748
FXUS63 KBIS 170913
AFDBIS
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE BISMARCK ND
313 AM CST TUE DEC 17 2024
KEY MESSAGES
- HIGH CHANCES FOR MEASURABLE SNOW WEDNESDAY INTO THURSDAY, WITH
A 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.
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. THE SNOW WILL LAST THROUGH THURSDAY
AFTERNOON. ANOTHER CONCERN WITH THIS SYSTEM IS THE FREEZING
RAIN POTENTIAL 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. 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 /06Z TAFS THROUGH 06Z WEDNESDAY/
ISSUED AT 310 AM CST MON DEC 16 2024
A BROAD SHIELD OF CLOUDS LOOKS TO LINGER THROUGH MUCH OF THE
FORECAST PERIOD ACROSS MOST TAF SITES. CEILINGS WILL MAINLY STAY
WITHIN THE MVFR RANGE, ALTHOUGH COULD LIFT BRIEFLY TO LOW VFR
HEIGHT, OR LOWER TO IFR HEIGHTS. PLACED IN BKN LAYERS TO COVER
THIS POTENTIAL AT MOST SITES. NORTHWEST WINDS WILL REMAIN LIGHT
THROUGH TUESDAY. BETTER CHANCES FOR SNOW RETURN TOMORROW,
MAINLY SOUTH OF INTERSTATE 94 AND HAS NOT BEEN PLACED IN ANY TAF
SITES YET.
BIS WATCHES/WARNINGS/ADVISORIES
NONE.
DISCUSSION...SMITH
AVIATION...SMITH
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