Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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160 FXUS63 KIND 081744 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 144 PM EDT Wed May 8 2024 .KEY MESSAGES... - Severe storms possible today, especially during the late afternoon and evening. Hail and wind are the primary threats. - Heavy rain is possible at times through Wednesday night. Localized flooding will also be possible. - Periodic chances for showers and a few storms late week into early next week. - Normal to slightly below normal temperatures Thursday through Saturday with warmer temperatures next week. && .FORECAST UPDATE... Issued at 1004 AM EDT Wed May 8 2024 Watching the forecast closely today as another round of severe weather is expected later this evening and tonight. While the worst of the severe weather is forecast to be south of the Ohio River, there still is a severe threat for much of Central and Southern Indiana. Latest surface analysis depicts an area of low pressure over western Kansas with a warm front extending eastward through Missouri and then along the KY/TN border where storms are currently developing. Despite being north of the warm front, low level inversion overnight kept the boundary layer fairly saturated with dew points remaining in the 60s into this morning. Subsidence under ridging ahead the approaching system to the west has resulted in clear skies this morning for all of Central Indiana. Latest ACARS sounding from IND does show a very dry column aloft, so once boundary layer heating and mixing begin, expect drier air aloft to mix down to the surface, lowering dew points back into the 50s, with the driest conditions expect north of I-70. Will be watching the northward progression of the warm front closely today as this may be the focus for storms to develop and move eastward along later this afternoon and evening. A concern is that widespread convection across KY/TN this morning may inhibit the northward movement of the front some, keeping the main focus for storms further south. Confidence on how far north the warm front makes it is lower than what is preferred for being the day of the event. Higher confidence does exist in that boundary making it into Southern Indiana later today, where a more moist, and unstable environment will develop with the best potential for severe storms. Currently watching a complex of storms in Central Missouri developing and pushing eastward, just north of the main warm front and along an MUCAPE and Theta-E gradient. Expect additional storms to form with this cluster through the rest of the morning hours. These storms will likely continue to push eastward or southeastward along instability/moisture gradients. That is why tracking these sharp boundaries and fronts are so important for determining where the severe threat will be later today. If these boundaries remain south, then the storms will likely remain south along the boundaries. Inversely, if these boundaries shift northward into Southern Indiana, which is what short term guidance suggests, then some severe storms will be likely in that region. Main forecast challenge will be tracking these boundaries and highlighting which areas/counties will be at the greatest risk for storms and which areas will escape most of the threats. Higher confidence does exist in a lower threat north of the I-70 corridor in North Central Indiana. && .SHORT TERM (Today and tonight)... Issued at 303 AM EDT Wed May 8 2024 Synoptic Overview: Central Indiana is now on the cool side of a warm front, which will likely end up somewhere along a Kansas City to Paducah line later this morning. For now, this frontal boundary is over southern IN, and has suppressed surface winds, keeping a large portion of central Indiana under light and variable conditions. On a separate, non thunderstorm related note, these light winds in combination with elevated surface moisture from prior rainfall will likely result in patchy, dense ground fog over this area. As daybreak occurs, surface heating should quickly mix out any fog, with 10mi or greater visibility by 9AM. For most of the day, central Indiana will be positioned within a weak low level ridge, but also within strong upstream forcing and moisture return. This ridge will act to suppress warm frontal progression some, but high amounts of theta-e advection will counteract this eventually lifting the warm front into central Indiana. All CAMs have the warm front lifting northward throughout the day, but even just 12-18 hours out, there is still significant variability in placement. Generally, this frontal boundary is expected to reach a Sullivan to Bloomington to Columbus line. This is important as a majority of convective initiation is expected to occur south of the front. The aforementioned ridge will still have some influence on the environment, keeping low level winds marginal and drying out the near surface layer north of the front. Still, the impacts of the upper level trough will allow for steep mid level lapse rates deep instability profiles across much of the region. Theta-e advection within the warm sector will also act as a lifting mechanism helping establish CI later this afternoon. Severe Weather Hazards and Timing: As stated, CI is expected to occur continuously this evening south of the warm front once convective temperatures are reached. There will also be a convective threat overnight, but that will be highly depending on the location of MCS development. For today, the wind profile will look much differently than yesterday, with winds in the lower 3km much weaker due to the aforementioned ridge. However, winds aloft will remain rather robust with a westerly 500mb to 300mb jet placed direction aloft. This will likely lead to a variety of storm modes including multicell clusters and lines as well as a few supercells. Any supercells that due develop will have the tendency to split. Within the initial evening threat. Tornadoes look unlikely given the lack of low level winds, and high LCLs, but a strongly deviant right movers in far southern central Indiana where dew points are elevated could have enough streamwise vorticity ingestion for isolated tornadoes. Hail and wind on the other hand will pose the main threat for central Indiana. Deep CAPE profiles with strong flow through the Hail Growth Zone will promote a large hail threat, and dry mid-level air and DCAPE values over 1000J/kg should create a environment capable of efficient downward momentum transfer and a damaging wind threat. These threats will be greatest in any supercells that form (especially hail within left movers). The overnight threat will be primarily due to any MCS that potentially forms west of central Indiana. This is currently highly uncertain, due to substantial model inconsistency. However, if an MCS does pass through overnight, a high wind threat will be possible. Given the west to east placement of the warm front and the resulting upshear vectors, training thunderstorms will be possible in this overnight regime. Because of this localized flooding will be possible. && .LONG TERM (Thursday through Tuesday)... Issued at 303 AM EDT Wed May 8 2024 Thursday through Saturday... A pair of upper waves and associated cold fronts in northwest flow aloft will dive southeast across central Indiana and bring more convection to mainly northeastern sections Thursday and again Friday night and Saturday. Model agreement is good on the handling of these features. Temperatures will be noticeably cooler, especially Friday and Saturday with below normal highs in the 60s. Saturday night and Sunday... Weak ridging and a fairly dry column will lead tranquil weather late in the weekend along with temperatures moderating back to near normal Sunday with afternoon highs in the upper 60s to middle 70s. Sunday night through Wednesday... Confidence is low on PoPs and temperatures next week as models agree that split flow will develop over the Plains and a broad trough will eventually move through the Ohio Valley. The question is when as models and their ensembles are having trouble coming together with big timing spreads. With these differences, did not make any changes and left small convection chances in through the period along with a warming trend due to the winds shifting to a southerly component. && .AVIATION (18Z TAF Issuance)... Issued at 144 PM EDT Wed May 8 2024 Impacts: - Severe weather threat shifting south of Central Indiana - Expect showers and sub-severe storms pushing in this evening - Potential for MVFR cigs late tonight Discussion: As with a lot of large severe weather events, things can change rapidly depending on where boundaries set up and other smaller mesoscale details. Latest indications are that the main severe weather threat will be south of Central Indiana TAF sites this evening and tonight. With that said, latest satellite and radar imagery show a cluster of storms in Missouri and Southern Illinois along a warm front. Latest guidance does indicate this warm front remaining south of the TAF sites, keeping the main severe weather threat south. However, sub- severe storms and showers are still possible later this evening at KHUF and KBMG. Lower confidence exists if KIND will even see lightning with showers later on this evening. Currently, timing for any convection in the area looks to be around 23z to 05z, with lingering isolated showers and MVFR cigs after that. Winds have been light and variable much of the day remaining under 7 kts at most sites. As the main low pressure pushes near the region tonight, expect winds to become southerly at all locations, then becoming west-southwest during the day tomorrow increasing to 10-15 kts. Additional chances for showers and thunderstorms are possible tomorrow morning into tomorrow afternoon; however confidence remains low on coverage of convection and exact timing. && .IND WATCHES/WARNINGS/ADVISORIES... Flood Watch from 6 PM EDT this evening through late tonight for INZ056-064-065-071-072. && $$ UPDATE...CM SHORT TERM...Updike LONG TERM...MK AVIATION...CM