084
FXUS63 KGRR 171738
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
1238 PM EST TUE DEC 17 2024
KEY MESSAGES
- LIGHT SNOW ACCUMULATION WEDNESDAY MORNING
- ACCUMULATING SNOW AND SLICK ROADS FAVORED LATE THU TO EARLY FRI
- COLD WEEKEND
DISCUSSION
ISSUED AT 340 AM EST TUE DEC 17 2024
- LIGHT SNOW ACCUMULATION WEDNESDAY MORNING
OF THE TWO CLIPPER-STYLE TROUGHS TO AFFECT US THROUGH THE WORKWEEK,
LATE TONIGHT TO WEDNESDAY MORNING IS LIKELY TO BE MORE MODEST
WITH SNOW AMOUNTS AND IMPACTS. THE 500 MB TROUGHS (ONE FROM THE
NORTHWEST CONUS AND ONE FROM NORTHERN ALBERTA/SASK) WILL NOT BE
WELL PHASED AS THEY APPROACH MICHIGAN, AND THE 850-SURFACE LOW WILL
BE MORE OPEN AND FOCUSED OVER THE OHIO RIVER VALLEY. AS A RESULT OF
RATHER PALTRY LIFT AND REMNANTS OF DRY AIR AT AND BELOW THE DGZ, QPF
SHOULD BE IN THE BALLPARK OF 0.10 INCH, THOUGH THERE ARE PLENTY OF
ENSEMBLE MEMBERS THAT YIELD LESS.
PER THE HREF, SNOW MAY START IN WEST MICHIGAN AFTER 1 AM WEDNESDAY,
BUT IS MORE LIKELY TO AFFECT A LARGER PORTION OF SOUTHWEST TO SOUTH-
CENTRAL MICHIGAN BETWEEN 6 AM AND 11 AM. MORNING LOW TEMPERATURES AT
OR BELOW 32 MAY HELP ROAD TEMPERATURES BE MARGINALLY RECEPTIVE TO
BECOMING SLICK DURING THE MORNING COMMUTE WITH THIS INCH-OR-LESS
SNOWFALL, BUT ANY IMPACTS SHOULD BE SHORT LIVED AS TEMPERATURES
TREND TOWARD THE MID 30S.
- ACCUMULATING SNOW AND SLICK ROADS FAVORED LATE THU TO EARLY FRI
THE NEXT CLIPPER IS LIKELY TO PRODUCE SNOW FROM MIDDAY THURSDAY
THROUGH FRIDAY MORNING. THIS WAVE IS FAVORED TO HAVE A CLOSED
LOW AT 850 MB AS IT TRACKS OVER THE SOUTHERN MICHIGAN VICINITY.
TEMPERATURES WILL BE A LITTLE COLDER THAN ON WEDNESDAY. MEAN QPF
IS ABOUT 0.1 INCH AT KALAMAZOO AND 0.2 INCH AT BIG RAPIDS, THOUGH
PLAUSIBLE HIGHER-END AMOUNTS MAY BE DOUBLE THAT. SLICK ROAD
CONDITIONS ARE A FAIR POSSIBILITY BETWEEN THU EVENING AND FRI
MORNING FROM GENERALLY A 1 TO 3 INCH SNOWFALL.
- COLD WEEKEND
A BRIEF INTRUSION OF MODIFIED ARCTIC AIR IS LIKELY TO PASS THROUGH
OVER THE WEEKEND AS THE SYNOPTIC PATTERN ACROSS NORTH AMERICA
AMPLIFIES BEFORE BREAKING DOWN AGAIN. 850 MB TEMPERATURES DOWN TO
MINUS 15 C OR COLDER WOULD KEEP SURFACE TEMPERATURES NO WARMER THAN
THE MID 20S, AND LOWS SUNDAY MORNING MAY FALL INTO THE SINGLE DIGITS
UNDER HIGH PRESSURE. SPEAKING OF HIGH PRESSURE, UPPER-LEVEL HEIGHT
RISES ARE EXPECTED TO OCCUR ACROSS THE REGION AND UPSTREAM WHILE THE
COLDEST AIR IS PASSING THROUGH MICHIGAN, SO A FAIRLY LARGE AND
STRONG SURFACE HIGH OVER MANITOBA/MINNESOTA MAY TURN OUR SURFACE
WINDS MORE NORTHERLY AND LIMIT THE INLAND EXTENT OF LAKE-EFFECT
SNOW ON SATURDAY.
AVIATION /18Z TAFS THROUGH 18Z WEDNESDAY/
ISSUED AT 1238 PM EST TUE DEC 17 2024
MVFR CIGS AROUND 2000 FT WILL PERSIST THROUGH THE DAY. THERE IS A
LOW CHANCE THAT A POCKET OF CLEARING SEEN ON SATELLITE JUST NORTH
OF ORD COULD ALLOW FOR CIGS TO BRIEFLY HIT VFR FOR AZO/BTL/JXN
LATE THIS AFTERNOON. HOWEVER, GIVEN CLOUD COVER TRENDS THIS
MORNING HAVE OPTED FOR A PERSISTENCE FORECAST OF MVFR. LIGHT SNOW
MOVES IN FROM WEST TO EAST BETWEEN 06-12Z. IFR CIGS ARE LIKELY
AFTER 12Z AT BTL/JXN WITH A LOWER CHANCE AT AZO/LAN BEING ON THE
EDGES OF THE FORECASTED LOW-LEVEL MOISTURE ENHANCEMENT. THIS WILL
SUPPORT MVFR AND POSSIBLY BRIEF PERIODS OF IFR VISBYS IN SNOW
SHOWERS FOR AZO/BTL/LAN/JXN AFTER 12Z. SNOW SHOWERS WILL BE
EXITING THE AREA JUST BEFORE 18Z THOUGH MVFR CIGS WILL REMAIN.
WESTERLY WINDS TO 15-20 KNOTS THIS AFTERNOON DIMINISH TO 5 KNOTS
OR LESS AND BECOME VARIABLE OVERNIGHT. WINDS INCREASE TO 5-10
KNOTS FROM THE WEST AGAIN AFTER DAYBREAK WEDNESDAY.
GRR WATCHES/WARNINGS/ADVISORIES
MI...NONE.
MARINE...SMALL CRAFT ADVISORY UNTIL 7 PM EST THIS EVENING FOR LMZ844>849.
DISCUSSION...CAS
AVIATION...THOMAS
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