Scientific Forecaster Discussion

Return to Local Conditions & Forecast

Without Abbreviations
With Abbreviations

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
224 PM MDT THU AUG 21 2014

.SHORT TERM...THIS EVENING THROUGH FRIDAY NIGHT
ISSUED AT 222 PM MDT THU AUG 21 2014

DEEP WESTERN NOAM TROUGH WILL CONTINUE TO SUPPORT 
ACTIVE SOUTHWEST FLOW OVER THE REGION THROUGH THE PERIOD...WITH
TWO STAUNCH IMPULSES AFFECTING THE REGION...AFTER THIS EVENING/S
ADVANCING WAVE. A WAVERING FRONTAL BOUNDARY WILL PROVIDE THE FOCUS
FOR LL CYCLOGENESIS AND ASSOCIATED LL LIFT...SUPPORTING GOOD
CHANCES FOR RAIN AND THUNDERSTORMS ACROSS THE AREA...ESP FRIDAY
NIGHT. AS OF 20Z A SFC TROUGH WAS ENTERING THE WESTERN FA WITH A
WEAK IMPULSE EJECTING NE OUT OF WY. THIS WAVE WILL CONTINUE TO
SUPPORT INCREASING CHANCES FOR SHOWERS AND THUNDERSTORMS OVER THE
NW HALF INTO THIS EVENING. A FEW CELLS HAVE DEVELOPED OVER THE
BLACK HILLS GIVEN WEAKER INHIBITION...WITH MORE ACTIVITY EXPECTED
OFF THE BIG HORNS AND HIGH TERRAIN OF WY. HIRES RUNS OF THE
NMM/ARW/HRRR INDICATE THAT ISOLD/SCT THUNDERSTORMS MAY COALESCENCE
INTO A BIGGER CLUSTER OF TS AND PROGRESS NE ACROSS THE NW ZONES
THIS EVENING AS THE WAVES PUSHES NE. BEST FORCING FOR ASCENT WILL
REMAIN NW OF THE FA. PREVIOUS POPS WORK WELL WITH LIKELIES ACROSS
THE FAR NW...WITH MORE ISOLATED CHANCES TO THE SE ALONG THE
ASSOCIATED SFC TROUGH PUSH WHERE STRONGER CAPPING AND WEAKER LIFT
WILL BE PRESENT.

FRIDAY...A FEW LINGERING SHRA MAY BE PRESENT OVER THE EASTERN ZONES  
FRI MORNING AS THE TROUGH PUSHES SE. THIS FEATURE WILL STALL IN 
RESPONSE TO THE NEXT IMPULSE...THE EJECTING SW CONUS UPPER TROUGH. 
WATER VAPOR IMAGERY CLEARLY SHOWS AMPLE DEEP LAYER MOISTURE BEING 
INGESTED INTO THE SYSTEM PER A FLOW CONNECTION TO KARINA. HENCE 
AMPLE DEEP LAYER MOISTURE WILL BE AVAILABLE WHEN THIS SYSTEM CROSSES 
THE PLAINS AND A LL GOMEX CONNECTION IS ESTABLISHED. HAVE PRECIP 
CHANCES INCREASING THROUGH THE DAY FRIDAY. HOWEVER...MOST SHRA/TS 
MAY NOT ARRIVE INTO THE FA UNTIL FRIDAY NIGHT GIVEN LINGERING 
SUBSIDENCE BEHIND TODAY/S WAVE. FORECAST MODEL CONSENSUS/AND 
RUN-RUN CONSISTENCY PER THE TRACK/EVOLUTION/AND RAIN TOTALS CONTINUE 
TO WAVER. HOWEVER...THERE IS A SIGNAL FOR HEAVY RAIN WITH THIS WAVE 
GIVEN THE DEEP MOISTURE AVAILABLE. VERY HIGH PW VALUES IN EXCESS OF 
ONE INCH IN MANY LOCATIONS...WITH SOME AREAS APPROACHING TWO WILL 
LIKELY SUPPORT AN AREA OF HEAVY RAIN WITH THIS SYSTEM...ESP WHERE 
H8-H7 POS THETA-E ADV IS STRONGEST. WHERE REMAINS THE QUESTION. 
LATEST GUIDANCE SUGGEST THE SE FA. HOWEVER...GIVEN THE STAUNCH UPPER 
JET ASSOCIATED WITH THE PAC NW UPPER TROUGH...THIS AREA MAY SHIFT NW 
WITH FUTURE MODEL RUNS. AT THIS POINT...FEEL A POP RAISE WAS 
WARRANTED WITH A LOCALLY HEAVY RAIN MENTION IN THE GRIDS FRIDAY 
NIGHT. AS FOR TEMPS...E/NE FLOW WITH EXPECTED INCREASED CLOUD COVER 
WILL SUPPORT A COOLER DAY NW AREAS. DID ADJUST TEMPS DOWN THERE. 

SAT...LINGERING SHRA/TS POSSIBLE WITH A DRY PERIOD EXPECTED SW HALF 
IN THE AFT. MAIN NW CONUS UPPER TROUGH WILL EJECT NE SAT/SAT 
NIGHT...SUPPORTING RENEWED SFC PRESSURE FALLS AND REFLECTED LL SE 
FLOW. POS THETA-E ADV REGIME SHOULD SUPPORT SHRA/TS ACROSS PORTIONS 
OF THE FA...ESP THE NW ZONES SAT NIGHT. HAVE RETAINED AT LEAST A MID 
POP VALUE ALL PLACES...WITH LIKELIES NW...ESP WITH AMPLE/SUFFICIENT 
DEEP LAYER MOISTURE PRESENT PER H7 THETA-E PROGS. DID LOWER TEMPS 
SAT GIVEN CLOUDS AND MOIST EASTERLY LL FLOW...ESP NW ZONES.

.LONG TERM...SATURDAY THROUGH THURSDAY
ISSUED AT 222 PM MDT THU AUG 21 2014

UPPER LOW LIFTS NORTHEAST INTO MONTANA SUNDAY...WITH DRY SLOT 
PUNCHING INTO WESTERN/CENTRAL SOUTH DAKOTA. BEST SUPPORT FOR 
PRECIPITATION WILL BE NORTH OF THE FORECAST AREA. POST FRONTAL 
STRATUS WILL LINGER THROUGH MUCH OF THE DAY SUNDAY...ESPECIALLY 
ACROSS NORTHEAST WYOMING/NORTHWESTERN SOUTH DAKOTA. UPPER LOW 
CONTINUES TO LIFT NORTHEAST INTO CANADA MONDAY...LEAVING SLOW
MOVING UPPER TROF ACROSS THE NORTHERN PLAINS. BELOW AVERAGE
TEMPERATURES WILL CONTINUE THROUGH MID WEEK...ALONG WITH A DAILY
CHANCE OF SHOWERS/THUNDERSTORMS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z FRIDAY)
ISSUED AT 222 PM MDT THU AUG 21 2014

SCATTERED SHOWERS AND THUNDERSTORMS EXPECTED OVER NORTHEASTERN 
WYOMING AND WESTERN SOUTH DAKOTA LATE THIS AFTERNOON THROUGH 
TONIGHT...WITH LCL MVFR CIGS/IFR VSBY. AREA OF STRATUS WILL DEVELOP 
LATE TONIGHT OVER NORTHEAST WYOMING/NORTHWEST SOUTH DAKOTA WITH 
MVFR/LCL IFR CIGS. 

&&

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

$$

SHORT TERM...JC
LONG TERM...7
AVIATION...7

National Weather Service Glossary of Abbreviations