Area Forecast Discussion
Issued by NWS Northern Indiana
Issued by NWS Northern Indiana
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553 FXUS63 KIWX 220121 AFDIWX Area Forecast Discussion National Weather Service Northern Indiana 921 PM EDT Sat Sep 21 2024 .KEY MESSAGES... - Chances for showers and storms increase Sunday into Sunday night, bringing at least some rainfall to the area. - A break in the rain is expected Monday into Monday evening before another chance arrives late Monday night into Tuesday. - Cooler temperatures will prevail through much of the period with highs in the 70s. && .UPDATE... Issued at 914 PM EDT Sat Sep 21 2024 No notable changes to previous forecast are warranted at this time. Ongoing convection this evening is confined to areas well to the west across southwest/south central Wisconsin at the nose of instability ridge. Stable bubble and dry low level air will persist locally through the early overnight hours. During the overnight, a series of convectively enhanced short waves from this upstream convection will begin to enter confluent mid/upper level flow eventually allowing the strong low-mid level theta-e gradient to push aggressively back across the area into Sunday morning. Near term isentropic progs would suggest best isentropic ascent shifting north of the local area Sunday morning, with a few showers possible toward daybreak feeding off this increase in elevated moisture and northward lifting isentropic forcing. More widespread showers/iso storms may work across the area from from west to east from mid morning through mid afternoon Sunday in association with pocket of pre-frontal moisture convergence and upper level short wave forcing, followed by larger scale frontal response. Timing of precip onset still a bit uncertain given multiple forcing mechanisms and highly advective moisture profiles, but general theme of previous forecast left intact at this time. && .DISCUSSION... Issued at 253 PM EDT Sat Sep 21 2024 Strong subsidence, well depicted on satellite, over the area will hold strong until towards 12Z Sun as the next wave edges into the region. Narrow area of showers/storms in western IL should quickly meet its demise as it runs into the western edge of the subsidence. Re-development will take place overnight across northern MO into western IL, and then tracking towards the region. Several models seem to suggest the bulk of this initial shot may pass near/south of US-24 as noted by the last shift. Despite this, models do agree on a better influx of moisture (PWATs 1.75" or higher) and instability to set the stage for development during the afternoon and evening hours with the 15Z RAP looking the most reasonable at this point. Overall severe threat quite low, but locally heavy rainfall would be the main concern, something that is welcome if it doesn`t runoff too fast. Will maintain likely pops through the day. Showers/storms are likely to linger in eastern areas into the evening and possibly overnight hours as the sfc boundary takes its time working east. Drier air will advect in Monday on N/NE winds as the upper level trough digs in. The increasing flow getting things stirred up beach wise with increasing waves and swim risk from Mi City to Bridgman. Yet another wave moves towards the area Tuesday, but models vary on potential impacts on the area partially due to differences in available moisture and sfc low development that will be starting to the west as a deeper wave resides somewhere in eastern KS/W MO. System could bring another good shot of rain to the area, but confidence is low on the evolution. Have kept pops in the chc to low end likely for now. Thereafter, models agree on the stronger wave cutting off but vary on how far west and south. Some minor moderation in temps could occur, but most likely we will stay below normal. && .AVIATION /18Z TAFS THROUGH 18Z SUNDAY/... Issued at 700 PM EDT Sat Sep 21 2024 A strong instability gradient sprawled across the Mid MS valley and lingering mid level subsidence across northern Indiana should limit any eastward expansion of shower activity across northern Illinois into this evening. By late this evening and especially into the overnight, broad mid/upper level upstream confluent flow will allow for more active short wave pattern to influence western Great Lakes, allowing for an eastward shift to strong low-mid level theta-e gradient. This should allow for uptick in rain shower potential, particularly late Sunday morning into Sunday afternoon as low level frontogenesis forcing also becomes more prevalent. Weak mid level lapse rates and moistening low/mid levels should temper overall instability. While some isolated-scattered thunder is possible Sunday, will continue to omit mention due to these limiting factors. Light and variable to light southeast winds will veer southwest 5 to 10 knots on Sunday in pre-frontal environment, before shifting west toward end of this forecast valid period with frontal passage. && .IWX WATCHES/WARNINGS/ADVISORIES... IN...None. OH...None. MI...None. MARINE...None. && $$ UPDATE...Marsili DISCUSSION...Fisher AVIATION...Marsili