686
FXUS63 KBIS 181835
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
1235 PM 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 TO HIGH
CHANCES FOR EXCEEDING 6 INCHES, AND LOW CHANCES FOR EXCEEDING
8 INCHES ACROSS NORTHERN NORTH DAKOTA INTO THE JAMES RIVER
VALLEY. GREATEST CHANCES FOR THE HEAVIEST SNOW IS OVER NORTH
CENTRAL AND VERY FAR NORTHWEST NORTH DAKOTA
- 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.
UPDATE
ISSUED AT 1227 PM CST WED DEC 18 2024
CLIPPER SYSTEM CONTINUES ITS APPROACH, WITH SNOW WORKING ITS WAY
THROUGH NORTHEAST MONTANA, WITH VISIBILITY DOWN TO UNDER 2
MILES AT WOLF POINT. ALL CONCERNS STATE BELOW REMAIN VALID AT
THIS TIME.
UPDATE
ISSUED AT 1005 AM CST WED DEC 18 2024
FOR MID-MORNING UPDATE MAIN CHANGE WAS TO DO WINTER WEATHER
HEADLINE CHANGES. SOUTHERN AREAS THAT WERE UNDER WINTER WEATHER
ADVISORIES AND/OR HIGH WIND WATCHES REMAIN THE SAME WITH EARLIER
CONCERNS REMAINING VALID. OVER AREAS THAT WERE UNDER A WATCH,
HAVE DECIDED TO GO WITH A WINTER STORM WARNING FROM BURKE
THROUGH ROLLETTE COUNTIES ALONG WITH MCHENRY AND PIERCE. WITH
THE TRACK OF THE LOW, SYNOPTIC FORCING LOOKS TO REMAIN QUITE
ELEVATED OVER THIS AREA BUT AS MENTIONED EARLIER, MESOSCALE
FACTORS COME INTO PLAY, WITH LATEST GUIDANCE SHIFTING A BAND OF
ELEVATED FRONTOGENESIS RIGHT THROUGH THIS AREA. WITH NBM
CONTINUING TO SHOW A 70-80 PERCENT CHANCE OF 6 INCHES OR MORE OF
SNOW, COMBINED WITH BANDING POSSIBLY SHIFTING THROUGH THIS AREA
(NOT TO MENTION THE BLOWING SNOW FACTOR), FIGURED A WARNING
WOULD BE PRUDENT GIVEN THE EXPECTED IMPACTS. TO THE SOUTH AND
WEST OF THIS AREA, CONFIDENCE IN HIGHER SNOW AMOUNTS IS NOT AS
HIGH, THUS HAVE DECIDED TO GO WITH ADVISORY (WHILE ALSO
MENTIONING THE BLOWING SNOW CONCERNS WITH POSSIBLE NEAR BLIZZARD
AT TIMES). WITH THAT SAID, SOME GUIDANCE IS PUSHING AN AREA OF
ELEVATED FRONTOGENESIS OVER PARTS OF SHERIDAN AND WELLS, BUT
STILL A LOT OF TIME BEFORE THIS COULD OCCUR AND MAY SHIFT. WITH
THAT SAID, WILL HAVE TO KEEP A CLOSE EYE ON THIS AREA TONIGHT,
AND MORE OR LESS THE HIGHWAY 52 CORRIDOR, TO SEE IF SOMETHING
SETS UP.
UPDATE
ISSUED AT 616 AM CST WED DEC 18 2024
WIDESPREAD LOW STRATUS REMAINS A FORECAST PROBLEM THIS MORNING, WITH
SURFACE RIDGING EXTENDING SOUTH FROM HIGH PRESSURE OVER SOUTHEAST
SASKATCHEWAN/SOUTHWEST MANITOBA FAILING TO CLEAR THE CLOUDS NO
FARTHER SOUTH THAN HIGHWAY 52. MODELS ARE NOT HANDLING OBSERVED
TRENDS WELL AT ALL, SO SATELLITE IMAGERY WAS RELIED ON HEAVILY FOR
UPDATES TO SKY COVER THROUGH THE MORNING.
06Z GUIDANCE DOES NOT APPEAR TO OFFER ANY SIGNIFICANT CHANGES TO THE
FORECAST FOR THE ALBERTA CLIPPER, ALTHOUGH THE HRRR HAS NOW BECOME
MORE OF A DISTINCT NORTHERN OUTLIER.
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 /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1227 PM CST WED DEC 18 2024
LOW STRATUS WILL CONTINUE THROUGH THIS AFTERNOON OVER SOUTHWEST
NORTH DAKOTA, RESULTING IN IFR TO LIFR CEILINGS AT THE KDIK
TERMINAL.
A STRONG ALBERTA CLIPPER WILL BEGIN TO IMPACT THE REGION THIS
AFTERNOON, WITH MULTIPLE HAZARDS TO AVIATION. SNOW WITH IFR TO LIFR
VISIBILITY WILL SPREAD FROM NORTHWEST TO CENTRAL NORTH DAKOTA THIS
AFTERNOON THROUGH THE EVENING, ENDING FROM WEST TO EAST LATER
TONIGHT INTO THURSDAY MORNING. A PERIOD OF MIXED PRECIPITATION,
INCLUDING FREEZING RAIN, IS ALSO LIKELY ACROSS MUCH OF WESTERN AND
SOUTH CENTRAL NORTH DAKOTA THIS EVENING. WINDS WILL BECOME SOUTH-
SOUTHEAST AROUND 10-15 KTS THIS AFTERNOON, STRONGEST IN THE WEST
WITH GUSTS TO 25 KTS. LATER TONIGHT, A VERY STRONG COLD FRONT WILL
ENTER THE STATE AND TURN WINDS TO THE NORTHWEST. THE STRONGEST WINDS
LATE TONIGHT THROUGH THURSDAY MORNING ARE EXPECTED IN SOUTHWEST AND
FAR SOUTH CENTRAL NORTH DAKOTA, WITH GUSTS AS HIGH AS 50-55 KTS.
BIS WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL NOON CST THURSDAY FOR NDZ001-009.
WINTER STORM WARNING UNTIL 3 PM CST THURSDAY FOR NDZ002>005-
012-013.
WINTER WEATHER ADVISORY UNTIL 3 PM CST THURSDAY FOR NDZ010-011-
021>023.
WINTER WEATHER ADVISORY UNTIL NOON CST /11 AM MST/ THURSDAY
FOR NDZ017>020-034.
WINTER WEATHER ADVISORY FROM 6 PM THIS EVENING TO 6 PM CST
THURSDAY FOR NDZ025-035>037-046>048-050-051.
WINTER WEATHER ADVISORY UNTIL 1 AM CST /MIDNIGHT MST/ THURSDAY
FOR NDZ031>033-041-042-045.
HIGH WIND WATCH FROM 11 PM CST /10 PM MST/ THIS EVENING
THROUGH THURSDAY AFTERNOON FOR NDZ031>033-040>045.
UPDATE...JJS
DISCUSSION...HOLLAN
AVIATION...HOLLAN/JJS
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