Area Forecast Discussion
Issued by NWS Aberdeen, SD

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000
FXUS63 KABR 202055
AFDABR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE ABERDEEN SD
255 PM CST THU NOV 20 2014

.SHORT TERM...TONIGHT AND FRIDAY
FORECAST CHALLENGES INCLUDE TEMPERATURES AND POTENTIAL FOR
FREEZING FOG/LOW STRATUS DEVELOPMENT TONIGHT/PERSISTENCE INTO
FRIDAY. THE POTENTIAL FOR FREEZING DRIZZLE ON FRIDAY HAS
DIMINISHED SIGNIFICANTLY.

CURRENTLY...A STRIPE OF LOW STRATUS REMAINS IN PLACE ACROSS THE
WESTERN FORECAST ZONES THIS AFTERNOON...ALTHOUGH THE EDGES OF IT
APPEAR TO BE VERY SLOWLY DISAPPEARING. TEMPERATURES THIS
AFTERNOON HAVE WARMED INTO THE TEENS AND 20S ON LIGHT AND VARIABLE
WINDS.

TONIGHT/FRIDAY...LOW LEVEL WAA IS SET TO BEGIN TONIGHT AND PERSIST
INTO THE DAY ON FRIDAY. MODELS DO DEPICT A BIT OF MOISTURE
ADVECTION OVERNIGHT AS WELL...OR AT LEAST LOW LEVEL SATURATION /FOG
AND OR LOW STRATUS FORMATION-REFORMATION/. ITS FEASIBLE THE STRIPE
OF LOW CLOUDS OUT WEST MAY END UP DISSIPATING THIS EVENING BEFORE
NEW STRATUS AND/OR FOG CONDITIONS DEVELOP OVERNIGHT. A SLIGHTLY
MORE PLAUSIBLE SCENARIO IS THAT AFTER SUNDOWN...THE LOW LEVEL
THERMAL INVERSION BECOMES ENHANCED BY WAA AND THE REMAINING LOW
CLOUDS BEGIN TO SLOWLY EXPAND NORTH AND EAST WITHIN THIS THERMAL
INVERSION ON THE STRENGTHENING LOW LEVEL SOUTH-SOUTHWESTERLY
BOUNDARY LAYER STEERING WINDS. RAPID REFRESH AND NAM OUTPUT FED
THROUGH BUFKIT SUGGESTS EITHER FOG OR VERY LOW STRATUS SHOULD BE
EVIDENT OVER AT LEAST THE WESTERN TWO-THIRDS OF THE CWA BY 6 AM
FRIDAY...AND LIKELY EXPANDING ALL THE WAY INTO FAR NORTHEAST SOUTH
DAKOTA AND WEST CENTRAL MINNESOTA BY LATE FRIDAY MORNING.
TEMPERATURES TONIGHT SHOULD FALL THE MOST ACROSS THE EASTERN CWA
WHERE WINDS WILL BE LIGHTEST AND SKIES ARE CLEAR. THERE SHOULD BE
A PRETTY GOOD PUSH OF LOW LEVEL WARM AIR INTO CENTRAL SOUTH DAKOTA
FRIDAY...AND POTENTIALLY TO THE I-29 CORRIDOR BY THE END OF THE
FRIDAY FORECAST PERIOD DEPENDING ON HOW MUCH EASTWARD PROGRESS
THE SURFACE PRESSURE TROF MAKES AND WIND SHIFT TO MORE OF A WEST
OR SOUTHWEST WIND DIRECTION THERE IS.

FORECAST CONFIDENCE IS MODERATE THAT FOG/LOW STRATUS WILL DEVELOP
OVER CENTRAL SOUTH DAKOTA AND SLOWLY SPREAD NORTH AND EAST
OVERNIGHT AND INTO FRIDAY.


.LONG TERM...FRIDAY NIGHT THROUGH THURSDAY
THERE IS A REASONABLE AGREEMENT AMONG MODELS WITH THE EVOLUTION OF
THE UPPER LEVEL FLOW PATTERN ACROSS THE CONUS THROUGH MOST OF THE
PERIOD. MODELS DIVERGE BY WEDNESDAY NIGHT WITH THE GFS SHOWING AN
UPPER LEVEL RIDGE BUILDING ACROSS THE REGION...WHILE THE ECMWF
SHOWS A RE-ENFORCING SHOT OF ARCTIC AIR.

MILD TEMPERATURES WILL FILTER INTO THE REGION SATURDAY AND SUNDAY
AHEAD OF OUR NEXT STORM SYSTEM. HIGH TEMPERATURES SHOULD WARM INTO
THE MID 30S ON BOTH DAYS. HOWEVER CAA WILL TAKE HOLD LATE IN THE
DAY ON SUNDAY WITH TEMPERATURES QUICKLY FALLING BEHIND A SURFACE
LOW PRESSURE...AND UPPER LEVEL TROUGH. STRONG NORTHWESTERLY WINDS
ARE LIKELY BEHIND THIS SYSTEM WITH THE HIGHEST SUSTAINED WINDS
OCCURRING SUNDAY NIGHT ALONG THE MISSOURI RIVER...AND THEN THE
EASTERN HALF OF THE CWA ON MONDAY. ACCUMULATING SNOWFALL SUNDAY
NIGHT/MONDAY LOOKS INCREASINGLY POSSIBLE...WHICH WHEN COMBINED
WITH THE STRONG WINDS SHOULD CAUSE AREAS OF BLOWING AND DRIFTING
SNOW. THIS SYSTEM STILL LOOKS PROGRESSIVE WITH PCPN ENDING BY
MONDAY EVENING.


&&

.AVIATION...
18Z TAFS FOR THE KABR...KATY...KPIR AND KMBG TERMINALS

KMBG HAS BEEN IN BETWEEN VFR/MVFR CIGS THIS MORNING AND BASED OFF
SATELLITE DATA...WILL PROBABLY SLIDE OVER TO THE VFR SIDE OF THE
FENCE THROUGH LATE THIS AFTERNOON. HOWEVER...IFR FREEZING
FOG/STRATUS WAITS JUST OFF TO THE WEST AND SHOULD MOVE INTO THE
KMBG TERMINAL BY 00Z. THERE IS A RELATIVELY HIGH PROBABILITY OF
AIRPORT CLOSING IFR CONDITIONS SETTING UP OVERNIGHT TONIGHT AT
KMBG. BE ADVISED.

KPIR IS SITTING UNDER AN MVFR STRATUS DECK...WHICH MAY CLEAR OFF
BY 22Z/23Z THIS AFTERNOON...LEAVING KPIR VFR HEADING INTO THE
EVENING HOURS. HOWEVER...ALL THE AVAILABLE MODEL
GUIDANCE/SOUNDINGS SUGGESTS THAT KPIR WILL LIKELY FREEZING FOG-UP
OR DEVELOP A LOW STRATUS DECK BY 03Z TONIGHT. THERE IS A
RELATIVELY HIGH PROBABILITY OF IFR CONDITIONS DEVELOPING TONIGHT
AT KPIR.

THERE IS RELATIVELY HIGH CONFIDENCE THAT KABR/KATY TERMINALS WILL
REMAIN VFR THROUGH THE REST OF TODAY. AFTER 00Z THOUGH...THE
PROBABILITY OF IFR CONDITIONS AND FREEZING FOG/LOW STRATUS REALLY
STARTS TO INCREASE...ESPECIALLY AT/AFTER 06Z. GOOD LOW LEVEL WAA
SIGNAL OVER A SNOWFIELD UNDER PRESUMABLY A MOSTLY CLEAR SKY NIGHT
AND THE SYNOPTIC SCALE PATTERN OF LIGHT SOUTHERLY WINDS. ALL THE
EARMARKS OF AN IFR FOG/LOW STRATUS EVENT.


&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...NONE.
MN...NONE.
&&

$$
SHORT TERM...DORN
LONG TERM...SD
AVIATION...DORN

WEATHER.GOV/ABERDEEN




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