Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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212 FXUS63 KIND 230507 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 107 AM EDT Thu May 23 2024 .KEY MESSAGES... - Scattered showers and storms possible south today. - Rain and thunderstorms possible on Friday, and again on Sunday. - Cooling trend possible next week. && .FORECAST UPDATE... Issued at 943 PM EDT Wed May 22 2024 Radar, satellite and CAMS trends support dry weather through at least the early overnight. Although, boundary has stalled over our far southeastern sections, so the plan is to lower the cloud cover through the early overnight but keep small thunderstorm chances in overnight over south central sections or closer to this boundary. CAMS hint at convection devloping and moving along this boundary toward daybreak. Otherwise, light northeast winds north of the boundary and a very dry boundary suggest any fog will be very localized and over areas to the south of the front. The lack of cloud cover and drier air supports temperatures getting down to as low as the middle 50s over nortwestern sections while southeastern sections closer to the front and convective cloud cover will likely only bottom out in the lower to middle 60s. && .SHORT TERM (This evening through Thursday)... Issued at 258 PM EDT Wed May 22 2024 Synoptic Pattern: Broad troughing continues over the Upper Rockies, ejecting a succession of waves eastward into the Great lakes region. Today is no different, as a compressed short wave axis is moving through aloft this afternoon and evening along with a deep surface low to the north. This low has gone through occlusion processes, with dry air cutting off the cold front from the trough aloft. This should leave a weak stationary front across central Indiana over the next 24 hours providing a dichotomy of impacts across the region. Also of note is a developing weak surface high over the southern Great Lakes region in the presence of confluence and AVA aloft. This will help reinforce dry air north of the stationary boundary tonight into tomorrow. Weather Conditions: South of the Boundary (Mainly south of the I-70 corridor) Within this area, surface moisture will remain elevated in the presence of broad SSW flow. This, along with modest mid level lapse rates will keep the atmosphere unstable and primed for convection with any source of lift. However, lift will remain weak through the afternoon and evening keeping conditions mainly dry outside of a rogue isolated thunderstorm within weak lift along the boundary. Late tonight greater lift along the mid level trough axis could be enough for isolated to scattered showers and thunderstorms. Even though most storms should remain weak due to the lack of substantial shear, high storm tops and precip loading could be enough for a few strong to severe storms. These scattered showers/storms may continue through portions of the day on Thursday before increased subsidence ends the threat in the evening. Temperatures will remain slightly higher today/tonight in this region with highs in the mid 80s this afternoon and lows in the mid 60s overnight. However, temperatures tomorrow may have a harder time climbing south of the boundary due to greater cloud coverage. Currently, temperatures tomorrow are expected to remain in the upper 70s for southern central Indiana. North of the Boundary (Generally along and north of the I-70 corridor) Much of this area will remain rather mundane over the next 24-36 hours. Dry air attached with increasing heights to the north will decrease instability and lift substantially leading to near zero rain chances this afternoon through early tonight. A slight resurgence of moisture overnight attached with a weak shortwave may be enough for a weak isolated thunderstorm to lift over the boundary overnight, but most areas north of the boundary should remain dry. For tomorrow, high pressure and associated subsidence should keep and showers/storms contained over south-central Indiana. Temperatures tomorrow will have an easier time increasing within deep PBLs and partly sunny skies; expect highs near to just above 80. && .LONG TERM (Thursday night through Wednesday)... Issued at 258 PM EDT Wed May 22 2024 A progressive and fairly active weather pattern looks to continue through the weekend. SYNOPTIC OVERVIEW The large-scale upper-level flow pattern across the CONUS can be described as western troughing with split flow over the east coast. While smaller-scale features ebb and flow through the overall pattern described above, the larger picture should mostly remain the same through the week into the weekend. By next week, guidance shows a bit of a reversal with troughing taking hold over the east coast and a split flow / ridge pattern over the western states. In terms of sensible weather here in Indiana, it will be the smaller- scale features that we`ll need to keep tabs on. The first of these is a potent vort max passing well to our northwest Thursday into Friday. Despite how far it is from Indiana it may still provide enough forcing for showers and thunderstorms on Friday. Guidance shows a few other smaller vorticity filaments passing nearby on Friday as well. These may be convectively induced by earlier convection upstream...so there is inherent uncertainty here, given how chaotic convection is and how difficult a time models have with it. Aside from convection, if low-level moisture return is quick enough there may be a chance of some patchy fog Friday morning. Probability appears low, however. Enough model agreement exists for likely PoPs later on Friday. Model soundings show little flow aloft so organized convection is not as likely. Nevertheless, a quick downburst and/or small hail is possible given a rather deep CAPE profile amid steep lapse rates. Additionally, profiles contain abundant moisture and so a locally heavy rain threat may present itself as well. After a bit of a break, the next vort max emerges from the western trough late Saturday. Guidance is generally in agreement showing surface cyclogenesis across the Plains overnight into Sunday. The resulting surface low then looks to pass over or just to the north of Indiana. In terms of rain and storms, we may end up seeing two rounds...one in the morning, and one later in the afternoon/evening. The morning round is associated with the system`s warm front and remnant upstream convection. The second round occurs in the system`s open warm sector and along the attendant cold front. Unlike Friday`s system, there is decently fast upper-level flow which may support more organized convection and therefore a severe weather threat. It is too soon to talk specifics, but the potential is there over a broad area. The eventual outcome will come down to placement and timing of key features (the low itself, the warm front and cold front, and any remnant cold pools from previous convection). Beyond that, next week appears less active due to broad troughing overhead. Even so, a few waves embedded within northwesterly flow may provide a chance for precip on Monday or Tuesday. Temperature- wise, a return to near or even slightly below normal temperatures is possible. FORECAST CONFIDENCE Overall confidence in the forecast is good. Ensemble guidance is in agreement through Friday with large-scale features. In fact, agreement within guidance is fairly good through much of next week as well. There is a strong signal for prolonged troughing through the end of May. Generally negative teleconnections (AO/NAO) add weight to this idea. Confidence decreases for finer scale features, such as convective timing and hazards. This is primarily due to the chaotic nature of convective patterns where features can interact and affect their evolution and subsequent days evolution. && .AVIATION (06Z TAF Issuance)... Issued at 107 AM EDT Thu May 23 2024 Impacts: - Small chance of MVFR fog through sunrise at all but KIND Discussion: Conditions are marginal for some fog development at the outlier sites. With odds this low, left it out of the TAFs but will watch. Otherwise, generally VFR conditions are expected. A few showers or thunderstorms are possible at the southern sites, especially KBMG, during the daylight hours today. Will only mention VCSH at KBMG and leave it out of the other sites for now given expected coverage. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...MK SHORT TERM...Updike LONG TERM...Eckhoff AVIATION...50