Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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696 FXUS63 KIWX 072001 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 401 PM EDT Sun Jul 7 2024 .KEY MESSAGES... - Low chances of showers and thunderstorms (20%) for NW IN/SW Lower Michigan tonight and Monday. Scattered showers and thunderstorms are possible Monday night, especially along and west of I-69. - Remnants of tropical system Beryl will likely bring showers and thunderstorms to the area between Tuesday afternoon and early Thursday with moderate to heavy rain being a possibility Tuesday night through Wednesday evening. Confidence remains low in more precise locations of heavier rainfall however. - Warmest conditions this forecast period expected on Monday (mid and upper 80s), and possibly again next weekend. && .DISCUSSION... Issued at 400 PM EDT Sun Jul 7 2024 Scattered showers and thunderstorms have developed this afternoon from eastern Iowa into northeast Illinois. This appears to be at interface of modest low level theta-e gradient. Several small scale short waves are also progressing through the southwest upper flow across the Mid MS Valley. There also appears to be a weak MCV across eastern Iowa that will lift northeast into this evening. Some question as to the eastern extent of this convection through the remainder of the afternoon in the early evening with a strong west to east instability gradient expected to remain anchored from northeast Illinois into SW Lower Michigan and northwest Indiana. Some potential should exist for isolated showers and thunderstorms across far west/northwest portions of the area into early this evening. Cannot completely discount some additional isolated showers and thunderstorms late evening into the overnight as the stronger convectively enhanced short wave works across the western Great Lakes. However, developing low level CIN this evening should limit these chances. A stronger upper level trough lagging back across the Dakotas this afternoon will dig across the Corn Belt Monday afternoon before beginning to shear out across the western Great Lakes Monday night. Modest southwesterly low level flow will allow for low level warm advection during the day Monday, and Monday should feature the warmest conditions of this forecast period with highs in the mid 80s to around 90. Not expecting heat indices to be much of a concern however as richer near sfc moisture remains upstream. Through the day Monday, best coverage of scattered showers and thunderstorms is expected back across northeast Illinois, but weak surface based instability and approach of some weak pre- frontal forcing may allow of isolated to scattered shower/thunderstorm development west of IN-15. A negative factor for convection on Monday is a possible lull in better/mid upper level forcing. On Monday evening will carry low chance PoPs into the area as primary upper level short wave shears out across the western Great Lakes, and axis of weak 925-850mb moisture/mass convergence shifts across the southern Great Lakes. While severe weather is not expected Monday night, there could be a few storms capable of some gusty winds given some increase in low/mid level flow and low level moisture. Tuesday through Thursday looks to be the primary period of concern for this forecast valid period as remnants of Beryl may impact the western Great Lakes and/or Ohio Valley. A rather complicated synoptic pattern makes predictability on the low side regarding finer details with exact track. An upper low in northwest upper flow is expected to eventually merge with remnants of Beryl later Tuesday with this consolidated upper level trough lifting northeast across the southern Great Lakes on Wednesday. The exact track/strength of the low/mid level height minimum remains of low confidence as initial warm core/latent heat dependent nature of this system is hard to pin down at this forecast distance. Ensemble spread appears to increase sharply with track of low level features after 00Z Wednesday. Scattered showers and storms may fill in during the day Tuesday well north of low center as low/mid level fgen axis extends north into southern Great Lakes. While details will need to be refined, the possibility of at least portions of the area getting into heavy rainfall Tuesday night/Wednesday still appears intact as PWATS may increase to 2+ inches late Tuesday/Wednesday. Antecedent conditions have been on the dry side most locations which could alleviate some of the concerns, but if higher end rainfall amounts in excess of 3 or 4 inches are realized in deformation forcing zone, some hydro issues are possible. Have issued an ESF this afternoon highlighting the late Tuesday-Wednesday evening period for some heavy rainfall potential. Possible northward advection of mid level dry slot midweek could sharpen up the axis of heaviest rain to a greater degree than current guidance indicates. If a slower/westward trend ends up verifying, there is some low possibility that a marginal severe risk could evolve in a brief window across the far southeast during this period. Additional chances of storms may arrive for next weekend as area may be on strong low level theta-e gradient. A transition to hot and humid conditions is possible toward late next weekend into early next week as eastward progression of upper level ridge allows this strong theta-e gradient to shift eastward. && .AVIATION /18Z TAFS THROUGH 18Z MONDAY/... Issued at 133 PM EDT Sun Jul 7 2024 Weak upper level energy was sustaining convective activity over northern IL. This activity should remain northwest of SBN; however, the bigger story in the tropical moisture plume reaching the area early Monday. Showers and storms and associated lower ceilings and visibilities will lag the arrival of the tropical air until well after the end of the TAF period. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ DISCUSSION...Marsili AVIATION...Skipper