Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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355 FXUS63 KIWX 151806 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 206 PM EDT Mon Jul 15 2024 .KEY MESSAGES... - There is high confidence in severe weather occurring overnight tonight, mainly in the 10 PM to 4 AM EDT timeframe. There is an Enhanced Risk (level 3 of 5) for severe weather across northern Indiana and southwest Lower Michigan. Damaging wind gusts 60 to 75 mph likely, with significant gusts over 75 mph possible and a few tornadoes too. A high-end impact damaging wind event is possible. - Alongside the severe threat, flash flooding is also possible overnight, especially in areas that remain saturated from recent heavy rainfall. A Flood Watch is in effect for along and west of US 31. - A cold front moves through Tuesday, bringing scattered rain/storm chances (30-60%) in the afternoon and evening. - Cooler, drier weather is anticipated midweek through next weekend with highs in the mid to upper 70s. && .DISCUSSION... Issued at 203 PM EDT Mon Jul 15 2024 There is high confidence in severe weather occurring late tonight into early Tuesday morning, mainly in the 10 PM to 4 AM EDT timeframe. SPC has expanded the 30% hatched wind probabilities east across our CWA in the newest Day 1 Outlook, prompting an expansion of the Enhanced Risk (level 3 of 5) further eastward into northwest Ohio. Scattered supercells/clusters of storms will develop across eastern Iowa this afternoon, and as those storms propagate eastward, they will become organized into a well defined bow- echo/MCS. This large linear complex of strengthening severe storms will race along the highest theta-e axis through eastern IA, northern IL, and into northern IN. Strong buoyancy, increasing vertical shear (30 to 35 kts), and favorable thermodynamics in place, which may result in a high impact damaging wind event overnight. Given that the ground is still so saturated from recent rain, especially in northwest Indiana, even wind gusts 40 to 50 mph will take down trees and powerlines. With damaging wind gusts of 60 to 70+ mph expected, widespread wind damage is possible. With MLCAPE of 3000 to 5000 J/kg across much of the Enhanced Risk, this bow-echo could sustain itself well after dark and maintain a widespread swath of wind damage (as seen in members of the HREF ensemble) into our CWA. A derecho is possible from eastern Iowa to northern Indiana. Widespread damaging winds 60 to 75 mph are likely overnight, with significant gusts over 75 mph possible. A few tornadoes are possible as well, especially in the Enhanced Risk area, given the expansion of the 5% tornado risk. There will be ample 0-1 km shear of 25 to 35 kts to work with and very strong 0-3 km SRH between 200 to 250 m2/s2. Stay weather aware tonight and have multiple ways to receive warnings that will wake you up!! In addition to the severe threat overnight, we are growing increasingly concerned with the flash flood threat overnight as well. Soundings depict extreme PWATs 2 to 2.25", a very deep warm cloud layer of up to 15,000 ft, and a favorable vertical CAPE profile. Thus, warm rain processes will be incredibly efficient overnight, especially if the bow-echo backbuilds, resulting in potentially extreme rainfall rates in excess of 2-3" per hour. Given that many locations in the Wabash and St Joseph river basins have accumulated 5 to 8+ inches of rain in the past week, the ground is saturated and river levels are still somewhat high. Instances of scattered flash flooding will be most common in the Flood Watch that in effect for along and west of the US 31 corridor. An upper level trough will pivot through the Great Lakes on Tuesday, resulting in chances for storms ahead of and along a cold front. The best chances for rain/storms will be along and south of the US 24 corridor in the afternoon and evening Tuesday. There is a Marginal Risk (level 1 of 5) for severe weather. A continental, cooler airmass from Canada will sink south midweek, resulting in seasonable highs in the 70s, a stark decrease in humidity, and dry conditions. It will be a nice change of pace compared to the active weather we have dealt with the past few days! && .AVIATION /18Z TAFS THROUGH 18Z TUESDAY/... Issued at 1239 PM EDT Mon Jul 15 2024 The onset of thunderstorms was delayed with this TAF issuance, but the overall TAFs remained on track. All eyes will be on eastern Iowa and western Wisconsin for thunderstorm development this evening which are anticipated to race eastward. The strength of these storms by the time they reach KFWA is questionable. Behind the thunderstorms, non-zero chance of bkn015 stratus near and after daybreak. However, guidance is highly variable with the time and location. Trends will be monitored behind the line of storms. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...Flood Watch until 2 AM EDT /1 AM CDT/ Tuesday for INZ012>015- 020-022-103-104-203-204. OH...None. MI...Flood Watch until 2 AM EDT Tuesday for MIZ078-177-277. MARINE...None. && $$ DISCUSSION...Johnson AVIATION...Cobb