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Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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738 FXUS63 KIND 160655 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 255 AM EDT Tue Jul 16 2024 .KEY MESSAGES... - Thunderstorms with strong winds possible early today, mainly southwest of Indianapolis - Flash flooding possible across portions of the area today and tonight, especially along and south of Interstate 70 - Dry weather along with a break from the heat and humidity Thursday through this weekend && .SHORT TERM (Today and tonight)... Issued at 254 AM EDT Tue Jul 16 2024 One final day in the very humid and at least marginally hot subtropical air mass will promote continued rain and storm chances ahead of and following a long-needed midday cold frontal passage. Following several rounds of isolated to scattered severe weather through the early week...one final opportunity for organized strong/severe storms early today will accompany a cluster of storms approaching the region from central Illinois as of 230A this morning. A more marginal threat of stronger storms embedded within increasing rain chances through PM hours is expected...courtesy adequate instability with mediocre lapse rates, and weak vertical wind shear through at least most of the day. The greater hazard will be flood potential amid increasing precip water and convergence ahead of the approaching boundary...with pwat values boosted above 2.00 inches during midday hours for all but far northern counties, and perhaps even briefly 2.50 inches over southwestern zones which would be more an a 1.00 inch anomaly. What should be a west-east band of best convergence is expected to align with mid-70s dewpoints by midday before trending southward through the region into the evening. Resultant precipitation through Tuesday night should reach 1.00 to 2.00 inches in areas, with the potential for localized maxima of 2.00 to 4.00 inches under the most impressive bands of training rain. Therefore have continued two- tier Flood Watch for all of CWA`s 39 counties...through 200PM near/north of I-70 corridor...and through 200AM Tuesday night for the region`s two southern tiers of counties. A secondary concern through the short term will be one final day of marginal heat ahead of the approaching front...lead by mid-70s dewpoints that, when coupled with low 90s in the afternoon across southern zones...will promote a few hours of heat indices at or just above 100F. This concern is somewhat conditional with generally BKN mid-level decks expected to prevail over southern counties, which may hold readings under 90F, and therefore heat indices under 100F...so have held off from issuing another SPS for this sub- Advisory threat. Turning to Tuesday night, north of I-70 and the continuing heavy rain/flooding potential rain chances should slowly decrease as slightly cooler ad drier air begins to enter the region. Fog formation will certainly be a threat over any areas where heavier rain falls, although low certainty so far on location and timing of any reduced visibility. Temperatures will have one final near/above normal day Tuesday with mid to upper 80s the general rule, and perhaps low 90s across the southern tier...with lows in the upper 60s to around 70F then expected Tuesday night. More noticeable drop in humidity and readings will occur early in the long term following the frontal zone`s passage. && .LONG TERM (Wednesday through Monday)... Issued at 254 AM EDT Tue Jul 16 2024 Big changes are in store for the long term as surface high pressure moves in, in the wake of a cold front. This will bring in a much drier and not as hot airmass starting Thursday. Wednesday is more up in the air as a cold front is expected to be over south central Indiana, perhaps even south of the CWA by 12z. That said, the dry air will take awhile to move in and with a sharp upper trough over the western Great Lakes and upper Midwest and lingering strong instability, will keep thunderstorm chances going with 40-60% PoPs over our far southern tier tapering off to 20% PoPs over our far northern tier, further away from the front. Thursday looks to be the most pleasant day a dry column per soundings supporting near full sunshine. Meanwhile, low level thermals support well below normal temperatures with highs only in the 70s and combined with dew points in the 50s, it will be a welcomed respite from the heat and humidity. As the airmass gradually modifies with high pressure overhead, temperatures will creep back up to near normal late in the weekend or early next week. The next chance of convection looks like it will hold off until next week as the high moves off to the east allowing for a gradually return of southerly flow to potentially interact with an upstream broad trough. && .AVIATION (06Z TAF Issuance)... Issued at 133 AM EDT Tue Jul 16 2024 Impacts: - One or two rounds of strong/severe TSHRA crossing region through at least 12Z from NW to SE...MVFR or worse possible within TSHRA - MVFR ceilings possible Tuesday morning, but low confidence - Southwesterly winds gusting to around 20KT midday Tuesday...before veering to westerly while decreasing by 22Z Discussion: Thunderstorm complex currently crossing central Indiana will continue to advance southeastward while weakening into pre-dawn hours. A second TSHRA complex will track from central Illinois into the region during pre-dawn hours...possibly impacting KHUF/KBMG through 14Z. Less confidence in convective potential Tuesday ahead of a slowly approaching cold front, with threat of TSHRA greatest along/south of I-70. Higher confidence in -SHRA/TSHRA late Tuesday and Tuesday night amid frontal passage with low-VFR/MVFR possible at KIND after 06Z. Gusts to 40KT will be possible under stronger cells through 14Z at KIND/KHUF/KBMG. Outside of storms/outflow, generally SW winds will be sustained under 15KT through dawn...with gusts up to 20KT after 15Z Tuesday after of a slight wind shift to westerly Thursday afternoon with the cold fropa. && .IND WATCHES/WARNINGS/ADVISORIES... Flood Watch until 2 PM EDT this afternoon for INZ021-028>031- 035>049-051>057. Flood Watch from 8 AM EDT this morning through late tonight for INZ060>065-067>072. && $$ SHORT TERM...AGM LONG TERM...MK AVIATION...AGM