882
FXUS63 KIND 200841
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
341 AM EST WED NOV 20 2024
KEY MESSAGES
- RAIN THIS MORNING, BREEZY THIS AFTERNOON AND TONIGHT WITH FREQUENT
GUSTS OF 25-35 MPH, LOCALLY HIGHER GUSTS POSSIBLE.
- FIRST SNOW OF THE SEASON TONIGHT INTO THURSDAY WITH AS MUCH AS 1-3
INCHES POSSIBLE ACROSS PORTIONS OF THE AREA; MINOR TRAVEL IMPACTS
POSSIBLE
- DRY WITH A WARMING TREND STARTING THIS WEEKEND.
- RAIN CHANCES RETURN LATE MONDAY AND TUESDAY.
SHORT TERM (TODAY AND TONIGHT)
ISSUED AT 341 AM EST WED NOV 20 2024
COUPLE OF ROUNDS OF PRECIPITATION EXPECTED TODAY INTO TONIGHT.
A STRONG FRONTOGENETIC BAND AT THE LEADING EDGE OF THE INITIAL VORT
LOBE ASSOCIATED WITH THE VERY STRONG UPPER LOW HEADED OUR WAY WILL
SWEEP ACROSS THE AREA THIS MORNING. THIS FORCING FOR ASCENT IS
PROMOTING DEVELOPMENT OF A BAND OF SHOWERS WHICH APPEARS POISED TO
SWEEP ACROSS THE AREA IN ROUGHLY THE 6 AM TO NOON TIME FRAME THIS
MORNING. THE AFOREMENTIONED STRONG FORCING FOR ASCENT WILL ALLOW
RAINFALL RATES TO BE PRETTY SOLID, BUT THE LIMITED DURATION OF RAIN
AT ANY ONE LOCATION WILL LIMIT TOTALS TO AROUND A TENTH TO QUARTER
OF AN INCH OR SO, WITH THE HIGHEST TOTALS LIKELY IN THE
NORTH/NORTHEASTERN PORTIONS OF THE FORECAST AREA.
THIS RAIN WILL MOVE OUT, AND A DRY BUT QUITE BREEZY AFTERNOON IS
EXPECTED ACROSS CENTRAL INDIANA. THOUGH SOME CLEARING AND RESULTANT
INSOLATION IS EXPECTED, CONTINUED COLD ADVECTION WILL LIMIT DIURNAL
WARMING, AND TEMPERATURES ARE LIKELY TO STRUGGLE TO GET OUT OF THE
40S ACROSS MUCH OF THE AREA, EXCEPT PERHAPS THE SOUTHWESTERN
FORECAST AREA, WHICH WILL BE THE FIRST TO SEE BREAKS OF SUN.
SURFACE CYCLOGENESIS IS EXPECTED TO OCCUR NEAR OR JUST TO OUR EAST
THIS AFTERNOON INTO TONIGHT ASSOCIATED WITH THE LEADING VORT MAX
PIVOTING AROUND THE UPPER LOW, AND THE INTENSIFYING PRESSURE
GRADIENT ALONG WITH DEEPENING BOUNDARY LAYER MIXING WILL PROMOTE
GUSTY WINDS, PARTICULARLY THIS AFTERNOON INTO TONIGHT. GUSTS THIS
AFTERNOON OF 30-35 MPH WILL BE COMMON, WITH ISOLATED HIGHER GUSTS
POSSIBLE. GUSTS OVERNIGHT TONIGHT MAY BE MORE IN THE 20-25 MPH
RANGE, ESPECIALLY EARLY, THOUGH SOME STRENGTHENING IS POSSIBLE LATE
TO NEAR 30 MPH.
EVEN MORE SUBSTANTIAL COLD ADVECTION WILL ARRIVE LATE TODAY INTO
TONIGHT AS THE UPPER LOW CONTINUES TO SETTLE OVER THE GREAT LAKES
AND OHIO VALLEY, AND THE RAPIDLY DEVELOPING SURFACE LOW PIVOTS OVER
MICHIGAN THROUGHOUT THE NIGHT. FORECAST PROFILES SHOW DEVELOPMENT OF
A FAIRLY WELL SATURATED AIRMASS OVERNIGHT TONIGHT, ALONG WITH STEEP
LOW LEVEL LAPSE RATES AND INCREASING FORCING FOR ASCENT AS ANOTHER
VORT LOBE PIVOTS AROUND THE LARGER UPPER LOW LATE THIS EVENING INTO
TONIGHT. THIS, COUPLED WITH A DENDRITIC GROWTH ZONE THAT MAY BE
QUITE DEEP AT TIMES, COULD SET THE STAGE FOR SOME SUBSTANTIAL SNOW
SHOWERS, PARTICULARLY LATE THIS EVENING INTO THE OVERNIGHT HOURS AS
THE AFOREMENTIONED ASCENT INCREASES AND LOW LEVEL THERMAL PROFILES
BECOME FULLY SUPPORTIVE OF SNOW. IT APPEARS LIKELY THAT ONE ROUND OF
MODERATE SNOW SHOWERS WILL PUSH THROUGH THE AREA OVERNIGHT TONIGHT,
WITH PERHAPS A BREAK NEAR DAYBREAK THURSDAY PRIOR TO A MORE
SUBSTANTIAL ROUND TWO THURSDAY INTO THURSDAY EVENING AS THE SURFACE
CYCLONE FULLY PIVOTS BACK INTO THE REGION.
THESE EARLY SEASON SETUPS ARE ALWAYS INCREDIBLY TRICKY WHEN IT COMES
TO ACCUMULATION, PARTICULARLY WHEN SURFACE TEMPERATURES WILL BE
MARGINAL, AND WHEN THE GROUND HAS BEEN AS WARM AS IT HAS BEEN
RECENTLY IN THE PROLONGED ABOVE NORMAL TEMPERATURE REGIME OF RECENT
DAYS AND WEEKS. THAT SAID, RATES ARE OFTEN ABLE TO COMPENSATE FOR
THIS EFFECT FASTER THAN MIGHT OTHERWISE BE EXPECTED, AND AT THE VERY
LEAST, LIGHT ACCUMULATIONS ON GRASSY AND ELEVATED SURFACES APPEAR TO
BE A GOOD BET TONIGHT, WITH SOME IMPACT TO ROADWAYS, PRIMARILY
BRIDGES AND OVERPASSES, POSSIBLE, PARTICULARLY OVER NORTHERN
PORTIONS OF THE AREA, WHERE SURFACE TEMPERATURES ARE MOST LIKELY TO
DROP BELOW FREEZING FOR AT LEAST A FEW HOURS LATE TONIGHT INTO
THURSDAY MORNING.
ACROSS CENTRAL INDIANA, THE MOST LIKELY SCENARIO FOR TONIGHT IS A
DUSTING TO PERHAPS A HALF INCH OR SO OF SNOWFALL BY DAYBREAK
THURSDAY, AGAIN PRIMARILY ON GRASSY AND ELEVATED SURFACES, WITH SOME
LIGHT COATING POSSIBLE ON BRIDGES AND OVERPASSES. THIS COULD HAVE
MINOR IMPACTS TO THE THURSDAY MORNING COMMUTE, BEING THE FIRST
SNOWFALL OF THE YOUNG SEASON.
LONG TERM (THURSDAY THROUGH TUESDAY)
ISSUED AT 341 AM EST WED NOV 20 2024
ACCUMULATING SNOW IS LIKELY FOR PORTIONS OF THE AREA ON THURSDAY
WITH MINOR TRAVEL IMPACTS POSSIBLE. WE ALSO EXPECT THE COLDEST
DAYTIME TEMPERATURES SINCE LAST MARCH ALONG WITH WINDY CONDITIONS
CAUSING WIND CHILLS IN THE 20S. THE SYNOPTIC SETUP IS COMPLICATED
BUT GOOD ALIGNMENT AND RUN-TO-RUN MODEL STABILITY MEANS THAT
FORECAST UNCERTAINTIES ARE MAINLY CENTER AROUND THE SENSITIVITY OF A
MARGINAL TEMPERATURE SCENARIO. METEOROLOGICAL DETAILS AND FORECAST
UNCERTAINTIES ARE COVERED BELOW.
TWO DISTINCT VORTICITY MAXIMA ARE MODELED WITHIN THE BROAD DEEP
OCCLUDED LOW OVER OUR REGION. THE FIRST WILL MOVE SOUTH OF US DURING
THE MORNING, BRINGING A DECREASE IN A DEEPER ASCENT-DRIVEN
PRECIPITATION SCENARIO. SNOW SHOWERS SHOULD SHIFT SOUTHEAST OF THE
AREA. HOWEVER, LOWER TROPOSPHERIC MOISTURE REMAINS, ALONG WITH
STEEPENING LAPSE RATES. DESPITE TEMPORARILY DRYING MIDLEVELS,
SHALLOW CONVECTIVE PRECIPITATION MAY CONTINUE INTO THE LATE
MORNING/MIDDAY TIME FRAME ALBEIT RESULTING IN MINIMAL AMOUNTS.
POTENTIAL LOSS OF ICE DUE TO BRIEF DRYING OF MIDLEVELS (CRITICAL
TEMPERATURE LAYER FOR ICE CRYSTAL GROWTH) MAKES PRECIPITATION TYPE
DURING THIS PERIOD A LITTLE UNCERTAIN. ONLY MODEST HEATING WILL
OCCUR DURING THIS TIME FRAME OWING TO ONGOING COLD ADVECTION.
TEMPERATURES LIKELY WILL PEAK ONLY IN THE MID TO UPPER 30S.
THE SECOND (AND MORE INTENSE) VORT MAX/PV ANOMALY IS MODELED TO
PROGRESS SOUTHWARD ACROSS THE AREA DURING THE AFTERNOON AND EVENING
AND WILL BE ACCOMPANIED BY INCREASING FORCING FOR ASCENT AND DEEP
MOISTENING. ROUGHLY A 6-HOUR PERIOD OF PRECIPITATION IS LIKELY, WITH
LINGERING LIGHTER PRECIPITATION CONTINUING THEREAFTER. HREF MEMBERS
AND GLOBAL MODELS HAVE ALL CLUSTERED ON AROUND 0.25" QPF OR SLIGHTLY
MORE. TEMPERATURES MAY INITIALLY RISE ENOUGH TO BE MARGINAL FOR
RAIN/SNOW FOR AT LEAST PORTIONS OF THE AREA, BUT IT APPEARS THE
LOWER TROPOSPHERE WILL BE DRY ENOUGH FOR DIABATIC EFFECTS TO RESULT
IN SNOW BEING DOMINANT. HIGHER LOW LEVEL MOISTURE FROM REMNANT WARM
CONVEYOR BELT WRAPPING ALL THE WAY AROUND THE LOW, AND POTENTIALLY
AUGMENTED SOME BY THE GREAT LAKES, LOOKS TO REACH OUR AREA AFTER THE
MAIN AREA OF PRECIPITATION DEPARTS DURING THE EVENING. EVEN IF
RISING DEW POINTS AND LESS POTENTIAL FOR WET BULB/DIABATIC PROCESSES
TO FAVOR SNOW, LOSS OF ICE DUE TO MIDLEVEL DRYING MAY CAUSE A
TRANSITION BACK TO RAIN WITH LINGERING PRECIPITATION LATE EVENING OR
OVERNIGHT.
USING THIS A CLIMATOLOGICAL SNOW-LIQUID RATIO AND EXCLUDE
MELTING FROM WARM ANTECEDENT CONDITIONS, THIS WOULD YIELD AROUND 2.5-
3" OF SNOW ALONG THE QPF MAXIMA ACROSS NORTHERN PORTIONS OF CENTRAL
INDIANA. HOWEVER, IT APPEARS THAT THE BEST ALIGNMENT OF ASCENT AND
MOISTURE WITHIN THE DENDRITIC GROWTH ZONE FOR ~10-12:1 SLR WILL BE
RELATIVELY BRIEF, AND WE'VE ALSO ARTIFICIALLY LOWERED THESE TO
ACCOUNT FOR SOME ANTECEDENT WARM CONDITIONS AND AT LEAST SOME
INITIAL MELTING. IT DOES APPEAR THAT RATES AND DURATION OF THE SNOW
IN COMBINATION WITH ONGOING COLD ADVECTION WILL BE ENOUGH TO
OVERCOME THE WARM GROUND AND MELTING TO SOME EXTENT. SO, SOME SLICK
CONDITIONS ON BRIDGES, OVERPASSES, AND LESS TRAVELED ROADS WILL BE
POSSIBLE, ESPECIALLY WHERE SNOWFALL RATES ARE THE HIGHEST. WARM
GROUND INFLUENCE MAY BE MORE NOTICEABLE ON THE FRINGES OF THE CORE
OF THE PRECIPITATION AND WHERE TEMPERATURES ARE MORE MARGINAL,
ACROSS WEST-CENTRAL INTO SOUTHERN INDIANA.
REMNANT LOWER TROPOSPHERIC MOISTURE, STEEP LAPSE RATES, AND CYCLONIC
LOW-LEVEL FLOW MAY RESULT IN SOME CONVECTIVE PRECIPITATION
ESPECIALLY ACROSS THE NORTHEAST HALF OF THE AREA FRIDAY.
TEMPERATURES SHOULD WARM SUFFICIENTLY FOR THESE TO BE RAIN SHOWERS.
STRATUS APPEARS LIKELY INTO AT LEAST EARLY SATURDAY, AT WHICH TIME
LOW AMPLITUDE MEAN RIDGING BUILDS IN AND A WARMING TREND
ACCELERATES. RAIN CHANCES WILL INCREASE EARLY NEXT WEEK AS AT LEAST
THE FRINGE OF DEEPER SUBTROPICAL MOISTURE PLUME AND FORCING FROM ONE
OR MORE LOW AMPLITUDE SHORTWAVE TROUGHS ALIGN OVER OUR REGION. THE
BETTER PRECIPITATION COVERAGE WILL PROBABLY BE RELEGATED TO DEEPER
WITHIN THE MOISTURE PLUME NEAR/SOUTH OF THE OHIO RIVER.
THE DAY 8-14 PERIOD LOOKS TO FEATURE WARM/COOL PERIODS AVERAGING TO
NEAR NORMAL, AND PERIODIC PRECIPITATION CHANCES, BUT NO SIGNAL FOR
SIGNIFICANT WEATHER HAZARDS AT THIS TIME.
AVIATION (06Z TAF ISSUANCE)
ISSUED AT 1235 AM EST WED NOV 20 2024
IMPACTS:
- GUSTY WINDS 20-27KT WEDNESDAY
- SHOWERS AND AT LEAST OCCASIONAL MVFR CEILINGS WEDNESDAY MORNING
DISCUSSION:
VFR CONDITIONS WILL PERSIST THROUGH DAYBREAK ACROSS THE AREA. A
LARGE INCOMING UPPER LEVEL LOW WILL PROMOTE A SURFACE RESPONSE IN
THE FORM OF SURFACE CYCLOGENESIS, WHICH IS LIKELY TO PRODUCE SOME
LIGHT RAIN SHOWERS, PARTICULARLY FROM LAF/IND EAST/NORTHEAST.
HUF/BMG WILL LIKELY SEE SOME SHOWERS, BUT IT MAY BE MORE TRANSIENT.
WILL CARRY PREVAILING SHOWERS AT LAF/IND AND TEMPO ELSEWHERE.
WINDS WILL BECOME NORTHWESTERLY WHERE THEY HAVE NOT ALREADY, AND
STRENGTHEN DURING THE DAY ON WEDNESDAY TO AROUND 12-17KT, WITH GUSTS
20-27KT. THESE GUSTS MAY PERSIST INTO THE EVENING HOURS IN SOME
SPOTS DEPENDING UPON THE EVOLUTION OF THE SURFACE LOW, AND WILL
NEED TO REEVALUATE THIS WITH THE LATER PACKAGES.
ANY MVFR CEILINGS WILL LIKELY RETURN TO VFR BY MIDDAY TO EARLY
AFTERNOON.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...NIELD
LONG TERM...BRB
AVIATION...NIELD
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