705
FXUS63 KBIS 180646
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
1246 AM CST WED DEC 18 2024
KEY MESSAGES
- HIGH CHANCES FOR MEASURABLE SNOW WEDNESDAY INTO THURSDAY, WITH
A 60 PERCENT CHANCE OF AT LEAST 6 INCHES OF SNOW ACROSS
NORTHERN NORTH DAKOTA AND INTO THE NORTHERN JAMES RIVER
VALLEY. A WINTER STORM WATCH HAS BEEN ISSUED.
- MEDIUM CHANCES OF IMPACTFUL BLOWING SNOW WEDNESDAY AFTERNOON
THROUGH THURSDAY MORNING. VISIBILITY COULD BE SIGNIFICANTLY
REDUCED, ESPECIALLY IN OPEN COUNTRY.
- THERE IS A MEDIUM CHANCE OF FREEZING RAIN WEDNESDAY AFTERNOON
AND EVENING IN AREAS SOUTH AND WEST OF THE MISSOURI RIVER,
WHICH COULD LEAD TO A GLAZE OF ICE.
- TEMPERATURES COOL THROUGH THE REST OF THE WEEK. OVERNIGHT
LOWS AS COLD AS 15 DEGREES BELOW ZERO ARE FORECAST IN NORTHERN
NORTH DAKOTA WEDNESDAY AND FRIDAY MORNING.
- ABOVE NORMAL TEMPERATURES ARE STRONGLY FAVORED FOR NEXT WEEK
AROUND THE CHRISTMAS HOLIDAY.
UPDATE
ISSUED AT 1246 AM CST WED DEC 18 2024
SKY COVER AND CHANCES FOR FLURRIES WERE ADJUSTED BASED ON OBSERVED
TRENDS. OTHERWISE, THE NEAR-TERM FORECAST REMAINS ON TRACK.
UPDATE ISSUED AT 916 PM CST TUE DEC 17 2024
MINIMAL CHANGES WERE NEEDED FOR THE LATE EVENING UPDATE. JUST
TWEAKED THE SKY COVER A LITTLE BIT TO BETTER ACCOUNT FOR SOME
OF THE CLEARING ACROSS THE NORTH. ALSO ADJUSTED FLURRIES TO
MATCH UP.
UPDATE
ISSUED AT 539 PM CST TUE DEC 17 2024
EARLIER GUIDANCE HAD CLOUDS CLEARING OUT RATHER QUICKLY TONIGHT,
BUT LOOKING AT THE LATEST OBSERVATIONS THAT SEEMS UNLIKELY. WE
ALSO CONTINUE TO SEE SOME LIGHT SNOW/FLURRIES WHEREVER CLOUD
COVER IS. THUS, WE DECIDED TO MENTION FLURRIES ANYWHERE ACROSS
THE FORECAST AREA WHERE CLOUD COVER WAS FORECAST TO BE 60
PERCENT OR GREATER THROUGH 15Z WEDNESDAY. OTHERWISE, NO MAJOR
CHANGES WERE NEEDED FOR THIS UPDATE AND JUST BLENDED IN THE
LATEST OBSERVATIONS TO THE GOING FORECAST.
DISCUSSION
ISSUED AT 405 PM CST TUE DEC 17 2024
NO MAJOR WEATHER IN THE NEAR TERM FORECAST, WITH ON AND OFF
LIGHT SNOW ONGOING UNDERNEATH AN EXPANSIVE LOW STRATUS DECK
ACROSS THE STATE, AS WEAK, EMBEDDED IMPULSES MOVE THROUGH
CYCLONIC FLOW ALOFT. HIGHS THIS AFTERNOON WILL BE IN THE UPPER
TEENS TO UPPER 20S, WITH RELATIVELY LIGHT NORTHWEST WINDS AS
HIGH PRESSURE CENTERED TO OUR NORTHWEST CONTINUES TO BUILD INTO
THE REGION. QUIET BUT CHILLY TONIGHT, ALTHOUGH SOME UNCERTAINTY
IN OVERNIGHT LOWS IF LOW CLOUDS DON'T MOVE OUT AS MUCH AS
EXPECTED. CURRENT FORECAST HAS LOWS DROPPING TO AROUND 10
DEGREES BELOW ZERO ACROSS FAR NORTHERN NORTH DAKOTA, AND THE
SINGLE DIGITS ABOVE ZERO ELSEWHERE.
THE MAIN FORECAST CONCERN FOR THE NEXT FEW DAYS IS AN ALBERTA
CLIPPER THAT IS PROGGED TO DEVELOP OVER THE NORTHERN ROCKIES
BEFORE DIVING THROUGH MONTANA AND THE DAKOTAS, BRINGING
IMPACTFUL WINTER WEATHER WEDNESDAY AND THURSDAY. A HYBRID SYSTEM
WITH A MIX OF SYNOPTIC AND MESOSCALE FORCING HAS MADE THIS A
TRICKY FORECAST. THERE IS HIGH CONFIDENCE IN A LARGE AREA OF
ADVISORY-LEVEL SNOW ACROSS NORTHWEST AND PARTS OF CENTRAL NORTH
DAKOTA FROM SUFFICIENT SYNOPTIC SCALE FORCING, WITH MID-LEVEL
HEIGHT FALLS AND WARM AIR ADVECTION OVERSPREADING THE FORECAST
AREA AHEAD OF THE APPROACHING SHORTWAVE. DETERMINISTIC GUIDANCE
HAS BEEN CONSISTENT IN ADVERTISING MODERATE FRONTOGENESIS
OVERLAID WITH SUFFICIENT Q-VECTOR CONVERGENCE AND MODESTLY STEEP
MID- LEVEL LAPSE RATES, WITH THE HREF SNOWBAND PROBABILITY
TRACKER PAGE AGREEING WITH THIS POTENTIAL BY HIGHLIGHTING A
NORTHWEST-SOUTHEAST ORIENTED BAND IN VARIOUS MEMBERS. ASSUMING
A BROAD 15:1 SNOW RATIO, WE UTILIZED 12Z HREF NEIGHBORHOOD
PROBABILITIES OF 0.40 INCHES OF QPF TO HIGHLIGHT THE MOST LIKELY
AREA OF SNOWFALL OF AT LEAST 6 INCHES. IN COLLABORATION WITH FGF,
DECIDED THERE WAS ENOUGH CONFIDENCE FOR A WINTER STORM WATCH FOR
AREAS FROM DIVIDE AND WILLIAMS COUNTIES, TO ROLETTE AND PIERCE,
DOWN TO FOSTER AND STUTSMAN COUNTIES. BROADLY, THERE IS A 60
PERCENT CHANCE FOR AT LEAST 6 INCHES OF SNOW IN THESE AREAS,
WITH A LOW CHANCE OF EXCEEDING 8 INCHES. WE DO RECOGNIZE THAT
THE POTENTIAL FOR SOMEWHERE IN AN AREA TO RECEIVE HEAVY SNOW IS
LIKELY HIGHER THAN POINT-SPECIFIC PROBABILITIES WILL SHOW, AS
THESE SIGNALS CAN GET WASHED OUT IN ENSEMBLE GUIDANCE.
FORECAST SNOW AMOUNTS DECREASE TO THE SOUTH, BUT STRONGER WINDS WILL
LEAD TO MORE SIGNIFICANT BLOWING SNOW CONCERNS. VERY STRONG
WINDS ARE LIKELY IN PARTS OF WESTERN AND SOUTHERN NORTH DAKOTA
WITH THIS SYSTEM, WITH STRONG PRESSURE RISES AND COLD AIR
ADVECTION. THE TIMING OF THESE FEATURES ISN'T AS FAVORABLE FOR
UPPER END WINDS, HOWEVER, AS THE MAIN PUSH OF WINDS WILL BE
MOVING IN AROUND MIDNIGHT WEDNESDAY NIGHT, CONTINUING INTO
THURSDAY MORNING. 12Z DATA SHOWS A HIGH LIKELIHOOD OF WIND GUSTS
OF AT LEAST 50 MPH ACROSS SOUTHWEST NORTH DAKOTA, WITH A BROAD
40 TO 50 PERCENT CHANCE OF WINDS REACHING 60 MPH. ANY
PRECIPITATION FALLING COULD HELP IN MIXING DOWN STRONGER WINDS
AS WELL, WITH FORECAST SOUNDINGS SHOWING A BRIEF PERIOD OF 65
MPH WINDS AT THE TOP OF THE MIXED LAYER. NOT SURE HOW WIDESPREAD
THOSE HIGHER END WINDS WILL BE, BUT IT CERTAINLY LOOKS POSSIBLE
THAT WE HAVE ISOLATED GUSTS UP TO 60 MPH OVERNIGHT WEDNESDAY
INTO THURSDAY MORNING.
A WINTER WEATHER ADVISORY WILL LIKELY BE NEEDED FOR AREAS SOUTH OF
THE WINTER STORM WATCH FOR LOWER SNOW AMOUNTS AND BLOWING SNOW,
AS WINDS BECOME STRONGER IN THIS AREA. COUNTIES WITHOUT MUCH
SNOW AND BLOWING SNOW WILL NEED TO BE IN A WIND ADVISORY, BUT
THERE IS UNCERTAINTY ON WHERE THIS DIVIDING LINE WILL END UP, IN
CASE THERE IS A SOUTHWARD SHIFT. WE DID ISSUE A SPECIAL WEATHER
STATEMENT FOR COUNTIES NOT IN THE WATCH, WITH A GENERAL 1 TO 3
INCHES OF SNOW FAVORED IN A LINE FROM WATFORD CITY, TO GARRISON,
TO ELLENDALE, AND LOWER AMOUNTS SOUTH.
THE OTHER POTENTIAL HAZARD IS FREEZING RAIN, FOCUSED IN AREAS
SOUTH AND WEST OF THE MISSOURI RIVER. DETERMINISTIC GUIDANCE
BRINGS IN A SWATH OF WARM AIR ALOFT WEDNESDAY EVENING, WITH
SOUNDINGS SHOWING A BRIEF WINDOW OF ENOUGH OF A WARM NOSE TO
FAVOR FREEZING RAIN. FAR SOUTHWEST NORTH DAKOTA MIGHT BE TOO
WARM AT THE SURFACE FOR FREEZING RAIN, WITH FORECAST HIGHS IN
THE UPPER 30S ON WEDNESDAY, SO THERE MIGHT BE A SWEET SPOT IN
COUNTIES IMMEDIATELY ALONG THE RIVER THAT END UP WITH THE MAIN
FREEZING RAIN. HIGH-RES MODEL RUNS ARE SHOWING THIS MIXED
P-TYPE AS WELL, WITH SOME RAIN IN THE FAR SOUTHWEST WHERE TEMPS
ARE WARMER. CURRENTLY ADVERTISING A MEDIUM CHANCE OF FREEZING
RAIN THAT COULD LEAD TO A GLAZE OF ICE, BUT NOT A LOT OF
CONFIDENCE IN HOW P-TYPES WILL EVOLVE IN THIS NARROW WINDOW. BY
THE TIME IT GETS TO LATE WEDNESDAY NIGHT / EARLY THURSDAY
MORNING, PRECIPITATION IS EXPECTED TO BE ALL SNOW.
AS THE CLIPPER DROPS SOUTHEAST THROUGH THE DAY THURSDAY, SNOW
CHANCES WILL TAPER OFF FROM NORTHWEST TO SOUTHEAST, WITH LIGHT
SNOW LINGERING THROUGH THE AFTERNOON IN THE JAMES RIVER VALLEY.
THE SURFACE PRESSURE GRADIENT WILL WEAKEN RELATIVELY QUICKLY,
LETTING WINDS DIMINISH THROUGH THE DAY, DECREASING THE BLOWING
SNOW THREAT BEFORE WEAK WINDS OVERNIGHT. A STOUT SURFACE HIGH
PRESSURE WILL BUILD IN BEHIND THE EXITING SYSTEM, BRINGING A
PUSH OF ARCTIC AIR THURSDAY NIGHT INTO FRIDAY, WHICH NBM
TEMPERATURE PERCENTILES SHOW AS THE COLDEST NIGHT OF THE PERIOD.
FORECAST LOWS RANGE FROM 15 DEGREES BELOW ZERO NORTH TO AROUND
ZERO SOUTHWEST. WE WILL LIKELY BE APPROACHING COLD WEATHER
ADVISORY CRITERIA ACROSS THE NORTH (30 BELOW), BUT NOT SURE WE
WILL REACH THAT THRESHOLD.
ANOTHER SHOT OF SNOW IS POSSIBLE ON FRIDAY (20 TO 35 PERCENT
CHANCE) AS A PROGRESSIVE, SHALLOW SHORTWAVE MOVES THROUGH
NORTHWEST FLOW. THE PROBABILITY OF EXCEEDING ONE INCH OF SNOW
WITH THIS WAVE IS LOW. HIGHS ON FRIDAY AND SATURDAY WILL VARY
SIGNIFICANTLY ACROSS THE STATE, RANGING FROM AROUND 10 DEGREES
NORTH CENTRAL AND EAST TO AROUND FREEZING SOUTHWEST, AS UPPER
RIDGING BEGINS TO BUILD OUT WEST.
THE RIDGE AXIS BEGINS TO SHIFT WEST AND FLATTEN LATE IN THE
WEEKEND, WARMING TEMPERATURES TO NEAR NORMAL EAST AND WELL ABOVE
NORMAL WEST. THERE ARE SOME SIGNS OF A WAVE MOVING THROUGH ON
SUNDAY, BUT BLENDED PRECIPITATION CHANCES ARE STILL VERY LOW.
FOR THE WEEK OF CHRISTMAS, CONTINUED HIGH CONFIDENCE IN ABOVE
AVERAGE TEMPERATURES, WITH A MEDIUM PROBABILITY OF HIGHS
EXCEEDING 40 DEGREES F ON MONDAY AND CHRISTMAS EVE IN SOUTHWEST
NORTH DAKOTA. SEASONABLY MILD TEMPERATURES ARE FAVORED TO
CONTINUE THROUGH THE WEEK, ALTHOUGH IT SHOULD BE NOTED THAT THE
PATTERN IS NOT NECESSARILY DRY, SO THE FORECAST IS STILL WORTH
WATCHING IF YOU HAVE HOLIDAY TRAVEL PLANS.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 1246 AM CST WED DEC 18 2024
MVFR CEILINGS ACROSS SOUTHERN NORTH DAKOTA ARE LIKELY TO LIFT
OVERNIGHT, EXCEPT IN THE SOUTHWEST WHERE THEY MAY PERSIST THROUGH
THE FORECAST PERIOD. A STRONG ALBERTA CLIPPER WILL BRING MULTIPLE
HAZARDS ACROSS WESTERN AND CENTRAL NORTH DAKOTA WEDNESDAY AFTERNOON
THROUGH WEDNESDAY NIGHT. SNOW WITH IFR/LIFR VISIBILITY IS EXPECTED
TO BEGIN IN NORTHWEST NORTH DAKOTA WEDNESDAY AFTERNOON, SPREADING
SOUTH AND EAST THROUGH THE EVENING. WESTERN AND SOUTHERN PARTS OF
THE STATE COULD SEE A PERIOD OF MIXED PRECIPITATION WEDNESDAY
EVENING, INCLUDING FREEZING RAIN AND SLEET. WINDS WILL BECOME SOUTH-
SOUTHEAST WEDNESDAY AFTERNOON AROUND 10-15 KTS, GUSTING TO 25 KTS IN
THE WEST. BY THE END OF THE FORECAST PERIOD, WINDS IN FAR WESTERN
PARTS OF THE STATE WILL BEGIN TURNING TO THE NORTHWEST AND BECOME
VERY STRONG. LOW LEVEL WIND SHEAR IS EXPECTED ACROSS WESTERN AND
SOUTH CENTRAL NORTH DAKOTA WEDNESDAY EVENING.
BIS WATCHES/WARNINGS/ADVISORIES
WINTER STORM WATCH FROM NOON CST TODAY THROUGH THURSDAY
MORNING FOR NDZ001>003-009>011.
WINTER STORM WATCH FROM THIS EVENING THROUGH THURSDAY
AFTERNOON FOR NDZ004-005-012-013-022-023-025-037.
UPDATE...HOLLAN
DISCUSSION...JONES
AVIATION...HOLLAN
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