Area Forecast Discussion
Issued by NWS Bismarck, ND

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000
FXUS63 KBIS 201216
AFDBIS

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
616 AM CST SAT DEC 20 2014

.UPDATE...
ISSUED AT 616 AM CST SAT DEC 20 2014

MID LEVEL CLOUD COVER ACROSS WESTERN NORTH DAKOTA HAS LEAD TO THE
SEEDING OF THE LOW LEVEL STRATUS ACROSS THE FAR NORTHWEST. THE
RESULT IS LIGHT FLURRIES AND GREATLY IMPROVED VISIBILITIES FROM
THE PREVIOUS DENSE FOG. THUS...LET THE DENSE FOG ADVISORY EXPIRE
ON TIME FOR DIVIDE AND WILLIAMS COUNTIES. ELSEWHERE...GIVEN
OBSERVED TRENDS AND THE 11 UTC HRRR VISIBILITY FORECAST...EXTENDED
THE REMAINDER OF THE ADVISORY THROUGH 16 UTC AND ADDED LAMOURE AND
DICKEY COUNTIES. GIVEN THE TRENDS IN THE HRRR...PORTIONS OF THE
ADVISORY ACROSS THE JAMES RIVER VALLEY MAY NEED TO BE EXTENDED
INTO THE AFTERNOON.

&&

.SHORT TERM...(TODAY AND TONIGHT)
ISSUED AT 352 AM CST SAT DEC 20 2014

MAIN CONCERNS IN THE SHORT TERM ARE THE PERSISTENT FOG IN THE NORTH
AND CENTRAL TODAY...AND PRECIPITATION CHANCES AND WEATHER TYPE FOR
TODAY AND TONIGHT.

CURRENTLY...WATER VAPOR SATELLITE LOOP INDICATES THE NEXT UPPER
LEVEL SHORTWAVE TO AFFECT THE STATE TODAY WAS OVER NORTH CENTRAL
MONTANA/SOUTHERN SASKATCHEWAN/ALBERTA. AT THE SURFACE...LOW PRESSURE
WAS CENTERED OVER THE SOUTHERN BORDER OF ALBERTA/SASKATCHEWAN WITH A
TROUGH EXTENDING SOUTHEAST ACROSS EASTERN MONTANA. WIDESPREAD FOG
WITH VISIBILITIES RANGING FROM 1/4 MILE TO 1 MILE EXTENDED ACROSS
NORTHWESTERN AND MUCH OF CENTRAL NORTH DAKOTA.

TODAY THE UPPER LEVEL LOW/TROUGH IS PROGGED TO ENTER WESTERN NORTH
DAKOTA THIS MORNING AND ENTER CENTRAL NORTH DAKOTA THIS
AFTERNOON...EXITING NORTH DAKOTA SUNDAY MORNING. AT THE
SURFACE...THE SURFACE LOW AND ATTENDANT WARM FRONT IS FORECAST TO
MOVE EAST TODAY. THE LOW SHOULD MOVE EAST ACROSS SOUTHERN
SASKATCHEWAN/MANITOBA...WITH THE WARM FRONT ENTERING WESTERN NORTH
DAKOTA THIS MORNING...AND CENTRAL NORTH DAKOTA THIS AFTERNOON.

REGARDING THE FOG...AS THE AFOREMENTIONED SYSTEM MOVES INTO WESTERN
NORTH DAKOTA VISIBILITIES SHOULD IMPROVE WITH SUFFICIENT LOW TO MID
LEVEL MIXING. THE HRRR VISIBILITY PROGS SUPPORT THIS AS WELL. AREAS
OF FOG SHOULD PERSIST IN CENTRAL NORTH DAKOTA INTO THE
AFTERNOON...IMPROVING VISIBILITIES WITH TIME FROM WEST TO EAST AS THE
LOW PRESSURE SYSTEM ADVANCES EASTWARD.

THE SHORTWAVE AND SURFACE WARM FRONT WILL ALSO BRING LIGHT SCATTERED
PRECIPITATION TODAY AND TONIGHT. LOOKING AT INCREASING CHANCES THIS
MORNING IN THE WEST...EXPANDING INTO CENTRAL NORTH DAKOTA THIS
AFTERNOON. WARM ADVECTION ALOFT WILL RESULT IN MIXED PRECIPITATION
OF FREEZING DRIZZLE OR DRIZZLE EARLY THIS MORNING WITH CHANCES OF
LIGHT RAIN/DRIZZLE THIS AFTERNOON IN THE WEST AS TEMPERATURES RISE
INTO THE 30S. FARTHER EAST FREEZING DRIZZLE OR LIGHT SNOW SHOULD BE
THE PREDOMINANT WEATHER TYPE.

TONIGHT THE MAIN ENERGY FROM THE UPPER LEVEL TROUGH SHOULD KEEP THE
CHANCE OF PRECIPITATION CONFINED TO THE NORTH CENTRAL AND JAMES
RIVER VALLEY AND EASTWARD. FREEZING DRIZZLE OR LIGHT SNOW WOULD BE
THE MAIN WEATHER TYPE THERE TONIGHT.

.LONG TERM...(SUNDAY THROUGH FRIDAY)
ISSUED AT 330 AM CST SAT DEC 20 2014

A WINTRY MIX POSSIBLE SUNDAY EVENING INTO MONDAY NIGHT...FOLLOWED
BY SNOWFALL POTENTIAL EARLY NEXT WEEK IMPACTING CHRISTMAS TRAVEL
HIGHLIGHT THE EXTENDED FORECAST.

FOR THE 00 UTC GUIDANCE SUITE...WHILE IN AGREEMENT ON GENERAL
FEATURES THROUGH THE EXTENDED FORECAST...SPATIAL DIFFERENCES IN
THE MASS FIELDS AND TIMING RESULT IN NON-TRIVIAL IMPACTS TO
SENSIBLE WEATHER THROUGH THE PERIOD. OVERALL...WEIGHED HEAVILY ON
THE 00 UTC ECMWF AND 03 UTC SREF WHICH RESIDE IN THE MIDDLE OF THE
ENVELOPE OF SOLUTIONS. FOR SUNDAY...A LEAD SHORTWAVE EJECTING OUT
OF THE ROCKIES IS FORECAST TO RESULT IN A RAIN AND SNOW MIX
DEPENDING ON SURFACE TEMPERATURES ACROSS WESTERN NORTH DAKOTA IN
THE AFTERNOON.

THE CHALLENGE IS SUNDAY EVENING INTO MONDAY NIGHT IN REGARDS TO
PRECIPITATION TYPE ACROSS CENTRAL NORTH DAKOTA. A MELTING LAYER
ALOFT ABOVE SUB-FREEZING SURFACE TEMPERATURES IS FORECAST TO
EXIST. HOWEVER...DRY AIR IN THE 900-750 MB LAYER WILL HAVE TO BE
SATURATED FOR PRECIPITATION TO REACH THE GROUND. THUS ENTERS THE
UNCERTAINTY AS TO HOW MUCH OF THE MELTING LAYER WILL REMAIN POST-
SATURATION DUE TO THE WET-BULB EFFECT. THERE APPEARS TO BE A BRIEF
WINDOW...ESPECIALLY ACROSS SOUTH CENTRAL NORTH DAKOTA...FOR THE
WARM LAYER TO BE AROUND +2 TO +2.5 C AROUND 00-03 UTC FOR A WINTRY
MIX OF FREEZING RAIN...SLEET AND MELTED SNOW TO BE POSSIBLE.
OVERALL AMOUNTS WILL BE LIGHT WITH THE COLUMN QUICKLY COOLING TO
SUPPORT ALL SNOW BETWEEN 03-06 UTC. THEREAFTER...ATTENTION TURNS
TO CYCLOGENESIS ACROSS THE EASTERN DAKOTAS AND INTO THE UPPER
MISSISSIPPI VALLEY MONDAY. THE 00 UTC DETERMINISTIC AND ENSEMBLE
SOLUTIONS SHOW A VARIED UPPER LEVEL LOW POSITION FROM NORTH
DAKOTA ON THE NAM TO IOWA ON THE GFS...WITH THE SREF AND ECMWF IN
BETWEEN. THUS...WIDESPREAD LIGHT SNOW IS EXPECTED FOR THE AREA
MONDAY ON ALL SOLUTIONS...WITH HIGHER AMOUNTS IN BANDING POSSIBLE.
HOWEVER...UNCERTAINTY IN THESE BANDS IS RATHER HIGH UNTIL THE MASS
FIELDS COME INTO BETTER AGREEMENT.

&&

.AVIATION...(FOR THE 12Z TAFS THROUGH 12Z SUNDAY MORNING)
ISSUED AT 616 AM CST SAT DEC 20 2014

LIFR CEILINGS/VISIBILITIES CONTINUE AT KMOT AND KJMS. KBIS WAS
VARYING FROM IFR TO LIFR. FARTHER WEST KISN HAD JUST IMPROVED TO
VFR. KDIK SHOULD REMAIN VFR. STRATUS AND FOG SHOULD ERODE FROM
WEST TO EAST AS AN APPROACHING SYSTEM BRINGS A DRIER SOUTHWEST
FLOW. KMOT AND KBIS SHOULD BECOME VFR BEFORE/BY 18Z. KJMS NOT
IMPROVING UNTIL AROUND MID TO LATE AFTERNOON. THERE IS A RISK OF
ISOLATED TO SCATTERED MIXED PRECIPITATION AT KDIK/KISN THIS
MORNING...AND TO ALL TAF SITES THIS AFTERNOON. DID NOT MENTION IN
TAFS AS LESS THAN 50 PERCENT CHANCE.

&&

.BIS WATCHES/WARNINGS/ADVISORIES...
DENSE FOG ADVISORY UNTIL 10 AM CST THIS MORNING FOR NDZ002>005-
010>013-019>023-025-035>037-048-051.

&&

$$

UPDATE...AYD
SHORT TERM...JV
LONG TERM...AYD
AVIATION...JV







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