Area Forecast Discussion
Issued by NWS Rapid City, SD

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026
FXUS63 KUNR 160533
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1133 PM MDT FRI MAY 15 2015

.SHORT TERM...THIS EVENING THROUGH SATURDAY NIGHT
ISSUED AT 157 PM MDT FRI MAY 15 2015

WATER VAPOR SHOWS LARGE AND COMPLEX UPPER LOW OVER THE SWRN CONUS
WITH STRONG JET STREAK EJECTING NEWD THROUGH THE CNTRL ROCKIES. AT
THE SFC...LOW IS DEEPENING OVER ERN CO WITH ELY BL FLOW AND WDSPRD
LOW STRATUS ACRS OUR CWFA. SFC BASED CONVECTION IS INITIATING OVER
ERN CO/NEB PANHANDLE IN RESPONSE TO THE JET STREAK.

THIS AFTN/EVE...CONVECTION WILL DEVELOP NWD INTO THE CWFA BY LATE
AFTN AS JET STREAK NOSES INTO WRN SD. MLCAPE EXPECTED TO RISE TO
NEAR 1500-2000J/KG ALONG SD/NEB BORDER WITH PLENTY OF DEEP LAYER SHEAR
FOR SUPERCELLS AND POSSIBLE TORNADOES GIVEN SUBSTANTIAL 0-1KM
SHEAR. THE BIG QUESTION MARK REMAINS LOW CLOUDS...WHICH CONTINUE
TO REMAIN STUBBORN IN ERODING ACRS THE CWFA. WHILE THIS MAY NOT
LIMIT THE POTENTIAL FOR ELEVATED HAIL PRODUCING SUPERCELLS...IT
WOULD LIMIT THE ABILITY FOR SUPERCELLS TO BECOME TORNADIC. CURRENT
THINKING IS THERE WILL BE ENOUGH LOW CLOUD EROSION FROM THE FAR
NRN NEB PANHANDLE INTO SCNTRL SD FOR SOME SFC BASED CONVECTION AND
POTENTIAL TORNADIC SUPERCELLS INTO THIS EVENING.

A BAND OF MDT/HEAVY RAINFALL WILL THEN LIFT NWD ACRS MUCH OF THE
CWFA ON THE NOSE OF JET...WITH PCPN DISSIPATING FROM SOUTH TO
NORTH BY LATER THIS EVENING AS DRY SLOT WORKS IN FROM THE SOUTH.
CURRENT THINKING IS THAT CELLS SHOULD MOVE FAST ENOUGH AND LIMIT
THE FLASH FLOOD THREAT...THUS NO WATCH WILL BE ISSUED AT THIS
TIME.

SATURDAY...DRY SLOT SHOULD KEEP MUCH OF THE AREA PCPN FREE
THROUGH THE MRNG BEFORE NEXT POTENT SHORT WAVE ARRIVES IN THE
AFTN/EVE...PROVIDING ANOTHER ROUND OF WDSPRD SHRA/TSRA TO THE
CWFA. LOW CLOUDS SHOULD NOT BE AS MUCH OF AN ISSUE WITH BEST SVR
THREAT IN OUR ERN ZONES WHERE BEST INSTABILITY/SHEAR WILL RESIDE.
WINDS WILL SHIFT NW SATURDAY NIGHT AS CDFNT WORKS THROUGH.

.LONG TERM...SUNDAY THROUGH FRIDAY
ISSUED AT 157 PM MDT FRI MAY 15 2015

PERSISTENT WESTERN TROF WILL CONTINUE TO EJECT SHORTWAVE ENERGY
INTO THE NORTHERN PLAINS THROUGH MUCH OF THE EXTENDED PERIOD.
MODELS IN GOOD AGREEMENT ON MOVING FIRST UPPER LOW ACROSS THE
DAKOTAS INTO NORTHERN MN SUNDAY AND SUNDAY NIGHT. RAIN SHOWERS
WILL BE MOST NUMEROUS ON SUNDAY ACROSS THE BLACK HILLS INTO
CENTRAL SD...WITH ISOLATED THUNDERSTORMS OVER EASTERN PORTIONS OF
THE CWA. A LITTLE LIGHT SNOW IS POSSIBLE ACROSS THE HIGHER
ELEVATIONS OF THE BLACK HILLS AND ACROSS PORTIONS OF NORTHWEST
SOUTH DAKOTA. STRONG NORTHWESTERLY WINDS ARE EXPECTED TO DEVELOP
ON SUNDAY ACROSS THE WESTERN SD PLAINS...ESPECIALLY FROM 2WX TO
RAP. SHOWERS WILL TAPER OFF FROM WEST TO EAST OVERNIGHT....WITH
WINDS ALSO DECREASING.

A DRY DAY CAN BE EXPECTED MONDAY AS THE AREA WILL BE BETWEEN
SYSTEMS. THE NEXT SYSTEM WILL MOVE ACROSS THE WESTERN STATES MONDAY
NIGHT AND TUESDAY...WITH SOUTHWEST FLOW ALOFT DEVELOPING OVER THE
AREA AHEAD OF IT. CHANCES FOR SHOWERS WILL INCREASE FROM SOUTHWEST
TO NORTHEAST ACROSS THE CWA ON TUESDAY. WIDESPREAD CHANCES FOR
SHOWERS CAN BE EXPECTED TUESDAY AFTERNOON INTO WEDNESDAY AS THE
UPPER LOW TRACKS OVER THE AREA AND EVENTUALLY WEAKENS. ANOTHER
SYSTEM COULD DEVELOP OVER THE WESTERN STATES LATE IN THE WEEK...WITH
CHANCES FOR SHOWERS AND THUNDERSTORMS INCREASING AGAIN TOWARD THE
END OF THE WEEK. TEMPERATURES WILL MOSTLY BE BELOW AVERAGE NEXT
WEEK...WITH HIGHS IN THE MID 40S TO UPPER 50S MOST DAYS.

&&

.AVIATION...FOR THE 06Z TAFS THROUGH 06Z SATURDAY NIGHT
ISSUED AT 1127 PM MDT FRI MAY 15 2015

RAIN AND ISOLATED THUNDESRTORMS CURRENTLY OVER NORTHWESTERN AND
CENTRAL SOUTH DAKOTA WILL CONTINUE TO GRADUALLY MOVE TO THE
NORTHEAST DURING THE REST OF THE NIGHT AND ARE EXPECTED TO BE
MOSTLY OUT OF WESTERN SOUTH DAKOTA AFTER SUNRISE SATURDAY MORNING.
WIDESPREAD IFR...WITH LOCAL LIFR...CIGS AND VSBYS IN FG WILL
CONTINUE OVER MUCH OF THE AREA THROUGH THE NIGHT...GRADUALLY
IMPROVING TO VFR ON SATURDAY MORNING. SCATTERED SHOWERS AND
THUNDERSTORMS WILL REDEVELOP ON SATURDAY AFTERNOON WITH LCL MVFR
CONDITIONS.

&&

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

$$

SHORT TERM...JOHNSON
LONG TERM...15
AVIATION...15



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