733
FXUS63 KGRR 171953
AFDGRR
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE GRAND RAPIDS MI
253 PM EST TUE DEC 17 2024
KEY MESSAGES
- A PERIOD OF LIGHT SNOW/RAIN FOR LATER TONIGHT INTO WEDNESDAY
MORNING
- INCREASING RISK FOR IMPACTS THURSDAY AFTERNOON INTO FRIDAY MORNING
- VERY COLD OVER THE WEEKEND
DISCUSSION
ISSUED AT 238 PM EST TUE DEC 17 2024
- A PERIOD OF LIGHT SNOW/RAIN FOR LATER TONIGHT INTO WEDNESDAY
MORNING
THE MID LEVEL WAVE IN THE UPPER PLAINS MOVES INTO THE CWA LATER
TONIGHT. AT THE SAME TIME A SURFACE WAVE WILL BE TRACKING UP THE OH
VALLEY. MOISTURE PROFILES SHOW THE DGZ MOISTENING UP LATER TONIGHT BUT
THE LOW LEVELS WILL INITIALLY BE DRY. THEN AS THE LOW LEVELS
MOISTEN UP, THE DGZ STARTS TO DRY OUT. THE LIFT THROUGH THE
COLUMN IS SHOWN TO BE RELATIVELY WEAK. AS A RESULT, WE WILL CARRY
HIGH POPS FOR THIS SHORT DURATION EVENT, BUT AT THIS TIME IT
APPEARS THAT QPF WILL BE LIGHT. ALSO, SURFACE TEMPERATURES MAY
STRUGGLE TO FALL BELOW FREEZING, ESPECIALLY AS INDICATED BY THE
HRRR. BASED ON THIS, AT THIS TIME, ANY IMPACTS SHOULD REMAIN
LIMITED. NO HEADLINES FOR THIS EVENT.
- INCREASING RISK FOR IMPACTS THURSDAY AFTERNOON INTO FRIDAY MORNING
THE NEXT MID LEVEL WAVE WILL BE DIGGING INTO THE GREAT LAKES REGION
FROM THE CANADIAN PRAIRIES DURING THIS TIME. FGEN WAS NOTED IN THE
700-600 MB LEVEL, ESPECIALLY OVER CENTRAL/SOUTHERN PARTS OF THE
CWA. MID LEVEL LAPSE RATES DO STEEPEN UP AS WELL. MOISTURE
PROFILES REFLECT DEEP MOISTURE FROM ABOUT MID AFTERNOON THURSDAY
INTO FRIDAY MORNING. INITIALLY THE LOW LEVELS ARE SHOWN TO BE DRY
BUT THAT LEVEL SATURATES FAIRLY QUICKLY. AS A RESULT, THE REGION
IS LOOKING AT AN EXTENDED PERIOD OF SNOW. THIS SYSTEM WILL BE
COLDER SO, MUCH OF THE EVENT WILL FEATURE SURFACE TEMPS AT OR
BELOW FREEZING. BASED ON ALL THIS, IMPACTS WILL BE GREATER WITH
THIS SECOND SYSTEM AND THEY COULD RISE TO A HEADLINE LEVEL.
HOWEVER, ENSEMBLE MEAN SNOW AMOUNTS SUGGEST MOST LOCATION WILL END
UP WITH AN INCH OR TWO DURING THIS PERIOD FOR MOST OF THE CWA. IT
SHOULD BE NOTED THAT THERE IS STILL A LOT OF SPREADS AMONGST THE
MEMBERS, SO THERE STILL EXISTS A DECENT AMOUNT OF UNCERTAINTY WITH
THE SNOW AMOUNTS.
- VERY COLD OVER THE WEEKEND
AN ARCTIC HIGH PRESSURE SYSTEM GRADUALLY BUILDS IN FROM THE
NORTHWEST OVER THE WEEKEND. MOST OF THE TIME AN OFFSHORE COMPONENT
TO THE FLOW WILL BE PRESENT AND THAT WILL FOCUS THE BULK OF LAKE
EFFECT SNOW WEST OF THE CWA. SOME INLAND CLEARING IS LOOKING
LIKELY SATURDAY NIGHT AS THE COLDER AIR DRAINS TOWARDS LAKE MI.
THE COMBINATION OF CLEARING SKIES, WEAKER WINDS AND ARCTIC AIR
MASS IN PLACE AND FRESH SNOW COVER, SUPPORTS VERY COLD LOW
TEMPERATURES SATURDAY NIGHT, AND POSSIBLY SUNDAY NIGHT.
CONSERVATIVE ESTIMATES ARE FOR THE SINGLE DIGITS AND THEY COULD GO
LOWER AS WE GET CLOSER TO THAT TIME.
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...MJS
AVIATION...THOMAS
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