Area Forecast Discussion
Issued by NWS Cleveland, OH
Issued by NWS Cleveland, OH
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537 FXUS61 KCLE 272324 AFDCLE Area Forecast Discussion National Weather Service Cleveland OH 724 PM EDT Thu Jun 27 2024 .SYNOPSIS... High pressure will persist over the area through Friday before moving off the Northeast Coast Friday evening. A low pressure system will impact the Great Lakes region on Saturday and Saturday night before high pressure builds back in Sunday through Tuesday. && .NEAR TERM /THROUGH FRIDAY NIGHT/... Scattered to broken cumulus field across the area gradually dissipates this evening as we lose boundary layer mixing with sunset. High pressure continues to build in tonight with patchy fog in parts of eastern Ohio and inland Northwest Pennsylvania before this high moves off to the east Friday and Friday night. Temperatures increase on the backside of the departing high with temperatures into the 80s by Friday afternoon. Approaching trough from the west will result in increasing southwest moisture advection and showers and thunderstorms Friday night. PoPs start off around 20% Friday evening increasing to 60% by late Friday night. && .SHORT TERM /SATURDAY THROUGH SUNDAY NIGHT/... Saturday continues to look like an active day with both severe storm potential as well as heavy rainfall and resultant flash flooding. However, confidence is greater for heavy rainfall than severe weather. See details below. A mid/upper shortwave trough will track from the Upper Midwest through the central and eastern Great Lakes Saturday through Sunday. An associated surface low will track from the Lake Superior/Upper Michigan vicinity Saturday morning into Quebec by late Sunday, dragging a cold front southeast across the region Saturday night into Sunday morning. The warm front looks to lift out of NE Ohio and NW PA rather quickly Saturday morning placing the entire region in the warm sector. Deep west-southwesterly flow and resultant warm air advection will tap into a broad heat dome over the central Mississippi and Tennessee Valleys with 850 mb temps rising to around +18 C along with rich low-level moisture advection bringing dew points into the low to mid 70s. This pattern could support very oppressive conditions with temperatures around 90F, but extensive cloud cover and areas of showers will likely hold temperatures down in the low to mid 80s in most areas Saturday afternoon. This makes the degree of the severe threat highly uncertain as the cold front approaches Saturday evening. NAM forecast soundings and plan views are suggesting a saturated, cloudy profile holding MLCAPE values below 1000 J/Kg in most of the region Saturday afternoon with only around 1500 J/Kg at the surface. This combined with flat mid-level lapse rates of 5 to 5.5 C/Km could make it tough to sustain deep updrafts. Overcast skies and scattered showers Saturday morning into the afternoon are the result of decaying convection expected to move in from the NW Friday night, so there will likely be outflow boundaries and differential heating boundaries over the region for the afternoon. This makes the convective initiation messy, and it is likely that numerous showers and thunderstorms will redevelop on these boundaries in the warm sector Saturday afternoon and evening well ahead of the cold front. For this reason, went with categorical PoPs. There is plenty of shear for damaging winds and a few tornadoes given 45-50 knots of westerly 500 mb flow yielding 30-40 knots of effective bulk shear, with 25-30 knots of low-level shear. This leads to low-level SRH values of 100-200 m2/s2, especially in NE Ohio and NW PA. With these shear values and the overall synoptic forcing near the base of the progressive shortwave trough, feel that there will be a few severe storms, but how widespread and organized they will be is uncertain due to the potential for the instability to stay weak as mentioned above. If greater heating can be realized, then the severe potential could increase. The SWODY3 slight risk still looks reasonable at this point, but CSU Machine Learning probabilities have come down from previous runs and now suggest a marginal potential for severe weather, so it seems to be keying on the lack of instability. We are much more confident on heavy rainfall rates from thunderstorms Saturday afternoon and evening. PWAT values look to rise to 2 to 2.25 inches which is around the climatological max for the date. Forecast soundings suggest deep warm cloud layers too and LCL heights below 1000 m which will limit evaporation. This all points to highly efficient rainfall rates. The aforementioned mid- level flow and shear will keep convection moving, but with numerous boundaries in place, there could be repeat rounds in some areas. Drought has been expanding across the region, so rainfall is greatly needed, but high rates could still cause some flash flooding in urban areas, as well as low-lying and poor drainage areas. The WPC Day 3 Marginal risk for excessive rainfall has been expanded westward to account for this potential. Showers and thunderstorms will end from NW to SE Saturday night, with all areas expected to be dry behind the front by Sunday morning as Canadian high pressure builds in from the Upper Midwest. This high will slide overhead Sunday and Sunday night, and this combined with fairly deep mid/upper troughing over the eastern Great Lakes and New England will lead to a sunny, pleasantly cool day. Expect highs Sunday to stay in the mid/upper 70s with much lower humidity. Lows Sunday night will fall into the low/mid 50s. && .LONG TERM /MONDAY THROUGH THURSDAY/... Mid/upper troughing and Canadian high pressure will remain across the eastern Great Lakes to start the week. This will maintain the mostly sunny and pleasant weather for Monday with highs in the mid/upper 70s. The high will slide off the Mid Atlantic coast Tuesday and Wednesday as a large mid/upper ridge over the southern Plains and Mississippi Valley expands northeastward into the Great Lakes ahead of a broad mid/upper trough progressing through the northern Rockies and northern Plains. This will bring heat and humidity back into the region with highs returning to the mid 80s Tuesday and potentially low 90s Wednesday. The southern Great Lakes region will be near the northern edge of the associated thermal ridging (heat dome, so there will likely be a frontal boundary nearby to focus ridge riding convection and potential MCS activity. Ensemble guidance is keying in on Wednesday and Thursday to have some potential for organized severe weather due to a shortwave crossing the Great Lakes and starting to flatten the ridge, and the CSU Machine Learning severe weather probabilities suggest a marginal risk areawide those days. The front may push southward Thursday, so slightly cooler conditions are expected with mid/upper 80s, but still humid. Due to uncertainty on convective features this far out, kept broad chance PoPs Tuesday night through Thursday. && .AVIATION /00Z Friday THROUGH Tuesday/... VFR across the TAF sites early this afternoon with VFR to persist through the TAF period. High clouds will continue to thicken from the west through the period. Winds will gradually shift from north to northeast this evening and towards the east to southeast by Friday morning, 5 to 10 knots. Winds will then favor a south to southeast direction by Friday afternoon and evening, 5 to 10 knots. A lake breeze may develop at CLE/ERI early Friday afternoon, shifting winds towards the north to northeast, 5 to 10 knots. Outlook...Non-VFR possible in widespread showers and thunderstorms on Saturday. && .MARINE... Quiet conditions are expected on the lake the next few days. Light and variable winds tonight will become E at 10-15 knots Friday before turning S and increasing to 15-20 knots late Friday night and Saturday morning behind a warm front. Winds then veer a bit SW Saturday afternoon while staying in the 15-20 knot range. Winds will turn NNW behind a cold front by Sunday morning while staying 15-20 knots, and this will build wave heights to 3 to 4 feet in the central and eastern basins, so Small Craft headlines are likely to be needed Sunday. N winds of 10-15 knots Sunday night will diminish to 5-10 knots Monday while turning E then SE by Tuesday. Locally higher winds and waves are possible in and near thunderstorms Friday night and Saturday. && .CLE WATCHES/WARNINGS/ADVISORIES... OH...None. PA...None. NY...None. MARINE...None. && $$ SYNOPSIS...Saunders NEAR TERM...Saunders SHORT TERM...Garuckas LONG TERM...Garuckas AVIATION...Kahn MARINE...Garuckas