328
FXUS63 KIND 190800
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
300 AM 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
SHORT TERM (TODAY AND TONIGHT)
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
REACH, MOST OF CENTRAL INDIANA IS EXPECTED TO REMAIN UNDERNEATH
OVERCAST SKIES TODAY; OUTSIDE OF THE SOUTHERN TIER OF COUNTIES IN
OUR CWA. THIS GREATER CLOUD COVER WILL INHIBIT TEMPERATURE GAINS
THIS AFTERNOON, WITH THE NORTHERN 2/3S OF CENTRAL INDIANA FAILING TO
BREAK 35 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 WILL BE RELEGATED TO. 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.
AT THIS POINT MODELS THEN 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 SINCE THE LOWER LATITUDE MOISTURE WILL BE TOO
DETACHED FROM THE FLOW FIELDS. NEVERTHELESS, SNOW SHOWERS 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 SHOW THAT ALIGNMENT OF ASCENT/MOISTURE TO THE DGZ
ARE NOT PARTICULARLY FRUITFUL FOR AN ABUNDANCE OF DENDRITE GROWTH.
SLR MAY STRUGGLE TO REACH OUR CLIMATOLOGICAL NORMALS OF ~12:1,
ESPECIALLY IN THE INITIAL FRONTAL BAND ROUND WHERE DGZ MOISTURE MAY
BE LOW AND NEEDLES/COLUMNS MAY DOMINATE ICE CRYSTAL HABIT. 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 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 (06Z TAF ISSUANCE)
ISSUED AT 1202 AM EST THU DEC 19 2024
IMPACTS:
- MVFR CEILINGS WILL IMPROVE TO VFR AFTER 17Z-21Z THURSDAY
DISCUSSION:
HI-RES SOUNDINGS SUGGEST THERE WILL BE ENOUGH MOISTURE IN THE UPPER
PART OF THE BOUNDARY LAYER FOR MVFR CEILINGS THROUGH AT LEAST EARLY
AFTERNOON THURSDAY. THERE IS A LOW CHANCE OF EARLY BREAKING IN CLOUD
COVER AT KHUF TONIGHT, OF WHICH WOULD LIKELY LEAD TO PATCHY MVFR AND
OR WORSE FOG.
WINDS WILL BE LIGHT TO CALM OVERNIGHT AND THEN SHIFT TO S/SE AT LESS
THAN 10 KNOTS THURSDAY.
MVFR CEILINGS ARE EXPECTED TO RETURN THURSDAY NIGHT, BUT TIMING ON
ARRIVAL IN UNCERTAIN AT THIS TIME.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...UPDIKE/BRB
LONG TERM...50
AVIATION...UPDIKE
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