464
FXUS65 KGGW 150944
AFDGGW
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GLASGOW MT
244 AM MST SUN DEC 15 2024
DISCUSSION
KEY MESSAGES:
- WINTER WEATHER ADVISORY THROUGH 11 PM TODAY FOR ALL COUNTIES
EXCEPT PETROLEUM COUNTY, PRIMARILY FOR A LIGHT GLAZE UP TO 0.2"
OF ICE AND MINOR SNOW ACCUMULATION.
- MULTIPLE DISTURBANCES ARE FORECAST FOR MONDAY NIGHT INTO
TUESDAY, AND WEDNESDAY EVENING INTO THURSDAY. LIGHT SNOW IS
EXPECTED WITH THE FIRST DISTURBANCE.
WEATHER PATTERN OVERVIEW:
IN THE MORE RECENT DEVELOPMENT OF A SURFACE LOW PRESSURE WITH A
STRONG LOW LEVEL INVERSION AND SUFFICIENT MOISTURE TRANSPORT, HIGH
RESOLUTION AND GLOBAL ENSEMBLE MODELS HAVE COME INTO AGREEMENT.
ALTHOUGH THE MAJORITY OF THE GGW CWA WILL SEE A GLAZE OF FREEZING
RAIN, THERE IS A SWATH SET UP FROM EASTERN GARFIELD NORTHEAST TO
PLENTYWOOD OF UP TO TWO TENTHS EXPECTED THROUGH THE LATE AFTERNOON
TODAY. THERE IS HIGH (60 PERCENT) CONFIDENCE PRECIPITATION WILL
TRANSITION TO SNOW BY EARLY EVENING FOR MOST OF THE AREA BEFORE
ENDING ON SUNDAY NIGHT. FOR SOUTHWEST PHILLIPS COUNTY, A LESS
DRAMATIC INVERSION WILL ALLOW MOST OF THE PRECIPITATION TO
ACCUMULATE IN THE WAY OF SNOW.
A SHORT TIME PERIOD OF DRYING IS EXPECTED WITH A SHORTWAVE RIDGE
MOVING ON MONDAY, FOLLOWED BY ANOTHER DISTURBANCE MONDAY NIGHT
INTO TUESDAY. A MORE SIMPLIFIED SNOW EVENT THAN TODAY WILL PASS
THROUGH THE AREA. THERE IS LOW TO MODERATE (30 TO 50 PERCENT)
CONFIDENCE OF SNOW ACCUMULATION SINCE THERE IS NOT MODEL
AGREEMENT ON THE STRONGEST FORCING PLACEMENT. GENERALLY HIGHER
AMOUNTS ARE EXPECTED CLOSER TO CENTRAL MONTANA.
ALTHOUGH THERE IS LOW CONFIDENCE ON TIMING AND LOCATION OF
PRECIPITATION, THERE APPEARS TO BE ANOTHER SHORTWAVE TROUGH THAT
WILL MOVE THROUGH FAIRLY ZONAL FLOW WEDNESDAY EVENING INTO
THURSDAY. ALTHOUGH DETERMINISTIC MODEL SOUNDINGS FROM THE GFS AND
ECMWF INDICATE A STRONG LOW LEVEL INVERSION WILL BE PRESENT AT THE
ONSET OF THE EVENT, THERE IS STILL LOW (20 PERCENT) CONFIDENCE ON
THE SPEED AT WHICH THIS INVERSION ERODES, AND THEREFORE
PRECIPITATION TYPE.
FORECAST CONFIDENCE & DEVIATIONS:
THERE IS HIGH CONFIDENCE PRECIPITATION WILL TRANSITION FROM
FREEZING RAIN TO SNOW BY MID AFTERNOON TODAY. THERE IS HIGH
CONFIDENCE SOUTHWEST PHILLIPS COUNTY WILL SEE ACCUMULATING SNOW
RATHER THAN FREEZING RAIN. THERE IS MODERATE CONFIDENCE ON LIGHT
SNOW ACCUMULATION OCCURRING ON MONDAY NIGHT INTO TUESDAY, WITH LOW
CONFIDENCE ON PRECIPITATION AMOUNT AND TYPE FOR THE WEDNESDAY
EVENING INTO THURSDAY SYSTEM.
AVIATION
LAST UPDATED: 0930Z
FLIGHT CAT RANGE: VFR TO IFR.
DISCUSSION: ALTHOUGH VFR CEILINGS AND VISIBILITY WILL CONTINUE
THROUGH ABOUT 12Z, A MIX OF FREEZING RAIN AND SNOW HAS BEGUN FOR
EACH TAF SITE BESIDE KGGW IN RESPONSE TO A SURFACE LOW MOVING
THROUGH THE AREA. IFR CONDITIONS ARE EXPECTED FROM AROUND 14Z TO
00Z MONDAY FOR KSDY AND KGDV. THERE IS MODERATE (50 PERCENT)
CONFIDENCE OF IFR CONDITIONS OCCURRING FOR KOLF. FOR KGGW, THERE
IS MODERATE (50 PERCENT) CONFIDENCE OF IFR CEILINGS BETWEEN 14Z
AND 19Z. THERE IS HIGH (60 TO 80 PERCENT) CONFIDENCE OF AT LEAST
A LIGHT GLAZE OF FREEZING RAIN OCCURRING BEFORE 18Z, UP TO AROUND
A TENTH OF AN INCH FOR THE TAF SITES. REGARDLESS OF AMOUNT, THERE
IS MODERATE TO HIGH CONFIDENCE THAT ICING AND SLIPPERY RUNWAYS
WILL OCCUR. FREEZING RAIN CHANCES ARE AT THEIR HIGHEST PRIMARILY
BETWEEN 09Z-15Z BEFORE TRANSITIONING TO SNOW.
WIND: LIGHT AND VARIABLE, BECOMING NORTHWEST AT 15-25 KNOTS WITH
GUSTS UP TO 35 KNOTS AFTER 18Z.
GGW WATCHES/WARNINGS/ADVISORIES
WINTER WEATHER ADVISORY UNTIL 11 PM MST THIS EVENING FOR CENTRAL
AND SOUTHEAST PHILLIPS-CENTRAL AND SOUTHERN VALLEY-DANIELS-
DAWSON-EASTERN ROOSEVELT-GARFIELD-MCCONE-NORTHERN PHILLIPS-
NORTHERN VALLEY-PRAIRIE-RICHLAND-SHERIDAN-SOUTHWEST PHILLIPS-
WESTERN ROOSEVELT-WIBAUX.
WEATHER.GOV/GLASGOW
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