458 FXUS63 KTOP 170927 AFDTOP Area Forecast Discussion National Weather Service Topeka KS 427 AM CDT Fri May 17 2019 .SHORT TERM...(Today and tonight) Issued at 425 AM CDT Fri May 17 2019 08Z water vapor imagery shows an upper low over northern NV with an upper trough axis extending southeast through AZ. With a second upper low near Hudson Bay, shortwave ridging had set up from the southern plains into Saskatchewan. Surface obs showed a high pressure system over the lower MS river delta. An area of low pressure was noted over the central high plains of CO with an inverted trough/cold front extending east across southern NEB and southern IA. The surface pattern has favored southerly return flow and higher dewpoints had been advecting inland over south TX. For today models are in good agreement that the dynamics associated with the upper low across NV should remain west of the forecast area. As a result the surface low and dryline extending south of the low are progged to remain out across the high plains and western KS. Meanwhile the surface front is expected to retreat north as a warm front due to the deepening surface low and continued warm and moist air advection north. Forecast soundings show a reasonable capping inversion remaining over the boundary layer through peak heating. So think precip chances are less than 20 percent today. The RAP is the one solution that develops some QPF across north central KS by this evening. It also happens to be the most aggressive in developing convection along the dryline this afternoon. With not much movement of the surface low or the dryline, boundary layer winds are generally forecast to parallel the dryline with any convergence localized to western KS. So there is some question as to whether storms will be that numerous along the dryline. Since the majority of the convective allowing models show storm development closer to the surface low, think the RAP may be overdone. If storms are able to make it into north central KS, there would be more than enough CAPE for severe hail and winds. Forecast soundings prog a weakness in the mid level wind profile late this afternoon suggesting discrete storms this far east of the dry line may be hard to come by. There is good agreement in a strong pressure gradient once again today. So south winds are expected to gust around 35 MPH. As for highs, the models all show a general cooling at 850MB implying temps may not be as hot as they were on Thursday. With forecast soundings mixing the boundary layer to around 825MB, think mid and upper 80s are plausible and have generally gone a little warmer the MOS guidance expecting good insolation. Winds should remain breezy for much of tonight. There are some indications from the forecast soundings for some elevated instability to remain in place as height falls spread east and inhibition weakens. So there is some potential for thunderstorm development overnight tonight. Although it's not clear if there will be any focus for lift as the nose of the low level jet and better theta-e advection is forecast to be east and north of the forecast area. So I only show a chance for showers and thunderstorms mainly after midnight. Forecast sounding progs of elevated CAPE values between 1500 and 2000 J/kg would support a risk for severe storms with large hail and damaging winds. Southerly winds and continued moisture advection into eastern KS should keep lows tonight in the upper 60s to around 70. A surface boundary may move into north central KS from the west late enough in the night to allow winds to calm down and help temps fall into the lower 60s. .LONG TERM...(Saturday through Thursday) Issued at 425 AM CDT Fri May 17 2019 Saturday... By Saturday morning, the second of a series of shortwave troughs will be positioned across the High Plains region with a surface trough axis extending from the TX Panhandle through north-central KS. Warm advection showers and storms may be ongoing by sunrise across portions of the forecast area. There is varying depictions with respect to the strength of EML amongst guidance, although the combination of modest midlevel height falls and WAA should allow for scattered storms through mid-morning. A few could be severe with upwards of 2000 J/kg of MUPCAPE and 35-40 kts of effective shear. Stronger height falls are progged to overspread the CWA by peak heating Saturday afternoon as the midlevel shortwave trough pivots across the Plains. This should allow for additional surface based convection during the afternoon and evening. Steep lapse rates will contribute to 2000-3000 J/kg of MLCAPE. While overall deep shear is progged to near 50 kts by afternoon, the high-amplitude nature of the midlevel trough will result in backed midlevel winds -- not favorable for discrete convection. As a result, anticipate numerous storm clusters capable of large hail and damaging winds. Deterministic and ensemble guidance suggest widespread 1-2" rainfall amounts through Saturday evening. Flood/flash-flood threats should remain low through Saturday, given the recent stretch of dry weather. Saturday night through Sunday night... Any lingering shower/storm activity will end from southwest to northeast Saturday night/Sunday morning as the shortwave trough ejects northeast of the forecast area. A brief period of dry conditions are expected Sunday night through Sunday night as subsidence behind the initial shortwave trough overspreads the CWA. Weak CAA behind the surface front will limit temperatures to the 60s and lower 70s Sunday with Monday morning lows in the 40s and 50s. Monday and Tuesday... The third of a series of midlevel trough axis will eject into the Plains Monday into Monday night. A warm front is progged to lift northward through the day, nearing the KS/OK border by late afternoon. As forcing for ascent overspreads the warm sector by midday Monday, widespread thunderstorm activity is expected across southwest KS/western OK/TX Panhandle. Similar to Saturday's scenario, the high amplitude nature of the trough will result in numerous storm interactions and upscale growth into an MCS by early afternoon. The warm front is progged to continue lifting northward through the evening, with the MCS tracking along the boundary across the forecast area. Storms will likely be elevated upon arrival to the forecast area, and the strongest updrafts could produce large hail. In addition, any established cold-pools could pose a damaging wind threat. Flash-flooding is likely to be the primary concern however. A very moist profile consisting of Pwat values exceeding 1.25" -- near the 90th percentile at TOP -- will result in very heavy rainfall. Deterministic and ensemble guidance are quite alarming with QPF outputs ranging from 2 to 5+ inches Monday - Tuesday morning. Generally the heaviest axis of precipitation is currently progged to track across the southeastern half of the CWA. This scenario would likely result in widespread flash- flooding and river rises. The exact track of the MCS and associated rainfall swath can and will likely shift over the coming days, please continue to check back through the weekend as this has the potential to be a significant flood event. This round of shower/storm activity should push east of the forecast area by Tuesday afternoon with the northeastward progression of the midlevel trough. Wednesday through Thursday... Additional shower and thunderstorm activity is possible Wednesday night through Thursday. Model solutions diverge with the track of the next midlevel trough, therefore confidence beyond Wednesday is low. That being said, any additional rainfall will only worsen flooding concerns through the remainder of the week. && .AVIATION...(For the 06Z TAFS through 06Z Friday night) Issued at 1149 PM CDT Thu May 16 2019 LLWS continues overnight, with gusty south to southwesterly winds increasing by mid-morning and persisting until sunset. LLWS once again develops by sunset. VFR conditions are otherwise expected through the period. && .TOP WATCHES/WARNINGS/ADVISORIES... NONE. && $$ SHORT TERM...Wolters LONG TERM...Baerg AVIATION...Skow