Area Forecast Discussion
Issued by NWS Aberdeen, SD

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FXUS63 KABR 242352 AAA
AFDABR

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE ABERDEEN SD
552 PM CST WED DEC 24 2014

.UPDATE...
MADE SOME TIMING ADJUSTMENTS TO OVERNIGHT POPS TO SLOW DOWN
EASTWARD PROGRESSION. LATEST HI-RES GUIDANCE INDICATES A SLOWER
ADVANCE...NOT PUSHING INTO THE JAMES VALLEY UNTIL AROUND 12Z.
OTHERWISE FORECAST IS ON TRACK AND NO FURTHER CHANGES ARE PLANNED.

SEE UPDATED AVIATION DISCUSSION BELOW.


&&
.PREVIOUS DISCUSSION...
.SHORT TERM...TONIGHT THROUGH THURSDAY NIGHT
FORECAST CHALLENGES INCLUDE SNOWFALL ACCUMULATIONS AND PLACEMENT
AND TIMING LATE TONIGHT THROUGH EARLY FRIDAY MORNING.

CURRENTLY...TEMPERATURES ARE IN THE 20S AND 30S THROUGHOUT THE
REGION. LOW CLOUDS...FOG AND PATCHY FREEZING DRIZZLE HAS BEEN
HANGING AROUND MOST OF THE DAY ACROSS THE EASTERN FORECAST ZONES.
THERE MAY CONTINUE TO BE PATCHES OF FOG/LOW CLOUDS AROUND OVER THE
FAR EASTERN FORECAST AREA THIS EVENING.

TONIGHT THROUGH THURSDAY NIGHT...FORECAST CONFIDENCE: MODERATE

THE LOW PRESSURE SYSTEM OF INTEREST...WHICH APPEARS RATHER
VIGOROUS ON WATER VAPOR THIS AFTERNOON...HAS MADE LANDFALL AND IS
CURRENTLY WORKING ACROSS OREGON AND NORTHERN CALIFORNIA. LATE
TONIGHT /MAINLY AT OR AFTER 09Z/...PRECIPITATION CHANCES BEGIN
RAMPING UP IN EARNEST ACROSS THE WESTERN HALF OF THE CWA. THE
BANDED PRECIPITATION THAT IS EXPECTED TO DEVELOP SHOULD MAKE IT AS
FAR EAST AS THE JAMES RIVER VALLEY BY LATE MORNING OF CHRISTMAS
DAY. HOWEVER...THE BANDED PRECIPITATION IS EXPECTED TO PULL BACK
AND RE-CONSOLIDATE OR RE-FOCUS ACROSS CENTRAL SOUTH DAKOTA THURSDAY
NIGHT.

AS THE PRECIPITATION BEGINS TO WORK INTO THE CWA...TEMPERATURES
ARE IN THE PROCESS OF COOLING/WET-BULBING DOWN TO ALL FROZEN
PRECIP THERMAL PROFILES...SO THE VERY LEADING EDGE OF
PRECIPITATION COULD BE FALLING FOR PERHAPS AN HOUR OR TWO AS
FREEZING RAIN AND/OR SLEET MIXING WITH SNOW ACROSS THE WESTERN
HALF OF THE CWA BEFORE PRECIPITATION SWITCHES COMPLETELY TO SNOW
P-TYPE.

WILD CARDS: LOW LEVEL WINDS ARE COMING STRAIGHT OUT OF THE NORTH
TOMORROW AND TOMORROW NIGHT...WHICH USUALLY MEANS THERE IS LOW
LEVEL DRY AIR ENTRAINMENT HAPPENING AT THE SAME TIME THE ATMOS IS
TRYING TO SATURATE DOWN AND PRODUCE SNOWFLAKES THAT CAN REACH THE
GROUND. SYNOPTIC-SCALE LIFT /LIGHT TO MODERATE STRENGTH/ AND
FORCING /MODERATE STRENGTH/ SHOULD BE ABLE TO OVERCOME THE DRY AIR
ENTRAINMENT ACROSS CENTRAL SOUTH DAKOTA...BUT FURTHER NORTH
ESPECIALLY APPROACHING THE BORDER OF THE DAKOTAS...DRY AIR COULD
WIN OUT...RESULTING IN LITTLE OR NO SNOWFALL/ACCUMULATION THERE
/PRESENTLY A TRACE TO 3 INCHES OF SNOW ACCUM IS BEING FORECAST
THERE/. SO THERE IS CERTAINLY SOME ROOM FOR ADDITIONAL ADJUSTMENT
OR TIGHTENING UP OF THE SNOW/NO-SNOW GRADIENT. BUT FOR NOW...MOST
ALL OF THE DETERMINISTIC MODEL OUTPUT...PROBABILISTIC OUTPUT AND
WWD GUIDANCE SEEMS TO SUGGEST THAT THE PORTION OF THE CWA THAT
RESIDES SOUTH OF US HIGHWAY 212 WILL SEE ACCUMULATING
SNOW...INCLUDING ANYWHERE FROM 2 TO 5 INCHES WITH LOCALLY HIGHER
AMOUNTS POSSIBLE ALONG AND SOUTH OF A LINE FROM MISSION RIDGE TO
MILLER. DECENT UPPER LEVEL COUPLED-JET STRUCTURE SHOWING UP IN THE
12Z MODELS AND THERE APPEARS TO EVEN BE A LITTLE BIT OF "COLD AIR
INSTABILITY" AROUND TOMORROW/TOMORROW NIGHT. THESE TWO INGREDIENTS
TEND TO SUPPORT THE NARROWING OF PRECIPITATION BANDS AND SOMEWHAT
MORE CONCENTRATED OR HIGHER PRECIPITATION RATES/AMOUNTS. SO...FOR
NOW...WILL JUST HAVE TO WAIT AND SEE WHERE THE INITIAL SNOW BAND
SETS UP LATE TONIGHT/EARLY CHRISTMAS DAY MORNING AND GO FROM
THERE.

.LONG TERM...FRIDAY THROUGH WEDNESDAY

THE PRIMARY FORECAST CHALLENGES IN THE EXTENDED PERIOD ARE SEVERAL
LOW CHANCES FOR SNOW ALONG WITH TEMPERATURE TRENDS.

OVERALL FORECAST CONFIDENCE...MODERATE TO HIGH

THE SYNOPTIC PATTERN OVER THE CONUS WILL BEGIN WITH A SPLIT FLOW
REGIME IN THE UPPER LEVELS...BEFORE TRANSITIONING TO MORE OF A
FULL LATITUDE TROUGH TOWARDS THE MIDDLE OF NEXT WEEK. THIS WILL
RESULT IN SIGNIFICANT PATTERN CHANGE TO A MUCH COLDER AND DRIER
CONDITIONS.

A DEPARTING WEATHER SYSTEM WILL IMPACT THE SOUTHERN PORTION OF THE
FORECAST AREA ON FRIDAY MORNING BEFORE SHIFTING OFF TO THE EAST.
THE ONLY OTHER CHANCE FOR SNOW WILL OCCUR ON SUNDAY NIGHT AND
MONDAY ASSOCIATED WITH THE INITIAL PUSH OF ARCTIC AIR...ALTHOUGH
PRELIMINARY SNOW ACCUMS LOOK LIGHT.

TEMPERATURES WILL START OFF NEAR CLIMATOLOGICAL AVERAGES ON FRIDAY
THROUGH SUNDAY...WITH HIGHS IN THE TEENS AND 20S. THE ARCTIC
AIRMASS MOVES INTO THE REGION ON MONDAY THROUGH WEDNESDAY WITH H8
TEMPS FALLING INTO THE -15C TO -22C RANGE. AS SUCH...HIGHS ARE
ONLY EXPECTED TO RISE INTO THE SINGLE DIGITS ABOVE ZERO...WITH
LOWS WELL BELOW ZERO IN MOST LOCALES. COMBINE THESE TEMPS WITH A
BLUSTERY NORTH/NORTHWEST WIND OF 15 TO 25 MPH AND WIND CHILL
VALUES WILL LIKELY DROP INTO THE 20 TO 30 DEGREE BELOW ZERO
RANGE.


&&

.AVIATION...
00Z TAFS FOR THE KABR...KATY...KPIR AND KMBG TERMINALS

KABR/KATY...IFR CIGS AND PATCHY MVFR VSBY CONTINUE. SATELLITE
IMAGERY AND REGIONAL OBSERVATIONS INDICATE THAT THIS AREA OF IFR
CLOUD/FOG CONDITION IS SHRINKING EASTWARD ACROSS THE EASTERN
DAKOTAS STILL THIS EVENING. EXPECT KATY TO REMAIN IFR BUT KABR MAY
IMPROVE LATE THIS EVENING BEFORE DETERIORATING BY THU AFTERNOON IN
LIGHT SNOW. KPIR/KMBG...VFR CONDITIONS ARE EXPECTED TO PERSIST
HERE UNTIL BETWEEN 9Z AND 12Z THURSDAY WHEN CHANCES FOR IFR/MVFR
VSBY IN LIGHT SNOW AND POSSIBLY MVFR CIGS SHOULD INCREASE.





&&

.ABR WATCHES/WARNINGS/ADVISORIES...
SD...WINTER WEATHER ADVISORY FROM NOON CST /11 AM MST/ THURSDAY TO 6
     AM CST /5 AM MST/ FRIDAY FOR BUFFALO-HAND-HUGHES-HYDE-JONES-
     LYMAN-STANLEY-SULLY.

MN...NONE.
&&

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

WEATHER.GOV/ABERDEEN






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