Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 040523
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1123 PM MDT SUN MAY 3 2015

.UPDATE...
ISSUED AT 753 PM MDT SUN MAY 3 2015

00Z KUNR SOUNDING HAD WELL MIXED AND FAIRLY DRY BOUNDARY LAYER
BELOW 700MB...FED BY NORTH/NORTHEAST FLOW OFF SURFACE ANTICYCLONE
CENTERED OVER THE DAKOTAS. OVERNIGHT...HIGH SHIFTS EAST AND LOW
LEVEL FLOW WILL TURN UPSLOPE WITH 20KT SOUTHEAST BOUNDARY LAYER
FLOW MONDAY MORNING. THIS WILL FEED LOW LEVEL MOISTURE INTO THE
CWA AND SLOWLY ERASE DRIER AIR. ALOFT...RIGHT ENTRANCE REGION OF
90KT JET STREAK WILL BRING SYNOPTIC LIFT PER UPPER LEVEL
DIVERGENCE. MODEST 850-700MB THETA-E ADVECTION DEVELOPS OVER
NORTHERN PORTIONS OF CWA. ACTIVITY OVER WY ASSOCIATED WITH WEAK
SHORTWAVE SHOULD PUSH SLOWLY NORTHEAST OVERNIGHT AND THUS HAVE
UPPED POPS ACROSS FAR NORTHEAST WY/FAR NORTHWEST SD.

REST OF FORECAST TWEAKED FOR LATEST TRENDS.

&&

.SHORT TERM...THIS EVENING THROUGH MONDAY NIGHT
ISSUED AT 220 PM MDT SUN MAY 3 2015

LL FRONTAL BOUNDARY BACKED UP AGAINST THE ROCKIES THIS
AFTERNOON WITH DISTURBED FAST WESTERLY FLOW ALOFT. SW CONUS UPPER
LOW COMING ON SHORE AND IS PROVIDING BACKING LL FLOW OVER THE
SOUTHERN HIGH PLAINS INTO THE CENTRAL PLAINS...AND WILL SUPPORT A
SLOW INCREASE IN DEEP LAYER MOISTURE IN THE PERIOD. WEAK UPPER
LEVEL IMPULSE NOW SPREADING INTO THE NORTHERN PLAINS AS EVIDENCED
BY WATER VAPOR. THIS WILL SUPPORT AN INCREASE IN SHOWER ACTIVITY
TO THE WEST OF THE REGION. UPTICK IN LSA WITH STRONG WESTERN BH
EDDY CONVERGENCE SHOULD SUPPORT ISOLD TO SCT SHRA THERE THIS
AFTERNOON...WITH OTHER SHOWERS POSSIBLY SPREADING INTO THE FAR SW
FA /NE WY/ THIS EVENING. HAVE RETAINED LOW CHANCE POPS FOR THIS.
AFOREMENTIONED IMPULSE WILL SHIFT EAST OVERNIGHT WITH INCREASING
DEEP LAYER ASCENT COUPLED WITH LINGERING CONVECTIVE DRIVEN MESO
FORCING. THIS WILL SUPPORT INCREASING SHOWER CHANCES OVER THE
WESTERN FA OVERNIGHT WITH ACTIVITY SLOWING SHIFTING EAST. UPPER
IMPULSE WILL SHIFT EAST WITH SHRA WAINING OVER THE WESTERN
FA...WITH LITTLE EASTWARD PROGRESSION EXPECTED ACROSS THE FA. DID
SHIFT/RETAIN LOW CHANCE POPS OVER THE CENTRAL SD PLAINS TOMORROW
AFTERNOON. HOWEVER...THE MAJORITY OF ACTIVITY SHOULD BE OVER THE
WESTERN 2/3 OF THE FA MONDAY MORNING. DID REMOVE THUNDER MENTION
GIVE LACK OF SUFFICIENT INSTABILITY...WITH PROGGED MU CAPES UNDER
200 J/KG. LINGERING CHANCES FOR ADDITIONAL SHOWERS WERE RETAINED
OVER SCENTRAL SD WHERE THE NORTHERN EXTENT OF THE DEEPEST MOISTURE
WILL GRAZE WITH A FGEN RESPONSE. OTHERWISE...LINGERING SHRA MAY BE
POSSIBLE OVER SCENTRAL SD INTO MONDAY NIGHT...WITH THE REMAINDER
OF THE FA EXPECTED TO BE DRY UNDER WEAK SUBSIDENCE. TEMPS LOOK
TRICKY MONDAY...STRUGGLING WITH EXPECTED CLOUDS AND MOISTURE IN
THE AREA. DID CUT HIGHS...ESP OVER THE WEST...WITH MANY PLACES
STRUGGLING OUT OF THE 50S WHERE INSOLATION IS HAMPERED.

.LONG TERM...TUESDAY THROUGH SUNDAY
ISSUED AT 220 PM MDT SUN MAY 3 2015

UPPER FLOW BECOMES SOUTHWESTERLY TUESDAY AS A DEEP TROUGH
DEVELOPS OVER THE WESTERN CONUS. A STRONG DISTURBANCE WILL EJECT
INTO THE CENTRAL/NORTHERN PLAINS...BRINGING INCREASING CHANCES FOR
PRECIPITATION. GFS AND ECM ARE STILL SHOWING MUCH OF THE PRECIP
BEGINNING TUESDAY NIGHT...WITH AROUND A HALF TO ONE INCH OF QPF
FOR MANY LOCATIONS ACROSS WRN SD BY THURSDAY NIGHT. CYCLONIC FLOW
WILL KEEP CHANCES OF SHOWERS AROUND THROUGH NEXT WEEKEND...AND
BOTH MODELS ARE SHOWING THE MAIN UPPER LOW BECOMING NEGATIVELY
TILTED NEXT WEEKEND JUST W/SW OF THE CWA. LATEST GUIDANCE IS
DELAYING THE STORM UNTIL SUNDAY. THE GFS HAS NOW BROUGHT IN COLDER
AIR INTO THE NRN PLAINS WRAPPING AROUND THE LOW. THIS SOLUTION
COULD MEAN THE PRECIP FALLS AS SNOW...BUT STILL MUCH UNCERTAINTY
EXISTS. EITHER WAY THE AREA COULD SEE ANOTHER ONE OR MORE INCHES
OF QPF. TEMPERATURES THROUGH THE EXTENDED PERIOD WILL BE NEAR TO
SLIGHTLY ABOVE AVERAGE...IN THE 60S TO LOWER 70S. HOWEVER COOLER
TEMPS ARE POSSIBLE WITH THE STORM NEXT SUNDAY.

&&

.AVIATION...(FOR THE 06Z TAFS THROUGH 06Z MONDAY NIGHT)
ISSUED AT 1121 PM MDT SUN MAY 3 2015

SCATTERED -SHRA WILL SLOWLY EXPAND FROM NORTHEAST WY INTO WESTERN
SD OVERNIGHT INTO MONDAY MORNING. VFR CONDITIONS EXPECTED
INITIALLY...BUT PERSISTENT UPSLOPE FLOW COMBINED WITH EXPANDING
PRECIPITATION AREA WILL CREATE AREAS MVFR CIGS IN/NEAR
PRECIPITATION AS WELL AS LOCAL MVFR VSBYS...ESPECIALLY OVER THE
HIGHER TERRAIN. AS PRECIPITATION DECREASES MONDAY
AFTERNOON...CONDITIONS WILL RETURN TO MAINLY VFR.

&&

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

$$

UPDATE...HELGESON
SHORT TERM...JC
LONG TERM...13
AVIATION...HELGESON


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