Area Forecast Discussion
Issued by NWS Rapid City, SD

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FXUS63 KUNR 260903
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
303 AM MDT TUE AUG 26 2014

.SHORT TERM...TODAY THROUGH WEDNESDAY NIGHT
ISSUED AT 302 AM MDT TUE AUG 26 2014

LATEST WATER VAPOR IMAGERY SHOWS A TROF DIGGING DOWN THE CALIFORNIA
COAST WITH HIGH PRESSURE CONTINUING ACROSS THE ERN CONUS. THE RESULT
OF THIS IS ACTIVE SOUTHWEST FLOW AND MONSOONAL MOISTURE MOVING INTO
THE CENTRAL ROCKIES AND HIGH PLAINS TODAY. CURRENT SURFACE
ANALYSIS SHOWS HIGH PRESSURE ACROSS THE DAKOTAS AS A WEAK
SHORTWAVE PUSHES INTO THE WRN AND SRN PORTIONS OF THE FORECAST
AREA. AS THE SURFACE HIGH PUSHES EAST...WILL SEE RETURN FLOW WINDS
AND WEAK WARM AIR ADVECTION TODAY. THIS COMBINED WITH THE
SHORTWAVE MOVING THROUGH WILL CREATE SOME SCATTERED SHOWERS AND
ISOLATED THUNDERSTORMS.

FOR TONIGHT...UPPER LOW PUSHES INTO NEVADA/UTAH. THIS WILL KEEP SOME
ENERGY FROM EMBEDDED SHORTWAVES ACROSS THE SRN PORTIONS OF THE CWA.
THUS HAVE KEPT CHANCE POPS IN THE FORECAST. WITH AMPLE CLOUD
COVER AND WARM AIR ADVECTION...OVERNIGHT LOWS WILL BE CLOSER TO
NORMAL THAN THE PAST FEW NIGHTS.

ON WEDNESDAY THE UPPER LOW TRACKS INTO WRN COLORADO PUTTING THE
FORECAST AREA INTO A MORE ZONAL FLOW PATTERN. THIS PATTERN WILL
KEEP THE BULK OF THE ENERGY AND PRECIPITATION CONFINED TO THE
SOUTHERN PORTION OF THE CWA AND AREAS FURTHER SOUTH. UPPER FLOW
REMAINS FAIRLY WEAK...THUS AM NOT EXPECTING ANY AREAS OF ORGANIZED
CONVECTION IN THE FORECAST AREA. FAIRLY LIGHT EASTERLY WINDS
SHOULD KEEP TEMPERATURES ONCE AGAIN BELOW AVERAGE.

&&

.LONG TERM...THURSDAY THROUGH MONDAY
ISSUED AT 302 AM MDT TUE AUG 26 2014

PROGRESSIVE PATTERN WILL CONTINUE THROUGH THE PERIOD...WITH
LONGWAVE PHASED FLOW PERSISTING ACROSS NOAM. THREE MAIN SYSTEMS
EXPECTED TO AFFECT THE REGION IN THE PERIOD...THE EJECTING SW
CONUS UPPER LOW THUR...A WEAK NORTHERN STREAM TROUGH FRIDAY...AND
A MORE ROBUST LONGWAVE UPPER TROUGH SAT NIGHT INTO MONDAY.
FORECAST MODELS IN GOOD AGREEMENT PER WAVE AMPLITUDE AND
TRACK...WITH SOME DIFFERENCE NOTED PER WAVE TIMING. THE GFS ONCE
AGAIN DISPLAYS A FAST BIAS PER TROUGH PHASE SPEED...ESP WITH
SUNDAY/S WAVE...ALTHOUGH CERTAINLY NOT AS SIG AS PREVIOUS CASES.
MAINLY DRY WEATHER EXPECTED THROUGH MOST OF THE PERIOD GIVEN LACK
OF APPRECIABLE LARGE SCALE FORCING AND REMOVAL OF DEEP LAYER
MOISTURE PER THE MIDWEEK SYSTEM. SAVE FOR LINGERING SLIGHT CHANCES
THUR /MAINLY THUR MORNING SCENTRAL SD/ THE NEXT CHANCE FOR RAIN IS
NOT UNTIL SAT NIGHT FAR NW AREAS. DID RETAIN A DRY FORECAST FRI
WITH A NORTHERN STREAM TROUGH PASSING THROUGH THE FLOW. GIVEN
SYSTEM TRACK...BULK OF DYNAMIC FORCING AND ASSOCIATED LSA WILL
PASS NORTH OF THE FA. THERE IS SOME INDICATION FOR POSSIBLE HIGH
BASED SHRA ACTIVITY OVER NE WY FRIDAY AFTERNOON. HOWEVER...GIVEN
THE PERIOD FEEL SUCH A SMALL PRECIP CHANCE IS NOT WARRANTED ATTM.
HAVE INCLUDED A LOW POP SUN INTO MONDAY AS ANOTHER NW PAC LONG
WAVE UPPER TROUGH PUSHES INTO THE NORTHERN PLAINS. SW FLOW WITH
INCREASING UPPER LEVEL PAC MOISTURE WITH MOIST LL SE FLOW WILL BE
SUFFICIENT TO SUPPORT SHRA/TS POTENTIAL GIVEN INCREASING LSA PER
THIS WAVE. WAVE TIMING UNCERTAINTY WARRANTS A NEAR TWO DAY WINDOW
FOR POPS...ALTHOUGH MOST OF THE PERIOD WILL LIKELY BE DRY SUN-
MONDAY. THE POTENTIAL FOR APPRECIABLE RAINFALL IN A PORTION OF THE
CWA IS CERTAINLY PRESENT WITH THIS SYSTEM...ESP IF A DEEPER
REFLECTED SFC CYCLONE DEVELOPS. SOMETHING TO WATCH. SEASONAL TEMPS
CAN BE EXPECTED THUR THROUGH SUN WITH COOLER CONDS LOOKING
PROBABLE EARLY NEXT WEEK GIVEN CAA UNDER THE PASSING LONGWAVE
NORTHERN STREAM TROUGH.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY NIGHT
ISSUED AT 302 AM MDT TUE AUG 26 2014

SCT SHOWERS AND ISOLD THUNDERSTORMS ARE POSSIBLE ACROSS THE AREA
THIS MORNING...WITH ACTIVITY POSSIBLY LINGERING THROUGH THE
AFTERNOON. AREAS OF MVFR CIGS MAY DEVELOP ACROSS NORTHEAST WYOMING
LATE THIS MORNING. OTHERWISE...MAINLY VFR CONDS CAN BE EXPECTED
OUTSIDE OF HEAVIER SHOWERS.

&&

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

$$

SHORT TERM...MLS
LONG TERM...JC
AVIATION...JC





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