220
FXUS63 KIND 191750
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
1250 PM EST THU DEC 19 2024
KEY MESSAGES
- LIGHT SNOW POSSIBLE THURSDAY NIGHT INTO FRIDAY. THE SNOW COULD
IMPACT THE FRIDAY MORNING COMMUTE.
- NEXT WEEK WILL SEE A WARMING TREND ALONG WITH RAIN FOR CHRISTMAS
EVE INTO CHRISTMAS DAY
FORECAST UPDATE
ISSUED AT 1006 AM EST THU DEC 19 2024
CLOUDS HAVE BEEN STUBBORN TO CLEAR ACROSS MUCH OF CENTRAL INDIANA
THIS MORNING... AS WAS EXPECTED THOUGH. LATEST ACARS SOUNDINGS FROM
AROUND THE REGION CONFIRM MOISTURE STUCK NEAR THE SURFACE UNDER A
STRONG SUBSIDENCE INVERSION ALOFT, WHICH WILL MAKE IT DIFFICULT FOR
AREAS TO CLEAR OUT FULLY. SATELLITE IMAGERY DOES SHOW SMALL POCKETS
OF CLEARING PUSHING INTO WESTERN AND SOUTHWESTERN INDIANA; HOWEVER
HIGHER CLOUDS AHEAD OF THE NEXT WEATHER SYSTEM SHOULD QUICKLY FILL
IN LATER THIS AFTERNOON. NORTH CENTRAL AND NORTHEASTERN PORTIONS OF
THE STATE LIKELY WILL REMAIN UNDER MOSTLY CLOUDY SKIES MUCH OF THE
DAY AS LARGER AREAS OF CLEARING REMAIN FURTHER SOUTH.
KEEPING HIGH TEMPERATURES BELOW GUIDANCE FOR TODAY IN THE LOW TO MID
30S ACROSS THE NORTH AND UPPER 30S IN THE SOUTH. WILL HAVE TO WATCH
BOTH TEMPERATURE AND DEW POINT TRENDS TODAY AS THIS COULD HAVE AN
IMPACT ON PRECIP TYPE AND SNOW AMOUNTS LATER TONIGHT. COLDER SURFACE
TEMPERATURES THAN WHAT GUIDANCE SHOWS...EVEN BY JUST A DEGREE CAN
REALLY INCREASE SNOWFALL CHANCES, AMOUNTS, AND IMPACTS TO TRAVEL.
LATEST HI-RES GUIDANCE DOES SHOW THE POTENTIAL FOR MESOSCALE BANDING
TONIGHT FOR PORTIONS OF CENTRAL, NORTH CENTRAL, AND EASTERN INDIANA
WHICH COULD CAUSE A WET BULB COOLING EFFECT LOCALLY WITH THE
POTENTIAL FOR ISOLATED AREAS OF 1-2" INCHES OF SNOW. THIS IS ALSO
SOMETHING TO WATCH FOR LATER TONIGHT.
SHORT TERM (TODAY THROUGH FRIDAY)
ISSUED AT 258 AM EST THU DEC 19 2024
HIGH PRESSURE WILL SLOWLY SHIFT EASTWARD THROUGHOUT THE DAY AHEAD OF
THE NEXT APPROACHING CLIPPER SYSTEM FROM THE NORTHWEST. WINDS WILL
EVENTUALLY SHIFT TOWARDS SOUTHERLY AS THE HIGH PASSES. EVEN THOUGH
THIS WILL AID IN MIXING, WEAK LOW LEVEL FLOW WILL HAVE A DIFFICULT
TIME BREAKING INTO A FAIRLY DEEP ANTECEDENT STRATUS LAYER. FOR THIS
REASON, MOST OF CENTRAL INDIANA IS EXPECTED TO REMAIN UNDERNEATH
OVERCAST SKIES TODAY; OUTSIDE OF FAR SOUTHERN AND SOUTHWESTERN
CENTRAL INDIANA. THIS GREATER CLOUD COVER WILL INHIBIT
TEMPERATURE GAINS THIS AFTERNOON, WITH THE NORTHERN 2/3S OF
CENTRAL INDIANA FAILING TO BREAK 36 THIS AFTERNOON.
THE FOCUS SHIFTS TO INCREASING PRECIPITATION CHANCES OUT AHEAD OF
THE AFOREMENTIONED CLIPPER TONIGHT. THE STRUCTURE AND TRACK OF THE
INCOMING MIDLEVEL SHORTWAVE TROUGH WILL BE KEY TO UNDERSTANDING SNOW
ACCUMULATION POTENTIAL, OF WHICH IS SEEMING TO BE RATHER PECULIAR.
THE INITIAL ASCENT WILL COME AFTER DUSK THURSDAY MOSTLY ALIGNED WITH
A CORRIDOR OF ISENTROPIC ASCENT. LOW LEVEL MOISTURE WILL BE LACKING
INITIALLY WITH GREATEST CONDENSATION PRESSURE DEFICITS FOCUSED TO
OUR NORTH. THEREFORE, THIS WILL BE THE INITIAL FOCUS FOR CHANCES OF
LIGHT PRECIPITATION AMOUNTS. TEMPERATURE WILL BE MARGINAL AT
PRECIPITATION ONSET, BUT TRANSITION TO SNOW SHOULD OCCUR QUICKLY
WITH COLD AIR ALOFT AND WEB BULB SURFACE TEMPERATURES NEAR 32.
AFTER MIDNIGHT TONIGHT, MODELS START TO DIVIDE IN SOLUTIONS.
THERE SEEMS TO BE A SIGNAL FOR A CONVERGENT BOUNDARY ALONG A
DEVELOPING PRESSURE TROUGH OUT AHEAD OF THE INITIAL SHORTWAVE
THURSDAY NIGHT BETWEEN 06- 12Z. THIS IS MOST PRONOUNCED IN THE RAP
AND NAM SOLUTIONS, AS STRONGER CAA IS MODELED TO OCCUR BEHIND
THIS PRESSURE TROUGH. THE GREATER CONVERGENCE WOULD WORK TWO FOLD,
INCREASE LOW LEVEL ASCENT, BUT ALSO MARGINALLY INCREASING SURFACE
TEMPERATURES THROUGH WAA (AT AN ATYPICAL DIURNAL PERIOD). AS
MENTIONED BEFORE, MOISTURE WILL ALSO MITIGATE PRECIPITATION
INITIATION SOME, ADDING TO A HOST OF UNCERTAINTIES FOR THE PERIOD.
FOR NOW, 20-40% POPS HAVE BEEN ADDED FOR A RAIN/SNOW MIX PASSING
THROUGH SOUTHERN IN, ON TOP OF THE CONTINUED 50-70% POPS
PREVIOUSLY FORECASTED FOR N/NE CENTRAL IN. IF OVERPERFORMANCE
VERSUS MODEL GUIDANCE WERE TO OCCUR ON THURSDAY NIGHT, IT WOULD
LIKELY BE ALONG THIS CONVERGENT BOUNDARY; AS SUCH THIS SHOULD BE
MONITORED CLOSELY FOR TRENDS THROUGHOUT THE DAY
AS WE HEAD INTO FRIDAY MORNING, THE MORE PRONOUNCED WAVE WILL
ARRIVE, LEADING TO AN ADDITIONAL ROUND OF SNOW CHANCES. THIS WAVE
WILL BE ATTACHED TO COOLER AIR, LIMITING ANY P-TYPE CONCERNS (ALL-
SNOW). DEEP/ANOMALOUS MOISTURE ADVECTION IS NOT INDICATED WITH THIS
PORTION OF THE WAVE EITHER SINCE THE LOWER LATITUDE MOISTURE WILL
BE TOO DETACHED FROM THE FLOW FIELDS LIMITING OVERALL QPF.
NEVERTHELESS, SNOW BANDS SHOULD FORM ACROSS CENTRAL INDIANA DUE TO
A COMBINATION OF A WEAK DEFORMATION ZONE AS THE SURFACE LOW
PASSES AND POST-FRONTAL STEEPENING LOW LEVEL LAPSE RATES AND
SHALLOW CONVECTIVE PROCESS.
SOUNDING ANALYSIS SHOWS THAT ALIGNMENT OF ASCENT/MOISTURE TO THE
DGZ ARE NOT PARTICULARLY FRUITFUL FOR AN ABUNDANCE OF DENDRITE
GROWTH, ESPECIALLY DURING THE OVERNIGHT PERIOD. SLR MAY STRUGGLE
TO REACH OUR CLIMATOLOGICAL NORMALS OF ~12:1. THIS SHOULD SHIFT
FRIDAY MORNING AS LAPSE RATES STEEPEN AND THE SATURATED LAYER
PUSHES INTO THE DGZ. ENSEMBLE MEAN QPF IS IN THE 0.05-0.10 INCH
RANGE, LEADING TO SNOWFALL EXPECTATIONS TO GENERALLY BE AROUND ONE
INCH OR UNDER BY LATE FRIDAY. HIGHEST AMOUNTS WILL BE ACROSS THE
NORTH, TAPERING WITH SOUTHWARD EXTENT.
LONG TERM (FRIDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 258 AM EST THU DEC 19 2024
SOME LAKE EFFECT SNOW SHOWERS MAY DIP INTO NORTHWESTERN PORTIONS OF
THE AREA FRIDAY NIGHT, WITH SOME FLURRIES ACROSS PORTIONS OF THE
NORTHERN HALF OF THE AREA.
SATURDAY INTO SUNDAY NIGHT WILL BE QUIET ACROSS CENTRAL INDIANA WITH
SURFACE HIGH PRESSURE IN CONTROL. BY SUNDAY, SOME UPPER RIDGING WILL
MOVE IN BRIEFLY AS WELL, KEEPING CONDITIONS QUIET. TEMPERATURES WILL
BE BELOW NORMAL, WITH TEMPERATURES GETTING AS COLD AS THE TEENS FOR
MUCH OF THE AREA FOR EARLY SUNDAY MORNING.
MONDAY THROUGH CHRISTMAS AND BEYOND GETS MORE COMPLICATED. A SERIES
OF UPPER TROUGHS IN BOTH NORTHERN AND SOUTHERN STREAMS WILL IMPACT
THE AREA THROUGH THIS PERIOD, PROVIDING FOR FREQUENT CHANCES FOR
PRECIPITATION. MANY QUESTIONS REMAIN ON TIMING AND ANY PHASING THAT
WILL OCCUR, WHICH LEADS TO LOWER CONFIDENCE IN DETAILS.
WHAT IS KNOWN THAT COLD AIR WILL BE BOTTLED UP TO THE NORTHWEST OF
THE AREA, WHICH WILL LEAD TO RAIN AS THE PRECIPITATION TYPE FOR MOST
OF THE PERIOD. TEMPERATURES MAY BE COOL ENOUGH MONDAY FOR A PERIOD
OF MIXED PRECIPITATION. OTHERWISE, TEMPERATURES WILL BE ABOVE NORMAL
FOR LATE DECEMBER.
THE 00Z OPERATIONAL GFS STILL KEEPS OVER AN INCH OF RAIN IN SOUTHERN
PORTIONS OF THE AREA BY THE END OF CHRISTMAS DAY, THE 00Z ECMWF HAS
AROUND AN INCH AS WELL BUT FARTHER NORTH. ENSEMBLES HAVE COME
NORTHWARD A BIT WITH THE RAIN AXIS AS WELL. THEIR VALUES ARE LOWER
GIVEN THAT IT INCLUDES THE MEMBERS THAT HAVE LOWER AMOUNTS.
UNCERTAINTY IS HIGH ENOUGH THAT NO MENTION OF LOCALLY HEAVY RAIN
WILL BE GIVEN, BUT WILL HAVE TO KEEP AN EYE OUT WITH LATER FORECASTS.
AVIATION (18Z TAF ISSUANCE)
ISSUED AT 1249 PM EST THU DEC 19 2024
IMPACTS:
- MVFR TO VFR CIGS TODAY, BECOMING MVFR TO IFR AFTER 08Z
- SNOW DEVELOPING AFTER 08Z WITH DETERIORATING CIGS AND VIS THROUGH
THE MORNING.
- GREATEST IMPACTS FROM SNOW EXPECTED AT KLAF AND KIND
DISCUSSION:
LATEST SATELLITE IMAGERY SHOWS MVFR STRATUS HOLDING STRONG ACROSS
CENTRAL AND NORTH CENTRAL INDIANA. CLEARING IS TAKING PLACE AROUND
KHUF AND KBMG WITH CIGS BECOMING AND REMAINING VFR THROUGH THE
EVENING THERE. LOWER CONFIDENCE WHEN KIND AND KLAF WILL BREAK OUT OF
THE STRATUS.. IF IT EVEN HAPPENS. POTENTIAL IS THERE FOR CIGS TO
BRIEFLY BECOME VFR AT KIND AND KLAF WITHIN THE 20Z-03Z TIMEFRAME
BEFORE LOW CLOUDS DEVELOPING AHEAD OF THE INCOMING SNOW.
ANOTHER ROUND OF PRECIPITATION WILL ARRIVE QUICKLY FRIDAY MORNING.
THE WORST CONDITIONS WILL LIKELY REMAIN JUST N/NE OF KHUF AND KBMG,
BUT THERE IS STILL SOME UNCERTAINTY. KIND AND KLAF LIKELY FALL BELOW
1000FT CIGS WITH VIS BETWEEN 2-4SM WITHIN THE 08-15Z TIMEFRAME. THIS
SHOULD END MIDDAY ON FRIDAY WITH THE REMAINDER OF THE DAY GUSTY AND
SCATTERED SHSN.
WINDS HAVE SHIFTED SOUTHERLY ACROSS ALL OF CENTRAL INDIANA WITH
SPEEDS LESS THAN 8 KTS. A FRONTAL BOUNDARY APPROACHES FROM THE WEST
08Z-12Z SHIFTING WINDS TO THE WEST AND THEN WEST NORTHWEST BY
MIDDAY FRIDAY. WINDS WILL INCREASE TO 10-15 KTS WITH GUSTS UPWARDS
OF 20-25 KTS AT ALL TAF SITES MIDDAY FRIDAY.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
UPDATE...CM
SHORT TERM...UPDIKE/BRB
LONG TERM...50
AVIATION...CM
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