Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 211542 AAA
AFDABR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
1042 AM CDT MON JUL 21 2014

.UPDATE...
LOW STRATUS CLOUDS HOLDING ON ACROSS PARTS OF THE CWA THIS
MORNING...EVIDENCE OF THE VERY HIGH LOW LEVEL MOISTURE ACROSS THE
REGION. ALSO...WAA/STEEP LAPSE RATE ACCAS CLOUDS WILL CONTINUE TO
ADVECT ACROSS THE CWA THROUGH THE AFTERNOON. RADAR ALSO SHOWING
THESE WEAK RETURNS WITH THE ACCAS OUT WEST THIS MORNING. WITH DEW
POINTS IN THE 70S THROUGH THE DAY ALONG WITH TEMPERATURES RISING
INTO THE 90S...HIGH HEAT INDICES ARE STILL EXPECTED THIS AFTERNOON
AND EVENING AND THE HEAT ADVISORY STILL LOOKS GOOD. OTHERWISE...COULD
SEE THE START OF THUNDERSTORM DEVELOPMENT OUT WEST BY LATE THIS
AFTERNOON. THE WARM 70H TEMPERATURES ARE STILL EXPECTED TO BE A
BIG FACTOR IN HOW FAR SOUTH THE STORMS DEVELOP INTO THE EVENING.
IT STILL LOOKS LIKE MOST THE STORMS WILL TRACK TO OUR NORTH IN ND
AND ALONG THE ND/SD BORDER. FARTHER SOUTHWARD DEVELOPMENT COULD
OCCUR WITH A STRONGER COOL POOL DEVELOPING INTO THE MOIST UNSTABLE
AIR. STORMS COULD QUICKLY BECOME SEVERE. CURRENT WX/POP FORECAST
LOOKS GOOD.


&&
.PREVIOUS DISCUSSION...
..SHORT TERM...TODAY THROUGH THROUGH WEDNESDAY

...SIGNIFICANT SEVERE WEATHER EPISODE POSSIBLE LATE THIS AFTERNOON
THROUGH TONIGHT...

TODAY/TONIGHT...FORECAST CONFIDENCE: HIGH (OCCURRENCE) - MEDIUM (LOCATION)

CONFIDENCE IS FAIRLY HIGH REGARDING THE DEVELOPMENT OF A SIGNIFICANT SEVERE
WEATHER EVENT THIS AFTERNOON THROUGH TONIGHT ACROSS PARTS OF THE
DAKOTAS AND MN. THE PRIMARY ISSUE AT THIS TIME IS THE LOCATION AND AREAL
COVERAGE OF THE SEVERE WEATHER...SPECIFICALLY THE SOUTHERN EXTENT.

WATCHING A COUPLE ISOLATED STRONG TSTMS EARLY THIS MORNING OVER
SRN ND. LATEST GUIDANCE SUGGESTS THESE STORMS WILL STAY NORTH OF
THE ND/SD STATE-LINE.

LATER TODAY...A SEASONALLY STRONG UPPER SHORTWAVE OVER THE PAC NW WILL
TRACK ACROSS SOUTHERN CANADA BY LATE IN THE DAY...WHILE A SECOND
WEAKER IMPULSE EMANATES OUT OF THE 4-CORNERS REGION AND INTO THE
DAKOTAS BY EVENING. THESE FEATURES WILL INDUCE A WEAK SFC LOW OVER
CENTRAL/N-CENTRAL SD BY 00Z TUESDAY...WITH A WARM FRONT LIKELY
EXTENDING JUST NORTH OF THE ND/SD BORDER. EXTREME VALUES OF MLCAPE
/4000+ J/KG/ ARE FORECAST FROM THE JAMES RIVER VALLEY AND EASTWARD
BY AFTERNOON DUE TO SFC DEWPOINTS IN THE LOW/MID 70S AND VERY
STEEP H7-H5 LAPSE RATES ASSOCIATED WITH A STRONG EML. STILL
EXPECTING STORMS TO INITIATE OVER THE WESTERN DAKOTAS BY LATE IN
THE AFTERNOON /19Z-21Z/...AND THEN GRADUALLY GROW UPSCALE AND
ADVECT EWD. IN FACT...A FORWARD PROPAGATING MCS /BOW ECHO/ IS
BECOMING INCREASINGLY LIKELY DUE TO A FAVORABLE CAPE/SHEAR/COLD
POOL BALANCE. THE BIG QUESTION IS HOW FAR SOUTH WILL STORMS
DEVELOP/PROPAGATE DUE TO INCREASING CINH ASSOCIATED WITH VERY WARM
H7 TEMPS OF +13C TO +15C?? A CONSENSUS OF THE 00Z LOW RESOLUTION
AND CONVECTIVE ALLOWING MODELS NOW SUGGEST THAT CI AND SUBSEQUENT
STORM PROPAGATION WILL REMAIN A BIT FARTHER NORTH THAN THE
PREVIOUS FORECAST...PRIMARILY ALONG AND NORTH OF THE US HIGHWAY 12
CORRIDOR. AS SUCH...MADE SOME EDITS TO THE POP/WX GRIDS TO ACCOUNT
FOR THIS NWD SHIFT. THIS MATCHES UP WELL WITH THE CURRENT SPC DAY
ONE OUTLOOK WHICH SHIFTED THE MODERATE RISK NORTH. ALL IN ALL
EXPECTING THE BIGGEST IMPACTS TO OCCUR FROM ABOUT 4PM-7PM WEST
RIVER...AND FROM 6PM TO MIDNIGHT EAST RIVER. IT SHOULD BE NOTED
THAT PREDICTING THE TRACK OF BOW ECHOES IS EXTREMELY CHALLENGING!
IT IS QUITE POSSIBLE THAT 1) ALL STORMS COULD REMAIN IN ND OR 2)
STORMS MAKE A SHARPER SWD TURN AND IMPACT MORE OF THIS FORECAST
AREA. EITHER WAY...THIS APPEARS TO BE A POTENTIALLY DANGEROUS
EVENT...WITH DAMAGING WIND GUSTS IN EXCESS OF 75 MPH...HAIL TO
TENNIS BALL SIZE...AND ISOLATED TORNADOES. ANYONE WITH WEATHER
INTERESTS ARE ENCOURAGED TO STAY TUNED FOR LATER UPDATES.

ADDITIONALLY...THE COMBINATION OF HEAT AND HUMIDITY WILL ALLOW
HEAT INDEX VALUES TO REACH DANGEROUS LEVELS TODAY. PER COORDINATION
WITH SURROUNDING OFFICES...DECIDED TO ADD ALL EAST RIVER COUNTIES
TO THE HEAT ADVISORY.

TUESDAY THROUGH WEDNESDAY...FORECAST CONFIDENCE: MEDIUM

IN THE WAKE OF THE ABOVE MENTIONED SYSTEM...COOLER AND LESS HUMID
CONDITIONS ARE EXPECTED TUE/WED AS HIGH PRESSURE DEVELOPS IN FROM
THE NORTH. WILL NEED TO WATCH THE POTENTIAL FOR A FEW
SHOWERS/TSTMS...BUT POTENTIAL LOOKS LOW ATTM.

.LONG TERM...WEDNESDAY NIGHT THROUGH SUNDAY
NOT MUCH CHANGE IN THE MEDIUM RANGE MODEL RUNS COMPARED TO 24
HOURS AGO. STILL DEALING WITH PRECIPITATION CHANCES ANCHORED
PRIMARILY ACROSS THE WEDNESDAY NIGHT THROUGH FRIDAY NIGHT FORECAST
PERIODS DURING THE NEXT ROUND OF SHEAR/INSTABILITY ALONG A
BOUNDARY SLOWLY WORKING EAST ACROSS THE REGION. SIMILAR TO LAST
NIGHT...THESE PRECIP CHANCES ARE CENTERED BASICALLY JUST EAST OF
OR RIGHT UNDER A DEVELOPING MID AND UPPER LEVEL RIDGE OF HIGH
PRESSURE...SO THERE WILL BE PLENTY OF WARM MID-LEVEL AIR ADVECTING
ACROSS THE REGION TOO. OVER THE WEEKEND...THE FLOW PATTERN ALOFT
BECOMES NORTHWESTERLY WITH A LARGE UPPER LOW SWEEPING THROUGH THE
GREAT LAKES REGION...LIKELY REINFORCING COOLER...DRY/STABLE
CONDITIONS ACROSS MOST OF THIS AREA SATURDAY/SUNDAY. MODELS HAVE
NOT VARIED MUCH TONIGHT FOR LOW LEVEL THERMAL ADVECTION/THERMAL
PROGS IN THE OUT PERIODS. HIGH/LOW TEMPS ARE EXPECTED TO BE CLOSE
TO IF NOT PERHAPS A FEW DEGREES BELOW NORMAL THROUGH THE PERIOD.




&&

.AVIATION...
12Z TAFS FOR THE KABR...KATY...KPIR AND KMBG TERMINALS

SIMILAR TO SUNDAY MORNING...AREAS OF LOW CLOUDS AND FOG ARE
DEVELOPING AT KATY AND THIS MORNING KABR HAS ENTERED THE FRAY.
SUB-VFR FOG AND/OR LOW STRATUS COULD END UP AT KPIR AND KMBG THIS
MORNING FOR A COUPLE OF HOURS...PER FOG SATELLITE IMAGERY THIS
MORNING...BEFORE JULY SUNSHINE KICKS IN AND WIPES IT ALL OUT.

AREAS OF BKN/OVC STRATUS MAY MIX THROUGH MVFR FLIGHT CATEGORY FOR
A FEW HOURS THIS MORNING ON THEIR WAY TO BECOMING SCT/BKN VFR
CLOUDS...BUT OTHERWISE VFR CONDITIONS ARE EXPECTED TO PREVAIL
THROUGH THE PERIOD. DEPENDING ON WHERE THEY INITIATE THIS
AFTERNOON...THUNDERSTORMS...POSSIBLY SEVERE...COULD BE DEVELOPING
OR MOVING INTO THE KMBG TERMINAL BY EARLY THIS EVENING...BEFORE
CONVECTION SPREADS EAST TOWARD THE KABR/KATY TERMINALS. SOME OF
THESE THUNDERSTORMS COULD PACK QUITE A PUNCH...CAPABLE OF
PRODUCING RATHER LARGE HAIL AND SIGNIFICANT STRAIGHT-LINE DAMAGING
WINDS.



&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...HEAT ADVISORY UNTIL 9 PM CDT /8 PM MDT/ THIS EVENING FOR BROWN-
     BUFFALO-CAMPBELL-CLARK-CODINGTON-DAY-DEUEL-EDMUNDS-FAULK-
     GRANT-HAMLIN-HAND-HUGHES-HYDE-JONES-LYMAN-MARSHALL-
     MCPHERSON-POTTER-ROBERTS-SPINK-STANLEY-SULLY-WALWORTH.

MN...HEAT ADVISORY UNTIL 9 PM CDT THIS EVENING FOR BIG STONE-TRAVERSE.

&&

$$
UPDATE...MOHR
SHORT TERM...FOWLE
LONG TERM...DORN
AVIATION...DORN

WEATHER.GOV/ABERDEEN




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