Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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033 FXUS63 KIWX 071532 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 1131 AM EDT Tue May 7 2024 .KEY MESSAGES... - Severe storms are likely mid afternoon into mid evening. The primary threat with any severe storms that occur include damaging winds, large hail, and a few tornadoes. Confidence is high. - Isolated strong to severe storms are possible again Wednesday evening, mainly south of US 24. Localized heavy rain and flooding is the primary threat but a few storms could contain hail. Confidence is low. - Cooler with chances for showers later this week into the weekend. Highs Friday into Sunday will be in the 60s. Otherwise temperatures will warm back into the mid 60s to mid 70s next week. && .MESOSCALE UPDATE... Issued at 1131 AM EDT Tue May 7 2024 Warm advection downstream of wrapped up low over SD had allowed leftover plains convection to progress into the wrn OH valley this morning. This will clear far ern zones by 18Z as attention focuses wwd into IL. Rapid destabilization ongoing here as skies have cleared ahead of cold front back west along the MS river. Of note is sig mid lvl jet streak back across MO which will shift out atop a moist and unstable warm sector here late this aftn with storms developing into nw IN by 20Z. Most favorable 0-3km shear and enlarged hodos expected invof warm frontal zone from ne IN sewd into wrn OH which aligns spot on with dy1 enhanced tor risk. Otherwise sig hail possible with more robust supercells late aftn into mid evening before storms clear east. && .DISCUSSION... Issued at 536 AM EDT Tue May 7 2024 The day 1 SPC outlook was upgraded to expand the enhanced risk for severe storms across much of our area, with a slight risk elsewhere. Confidence has increased in at least scattered severe storms developing in the 2 to 10 pm EDT time frame, and much of the model guidance is within that general window. Confidence in the event occurring as forecast overall is medium, with less confidence in the exact intensity/exact location of the strongest storms. However, feel SPC has a great first guess at the most likely location of the worst storms-and greater tornado risk. Models are in reasonably good agreement regarding the overall event evolution and general parameters. As of this writing, a warm front extends from southwestern IA and into far southern IL/IN. This warm front will lift north through the afternoon as the LLJ takes aim at our CWA this morning, orienting itself E-W just south of the IN/MI border (depending on the model) by 18z. By 00z, the front will extend across Lower Michigan, with the cold front along the western Lake Michigan shore down through the IN/IL Stateline. This cold front will cross our southern/central CWA from the evening into the overnight hours. Models suggest two main rounds of thunderstorm activity. The first is a squall line, which is entering IL at the moment. This line will likely decay some as it moves eastward, reaching our area this morning sometime around 10 am. There could be a few showers that pop up with the moisture/warm air advection out ahead of the line, so have pops increasing after about 8 am EDT. It is possible that the line holds together or reinvigorates a little bit later this afternoon in the northern portions as the environment becomes more unstable, but the threat of severe weather before 2 pm EDT is low. This line also adds some uncertainty to the afternoon forecast, as it will likely leave behind outflow that can limit destabilization at first. However, given the lull in between the two rounds (could be a few hours), I think we`ll be able to recover adequately. Cooked outflow (from daytime heating) can sometimes be helpful fuel and lift for storms later on (and vorticity augmentation in mesocyclones/moisture pooling-both favorable for tornado development). The second round will develop behind the exiting morning/early afternoon line, but models disagree on exactly where and how long it takes before these discrete cells develop (again, what are the leftover boundaries and environmental conditions after round 1). Some are as early as 18z in IL/IN and others are later like the NAM, which is closer to 21-00z for initiation in IL, moving eastward into IN in the later evening/overnight. Either way, the environment will likely be conducive to discrete supercells, with 50-70 knots of bulk effective shear, 0-1 km bulk shear of 20-30 knots, and PWATS upwards of 200 percent of normal. Surface based CAPE in the 18-00z time frame is higher than what we usually see in this area---around 1500- 2500 J/kg! Some of the models suggest closer to 3000 J/kg. LCL`s are around 500 to 1000, with the dewpoints in the warm sector (close the enhanced risk area) in the low to even mid 60s. Mid level lapse rates are another factor I`m not too impressed with---usually our better severe weather events we have 7-8 C/km lapse rates in the 500- 700 mb layer but for this event models really suggest more like 5.5 to 6.5 C/Km (outlier is the NAM, which has LR of 7 to 7.5 C/KM). However, given the other factors at play, we have plenty of severe weather ingredients to work with-and I think it warrants paying attention to. It`s not out of the question with the SRH values of 100-200 m2/s2 and the higher cape/bulk effective shear/high moisture we see a few stronger tornadoes. Obviously focused most of this discussion on today-tonight, but there is a severe threat for Wednesday night as well. However, it is looking less likely than yesterday, and delayed slightly (yesterday threat included the afternoon hours). The better threat will be south of our area, but we could see some stronger storms (SPC kept us in a marginal risk generally from LaPorte, IN to Lima, OH and south and west from there). Otherwise, rain is likely with thunderstorms. Confidence in severe weather threat is lower, with the main hazards (if any) being damaging wind, large hail, and heavy rain with localized flooding. Expect wet weather to continue through early next week, with chances for showers most days. Thunderstorms are possible. It will be slightly cooler, with highs will be in the 60s this weekend. Temperatures warm back into the mid to upper 70s by early next week. && .AVIATION /12Z TAFS THROUGH 12Z WEDNESDAY/... Issued at 601 AM EDT Tue May 7 2024 Spotty MVFR cigs will likely linger in the vicinity of the terminals this morning as moisture begins to stream northward in advance of a warm front. This warm front will lift into northern IN late this morning and afternoon with a couple rounds of convection expected. The first will be associated with a decaying line of convection that will track through from west to east late this morning into the early afternoon. Moisture advection in advance should allow cigs to range in the MVFR to low VFR with an hour or two of showers and embedded thunder expected. Greater concern is for a round of more vigorous surface based convection mid-late afternoon as instability increases just in time for a MCV to track through with scattered strong-severe storms. VFR/dry otherwise into tonight behind this feature. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ MESOSCALE---T DISCUSSION...MCD AVIATION...Steinwedel