####018011081#### FXUS63 KIND 031858 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 258 PM EDT Fri May 3 2024 .KEY MESSAGES... - Potential for patchy fog and low clouds late tonight and early Saturday. - Isolated to scattered showers and storms through this evening then again on Saturday. - Multiple chances for showers and storms throughout most of the forecast period, with continued above normal temperatures. - Potential for severe weather during the middle of next week, highest chances Tuesday evening and Wednesday night. && .SHORT TERM (This evening through Saturday)... Issued at 256 PM EDT Fri May 3 2024 Damp and mainly cloudy afternoon in progress across the forecast area as a diffuse frontal boundary lingers over the southeast half of central Indiana. Have seen some breaks in the lower stratocu develop behind the boundary but tend to fill right back in with an abundance of low level moisture lingering. Scattered showers have redeveloped over southeast counties over the last hour or two. 18Z temperatures ranged from the upper 60s to mid 70s. Today marks the beginning of a more unsettled regime setting up over the Ohio Valley for the next several days and not expected to reach its zenith until the early to middle part of next week. However the presence of lingering low level moisture at least across parts of the region and the remnant boundary likely to settle near the Ohio River tonight will bring at least a periodic threat for isolated to scattered convection through late day Saturday and eventually beyond. Through Tonight Expect any isolated showers or thunder will focus in the vicinity of the boundary and deepest portion of the moisture plume...focused across the southeast half of the forecast area. The current ACARS sounding highlights weak instability levels that have increased slightly courtesy of diurnal heating despite the clouds. It should be noted however that the actual primary windshift and dewpoint boundary lags back to the northwest from the front...and that could aid in additional isolated development early this evening focused back near the I-70 corridor. Will hold onto isolated pops for a short period as far northwest as a Terre Haute-Indy Metro-Muncie line as a result. Could certainly see a few rumbles of thunder but overall any convection over the next few hours will be disorganized and weak in the absence of little if any BL shear and light winds through the lower levels. Broad area of clear skies and dry air noted on current satellite imagery this afternoon back across Wisconsin and northern Illinois associated with a high pressure ridge. This feature will drift east into the Great Lakes tonight and while the bulk of the subsidence and dry air will remain to the north of the forecast area...this will sway enough influence locally to allow for clearing skies late tonight focused across the northern Wabash Valley. Further south across the forecast area...the dewpoint boundary will shift south a bit before stalling overnight with much of the forecast area south of I-70 remaining at 60 degree dewpoints or higher. While any threat for a shower is minimal overnight considering little forcing aloft and negligible instability...the presence of the deeper moisture will keep the potential for lower stratus across the southern half of the forecast area and may also bring patchy fog into play prior to daybreak. While the air will be slightly drier in northwest counties...there is an increased potential for some fog formation in these areas as well with skies set to clear late. Saturday The aforementioned surface ridge will move northeast away from the Great Lakes on Saturday...leaving a residual axis of drier air extending southwest from lower Michigan into eastern Missouri. This will be slowly gobbled up through the course of the day between the deeper moisture plume focused across the Ohio Valley and our southern counties and a frontal boundary tracking through the Missouri Valley. The veering of low level winds to easterly and eventually southeasterly by the afternoon will enable the deeper moisture to advance back to the northwest across central Indiana and interact with an increasingly unstable airmass as CAPE values climb to 1000-2000 j/kg. While overall forcing aloft and shear remain weak...the combination of the instability and moisture will be enough to generate scattered convection again on Saturday with the best focus once again over the southeast half of the forecast area. Storms will be of pulse intensity and may see a few stronger cells that can throw out localized higher wind gusts. Otherwise... lightning and brief/localized heavy rainfall will be the primary impacts to outdoor activities on Saturday from any convection. Temps...lows will fall back into the middle 50s tonight across the northern Wabash Valley but most of the rest of the forecast area will remain closer to 60. Low level thermals support highs rising into the upper 70s and lower 80s across much of central Indiana Saturday with the warmest reading likely to be across western portions of the forecast area where convective coverage will be lower and more sunshine will be realized. && .LONG TERM (Saturday night through Friday)... Issued at 256 PM EDT Fri May 3 2024 We're looking at a fairly active long range with precipitation chances nearly every day. Severe weather is not expected through the weekend, though this may change by early to mid next week. SYNOPTIC OVERVIEW The upper-level flow pattern across North America is rather simple. A long ridge axis stretches up the eastern seaboard and a broad trough exists over the northern Plains. Along the Mexican border, a zonal but fairly fast subtropical jet extends into the Gulf. Further west, over the Pacific Ocean, another trough can be found diving southward out of the Gulf of Alaska. It's this Pacific trough that may become the driving factor for active weather next week. Through the weekend, however, we'll be dealing with occasional showers and thunderstorms as a few impulses aloft pass by. The first, covered in the short term, is more a part of the northern jet while a second lifts northeast from the subtropical jet Sunday into Monday. With no strong push of continental air, a warm and buoyant air mass is likely to be in place through the weekend and into next week. As such, any system passing by should have access to enough instability for convective precipitation. In fact, model soundings Sunday-Monday show essentially a moist adiabatic profile. Low LCLs with high freezing levels may promote more contribution from warm rain processes. Available moisture is high (PWAT over 1.5 inches) and deep, so rainfall may be quite efficient at times. This of course depends on how much forcing there is for convection, and some model uncertainty remains regarding where exactly the vort max tracks. By Monday afternoon, the Pacific trough should be ejecting into the Plains in a highly amplified manner. Guidance shows the trough occluding quickly, with upper-level flow regaining a more zonal orientation Tuesday and Wednesday. The occluded low meanders over the northern Plains for a few days, with vort maxes occasionally rotating around and progressing eastward over the Midwest. Guidance is in good agreement regarding the larger-scale pattern but disagrees with the smaller features (vort maxes). The placement and timing of these vort maxes may play a critical role determining severe potential Tuesday and Wednesday. FORECAST CONFIDENCE COnfidence is good with the large-scale pattern, but decreases with regards to sensible weather. The primary driver of this uncertainty is variations in track/timing of various vort maxes. Additionally, convective regimes can have a cascading affect on subsequent convective evolution...so uncertainty can be high even if the larger- scale pattern is more certain. That being said, a few things can still be said about our potential for severe weather / flooding next week. As mentioned before, ensemble guidance is in good agreement with the larger pattern. Additionally, NAEFS/ECMWF situational awareness tables show anomalous moisture through this weekend and much of next week. Deterministic guidance, while showing more disagreement between individual models, is still useful in visualizing how this moisture interacts with passing waves. Periodic surges of richer/deeper moisture advect northward ahead of each wave, signifying potential for heavy rainfall in addition to severe weather through the period. Regarding severe weather, CSU machine learning and CIPS analogs have been honing in on the Tuesday-Wednesday period over our region. It remains a rather broad area, and favorable synoptic conditions (Occasional synoptic forcing, instability, shear) add confidence to these signals. It's difficult to downscale things any further at this range since the final outcome will likely rely on features not yet resolvable. Still, the potential exists for severe weather along with heavy rainfall next week. Stay tuned for updates. && .AVIATION (12Z TAF Issuance)... Issued at 637 AM EDT Fri May 3 2024 Impacts: - Scattered showers early in the period, with occasional MVFR conditions mid morning into early afternoon. - Isolated thunderstorms possible, but too uncertain for inclusion. - Fog possible very late in the period, depending upon how much cloud cover lingers tonight. Discussion: Scattered showers have overspread much of the area this morning. This activity will continue much of the morning into early afternoon, before lessening from west to east as a front moves through the area. Some occasional MVFR conditions will be possible in these showers, though not as widespread as previous expectations. Will carry TEMPO MVFR conditions at all sites but LAF. A few thunderstorms will be possible, but too low probability/uncertain for inclusion in the TAFs. Winds will be variable or westerly early on, becoming more northerly and then northeasterly later in the period, 10KT or less throughout. Depending upon the character of the mid and high cloud cover that will linger tonight, and the degree of clearing, some fog will be possible, but will not mention at this time. If clearing is substantial, wet ground from the rainfall may promote patchy dense fog late tonight into Saturday morning. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ SHORT TERM...Ryan LONG TERM...Eckhoff AVIATION...Nield