660
FXUS63 KGRR 181954
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
254 PM EST WED DEC 18 2024
KEY MESSAGES
- RISK FOR SNOW RELATED IMPACTS THURSDAY AFTERNOON INTO FRIDAY
- VERY COLD OVER THE WEEKEND
- PATCHY FLURRIES/SPRINKLES THIS EVENING
DISCUSSION
ISSUED AT 147 PM EST WED DEC 18 2024
- RISK FOR SNOW RELATED IMPACTS THURSDAY AFTERNOON INTO FRIDAY
AT THIS TIME, NO WINTER WEATHER HEADLINES.
MODELS CONTINUE TO SHOW A DECENT MID LEVEL WAVE TRACKING DOWN FROM
THE UPPER PLAINS THROUGH NORTHERN ILLINOIS AND INTO INDIANA LATER
THURSDAY INTO FRIDAY. AS THIS SYSTEM TRACKS TOWARDS MICHIGAN THE
DGZ MOISTENS UP NEAR AND NORTH OF INTERSTATE 96 THURSDAY MORNING,
HOWEVER BELOW THAT IT IS SHOWN TO BE RELATIVELY DRY. THIS SHOULD
ACT TO DELAY ANY STEADIER SNOW UNTIL THE AFTERNOON AND EVENING
WHEN THE LOW LEVELS MOISTEN UP. THE HRRR IS SHOWING THE REGION
FROM NEAR AND NORTH OF MUSKEGON WITH AN EARLIER ONSET OF THE SNOW
GIVEN SOME INFLUENCE OF LAKE MICHIGAN. HOWEVER OTHER HIGH RES
MODELS KEEP THIS INFLUENCE OFFSHORE FOR MOST OF THE EVENT. AS A
RESULT SOME UNCERTAINTY WITH THE TIMING AND AMOUNTS FOR THAT
REGION AS WELL. ALONG INTERSTATE 94, THE DGZ WILL BE UNSATURATED
AT TIMES FOR THIS EVENT AND THAT COULD RESULT IN A VARIETY OF
PRECIPITATION TYPES. THE MODELS DO VARY ON THE
SATURATED/UNSATURATED DGZ SCENARIO AND THAT WILL PLAY A
SIGNIFICANT ROLE ON HOW MUCH THIS SYSTEM ULTIMATELY IMPACTS THE
REGION. FOR NOW, WE WILL KEEP IT AS MAINLY A SNOW EVENT, BUT MAY
HAVE TO FEATURE SOME WINDOWS FOR MIXED PRECIPITATION, ESPECIALLY
CLOSER TO INTERSTATE 94. ALSO, THE SURFACE TEMPERATURES WILL
LIKELY BE NEAR FREEZING OR POSSIBLY A DEGREE OR TWO HIGHER IN THE
MIDDLE PART OF THURSDAY. COMMONLY THIS LEADS TO MELTING ON THE
ROADS. IF THIS IS THE CASE, IMPACTS MAY HOLD OFF UNTIL THE EVENING
COMMUTE WHEN THE SURFACES START TO COOL OFF.
THIS SYSTEM IS ALREADY FAIRLY ORGANIZED OVER THE PACIFIC NW AND
THE 500 MB TROUGH DOES SHARPEN UP AS IT TRACKS THROUGH LATER
THURSDAY NIGHT INTO FRIDAY MORNING. EASTERLY FLOW THURSDAY NIGHT
COULD DRAW SOME MOISTURE OFF OF LAKE HURON WHICH MAY LOCALLY
ENHANCE THE SNOW FOR OUR NORTHEAST ZONES. FGEN WAS NOTED IN THE
700-600 MB LEVEL AND PARTS OF OUR AREA WILL BE FAVORED FOR THE
TROWAL WHICH SHOULD EXTEND THE SNOW. THE FLOW TURNS NORTH FRIDAY
ON THE BACKSIDE OF THE DEPARTING WAVE. COMMONLY LOW LEVEL
NORTHERLY FLOW DRAWS DOWN DRIER AIR WHICH CUTS OFF THE
ACCUMULATING SNOW. THUS WE WILL FEATURE A SOONER DEPARTURE OF THE
SNOW FOR OUR NORTHERN ZONES AS COMPARED TO AREAS NEAR AND SOUTH OF
INTERSTATE 96. . BASED ON ALL THIS WE WILL GENERALLY FEATURE A 2
TO 5 INCH SNOWFALL WHICH IS IN LINE WITH MOST ENSEMBLE GUIDANCE.
ANY PROLONGED LAKE INFLUENCE COULD QUICKLY TURN THE AMOUNTS HIGHER
AND THE REGION NEAR AND NORTH OF MUSKEGON WILL NEED TO BE
MONITORED CLOSELY.
- VERY COLD OVER THE WEEKEND
AN ARCTIC HIGH PRESSURE SYSTEM WILL BE TRACKING EASTWARD THROUGH
SOUTHERN ONTARIO DURING THIS TIME. SUBSIDENCE WILL ACT TO LIMIT
THE CLOUD COVER THROUGH MOST OF THE COLUMN HERE IN MICHIGAN.
HOWEVER THERE WILL BE SOME LAKE EFFECT CLOUDS AROUND. WITH FRESH
SNOW AND LIGHT WINDS EXPECTED ALONG WITH A COLD START TO SATURDAY
NIGHT, MUCH OF THE REGION WILL LIKELY FALL INTO THE SINGLE DIGITS.
ANY CLEARING COULD EASILY LEAD TO SOME SUB ZERO READINGS,
ESPECIALLY INLAND.
- PATCHY FLURRIES/SPRINKLES THIS EVENING
THERE WILL BE A PERIOD OF LOW LEVEL CONVERGENCE AS NORTHWEST FLOW
PERSISTS THIS AFTERNOON AND EVENING. THE DGZ IS SHOWN TO BE MAINLY
DRY. THUS ANY PRECIPITATION THAT FALLS IS EXPECTED TO REMAIN VERY
LIGHT. SURFACE TEMPERATURES RANGE FROM NEAR 32 AT LUDINGTON TO THE
MID 30S AROUND BATTLE CREEK AND JACKSON. GIVEN THIS SCENARIO THE
RISK FOR FREEZING DRIZZLE IS NOT ZERO BUT WITH THE TEMPERATURE
EXPECTED TO REMAIN NEARLY STEADY THROUGH THE EVENING, WE WILL NOT
FEATURE THAT IN THE FORECAST AT THIS TIME.
-
AVIATION /18Z TAFS THROUGH 18Z THURSDAY/
ISSUED AT 1201 PM EST WED DEC 18 2024
MVFR CIGS PERSIST INTO THE EVENING, LIFTING TO VFR AFTER 02Z AS
A HIGH PRESSURE SYSTEM SLIDES SOUTH OF THE REGION. ISOLATED SNOW
SHOWERS ARE EXPECTED TO DEVELOP THIS AFTERNOON AND CONTINUE INTO
THE EVENING, WITH QUICK REDUCTIONS IN VISIBILITY LIKELY UNDER ANY
SHOWERS. GIVEN ISOLATED NATURE OF SHOWERS, HAVE CONTINUED PROB30
FOR MVFR SHSN AT ALL TAF SITES INTO THE EVENING. CONDITIONS THEN
FALL BACK TO MVFR FOR MKG AND POSSIBLY GRR AFTER 15Z THURSDAY AS
OUT NEXT SYSTEM ARRIVES. ISOLATED MVFR SNOW SHOWERS ARE POSSIBLE
AT MKG AFTER 15Z WARRANTING A PROB30 FOR THAT SITE THURSDAY
MORNING. WEST-NORTHWEST WINDS OF 5-10 KNOTS BECOME LIGHT AND
VARIABLE TONIGHT BEFORE BECOMING SOUTHEAST AT 5-10 KNOTS THURSDAY
MORNING.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 3 AM EST THURSDAY FOR LMZ844>849.
DISCUSSION...MJS
AVIATION...THOMAS
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