Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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481 FXUS63 KIWX 220752 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 352 AM EDT Sat Jun 22 2024 .KEY MESSAGES... * Dangerous heat continues today and becoming breezy, but relief from the heat arrives for Sunday and Monday. * Showers and scattered storms expected to move in tonight with some potential of wind gusts in excess of 50 mph late evening into early overnight hours. * Depending on evolution of clouds and storms on Tuesday, heat indices may reach closer to 100 degrees again Tuesday afternoon. && .DISCUSSION... Issued at 350 AM EDT Sat Jun 22 2024 No changes will be made to ongoing heat headlines, with one more day of peak afternoon heat indices in the 95 to 100 degree range. Some potential of gusty thunderstorms tonight, particularly northwest Indiana into southwest Lower Michigan. Heat may make brief return for Tuesday with additional thunderstorm chances for Tue-Wed. Primarily dry weather is expected today, but will be monitoring a cluster of showers and thunderstorms moving out of northern Illinois/southern Wisconsin this morning. This area of storms appears to be tied to some broad low level theta-e advection and perhaps earlier enhanced by some anvil seeding from upstream Corn Belt convection. Bulk of these showers and thunderstorms should bypass the local area to the northwest following progression of pocket of 500-1000 J/kg MUCAPEs from southeast Wisconsin into west central Lower Michigan. Otherwise, still expecting today to be dry as weak mid level troughing swings northeast across central Lake Michigan with a robust +9 to +11 C 700 mb thermal ridge nosing into southern Lower Michigan. Weak cyclogenesis across WI today will allow for respectable strength to low level height gradient across the Great Lakes and Ohio Valley. Mixing up to 850-800 mb should allow for some peak afternoon gusts into the 20 to 30 mph range. This good mixing should result in dew points being held in check in the 60s for most areas similar to yesterday. The combination of high temperatures in the low to mid 90s and these modest dew points should result in another day of peak afternoon heat indices between 95 and 100 degrees. For late this afternoon into this evening, a stronger upper level trough will race east out of the eastern Dakotas allowing for cold frontal progression into northwest IL/southeast WI by late evening. Showers and storms should fill in along or just in advance of the front in pre-frontal moisture pooling zone early this evening. All indications still point to a sharp gradient in convective environment from western Great Lakes to the southern Great Lakes/Ohio Valley with best instability axis remaining from northern IL into southeast WI. Dampening of the mid/upper level ridge later today will allow some modest deep layer shear values into the 25 to 30 knot range by this evening across far northern Indiana/southern Lower Michigan. However, convective line will have less downstream instability to work with across the local area late evening/early overnight, and given marginal shear profiles, should see a transition to outflow dominant line. SPC Day 1 severe probs have been increased across the area with a Slight Risk across the far northwest. Still feel that thunderstorm wind gusts in the 35 to 50 mph range will be of higher confidence with this convective line, with some lower confidence in isolated severe gusts. Best chance of near severe/severe wind gusts should be in a fairly narrow temporal window in the 04-07Z timeframe from northwest IN into perhaps far SW Lower Michigan. The convective line should gradually wane with time during the overnight hours tonight. A few storms are possible into Sunday with cold frontal progression across the area, but effective sharper convergence zone resulting from outflow evolution may be focused just southeast of the area. Less humid conditions will overspread the area behind this front Sunday afternoon into Monday. Monday will be a transition day and appears to feature pleasant conditions with seasonable temperatures and low humidity levels. A progressive northern stream pattern will allow for a quick transition to a dampening of incoming upper level ridge Monday night/early Tuesday and a period of very strong return positive low/mid level theta-e advection late Monday night into Tuesday. Forecast soundings still suggest capping may hold into midday Tuesday, but elevated moisture return could be enough for isolated-scattered storms moving in from the west late Monday night into Tuesday morning across the west. While current indications still suggest a potentially more active convective pattern Tuesday afternoon into Wednesday, forecast confidence in details remains low given lead forcing on Tuesday will be driven largely by upstream diabatic processes across the Upper Midwest, and the fact that stronger synoptic forcing lags across US/Canadian border later Tuesday night into Wednesday. This pattern may support MCS activity, but mesoscale details including instability magnitudes and shear magnitudes with southward extent across local area will need to be resolved in later forecasts. Depending on how clouds/convection play out Tuesday, a brief return of heat indices from the mid 90s to around 100 is possible Tuesday afternoon. Chances of storms may persist with cold frontal progression into Wednesday, but quieter and cooler weather spreads back into the area for Thursday. Temps should warm to above normal again for Fri-Sat, but another frontal passage is possible toward end of this forecast valid period. && .AVIATION /06Z TAFS THROUGH 06Z SUNDAY/... Issued at 140 AM EDT Sat Jun 22 2024 Predominantly VFR conditions at the TAF sites today, with mainly high and mid level clouds around through the period. MVFR/IFR conditions are possible towards the end of the period (around 3-6z) at KSBN, then probably just beyond the TAF period at KFWA as a cold front approaches the area. Models have the prevailing conditions staying VFR at this moment in terms of ceilings, but as we usually see, a 1-3SM visibility is a reasonable first guess in the event any heavier showers/storms impact the terminal. Carried this in a prob30 for KSBN this issuance given lower confidence. Otherwise, SSW winds will gust up to around 20-25 knots today. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...Heat Advisory until 8 PM EDT /7 PM CDT/ this evening for INZ005>008-012>015-020-022-023-103-104-116-203-204-216. Excessive Heat Warning until 8 PM EDT this evening for INZ009- 017-018-024>027-032>034. OH...Excessive Heat Warning until 8 PM EDT this evening for OHZ001- 002-004-005-015-016-024-025. MI...Heat Advisory until 8 PM EDT this evening for MIZ078>081-177- 277. MARINE...None. && $$ DISCUSSION...Marsili AVIATION...MCD