636  
FXUS63 KBIS 181218  
AFDBIS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BISMARCK ND  
618 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.  
 
 
   
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 /12Z TAFS THROUGH 12Z THURSDAY/  
 
ISSUED AT 616 AM CST WED DEC 18 2024  
 
CEILINGS ARE EXPECTED TO REMAIN AT MVFR TO IFR LEVELS IN SOUTHWEST  
NORTH DAKOTA THIS MORNING, POSSIBLY LIFTING TO VFR LATER THIS  
AFTERNOON. OTHERWISE, VFR CEILINGS AROUND 3,000 TO 5,000 FEET ARE  
EXPECTED THROUGH THE MORNING AND INTO THE AFTERNOON.  
 
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. LOW  
LEVEL WIND SHEAR COULD BECOME A CONCERN ACROSS PARTS OF WESTERN AND  
SOUTH CENTRAL NORTH DAKOTA THIS EVENING, BUT CONFIDENCE IN THIS HAS  
LOWERED. REGARDLESS, WINDS AROUND 1,000 TO 2,000 FEET ABOVE THE  
SURFACE ARE STILL EXPECTED TO INCREASE TO AROUND 45-60 KTS LATER  
THIS EVENING, STRONGEST IN THE SOUTHWEST CORNER OF THE STATE.  
 
 
   
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.  
 
 
 
 
 
UPDATE...HOLLAN  
DISCUSSION...HOLLAN  
AVIATION...HOLLAN  
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