Area Forecast Discussion
Issued by NWS Bismarck, ND

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FXUS63 KBIS 241810
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
1210 PM CST WED DEC 24 2014

.UPDATE...
ISSUED AT 1206 PM CST WED DEC 24 2014

REGIONAL RADAR MOSAIC CONTINUES TO SHOW LIGHT RETURNS ACROSS PARTS
OF NORTH DAKOTA INTO WESTERN MONTANA. MUCH OF THE PRECIPITATION
HAS NOT BEEN REACHING THE GROUND DUE TO DRY AIR IN THE LOW AND MID
LEVELS. WILL CONTINUE TO CARRY A SMALL CHANCE OF SNOW / RAIN THIS
AFTERNOON...WITH THE RAIN CHANCES MAINLY IN THE SOUTHWEST WHERE
H85 TEMPERATURES HAVE WARMED ABOVE ZERO DEGREES CELSIUS.

LOOKING AT TONIGHT INTO CHRISTMAS DAY...MODELS STILL SUPPORT LIGHT
SNOW ACCUMULATIONS ACROSS THE SOUTHWEST AND FAR SOUTHERN PART OF
THE STATE. THE LATEST WPC GUIDANCE PLACES AN INCH OR TWO IN THE
SOUTHWEST...WHICH IS IN LINE WITH THE GOING FORECAST.

UPDATE ISSUED AT 945 AM CST WED DEC 24 2014

UPDATE HAS BEEN ISSUED. OBSERVATIONS SHOW FOG CONTINUES IN PARTS
OF CENTRAL NORTH DAKOTA...SO EXTENDED PATCHY FOG FOR THE REMAINDER
OF THE MORNING HOURS. EARLY MORNING RADAR MOSAIC SHOWS WEAK ECHOES
MOVING ACROSS PARTS OF WESTERN AND CENTRAL NORTH DAKOTA...BUT
LITTLE TO NO PRECIPITATION HAS BEEN REACHING THE GROUND. A DRY
LAYER IS APPARENT FROM THE 24.12Z BISMARCK SOUNDING WHICH HAS BEEN
INHIBITING THE PRECIPITATION. THINK THE CURRENT SMALL POPS COVER
THIS SCENARIO. DEBATED THE POTENTIAL FOR A BRIEF PERIOD OF VERY
LIGHT FREEZING RAIN / SPRINKLES IN THE SOUTHWEST WHERE WARMER AIR
ALOFT HAS ARRIVED. DECIDED TO ADD IT INTO THE FORECAST FOR JUST A
COUPLE HOURS UNTIL SURFACE TEMPERATURES RISE ABOVE FREEZING.

UPDATE ISSUED AT 637 AM CST WED DEC 24 2014

THE MAIN CHANGE WITH THIS UPDATE WAS TO ADJUST HOURLY FORECAST TEMPS
TO MATCH OBSERVED VALUES IN CENTRAL AND EASTERN LOCATIONS WHERE
TEMPS WERE RUNNING ABOVE FORECAST VALUES DUE TO CLOUD COVER. THE
SAME AREA HAS NUMEROUS REPORTS OF FOG...THOUGH NO SIGNIFICANT
REDUCTIONS IN VISIBILITY AT THIS TIME...GENERALLY 3-5SM VIS.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 339 AM CST WED DEC 24 2014

THE MAIN CONCERN IN THE SHORT WILL BE FOG THIS MORNING...THEN
ATTENTION TURNS TO CHANCES OF PRECIPITATION...WITH AND WEATHER TYPE
DURING THE DAY.

CURRENTLY...A WEAK SURFACE RIDGE AXIS EXTENDED ACROSS EASTERN NORTH
DAKOTA - BETWEEN A STRONG LOW PRESSURE SYSTEM OVER THE GREAT LAKES
AREA AND DEVELOPING LOW PRESSURE IN THE LEE OF THE ROCKIES. ALONG
AND EAST OF THIS RIDGE IS A LARGE STRATUS CLOUD FIELD EXTENDING FROM
THE EASTERN DAKOTAS TO THE GREAT LAKES. IN THE WESTERN DAKOTAS
CIRRUS CLOUDS COVERED MOST OF THE AREA...WITH PATCHY/OCCASIONAL FOG
REPORTED...SOMETIMES LIGHT FOG AND SOMETIMES VISIBILITIES DROP DOWN
TO 1/2 MILE OR LESS FOR SHORT PERIODS.

THE VARIOUS RUNS OF THE HRRR MODEL HAVE SUGGESTED THAT THE WESTERN
EDGE OF THE STRATUS DECK SHOULD ERODE WITH TIME...WITH PATCHY AREAS
OF DENSE FOG FORMING IN THE IMMEDIATE CLEARING OF THE STRATUS.
HOWEVER THE MODEL SUGGESTS THE DENSE FOG NOT LASTING/LINGERING IN
ANY ONE AREA. MEANWHILE INCREASING MID LEVEL CLOUDS MOVING IN FROM
EASTERN MONTANA SHOULD EVENTUALLY LIMIT ANY FOG FORMATION. THUS WILL
KEEP A MENTION OF PATCHY FOG OVER THE WESTERN HALF OF THE STATE
THROUGH AROUND 6 AM...THEN CONTINUE THE PATCHY FOG MENTION OVER ALL
OF CENTRAL NORTH DAKOTA UNTIL AROUND 9 AM.

THE NEXT WEATHER SYSTEM TO AFFECT NORTH DAKOTA IS OVER THE WESTERN
COAST OF NORTH AMERICA EARLY THIS MORNING. BROAD ZONAL FLOW WAS OVER
THE NORTHERN PLAINS AHEAD OF THE SYSTEM WITH LOW PRESSURE IN NORTH
CENTRAL CANADA. THE ZONAL FLOW CONTAINS SOME UPPER LEVEL IMPULSE
ENERGY THAT WAS ASSOCIATED WITH A MID-LEVEL DECK OF CLOUDS OVER
SASKATCHEWAN/MONTANA MOVING EASTWARD...WITH SOME LIGHT RADAR RETURNS
SEEN ON THE RADAR MOSAIC. SURFACE LOW PRESSURE IN THE LEE OF THE
ROCKIES THIS MORNING WILL MOVE EAST ACROSS THE DAKOTAS TODAY. WARM
ADVECTION AHEAD/ALONG THE SYSTEM WAS MOVING INTO WESTERN NORTH
DAKOTA THIS MORNING. THERE IS A SLIGHT CHANCE OF LIGHT PRECIPITATION
WITH THIS UPPER LEVEL ENERGY AS IT MOVES EAST ACROSS THE REGION. THE
MAIN QUESTION IS WHETHER FREEZING RAIN WILL BE AN ISSUE THIS
MORNING. THE APPROACH OF THE MID CLOUD DECK WILL MEAN THAT ICE
CRYSTALS WILL BE LIKELY AT MID AND UPPER LEVELS. SHOULD ANY OF THESE
ICE CRYSTALS FALL INTO LOWER LAYERS OF THE ATMOSPHERE...PROGGED
MODEL SOUNDINGS SUGGEST THAT INITIALLY THERE IS A WARM
LAYER/INVERSION - BUT THAT THE FROST POINT WITHIN THIS LAYER IS MUCH
COOLER THAN THE DRY BULB TEMPERATURE. THUS PARTICLES FALLING THROUGH
SHOULD COOL TOWARDS THE FROST POINT AND REMAIN COOL ENOUGH FOR ALL
SNOW. LATER IN THE DAY AS SURFACE TEMPERATURES WARM ABOVE FREEZING -
MAINLY IN THE WEST - PRECIPITATION WOULD CHANGE TO RAIN.

TONIGHT THE COLD FRONT PORTION OF THE WEATHER SYSTEM WILL MOVE
SOUTHEAST ACROSS THE STATE. AS THIS OCCURS...THE UPPER LEVEL FLOW
BECOMES MORE SOUTHWESTERLY ACROSS THE DAKOTAS - AND THE LEADING EDGE
OF A SERIES OF UPPER LEVEL ENERGY IMPULSES AND MID LEVEL MOISTURE
ARRIVES. BY THIS TIME ANY PRECIPITATION THAT FALLS SHOULD BE IN THE
FORM OF SNOW...OR AT LEAST CHANGING OVER FROM RAIN TO SNOW. MOST OF
THE SNOW SHOULD OCCUR OVER MONTANA AND NORTHERN WYOMING...WITH
SOUTHWESTERN NORTH DAKOTA AND NORTHWESTERN SOUTH DAKOTA RECEIVING
SOME LIGHT SNOW BY CHRISTMAS MORNING. ESTIMATES ARE THAT BY
CHRISTMAS MORNING SNOW AMOUNTS OF AROUND 1/2 INCH WOULD BE COMMON IN
THE SOUTHWEST...MAINLY FROM BEACH TO DICKINSON TO HETTINGER AND
POINTS SOUTH AND WEST.

.LONG TERM...(THURSDAY THROUGH TUESDAY)
ISSUED AT 339 AM CST WED DEC 24 2014

MAIN FORECAST CHALLENGES INVOLVE LIGHT SNOW ACROSS SOUTHERN NORTH
DAKOTA CHRISTMAS DAY AND MUCH COLDER WEATHER BY FRIDAY AND
CONTINUING INTO NEXT WEEK. LATEST 00Z DETERMINISTIC MODELS AS WELL
AS SREF ARE IN GOOD AGREEMENT WITH KEEPING MEASURABLE PRECIP IN THE
FORM OF SNOW ALONG AND SOUTH OF THE ND/SD BORDER ON CHRISTMAS DAY.
THIS INCLUDES THE 00Z NAM WHICH HAS COME BACK IN LINE WITH OTHER
MODEL GUIDANCE WITH A MORE SOUTHWARD LOCATION OF SNOW. MAY SEE
AROUND AN INCH OF SNOW ACCUMULATION CLOSE TO THE STATE BORDER.

WHILE THE SURFACE LOW RESPONSIBLE FOR THIS SNOW MOVES NORTHEAST FROM
THE CENTRAL PLAINS TO THE GREAT LAKES REGION THURSDAY/FRIDAY...
NORTHERLY WINDS WILL ADVECT ARCTIC AIR ACROSS THE NORTHERN PLAINS.
HIGH TEMPS WILL BE IN THE TEENS AND 20S FRIDAY THROUGH THE WEEKEND
BEFORE A STRONGER ARCTIC FRONT PUSHES ACROSS THE REGION EARLY
SUNDAY. SOME DIFFERENCES IN HEIGHT FIELDS DEVELOP BETWEEN
GFS/ECMWF EARLY NEXT WEEK ALTHOUGH BOTH ARE IN AGREEMENT WITH
EXTENSIVE LONG WAVE TROUGH APPROXIMATELY FROM HUDSON BAY TO
INTERMOUNTAIN WEST. GFS HAS -30C CORE AT 850MB OVER NORTHEAST ND
ON TUESDAY WITH THE ECMWF SLIGHTLY WARMER. REGARDLESS...VERY COLD
CONDITIONS EXPECTED WITH WIND CHILLS REACHING DANGEROUS LEVELS
UNDER NORTHWEST FLOW MONDAY NIGHT AND TUESDAY NIGHT WITH 1050MB
SURFACE HIGH SETTING UP OVER WESTERN MONTANA. MAJORITY OF THE CWA
CURRENTLY LOOKS TO REACH WIND CHILL ADVISORY CRITERIA FOR THESE
TIME PERIODS.

&&

.AVIATION...(FOR THE 18Z TAFS THROUGH 18Z THURSDAY AFTERNOON)
ISSUED AT 1206 PM CST WED DEC 24 2014

MANY LOCATIONS ACROSS WESTERN AND CENTRAL NORTH DAKOTA HAVE SEEN
CEILINGS IMPROVE TO VFR...WITH MVFR AND IFR BECOMING LESS
PRONOUNCED. KJMS IS STILL REPORTING IFR CEILINGS...BUT EXPECT
THOSE TO SLOWLY IMPROVE THIS AFTERNOON. A CHANCE OF LIGHT SNOW
WILL INCREASE TONIGHT...MAINLY FOR KDIK AS LOW PRESSURE GATHERS IN
SOUTHWEST SOUTH DAKOTA. COULD ALSO SEE MVFR CEILINGS LATER TONIGHT
AT THE REMAINDER OF THE AERODROMES...KISN..KMOT...KBIS AND KJMS.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
NONE.
&&

$$

UPDATE...CK
SHORT TERM...JV
LONG TERM...JNS
AVIATION...CK






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