####018009298#### FXUS63 KIND 152247 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 647 PM EDT Thu May 15 2025 .KEY MESSAGES... - Isolated to scattered thunderstorms this evening with the potential for severe weather - Higher-end threat for severe weather tomorrow evening, especially across southern Indiana - High temperatures in the upper 80s again tomorrow - Cooler and quiet for the weekend, additional precipitation again next week && .MESOSCALE UPDATE... Issued at 556 PM EDT Thu May 15 2025 RECENT SURFACE ANALYSIS SHOWS THE MAXIMUM TEMP AXIS OVER ILLINOIS WITH TEMPS IN THE LOW 90S. THE MOISTURE AXIS IS MORE BROAD WITH LOWER 70S DEWPTS EXTENDING FROM CETNRL/SW INDIANA INTO CENTRAL IL/SE MO. INSTABILITY REMAINS EXTREMELY HIGH OVER MOST OF THE FORECAST AREA WITH MLCAPE VALUES FROM 3500-4000 J/KG, WITH OVER 4500 J/KG OVER CENTRAL IL. A SUBTLE OUTFLOW BOUNDARY GENERATED BY CONVECTION OVER THE MO BOOTHEEL EXTENDS INTO SE MO AND FAR S IL. A DRYLINE EXTENDS ACROSS THE MS RIVER FROM NEAR THE QUAD CITIES DOWN TO JUST WEST OF ST.LOUIS AND IS MOVING EAST AROUND 20 KTS. SATELLITE IMAGERY SHOWS THE 850-700 MB FRONT NICELY OVER WEST/CNTRL MO WITH BANDS OF AGITATED ALTOCUMULUS ALSO CAUSING TURBULENCE FOR AICRAFT. ACARS (AIRCRAFT REPORTED) SOUNDINGS OUT OF ST. LOUIS SHOW A VERY STRONG INHIBITION LAYER CENTERED NEAR THE 850 MB LAYER (TEMPS NEAR 22C) WITH SOUNDINGS FROM KANSAS CITY SHOWING SUBSTANTIAL COOLING (850 TEMPS NEAR 12C). THERE REMAINS TWO SCENARIOS FOR CONVECTIVE DEVELOPMENT IN CENTRAL IN LATER THIS EVENING (AFTER 02Z/10PM EDT). THERE IS AN OUTSIDE CHANCE THAT THE ELEVATED SHOWERS/ACCAS CLOUD FIELD OVER SE MO/FAR S IL WILL MOVE INTO FAR SOUTH PARTS OF CENTRAL IND (NEAR THE US 50 CORRIDOR) AND ERODE THE CAP FROM ABOVE TO INITIATE SURFACE BASED STORMS. THE MORE LIKELY AND SECOND SCENARIO IS THAT CONVECTIVE LINE DEVELOP ALONG THE MS RIVER NEAR THE QUAD CITIES WILL CONTINUE TO BUILD FURTHER SOUTH AIDED BY INCREASING MID-UPPER LEVEL DYNAMICS AND LOW LEVEL FORCING/CAA. CONVECTION IS EXPECTED TO DEVELOP DOWN TO CENTRAL IL BY 8 PM EDT EVENTUALLY MOVING INTO WESTERN PARTS OF CENTRAL IND AFTER 10 PM EDT. && .SHORT TERM (This evening through Tonight)... Issued at 204 PM EDT Thu May 15 2025 Rest of Today and Tonight. Diurnally driven cu continues to expand in coverage across central Indiana with temperatures in the low 80s across the state. Dew points continue to rise with little mixing so far. Expectations going through the rest of the afternoon remain the same with a continual expansion of cu while dew points begin to fall towards the middle of the afternoon once the wind gusts become more frequent and the boundary layer steepens to around 4kft. The threat for 90 degree temperatures continue to look low for all but the far western counties where rain didn't fall as widespread yesterday. Latest ACARs soundings show the cap is well in place but a bit higher up than models have forecast with the strongest portions of the cap from 800mb to 700mb. A plume of even warmer aloft is moving in from the southwest which will further strengthen the cap through 23Z with models showing convective initiation on the western edge of the warmer air across Illinois towards 23Z. Forecast remains on track for the convective threat late today into tonight with better model agreement in scenario #2 of the previous forecast discussions where convection initiates across Illinois towards 23Z to 01Z and moves into central Indiana but doesn't strongly organize. There is a potential that the convection remains elevated above the gradually eroding cap with hail being the primary threat. The primary timeframe of concern for central Indiana will be from 00Z to 04Z with confidence highest across the far western and northern portions of the forecast area. Confidence is lower towards the Indianapolis area as there is a fairly low potential that storms will have enough time with high instability to develop a mature cold pool which would help them propagate into an increasingly less favorable thermodynamic atmosphere. There could be a few lingering storms across the southern portions of the area during the second half of the overnight, but chances look minimal. The residual humid airmass will keep temperatures very mild through the night with overnight lows only falling into the mid to upper 60s with the potential for some sites to see lows near 70. Skies will gradually begin to clear after midnight with gusts falling off after 03Z. && .LONG TERM (Friday through Thursday)... Issued at 204 PM EDT Thu May 15 2025 Friday and Friday Night. Another round of severe weather is expected for late Friday into the early overnight hours with much higher confidence in weather impacts for central Indiana. Another surface low will be tracking across the Midwest with strong moisture advection ahead of the low as the LLJ ramps up. 40-50kts of effective bulk shear will combine with nearly 4000 J/kg of ML CAPE with a much weaker cap to create a favorable environment for the development of severe storms. All severe weather types will be on the table with damaging winds the most likely threat as models continue to trend more towards an organized complex of storms vs discrete supercells. Highest confidence in timing will be from 6PM to 10 PM with the greatest threat for severe weather across the southern counties where most models show the progression of a storm complex. If storms remain discrete, which is not the most likely outcome, there will be a threat for higher-end tornadoes with STP values maxing out between 8 and 12 at times. Saturday Through Monday. Broad ridging across the Central US states will then dominate the weather pattern for the first half of the weekend with some residual near surface pressure gradients creating an environment favorable for wind gusts to around 25 mph during the afternoon hours on Saturday. With the surface flow now westerly, dew points will be much more comfortable with highs in the low to mid 70s. A weak upper level wave will move through the Tennessee Valley late Sunday into Monday but other than some increased clouds, no impacts expected for the forecast area. Tuesday Through Thursday. The pattern then looks to become much more active during the middle to latter portions of the week as a warm front associated with the late weekend system begins to move northward and interacts with forcing from another low pressure system. Models are struggling to resolve the details and strength of this upper level low, but there is fairly high confidence in a multi-day heavy rain threat for the Ohio Valley as early as Tuesday but more likely Wednesday into Thursday. Models are all over the place with QPF, but there is a decent threat for at least 1-2 inches over the course of the event. Rain chances then look low for the holiday weekend with broad northwesterly flow and mild temperatures in the 70s. && .AVIATION (00Z TAF Issuance)... Issued at 647 PM EDT Thu May 15 2025 Impacts: - S/SW winds gusty through this evening - Broken line of convection impacting the area for a few hours from mid to late evening into the overnight - Gusty winds developing again Friday afternoon - Scattered to numerous thunderstorms developing late afternoon and evening Friday Discussion: Breezy evening ongoing with a denser layer of cirrostratus expanding across the region from the southwest. Convection has begun to fire along a dryline over western Illinois and is expected to gradually expand south as it moves east across Illinois over the next few hours. Uncertainty remains as to how far south convection will build and to what state it will be in later this evening as it moves into the region. Considering the deep instability present above the lingering capping inversion...any storm will be capable of large hail and damaging winds later this evening should the cap sufficiently weaken. KLAF is the most likely to be impacted with lower confidence at the other three terminals. The most likely window for impacts will be from 02Z through 07Z from northwest to southeast. Skies will clear in the predawn hours as weak surface ridging is accompanied by deeper subsidence in the wake of the storms. Expect mainly clear skies to persist through midday with southerly winds gradually increasing as the pressure gradient tightens. A sharp wave aloft will pivot around the base of the upper low over the upper Midwest and approach the late day in tandem with a cold front at the surface. With a highly moist and unstable airmass again over central Indiana...robust convective development is expected by late afternoon and evening. && .IND WATCHES/WARNINGS/ADVISORIES...None. && $$ MESOSCALE...Crosbie SHORT TERM...White LONG TERM...White AVIATION...Ryan