133
FXUS63 KGRR 200837
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
337 AM EST FRI DEC 20 2024
KEY MESSAGES
- MORNING SNOW AND SLICK ROADS
- SPOTTY LAKE EFFECT SNOW SHOWERS THIS AFTERNOON INTO TONIGHT
- COLD WEEKEND
- PATTERN CHANGE TOWARDS WARMER WEATHER NEXT WEEK
- A FEW POSSIBILITIES FOR PRECIPITATION NEXT WEEK
DISCUSSION
ISSUED AT 337 AM EST FRI DEC 20 2024
- MORNING SNOW AND SLICK ROADS
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, LOCALLY 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. THIS HAS BEEN MORE
ROBUST AND A LITTLE SOUTH OF WHERE YESTERDAY'S HREF GUIDANCE WAS
SUGGESTING IT WOULD BE. LIGHTER BUT PERSISTENT SNOW CAUSING
SLOWER TRAVEL SPEEDS IS STILL OCCURRING IN CENTRAL MICHIGAN WITHIN
THE ORIGINAL ADVISORY. NORTHWEST AREAS NEAR LUDINGTON MAY SEE
SNOW TAPER OFF BY 7 AM. DOWN BY I-94, OCCASIONAL BURSTS OF SNOW
SHOULD BECOME MORE COMMON AS THE 850-700 MB LOWS WITH THEIR FGEN
SLIDE SOUTHEAST. THERE IS ONE MORE SHORTWAVE 500 MB VORT MAX
MOVING THROUGH WISCONSIN-ILLINOIS, ON THE BACK SIDE OF THE BROADER
TROUGH, THAT IS MAINTAINING HEIGHT FALLS OVER LOWER MICHIGAN
THROUGH 12Z, SUPPORTING A BACKGROUND STATE OF WIDESPREAD WEAK
SYNOPTIC-SCALE LIFT EARLY THIS MORNING. IMPACT-WISE, THE
COMBINATION OF MARGINALLY WARM ROAD TEMPERATURES AND AIR
TEMPERATURES AROUND 30 DEGREES HAS BEEN A GOOD RECIPE FOR ICY
ROADS TO FORM UNDERNEATH QUICK BURSTS OF SNOW.
- SPOTTY LAKE EFFECT SNOW SHOWERS THIS AFTERNOON INTO TONIGHT
IN THE WAKE OF THE LOW-PRESSURE SYSTEM, LOW-LEVEL WIND FIELDS WILL
SHIFT FROM NORTHEAST TO NORTH-NORTHWEST THIS AFTERNOON INTO
TONIGHT. DESPITE SUBSIDENCE AND WARMING OCCURRING ABOVE 850 MB,
SOME LAKE-EFFECT SNOW SHOWERS SHOULD STILL PERSIST AS COLDER 850
MB AIR FLOWS IN TO ALLOW SHALLOW BOUNDARY LAYER CONVECTION TO
REACH THE DGZ. THE INTENSITY SHOULD BE LIMITED BY DECREASING LOW-
LEVEL MOISTURE, SHALLOW CLOUD DEPTH, AND A LACK OF LARGER-SCALE
LIFT.
SOME MINOR ADDITIONAL ACCUMULATIONS ARE POSSIBLE NEAR AND EAST OF
US-127 FROM LAKE HURON THIS AFTERNOON. THERE MAY BE A BRIEF BURST
OF MODERATE SNOW IN WESTERN MASON AND OCEANA COUNTIES LATER THIS
AFTERNOON FROM LAKE MICHIGAN, THEN LIGHT SNOW SHOWERS PERSIST
ALONG MUCH OF THE LAKE MICHIGAN SHORE THROUGH TONIGHT. LUDINGTON
AND PENTWATER AREAS COULD SEE A HALF INCH TO 1.5 INCH. SOME
WAVERING LAKE SUPERIOR TO TRAVERSE BANDS MAY SNEAK INTO CLARE AND
OSCEOLA COUNTIES LATER IN THIS EVENING WITH A HALF-INCH.
- COLD WEEKEND
APPROACHING SURFACE HIGH PRESSURE ON SATURDAY SHOULD TURN SURFACE
WINDS NORTH-NORTHEAST AND KEEP MUCH OF THE LAKE MICHIGAN LAKE
EFFECT OFFSHORE WHILE OPENING UP SUNNIER SKIES OVER MUCH OF
INTERIOR LOWER MICHIGAN. A GLANCING PASS-THROUGH OF 850 MB AIR
WITH ARCTIC ORIGINS SHOULD KEEP HIGH TEMPERATURES MOSTLY IN THE
20S FOR MUCH OF THE AREA. SATURDAY NIGHT TO SUNDAY MORNING, THE
SURFACE HIGH WILL BE CENTERED OVER LOWER MICHIGAN, AND THE MOSTLY
CLEAR SKIES, LIGHT WINDS, AND SNOW COVER SHOULD SEND LOW
TEMPERATURES INTO THE SINGLE DIGITS OVER MUCH OF MIDDLE LOWER
MICHIGAN, POSSIBLY BELOW ZERO IN SPOTS.
- PATTERN CHANGE TOWARDS WARMER WEATHER NEXT WEEK
AFTER A WEEKEND OF UPPER TROUGHING THE PATTERN SHIFTS NEXT WEEK INTO
ONE OF ZONAL FLOW AND HIGHER HEIGHTS. 500MB HEIGHTS THIS WEEKEND
WILL BE IN THE 540'S DM. MUCH OF NEXT WEEK 500MB HEIGHTS ARE
FORECAST TO BE IN THE 560'S. SO, AFTER A WEEKEND OF HIGHS IN THE
20S, A WARMING TREND WILL SEE HIGHS IN THE 30S EARLY NEXT WEEK RISE
INTO 40S FOR THE LATTER HALF OF THE WEEK. WHAT SNOW WE END UP WITH
AFTER TODAY WILL BE MELTING NEXT WEEK. SOIL TEMPERATURES LAST
EVENING HERE AT THE OFFICE WERE 33F AT 2 INCHES AND 34F AT 4 INCHES.
BY NEXT WEEK THE SNOW WILL BE MELTING BOTH FROM ABOVE AND BELOW.
- A FEW POSSIBILITIES FOR PRECIPITATION NEXT WEEK
AS FAR AS THE DETAILS OF THE SENSIBLE WEATHER THERE ARE A FEW
CHANCES FOR PRECIPITATION (ON MONDAY, AGAIN WEDNESDAY AND POSSIBLY
THURSDAY/FRIDAY). ON MONDAY A SHORTWAVE ALOFT THAT IS CURRENTLY WELL
OFF SHORE OF THE WEST COAST OVER THE PACIFIC MOVES INTO THE GREAT
LAKES. THIS WAVE IS WEAK AND LOSING STRENGTH AS IT MOVES IN. THE
SURFACE LOW ASSOCIATED WITH THE WAVE IS ALSO ON THE WEAKER
SIDE/FILLING AND GETS ABSORBED BY THE SURFACE HIGH OVER THE REGION
WITH TIME. THAT SAID, WE DO EXPECT SOME LIGHT RAIN OR SNOW WITH THE
SYSTEM BEFORE IT WASHES OUT. THE GFS AND ECMWF ARE INDICATING A
QUARTER OF AN INCH OR LESS OF PRECIPITATION AT ALL SITES. WE FEEL
ANY FREEZING RAIN THREAT AT THIS POINT IS SMALL AND NOT INCLUDED IN
THE FORECAST (ONLY A MIX OF RAIN AND SNOW IS IN THE FORECAST).
THE MID TO LATE WEEK UPPER PATTERN IS COMPLEX AND ITS A LOW
CONFIDENCE FORECAST. BOTH THE GFS AND ECMWF HAVE CUT OFF LOWS IN THE
PLAINS. THE GFS IS A BIT MORE BULLISH ON A LOW EJECTING TOWARDS THE
GREAT LAKES MID WEEK, BUT WE ARE NOT BULLISH ON THIS SCENARIO. IF IT
WERE TO HAPPEN IT LOOKS MORE LIKE A LIGHT RAIN.
A SIMILAR SCENARIO LOOKS POSSIBLE LATE IN THE WEEK ON THURSDAY AND
FRIDAY WITH ANOTHER LOW CONFIDENCE SHORTWAVE FORECAST TO MOVE OUR
DIRECTION. MAINLY RAIN IF WE SEE ANY PRECIPITATION DURING THIS TIME
FRAME. THE ENSEMBLE MEANS OF THE GFS AND ECMWF DO NOT HAVE A GREAT
SIGNAL FOR PRECIPITATION WITH EITHER THE MID WEEK OR THE END OF WEEK
POTENTIAL SYSTEMS. BETTER CHANCES ARE WE SEE A MAINLY DRY PERIOD
FROM TUESDAY THROUGH FRIDAY.
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...SMALL CRAFT ADVISORY FROM 10 AM THIS MORNING TO 10 AM EST
SATURDAY FOR LMZ844-845-848-849.
DISCUSSION...CAS/DUKE
AVIATION...DUKE
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