Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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822 FXUS63 KIWX 211053 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 653 AM EDT Fri Jun 21 2024 .KEY MESSAGES... * Hot and humid conditions will persist through Saturday. Peak afternoon heat indices will approach 100 degrees in many locations, hazardous to sensitive and vulnerable groups. * Isolated to scattered thunderstorms (20-40%) are possible during the afternoon and early evening hours today especially across far northeast Indiana/northwest Ohio, along with south central Lower Michigan. A few storms may produce wind gusts to 50 mph. * Better shower and thunderstorm chances (50-80%) arrive Saturday night into early Sunday along a cold front followed by additional chances Tuesday and Wednesday. && .DISCUSSION... Issued at 355 AM EDT Fri Jun 21 2024 Dangerous multi-day heat event will continue into Saturday. Heat indices this afternoon into Saturday will top out around 100 degrees for many locations. No changes will be made to heat headlines this morning with both the Heat Advisory and Excessive Heat Warning in effect through 00Z Saturday evening. Stagnant upper level pattern will allow for a persistence forecast to be a good first estimate for today. Old stalled weak surface boundary currently resides just south of the US 6 corridor this morning. Some weak overrunning flow atop this boundary has allowed for continuation of some isolated showers across Lake Michigan vicinity this morning, but trends should continue to be downward over the next few hours. This sfc trough will continue to lose its integrity across northern portions of the forecast area today, but some weak pooled moisture and dew points around 70 or lower 70s could persist this afternoon. The combination of remnants of this pooled moisture, favored track of weak short waves across the southern Great Lakes, and slightly cooler mid level temps from south central Lower Michigan into far northwest Ohio, should favor best chances of afternoon/early evening storms in roughly the Hillsdale MI to Wauseon OH corridor. Convective temperatures looked to be reached in the 16Z-17Z timeframe once again. In terms of severe weather potential, similar ingredients appear to be in place today including low shear environment, steep low level lapse rates, and dry mid level air. This could support an isolated gusty wind threat to 50 mph with the strongest cores in the 18Z-23Z timeframe, with a low end potential of an isolated damaging wind gust. Any isolated to scattered storms should weaken around 00Z timeframe similar to last evening. Heat indices are expected to to range from the mid 90s to around 100 today. Slightly cooler temperatures across northern portions of the heat headlines should be partially offset by slightly higher dew points for what should be fairly uniform distribution of peak heat indices. For this evening, some subtle increase in low level southwesterlies should take remnants of the old sfc trough north of the local area, and any isolated showers should be confined north of the area after 02Z this evening. For tonight into Saturday, mid/upper level ridging will finally experience more suppression, but as this occurs stronger southwesterly flow downstream of more notable eastern Pacific short wave troughs will allow an increase in low level warm advection. Saturday should feature highs in the mid 90s across much of the area, although some better low level mixing could temper dew points into the mid-upper 60s for another afternoon of peak heat indices around 100. Deep dry adiabatic lapse rates in low levels should promote peak wind gusts to 25 to 30 mph Saturday afternoon. For Saturday night into Sunday morning, attention turns to approach of a couple of low amplitude short waves that will eventually allow cool frontal progression into the local area Saturday night into Sunday. Some uptick in deep layer shear to 20 to 30 knots is expected ahead of the cool front Saturday night, but instability should be a limiting factor for a more expansive severe weather threat. Best MUCAPE should reside across the Mid MS Valley with a possibility that more vigorous convection could tend to propagate upwind to the west of the local area. Expecting upstream convection to have more of an outflow dominance as it approaches the local area Saturday night given lack of instability and marginal shear profiles. SPC has placed northwest half of the area in Day 2 Marginal Risk, primary for isolated strong wind gusts late evening/early overnight Saturday. During the day Sunday, effective frontal position will likely take potential for more vigorous convection to the southeast of the local area with a reduction in PoPs from NW to SE during the day. Temperatures will trend to more seasonable levels post-frontal Sunday. Monday shaping up to be a nice day across the area with low humidity and seasonable temps as sfc anticyclone drifts across the Ohio Valley. Rapid departure of this anticyclone will allow for renewed warm/moist advection into Tuesday, with a potential of 1 day heat indices approaching the 95 to 100 degree range Tuesday afternoon. Additional storm chances persist Tuesday and Wednesday although details in timing still murky at this forecast distance. A more vigorous upper level short wave tracking across Upper Midwest/northern Great Lakes will dampen upper ridging once again with another frontal passage midweek. Some potential of strong storms could accompany this period, but much of this will depend on timing and southward extent of better shear profiles. A trend to quieter conditions is anticipated for Thursday and Friday as mid level heights rise once again in wake of midweek system. && .AVIATION /12Z TAFS THROUGH 12Z SATURDAY/... Issued at 651 AM EDT Fri Jun 21 2024 VFR conditions are expected for the TAF period. As of 11z, MVFR conditions were observed at both KSBN/KFWA thanks to BR that formed overnight in the calm winds/clear skies. Expect visibility to be between 4-6SM through 12z when we expect improvement to 6SM or greater. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...Heat Advisory until 8 PM EDT /7 PM CDT/ Saturday for INZ005>008-012>015-020-022-023-103-104-116-203-204-216. Excessive Heat Warning until 8 PM EDT Saturday for INZ009-017- 018-024>027-032>034. Air Quality Alert until midnight EDT /11 PM CDT/ tonight for INZ020-103-203. OH...Excessive Heat Warning until 8 PM EDT Saturday for OHZ001-002- 004-005-015-016-024-025. MI...Heat Advisory until 8 PM EDT Saturday for MIZ078>081-177-277. MARINE...Dense Fog Advisory until 11 AM EDT this morning for LMZ046. && $$ DISCUSSION...Marsili AVIATION...MCD