Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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270 FXUS63 KIND 250438 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 1238 AM EDT Sat May 25 2024 .KEY MESSAGES... - Scattered to numerous showers and isolated thunderstorms through early Saturday - Thunderstorms, possibly severe on Sunday/Sunday Night/Monday - Shower chances and cooler temperatures Tuesday-Wednesday - Dry and Seasonable Thursday and Friday && .FORECAST UPDATE... Issued at 924 PM EDT Fri May 24 2024 The dilemma the rest of the night is whether or not the Illinois and Missouri convection will still be a severe threat as it starts rolling in late this evening and early overnight per radar trends and CAMs. Early evening convection that produced marginally severe hail and a few damaging wind reports. SPC mesoanalysis was showing an instability axis extending northeast across the Ozarks this evening ahead of an advancing cold front that extended from eastern Iowa to northern Missouri and northeastern Oklahoma. Meanwhile, radar was indicating a broken line of strong to severe storms extending from western Illinois to southwestern Missouri and northeastern Oklahoma. In addition, out ahead of this broken line, there were small clusters of thunderstorms within a large area of stratiform, advancing to the Indiana border. Earlier and still ongoing central Indiana convection has resulted in a outflow spreading quickly southeast across central Indiana with stable air replacing 2500 J/kg CAPE that is holding on momentarily over far southeastern sections of central Indiana. It would stand to reason that the incoming convection will have a difficult time maintaining itself as it attempts to flourish in the stable central Indiana cold pool. More likely, the activity will weaken and or get steered southeast toward the most unstable air. At any rate, will need to maintain good chance to likely Pops through much of the overnight with the incoming stratiform and convection. Note: Just as this was being ready to be disseminated, the new SPC Day 1 Severe Weather Outlook came out and it removes the slight risk and only contains a marginal risk of severe storms over southwestern sections which falls nicely in line with our thinking. Had to lower temperatures a degree or two over most of the area despite mostly 60s dew points and thick cloud cover due to the cold pool. && .SHORT TERM (This evening through Saturday)... Issued at 227 PM EDT Fri May 24 2024 Rest of Today/Tonight. Storms have begun to initiate along the outflow boundary from the late overnight/early morning derecho that moved across Iowa as surface instability continues to increase. As of 2PM, Hi-Res models are showing upwards of 1500-2000 J/kg of surface based CAPE across central Illinois which is where the better axis of effective bulk shear. Across western Indiana values are generally less than 20kts with the weaker flow aloft. This will improve a bit closer to 00Z as the LLJ begins to ramp up but with a lack of shear the severe threat looks minimal without a more organized cold pool developing across Illinois which could push things eastward. The other potential concern for this evening/early overnight is a residual MCV from yesterday`s convection across the Southern Plains as it pushes further into Arkansas and Tennessee and gets ingested into the LLJ and turns more northerly. So far the storms associated with this system have been brief and sub-severe with a lack of instability along and ahead of the MCV limiting the threat. Hi-Res models are picking up on the locally enhanced shear, but this seems rooted more in the 700-500mb layer which has generally been higher than the storms have been able to tap into so far. The tornado threat that often is enhanced by an MCV doesn`t look to be the case this time around with observations not showing a stronger easterly wind component compared to what would normally be seen. Thoughts going into the evening hours are that the disorganized convection across Illinois will push in and gradually weaken after 3-4PM with additional pulse thunderstorms caused by forcing from the MCV across the southern half of the state through the early evening. It doesn`t look likely that the southern storms will be able to root into the better shear aloft with a lack of instability and the lack of shear across the northwest will keep the severe threat minimal with lightning and a brief gust of wind from downburst as the primary threats. Isolated to scattered showers will continue through the rest of the night with dry weather by tomorrow morning. Saturday. A brief break in the more active weather is expected for Saturday as the parent upper level low from the Friday system pushes into Canada and the next low ejects from the Rockies. This low is expected to bring more widespread and intense strong to severe storms but that will be covered in the long term section below. For Saturday expect pleasant conditions as the skies clear through the morning and northwesterly surface flow keeps temperatures in the upper 70s to low 80s with dewpoints in the low to mid 50s for all but the southern third of the state which will be closer to 60. && .LONG TERM (Saturday night through Friday)... Issued at 227 PM EDT Fri May 24 2024 Saturday Night... Models shows moderate southwest flow in place aloft with little in the way of forcing dynamics present through the evening hours along with a dry forecast column. Surface high pressure will be set up over the southeastern states and low pressure is expected over Kansas. The low is expected to extend a warm frontal boundary across MO to Indiana. Dry weather will be expected in the evening, however overnight convection over middle Mississippi valley associated with an approaching wave aloft will push forcing dynamics toward Central Indiana overnight. Forecast soundings overnight are trending toward saturation late as the earlier convection advects east. Models are differing a bit on the timing, but for now at least chance pops during the overnight, especially across the west seem appropriate. With Central Indiana within the warm sector, lows will be in the middle and upper 60s. Sunday, Sunday Night and Monday... Confidence is high for a precipitation event on Sunday and Sunday Night. Confidence for precise timing of the showers/storms is much less so. Models suggest the moderate trough aloft pushing east into the middle Mississippi and Ohio Valleys. The trough looks to become slightly negatively tilted aloft as it pushes toward Indiana. Ample forcing dynamics appear present. After the possible morning convection, another round is suggested during the afternoon hours. Models suggest CAPE present ranging from 1500 to 3000 J/kg across the forecast area as a favorable atmosphere for convection will present. Thus with the warm frontal boundary in place to across Central Indiana and much of the forecast area within the forecast area. Thus we will include high pops through the course of the day on Sunday, although there still will be periods of dry weather. More precise timing will come into focus in the next 24-36 hours. On Sunday Night and into Monday, the upper low is expected to push northeast toward the Great Lakes and drag another trough axis across Indiana. Again this feature has ample forcing with plentiful CAPE available on Sunday night through early Monday. The associated surface low pressure system expected to push through the Great Lakes on Monday and will also drag a cold front across Central Indiana, exiting by late afternoon. Thus will need to keep some chance pops for the time period on Monday when our area resides within the warm sector ahead of the front. 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. && $$ UPDATE...MK SHORT TERM...White LONG TERM...Puma AVIATION...BRB