335
FXUS63 KIND 191126
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
626 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 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
CENRAL 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 EATHER 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 LASPE 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 (12Z TAF ISSUANCE)
ISSUED AT 619 AM EST THU DEC 19 2024
IMPACTS:
- MVFR CEILINGS AT KIND AND KLAF FOR THE ENTIRE TAF PERIOD; VFR AT
KBMG AND KHUF AFTER 15Z, WITH MVFR RETURNING POST 02Z
- RASN POSSIBLE OVERNIGHT WITH REDUCED VIS AND CIGS
- SN AND SHSN POSSIBLE TOMORROW, GREATEST IMPACTS ARE KLAF AND KIND
DISCUSSION:
A MAJORITY OF CENTRAL INDIANA REMAINS UNDERNEATH A 1800-2500FT
STRATUS DECK. THERE IS SOME RETREATING/CLEARING ONGOING OVER SW
INDIANA, OF WHICH IS EXPECTED TO REACH KHUF AND KBMG THIS MORNING.
CONFIDENCE IS LOWER IN THIS OCCURRING AT KBMG.
THIS EVENING, ANY AREAS THAT ARE WITHIN VFR CIGS WILL TRANSITION
BACK TO MVFR. THIS WILL BE ASSOCIATED WITH AN APPROACHING WAVE, OF
WHICH WILL ALSO PROVIDE CHANCES FOR RASN FOR ALL TAF SITES
OVERNIGHT. THIS COULD TRANSITION TO ALL SNOW AT KLAF OVERNIGHT.
WITHIN RASN, CEILINGS WILL DROP TO NEAR IFR WITH VIS BETWEEN 4SM AND
6SM.
ANOTHER ROUND OF PRECIPITATION WILL ARRIVE QUICKLY FRIDAY MORNING,
THIS TIME AS ALL SNOW. THIS WILL LIKELY REMAIN N/NE OF KHUF AND
KBMG, BUT THERE IS STILL SOME UNCERTAINTY. TAF SITES THAT RECEIVE SN
ON FRIDAY WILL LIKELY FALL BELOW 1000FT CIGS WITH VIS BETWEEN 2-4SM.
THIS SHOULD END MIDDAY ON FRIDAY WITH THE REMAINDER OF THE DAY GUSTY
AND SCATTERED SHSN.
WINDS INITIALLY WILL BE OUT OF THE NNW THIS MORNING, BUT WILL SLOWLY
SHIFT TOWARDS SE/S BY NOON; SUSTAINED BETWEEN 6-10KT. OVERNIGHT,
THERE WILL BE ANOTHER WIND SHIFT TO THE W WITH WINDS ONCE AGAIN
BETWEEN 6-10KT.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...UPDIKE/BRB
LONG TERM...50
AVIATION...UPDIKE
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