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Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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715 FXUS63 KIND 161859 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 259 PM 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 - A return to warm and humid weather with thunderstorm chances next week. && .SHORT TERM (This evening through Wednesday)... Issued at 259 PM EDT Tue Jul 16 2024 Significant convective overturning occurred across central Indiana with the morning MCS. The classic "onion" sounding in a convectively- processed environment is present with vertical redistribution of low level moisture. The near-surface layer is moist still with mid 60 to low 70 degree dew points, and this is modifying gradually through a deeper layer. However, the upstream environment has continued to be convectively active on the western flank of the cold pool, so moisture will not be as rich as originally thought. Nevertheless, surface heating should eventually be sufficient for isolated to scattered convection, with no preference initiation area apparent yet. Along the synoptic front as it drives southeastward tonight, additional convection will be possible, but should be limited in coverage and intensity. CAPE/shear parameter space indicates severe storms are unlikely. Opportunity for flash flooding is limited now to where heavier cells occur over moist/near-saturated ground. Convection will be possible in modestly unstable environment ahead of the front Wednesday, across roughly the southern half of the area. Convective hazards should be limited to localized flooding and lightning, with probability for severe being quite low given expected parameter space. Any chance of more intense convection and strong wind gusts would occur during the afternoon as surface destabilization occurs, and probably in the far south or just south of our area, along the front. Meanwhile, the post-frontal air mass will be drier and cooler, and this will be a noticeable change by late in the day tomorrow. && .LONG TERM (Wednesday night through Tuesday)... Issued at 259 PM EDT Tue Jul 16 2024 An upper-level trough and cold front are currently approaching Indiana form the north. These features will bring about a pattern change where cooler and drier air take hold through the coming weekend. Ensemble guidance is in fairly good agreement regarding the timing and magnitude of the trough. Temperatures at 850mb dip as low as 10- 14 degrees C, which corresponds to highs in the upper 70s / low 80s assuming full mixing. Overnight lows may dip into the upper 50s in rural locations, low 60s elsewhere, with good radiational cooling potential. Dew points drop as well, and the remainder of the week and this weekend should be rather pleasant for mid July. Ensembles show a strong blocking pattern taking shape over CONUS. The aforementioned trough is modeled to just sit over the midwest. The cool/dry continental air mass will have to moderate in place, rather than quickly exiting eastward. Deterministic guidance shows a slow but steady increase in moisture around the back end of a surface high pressure over the southeast states. The air mass overhead gradually becomes warmer and more moist by Monday or Tuesday. With no synoptic systems impacting the region due to the blocked flow, precipitation chances should arise from diurnal convection typical of hot humid air masses. By the middle to end of next week, signals within guidance show a strong ridge over the western states breaking down. In turn, the warm air mass to our west begins to advect eastward. This should, combined with the weak moist southerly flow, should lead to a gradual warming trend next week. FORECAST CONFIDENCE Confidence in the temperature forecast is good. There is strong model consensus on troughing through this weekend leading to near- normal to cooler-than-normal temperatures along with dry conditions. Confidence in a return to warmer and more humid conditions next week is also good. Confidence in precipitation chances next week is average. A trend towards warmer and more buoyant air is likely, but the shower/thunderstorm potential will largely depend on diurnal instability and mesoscale features that are not yet resolvable at this time. && .AVIATION (18Z TAF Issuance)... Issued at 108 PM EDT Tue Jul 16 2024 Impacts: - VFR Conditions this afternoon. - Afternoon TSRA possible at HUF and BMG. - Overall TSRA possible at all Taf Sites, best chances south. - Any TSRA will result in brief MVFR to IFR conditions. Discussion: Convective complex over southern IL is expected to remain southwest of the TAF sites this afternoon. Forecast soundings show convective temperatures may be reached this afternoon, resulting some diurnal CU. HRRR suggests by late afternoon isolated convection may be possible over HUF and BMG. Thus a VCTS window was used at that time given the warm and humid air mass. Overnight, another upper wave is suggested to pass across Indiana, with the best forcing found across southern Indiana. Forecast soundings at most spots trend toward saturation overnight, while the HRRR suggests convection pushing across BMG IND and HUF overnight. Best confidence for this is at BMG which is closest to the lingering boundary that remains from earlier convection. Thus have used a tempo group for BMG while other locations only get a VCTS wind for lower confidence at this time. Any TSRA that strikes a TAf site may result in MVFR/IFR conditions. High pressure and VFR will return on Wednesday morning as high pressure begins to build across the region. && .IND WATCHES/WARNINGS/ADVISORIES... Flood Watch until 2 AM EDT Wednesday for INZ060>065-067>072. && $$ SHORT TERM...BRB LONG TERM...Eckhoff AVIATION...Puma