Area Forecast Discussion
Issued by NWS Cleveland, OH
Issued by NWS Cleveland, OH
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543 FXUS61 KCLE 210543 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 143 AM EDT Sat Sep 21 2024 .SYNOPSIS... The trough will drift eastward through northern Ohio and northwest Pennsylvania during the early morning through early evening hours today. Behind the trough axis, a very weak ridge builds from the west through Saturday night. Another trough accompanying a cold front begins to overspread our region from the Upper Mississippi Valley and western Great Lakes by Sunday. && .NEAR TERM /THROUGH TONIGHT/... 9:00 PM Update... Very dry and stable air over our region allowed for showers and thunderstorms along a weak trough to diminish as they entered Northern Ohio earlier this evening. Fairly quiet night in store with above normal overnight low temperatures settling in the low to mid 60s. Previous discussion... A ridge at the surface and aloft exits E`ward through this early evening. Behind the ridge, W`erly to WNW`erly flow aloft and embedded shortwave disturbances affect our CWA through Saturday as a weak trough, associated with a dissipated cold front, overspreads our region from the western Great Lakes and vicinity. The axis of this surface trough is expected to drift E`ward across our region during the early morning through early evening hours of Saturday. Lows are expected to reach mainly the lower to mid 60`s around daybreak Saturday as an unusually-warm air mass persists and intervals of cloud cover limit nocturnal cooling. Daytime heating is expected to allow late afternoon highs to reach the upper 70`s to near 80F in NW PA and mainly the 80`s to near 90F in northern OH late Saturday afternoon. Similar to today, a weak synoptic MSLP gradient and sufficient daytime heating of surrounding land should allow a lake breeze to occur over/within several miles of Lake Erie during the late morning through early evening hours of tomorrow. As of 3:45 PM EDT Friday, clusters of multicell showers and thunderstorms were persisting generally E`ward over/near the MI/IN/NW OH border. Expect this convection to weaken considerably before reaching portions of our I-75 counties by this late afternoon given weak boundary layer instability per latest SPC mesoanalysis and the lack of cumuli in the aforementioned area. Remnant/isolated showers should then dissipate early this evening, west of I-71, as the pre- convection boundary layer stabilizes via nocturnal cooling. As mentioned before, the surface trough axis will drift E`ward through our CWA during the early morning through early evening hours of Saturday. A modest low-level return flow of warm/humid air originating over the Gulf of Mexico, ahead of the aforementioned surface trough axis, should allow convergence/ascent along the trough axis to coincide with sufficient low-level moisture and release at least weak boundary layer instability for renewed development of isolated showers/thunderstorms beginning after midnight tonight. Diurnal heating of the relatively-moist boundary layer should yield moderate MUCAPE and a somewhat greater chance for isolated showers/thunderstorms along/ahead of the surface trough axis Saturday afternoon through early evening, especially in far-NE OH and NW PA, as deep layer bulk shear remains moderate. This is where a few strong thunderstorms with small hail and strong convective wind gusts are possible amidst sizable MUCAPE in the hail growth zone, ambient atmospheric melting levels near 10.5kft AGL, steep low-level lapse rates, and moderate DCAPE near 500 to 800 J/kg. Thus, cannot totally rule-out a few instances of straight-line convective wind damage. In fact, SPC has outlined a marginal risk of severe thunderstorms for much of western PA and vicinity tomorrow, including southeastern Crawford County. Behind the surface trough axis, fair weather is expected through Saturday night as a shortwave ridge aloft and attendant/weak surface ridge build from the western Great Lakes area and the ridge is accompanied by stabilizing subsidence. Partial clearing associated with the subsidence and weak low-level dry air advection behind the surface trough axis will permit greater nocturnal cooling Saturday evening through daybreak Sunday morning, when lows are expected to reach mainly the mid 50`s to lower 60`s. && .SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/... Entering a more active period with higher chances of precipitation that will be welcome across the whole CWA. Upper level flow becomes more zonal with a weak low pressure system/cold front tracks through Sunday night/Monday with the boundary sinking just south of the CWA, then pushing back into the CWA Monday night with the approach of a secondary and stronger area of low pressure from the southwest. This will bring waves of showers and storms entering the western zones first around 21Z Sunday. Best forcing will occur when 500mb PVA coincides with the surface system/low level f-gen from 00-03Z Monday and then again at 06-12Z Tuesday and into the extended forecast time frame. Should be a wetting rain for the region off and on during this period, but still will take some time to make a significant dent in the current drought status. That said, it should be a good start heading into the long term. Cooler weather in this pattern as 500mb heights/850mb temperatures decrease along with rainfall for Monday. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Diverging operational models into midweek once the cold front from the secondary area of low pressure from the short term exits, and the confidence in additional rainfall wanes, so will need a few more forecast cycles to try and pin anything down here. The cooler trend should continue through the period off the short term however, and will carry low end POPs for now. Upper 60s to lower 70s expected by Thursday. && .AVIATION /06Z Saturday THROUGH Wednesday/... Some elevated showers have developed over Lake Erie, although there`s still quite a bit of dry air over the local area so any overnight showers that manage to develop over land may not reach the surface or will be very light. There may be a brief period of non-VFR conditions in fog at KTOL early this morning, but it`s possible that the lower visibilities/ceilings remain to the west of the terminal. Additional diurnally-enhanced showers and perhaps a few thunderstorms may develop in the vicinity of KERI late this morning into early this afternoon as a cold front pushes east into PA, however activity will be isolated and the higher coverage will occur when the front is to the east of the local area this afternoon. Have VCSH at KERI between 15Z and 18Z. Light and variable/southeast winds will gradually shift to the west/northwest and increase to 5 to 10 knots behind the cold front today. Expect winds to become light and variable after 00Z Sunday. Outlook...Non-VFR possible in periodic showers and thunderstorms Sunday evening through Wednesday. && .MARINE... Briefly stronger ENE winds this evening could bring g 2ft waves in the west central/western basin of Lake Erie, but varying wind directions tonight through Saturday night will keep the lake nearshore zones less than a foot, with only pockets of 1-2ft in the open water zones. Offshore flow Sunday/Sunday night, but then back to highly variable winds with shower/storm chances increasing with a low pressure system approaching Monday and affecting the region into mid week. Some chop should be expected during this time. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...None. MARINE...None. && $$ SYNOPSIS...Jaszka/Maines NEAR TERM...Iverson/Jaszka SHORT TERM...26 LONG TERM...26 AVIATION...Maines MARINE...26