931
FXUS63 KBIS 171200
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
600 AM CST TUE DEC 17 2024
KEY MESSAGES
- HIGH CHANCES FOR MEASURABLE SNOW WEDNESDAY INTO THURSDAY, WITH
A MEDIUM TO HIGH PROBABILITY OF AT LEAST 4 INCHES OF SNOW
ACROSS NORTH CENTRAL NORTH DAKOTA, AND A MEDIUM CHANCE OF 6
INCHES IN THE NORTH, AND A LOW CHANCE OF 8 INCHES.
- MEDIUM CHANCES OF IMPACTFUL BLOWING SNOW WEDNESDAY AFTERNOON
THROUGH THURSDAY MORNING.
- LOW TO MEDIUM CHANCES FOR FREEZING RAIN ACROSS THE SOUTHWEST
WEDNESDAY.
- 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.
- WARMER TEMPERATURES ARE STRONGLY FAVORED FOR NEXT WEEK AROUND THE
CHRISTMAS HOLIDAY.
UPDATE
ISSUED AT 600 AM CST TUE DEC 17 2024
VERY LITTLE UPDATES WERE MADE THIS MORNING, WINDS REMAIN CALM
AND SKY COVER MOSTLY OVERCAST. A SPS WAS ISSUED FOR THE MID-WEEK
SNOW STORM.
DISCUSSION
ISSUED AT 310 AM CST TUE DEC 17 2024
CURRENTLY A SHORTWAVE RIDGE IS MOVING THROUGH, WHILE A SHORTWAVE
TROUGH IS SITTING OVER MONTANA. THIS TROUGH HAS A SURFACE LOW
SITTING IN EASTERN WYOMING. THIS LOW TODAY, WILL MOVE EAST
ACROSS NEBRASKA, PRODUCING SNOW IN SOUTH DAKOTA. THE MODEL TREND
THE LAST 24 HOURS HAS SHIFTED THE SYSTEM SOUTH. THE CURRENT NBM
RUN HAS THE SNOW ALMOST COMPLETELY MISSING NORTH DAKOTA. THE
FAR SOUTHWESTERN COUNTIES HAVE A 20 PERCENT CHANCE OF SEEING
SOME LIGHT SNOW. HIGHS TODAY WILL BE RIGHT AROUND AVERAGE IN THE
SOUTH, AND ABOUT 10 DEGREES BELOW AVERAGE IN THE CENTRAL AND
NORTH. WINDS TODAY WILL BE MUCH CALMER WITH SURFACE HIGH
PRESSURE INFLUENCE FROM A HIGH IN CANADA. WEDNESDAY MORNING WILL
BE OUR FIRST MORNING THIS WEEK WITH WELL BELOW ZERO LOWS IN THE
NORTH.
THE BIG SNOW SYSTEM IS STILL SET TO TAKE AIM WEDNESDAY TO
THURSDAY. A SHORTWAVE AND LOW PRESSURE SYSTEM WILL MOVE ON SHORE
IN THE PACIFIC NORTHWEST TONIGHT, WHILE NORTHWEST FLOW REMAINS
OVER US. WEDNESDAY AFTERNOON THE FLOW WILL TURN TO A DIVERGENT
SOUTHWEST PATTERN, JUST AHEAD OF THE LOW. VERY STRONG Q-VECTOR
DIVERGENCE WILL BE PRESENT ACROSS THE STATE, ALONG WITH
FRONTOGENESIS (FGEN) IN THE NORTH THROUGH THURSDAY. ALL THESE
INGREDIENTS WILL CREATE A SNOW STORM STRONGER THAN THE PREVIOUS
ONES THIS FALL AND EARLY WINTER THAT WE'VE HAD. WITH EACH NBM
MODEL RUN, PROBABILITIES KEEP INCREASING FOR 4 AND 6 INCHES. FOR
4 INCHES MOST OF THE CENTRAL AND NORTH HAVE MEDIUM TO HIGH
CHANCES, AND FOR 6 INCHES THE FAR NORTH HAS A MEDIUM CHANCE.
WITH THE FGEN PRESENT IN THE NORTH, A BANDED SNOW EVENT LOOKS
VERY LIKELY, AND THIS IS WHERE 6 INCHES HAS THE HIGHEST
PROBABILITY. EVEN UP TO 8 INCHES IS NOT OUT OF THE QUESTION!
THERE ARE LOW CHANCES (ABOUT 25% CHANCE) WHERE THE SNOW BAND
SITS FOR THE 8 INCHES OF SNOW. UNFORTUNATELY WE DO NOT KNOW
WHERE EXACTLY THIS WILL SETUP, BUT IT LOOKS LIKELY SOMEWHERE
ALONG OR NORTH OF HIGHWAY 2, IN THE HIGHWAY 52 CORRIDOR. THE
SNOW WILL LAST THROUGH THURSDAY AFTERNOON. ANOTHER CONCERN WITH
THIS SYSTEM IS THE FREEZING RAIN POTENTIAL (ABOUT A 30 TO 60%
CHANCE) IN THE SOUTHWEST WEDNESDAY. SURFACE TEMPERATURES ARE IN
THE LOW 20S. MODEL SOUNDINGS HAVE A SLIGHT WARM NOSE THAT COULD
LEAD TO A BRIEF PERIOD OF FREEZING RAIN WEDNESDAY AFTERNOON AND
EVENING. A THIRD CONCERN IS THE BREEZY WINDS AS THE LOW
PRESSURE MOVES THROUGH THE STATE WEDNESDAY NIGHT. THE PRESSURE
GRADIENT IS VERY TIGHT, AND THERE IS A VERY STRONG PRESSURE
BUBBLE ON THE BACKSIDE, ENTERING INTO THE NORTHWEST. WE
INCREASED THE WIND SPEEDS FROM THE NBM FOR THIS REASON, ALONG
WITH AMPLE COLD AIR ADVECTION. MODEL SOUNDINGS SHOW MIXING TO
45KTS OF WIND AND THE EFI HAS A 0.80 VALUE WHICH USUALLY MEANS
AT LEAST ADVISORY LEVEL WINDS, AROUND 55 MPH. THIS WILL CREATE
IMPACTFUL BLOWING SNOW WHERE THERE IS NOT CRUSTED SNOW ON THE
GROUND OR WITH THE FRESH SNOW. THE STRONG WINDS WILL MOVE
NORTHWEST TO SOUTHEAST THROUGH THURSDAY. WE WILL ISSUE A SPS IN
PLACE OF A WINTER STORM WATCH FOR NOW, AS THE HIGHER SNOW TOTALS
AND BLOWING SNOW DO NOT OVERLAP, LEADING TO A CHALLENGING
HEADLINE DECISION TODAY. PLUS WE ARE NOT CONFIDENT IN THE
LOCATION OF THE 6 PLUS INCH SNOW POTENTIAL YET.
ON THE BACKSIDE OF THIS MID-WEEK SYSTEM, A LARGE WESTERN CONUS
RIDGE MOVES IN, ALONG WITH SURFACE HIGH PRESSURE. THIS WILL LEAD
TO ANOTHER SHORT COLD STRETCH WHERE LOWS COULD BE AT LEAST 15
DEGREES BELOW ZERO IN THE NORTH. ELSEWHERE WILL ALSO BE JUST
BELOW FREEZING THURSDAY NIGHT. WHERE THE SNOW DOES NOT
ACCUMULATE, HIGH TEMPERATURES WILL BE IN THE 30S, AKA THE
SOUTHWEST AND MAYBE SOUTH CENTRAL. WITH THE RIDGE AXIS NEARING
BY SUNDAY, HIGHS SHOULD BE BACK TO AVERAGE. THE QUESTION IS, IS
THE FRESH SNOW THAT WILL FALL ACCOUNTED FOR IN THE NBM FOR THESE
HIGHS? NEVERTHELESS, TEMPERATURES WILL BE WARMER THIS WEEKEND
THAN THE END OF THE WEEK TEMPERATURES. SUNDAY NIGHT MODELS ARE
HINTING AT A NORTHERN ROCKIES LOW MOVING THROUGH IN QUASI-ZONAL
FLOW. THE QPF LOOKS MINIMAL SO FAR WITH THIS. ABOVE AVERAGE
TEMPERATURES LOOK TO CONTINUE NEXT WEEK. THIS IS BACKED UP WITH
THE CPC TEMPERATURE OUTLOOK AND THE CFS FORECAST TEMPERATURES
ANOMALIES.
AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/
ISSUED AT 600 AM CST TUE DEC 17 2024
MAINLY MVFR CIGS UNTIL THIS AFTERNOON WHEN MOST TERMINALS GO
BKN VFR CIGS. WINDS WILL STAY FROM 330 5 TO 10 KNOTS THROUGH THE
PERIOD. WEDNESDAY MORNING THE NORTH WILL GO SCT WITH VERY COLD
WIND CHILLS.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...SMITH
DISCUSSION...SMITH
AVIATION...SMITH
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