Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 210930
AFDUNR

AREA FORECAST DISCUSSION FOR WESTERN SD AND NORTHEASTERN WY
NATIONAL WEATHER SERVICE RAPID CITY SD
330 AM MDT MON APR 21 2014

.SHORT TERM...TODAY THROUGH TUESDAY NIGHT
ISSUED AT 330 AM MDT MON APR 21 2014

CURRENT SURFACE ANALYSIS SHOWS COOL FRONT SOUTH AND EAST OF THE
REGION...WITH HIGH PRESSURE OVER MT. UPPER LEVEL ANALYSIS SHOWS
SHORTWAVE TROF OVER THE EASTERN DAKOTAS...WITH RIDGING OVER THE
ROCKIES. LOW PRESSURE IS OFF THE PACIFIC NW COAST. SKIES ARE
MAINLY CLEAR ACROSS THE AREA WITH TEMPS MOSTLY IN THE 30S AND
LOWER 40S...A BIT WARMER OVER SOUTH CENTRAL SD. WINDS ARE MOSTLY
LIGHT FROM THE NORTHWEST...LIGHT AND VARIABLE ACROSS NORTHEAST WY
AND THE BLACK HILLS.

WARM AND MAINLY DRY WEATHER WILL CONTINUE INTO TUESDAY AS RIDGE TO
THE WEST SLIDES EAST OVER THE PLAINS. TODAY WILL BE A VERY PLEASANT
DAY...WITH MAINLY SUNNY SKIES AND HIGHS IN THE MID 60S TO LOWER 70S
ACROSS THE PLAINS...60S OVER THE BLACK HILLS. HIGH PRESSURE WILL
PASS THROUGH THE AREA THIS AFTERNOON...SHIFTING EAST OF THE AREA
TONIGHT. WINDS WILL BE RELATIVELY LIGHT FROM THE NORTH-NORTHWEST
ACROSS THE SD PLAINS TODAY...WITH LIGHT SOUTHERLY WINDS OVER MOST OF
NORTHEAST WY. WINDS WILL SWITCH TO THE SOUTH-SOUTHEAST ACROSS THE
ENTIRE AREA TONIGHT AS HIGH CLOUDS INCREASE FROM WEST TO EAST. LOWS
WILL MOSTLY BE IN THE UPPER 30S AND LOWER 40S.

WARMER AIR WILL BUILD INTO THE AREA FROM THE SOUTHWEST ON TUESDAY AS
LOW PRESSURE DEVELOPS AND STRENGTHENS ACROSS WESTERN MT AND MOVES
EAST. SOUTH TO SOUTHEAST WINDS WILL INCREASE THROUGH THE DAY...
ESPECIALLY TO THE NORTH AND EAST OF THE BLACK HILLS. HIGHS WILL
REACH WELL INTO THE 70S ACROSS THE PLAINS...WITH SOME 80S LIKELY TO
THE EAST AND SOUTHEAST OF THE BLACK HILLS. THE SOUTHERLY FLOW WILL
BRING INCREASING LOW LEVEL MOISTURE INTO THE AREA. FLOW ALOFT WILL
TURN SOUTHWESTERLY AHEAD OF TROF MOVING ACROSS THE ROCKIES AND
EXITING RIDGE. A FEW SHOWERS AND THUNDERSTORMS WILL LIKELY DEVELOP
OVER NORTHEAST WY INTO SOUTHWESTERN SD LATE IN THE DAY AS ATMOSPHERE
DESTABILIZES AND ENERGY MOVES NORTHEAST INTO THE AREA. CHANCES FOR
SHOWERS AND STORMS WILL SPREAD NORTHEAST ACROSS THE REST OF THE AREA
TUESDAY EVENING. ISOLATED STRONG STORMS WITH GUSTY WINDS AND SMALL
HAIL ARE POSSIBLE...WITH THE THREAT FOR SEVERE STORMS LOOKING RATHER
MINIMAL RIGHT NOW. STRONG SOUTHERLY LOW LEVEL JET WILL DEVELOP OVER
CENTRAL SD IN THE EVENING...WHICH COULD HELP KEEP ACTIVITY GOING
INTO THE OVERNIGHT OVER EASTERN PORTIONS OF THE CWA. BREEZY TO WINDY
CONDITIONS WILL PERSIST TUESDAY NIGHT...ESPECIALLY TO THE EAST AND
SOUTHEAST OF THE BLACK HILLS NEAR THE LOW LEVEL JET.

&&

.LONG TERM...WEDNESDAY THROUGH SUNDAY
ISSUED AT 330 AM MDT MON APR 21 2014

WEDNESDAY THROUGH FRIDAY GUIDANCE IN REASONABLE AGREEMENT.
WEDNESDAY MORNING...UPPER LOW/TROUGH WILL SPIN FROM THE NORTHERN
ROCKIES INTO THE NORTHERN PLAINS THROUGH THURSDAY AFTERNOON.
SURFACE LOW OVER SOUTHEAST MT WEDNESDAY MORNING WILL MOVE INTO
SOUTHEAST SD BY WEDNESDAY EVENING DRAGGING A COLD FRONT ACROSS THE
CWA. GUSTY SOUTHERLY WINDS AHEAD OF IT WILL SHIFT TO THE
WEST/NORTHWEST BEHIND IT. MOISTURE WILL BE LIMITED WITH THE SYSTEM
WITH MAIN SYNOPTIC LIFT NORTH OF THE CWA...BUT A NARROW SLIVER OF
LOW END SBCAPE VALUES WILL DEVELOP ALONG THE COLD FRONT BRINGING A
FEW SHRA/TSRA TO THE CWA. TEMPERATURES WILL BE TRICKY WEDNESDAY
WITH POTENTIAL TEMPERATURES NEAR 80 AHEAD OF THE FRONT/60S BEHIND
IT...TIMING WILL BE CRITICAL. UPPER TROUGH/LOW SHIFTS INTO THE
UPPER MIDWEST BY THURSDAY EVENING WITH ANOTHER SURFACE LOW
TRACKING FROM EASTERN MT INTO MN. IT WILL DRAG A SECONDARY COLD
FRONT THROUGH THE CWA WITH SHRA POSSIBLE. BEHIND IT...COMBINATION
OF COLD AIR ADVECTION/CYCLONIC FLOW SHOULD MIX A GOOD PORTION OF
40KT 850MB WINDS TO THE SURFACE RESULTING IN A VERY WINDY DAY.
FORECAST SOUNDINGS SUPPORT A BIT OF SNOW THURSDAY NIGHT AS COLDER
AIR SETTLES INTO THE CWA.

FRIDAY...LULL IN THE WEATHER EXPECTED AS UPPER LEVEL RIDGE POKES
INTO THE AREA.

FRIDAY NIGHT INTO SUNDAY...NEXT UPPER TROUGH MOVES FROM THE WEST
COAST INTO THE PLAINS STATES. MODELS ARE NOT IN VERY GOOD AGREEMENT
WITH PARTICULARS OF THIS SYSTEM. THEY GENERALLY AGREE ON THE
LOCATION OF UPPER AIR FEATURES BUT DIFFER GREATLY ON LOW LEVEL
THERMAL PROFILES. 00Z GFS/ECMWF SHOWS 15C DIFFERENCE IN 850MB
TEMPERATURES BY SUNDAY...WHICH WOULD MAKE A HUGE DIFFERENCE FOR
PRECIPITATION TYPE. WILL CUT THINGS DOWN THE MIDDLE FOR NOW WITH
CHANCE POPS AND A MIX OF RASN AT NIGHT.

&&

.AVIATION...FOR THE 12Z TAFS THROUGH 12Z TUESDAY MORNING
ISSUED AT 330 AM MDT MON APR 21 2014

VFR CONDITIONS EXPECTED TODAY/TONIGHT.

&&

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

$$

SHORT TERM...26
LONG TERM...HELGESON
AVIATION...HELGESON






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