157
FXUS63 KIND 190800
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
300 AM EST TUE NOV 19 2024
KEY MESSAGES
- RAIN COMES TO AN END LATER THIS MORNING, WITH A WARM AND DRY
AFTERNOON EXPECTED
- WINDS GUSTING 25-30+ MPH THIS MORNING WILL SUBSIDE TO 15-25 MPH
THIS AFTERNOON
- COOLER WITH LIGHT RAINFALL AMOUNTS WEDNESDAY
- WINDY THURSDAY WITH RAIN/SNOW SHOWERS; LIGHT ACCUMULATION IF ANY
SHORT TERM (TODAY AND TONIGHT)
ISSUED AT 300 AM EST TUE NOV 19 2024
CENTRAL INDIANA IS CURRENTLY IN THE WARM SECTOR OF A RAPIDLY
OCCLUDING LOW PRESSURE SYSTEM THIS MORNING, WITH THE PRIMARY WARM
CONVEYOR BELT BAND OF PRECIPITATION RAPIDLY PUSHING ACROSS THE AREA.
THIS BAND OF RAIN WILL RAPIDLY CLEAR THE AREA LATER THIS MORNING,
WITH MUCH OF THE AREA DRY AND BREEZY TODAY, WITH PLENTIFUL CLEARING
EXPECTED THIS AFTERNOON IN THE WAKE OF THE INITIAL FRONT.
THAT SAID, HIGH TEMPERATURES TODAY ARE STILL EXPECTED TO BE WELL
ABOVE NORMAL, AS THE PRIMARY LOW LEVEL PUSH OF COLD AIR IS STILL
BOTTLED UP WITH THE MAIN COLD FRONT WELL BACK TO THE WEST. THIS COLD
ADVECTION WILL ARRIVE IN EARNEST THIS EVENING, TAKING TEMPERATURES
FROM AFTERNOON NUMBERS IN THE MID TO UPPER 60S DOWN WELL INTO THE
40S IF NOT UPPER 30S IN A FEW SPOTS BY LATE TONIGHT.
CLOUD COVER WILL BEGIN TO INCREASE AGAIN LATE TONIGHT AS THE
CONSOLIDATED UPPER LOW APPROACHES. CANNOT COMPLETELY RULE OUT A FEW
SPRINKLES WITH A VORT LOBE SWINGING INTO THE AREA NEAR DAYBREAK
WEDNESDAY, BUT FORECAST PROFILES SUGGEST THIS SHOULD HOLD OFF UNTIL
NEAR OR JUST AFTER 12Z, AND WILL KEEP A DRY FORECAST THROUGHOUT
TONIGHT.
WIND GUSTS WILL BE STRONGEST FROM NEAR DAYBREAK THROUGH THE MORNING
HOURS, WITH A FEW GUSTS PUSHING 30KT POSSIBLE AS THE INITIAL FRONT
SWEEPS THROUGH THE AREA - THOUGH MOST GUSTS WILL BE CONFINED TO THE
25KT RANGE GIVE OR TAKE A FEW. THESE GUSTS WILL GRADUALLY SUBSIDE
THROUGH THE DAY, THOUGH INCREASED MIXING AS SKIES CLEAR MAY KEEP
THEM GOING, ALBEIT A BIT WEAKER, INTO THE MID TO LATE AFTERNOON
HOURS.
LONG TERM (WEDNESDAY THROUGH MONDAY)
ISSUED AT 300 AM EST TUE NOV 19 2024
TWO FACTORS SHOULD LIMIT PRECIPITATION COVERAGE AND INTENSITY
SOMEWHAT ON WEDNESDAY. 1. MODELS IVT FIELDS SHOW RICH SUBTROPICAL
MOISTURE PLUME WILL BE WELL EAST OF OUR REGION OWING TO THE
SPRAWLING NATURE OF BROAD OCCLUDED LOW. 2. THE STAGE THIS MID-
LATITUDE CYCLONE IS IN SUGGEST LIMITED CROSS-THERMAL GRADIENT FLOW
(I.E., TEMPERED ISENTROPIC ASCENT). NEVERTHELESS, ASCENT WITHIN THE
EXIT REGION OF INTENSE ~130-KT 500-MB JET STREAK SHOULD BE ENOUGH
FOR SOME LIGHT PRECIPITATION. THESE STRONGER FORCED PRECIPITATION
EVENTS AMIDST MARGINAL MOISTURE TEND TO FALL ON THE WETTER END OF
THE ENSEMBLE SUITE MORE TIMES THAN NOT. 75TH PERCENTILE OF THE GRAND
ENSEMBLE RANGES FROM AROUND 0.10" TO 0.25" (AND A BIT HIGHER IN EAST-
CENTRAL INDIANA). HREF 75TH PERCENTILE IS COMPARATIVELY MUCH LOWER,
BUT ITS STRENGTH IS MORE IN CONVECTIVE REGIMES, WHICH THIS IS NOT,
SO WE'LL FAVOR THE GLOBAL MODEL ENSEMBLE AMOUNTS. PEAK COVERAGE
SHOULD BE IN THE MID-MORNING THROUGH EARLY AFTERNOON TIME WINDOW.
THE STRENGTHENING MIDLEVEL SPEED MAXIMA IS ACTUALLY SHOWN IN THE
MODELS TO SPAWN A SECONDARY SURFACE LOW ACROSS THE EASTERN GREAT
LAKES. AS THIS LOW STRENGTHENS, ISALLOBARIC MASS RESPONSE WILL
RESULT IN INCREASINGLY BREEZY CONDITIONS AS THE DAY PROGRESSES. COLD
ADVECTION WILL STRENGTHEN COINCIDENTALLY, PROBABLY EFFECTIVELY
NEGATING THE DIABATIC SURFACE HEATING-DRIVEN DIURNAL CLIMB. WE MAY
STRUGGLE TO REACH 50 AND BE RIGHT AROUND CLIMATOLOGICAL NORMAL.
THURSDAY, A COMPLICATED AND UNIQUE SYNOPTIC-SCALE EVOLUTION IS NOTED
IN THE MODELS. MOST SHOW THE NEW GREAT LAKES LOW PEAKING IN
INTENSITY AS IT IS PULLED WEST WITHIN THE ORIGINAL OCCLUDED LOW.
SOME ENSEMBLE MEMBERS AND NAM-BASED GUIDANCE HOLD THE LOW FURTHER
EAST. AND, INTERESTINGLY MOST SHOW A NEW DOMINANT MSLP LOW CENTER
DEVELOPING ALONG THE ATLANTIC COAST. REGARDLESS, WE WILL BE IN THE
PROXIMITY OF THE SECOND SURFACE LOW WITH FAIRLY TIGHT MSLP GRADIENT
AND STEEP TROPOSPHERIC LAPSE RATES NEAR THE CORE OF THE DEEP LOW.
THERE ARE ALSO INDICATIONS OF STRENGTHENING PERIPHERAL FLOW IN CLOSE
ENOUGH PROXIMITY FOR MOMENTUM TRANSFER TO POTENTIALLY RESULT IN
QUITE STRONG WIND GUSTS (>40-MPH). WE WILL REFINE WIND SPEEDS AS
ENSEMBLE SPREAD AND RUN-TO-RUN INCONSISTENCY LESSENS.
MODELS SHOW MODEST MOISTURE RETURN WRAPPING AROUND THE DEEP LOW AND
IMPINGING ON INDIANA COINCIDENT WITH TWO DISTINCT VORTICITY
MAXIMA/PV ANOMALIES. ONE DURING THE MORNING AND ANOTHER LATE IN THE
DAY. THIS SHOULD BE ENOUGH, AMIDST STEEP LAPSE RATES, FOR CONVECTIVE
SHALLOW SHOWERS, PERHAPS MOST CONCENTRATED ALONG THE LATTER
SOUTHWARD MOVING INTENSE PV ANOMALY. THERMAL PROFILE MAY BE MARGINAL
FOR RAIN/SNOW, BUT AT THIS TIME TENDS TO FAVOR SNOW, ESPECIALLY WITH
SUCH STEEP LAPSE RATES WHICH WOULD SUPPORT SNOW PTYPE WITH 2-M
TEMPERATURES IN THE MID-UPPER 30S. WHERE TEMPERATURES ARE WARMER,
THERMAL PROFILES MAY EVEN SUPPORT SOME GRAUPEL.
IT'S WORTH NOTHING THAT IF THE SECOND PV ANOMALY IS FURTHER EAST, AS
IS SUGGESTED IN SOME ENSEMBLES AND NAM-BASED GUIDANCE, PRECIPITATION
COVERAGE THE LATTER HALF OF THE DAY WOULD BE MORE LIMITED. WITH SUCH
A PLAUSIBLE ALTERNATE SCENARIO, POTENTIAL SNOWFALL ACCUMULATION
AMOUNTS ARE UNCERTAIN. A REASONABLE WORST CASE SCENARIO COULD RESULT
IN AN INCH OR TWO ACROSS NORTHERN AND EASTERN PORTIONS OF THE AREA.
THIS MAY BE REGULATED SOME BY WARM GROUND, SINCE SNOWFALL RATES
LIKELY WON'T BE PARTICULARLY HIGH. BUT QPF/SLR COMBINATIONS WITHIN A
SUBSET OF ENSEMBLE MEMBERS DO SUPPORT THESE AMOUNTS. A MORE LIKELY
SCENARIO TO MESSAGE NOW GIVEN THE UNCERTAINTY IS A DECENT CHANCE OF
<1" ACCUMULATION MAINLY IN GRASSY AREAS AND ELEVATED SURFACES FOR
ROUGHLY THE NORTHEAST HALF OF CENTRAL INDIANA. BLENDED MODEL >1"
SNOWFALL PROBABILITIES PEAK AT AROUND 60% IN EAST-CENTRAL INDIANA
TAPERING TO AROUND 30% FOR INDIANAPOLIS. IT'S IMPORTANT TO KNOW THAT
THERE ARE MULTIPLE COMPONENTS TO CONSIDER WHICH CAN JEOPARDIZE THE
CALIBRATION OF THESE GRANULAR MODEL EXCEEDANCE THRESHOLD VALUES.
STRATUS MAY BE SLOW TO CLEAR AS THIS SYSTEM DEPARTS, MUCH LIKE THE
LAST SYSTEM. RESIDUAL LOW LEVEL MOISTURE IS INDICATED IN MODELS,
ALONG WITH PERIPHERAL CYCLONIC LOWER TROPOSPHERIC FLOW CONTINUING
INTO SATURDAY, WITH A SUBSIDENT REGIME UPSTREAM OF THE DEPARTING
TROUGH. WE WILL INCREASE CLOUD COVER THROUGH THE FIRST PART OF
SATURDAY, AND EVEN HAVE SOME PESSIMISM ABOUT THE POTENTIAL FOR
STRATUS TO CLEAR ON SATURDAY. BY LATE SATURDAY OR SUNDAY, MEAN RIDGE
AXIS WILL MOVE OVERHEAD WITH POSITIVE MIDLEVEL HEIGHT ANOMALIES AND
A SHIFT IN LOW LEVEL FLOW FAVORING SOME MODEST DRY ADVECTION.
ALTHOUGH, AT THAT TIME, PACIFIC MOISTURE PLUME WITHIN FAST
WESTERLIES ALOFT WILL PROBABLY RESULT IN EXTENSIVE CIRRUS.
A BROAD LOW-AMPLITUDE TROUGH IS SHOWN IN THE MODELS APPROACHING
EARLY NEXT WEEK, BUT THE DIVERSITY OF ITS AMPLITUDE AND TIMING IS
BROADER THAN WOULD BE IDEAL IN THE MEDIUM RANGE MODELS. GEFS/GFS-
WEIGHTED CLUSTER AND EPS/EUROPEAN-WEIGHTED CLUSTER ARE OUT OF PHASE
WITH TROUGH/RIDGE POSITION, ALTHOUGH BOTH SHOW IT AND ARE
PROGRESSIVE, SO IT'S MAINLY A TIMING ISSUE. GEPS/CANADIAN-WEIGHTING
IS DISTRIBUTED FAIRLY UNIFORMLY AMONG THE TWO CLUSTERS. SOME OF THE
OUTLIER ENSEMBLE MEMBERS ARE DRIVING TWO OTHER SCENARIOS REPRESENTED
BY THE OTHER TWO CLUSTERS. SO, FORECAST UNCERTAINTY IS HIGHER THAN
TYPICAL EARLY NEXT WEEK. FOR NOW WE HAVE MID-RANGE PRECIPITATION
PROBABILITIES SPREAD ACROSS A BROAD TIME RANGE. WE WILL REFINE LATER
ONCE THE TROUGH/RIDGE PATTERN BECOMES MORE CLEAR, AS WELL AS HOW THE
MORE EASTWARD-BENDING MOISTURE PLUME SEEN IN MODEL IVT IS ABLE TO
INTERACT WITH THE TROUGH. THE GENERAL PATTERN WILL BE WARM ENOUGH
FOR RAIN AND COULD PEAK AT AROUND 5-7 DEGREES ABOVE MID-LATE
NOVEMBER CLIMATOLOGY.
FORECAST SKILL IN THE DAY 8-14 PERIOD APPEARS TO BE LESS THAN
TYPICAL. THERE IS NEARLY AN EVEN SPLIT WITHIN THE MULTI-MODEL
ENSEMBLE OF WHETHER WE'LL SEE A RIDGE OR TROUGH IN THE EAST AT THE
START OF THIS PERIOD. FURTHERMORE, THE UPSTREAM SYNOPTIC PATTERN
DIFFERS SIGNIFICANTLY. ALL THAT CAN BE SAID AT THIS TIME IS THAT IT
APPEARS THERE WILL BE VARIABILITY IN TEMPERATURE AND OPPORTUNITIES
FOR PRECIPITATION, GIVEN THE INDICATION OF A CONTINUATION OF A
PROGRESSIVE AT LEAST SOMEWHAT AMPLIFIED SYNOPTIC FLOW PATTERN.
AVIATION (06Z TAF ISSUANCE)
ISSUED AT 1244 AM EST TUE NOV 19 2024
IMPACTS:
- GUSTY WINDS THROUGH MUCH OF THE NIGHT INTO TUESDAY AFTERNOON
- MVFR CEILINGS IN SHOWERS LATE TONIGHT INTO TUESDAY MORNING
DISCUSSION:
A FRONTAL SYSTEM IS QUICKLY APPROACHING THE AREA, WITH SHOWERS
EXPECTED TO BEGIN AT THE SITES WITHIN THE FIRST HOUR OR TWO OF THE
TAF PERIOD AND CONTINUE INTO EARLY TO MID MORNING TUESDAY. MVFR
CEILINGS WILL DEVELOP ASSOCIATED WITH THE SHOWERS, AND BRIEF PERIODS
OF IFR CANNOT ENTIRELY BE RULED OUT, BUT WILL BE TRANSIENT/LOW
PROBABILITY ENOUGH TO EXCLUDE.
VFR CONDITIONS SHOULD RETURN BY MIDDAY AT THE LATEST, PERSISTING
THROUGH THE REST OF THE PERIOD.
WINDS ARE GENERALLY SOUTHEASTERLY AT THE MOMENT, AND WILL GRADUALLY
VEER TO SOUTHWESTERLY AND WESTERLY BY THE END OF THE PERIOD. GUSTS
OVERNIGHT INTO TUESDAY AFTERNOON IN THE LOW TO MID 20KT RANGE CAN BE
EXPECTED, WITH SUSTAINED WINDS 10-15KT. GUSTS SHOULD SUBSIDE LATE
AFTERNOON/EARLY EVENING ON TUESDAY.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...NIELD
LONG TERM...BRB
AVIATION...NIELD
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