Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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961 FXUS63 KIND 312301 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 701 PM EDT Thu Oct 31 2024 .KEY MESSAGES... - Dry and breezy for trick-or-treating except for far southeastern Indiana where light rain is likely. - Cooler and dry Friday and Saturday. - Periodic rain chances Saturday night through Tuesday night with a warming trend. && .SHORT TERM (This evening through Friday)... Issued at 231 PM EDT Thu Oct 31 2024 Synopsis: Surface analysis early this afternoon shows strong low pressure over NW WI with an associated cold front extending south across Central IL to SE MO and Arkansas. A moderate pressure gradient remained across Central Indiana, with southerly flow ahead of the front. Water vapor imagery, shows a plume of moisture streaming across MO/IL toward Indiana, ahead of a negatively tilted upper trough over WI/MN. Radar shows gaps developing in the rain shield that has been arriving across Central Indiana through the day. Skies were cloudy across Central Indiana and temperatures were falling in the 60s. Halloween (Tonight) - Beware! Models tonight reveal a chilling cold front sweeping across Indiana in the witching hours from 5 PM to the end of trick or treating. Forecast soundings show deep moisture lingering in the shadows, rapidly drying out as eerie subsidence takes hold. Aloft, an ominous upper trough is set to glide toward the eastern Great Lakes, giving way to a nearly ghostly zonal flow by Friday. The HRRR predicts that most of the spectral rainfall will creep to SE Indiana between 8-10PM, fading into the night as it becomes detached from the dynamic forces pulling away to the north. By 3 AM, the pwats will drop below 0.35 inches, leaving behind a hauntingly dry atmosphere. A moderate pressure gradient will keep the winds howling this evening, with gusts reaching 15-25 mph, creating an unsettling chill. These winds will ease as high pressure rises from the plains overnight. Prepare for strong cold air advection, with temperatures at 850mb plummeting to a frigid 6C by dawn. Expect lows to dip into the eerie lower 40s across much of Central Indiana. Stay cozy and watch for ghosts and goblins in the night! Friday - The new month will arrive with sunny and cooler conditions. As mentioned above, nearly zonal flow is expected aloft with little in the way of forcing dynamics present. Meanwhile, strong high pressure is expected to develop over the plains, strengthen and push toward the Great Lakes. A strong mid level inversion and a very dry column as seen on the forecast soundings will result in sunny skies with light easterly winds. With cooler air in place, highs will only reach the middle 50s to near 60s. && .LONG TERM (Friday night through Thursday)... Issued at 231 PM EDT Thu Oct 31 2024 The drier and cooler continental air mass will still be in place Friday night but should begin to moderate Saturday as lower tropospheric flow veers around to southeasterly. Temperatures should be about five degrees above climatology. High-level Pacific moisture and upstream cross-mountain flow should result in increasing cirrus during the day, potentially becoming quite thick. MSLP gradient will tighten between the eastward drifting high and strengthening Plains cyclogenesis. This pattern will favor poleward movement of deep subtropical moisture into Indiana Saturday night. Warm/moist advection and weak broader isentropic ascent coupled with a compact midlevel perturbation in southwesterly flow could result in some precipitation Saturday night into Sunday. Multi-model ensemble mean is sharper with the gradient on the eastern end of the QPF maxima centered to our west, and generally has trended downward for rainfall amounts in Indiana on Sunday. It appears the best chance will be early in the day across the northwest half of our forecast area, with minimal coverage the latter half of the day. The entire synoptic trough/ridge pattern shifts slowly east Monday placing the axis of QPF a little further east. A couple waves of remnant convection will occur Sunday night and Monday, but timing and amounts still need to be refined given the sensitivity of small variations in modeling convectively-induced midlevel shortwave perturbations and attendant precipitation footprint. It appears the best chance of meaningful precipitation across central Indiana will be Tuesday/Tuesday night as the Plains trough and associated DCVA/forcing for ascent interact with the anomalous moist plume resulting in a band of rain migrating through. Convective intensity and potential for lightning will be limited by the displacement of cooler midlevel temperatures closer to the trough center to our north from the warm/moist lower troposphere over us. Post-frontal air mass Wednesday and Thursday will be similar to the last couple of fronts. Drier, and near-climatology temperatures. But, again, the southeast anomalous ridge holds and the departing wave and associated cold continental air mass isn`t very intrusive. The Day 8-14 period has below normal predictability. At the start, there is quite a dipole in handling of western trough. The deterministic GFS and a handful of its ensembles are aggressive with eastward movement and a potentially significant precipitation event late next week into the weekend, while the EPS and several other multi-model ensemble members are more dominate with the ridge and a dry pattern. So, there`s not much signal to determine if we`ll be above or below normal precipitation, but a reasonably clear signal on a warmer than normal pattern. && .AVIATION (00Z TAF Issuance)... Issued at 700 PM EDT Thu Oct 31 2024 Impacts: - Sporadic gusts 17-22KT from 270-280 degrees through 02-03Z post cold frontal passage - Periods of MVFR ceiling through 02-03Z Discussion: A cold front is sweeping across the sites this evening, and winds will rapidly become westerly where they have not already as it does so. Sporadic gusts in the wake of the boundary will occur in the first few hours before subsiding completely later this evening. Additionally, occasional MVFR ceilings can be expected. Will cover both gusts and MVFR ceilings with TEMPO groups early. VFR conditions will return beyond 02-03Z and persist through the remainder of the period as high pressure continues to build into the region and skies rapidly clear. Winds will drop below 10KT overnight into Friday, with wind directions veering to the northwest and then northerly late in the period in response to the movement of the high. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ SHORT TERM...Voorhees LONG TERM...Krueger AVIATION...Myers