Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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090 FXUS63 KIWX 240107 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 907 PM EDT Mon Sep 23 2024 .KEY MESSAGES... - Rain showers will expand in coverage overnight with greatest coverage expected across northeast Indiana and northwest Ohio late night. - Scattered showers and storms expected later Tuesday afternoon/early Tuesday evening. An isolated strong to severe thunderstorm is possible. - Dry midweek before a low chance (20-30%) of showers late this week into the weekend. && .UPDATE... Issued at 900 PM EDT Mon Sep 23 2024 Low level winds have backed this evening in response to emergence of next upstream mid/upper level trough across the Central Plains. This has allowed for some strengthening of advective forcing as low level theta-e gradient from central IL to central IN has started a retreat back northward. Showers south of the US-24 corridor this evening should remain on the light side with little support for more organized synoptic lift behind this advective forcing. A more focused area of stronger showers/embedded storms has developed across eastern MO/southwest IL this evening. This appears to be at the nose of a 90 knot upper jet streak sampled by KOUN 00Z RAOB data. The left exit region of this upper jet streak will continue to migrate across the Ohio River Valley into early Tuesday morning. Another area of forcing to monitor for the overnight may be tied more to a maturing 900-800 mb circulation across central IL as the Central Plains upper level wave lifts northeast. This low level frontogenetic flow may support enhancement to showers from central IL into NW IN/SW MI late tonight/early Tuesday. Best rainfall rates overnight into early Tuesday are still expected in association with more pronounced upper jet forcing, which should also be co-located with some strengthening low level moisture convergence from central IN into northwest OH via a modest southerly low level jet. Additional refinement to PoPs will certainly be needed as these sharper forcing areas evolve overnight, but previous forecasted trends to likely/categorical PoPs still seem in order. && .DISCUSSION... Issued at 125 PM EDT Mon Sep 23 2024 Abundant cloud cover today has effectively kept temperatures down. Most locations will only see highs in the 60s, although a few may get up to around 70 degrees. A low pressure system currently centered over Arkansas and Missouri will make its way northeastward this evening. Showers could begin moving into southwest portions of the forecast area as early as 6-7 pm EDT. While isolated thunder is possible, chances are slim due to a lack of instability. Showers will continue through the night, mainly south of US 24. Then as the low tracks farther northeast by daybreak, shower activity will also shift northward. The surface low will cross the region from southwest to northeast (White County, IN to Williams and Fulton counties in Ohio) on Tuesday afternoon. In its vicinity and in the warm sector to the southeast will be the best chances for thunderstorms. It is in this area where bulk shear will be 30-40 kts and CAPE in excess of 1500 J/kg that SPC has extended the Marginal Risk for severe storms from around 3 pm through 9 pm. Damaging wind or hail could be possible, or even an isolated tornado. Wednesday will be mostly dry, but a few lingering showers may still be possible as the upper trough crosses the Great Lakes. On Thursday and Friday, the region will again be stuck between low pressure systems and high pressure will build back in. It will be dry and temperatures will warm, although it will not be as hot as last week, with highs confined mainly to the upper 70s or low 80s. Model uncertainty comes into play for the weekend concerning the position of an upper low to the southwest and a tropical system near the west coast of Florida. Consensus is that we should see more rain by Sunday into Monday. && .AVIATION /00Z TAFS THROUGH 00Z WEDNESDAY/... Issued at 744 PM EDT Mon Sep 23 2024 Backing of low level flow downstream of Central Plains upper trough has allowed for some renewed advective forcing to spread some light rain showers back across northern Indiana south of the US 24 corridor. Some question as to how far north these showers will progress this evening given more impressive mid/upper level forcing remains upstream. During the overnight hours, an upper level jet stream will nose northeast across the Ohio River valley, placing northeast Indiana in more favorable synoptic positioning for vertical motion. Will continue trend of prevailing showers overnight at terminals, with greater confidence at KFWA. Cigs will likely fluctuate between MVFR/VFR this evening, but renewed moist advection overnight into early Tuesday should bring back more IFR conditions. The earlier onset of improving conditions Tuesday is expected at KFWA as sfc low track would place KFWA in a weak warm sector, with slower improvements at KSBN. The upstream upper level vort should dampen across the southern Great Lakes Tuesday, but could provide impetus for scattered showers/storms Tuesday afternoon/early evening. With still some uncertainty as to instability magnitudes, will hold off on TS mention at this time. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...Beach Hazards Statement until 9 PM CDT this evening for INZ103. OH...None. MI...Beach Hazards Statement until 10 PM EDT this evening for MIZ177-277. MARINE...None. && $$ UPDATE...Marsili DISCUSSION...Cobb AVIATION...Marsili