099
FXUS63 KIND 181950
AFDIND
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE INDIANAPOLIS IN
250 PM EST WED DEC 18 2024
KEY MESSAGES
- COOLER THAN NORMAL TEMPERATURES WILL RETURN THURSDAY THROUGH THE
WEEKEND
- LIGHT SNOW POSSIBLE THURSDAY NIGHT INTO FRIDAY. THE SNOW COULD
IMPACT THE FRIDAY MORNING COMMUTE.
- A WARMING TREND IS EXPECTED NEXT WEEK AND RAIN WILL RETURN FOR
CHRISTMAS EVE INTO CHRISTMAS DAY
SHORT TERM (THIS EVENING THROUGH THURSDAY)
ISSUED AT 250 PM EST WED DEC 18 2024
COOL AND CLOUDY CONDITIONS PERSIST ACROSS CENTRAL INDIANA THROUGH
THE SHORT TERM PERIOD. LATEST SATELLITE IMAGERY SHOWS THE MAIN FETCH
OF MOISTURE, ASSOCIATED WITH THE DEPARTING SYSTEM, EXITING INDIANA
TO THE EAST WITH LOW STRATUS ADVECTING IN FROM THE NORTHWEST. LATEST
ACARS SOUNDINGS FROM AROUND SHOW A SHALLOW SATURATED LAYER STUCK
NEAR THE SURFACE UNDER A DEVELOPING SUBSIDENCE INVERSION. THIS
SHOULD KEEP LOW LEVEL STRATUS OVER MUCH OF CENTRAL INDIANA INTO THE
OVERNIGHT HOURS. DRIER AIR WILL BE ADVECTING IN AS HIGH PRESSURE
BRIEFLY BECOMES CENTERED OVERHEAD LATER TONIGHT; HOWEVER WITH RECENT
RAINFALL AND WET SURFACES, IT IS LIKELY THAT LOW LEVEL MOISTURE WILL
REMAIN HIGH ENOUGH TO SUPPORT LOWER CLOUDS INTO AT LEAST THE MORNING
HOURS. CROSS SECTIONAL PROFILES FROM HI-RES MODELS SUPPORT THIS
THINKING. KEEPING LOW TEMPERATURES TONIGHT A TAD ABOVE GUIDANCE IN
THE MID TO UPPER 20S TO NEAR 30 DUE TO THE CLOUD COVER. POTENTIAL IS
THERE FOR PATCHY FOG DEVELOPMENT IN LOW LYING AND WIND SHELTERED
SPOTS AS WINDS BECOME CALM UNDER THE AREA OF HIGH PRESSURE. HIGHER
CONFIDENCE REMAINS IN MOST AREAS REMAINING UNDER LOW STRATUS
INSTEAD; HOWEVER THERE COULD BE A FEW AREAS THAT SEE BREAKS IN THE
CLOUDS RESULTING IN PATCHY FOG DURING THE EARLY MORNING HOURS.
HIGHEST PROBABILITY OF ANY FOG WOULD BE IN SOUTH CENTRAL INDIANA AND
IN THE WABASH RIVER VALLEY.
HIGH PRESSURE SLOWLY SHIFTS EASTWARD TOMORROW AHEAD OF THE NEXT
APPROACHING CLIPPER SYSTEM FROM THE NORTHWEST. WHILE WINDS DO BECOME
SOUTHERLY, CURRENT THOUGHTS ARE THAT ANY MIXING AND WINDS SHOULD
REMAIN WEAK ENOUGH TO KEEP LOW LEVEL CLOUDS AROUND THROUGH THE FIRST
HALF OF THE DAY. BEST CHANCE FOR ANY PEAKS OF SUNSHINE WILL BE OVER
FAR SOUTHERN AND SOUTHWESTERN INDIANA; HOWEVER EXPECT CLOUDS TO
THICKEN BY THE EVENING. KEEPING HIGHS BELOW GUIDANCE WITH THICKER
CLOUD COVER LIKELY WITH TEMPERATURES ONLY RISING INTO THE MID 30S
FOR NORTH CENTRAL INDIANA AND UPPER 30S TO NEAR 40 FURTHER SOUTH.
LONG TERM (THURSDAY NIGHT THROUGH WEDNESDAY)
ISSUED AT 250 PM EST WED DEC 18 2024
THE STRUCTURE AND TRACK OF THE INCOMING MIDLEVEL SHORTWAVE TROUGH
WILL BE KEY TO UNDERSTANDING SNOW ACCUMULATION POTENTIAL THURSDAY
NIGHT INTO FRIDAY. THE INITIAL ASCENT WILL COME LATE THURSDAY WITH
THE LEAD WAVE THAT WILL BE DAMPENING. THE MOST PRONOUNCED ISENTROPIC
ASCENT SIGNAL WITH LOWEST CONDENSATION PRESSURE DEFICITS WILL BE
FOCUSED TO OUR NORTH, AND THIS WILL BE WHERE THE LIGHT PRECIPITATION
AMOUNTS WILL BE RELEGATED TO. IT FITS THE CONCEPTUAL MODEL GIVEN THE
SYSTEM'S TRACK.
MODELS THEN AGREE ON A SUBSEQUENT SHORTWAVE TROUGH BECOMING DOMINANT
AS IT AMPLIFIES. DEEP/ANOMALOUS MOISTURE ADVECTION IS NOT INDICATED
WITH THIS SYSTEM SINCE THE LOWER LATITUDE MOISTURE WILL BE TOO
DETACHED FROM THE FLOW FIELDS OF THE INCOMING SYSTEM. NEVERTHELESS,
SNOW SHOWERS MAY REACH DEEPER INTO CENTRAL INDIANA WITH (1) THE
INITIAL FRONTAL FORCING, MANIFESTING IN A FAIRLY NARROW BAND OF
SNOW, (2) 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. THESE DETAILS WILL BE REFINED LATER, BUT
WITH AN ENSEMBLE MEAN QPF IN THE 0.05-0.10 INCH RANGE, SNOWFALL
AMOUNTS WILL GENERALLY BE AROUND ONE INCH OR UNDER BY LATE FRIDAY.
HIGHEST AMOUNTS WILL BE ACROSS THE NORTH, TAPERING WITH SOUTHWARD
EXTENT.
COLD ADVECTION WILL KEEP TEMPERATURES NEAR OR BELOW FREEZING THIS
WEEKEND, FOLLOWED BY A WARMING TREND NEXT WEEK AND PRECIPITATION
CHANCES RETURNING. WITH THE WARM ADVECTION REGIME PRECIPITATION TYPE
IS EXPECTED TO BE RAIN, BUT COULD START AS SNOW FOR AT LEAST A BRIEF
PERIOD LATE MONDAY. IT APPEARS THAT THE BEST PAIRING FOR PROLONGED
FORCING FOR ASCENT AND ANOMALOUS MOISTURE WILL AGAIN OCCUR NEAR AND
SOUTH OF THE OHIO RIVER. MULTI-MODEL ENSEMBLE MEAN QPF OF AROUND
0.50 INCHES IS SHOWN THROUGH MID WEEK, AND CLUSTERING IS REASONABLY
TIGHT FOR THIS TIME RANGE.
DAY 8-14: MEDIUM-RANGE MODELS SHOW A SLIGHTLY MORE AMPLIFIED AND
SLIGHTLY LESS PROGRESSIVE SYNOPTIC SCALE PATTERN. IT APPEARS RIDGING
WILL HOLD STRONG ENOUGH FOR ABOVE NORMAL TEMPERATURES. ALTHOUGH
MODELS VARY WITH THE DETAILS ON TROUGH PROGRESSION, THERE IS ENOUGH
OF A SIGNAL TO WEIGHT TOWARD ABOVE NORMAL TOTAL PRECIPITATION DURING
THIS PERIOD. ANY WEATHER HAZARDS DURING THIS TIME ARE NOT CURRENTLY
EVIDENT.
AVIATION (18Z TAF ISSUANCE)
ISSUED AT 1243 PM EST WED DEC 18 2024
IMPACTS:
- VFR CEILINGS BECOMING MVFR THIS EVENING
- IFR TO MVFR CIGS OVERNIGHT WITH PATCHY FOG DEVELOPING
DISCUSSION:
LATEST SATELLITE IMAGERY SHOWS VFR CIGS FOR THE SOUTHEASTERN HALF OF
INDIANA WITH AN AREA OF LOW MVFR TO IFR STRATUS PUSHING IN FROM THE
NORTHWEST. KLAF HAS ALREADY REPORTED CIGS AROUND OVC009 WITH
UPSTREAM OBSERVATIONS INDICATING THESE LOW CEILINGS WILL LIKELY
PERSIST THROUGH THE REST OF THE AFTERNOON AND CONTINUE PUSHING SOUTH
AND EAST. HAVE CEILINGS LOWERING AT ALL TAF SITES TO LOW MVFR LEVELS
OVER THE NEXT FEW HOURS. CIGS WILL LIKELY BECOME BKN OVERNIGHT AS
DRIER AIR MOVES IN ALOFT; HOWEVER LEFTOVER MOISTURE TRAPPED AT THE
SURFACE UNDER A DEVELOPING INVERSION MAY KEEP A LOW BKN DECK AROUND
FOR MUCH OF THE OVERNIGHT HOURS.
ALSO CONCERNED WITH THE POSSIBILITY OF FOG DEVELOPMENT OVERNIGHT AS
HIGH PRESSURE BRIEFLY BECOMES CENTERED OVER THE REGION. ADDED PATCHY
FOG TO ALL TAF SITES WITHIN THE 08-15Z TIMEFRAME TONIGHT INTO
TOMORROW MORNING. THINKING LOWEST CIGS AND VIS WILL LIKELY BE IN THE
WABASH RIVER VALLEY AND AROUND KBMG. THERE MAY BE AREAS ACROSS THE
STATE THAT SEE LOW STRATUS WITH NO VIS RESTRICTIONS, WHILE OTHERS
SEE PATCHY FOG WITH LOWER VIS. CONFIDENCE IS LOWER PINPOINTING WHICH
AREAS SEE WHICH, SO THAT WILL BE SOMETHING TO WATCH CLOSELY TONIGHT.
CEILINGS MAY HAVE TROUBLE RECOVERING TOMORROW AS SOME SHORT-TERM
GUIDANCE SHOWS MOISTURE REMAINING TRAPPED NEAR THE SURFACE MUCH OF
THE DAY. THINKING CIGS WILL AT LEAST RISE TO MVFR LEVELS BY THE END
OF THE TAF PERIOD THOUGH.
OTHER THAN THAT, NW WINDS IN THE 09-13 KT RANGE THIS AFTERNOON WILL
BECOME NEARLY CALM DURING THE OVERNIGHT HOURS, THEN BECOME
SOUTHEASTERLY BY LATE MORNING.
IND WATCHES/WARNINGS/ADVISORIES
NONE.
SHORT TERM...CM
LONG TERM...BRB
AVIATION...CM
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