394
FXUS63 KBIS 181036
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
436 AM CST WED DEC 18 2024
KEY MESSAGES
- AN ALBERTA CLIPPER WILL CAUSE NUMEROUS FORMS OF HAZARDOUS
WEATHER ACROSS WESTERN AND CENTRAL NORTH DAKOTA THIS AFTERNOON
THROUGH THURSDAY.
- HIGH CHANCES FOR EXCEEDING 4 INCHES OF SNOW, MEDIUM CHANCES
FOR EXCEEDING 6 INCHES, AND LOW CHANCES FOR EXCEEDING 8 INCHES
ACROSS NORTHERN NORTH DAKOTA INTO THE JAMES RIVER VALLEY.
- VERY STRONG NORTHWEST WINDS ACROSS WESTERN AND SOUTH CENTRAL
NORTH DAKOTA TONIGHT THROUGH THURSDAY, WITH GUSTS AS HIGH AS
65 MPH IN THE SOUTHWEST WHERE A HIGH WIND WATCH HAS BEEN
ISSUED.
- BLOWING SNOW COULD SIGNIFICANTLY REDUCE VISIBILITY FROM
NORTHWEST TO SOUTH CENTRAL NORTH DAKOTA LATE TONIGHT THROUGH
THURSDAY.
- MEDIUM CHANCES FOR FREEZING RAIN ACROSS WESTERN AND SOUTH
CENTRAL NORTH DAKOTA LATE THIS AFTERNOON THROUGH THIS EVENING,
WITH ICE ACCUMULATIONS UP TO A FEW HUNDREDTHS OF AN INCH.
DISCUSSION
ISSUED AT 436 AM CST WED DEC 18 2024
VERY COMPLEX AND CHALLENGING FORECAST FOR TODAY THROUGH THURSDAY. A
STRONG ALBERTA CLIPPER WILL BRING IMPACTFUL WEATHER TO ALL PARTS OF
WESTERN AND CENTRAL NORTH DAKOTA BEGINNING THIS AFTERNOON AND
LASTING THROUGH THURSDAY AFTERNOON. INDIVIDUAL ASPECTS OF THIS
SYSTEM ARE DISCUSSED SEPARATELY BELOW:
1) FORECAST CONFIDENCE/UNCERTAINTY: THERE IS VERY HIGH CONFIDENCE IN
THE OCCURRENCE OF IMPACTS, AND SLIGHTLY LOWER BUT STILL MEDIUM TO
HIGH CONFIDENCE IN THE SEVERITY OF IMPACTS. THERE IS LOWER
CONFIDENCE THOUGH IN THE EXACT TRACK OF THE CENTER OF THE SURFACE
LOW, WHICH WILL GREATLY INFLUENCE THE TYPE AND SEVERITY OF IMPACTS
AT ANY GIVEN LOCATION. IN GENERAL, 00Z GLOBAL MODELS/ENSEMBLES ARE
SHIFTED SLIGHTLY SOUTH OF 00Z CAMS, WHICH IS A WELL-DOCUMENTED
SYSTEMATIC MODEL BIAS FOR THESE TYPES OF SYSTEMS. THE NBM SLIGHTLY
FAVORS THE FURTHER NORTH SOLUTION, AS IT IS MORE HEAVILY WEIGHTED
TOWARD HIGHER-RESOLUTION GUIDANCE AT SHORTER TIME RANGES.
THEREFORE, WHILE OUR CURRENT FORECAST IS MORE REFLECTIVE OF THE
NBM, WE THINK THAT IF THERE IS A SHIFT IN SNOW AMOUNTS, IT IS
MORE LIKELY TO BE A SOUTHWARD SHIFT RATHER THAN A NORTHWARD
SHIFT.
2) SNOW AMOUNTS: BOTH SYNOPTIC AND MESOSCALE FORCING MECHANISMS WILL
BE AT PLAY FOR THIS EVENT. THE SYNOPTIC FORCING ALONE IS LIKELY TO
PRODUCE OVER 4 INCHES, BUT IT SEEMS THAT THE MESOSCALE FORCING WILL
BE REQUIRED FOR +6 INCH AMOUNTS. THERE IS HIGH CONFIDENCE THAT THERE
WILL BE A NARROW BAND OF AT LEAST 6 INCHES AND POSSIBLY AS HIGH AS 8
INCHES SOMEWHERE ALONG AND NORTH OF A LINE FROM WILLISTON TO
JAMESTOWN, BUT THE EXACT LOCATION IS LIKELY TO REMAIN UNKNOWN UNTIL
THE BANDING HAS DEVELOPED. BECAUSE THIS BANDING IS EXPECTED TO BE
THE DIFFERENCE BETWEEN ADVISORY AND WARNING LEVEL IMPACTS, THE
WINTER STORM WATCH WILL REMAIN IN EFFECT UNTIL WE HAVE HIGHER
CONFIDENCE IN THE LOCATION OF THE BANDED SNOW, WHICH AGAIN MAY NOT
OCCUR UNTIL AFTER THE WATCH GOES INTO EFFECT.
3) PRECIPITATION TYPE: ABOVE FREEZING TEMPERATURES ALOFT WILL
INTRODUCE MIXED PRECIPITATION TYPES TO WESTERN AND SOUTH CENTRAL
PARTS OF THE STATE LATE THIS AFTERNOON THROUGH THIS EVENING. THIS
PART OF THE SYSTEM SHOULD NOT OVERLAP WITH THE STRATIFORM SNOW TO
THE NORTH, AND CAMS SHOW A MORE SHOWERY APPEARANCE IN REFLECTIVITY
OUTPUT, WITH ALL TYPES POSSIBLE. MOST AREAS FROM WEST CENTRAL TO
SOUTH CENTRAL NORTH DAKOTA HAVE AROUND A 3 TO 6 HOUR WINDOW DURING
WHICH FREEZING RAIN IS THE MOST LIKELY TYPE. ICE ACCUMULATIONS ARE
UNLIKELY TO EXCEED A FEW HUNDREDTHS OF AN INCH, BUT IT ONLY TAKES
TRACE AMOUNTS TO CAUSE IMPACTS, AND THE FREEZING RAIN COULD BE WIND
DRIVEN. A WINTER WEATHER ADVISORY HAS BEEN ISSUED TO COVER THIS
HAZARD.
4) WINDS: THERE IS GROWING CONCERN FOR A HIGHER-END WIND EVENT IN
SOUTHWEST NORTH DAKOTA LATE TONIGHT THROUGH THURSDAY MORNING.
ALL REQUISITE PHYSICAL PROCESSES FOR STRONG MOMENTUM TRANSFER
ARE PRESENT IN DETERMINISTIC GUIDANCE, AND MEAN 900-800 MB WINDS
ARE VERY LIKELY TO EXCEED 50 KTS AND COULD BE AS HIGH AS 65
KTS. THE ONLY THING POSSIBLY WORKING AGAINST A HIGH WIND EVENT
IS THE OVERNIGHT AND EARLY MORNING TIMING OF THE FRONTAL
PASSAGE. HOWEVER, DETERMINISTIC GUIDANCE DOES SHOW LOW LEVEL
LAPSE RATES AROUND 7 C/KM WITH THE FRONTAL PASSAGE, AND IN
SITUATIONS WITH THIS MAGNITUDE OF PRESSURE RISES AND COLD AIR
ADVECTION, THE UNFAVORABLE TIME OF DAY USUALLY ONLY SEEMS TO
LIMIT THE DURATION OF MAXIMUM WIND GUSTS RATHER THAN COMPLETELY
INHIBITING THEM. THEREFORE, A HIGH WIND WATCH HAS BEEN ISSUED
FOR SOUTHWEST AND FAR SOUTH CENTRAL NORTH DAKOTA. WINDY
CONDITIONS ARE STILL EXPECTED ELSEWHERE OVER THIS TIME PERIOD,
WITH INTENSITY DECREASING TO THE NORTHEAST.
5) BLOWING SNOW: THERE IS UNCERTAINTY ON HOW MUCH THE STRONG WINDS
WILL OVERLAP WITH FRESH SNOW ACCUMULATIONS. CONCEPTUALLY SPEAKING,
IT SEEMS MORE LIKELY THAT HIGHER AMOUNTS OF BLOWABLE SNOW WILL
REMAIN DISPLACED TO THE NORTH OF THE STRONGEST WINDS. HOWEVER, THERE
ARE AT LEAST MEDIUM CHANCES FOR IMPACTFUL BLOWING SNOW (VISIBILITY
LESS THAN ONE HALF MILE IN OPEN AREAS) FROM NORTHWEST TO SOUTH
CENTRAL NORTH DAKOTA LATE TONIGHT THROUGH THURSDAY AFTERNOON. THE
SAME WINTER WEATHER ADVISORY THAT COVERS THE FREEZING RAIN THREAT
THIS EVENING CONTINUES INTO THURSDAY TO COVER THE BLOWING SNOW
POTENTIAL.
6) TIMING OF IMPACTS: SNOW WILL MOVE INTO NORTHWEST NORTH DAKOTA BY
MID AFTERNOON AND QUICKLY SPREAD SOUTH AND EASTWARD, REACHING THE
JAMES RIVER VALLEY EARLY THIS EVENING. THE HREF SHOWS MEDIUM TO HIGH
PROBABILITIES FOR SNOWFALL RATES EXCEEDING ONE INCH PER HOUR WITHIN
THE WINTER STORM WATCH THIS EVENING. SNOW IS EXPECTED TO CONTINUE
NORTH AND EAST OF THE MISSOURI RIVER THROUGH TONIGHT, WHILE AREAS TO
THE SOUTH AND WEST TRANSITION TO THE PREVIOUSLY MENTIONED MIXED
PRECIPITATION. CHANCES FOR SNOW DECREASE FROM WEST TO EAST LATE
TONIGHT THROUGH THURSDAY, BUT THERE IS GREATER UNCERTAINTY IN END
TIME ALONG AND EAST OF HIGHWAY 83.
7) TEMPERATURES: CLOUD COVER HAS KEPT EARLY MORNING TEMPERATURES A
BIT WARMER THAN EXPECTED, EXCEPT FAR NORTH CENTRAL WHERE CLEARER
SKIES HAVE ALLOWED TEMPERATURES TO FALL BELOW ZERO. AFTERNOON
TEMPERATURES WILL SLOWLY RISE TO JUST ABOVE ZERO IN THE TURTLE
MOUNTAINS TO THE MID 20S IN THE SOUTHWEST CORNER OF THE STATE. DAILY
HIGH TEMPERATURES FOR MOST AREAS ARE EXPECTED LATER THIS EVENING
WHEN THE WARM SECTOR OF THE CLIPPER WILL HAVE ITS GREATEST COVERAGE
OVER THE STATE, WITH VALUES RANGING FROM AROUND 5 ABOVE ZERO NORTH
TO AS WARM AS THE MID 30S SOUTHWEST. THURSDAY WILL THEN SEE THE
OPPOSITE EFFECT, WITH DAILY HIGH TEMPERATURES OCCURRING BEFORE
SUNRISE. BY THURSDAY AFTERNOON, MOST OF THE STATE WILL SEE
TEMPERATURES IN THE SINGLE DIGITS ABOVE ZERO, WITH TEENS IN THE
SOUTHEAST. THURSDAY NIGHT WILL BE VERY COLD, WITH LOWS IN THE TEENS
BELOW ZERO NORTH TO SINGLE DIGITS BELOW SOUTH. WINDS WILL BE MUCH
LIGHTER THURSDAY NIGHT, BUT WIND CHILLS COULD STILL FALL TO AROUND
25 BELOW IN NORTHERN PARTS OF THE STATE.
ENSEMBLES FAVOR A SLOW WARMING TREND LATE THIS WEEK INTO NEXT WEEK.
A SHORTWAVE RIDING OVER A NORTHWEST-SOUTHEAST ORIENTED BAROCLINIC
ZONE COULD BRING SOME LIGHT SNOW ACROSS PARTS OF THE STATE LATE
FRIDAY INTO EARLY SATURDAY, WITH THE HIGHEST CHANCES (30 PERCENT FOR
MEASURABLE SNOW PER THE NBM) NORTH CENTRAL.
AVIATION /06Z TAFS THROUGH 06Z THURSDAY/
ISSUED AT 436 AM CST WED DEC 18 2024
MVFR CEILINGS ARE EXCEPTED TO PERSIST IN SOUTHWEST NORTH DAKOTA
THROUGH THE FORECAST PERIOD. A STRONG ALBERTA CLIPPER WILL BRING
MULTIPLE HAZARDS ACROSS WESTERN AND CENTRAL NORTH DAKOTA
THIS AFTERNOON THROUGH TONIGHT. SNOW WITH IFR/LIFR VISIBILITY
IS EXPECTED TO BEGIN IN NORTHWEST NORTH DAKOTA THIS AFTERNOON,
SPREADING SOUTH AND EAST THROUGH THE EVENING. WESTERN AND
SOUTHERN PARTS OF THE STATE COULD SEE A PERIOD OF MIXED
PRECIPITATION THIS EVENING, INCLUDING FREEZING RAIN AND SLEET.
WINDS WILL BECOME SOUTH-SOUTHEAST THIS 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
THIS EVENING.
BIS WATCHES/WARNINGS/ADVISORIES
WINTER STORM WATCH FROM NOON CST TODAY THROUGH THURSDAY
MORNING FOR NDZ001-002-009-010.
WINTER STORM WATCH FROM 3 PM CST THIS AFTERNOON THROUGH
THURSDAY AFTERNOON FOR NDZ003>005-011>013-022-023-025-037.
WINTER WEATHER ADVISORY FROM 3 PM CST /2 PM MST/ THIS
AFTERNOON TO NOON CST /11 AM MST/ THURSDAY FOR NDZ017>021-034.
WINTER WEATHER ADVISORY FROM 3 PM CST /2 PM MST/ THIS
AFTERNOON TO 1 AM CST /MIDNIGHT MST/ THURSDAY FOR NDZ031>033-
041-042-045.
HIGH WIND WATCH FROM THIS EVENING THROUGH THURSDAY AFTERNOON
FOR NDZ031>033-040>045.
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
THURSDAY FOR NDZ035-036-046>048-050-051.
DISCUSSION...HOLLAN
AVIATION...HOLLAN
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