Area Forecast Discussion
Issued by NWS Indianapolis, IN
Issued by NWS Indianapolis, IN
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005 FXUS63 KIND 050532 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 132 AM EDT Sun May 5 2024 .KEY MESSAGES... - Isolated to scattered showers and thunderstorms into tonight. Severe storms are not expected. - Isolated flooding threat Monday. - Growing confidence in the potential for a few rounds of severe thunderstorms Tuesday through Wednesday. && .FORECAST UPDATE... Primary focus for the evening update was fine-tuning POPs with the higher confidence that isolated thunderstorms in addition to the widespread rain will reach into the western counties. Will gradually taper down coverage towards Indianapolis as these storms continue to downtrend as a result of the combination of a loss of daytime heating and the cold pool pushing out ahead of the parent thunderstorms. Latest radar imagery shows the gust front around 10-15 miles ahead of the convection with elevated showers popping up behind the main cold pool. This gust front has a history of producing 30-40 mph winds across eastern Illinois but as it continues to lose the connection to the parent convection, expect these wind gusts to gradually weaken further into Indiana. By the time this complex reaches I-65, expect that the thunder will have ended with residual light rain spreading across the area through 2AM before rain ends. Afterwards, quiet weather is expected through daybreak tomorrow with winds becoming more northerly. && .SHORT TERM (This evening through Sunday)... Issued at 258 PM EDT Sat May 4 2024 The low cloud deck has slowly given way over the last few hours as boundary layer mixing has commenced. Much of the forecast area is now enjoying a mix of sun and cu with a noted min in the cu field extending from Carroll County south into Putnam and Hendricks Counties and indicative of remnant subsidence and a stable layer courtesy of the high pressure ridge that moved off to the northeast earlier. 18Z temperatures ranged from the low 70s in eastern counties to near 80 in the Wabash Valley. Rest of This Afternoon and Tonight Messy pattern lingers across the Ohio Valley this afternoon with a trailing axis of moisture in the wake of the weak low over western Ohio. Stagnant wind flow has been unable to completely mix out the low level moisture and with a subtle instability axis present across southeast Indiana...have continued to see isolated convection pulse up generally east of a Muncie-Shelbyville-Bedford line. These cells will remain confined to mainly eastern portions of the forecast area over the next few hours producing brief heavier rainfall and a few lightning strikes as they pop up and down in an environment with virtually no shear or forcing aloft. Convection will be dependent on available instability which is likely to tick upwards a bit as we approach peak heating late this afternoon. Further west across the forecast area...the atmosphere is more stable and will remain so into the early evening hours as the axis of residual dry air and subsidence pivots east. Focus will turn to scattered convection associated with a cold front approaching the mid Mississippi Valley currently. Expect convective coverage and intensity to increase over the next few hours as it crosses into Illinois and interacts with an axis of moderate instability. The storms will approach the Wabash Valley by mid evening in a steadily weakening state as they move into a more stable environment. May continues to see a few rumbles of thunder as the convection shifts into the forecast area but will see a gradual decrease in coverage tonight to just isolated showers after 06-07Z. Sunday Low clouds will again expand across much of the forecast area in the predawn hours as the air dries aloft and low level moisture becomes trapped beneath a shallow inversion. While the clouds should mix out quicker on Sunday than they did earlier today with stronger winds present...it will likely be late morning before stratus begins to diminish setting up a nice afternoon with a mix of sun and clouds. It will be noticeably drier than today as high pressure shifts into the region and stronger subsidence is advected into the region from the north. This will be a temporary reprieve from the unsettled weather pattern which will return in earnest by early Monday with the back end of the front set to pass through central Indiana tonight returning north as a warm front. More on this and the expected multiple opportunities for severe weather Tuesday and Wednesday in the Long Term section below. Temps...despite the arrival of drier air in the post-frontal environment by early Sunday...the expansion of low clouds will keep temperatures from falling much lower than the upper 50s and lower 60s. Dry air and northerly flow will keep temperatures slightly cooler Sunday but still very pleasant for early May. Expect low to mid 70s for much of the forecast area. && .LONG TERM (Sunday night through Saturday)... Issued at 258 PM EDT Sat May 4 2024 Our primary forecast challenge in the long range is severe weather potential in the Tuesday and Wednesday timeframe. Occasional non- severe showers and thunderstorms are possible Sunday into Monday. Heavy rainfall potential exists through the period as well. SYNOPTIC OVERVIEW A trough moving ashore over the Pacific Northwest today is set to become our feature of interest over the next several days. Before that system arrives, a subtle mid-level wave developing over Texas will lift northeast tomorrow towards Indiana. Occasional showers and thunderstorms are possible, especially Monday morning as the core of the wave passes by. Weak flow aloft will preclude an organized severe threat. However, models show nearly moist adiabatic thermal profiles with deep moisture. Large LCL freezing level spread signifies that rainfall production could be quite efficient. A few locally heavy downpours are possible within any deeper convection that manages to form. Confidence is low regarding flood potential, as large-scale lift associated with the wave is weak and may be displaced to our south. Recent trends in guidance have taken this system a bit further south since yesterday. Turning our attention back to the western trough, guidance has it ejecting into the Plains Monday afternoon. A prolonged period of southerly flow has allowed a rather broad and buoyant warm sector to take hold ahead of the trough. Instability will not be in short supply going forward. Additionally, the trough flattens considerably as it heads eastward which will allow a fast quasi-zonal jet streak to impinge on the broad warm sector. Vort maxes embedded in the faster flow should provide larger-scale lift to help initiate convection ahead of the primary trough axis. Monday`s threat is well to our west, mainly over the Great Plains. However, the trough pushes east just enough to bring severe potential to our region by Tuesday and Wednesday. Beyond that, the trough wraps up and departs to our east leaving us with cooler and drier northwesterly flow. FORECAST CONFIDENCE Confidence in the evolution of the larger-scale pattern is good. Ensembles are in agreement regarding the position and timing of the western trough. However, models differ with respect to the embedded vort maxes and waves. Since these features may be the primary drivers of severe weather potential...confidence decreases a bit. Exact timing and location for the best severe weather chances cannot yet be pinpointed. However, our confidence in severe weather over the Midwest and Ohio River Valley is increasing. The synoptic-scale pattern is quite favorable for organized convection (large amounts of moisture, instability, and shear). Additionally, CSU machine learning and CIPS analogs are honing in on our region for severe weather Tuesday and Wednesday. They paint a rather broad area, however, and as mentioned above the exact location will need to be refined with time. Still, the potential exists, and is increasing, that multiple rounds of potentially severe storms affect the region next week. && .AVIATION (06Z TAF Issuance)... Issued at 132 AM EDT Sun May 5 2024 Impacts: -MVFR to briefly IFR cigs 04Z to 17Z Discussion: Cloud cover will gradually increase after 06Z with the arrival of MVFR cigs by 08z over all TAF sites. Some light lingering showers are possible between 08 and 12z, but the rule should be no WX. Winds will generally be light and variable through the TAF period with a predominately NW to N direction. && .IND WATCHES/WARNINGS/ADVISORIES... None. && $$ UPDATE...White SHORT TERM...Ryan LONG TERM...Eckhoff AVIATION...Updike