Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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858 FXUS63 KIND 060721 AAA AFDIND Area Forecast Discussion...UPDATED National Weather Service Indianapolis IN 321 AM EDT Mon May 6 2024 .KEY MESSAGES... - Showers likely with a few thunderstorms possible mainly near and south of I-70. - There is a chance for severe storms Tuesday, especially during the afternoon and evening. All forms of severe hazards are possible. - Additional strong to severe storms are possible Wednesday. - Heavy rain is possible at times through Wednesday. Flooding will also possible due, mainly Tuesday and Wednesday due to multiple rounds of convection. && .SHORT TERM (Today and tonight)... Issued at 318 AM EDT Mon May 6 2024 H20 vapor imagery was clearly showing an upper low spinning over the Ozarks within a broad trough, underneath an upper Midwest ridge. 305K Isentropic lift ahead of this feature was leading to an area of moderate showers that were lifting gradually northeast, north or a stationary front over northern Kentucky. Isentropic analysis of condensation pressure deficits suggest the showers will overspread areas near and south of I-70 through the morning. With precipitable water from an inch to 1.5 inches or up to the max moving average, heavy rain will be possible at times. DESI 24 hour rainfall totals near and south of I-70 range from around a quarter inch from the 25th percentile to three quarters of an inch from the 75th percentile. With a sharp cut off expected due to more northeasterly dry flow, precip amounts will drop-off a lot north of I-70 and some spots may not see any shower activity today. Model soundings and instability progs suggest only weak instability will be realized today, so not expecting anymore than a few embedded thunderstorms. With deep moisture around, look for rather solid morning cloud cover but some breaks this afternoon in the wake of the upper wave that will swing in from Missouri. This and the northeast and east winds should keep temperatures down. Northeastern sections may not even see 70 degrees depending on cloud cover. Most locales will likely see normal to slightly above temperatures in the 70s this afternoon. Upper ridging will move across tonight in the wake of the upper wave. This allow the stationary front to return northeast and winds shift to the southeast. This in turn should result in little to no convection until an approaching cold front gets closer Tuesday morning per all of the CAMs. The southeast winds should also keep temperatures from falling too much tonight with overnight lows in the upper 50s to middle 60s looking good. && .LONG TERM (Tuesday through Sunday)... Issued at 318 AM EDT Mon May 6 2024 A challenging but potentially potent thunderstorm forecast will be the main focus for the long term discussion. Details on the expected conditions for Tuesday and Wednesday are below. For Thursday and beyond expect near to below normal temperatures and cloudy conditions. Light rain chances are possible Friday and Saturday. Synoptic Overview: A negatively tilted trough is currently nearing the Lower Rockies, resulting in maximized CVA, collocated in the lee of the Rockies. This will lead to rapid surface pressure depression and cyclogenesis today. The low will then occlude later today as well, positioning itself over the Dakotas. As the low becomes stationary, strong jet dynamics will elongate the low, creating a succession of shortwaves. It is these waves that will be our primary focus for severe potential Tuesday and Wednesday. Not only do we have the proper atmospheric disturbances for lift across the Ohio Valley, we will also quickly destabilized as winds veer towards southerly and push a warm, moist airmass over the region. Temperatures should push back towards well above normal, with highs in the upper 70s to low 80s Tuesday and Wednesday. Tuesday Severe Threat: As mentioned an initial wave on the eastern edge of an elongated low will pass through the Midwest late Monday into Tuesday morning. Out ahead of this wave, strong surface based lift should lead to the development of an MCS over IA/MO late Monday. 50+kt deep layer sheer and a deep EML should allow for quick propagation eastward, reaching Indiana Tuesday morning. As the MCS moves eastward, it will eventually become displaced from the greater mid to upper level forcing resulting is strong but likely sub-severe convection by the time in passes through Indiana. Initially, this decaying MCS will act to stabilize the the lower levels, but this should quickly be overcome as winds veer to the south and push high theta-e values over central Indiana. The greatest area of uncertainty for Tuesday will be where initiation will occur, as it will largely be determined by upper level diffluence. Once initiation does begin, Eff Bulk Shear of 50-60kts and and a deep CAPE profile should allow for robust, organized updrafts to form. A few CAMs are depicting a lingering boundary formed by the prior MCS as the area of focus for CI. If this does occur, this will likely reduce the overall severe threat for northern portions of the area. Regardless, southern central Indiana will likely still be in a threat for organized convection Tuesday afternoon/evening. Orthogonal shear vectors and mid level jet ventilation should allow for discrete cells to develop. Some of them should be able to form a sustained mesocyclone given SRH values greater than 150 m2/s2, primarily over southern portions of the region. With that said, poor precip dispersion aloft within weak anvil level flow, may lead to precip loading in the updraft, and HP like supercells in those that due end up sustaining them selves. For now, the greatest risk looks to be damaging winds within downbursts over northern central Indiana, and large hail over southern Indiana. The atmosphere above 800mb looks rather dry and precip loading in the updrafts of multicell clusters could lead to lots of melting hail and dense cold pools. A few 70+ MPH gusts cannot be ruled out. High EL and steep mid level lapse rates should allow for some hail sorting. The biggest mitigating factor will be the lack of anvil ventilation to the north. For this reason hail could remain subsevere outside of any sustained rotating updrafts. Over southern IN, upper level winds become stronger, making this less of an issue. Given the potential for sustained mesocyclones, and low LCLs, tornadoes cannot be ruled out. Steamwise vorticity will likely need to be enhanced by strong deviant motion or some form of cell merging for tornadogenesis, but given how numerous CI could be and the potential for a stagnant boundary, this is definitely a possibility. Wednesday Severe Threat: Uncertainty increases for the severe threat on Wednesday, as a lot of it will be predicated by Tuesday. A secondary wave, and forward progression of the upper trough will help with creating a more potent atmospheric profile for severe convection, but it will depend on how far north the instability gradient will push northward ahead of the short wave during the day on Wednesday. Wherever the CAPE gradient does develop, robust, but mainly parallel shear profiles, and strong CVA should allow for rapid CI and quick upscale growth. There is still plenty of variability for timing of CI on Wednesday, but the general expectation is for this potential MCS to follow the CAPE gradient, pushing off to the east and eventually south through Wednesday late afternoon and evening (+/- a few hours) Once again, damaging wind gusts will likely be the greatest threat on Wednesday. Effective shear will be plenty sufficient for organized bowing segments. QLCS tornadoes will also be possible with this event. A stronger LLJ, and high 0-1km SRH should allow for line breaks and shallow mesocyclones to form within the MCS. && .AVIATION (06Z TAF Issuance)... Issued at 1242 AM EDT Mon May 6 2024 Impacts: - With the exception of KLAF, flying conditions MVFR flying conditions in showers are expected starting 11z-16z - Thunderstorms possible, especially after 18z at KHUF and KBMG Discussion: VFR flying conditions are expected to deteriorate to MVFR and possibly briefly worse this morning as a stalled front retreats to the north. However, KLAF should continue to see mainly VFR conditions with only small chances for showers. Winds will switch from mainly northeast to mainly east 10 knots and less. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...MK LONG TERM...Updike AVIATION...MK