812
FXUS63 KGRR 181701
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1201 PM EST WED DEC 18 2024
KEY MESSAGES
- LIGHT SNOW SHOWERS POSSIBLY MIXING WITH RAIN TODAY
- ACCUMULATING SNOW, SLICK ROADS FAVORED THU AFTERNOON TO EARLY
FRI
- COLD WEEKEND
DISCUSSION
ISSUED AT 339 AM EST WED DEC 18 2024
- LIGHT SNOW SHOWERS POSSIBLY MIXING WITH RAIN TODAY
A NARROW BAND OF SNOW, IN LINE WITH 700 MB FRONTOGENESIS EXTENDING
FROM NORTHERN ILLINOIS TOWARD GRAND RAPIDS, IS CUTTING THROUGH DRIER
AIR AT 850 MB. THIS IS EXPECTED TO SLIDE EASTWARD ACROSS AREAS
MOSTLY SOUTH OF I-96 WITH MODEST ACCUMULATION ON GRASS POSSIBLE. IT
MAY BE WARM ENOUGH TO MIX WITH RAIN IN SOUTHWEST MICHIGAN THIS
MORNING. BEHIND THIS, COLDER 850 MB AIR AND NORTHWEST FLOW WILL
SUPPORT LAKE ENHANCED SHOWERS DEVELOPING THROUGH AFTERNOON AND LATE
EVENING. MINOR ACCUMULATIONS ARE POSSIBLE, MORE FAVORED NORTHWEST OF
A MUSKEGON TO REED CITY LINE. TEMPERATURES BY EVENING MAY BE
MARGINALLY COLD ENOUGH FOR SLICKS SPOTS UNDER ANY BRIEF MODERATE
BURSTS OF SNOW.
- ACCUMULATING SNOW, SLICK ROADS FAVORED THU AFTERNOON TO EARLY FRI
THE NEXT CLIPPER IS STILL LIKELY TO PRODUCE SNOW AND SOME IMPACTS TO
ROAD CONDITIONS THURSDAY AFTERNOON TO FRIDAY MORNING. THIS SYSTEM
WILL HAVE A BETTER DEVELOPED SURFACE-850 LOW AND SOME ENHANCEMENT TO
PRECIP TO THE NORTH OF THE TRACK VIA MIDLEVEL FGEN, AND ALSO
SLIGHTLY COLDER TEMPERATURES IN PLACE COMPARED TO WEDNESDAY. THIS IS
LIKELY TO BE A DRAWN-OUT 1-TO-4 INCH EVENT FOR MUCH OF THE AREA,
THOUGH IT'S NOT WITHOUT SOME UNCERTAINTY. THE MEAN OF THE
ECE, GEFS, AND GEPS, ALSO THE UKMET AND MOST MODELS WITHIN THE
HREF, PLACE THE CENTER OF THE SURFACE LOW OVER CHICAGO BY 06 Z FRI.
HOWEVER, THE RAP/HRRR IS A NORTH OUTLIER WITH THE LOW MORE
TOWARD GREEN BAY OR THE U.P., WHICH WOULD RESULT IN LESS SNOW AND
OCCASIONAL TRANSITIONS TO FREEZING DRIZZLE ESPECIALLY FARTHER
SOUTH.
- COLD WEEKEND
A BRIEF INTRUSION OF MODIFIED ARCTIC AIR IS LIKELY TO PASS THROUGH
OVER THE WEEKEND. 850 MB TEMPERATURES DOWN TO ABOUT -15 C
WOULD KEEP SURFACE TEMPERATURES NO WARMER THAN THE MID 20S. LOWS
SUNDAY MORNING ARE FAVORED TO FALL INTO THE SINGLE DIGITS UNDER HIGH
PRESSURE AND PARTIALLY CLEARING SKIES. LAKE EFFECT POTENTIAL
MAY BE MITIGATED LATER SATURDAY INTO SUNDAY AS UPPER-LEVEL HEIGHT
RISES ARE EXPECTED TO OCCUR ACROSS THE REGION WHILE THE LOWER-LEVEL
COLD AIR IS PASSING THROUGH. AS A RESULT, A LARGE AREA OF HIGH
PRESSURE WILL TEND TO TURN WINDS MORE NORTH-NORTHEAST ON SATURDAY.
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...CAS
AVIATION...THOMAS
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