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Forecast Discussion for Indianapolis, IN
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000 FXUS63 KIND 280118 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 918 PM EDT Sat Apr 27 2024 .KEY MESSAGES... - Warm and active weather expected throughout the next seven days, with above normal temperatures and multiple opportunities for showers and thunderstorms. - Organized severe storms appear unlikely, though multiple rounds of rainfall may allow redevelopment of minor flooding along some rivers. && .FORECAST UPDATE... Issued at 917 PM EDT Sat Apr 27 2024 No major changes needed to the ongoing forecast with conditions generally evolving as expected. Did make some minor adjustments to POPs during the overnight hours to better delineate where the higher expected coverage for showers will be across the northwestern counties based on ongoing rain in east central Illinois. These showers are expected to continue to increase in coverage as the LLJ ramps up. Instability should be sufficient for occasional rumbles of thunder, but don`t expect any other hazardous weather outside of lightning. With strong southerly flow, expect a pretty flat diurnal temperature curve through the night with lows in the low to mid 60s. && .SHORT TERM (This evening through Sunday)... Issued at 254 PM EDT Sat Apr 27 2024 Not much going on at the moment as Hi-RES soundings are showing some dry air mixing in aloft. There were only a few showers over east central Illinois and southwestern Indiana seen on radar moving northeast around 35 mph per the AWIPS distance speed tool. Meanwhile, satellite data indicated warm cloud tops associated with weakening convection over southern Illinois. Earlier their had been a decent amount of lightning strikes with this activity, but latest ENTLN data was no longer showing any strikes. That said, LAPS data was showing over 1200 J/KG CAPE over the upper Wabash Valley, where a DAY1 SPC Marginal Severe Risk is residing. With deep shear not that impressive there at less than 30 knots and little upper support, not expected much development this afternoon. Hi-RES soundings show the column saturating again tonight and deep shear increasing a bit to the point where if enough instability can be present a few storms may become strong or marginally severe with hail and thunderstorm gusts the main threat. Despite the lack of synoptic forcing, 305K isentropic lift and saturating column will result in some showers with the best coverage over the upper Wabash Valley where the lower condensation pressure deficits will be residing and slightly better deep shear and instability. Would not rule out a storm or two again on Sunday. This will depend on whether or not a weak impulse in southwest flow aloft can combine with projected weak instability to trigger isolated convection. The bigger story will be temperatures and continued breezy southwest winds will support near record in the lower 80s. With the tight surface pressure gradient hanging around and some breaks in the clouds permitting mixing, will once again see gusts to 30 plus mph Sunday afternoon. && .LONG TERM (Sunday night through Saturday)... Issued at 254 PM EDT Sat Apr 27 2024 A warm and active period continues to be the expectation for this coming week, with multiple opportunities for showers and thunderstorms. Large scale troughing will predominate over much of the CONUS this week, with mean ridging of various intensity over or just off the eastern/southeastern CONUS. The strong surface cyclone currently bringing a regional severe weather outbreak to the central and southern Plains will swing northeastward into the Great Lakes early this week and weaken. The associated surface frontal zone will weaken as well, as it is stretched/washed out with time. Significantly boundary-parallel flow throughout the depth of the troposphere will keep the bulk of precipitation associated with this system in a relatively narrow zone along and near the boundary, which will concentrate the highest rain chances mainly early Monday morning into the early evening hours. With the main forcing for large scale ascent displaced well to our north and a secondary shortwave displaced to our south, as well as limited opportunity for destabilization given early arrival of precipitation, little to no severe threat is expected, though some very modest instability will necessitate low thunder probabilities. Another weak system is expected to follow in quick succession mid- week, before a third, stronger system develops in the lee of the southern Rockies late in the week, with potential for additional, perhaps somewhat higher precipitation chances late week into the weekend, though uncertainty increases with time both due to a complex evolution of these systems and model differences. Though precipitation chances will be frequent this week, several dry periods are likely. Analogs and experimental machine learning guidance suggest the area will be on the fringes of a low threat for strong to severe storms mid to late week, though the overall parameter space is much more robust well to our west and southwest during this time frame - an organized severe threat appears unlikely at this time. Ongoing and prolonged elevated streamflows, particularly in the Wabash valley and lower White River valley, will necessitate monitoring of hydrologic conditions and threats with time, as capacity is relatively low at the moment. That said, there is little to no signal for significant rainfall in any one period, but multiple potential rounds of convective precipitation could steadily worsen the hydrologic situation over time in the right mesoscale circumstances. At a minimum, streamflows will likely remain elevated well into early May, with some areas in the Wabash and lower White valleys rising back into minor flood. This is well-supported by hydrologic ensembles. Temperatures will be warm much of the week, with highs in the 70s to lower 80s at times, and lows in the 50s to mid 60s - running about a month ahead of time relative to climatology. Deterministic NBM remains concentrated much of the week in the lower half of its guidance envelope, though given its tendency to struggle in warm advection regimes, particularly during the transition seasons, have made some occasional upward adjustments to temperatures, particularly highs, where merited. && .AVIATION (00Z TAF Issuance)... Issued at 611 PM EDT Sat Apr 27 2024 Impacts: - Brief TSRA at LAF 01Z to 05Z - LLWS 06Z to 13Z - Southerly wind gusts to 30kts through TAF period Discussion: VFR conditions expected through the TAF period outside of brief MVFR vsbys at LAF if convection hits the terminal. Best chances would be from 01Z to 05Z with lesser chances afterwards and and HUF. LLWS returns tonight with a 50kt jet at 020 as southerly winds gust up to 25kts through the night. Additional gusts to 30kts are possible during the afternoon hours tomorrow. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...White SHORT TERM...MK LONG TERM...Nield AVIATION...White |
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