145  
FXUS63 KBIS 221046  
AFDBIS  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE BISMARCK ND  
446 AM CST SUN DEC 22 2024  
   
KEY MESSAGES  
 
- FREEZING RAIN IS EXPECTED ACROSS NORTHWEST AND CENTRAL NORTH  
DAKOTA LATER THIS MORNING THROUGH EARLY THIS EVENING. ICE  
ACCUMULATIONS UP TO ONE TENTH OF AN INCH CENTRAL AND TWO  
TENTHS OF AN INCH NORTHWEST ARE POSSIBLE.  
 
- THE FREEZING RAIN COULD MIX WITH OR CHANGE OVER TO SNOW THIS  
AFTERNOON AND EVENING, WITH SNOW ACCUMULATIONS UP TO ONE INCH.  
 
- AREAS OF DENSE FOG WILL IMPACT PARTS OF NORTHWEST AND NORTH  
CENTRAL NORTH DAKOTA THIS MORNING, AND WILL BE POSSIBLE AGAIN  
ACROSS ALL BUT SOUTHWEST NORTH DAKOTA TONIGHT THROUGH MONDAY  
MORNING.  
 
- ABOVE NORMAL TEMPERATURES ARE EXPECTED CHRISTMAS EVE THROUGH  
THE END OF THE WEEK.  
 
 
   
DISCUSSION  
 
ISSUED AT 444 AM CST SUN DEC 22 2024  
 
A BROAD AREA OF WEAK SURFACE TROUGHING UNDERNEATH TRANSIENT MID TO  
UPPER LEVEL RIDGING EXTENDS FROM SOUTHERN SASKATCHEWAN THROUGH THE  
WESTERN AND CENTRAL DAKOTAS EARLY THIS MORNING. DENSE FOG HAS  
DEVELOPED ACROSS NORTHWEST AND NORTH CENTRAL NORTH DAKOTA. THE FOG  
MAY CONTINUE TO SLOWLY EXPAND SOUTHWARD THROUGH MID MORNING AND LIFT  
FROM WEST TO EAST AS PRECIPITATION ENTERS THE STATE LATER THIS  
MORNING. SOME PARTS OF NORTH CENTRAL NORTH DAKOTA COULD SEE THE FOG  
PERSIST THROUGH THE AFTERNOON.  
 
A MID LEVEL SHORTWAVE WILL GLIDE FROM SOUTHERN ALBERTA THIS MORNING  
TO THE CENTRAL DAKOTAS THIS EVENING. CONFIDENCE REMAINS HIGH THAT  
THIS WAVE WILL PRODUCE A BAND OF LIGHT PRECIPITATION, WITH MAXIMUM  
LIQUID EQUIVALENT AMOUNTS VERY UNLIKELY TO EXCEED ONE QUARTER INCH,  
FROM NORTHWEST TO CENTRAL NORTH DAKOTA FROM MID MORNING INTO THE  
EVENING. RAP ANALYSIS SHOWS MAXIMUM TEMPERATURES ALOFT THIS MORNING  
ARE WELL ABOVE FREEZING, AND ARE EXPECTED TO REMAIN SO AS  
PRECIPITATION ENTERS NORTHWEST NORTH DAKOTA. WE THEREFORE EXPECT  
FREEZING RAIN AS THE DOMINANT PRECIPITATION TYPE IN THE NORTHWEST,  
WHERE A WINTER WEATHER ADVISORY FOR UP TO TWO TENTHS OF AN INCH OF  
ICE IS IN EFFECT. DURING THE AFTERNOON, THE MAJOR AXIS OF THE BAND  
OF PRECIPITATION IS FORECAST TO BE LOCATED FROM NORTHWEST TO CENTRAL  
NORTH DAKOTA, WITH A SLOW SOUTHEAST MOTION. WET-BULB COOLING IS  
EXPECTED TO TRANSITION THE DOMINANT PRECIPITATION TYPE FROM FREEZING  
RAIN TO SNOW, BUT IT REMAINS UNCERTAIN EXACTLY WHEN THIS PROCESS  
WILL OCCUR, WITH POSSIBLE OUTCOMES RANGING FROM AS EARLY AS NOON TO  
AS LATE AS 6 PM CST. IT IS ALSO POSSIBLE THAT TEMPERATURES ALOFT  
COOL SUFFICIENTLY FOR SNOW ONLY WHERE PRECIPITATION RATES ARE  
HIGHEST, LEAVING SURROUNDING EDGES AS LIGHTER FREEZING RAIN.  
CONFIDENCE IN AT LEAST A GLAZE OF ICE ACCUMULATION IS NOW HIGH  
ENOUGH TO ADD MUCH OF CENTRAL NORTH DAKOTA TO THE WINTER WEATHER  
ADVISORY, INCLUDING BISMARCK/MANDAN, BEULAH/HAZEN, AND MINOT. BUT  
THE THREAT FOR HIGHER ICE ACCUMULATIONS IS NOT AS GREAT HERE AS IT  
IS IN THE NORTHWEST. AT THIS TIME, ANY SNOW ACCUMULATIONS ARE  
EXPECTED TO REMAIN UNDER AN INCH, BUT THIS COULD CHANGE IF  
PRECIPITATION TRANSITIONS TO SNOW EARLIER AND/OR IS HEAVIER, THE  
LATTER OF WHICH IS PROJECTED BY A FEW CAMS.  
 
ACCUMULATING PRECIPITATION IS EXPECTED TO END FROM NORTHWEST TO  
SOUTHEAST THROUGH THE EVENING AS THE MID LEVEL WAVE DEPARTS.  
HOWEVER, MODEL GUIDANCE SHOWS POTENTIAL FOR ANOTHER ROUND OF DENSE  
FOG TONIGHT INTO MONDAY, POSSIBLY MORE WIDESPREAD THAN THIS MORNING.  
ANOTHER CONCERN THAT BEARS WATCHING OVER THIS TIME FRAME IS THE  
POTENTIAL FOR A DEEP ENOUGH OF A NEAR-SURFACE SATURATED LAYER  
COMBINING WITH LOW LEVEL FRONTOGENESIS TO PRODUCE LIGHT FREEZING  
DRIZZLE ACROSS CENTRAL NORTH DAKOTA. THIS ASPECT OF THE FORECAST MAY  
NEED TO BE FINE-TUNED AS THE DAY PROGRESSES.  
 
ABOVE FREEZING HIGH TEMPERATURES ARE EXPECTED TODAY FOR AREAS ALONG  
AND SOUTHWEST OF A LINE FROM WATFORD CITY TO FORT YATES, POSSIBLY  
REACHING THE MID 40S ALONG THE HIGHWAY 12 CORRIDOR. THE FORECAST  
HIGH TEMPERATURE GRADIENT IS SHARP ACROSS OUR AREA, COOLING TO AS  
LOW AS THE MID TEENS FROM THE TURTLE MOUNTAINS TO THE DEVILS LAKE  
BASIN. THE LOW TEMPERATURE FORECAST FOR TONIGHT MAINTAINS A SIMILAR  
GEOGRAPHIC GRADIENT, RANGING FROM THE SINGLE DIGITS ABOVE ZERO NORTH  
AND EAST TO AROUND 20 ABOVE SOUTHWEST.  
 
THE FAVORED SYNOPTIC PATTERN FOR MONDAY THROUGH AT LEAST THURSDAY  
CAN BE CHARACTERIZED BY A SERIES OF TRANSIENT RIDGES AND TROUGHS  
EMBEDDED IN SPLIT FLOW. THIS PATTERN IS EXPECTED TO ALLOW MILDER  
PACIFIC AIR TO SPILL OVER THE ROCKIES, BRINGING ABOVE NORMAL  
TEMPERATURES TO THE REGION FOR MOST OF THE HOLIDAY WEEK. THE EASTERN  
HALF OF THE STATE WILL LIKELY REMAIN IN THE 20S ON MONDAY ON ACCOUNT  
OF POOR TO NO BOUNDARY LAYER MIXING AND THE POTENTIAL FOR LOW  
STRATUS TO PERSIST THROUGH THE DAY. A DRYING WARM AIR ADVECTION IN  
THE LOWER LEVELS MONDAY NIGHT SHOULD HELP SCOUR OUT THE RESIDUAL  
BOUNDARY LAYER MOISTURE, PAVING THE WAY FOR HIGH TEMPERATURES MOSTLY  
AROUND 30 TO 35 NORTH AND EAST OF THE MISSOURI RIVER, AND 35 TO 45  
SOUTHWEST OF THE RIVER CHRISTMAS EVE THROUGH SATURDAY.  
 
THE NBM PROBABILITY OF PRECIPITATION DOES NOT EXCEED 15 PERCENT AT  
ANY TIME OR LOCATION THROUGHOUT THE EXTENDED PERIOD. HOWEVER, THERE  
IS A SYSTEM TO BE MONITORED AFTER CHRISTMAS DAY. THERE IS  
UNCERTAINTY IN THE PHASING OF TWO SEPARATE SHORTWAVES EJECTING INTO  
THE CENTRAL CONUS LATER THIS WEEK. ONE SCENARIO (ABOUT 70 PERCENT  
ENSEMBLE MEMBERSHIP) KEEPS THESE WAVES SEPARATE, AND THEIR ENERGY  
DISPLACED TO OUR SOUTH AND EAST. ANOTHER SCENARIO (ABOUT 30 PERCENT  
ENSEMBLE MEMBERSHIP) CREATES A FUJIWARA EFFECT WITH THE FIRST WAVE  
WRAPPING BACK INTO THE SECOND ONE. THIS OUTCOME WOULD INTRODUCE  
CHANCES FOR MIXED PRECIPITATION FROM LATE THURSDAY THROUGH FRIDAY,  
AS BOTH NEAR-SURFACE AIR TEMPERATURES AND MAXIMUM TEMPERATURES ALOFT  
ARE FORECAST TO BE AROUND FREEZING.  
 
 
   
AVIATION /06Z TAFS THROUGH 06Z MONDAY/  
 
ISSUED AT 957 PM CST SAT DEC 21 2024  
 
VFR CONDITIONS TO BEGIN THE 06Z TAF PERIOD ACROSS THE FORECAST  
AREA. FOG HAS DISSIPATED AROUND THE TURTLE MOUNTAINS, BUT LOW  
STRATUS/FOG IS FORECAST TO DEVELOP HERE AFTER MIDNIGHT AND  
SPREAD SOUTH INTO SUNDAY MORNING. THE SOUTHERN EXTENT OF THE FOG  
SUNDAY MORNING IS NOT AS FAR SOUTH AS EARLIER RUNS OF THE SHORT  
TERM MODELS AND FOG/STRATUS MAY STOP SHORT OF KBIS, IN ADDITION  
TO KDIK. ON SUNDAY, BEGINNING AROUND 15 UTC, MIXED  
PRECIPITATION WILL MOVE INTO NORTHWEST NORTH DAKOTA, TRACKING  
SOUTHEAST THROUGH THE REMAINDER OF THE DAY. KXWA WOULD BE THE  
MOST LIKELY TAF SITE TO RECEIVE FZRA SUNDAY, BUT A BRIEF PERIOD  
CAN'T BE RULED OUT AT KDIK, KMOT AND KBIS. HOWEVER KDIK  
PROBABILITIES ARE QUITE LOW, AND KMOT AND KBIS WOULD SEE A  
BETTER CHANCE OF FZRA AND SNOW, OR POTENTIALLY ALL SNOW. IF ANY  
PRECIP MAKES IT TO KJMS, IT WOULD BE AFT 00Z MONDAY. VARIABLE  
SURFACE WINDS GENERALLY 5-15KTS SUNDAY MORNING, THEN MORE NORTH  
TO NORTHWEST MONDAY AFTERNOON AND EVENING.  
 
 
   
BIS WATCHES/WARNINGS/ADVISORIES  
 
DENSE FOG ADVISORY UNTIL NOON CST TODAY FOR NDZ001>004-009>011.  
WINTER WEATHER ADVISORY FROM 9 AM CST /8 AM MST/ THIS MORNING  
TO 6 PM CST /5 PM MST/ THIS EVENING FOR NDZ001-002-009-010-017-  
018-031-032.  
WINTER WEATHER ADVISORY FROM NOON CST /11 AM MST/ TODAY TO 9  
PM CST /8 PM MST/ THIS EVENING FOR NDZ011-019>021-034-035.  
 
 
 
 
 
DISCUSSION...HOLLAN  
AVIATION...TWH  
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