Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 121723
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
1123 AM MDT SAT APR 12 2014

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 301 AM MDT SAT APR 12 2014

WATER VAPOR IMAGERY SHOWS ZONAL FLOW ACROSS THE REGION WITH SEVERAL
EMBEDDED WAVES. THE STRONGEST WAVE IS PUSHING SOUTHEAST ACROSS THE
PACIFIC NORTHWEST. SURFACE ANALYSIS SHOWS LOW PRESSURE STRETCHING
ACROSS ERN MT INTO WRN NEB WITH A DIFFUSE FRONTAL BOUNDARY
STRADDLING THE CWA.

COOLER TEMPERATURES ARE EXPECTED TODAY AS THE FRONT DRIFTS TO THE
SE. MAX TEMPS OVER NE WY WILL BE IN THE 50S WHILE SCNTRL SD REACHES
THE LOWER 70S. UPPER TROUGH WILL DEVELOP TODAY AS THE PACIFIC NW
WAVE CONTINUES TO DIG SOUTHEAST. SHOWERS ARE EXPECTED TO DEVELOP
THIS AFTERNOON ACROSS PORTIONS OF NE WY...AND THE BLKHLS AND
ADJACENT AREAS.

CHANCES FOR PRECIP WILL INCREASE TONIGHT AS THE UPPER TROUGH
APPROACHES THE AREA. THE BASE OF THE TROUGH WILL BE THE FOCUS FOR
THE BEST FORCING AS THE PACIFIC WAVE PUSHES INTO THE GREAT BASIN. A
SERIES OF WAVES ARE PROGGED TO CROSS THE AREA...AND WILL COMBINE
WITH A DEVELOPING BAND OF FRONTOGENESIS AS A SECONDARY SURGE OF
COLDER AIR ADVECTS IN TONIGHT. MODELS ARE STILL TRYING TO RESOLVE
THE TRACK OF THE SURFACE LOW. THE NAM CONTINUES TO BE THE OUTLIER
WITH A TRACK ACROSS NEB...WHICH KEEPS THE HEAVIEST PRECIP ACROSS SRN
PORTIONS OF THE CWA. THE GFS/ECMWF SHOW GOOD AGREEMENT WITH THE MORE
SOUTHERLY TRACK...AND THE 00Z RUNS ARE TRENDING FARTHER SOUTH THAN
PREVIOUS RUNS. NOW IT LOOKS LIKE RAIN WILL DEVELOP ACROSS PORTIONS
OF NE WY THROUGH SW SD THIS EVENING...WITH THE HEAVIEST PRECIP
STAYING SOUTH OF THE CWA. RAIN WILL CHANGE TO SNOW THROUGH THE
NIGHT...THEN CONTINUE UNTIL DRIER AIR MOVES IN FROM THE NORTHERN
EARLY SUNDAY MORNING. THE HEAVIER PRECIP WILL END AROUND THE 12Z-15Z
TIME FRAME...SO TOTAL SNOW ACCUMULATIONS ARE NOW EXPECTED TO BE IN
THE 1 TO 3 INCH RANGE OVER NE WY...THE BLKHLS...AND SW SD. LINGERING
PRECIP WILL BE POSSIBLE ACROSS THESE AREAS THROUGH THE DAY
SUNDAY...BUT WITH LITTLE TO NO ADDITIONAL ACCUMULATION. MAX TEMPS
SUNDAY WILL BE WELL BELOW AVERAGE...30S TO LOWER 40S. UPPER RIDGING
WILL BUILD ACROSS THE AREA SUNDAY NIGHT WITH DRIER WEATHER AND
DECREASING CLOUD COVER.


&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 301 AM MDT SAT APR 12 2014

UPPER TROF MOVES INTO THE WESTERN GREAT LAKES MONDAY...WITH
BUILDING HEIGHTS ACROSS THE NORTHERN PLAINS. RETURN FLOW ON BACK
SIDE OF SURFACE HIGH WILL KEEP TEMPERATURES BELOW AVERAGE ON
MONDAY.

SIGNIFICANT DIFFERENCES BETWEEN GFS/ECMWF FOR TUESDAY AND BEYOND.
GEFS SHOWING WIDE SPREAD IN 500MB HEIGHTS/850MB TEMPERATURES. ON
TUESDAY...ECMWF TAKES SURFACE LOW FURTHER NORTH THAN GFS...RESULTING
IN A DELAY TO COLD FRONT. DIFFERENCE OF 10C IN 850MB TEMPERATURES
ACROSS NORTHWEST SOUTH DAKOTA TUESDAY AFTERNOON. HAVE TRENDED
TOWARDS WARMER ECMWF.

FOR THE REST OF THE WEEK....UPPER TROF SETS UP ACROSS THE NORTHERN
AND CENTRAL PLAINS. LOW CONFIDENCE IN LOCATION/COVERAGE OF
PRECIPITATION WITH EMBEDDED WAVES AND POTENTIAL FOR UPPER LOW TO CUT
OFF. HIGHER CONFIDENCE IN BELOW AVERAGE TEMPERATURES. TEMPERATURE
WILL BE COLD ENOUGH FOR SOME SNOW...ESPECIALLY TUESDAY
NIGHT/WEDNESDAY NIGHT.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY)
ISSUED AT 1121 AM MDT SAT APR 12 2014

MAINLY VFR CONDITIONS WILL PREVAIL THROUGH MID-AFTERNOON. A COLD
FRONT WILL EASE THROUGH THE AREA LATER THIS AFTERNOON/TONIGHT WITH
INCREASING CHANCES FOR RAIN. AS COLD AIR ARRIVES OVERNIGHT...RAIN
WILL CHANGE TO SNOW. WIDESPREAD MVFR CIGS AND IFR/LIFR VSBYS WITH
PRECIPITATION WILL THEN OCCUR THROUGH SUNDAY MORNING.

&&

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

$$

SHORT TERM...13
LONG TERM...7
AVIATION...HELGESON



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