568
FXUS63 KUNR 171959
AFDUNR
AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
159 PM MDT TUE SEP 17 2019
DISCUSSION
(THIS EVENING THROUGH TUESDAY)
ISSUED AT 150 PM MDT TUE SEP 17 2019
19Z SURFACE ANALYSIS HAD LOW OVER NORTHEAST MT WITH WARM FRONT
INTO WESTERN IA AND DRY LINE/TROUGH THROUGH THE BLACK HILLS INTO
EASTERN WY. COLD FRONT EXTENDS SOUTHWEST FROM THE LOW INTO WESTERN
WY. DRY GUSTY SOUTHWEST WINDS OCCURRING BETWEEN COLD FRONT/TROUGH.
WATER VAPOUR LOOP HAD VIGOROUS SHORTWAVE WRAPPING UP OVER CENTRAL
WY WITH NARROW BAND OF LIFT ON NOSE OF 90KT JET STREAK PUNCHING
INTO SOUTHWEST WY. LOW LEVEL MOISTURE AHEAD OF SYSTEM SCANT WITH
INVERTED-V SOUNDINGS AND MLCAPE AROUND 500J/KG. HIGH-BASED ARC OF
TS/-SHRA WILL CONTINUE TO PERCOLATE NORTHEAST ACROSS WY INTO
WESTERN SD THIS AFTERNOON/EARLY EVENING. STRONG WIND GUSTS WILL BE
THE MAIN CONCERN. WRAP-AROUND PRECIPITATION WILL AFFECT THE FAR
NORTHWEST REACHES OF THE CWA LATER THIS EVENING INTO THE OVERNIGHT
HOURS, BUT MAIN BAND WILL QUICKLY EXIT EARLY THIS EVENING.
GUIDANCE UNCERTAIN WITH STRENGTH OF WIND AS COLD FRONT WHIPS
THROUGH LATE THIS AFTERNOON/EARLY THIS EVENING. QUITE A BIT OF
WIND AT 850MB WITH 2-4MB/3HR PRESSURE RISES, BUT DEGREE OF MIXING
UP IN THE AIR. STRONG WESTERLY COMPONENT SHOULD PROTECT THE LEE
SIDE OF THE BLACK HILLS FROM THE USUAL SQUEEZE, BUT THE OPEN
PLAINS OF NORTHEAST WY/NORTHWEST SD MAY SEE SHORT-LIVED GUSTS TO
50 MPH AT TIMES. CONSENSUS IS TO HOLD OFF ON WIND HEADLINES.
TEMPERATURES TONIGHT WILL BE NEAR GUIDANCE.
WEDNESDAY, SHORTWAVE RIDGE EXPECTED AS UPPER TROUGH DIGS OVER THE
NORTHWEST CONUS. SOME BREEZY SPOTS EXPECTED GIVEN MIXING.
TEMPERATURES WILL BE NEAR GUIDANCE.
THURSDAY/FRIDAY, UPPER TROUGH SLOWLY MOVES INTO THE NORTHERN PLAINS.
MOISTURE RETURN AHEAD OF THIS SYSTEM WILL BE NOTABLE SIGNALED BY
PWATS REACHING 100-150% OF NORMAL BY FRIDAY. INITIAL FORCING AHEAD
OF LOW/TROUGH THURSDAY AFTERNOON/NIGHT. SUFFICIENT CAPE/SHEAR
PRESENT FOR SOME STRONG/ISOLATED SEVERE STORMS, BUT SURFACE-BASED
CONVECTION MAY BE HARD TO COME BY GIVEN POTENTIAL CAP. SURFACE
TROUGH HANGS UP OVER THE EASTERN HALF OF THE CWA FRIDAY AS FLOW
ALOFT BECOMES PARALLEL TO BOUNDARY. SUSTAINED MOISTURE CONVERGENCE
WILL PUSH MLCAPE VALUES TO 1-2KJ/KG WITH MUCH WEAKER CAP GIVEN
COOLER MID-LEVEL TEMPERATURES. 35-50KT 0-6KM BULK SHEAR MAY
PROMOTE SEVERE STORMS LATER FRIDAY AFTERNOON/EARLY EVENING FOR
CENTRAL SD. TEMPERATURES WILL BE NEAR GUIDANCE.
NEXT WEEKEND INTO EARLY NEXT WEEK, SPLIT FLOW MAY DEVELOP WITH A FEW
WAVES ZIPPING BY. TEMPERATURES WILL BE SEASONAL.
AVIATION
(FOR THE 18Z TAFS THROUGH 18Z WEDNESDAY)
ISSUED AT 1122 AM MDT TUE SEP 17 2019
VFR CONDITIONS ARE GENERALLY EXPECTED THROUGH THE PERIOD. GUSTY
SOUTH TO SOUTHWEST WINDS CAN BE EXPECTED THIS AFTERNOON. A COOL
FRONT WILL BRING ISOLATED TO SCATTERED SHOWERS AND THUNDERSTORMS
TO MUCH OF THE AREA LATER THIS AFTERNOON AND EVENING. A FEW
STRONGER STORMS WITH SMALL HAIL AND GUSTY WINDS ARE POSSIBLE,
MAINLY FROM NORTHEAST WY TO FAR WESTERN SD. WINDS WILL SWITCH TO
THE WEST-NORTHWEST BEHIND THE FRONT.
UNR WATCHES/WARNINGS/ADVISORIES
SD...NONE.
WY...NONE.
DISCUSSION...HELGESON
AVIATION...26
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