Area Forecast Discussion
Issued by NWS Rapid City, SD

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000
FXUS63 KUNR 121534
AFDUNR

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

.UPDATE...
ISSUED AT 928 AM MDT SAT JUL 12 2014

15Z SURFACE ANALYSIS HAD MAIN FRONTAL BOUNDARY FROM SOUTHEAST MN
INTO EASTERN CO...BUT SECONDARY COOL FRONT/TROUGH NOTED FROM NORTH
CENTRAL ND INTO NORTHWEST WY. THIS BOUNDARY WILL SINK SOUTH TODAY
IN RESPONSE TO UPPER TROUGH ACROSS MT/ND SHIFT EAST/SOUTHEAST. 12Z
GUIDANCE SHOWS SYSTEM MOVING QUICKER WITH LESS MOISTURE THAN
PREVIOUS RUNS...WHICH SEEMS TO MATCH LATEST
SATELLITE/OBSERVATIONAL TRENDS. EFFECT WILL BE LESS MLCAPE TO WORK
WITH THIS AFTERNOON AS WELL AS POSSIBLE WEAK SUBSIDENCE GIVEN
POSITION OF UPPER LEVEL JET STREAK EAST OF CWA. STILL SHOULD SEE
POPCORN-TYPE SHRA/TSRA DURING DIURNAL HEATING CYCLE GIVEN LOW
MLCIN VALUES IN THE AFTERNOON. HAVE LOWERED POPS AND CLEANED THEM
UP FOR LITTLE/NO ACTIVITY THIS MORNING.

&&

.SHORT TERM...TODAY THROUGH SUNDAY NIGHT
ISSUED AT 238 AM MDT SAT JUL 12 2014

WESTERN NOAM RIDGE WILL AMPLIFY AND TREND WEST IN THE
PERIOD AS A POTENT EASTERN PERIPHERY UPPER LEVEL TROUGH DIGS INTO
THE UPPER MIDWEST AND GREAT LAKES. PRIMARY SFC TROUGH WILL ADVECT
THROUGH THE REGION TODAY...MAINLY SHUNTING LL MOISTURE SOUTH OUT OF
THE FA...WITH NEAR NEUTRAL TEMP ADV. BULK OF HEIGHT FALLS NOT
EXPECTED UNTIL SUNDAY NIGHT...AS THE ASSOCIATED MAIN SFC COLD FRONT
ADVECTS THROUGH THE REGION...SUPPORTING APPRECIABLE CAA SUNDAY
NIGHT.

SCT SHRA/TS REMAIN ONGOING ACROSS PORTIONS OF THE FA THIS MORNING
/ESP NW SD/ WITH BROAD LSA ASCENT CONTINUING PER IMPULSE LADEN
WESTERLY FLOW. LEAD NORTHERN STREAM SW TROUGH WILL PUSH THROUGH THE
FA TODAY...SUPPORTING A SFC TROUGH ACROSS THE AREA. THIS WILL
SUPPORT INCREASED CHANCES FOR SHRA/TS ESP ACROSS THE SE HALF WHERE
INSOLATION WILL LEAD TO INCREASED INSTABILITY AHEAD OF THE TROUGH
GIVEN LINGERING LL MOISTURE. HAVE ADJUSTED POPS UP ACROSS THE SE
HALF GIVEN SLIGHTLY SLOWER SYSTEM EVOLUTION...WHICH WILL ALLOW
BETTER SUPPORT FOR DIURNAL CONVECTION...ESP OVER THE BLACK HILLS.
OVERALL FORCING FOR LSA NOT THE BEST. HOWEVER...INCREASING FLOW
ALOFT COUPLED WITH DECENT ML CAPE AOA 1000 J/KG SHOULD BE MORE THAN
SUFFICIENT TO SUPPORT A FEW STRONGER CELLS...WITH AN ISOLD SEVERE
STORM POSSIBLE GIVEN INCREASING BULK SHEAR VALUES THROUGH THE DAY
AND STEEP LL LAPSE RATES WITH INVERTED V PROFILES.

TONIGHT...A FEW LINGERING SHRA MAY BE POSSIBLE ACROSS THE SOUTHERN
THIRD. OTHERWISE...QUIET CONDITIONS EXPECTED AS LARGE SCALE SINK
FLOW SPREADS OVER THE REGION. COOLER CONDITIONS EXPECTED WITH LOWS
IN THE 50S MANY AREAS.

SUNDAY...LL BAROCLINIC ZONE WILL REMAIN OVER THE REGION WITH NEAR
NEUTRAL TEMP ADVECTION. THIS WILL SUPPORT HIGHS IN THE 80S MOST
PLACES. DEEP MIXING WITH STRONG INSOLATION WILL SUPPORT BREEZY
CONDITIONS ACROSS NE PORTIONS OF THE FA GIVEN COLLOCATION OF FASTER
FLOW ALOFT PER THE SETTLING UPPER TROUGH. HAVE BUMPED WINDS UP
THERE. DRIER AIR WILL ADVECT INTO THE AREA THROUGH THE DAY...WITH
DEWPOINTS FALLING INTO THE 40S MANY PLACES NW HALF. THIS WILL SET
THE STAGE FOR COOLER OVERNIGHT LOWS MOST LOCATIONS...ESP WITH CAA
ENSUING PER A SECONDARY STRONG COLD FRONT.

&&

.LONG TERM...MONDAY THROUGH FRIDAY
ISSUED AT 238 AM MDT SAT JUL 12 2014

A HIGH AMPLITUDE RIDGE WILL REMAIN IN PLACE ACROSS THE FAR WESTERN
CONUS DURING THE EARLY PART OF THE EXTENDED PERIOD. MAINLY DRY
NORTHWESTERLY FLOW ALOFT WILL DEVELOP OVER THE NORTHERN PLAINS AS AN
UNSEASONABLY STRONG AND COOL UPPER LOW SETTLES SOUTH INTO THE GREAT
LAKES REGION. A MAINLY DRY AND COOL PATTERN CAN BE EXPECTED FOR THE
FIRST HALF OF THE WEEK...WITH HIGHS ONLY IN THE 60S AND 70S. WILL
KEEP SLIGHT CHANCES FOR SHOWERS AND THUNDERSTORMS OVER NORTHEAST WY
AND THE BLACK HILLS FROM LATE TUESDAY INTO WEDNESDAY AS A SHORTWAVE
SLIDES SOUTH ACROSS THE NORTHERN ROCKIES.

A WARMING TREND IS EXPECTED FOR THE LATTER PART OF THE WEEK AS THE
RIDGE SLIDES EAST INTO THE HIGH PLAINS AND EVENTUALLY WEAKENS...WITH
HIGH TEMPS BACK TO NEAR AVERAGE LEVELS BY FRIDAY. CHANCES FOR
SHOWERS AND STORMS WILL LIKELY INCREASE BY THE WEEKEND...ESPECIALLY
ACROSS WESTERN AREAS...AS LOW LEVEL MOISTURE INCREASES AND AN UPPER
TROF IS PROGGED TO MOVE ACROSS THE NORTHERN ROCKIES.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z SUNDAY)
ISSUED AT 928 AM MDT SAT JUL 12 2014

AREA OF IFR/LIFR CIGS HAS DEVELOPED JUST TO THE EAST OF THE BLACK
HILLS AND WILL PERSIST THROUGH AT LEAST 18Z...KRAP INCLUSIVE.
SCATTERED SHOWERS AND THUNDERSTORMS WILL REDEVELOP THIS AFTERNOON
IN MOST AREAS. MVFR/IFR CONDITIONS ARE EXPECTED WITH THE HEAVIER
SHOWERS. AN OVERALL DECREASE IN STORM COVERAGE IS EXPECTED BY THIS
EVENING...WITH MOSTLY VFR CONDITIONS EXPECTED INTO THE NIGHTTIME
HOURS.

&&

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

$$

UPDATE...HELGESON
SHORT TERM...JC
LONG TERM...26
AVIATION...15




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