Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 040245
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
845 PM MDT MON AUG 3 2015

.UPDATE...
ISSUED AT 842 PM MDT MON AUG 3 2015

00Z KUNR SOUNDING SHOWED GOOD CAP...EVEN FOR MU PARCELS. AS
BOUNDARY LAYER MOISTURE INCREASES UNDER WEAK LOW LEVEL
JET/850-700MB THETA-E ADVECTION REGIME...ELEVATED CONVECTION MAY
DEVELOP OVERNIGHT AHEAD OF UPPER LOW SPINNING OVER CENTRAL WY.
HAVE ADJUSTED FORECAST FOR LATEST TRENDS AS WELL AS ADD HEAVY RAIN
TO GRIDS FOR FLASH FLOOD WATCH TUESDAY AFTERNOON/EVENING...WHICH
STILL LOOKS ON TARGET GIVEN EXPECTED SLOW MOVEMENT OF CONVECTION.

&&

.SHORT TERM...THIS EVENING THROUGH TUESDAY NIGHT
ISSUED AT 325 PM MDT MON AUG 3 2015

UPPER LEVEL ANALYSIS SHOWS CLOSED LOW OVER THE GREAT SALT
LAKE...PUSHING CLOUDS INTO THE NORTHERN PLAINS. SURFACE HIGH
PRESSURE STRETCHES ACROSS THE CENTRAL DAKOTAS WITH SOUTHEASTERLY
RETURN FLOW AROUND 10 KTS. TEMPS ARE CLIMBING INTO THE 80S.

THETA-E ADVECTION WILL INCREASE TONIGHT ACROSS WESTERN SD AHEAD OF
APPROACHING TROUGH. A BAND OF SHOWERS/STORMS ARE EXPECTED TO MOVE
INTO THE CWA FROM THE SOUTHWEST AND EXPAND NORTHEASTWARD OVERNIGHT.
WIDESPREAD SEVERE WEATHER IS NOT EXPECTED...BUT WITH ML CAPE NEAR
2000 J/KG...COULD SEE AN ISOLATED STRONG TO SEVERE STORM.

A FEW SCATTERED SHOWERS MAY LINGER INTO TUESDAY MORNING. CHANCES
INCREASE BY THE AFTERNOON AS TROUGH AXIS AND SURFACE LOW CROSS THE
REGION. BREEZY SOUTHEASTERLY WINDS WILL HELP CREATE AN UNSTABLE
ENVIRONMENT...AND WITH ML CAPE VALUES AROUND 3500 J/KG...COULD SEE
SOME ISOLATED STRONG TO SEVERE STORMS. HOWEVER...SHEAR IS VERY WEAK
AND CLOUD COVER MAY INHIBIT HEATING AND LIMIT SEVERE DEVELOPMENT.
THE MAIN THREAT WITH THESE STORMS WILL BE HEAVY RAIN AND POSSIBLE
FLASH FLOODING...AS STORM MOTION IS ONLY AROUND 10 KTS AND PWATS ARE
180 TO 200 PERCENT OF NORMAL. BEST CHANCE OF HEAVY RAIN WILL BE TO
THE NORTH AND WEST OF THE LOW ALONG AN AREA OF ENHANCED
FRONTOGENESIS...ACROSS FAR NORTHEASTERN WY...NORTHWESTERN SD...AND
THE BLACK HILLS...INCLUDING STURGIS. THEREFORE A FLASH FLOOD WATCH
WILL BE ISSUED FOR THESE AREAS FOR TUESDAY AFTERNOON AND EVENING.
STORM MOTION INCREASES SIGNIFICANTLY AFTER MIDNIGHT AND PRECIP WILL
EXIT MUCH OF THE CWA BY WEDNESDAY MORNING. HIGHS TUESDAY WILL BE IN
THE 80S...70S IN THE BLACK HILLS...AND COULD BE COOLER WITH
AFOREMENTIONED CLOUD COVER.

.LONG TERM...WEDNESDAY THROUGH MONDAY
ISSUED AT 325 PM MDT MON AUG 3 2015

ACTIVE PROGRESSIVE FLOW WILL DOMINATE IN THE PERIOD AS LARGE
SCALE RIDGING REMAINS SUBDUED. THIS WILL SUPPORT PERIODIC CHANCES
FOR SHOWERS AND THUNDERSTORMS AS A SERIES OF TROUGHS PUSH THROUGH
THE REGION. LL MOISTURE WILL BE MORE THAN SUFFICIENT GIVEN WEAK
SOUTHWARD PROTRUSION OF DRY AIR WITH STAUNCH RETURN FLOW PER EACH
SYSTEM. CARRIED LOW CHANCE POPS THROUGH MUCH OF THE PERIOD...WITH
THUR AND SAT BEING BEING PROGGED FOR THE HIGHEST POPS ATTM. FASTER
FLOW ALOFT WILL SUPPORT A POTENTIAL SEVERE THREAT WITH EACH
SYSTEM...HOWEVER TIMING WILL BE KEY IN ANY COVERAGE. SEASONAL
TEMPS EXPECTED IN THE PERIOD.

&&

.AVIATION...(FOR THE 00Z TAFS THROUGH 00Z TUESDAY EVENING)
ISSUED AT 508 PM MDT MON AUG 3 2015

SCATTERED -TSRA WILL SPREAD NORTH ACROSS NORTHEAST WY/WESTERN SD
TONIGHT WITH LOCAL MVFR CIGS/IFR VSBYS AT TIMES. +TSRA WILL
REDEVELOP IN EARNEST MIDDAY TUESDAY AND AFFECT MUCH OF THE AREA
WITH LOCAL MVFR CIGS/IFR VSBYS. OUTSIDE OF STORMS...VFR CONDITIONS
SHOULD PERSIST.


&&

.UNR WATCHES/WARNINGS/ADVISORIES...
SD...FLASH FLOOD WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY EVENING
     FOR SDZ001-012-013-024>026-028>031-072>074.

WY...FLASH FLOOD WATCH FROM TUESDAY AFTERNOON THROUGH TUESDAY EVENING
     FOR WYZ056-057-071.

&&

$$

UPDATE...HELGESON
SHORT TERM...POJORLIE
LONG TERM...JC
AVIATION...HELGESON



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