595 FXUS63 KIND 102316 AFDIND Area Forecast Discussion National Weather Service Indianapolis IN 707 PM EDT Mon Aug 10 2020 .UPDATE... The AVIATION section has been updated below. && .SYNOPSIS... Issued at 340 PM EDT Mon Aug 10 2020 Severe weather is likely this evening with the main threat being damaging winds across the region. An unsettled pattern remains for much of the forecast period leading to daily chances for rain and storms. && .MESOSCALE /7 PM EDT to 9 PM EDT Tonight/... Issued 645 PM EDT Mon Aug 10 2020 Satellite imagery continues to show the intense line of convection approaching Central Indiana, now extending from Near Frankfort southwest through Rockville. The forward propagation has been steady to the southeast, and expect an arrival into the Indy metro area just after 7 PM. Satellite imagery the last hour has indicated some decrease in the vertical component to the cumulus field overhead; however, still considerable energy exists in near surface environment with CAPE values hovering around 4K J/KG. Flow remains uniform ahead of the gust front out of the southwest with speeds hovering around 15 to 20 kts, and ample low- level moisture as dewpoints remain in the mid 70s. A few locations are even flirting with the upper 70s to 80 deg dewpoints, which for this time of year is common due to the evapotranspiration that will occur from vegetation. This high- volume of low-level moisture is helping to further juice an already unstable atmosphere as a potent cold pool associated with the intense line of severe storms maintains itself. Gusts from the storms has been hovering in the 50 to 70 mph range as it is arriving in West Central Indiana, and expect this to persist as it pushes towards the Indy Metro area. Given the very unstable atmosphere coupled with very saturated low- levels, expect lightning production to be efficient with very heavy downpours. This will further aid in severe wind to occur as the higher winds aloft easily filter to the surface and maintain the potency of the convective line. Again timing into the Indy metro area will be just after 7pm. && .NEAR TERM /Rest of This Afternoon and Tonight/... Issued at 338 PM EDT Mon Aug 10 2020 ...Significant Severe Weather with Widespread Damaging Winds to Impact central Indiana This Evening... After the stormy start to the morning for some...skies had cleared across central Indiana. With deep moisture and strong heating... temperatures have shot up into the mid and upper 80s over much of the forecast area as of 19Z. Low 90s had developed along the Wabash Valley. With oppressive dewpoints ranging from the mid 70s to near 80...heat indices were in the 90s and low 100s currently. The focus for the next several hours is on a high confidence...high impact derecho with widespread damaging winds that began early this morning in the northern Plains and now sits in eastern Iowa and western Illinois. The amount of observed wind reports in excess of 90 mph from this complex over Iowa is for lack of a better term... alarming. The airmass this afternoon has the feel of a capped powder keg and mesoanalysis shows that SBCAPEs have surged since late morning...and are now in excess of 5000 j/kg. With a few more hours of heating...these values are likely to only increase ahead of the approaching convective complex. In addition...mid level lapse rates have increased to near 8 C/km immediately downwind of the derecho and now into our western counties. The complex has a well developed cold pool that will keep its engine running for the next several hours. In an nutshell...the airmass downstream of the convective complex supports a continued high confidence in severe weather across northern and central Illinois and by this evening...across the forecast area as the complex is likely to pivot and follow the theta- e ridge and instability gradient right into central Indiana. All severe threats are on the table but clearly...the damaging wind concerns are greatest considering what has already taken place...a strengthening westerly low level jet and the amount of instability already in place across the area. Timing for greatest impacts will be from northwest to southeast from 22Z through 02-03Z. In addition to the severe weather concern... flooding will become a threat...particularly in areas that saw 1-2 inches this morning. Also...derechos tend to be prolific lightning producers and the approaching convective cluster certainly appears to be just that. Should see convection diminish in coverage after midnight...although the presence of the westerly 850mb jet at least initially in the overnight may enable a backbuilding component to convection. Will maintain chance pops through the overnight although the greater risk for rain is the first half of the night. Temps...did not stray from NBM guidance too much as lows should fall back into the upper 60s and lower 70s overnight in wake of the convective complex. && .SHORT TERM /Tomorrow through Thursday/... Issued at 340 PM EDT Mon Aug 10 2020 The area will wit under an unsettle pattern for the short term as a couple of disturbances move overhead. This will lead to daily chances of scattered rain and storms. Best PoPs at the moment are for late tomorrow through Wednesday... could possibly see a weak surface low pass through bringing in the rain. Temperatures look to be near to slightly above normal with highs in the mid 80s and lows in the upper 60s. && .LONG TERM /Thursday Night through Monday/... Issued at 340 PM EDT Mon Aug 10 2020 A couple of disturbances look to impact the area in the long term, prompting daily rain chances. Models show a cold front passing through the area sometime Sunday to Monday... should get a better idea on timing as it gets closer. Temperatures will be near normal. Largely accepted guidance as it looked reasonable. && .AVIATION (Discussion for the 110000Z TAF Issuance)... Issued at 716 PM EDT Mon Aug 10 2020 Poor flying conditions in convection expected early in the period, then generally VFR. Convection will continue to move across mainly the southern sites for the first few hours of the TAF period. After a lull, additional convection is possible overnight. Used VC or TEMPO as appropriate. Additional convection is possible on Tuesday, but confidence is not high enough to add into the TAF at the moment. Generally VFR conditions are expected outside convection, but will watch for the possibility of some MVFR conditions Tuesday morning. && .IND WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SYNOPSIS...KH MESOSCALE...Beachler NEAR TERM...Ryan SHORT TERM...KH LONG TERM....KH AVIATION...50