Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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894 FXUS63 KIND 050209 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 1009 PM EDT Tue Jun 4 2024 .KEY MESSAGES... - Scattered thunderstorms this evening and tonight. Most storms should remain below severe limits. - Additional storm chances 16-22z tomorrow with the passage of the front. A few storms may be strong. - Below normal temperatures in the 70s late this week into the weekend && .FORECAST UPDATE... Issued at 1008 PM EDT Tue Jun 4 2024 Only some minor changes needed to the forecast this evening. We did lower the winds a bit from blended guidance during the nighttime hours. A common failure mode of higher-res guidance is to overdo nocturnal surface winds/gusts in an environment with a low-level jet. The higher-than-realistic speeds come from over-mixing despite boundary layer stabilization. We also decreased PoPs a bit based on latest radar trends. Ongoing activity in Illinois will take a few hours to translate eastward into Indiana. Will keep highest PoPs across the IN/IL border through much of the night. PoPs increase late in the night and through the morning as a surface front nears the area. && .SHORT TERM (This evening through Wednesday)... Issued at 255 PM EDT Tue Jun 4 2024 This evening and tonight... Scattered showers and thunderstorms are in the forecast this evening through tomorrow afternoon across Central Indiana. Latest satellite imagery and surface analysis show an area of low pressure over NE Missouri with a boundary extending SE into South Central Indiana. With the boundary pushing through the region this evening, expect the environment to continue to destabilize and become more supportive of convection. ACARs soundings from IND, SDF, and STL show sufficient moisture and surface based instability; however wind shear is very weak resulting in a low severe weather threat. A strong storm or two is not out of the question with strong wind gust or hail, but most storms should remain below severe limits with lightning and heavy rain being the main threats. Local mesoscale features such as outflow boundaries and storm mergers may lead to brief intensification of storms to strong to severe levels and/or lead to repeated thunderstorm activity over an area. Greatest storm chances and coverage this evening are along and south of the I-74 corridor closest to the boundary slowly pushing NE through the state. Expect the most widespread convective activity through around sunset then a slight decrease in coverage after sunset. Short-range guidance does not handle weakly forced scattered storms well, but confidence is moderate that periods of scattered convection will persist into the late evening and overnight hours as the low level jet ramps up overhead. While shear does increase some overnight, low level instability values weaken resulting in convection likely being elevated, keeping the severe threat low overnight. With increased clouds and convection in the area overnight, lows likely will not fall much below the upper 60s to low 70s tonight. Tomorrow... A cold front associated with the same system from Tuesday will be approaching Central Indiana from the west tomorrow morning bringing additional chances for storms to the region. Isolated to scattered convection may be ongoing during the early morning hours across Central Indiana as the region will be firmly within the warm sector of the system in a very humid, modestly unstable, and weakly sheared environment. Guidance does suggest a lull in convective activity around sunrise and through the mid morning hours, however confidence in this only moderate at best as how convection evolves further west the night before will directly impact how everything evolves overnight and through the morning hours. Best chance at morning storms seems to be across Western portions of Indiana, closer to the front and area of greater forcing. The main front is expected to push through Central Indiana from west to east in the 16-22z timeframe tomorrow. This round of storms has the best chance at producing strong to severe storms; however the risk is only marginal with the greatest threat along and east of the I-65 corridor. Low level shear values of 15-25 kts in addition to a modestly unstable environment ahead of a negatively tilted trough axis to the NW may support a damaging wind and very isolated tornado threat in the strongest storms. Highs tomorrow will reach the mid 70s to low 80s with highs likely occurring behind the line of storms later in the afternoon and evening. && .LONG TERM (Wednesday night through Tuesday)... Issued at 255 PM EDT Tue Jun 4 2024 Wednesday Night Through Thursday... By the evening hours most model guidance has the front and much of the convection through the area and into Ohio. We could see some lingering stratiform rain behind any storms but that should dissipate before midnight. A secondary front arrives on Thursday morning and could see a few very light showers/sprinkles with that. Otherwise, expect drier and cooler conditions on Thursday with highs in the mid to upper 70s and dewpoints falling into the 50s to upper 40s by Thursday evening. Friday through Monday... A ridge builds across the western US, leaving the eastern half in a broad trough regime. A couple of weak waves move through the broad trough but most of the forcing stays to our north over the Great Lakes. Northwesterly flow will keep conditions seasonably cool with highs in the low to mid 70s and lows in the low to mid 50s. Models begin to diverge on the eventual breakdown of the trough/ridge Sunday into early next week. The remnants of a tropical system over the eastern Pacific gets pulled into the flow with an uptick in PWATs over the central and southern US to end the weekend and into early next week. This coupled with a slightly stronger wave rotation around the backside of the eastern US trough could finally kick the trough out. Rain chances should return Monday through Tuesday but at this time nothing stands out for any severe risk. Ensemble guidance is in good agreement with temps staying in the 70s through at least Tuesday/Wednesday. Big differences begin to emerge after early next week. && .AVIATION (00Z TAF Issuance)... Issued at 758 PM EDT Tue Jun 4 2024 Impacts: -MVFR conditions developing by morning. -Isolated showers and possibly a thunderstorm overnight. -Greater coverage of showers and storms after 12z or so. -South winds shifting to WNW in the evening. Discussion: Generally VFR conditions persist across the area this evening with only a few isolated showers and storms. These should diminish as the sun sets but an occasional shower may occur at any point overnight. A period of MVFR conditions is likely in the morning as low- level moisture increases ahead of an approaching cold front. Greater coverage of showers and storms is likely in the morning and afternoon as the cold front approaches. Brief reduction to IFR is possible in heavier showers and storms. Frontal passage should be about 00z. Post front, winds shift to WNW and skies begin to clear. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ UPDATE...Eckhoff SHORT TERM...CM LONG TERM...Stumpf AVIATION...Eckhoff