207
FXUS63 KIWX 212041
AFDIWX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NORTHERN INDIANA
341 PM EST THU NOV 21 2024
KEY MESSAGES
- SNOW TAPERS FROM NORTH TO SOUTH THROUGH EARLY EVENING, WITH A
CHANGE OVER TO LIQUID ACROSS THE WEST/NORTHWEST. SOME MINOR
IMPACTS TO THE EVENING COMMUTE ARE EXPECTED MAINLY SOUTH OF US
30 ACROSS NORTHERN INDIANA.
- A NARROW MESOBAND OF RAIN/SNOW SHOWERS IS POSSIBLE THIS
EVENING AS SFC LOW PRESSURE MOVES INLAND FROM LAKE MICHIGAN.
- LAKE EFFECT RAIN SHOWERS FOR LATER TONIGHT THROUGH FRIDAY EVENING.
- SOME MODERATION IN TEMPERATURES SUNDAY AND MONDAY WITH NEXT
CHANCE OF RAIN SUNDAY NIGHT INTO MONDAY.
DISCUSSION
ISSUED AT 339 PM EST THU NOV 21 2024
SNOW WILL DIMINISH FROM NORTH TO SOUTH THIS EVENING AS STRONGER
UPPER VORT MAX DROPS SOUTH ACROSS SOUTHERN INDIANA. DEFORMATION
FLOW AND POCKET OF LOW LEVEL MOISTURE CONVERGENCE ASSOCIATED
WITH STRONG LOW LEVEL JET PROVIDED SOME ENHANCEMENT TO THE SNOW
ACROSS EAST CENTRAL WISCONSIN INTO FAR NORTHEAST ILLINOIS AND
EXTREME NORTHWEST INDIANA. SNOWFALL ACCUMULATION EFFICIENCY HAS
BEEN LIMITED LOCALLY BY WARM GROUND CONDITIONS, STRONG LOW LEVEL
FLOW, AND A VERY HIGH BASED MID LEVEL DENDRITIC GROWTH ZONE.
SOME DRIER MID LEVEL AIR IS BEGINNING TO PUSH SOUTHWARD ACROSS
THE WESTERN GREAT LAKES AND THIS SHOULD CONTINUE TO MINIMIZE
SNOWFALL EFFICIENCY OVER THE NEXT SEVERAL HOURS. WARMER AND MORE
MOIST AIR IS ALSO WRAPPING AROUND THIS SYSTEM WHICH HAS
EFFECTIVELY PUSHED NEAR SFC WET BULBS WARM ENOUGH FOR A
TRANSITION TO LIQUID PRECIP TYPE ACROSS NORTHERN SUBURBS OF
CHICAGO AND SW LOWER MICHIGAN AS OF 19Z. THIS RAIN/SNOW LINE
SHOULD CONTINUE TO PUSH SOUTHEASTWARD OVER THE NEXT FEW HOURS
WITH FOCUS FOR ADDITIONAL LIGHT SNOW ACCUMULATIONS SHIFTING
SOUTH OF THE US ROUTE 30 CORRIDOR IN NORTHERN INDIANA FOR THE
EVENING COMMUTE. PAVEMENTS SHOULD PRIMARILY REMAIN WET, BUT A
FEW SLICK SPOTS ARE STILL POSSIBLE OVER THE NEXT FEW HOURS.
ACTUAL SFC REFLECTION OF THIS SYSTEM IS STILL OVER SOUTHERN
LAKE MICHIGAN AND WILL NEED TO WATCH THE EVOLUTION OF LAKE MI
ENHANCED MESOLOW AS IT TRACKS INTO NORTHWEST INDIANA/NORTH
CENTRAL INDIANA THIS EVENING. THIS SFC REFLECTION HAS BEEN
ENHANCED BY HIGH EARLY SEASON FLUXES OFF LAKE MICHIGAN ALONG
WITH TIGHTENING OF THE CIRCULATION FROM A 12 TO 18 HOUR PERIOD
OF LATENT HEATING. PRECIP TYPES MAY BE MARGINAL WITH ANY
ENHANCED BANDING WITH THIS FEATURE AS LOW LEVEL WET BULB TEMPS
CREEP UPWARD. THIS EVOLUTION COULD PRODUCE A NARROW BAND OF
IMPACTS IF MESOBAND IS ABLE TO MATERIALIZE. ALSO CANNOT RULE OUT
A FEW REPORTS OF GRAUPEL WITH MESOLOW FEATURE AS IT PUSHES
INLAND. OUTSIDE OF THIS MESOLOW FEATURE, DEEP MOISTURE PROFILES
WILL BECOME PROGRESSIVELY LESS FAVORABLE FOR ACCUMULATING SNOW
THIS EVENING.
SOME BRIEF STRONGER DEEP LAYER SUBSIDENCE WILL PUSH INTO SOUTHERN
LOWER MICHIGAN AND NORTH CENTRAL INDIANA LATER THIS EVENING
WITH SOME BREAKS IN LOW CLOUDS POSSIBLE. LAKE EFFECT RAIN
SHOWERS SHOULD EVENTUALLY SHIFT BACK EASTWARD INTO THE AREA AS
AXIS OF MID LEVEL MOISTURE RECOVERY APPROACHES. NEGATIVE UPPER
HEIGHT ANOMALY PERSISTS ACROSS EASTERN CONUS FOR FRIDAY
MAINTAINING A FAVORABLE NORTHERLY FETCH FOR CONTINUED LAKE
EFFECT RAIN SHOWERS. MOISTURE DEPTHS WILL BE MORE LIMITED ON
FRIDAY WHICH WILL LIMIT OVERALL PRECIP AMOUNTS. MODERATION OF
LOW LEVEL AIRMASS ON FRIDAY SHOULD SUPPORT HIGHS IN THE MID-
UPPER 40S.
LAKE EFFECT RAIN SHOWERS SHOULD COME TO AN END LATER FRIDAY NIGHT
AS BETTER MID LEVEL HEIGHT RECOVERY COMMENCES ACROSS THE MID MS
VALLEY/WESTERN GREAT LAKES. A PERIOD OF MAINLY DRY CONDITIONS
IS THEN IN STORE THROUGH THE DAY SUNDAY AS TEMPERATURES WARM
BACK TO SLIGHTLY ABOVE NORMAL. A BRIEF BUT RESPECTABLE PERIOD OF
LOW LEVEL MOISTURE TRANSPORT WILL BE POSSIBLE SUNDAY EVENING
AHEAD OF ASSOCIATED COLD FRONT. WILL MAINTAIN HIGH CHANCE POPS
THIS PERIOD WITH MAIN QUESTION CENTERING ON DURATION AND
NORTHWARD EXTENT OF BETTER LOW LEVEL MOISTURE TRANSPORT. COLDER
CONDITIONS BUILD IN BEHIND THIS COLD FRONT EARLY WEEK. LOOKING
AHEAD, MEDIUM RANGE GUIDANCE DOES INDICATE ANOTHER SYSTEM FOR
MIDDLE-LATE WEEK, BUT STILL SOME QUESTION AS TO EXTENT OF
SUPPRESSION OF LOW LEVEL REFLECTION. GIVEN UNCERTAINTY AT THIS
FORECAST DISTANCE WILL MAINTAIN JUST CHANCE RAIN/SNOW POPS
HEADING INTO WED NIGHT/THU.
AVIATION /18Z TAFS THROUGH 18Z FRIDAY/
ISSUED AT 1200 PM EST THU NOV 21 2024
SYNOPTIC SNOW, NOW INTO KSBN, SHOULD REACH KFWA BY APPROXIMATELY
19Z. HEAVIER WIND-DRIVEN SNOW WITH 1/4 TO 1/2 MILE VISBYS SHOULD
MAINLY BYPASS THE TERMINALS, THOUGH A PERIOD OF LIFR TO IFR
RESTRICTIONS REMAIN LIKELY THIS AFTERNOON AS THE SNOW MOVES
THROUGH. MINOR ACCUMS ON MAINLY GRASSY/ELEVATED SURFACES MAINLY
EXPECTED. THIS VORT MAX AND ASSOCIATED SFC REFLECTION SINK SOUTH
OF THE AREA BY 23-00Z WITH QUICK IMPROVEMENT AND LIGHTER NW
WINDS INTO TONIGHT. THE LAKE PLUME DOES PIVOT BACK INTO NORTHERN
IN LATE TONIGHT INTO FRIDAY WITH MVFR CIGS AND SCATTERED LAKE
EFFECT RAIN SHOWERS AT MAINLY KSBN.
IWX WATCHES/WARNINGS/ADVISORIES
IN...NONE.
OH...NONE.
MI...NONE.
MARINE...GALE WARNING UNTIL 1 AM EST FRIDAY FOR LMZ043-046.
DISCUSSION...MARSILI
AVIATION...STEINWEDEL
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