261  
FXUS63 KIND 201826  
AFDIND  
 
AREA FORECAST DISCUSSION  
NATIONAL WEATHER SERVICE INDIANAPOLIS IN  
226 PM EDT MON SEP 20 2021  
   
SHORT TERM
 
(THIS EVENING THROUGH TUESDAY NIGHT)  
ISSUED AT 226 PM EDT MON SEP 20 2021  
 
THE CHANNEL OF GREATEST ISENTROPIC LIFT ASSOCIATED WITH A WEAK LLJ  
IS MOVING OFF TO THE EAST,ALONG WITH AN AREA OF WIDESPREAD SHOWERS.  
A WEAK SURFACE LOW OVER CENTRAL ILLINOIS HAS CONTINUED TO MOVE  
NORTHWARD WITHIN THE SOUTHERLY FLOW. EAST OF THIS LOW, A REGION OF  
LOCALIZED LIFT HAS HELPED INITIATE SCATTERED SHOWERS AND A FEW  
EMBEDDED THUNDERSTORMS. AS THE CLOUD LAYER THINS AND BECOMES MORE  
BROKEN, SURFACE BASED INSTABILITY SHOULD RISE SLIGHTLY, PEAKING  
BETWEEN 1000 AND 1500 J/KG OF SBCAPE LATER THIS AFTERNOON. THIS  
COULD ALLOW FOR A FEW MORE EMBEDDED THUNDERSTORMS OVER WEST CENTRAL  
INDIANA LATE THIS AFTERNOON AND EVENING. WIND SHEAR REMAINS  
EXTREMELY WEAK WITH THE SUBTLE LLJ OFF TO THE EAST. THIS SHOULD  
INHIBIT UPDRAFT GROWTH, KEEPING ANY THUNDERSTORMS MUNDANE. PWAT  
VALUES NEAR 2", AND A FAIRLY SATURATED ATMOSPHERIC PROFILE INDICATE  
THE POSSIBILITY OF RAIN BEING HEAVY AT TIMES. THIS COULD LEAD TO  
MINOR LOCALIZED FLOODING.  
 
TEMPERATURES WILL CONTINUE TO RISE OVER THE NEXT FEW HOURS AS THE  
CLOUD LAYER THINS OUT TO THE WEST. OVER EASTERN CENTRAL INDIANA, A  
THICK CLOUD LAYER REMAINS, WHICH WILL INHIBIT SURFACE WARMING;  
RESULTING IN A GRADUAL TEMPERATURE GRADIENT WITH HIGHS RANGING FROM  
LOW 80S TO THE WEST AND MID 70S TO THE EAST. EXPECTATIONS ARE FOR  
THERE TO BE LULL IN PRECIPITATION OVERNIGHT AS THE BOUNDARY LAYER  
STABILIZES AND A NARROW CORRIDOR OF DRIER LOW LEVEL AIR MOVES IN.  
CLOUD COVER SHOULD STILL REMAIN FAIRLY CONSISTENT, WITH A FEW  
BREAKS.  
 
AN AMPLIFIED TROUGH CURRENTLY OVER THE PLAINS WILL CONTINUE TO  
PROGRESS EASTWARD THROUGH TONIGHT IS THE NEXT SOURCE OF  
PRECIPITATION. THIS TROUGH HAS A DEEP POOL OF COLD AIR WITHIN IT,  
RESULTING IS A STRONG UPPER LEVEL JET. CURRENTLY, A SURFACE LOW IS  
CONTINUING TO DEEPEN OVER THE NORTHERN GREAT LAKES, FURTHER  
ADVANCING THIS COLD AIR MASS INTO THE MIDWEST. THE SOUTHERLY PUSH OF  
COLD AIR HAS CREATED AN INTENSE COLD FRONT, OF WHICH WILL APPROACH  
INDIANA SOMETIME TOMORROW MORNING.  
 
AS THE FRONT MOVES SOUTHWARD, INTO THE OHIO VALLEY, IT WILL BECOME  
FARTHER DISPLACED FROM THE OCCLUDING LOW LEVEL CYCLONE, WEAKENING  
THE FRONTOGENETICAL FORCING AND SLOWING ITS PROGRESSION. THIS HAS  
CREATED SOME UNCERTAINTY ON TIMING OF PRECIPITATION TOMORROW, AS THE  
FRONT WILL BE THE PRIMARY SOURCE OF LIFT. GENERAL CONSENSUS AMONG  
ENSEMBLES HAS FRONT PASSING THROUGH CENTRAL INDIANA EARLY TOMORROW  
AFTERNOON. FOR THIS REASON, HIGHEST POPS HAVE BEEN FORECASTED FOR  
AROUND THIS TIME, WITH AN INCREASE IN CHANCES FROM WEST TO EAST  
THROUGHOUT THE DAY. STRONG FORCING ALONG THE FRONT IN COMBINATION  
WITH HIGHER THAN NORMAL PWAT VALUES COULD RESULT IN PROLONGED  
DOWNPOURS. THIS, ALONG WITH AN ALREADY SATURATED GROUND FROM THE  
PREVIOUS RAINFALL, WILL LEAD TO A SLIGHT RISK OF FLASH FLOODING.  
 
WITH DEEP CLOUD COVER ALONG THE BOUNDARY AND WITHIN THE CYCLONIC  
FLOW, TEMPERATURES WILL STRUGGLE TO INCREASE THROUGHOUT THE DAY.  
CURRENT EXPECTATIONS ARE FOR HIGHS IN THE MID 70S, WITH A SLIGHT  
DROP OFF FOLLOWING FRONTAL PASSAGE. WITH UNCERTAINTY AS TO TIMING OF  
FRONTAL PASSAGE, HOURLY TEMPS HAVE BEEN KEPT FAIRLY DIURNAL, ALTHOUGH  
THIS WILL NOT BE THE CASE FOR LOCATIONS WEST OF THE FRONT. MOST  
LOCATIONS SHOULD BE WEST OF THE FRONT BY TOMORROW NIGHT WITH  
WIDESPREAD LOWS IN THE MID 50S AND SCATTERED SHOWERS IN THE WRAP  
AROUND MOISTURE.  
 

 
   
LONG TERM
 
(WEDNESDAY THROUGH MONDAY)  
ISSUED AT 226 PM EDT MON SEP 20 2021  
 
WEDNESDAY THROUGH THURSDAY...  
 
MODELS DISAGREEING ONCE AGAIN REGARDING THE POSITION AND STRENGTH OF  
AN UPPER TROUGH OR CUT-OFF LOW EXPECTED IN THE OHIO VALLEY AND  
SOUTHER GREAT LAKES ON WEDNESDAY. THE GFS IS FOLLOWING MORE OF THE  
UPPER TROUGH TYPE PATTERN...WHILE THE ECMWF SHOWS THE DEEPER CUT-OFF  
LOW PASSING THROUGH SOUTHERN INDIANA. DEEP MOISTURE DOES NOT APPEAR  
AVAILABLE TO THE SYSTEM AS THE EARLIER COLD FRONT WILL HAVE SWEPT  
THAT HIGH DEW POINT AIR EAST. NONETHELESS...SOME MID LEVEL  
SATURATION APPEARS AVAILABLE WITHIN THE FORECAST SOUNDINGS WITH  
PWATS NEAR 0.8 INCHES ON WEDNESDAY. THUS GIVEN THE UPPER DYNAMICS  
WILL TREND TOWARD CLOUDS AND LIKELY POPS FOR SOME VERY LIGHT  
RAINFALL POSSIBLE THROUGH THE DAY AND INTO THE EVENING.  
 
THE UPPER LOW/TROUGH BEGINS TO PUSH FARTHER NORTH ON  
THURSDAY...TAKING ANY CLOUDS AND LIGHT RAIN/DRIZZLE WITH IT.  
MEANWHILE AT THE SURFACE...A LARGE HIGH PRESSURE SYSTEM OVER THE  
PLAINS WILL BEGIN TO BUILD EASTWARD INTO THE OHIO VALLEY. THUS MAY  
INCLUDE SOME SMALL POPS ON THURSDAY MORNING...BUT TREND TOWARD A DRY  
FORECAST AS THE DAY PROGRESSES.  
 
FRIDAY THROUGH MONDAY...  
 
DRY AND COOL WEATHER IS EXPECTED TO RETURN TO THE AREA FOR MUCH OF  
THIS PERIOD. THE BEST CHANCE FOR ANY PRECIP WILL BE ON FRIDAY NIGHT  
AND EARLY SATURDAY.  
 
SURFACE HIGH PRESSURE WILL BE IN PLACE ACROSS INDIANA ON FRIDAY.  
ALOFT INDIANA WILL BE CAUGHT BETWEEN THE PREVIOUS UPPER LOW DEPARTING  
AND AN APPROACHING SHORT WAVE DROPPING OUT OF THE NORTHERN PLAINS.  
FORECAST SOUNDINGS REMAIN DRY. THUS DRY WEATHER WILL BE EXPECTED ON  
FRIDAY AND EARLY FRIDAY EVENING.  
 
THE PREVIOUSLY MENTIONED APPROACHING UPPER TROUGH IS SUGGESTED TO  
DEEPEN AND PUSH TOWARD AND ACROSS CENTRAL INDIANA LATE FRIDAY NIGHT  
AND INTO SATURDAY. FORECAST SOUNDINGS AT THIS TIME ARE SUGGESTING A  
PERIOD OF DEEP SATURATION...ALTHOUGH...GULF MOISTURE DOES NOT APPEAR  
PRESENT. WITHIN THE LOWER LEVELS...AN ACCOMPANYING WEAK COLD FRONT IS  
SHOWN TO PUSH ACROSS THE STATE. THUS...CHANCES FOR RAIN ON  
FRIDAY NIGHT AND EARLY SATURDAY APPEAR REASONABLE.  
 
DRY WEATHER SHOULD RETURN FOR SUNDAY AND MONDAY AS A SURFACE HIGH  
PRESSURE SYSTEM IS EXPECTED TO PUSH ACROSS THE AREA AND LITTLE IN  
THE WAY OF FORCING DYNAMICS IS EXPECTED TO PASS WITHIN THE NW FLOW  
ALOFT. AGAIN...WITH COOLER CANADIAN AIR IN PLACE LOOK FOR MORE  
SEASONABLE TEMPERATURES NEAR EXPECTED NORMALS.  
 

 
   
AVIATION
 
(18Z TAF ISSUANCE)  
ISSUED AT 136 PM EDT MON SEP 20 2021  
 
IMPACTS:  
- MVFR TO IFR CONDITIONS THROUGH THIS EVENING, WITH SCATTERED  
SHOWERS.  
- A FEW EMBEDDED THUNDERSTORMS WILL ALSO BE POSSIBLE THIS AFTERNOON  
- WINDS 160-190 DEGREES SUSTAINED FROM 10 TO 13 KTS. GUSTS UP TO 25  
KTS POSSIBLE AT ALL SITES THIS AFTERNOON.  
 
DISCUSSION: MAINLY POOR FLYING CONDITIONS OF MVFR TO IFR EXPECTED  
THROUGHOUT THIS EVENING WITH MULTIPLE ROUNDS OF RAIN AND POSSIBLE  
THUNDERSTORMS. A BRIEF BREAK IN RAIN LATE THIS EVENING INTO TONIGHT  
SHOULD PROVIDE AN EXTENDED PERIOD OF VFR. TOMORROW MORNING, A FRONT  
IS EXPECTED TO BRING A LINE OF SHOWERS AND STORMS, ONCE AGAIN  
DETERIORATING CONDITIONS. RAIN COULD BE HEAVY AT TIMES TOMORROW,  
LOWERING VISIBILITIES, BUT CONFIDENCE IS TOO LOW ON TIMING TO  
INCLUDE AT THIS TIME. WINDS WILL GENERALLY BE OUT OF THE S TO SE  
FROM 10-13 KTS, WITH GUSTS AROUND 25 KTS THIS AFTERNOON. GUSTS  
SHOULD DIE DOWN OVERNIGHT, BUT WINDS ARE EXPECTED TO REMAIN  
CONSISTENT AT AROUND 8-10KTS.  
 

 
   
IND WATCHES/WARNINGS/ADVISORIES
 
 
NONE.  

 
 

 
 
SHORT TERM...UPDIKE  
LONG TERM...PUMA  
AVIATION...UPDIKE  
 
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