389
FXUS63 KGRR 200722
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
222 AM EST FRI DEC 20 2024
KEY MESSAGES
- ACCUMULATING SNOW THROUGH THE FRIDAY MORNING COMMUTE
- POTENTIAL FOR LAKE EFFECT SNOW FRIDAY EVE INTO SATURDAY MORNING
- ANOTHER ROUND OF SNOW POSSIBLE MONDAY AFTERNOON/NIGHT
UPDATE
ISSUED AT 222 AM EST FRI DEC 20 2024
OPTED FOR AN IMPACT-BASED ADVISORY FOR THE FRIDAY MORNING TRAVEL
PERIOD, TO INCLUDE AREAS FARTHER SOUTH NEAR I-96 AND I-94. BURSTS
OF HEAVIER SNOW UP TO 1 INCH PER HOUR HAVE BEEN OCCURRING THE
LAST SEVERAL HOURS NEAR I-96 ASSOCIATED WITH 700 MB FRONTOGENESIS
THAT IS WITHIN THE DGZ LAYER. LIGHTER BUT PERSISTENT SNOW IS STILL
OCCURRING IN CENTRAL MICHIGAN WITHIN THE ORIGINAL ADVISORY. DOWN
BY I-94, ISOLATED BURSTS OF SNOW MAY BECOME MORE COMMON LATER IN
THE MORNING AS THE 850-700 MB LOWS WITH THEIR FGEN SLIDE
SOUTHEAST. THE COMBINATION OF MARGINALLY WARM ROAD TEMPERATURES
AND AIR TEMPERATURES AROUND 30 HAS BEEN A GOOD RECIPE FOR ICY
ROADS TO FORM UNDERNEATH QUICK BURSTS OF SNOW.
DISCUSSION
ISSUED AT 202 PM EST THU DEC 19 2024
- ACCUMULATING SNOW THROUGH THE FRIDAY MORNING COMMUTE
ON MID LEVEL VORT MAX WAS TRACKING EASTWARD THROUGH EASTERN WI AND
WILL PUSH THROUGH OUR NORTHERN ZONES THIS EVENING. WARM AIR
ADVECTION AHEAD OF THIS FEATURE HAS RESULTED IN A BAND OF SNOW
MAINLY IN WESTERN PARTS OF THE CWA AT THIS TIME. THIS FEATURE WILL
PIVOT UP INTO THE NORTHERN ZONES WHERE THE SNOW WILL PERSIST THE
LONGEST. SURFACE TEMPERATURES REMAIN BELOW FREEZING IN THIS AREA
WHICH IS WHERE THE MOST IMPACTS FOR THE EVENING COMMUTE ARE
EXPECTED. THIS IS BASICALLY NORTH OF A LINE FROM NEAR MUSKEGON,
EAST NORTHEASTWARD TO ALMA. THIS IS THE REGION WHERE WE HAVE THE
WINTER WEATHER ADVISORY OUT FOR AND THUS NO CHANGES ARE PLANNED TO
THE HEADLINE AT THIS TIME.
ANOTHER MID LEVEL VORT MAX WAS DIGGING DOWN THE BACKSIDE OF THE
TROUGH OVER THE UPPER MS VALLEY. AS THIS TROUGH SHIFTS EAST
TONIGHT, IT SHARPENS AS A RESULT. DECENT LIFT IN THE DGZ IS SEEN
IN THE MODELS OVER OUR NORTHERN ZONES IN THE EVENING WHERE FGEN
WAS NOTED. AS THIS TROUGH SHIFTS EAST THROUGH THE CWA LATER
TONIGHT/FRIDAY MORNING, THE BAND OF SNOW WILL SHIFT SOUTH. WE
COULD SEE AN ADDITIONAL INCH OR TWO OF SNOW SOUTH OF THE ADVISORY
AREA WHICH COULD LEAD TO SOME TRAVEL IMPACTS FOR THE MORNING
COMMUTE. WE WILL NEED TO MONITOR TRENDS CLOSELY THROUGH THE
EVENING. BY MID MORNING THE BULK OF THE SNOW SHOULD BE SOUTH OF
THE CWA.
- POTENTIAL FOR LAKE EFFECT SNOW FRIDAY EVE INTO SATURDAY MORNING
ARCTIC AIR POURS IN BEHIND THE DEPARTING WAVE FRIDAY INTO SATURDAY.
MODELS HAVE BEEN INDICATING A NORTHERLY FLOW SETTING UP. COMMONLY
THIS LEADS TO LAKE EFFECT SNOW FOR THE LAKESHORE COUNTIES GIVEN
THE ENHANCED LOW LEVEL CONVERGENCE. WE WILL RAISE POPS FOR THIS
REGION, ESPECIALLY NORTH OF MUSKEGON. BUFKIT FROM THE NAM3KM AT
LUDINGTON SHOWS ALL THE MOISTURE BELOW 5K FT, BUT THE DGZ IS AT
THE TOP OF THIS MOISTURE WHICH SUPPORTS AT LEAST SOME POTENTIAL
FOR SNOW. CLOSE MONITORING FOR POSSIBLE IMPACTS FROM THIS
POTENTIAL BAND WILL BE NEEDED.
- ANOTHER ROUND OF SNOW POSSIBLE MONDAY AFTERNOON/NIGHT
A MID LEVEL WAVE TRACKS IN FROM THE WEST DURING THIS TIME. WARM
AND MOIST AIR ADVECTION AHEAD OF IT WILL DEEPEN UP THE CLOUDS AND
THE DGZ BECOMES SATURATED AT TIMES. THUS IT'S LOOKING LIKELY THAT
WE WILL SEE A BAND OF PRECIPITATION LIFTING THROUGH THE CWA DURING
THIS TIME. FORECAST SOUNDINGS SUGGEST A WARM LAYER COULD LEAD TO
THE SNOW MIXING WITH AND/CHANGING TO RAIN. IT'S ALSO POSSIBLE THAT
A PERIOD OF FREEZING RAIN COULD OCCUR. THE ENSEMBLE 24 HOUR QPF
FROM THE MODELS HAS BEEN TRENDING DOWN WHICH MAKES SENSE AS THE
DGZ IS SHOWN TO NOT MAINTAIN ITS SATURATION.
AVIATION /06Z TAFS THROUGH 06Z SATURDAY/
ISSUED AT 130 AM EST FRI DEC 20 2024
LOW PRESSURE WILL MOVE FROM ILLINOIS TO OHIO TODAY. SNOW AND
IFR/MVFR CONDITIONS ARE OCCURRING TO THE NORTH OF THE LOW ACROSS
SOUTHERN LOWER MICHIGAN INCLUDING ALL OF THE SOUTHWEST LOWER
MICHIGAN TAF SITES. VISIBILITIES RANGE FROM 1SM TO 4SM WITH
CEILINGS BETWEEN 700FT AND 2500FT. THESE CONDITIONS WILL REMAIN
THE CASE FOR THE NEXT 8-10 HOURS OR THROUGH 15Z OR SO BEFORE
CONDITIONS STEADILY IMPROVE THEREAFTER. AS THE LOW BEGINS TO MOVE
EAST AND SOUTH, THE POOR AVIATION CONDITIONS WILL MOVE AWAY WITH
IT. THROUGH THE MORNING RUSH OF AVIATION TRAFFIC THOUGH POOR
AVIATION CONDITIONS AND SNOW ARE EXPECTED TO CONTINUE.
AS WE MOVE THROUGH THE AFTERNOON AND INTO THE EVENING WE WILL
TREND TO VFR AND THE SNOW WILL COME TO AN END. WINDS WILL SHIFT
FROM EAST BEFORE DAYBREAK TO NORTH AS WE HEAD INTO THE AFTERNOON.
GRR AIRPORT DSS UPDATE
THE CHANGE IN THE FORECAST FROM WHAT WAS SENT THURSDAY AFTERNOON
IS HIGHER SNOWFALL TOTALS. WE HAVE RECEIVED 3.0 INCHES THUS FAR
AS OF 06Z/1AM AND ANOTHER INCH OR TWO IS LIKELY TO FALL BEFORE IT
TAPERS OFF AROUND 15Z/10AM. SNOWFALL RATES THROUGH DAYBREAK WILL
LIKELY REACH THE 0.40 TO 0.80 PER HOUR RANGE.
GRR WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR
MIZ037>040-043>046-050.
WINTER WEATHER ADVISORY UNTIL 10 AM EST THIS MORNING FOR MIZ051-
052-056>059-064>067-071>074.
MARINE...NONE.
UPDATE...CAS
DISCUSSION...MJS
AVIATION...DUKE
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