERCENT OF NORMAL...BUT MEAN WIND IS AROUND
20KTS AND SUPERCELL MOTION IS 10-15KTS. TEMPERATURES WILL BE NEAR
GUIDANCE.

SUNDAY...DEPENDING ON WHERE TODAY/S CONVECTION ENDS UP...LEFTOVER
LEE TROUGH/WARM FRONT/SURFACE BOUNDARY WILL BE STRETCHED ACROSS CWA.
SOUTHWEST FLOW ALOFT WILL CONTINUE. DAYTIME INSOLATION WILL RESULT
IN 2-3KJ/KG MLCAPE...BUT SHEAR WON/T BE QUITE AS PRONOUNCED AS
TODAY. SLIGHT RISK OF SEVERE THUNDERSTORMS LOOKS REASONABLE GIVEN
THERMODYNAMICS PRESENT. TEMPERATURES WILL BE NEAR GUIDANCE.

&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 233 AM MDT SAT MAY 25 2013

PERSISTENT TROF ACROSS THE PACIFIC NORTHWEST WILL KEEP
THE NORTHERN PLAINS UNDER ACTIVE SOUTHWEST FLOW THROUGH THE MIDDLE
OF NEXT WEEK. DAILY CHANCES FOR TSTMS WILL CONTINUE AS LIGHT EAST TO
SOUTHEAST BOUNDARY LAYER FLOW CONTINUES TO BRING MOIST AIR INTO THE
REGION...AND WEAK ENERGY EJECTS OUT OF THE WESTERN TROF INTO THE
NORTHERN PLAINS. A STRONGER SHORTWAVE IS PROGGED TO CROSS THE AREA
ON MONDAY...LEADING TO THE POTENTIAL FOR STRONG TO POSSIBLY SEVERE
STORMS DURING THE AFTERNOON AND EVENING HOURS. LONGER RANGE GUIDANCE
IS STILL SUGGESTING A STRONG NEGATIVELY TILTED UPPER TROF WORKING
THROUGH THE NORTHERN PLAINS MID TO LATE NEXT WEEK...WHICH COULD
PROVIDE WIDE SPREAD SIGNIFICANT RAINFALL. TEMPERATURES WILL REMAIN
ABOVE AVERAGE...WITH HIGHS GENERALLY IN THE 70S AND LOWER 80S ACROSS
THE AREA THROUGH THE MIDDLE OF NEXT WEEK...WITH SOME COOLING
EXPECTED TOWARDS THE END OF THE WEEK AS THE UPPER TROF MOVES INTO
THE NORTHERN PLAINS.

&&

.AVIATION...FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT
ISSUED AT 233 AM MDT SAT MAY 25 2013

AN UPPER LEVEL WEATHER DISTURBANCE WILL CROSS THE REGION TODAY
BRINGING INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS TO THE
AREA. SOME STORMS COULD POSSIBLY BECOME SEVERE OVER PORTIONS OF
NORTHEASTERN WY AND WESTERN SD. MVFR TO IFR CIGS/VIS WILL BE
POSSIBLE IN ANY TS OR HEAVY SHRA. OTHERWISE...VFR CONDITIONS ARE
EXPECTED THROUGH LATE TONIGHT.

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

$$

SHORT TERM...HELGESON
LONG TERM...15
AVIATION...15