Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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011 FXUS63 KIND 250703 CCA AFDIND Area Forecast Discussion...CORRECTED National Weather Service Indianapolis IN 303 AM EDT Sat May 25 2024 .KEY MESSAGES... - Thunderstorms, possibly severe on Sunday/Sunday Night/Monday - Shower chances and cooler temperatures Tuesday-Wednesday - Dry and Seasonable Thursday and Friday && .SHORT TERM (Today and tonight)... Issued at 301 AM EDT Sat May 25 2024 A weakly baroclinic front tied to a deep occluding low near the Manitoba/Ontario border will pass through this morning. Although we will be at a diurnal minimum, warm/moist advection preceding the front may be enough for isolated convection. With diurnal heating and destabilization this afternoon, convection will redevelop but it should be relegated to our far southeast counties by then (east of a Seymour to Greensburg line). The post frontal air mass will probably not be noticeably cooler compared to yesterday, but drier continental air will feel less humid by comparison. Mid to upper 70s for maximas are expected with northwest winds 10 mph or less. Cirrus and an increasing MSLP gradient with mixing toward dawn may interrupt radiative cooling process to keep temperatures from falling substantially, but still 5- 7 degrees cooler than the previous couple of nights given dry air mass and steeper diurnal curve early in the night when radiative processes are more optimal. && .LONG TERM (Sunday through Friday)... Issued at 301 AM EDT Sat May 25 2024 Sunday through Monday... Look for an active start to the extended period as severe weather is likely Sunday and Sunday night as a mid-upper level trough with multiple embedded impulses traverses the Great Lakes region. An MCS is expected to be ongoing Sunday morning over portions of MO/IL which should progress towards central IN around mid-morning to early afternoon bringing the first potential round of strong to severe storms. Latest models still show disagreement regarding timing of the MCS due to uncertainty in how organized the line of storms or cold pool will be. The MCS is likely going to gradually weaken upon approach as it outpaces the stronger deep-layer shear further west. Despite this, there is still the potential for severe weather with this initial round of convection. The primary threat would be damaging wind gusts, but embedded tornadoes cannot be ruled out if the MCS remains organized. Mesoscale subsidence behind the line of storms may allow for a brief break during the afternoon before another round of severe storms moves in by the evening. Guidance shows the upper trough becoming more negatively tilted and amplified late Sunday resulting in a deepening surface low across the Midwest. A strong LLJ associated with the system will advect deeper moisture into central Indiana during the afternoon promoting further destabilization despite early day convection. Scattered to numerous storms are likely to develop ahead of a cold front over MO/IL late in the afternoon. A strongly unstable airmass along with strengthening deep-layer shear from increasing mid-upper level flow will likely support severe thunderstorms. Shear vector orientations and focus of low-level convergence suggest these storms should quickly grow upscale and progress towards the area during the evening and overnight hours. Some supercells are possible as well with all convective hazards on the table. In addition, there is an elevated threat for localized flooding given anomalous moisture return and the potential for training storms over saturated grounds. The aforementioned surface low should begin to move out early in the day Monday. Rain chances remain in the forecast though with broad cyclonic flow still in place. Tuesday and Wednesday... Strong ridging aloft is expected to build across the plains in the wake of the front. This will allow an area of cool, Canadian high pressure to settle across Indiana on Tuesday through Wednesday. Forecast soundings on these days show a dry column with little to no instability present. Thus will trend toward a dry forecast, partly cloudy days and mostly clear nights with seasonable temperatures. Thursday and Friday... Models suggest the strong ridging looks to remain over the mid section of the CONUS, but this will allow for the development of a weak Omega block, with the front end low setting up over the middle Atlantis States. This will bring cyclonic flow aloft over Indiana, influenced by the upper low to the east. Meanwhile at the surface, strong surface high pressure centered over the Great Lakes with cool easterly flow will be present across Central Indiana. The lower levels are not a favorable set-up for precipitation, but the cyclonic flow aloft cannot rule precipitation out. Thus it is likely that at least some small chance pops will be included at that time for now. && .AVIATION (06Z TAF Issuance)... Issued at 1238 AM EDT Sat May 25 2024 Impacts: - Brief MVFR stratus possible early-mid morning - Wind shift to northwesterly midday Saturday Discussion: Some variability in wind direction will occur around the beginning of the TAF period due to recent diminishing convection and its augmentation of the low-level pressure field. Winds should stabilize to southerly toward morning and then veer as a front moves through. A band of stratus will accompany the front and could result in brief MVFR ceilings. Post-frontal winds will be northwesterly. Probabilities of showers will be 20-30 percent at TAF sites until the front passes. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ SHORT TERM...BRB LONG TERM...Melo AVIATION...BRB