846
FXUS63 KGRR 190835
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
335 AM EST THU DEC 19 2024
KEY MESSAGES
- SNOW AND POTENTIALLY SLICK ROADS THIS AFTERNOON TO FRIDAY
- COLD WEEKEND
- WARMING TREND NEXT WEEK WITH CHANCES FOR MIXED PRECIPITATION
DISCUSSION
ISSUED AT 335 AM EST THU DEC 19 2024
- SNOW AND POTENTIALLY SLICK ROADS THIS AFTERNOON TO FRIDAY
ALBERTA CLIPPER UPPER-LEVEL TROUGH WILL PROPAGATE OVER THE GREAT
LAKES TONIGHT INTO FRIDAY. THIS WAVE WILL HAVE A WELL DEVELOPED
SURFACE-850 MB LOW UPSTREAM BUT IT WILL TEND TO SLOWLY FILL AND OPEN
UP BY THE TIME IT REACHES SOUTHERN MICHIGAN FRIDAY MORNING, AS
CYCLOGENESIS OCCURS OFF THE EASTERN US. A WIDESPREAD SNOW IS STILL
EXPECTED OVER MUCH OF LOWER MICHIGAN OVER A 12-18 HOUR PERIOD AS
MIDLEVEL MOISTURE WITHIN THE TROWAL IS LOCATED WITHIN THE DGZ AND
LIFT WILL BE FREQUENTLY AUGMENTED BY WEAK BUT PERSISTENT
FRONTOGENESIS AROUND 700 MB. THERE WILL BE A LAYER OF DRIER AIR
BETWEEN THE DGZ AND THE LOWER-LEVEL BOUNDARY LAYER OVERCAST THAT
WILL NEED TO BE OVERCOME INITIALLY, AND THIS WILL HAPPEN SOONER IN
WEST-CENTRAL MICHIGAN AND LATER IN SOUTHERN MICHIGAN.
THE ADVISORY IN CENTRAL MICHIGAN IS A TOUGH LINE TO DRAW AS THIS IS
A FAIRLY COMMON SNOW EVENT FOR OUR AREA, AND IT'S FAVORABLE THAT
SNOW MAY SLOW DOWN THE FRIDAY MORNING COMMUTE WITH SLICK ROADS ALSO
TO THE SOUTH OF THE ADVISORY. THE ADVISORY FOR M-20 AND US-10
VICINITY IS WHERE RELATIVELY HIGHER EVENT-TOTAL QPF IS FAVORED,
ALONG WITH COLDER TEMPERATURES AND EARLIER ONSET THAT MAY CREATE
ROAD IMPACTS SOONER THIS EVENING. HREF PROBABILITIES OF 2-4 INCHES
IS HIGHER IN THIS BELT OF CENTRAL MICHIGAN. 0.15 TO 0.25 INCHES OF
WATER FALLING AS SNOW OVERNIGHT IS A DECENT AMOUNT WHEN IT COMES TO
ROAD IMPACTS AND SNOW TOTALS REACHING PLOWABLE/SHOVELABLE AMOUNTS.
AND AGAIN, FARTHER SOUTH, THE 1 TO 2 INCHES OF SNOW THAT MAY FALL BY
FRIDAY MORNING SHOULD ALSO CREATE SOME IMPACTS TO ROADS.
SNOW SHOULD LIGHTEN UP CONSIDERABLY BY MID DAY FRIDAY, THOUGH SOME
LAKE-EFFECT SNOW SHOWERS MAY CONTINUE DOWN US-127 FROM LAKE HURON
DURING THE AFTERNOON, AND LAKE-EFFECT SNOW SHOWERS OFF LAKE MICHIGAN
MAY AFFECT PARTS OF WEST MICHIGAN FRIDAY EVENING INTO THE NIGHT.
- COLD WEEKEND
A COLD AIRMASS OF ARCTIC ORIGIN WILL PASS THROUGH THE GREAT LAKES
SATURDAY INTO SUNDAY. HIGH PRESSURE MOVING INTO THE REGION WILL TURN
WINDS NORTHERLY SATURDAY AND GREATLY REDUCE LAKE EFFECT POTENTIAL
WHILE PROVIDING SOME CLEARER SKIES TO INTERIOR PARTS OF THE LOWER
PENINSULA. HIGH PRESSURE CENTERED OVER MICHIGAN SATURDAY NIGHT,
ALONG WITH SNOW COVER AND AREAS OF CLEAR SKIES, MAY SET UP LOW
TEMPERATURES TO FALL TO NEAR OR BELOW ZERO FOR SUNDAY MORNING IN
INTERIOR LOWER MICHIGAN.
- WARMING TREND NEXT WEEK WITH CHANCES FOR MIXED PRECIPITATION
WE'LL SEE A PATTERN SHIFT NEXT WEEK THAT WILL BRING WARMING
TEMPERATURES AND A COUPLE CHANCES FOR PRECIPITATION STARTING MONDAY.
AN UPPER LEVEL LOW WILL MOVE THROUGH THE NORTHERN GREAT LAKES.
WITHIN THE SOUTHWEST FLOW MOISTURE WILL INCREASE WITH WARM AIR
ADVECTION AND THE LOW LEVEL JET MOVING THROUGH THE AREA. THERE ARE
VARYING LOW TRACKS ALONG WITH HOW QUICKLY TEMPERATURES WARM.
INITIALLY SNOW IS EXPECTED MONDAY WITH A TRANSITION TO RAIN AS THE
TEMPERATURE PROFILE WARMS. AFTER A COLD WEEKEND, THERE COULD BE A
BRIEF PERIOD OF FREEZING RAIN DEPENDING ON HOW FAST SURFACES CAN
WARM.
THE LOW PRESSURE SYSTEM RESPONSIBLE FOR MONDAY'S WEATHER WILL
GRADUALLY WEAKEN OVERHEAD WITH HIGH PRESSURE BUILDING INTO THE AREA.
WITH THE LOW WEAKENING OVERHEAD, LOW LEVEL MOISTURE WILL REMAIN
RESULTING IN LOW CLOUDS AND POTENTIALLY SOME DRIZZLE/LIGHT RAIN.
KEPT THE NBM POPS (20-40 PERCENT) ALONG WITH PRECIPITATION TYPES OF
RAIN/FREEZING RAIN FOR CHRISTMAS EVE AND CHRISTMAS.
HIGH TEMPERATURES DURING THIS TIME WILL GO FROM THE UPPER 20S LOW
30S MONDAY TO MID 30S TO AROUND 40 FOR CHRISTMAS EVE AND CHRISTMAS
DAY WITH LOWS IN THE UPPER 20S TO LOW 30S. THIS IS AROUND 5 DEGREES
ABOVE NORMAL FOR THIS TIME OF YEAR.
AVIATION /06Z TAFS THROUGH 06Z FRIDAY/
ISSUED AT 1159 PM EST WED DEC 18 2024
MVFR CIGS AROUND 2500 FT ARE EXPECTED TO PREVAIL TONIGHT AND
THURSDAY ALTHOUGH SOME VFR CIGS SLIGHTLY ABOVE 3000 FT ARE ALSO
POSSIBLE. LIGHT SNOW MOVES INTO MKG AFTER 18Z THURSDAY WITH VSBYS
LOWERING INTO IFR CATEGORY TOWARD 00Z FRIDAY. HOWEVER FOR THE
OTHER TERMINALS THE SNOW WILL ARRIVE SEVERAL HOURS LATER AND
SHOULD BE LIGHTER.
NO SUBSTANTIAL REDUCTION IN VSBY EXPECTED SOUTH AND EAST OF GRR
UNTIL AFTER 00Z FRIDAY ALTHOUGH THERE IS LOW PROBABILITY (LESS
THAN 20 PCT) OF SOME FREEZING DRIZZLE THURSDAY AFTERNOON BEFORE
THE SNOW GETS GOING. HAVE LEFT THIS LOW PROBABILITY SCENARIO OUT
OF THE TAFS. NORTHWEST SFC WINDS 5-10 KTS BECOMING LIGHT AND
VARIABLE OVERNIGHT THEN SOUTHEASTERLY AROUND 10 KTS ON THURSDAY.
FOR THE GRR AIRPORT DSS... NO CHANGES AT THIS TIME TO WEDNESDAY'S
BRIEFING.
GRR WATCHES/WARNINGS/ADVISORIES
MI...WINTER WEATHER ADVISORY FROM 4 PM THIS AFTERNOON TO 10 AM EST
FRIDAY FOR MIZ037>040-043>046.
MARINE...NONE.
DISCUSSION...CAS/RAH
AVIATION...MEADE
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