textproduct: Cleveland

SYNOPSIS

A weak ridge moves eastward across our region today before a cold front sweeps generally southeastward through northern Ohio and northwest Pennsylvania on Saturday. Behind the cold front, a trough lingers over and near Lake Erie through Sunday as a ridge builds from the north-central United States to the Ohio Valley. The ridge should build eastward across our entire region Sunday night and eventually exit eastward toward New England and the Mid-Atlantic region on Monday.

NEAR TERM /THROUGH TONIGHT/

Primarily dry weather and periodic cloud breaks are expected through sunset this evening as a ridge at the surface and aloft moves E'ward across our region and is accompanied by stabilizing subsidence. Lingering and light lake-effect snow (LES) streaming generally SE'ward amidst a sufficiently-cold/moist WNW'erly to NW'erly mean low-level flow over/downwind of ~3C Lake Erie should end by 7 AM EST or so this morning, as weak lake-induced CAPE (LICAPE) wanes via synoptic low-level dry air advection and a lowering subsidence inversion accompanying the building ridge. Additional snow accumulations should be less than one inch. Thus, the Winter Storm Warning and Winter WX Advisory for portions of the NE OH/NW PA snowbelt has been cancelled. Late afternoon highs are expected to reach the upper 20's to lower 30's as an abnormally-cold air mass remains over northern OH and NW PA.

Tonight, the ridge at the surface and aloft exits E'ward and gives way to cyclonic W'erly flow aloft as a shortwave trough aloft approaches from the Upper Midwest. The attendant cold front will approach from the western Great Lakes as associated surface troughing overspreads our CWA generally from the west. Moistening isentropic ascent ahead of the approaching cold front and shortwave trough axis may allow isolated snow showers to blossom over NE OH and NW PA after roughly 2 AM Saturday morning. In addition, 850 mb temperatures near -10C over/downwind of ~3C Lake Erie, low/mid-level moisture advection ahead of the cold front and shortwave trough axis, and weak lake-induced CAPE (LICAPE) will allow LES to blossom this evening and especially after midnight tonight. A SW'erly to WSW'erly mean low-level flow will allow the bulk of LES to impact portions of western NY. However, after midnight and especially toward daybreak, the LES should brush the lakeshore from northeastern Cuyahoga County to Erie County, PA as mean low-level flow begins to veer toward W'erly. The LES should be steady to heavy at times per model soundings, which suggest low- level convergence along the major axis or axes of LES banding will result in a crosshair signature (i.e. allow moderate to strong ascent to be maximized in a cloudy DGZ at least 0.5 to 1 km deep). Any nighttime snow accumulations should be one inch or less. Overnight lows should reach mainly the 15F to 25F range.

SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/

- Winter Storm Watch in effect for the primary snowbelt of NE OH/NW PA and Cuyahoga County from 7 AM Saturday to 1 AM EST this Monday

On Saturday, the surface cold front should sweep SE'ward across our region between about daybreak and late afternoon, while the passage of the aforementioned shortwave trough axis should lag the surface front's passage by several hours. Isolated and primarily light snow showers should accompany the front's passage. However, low-level convergence/moist ascent along the front should enhance the ongoing LES for a time. In addition, the LES should settle S'ward into our primary snowbelt counties and vicinity as the front's passage causes mean low-level flow to veer to W'erly and then WNW'erly, LICAPE remains weak, and 850 mb temps near -10C ahead of the cold front plummet to near 15C below zero behind the front. The LES will be steady to heavy at times due, in part to a crosshair signature. In addition, another and strengthening shortwave trough should approach our region from the Upper Midwest and vicinity as Saturday elapses. The approach of the latter shortwave trough should allow cyclonic flow aloft to back from W'erly to WSW'erly over portions of our region and allow frontogenetical convergence aloft to develop, which combined with moist isentropic ascent ahead of the shortwave trough axis, should allow widespread snow to overspread our region generally from west to east from about midday through late Saturday afternoon. This widespread snow should be steady to heavy at times, especially roughly along and south of U.S. Route 30, where the FGEN aloft and moist isentropic ascent should allow moderate to strong ascent to be maximized in a cloudy DGZ at least 1 to 2 km deep, which is a concerning crosshair signature. Will let the day shift reevaluate trends in NWP model guidance, but we may need to issue a Winter WX Advisory for the widespread accumulating snow, especially for our snowbelt counties outside the current Winter Storm Watch and for our counties roughly along and south of U.S. Route 30. Note: the seeder-feeder process and continued presence of weak LICAPE over Lake Erie should enhance the aforementioned LES further during the afternoon hours through sunset. Saturday's daytime highs should reach the lower 20's to lower 30's and be "warmest" farther east, where a later cold front passage will occur.

During Saturday evening, the latter shortwave trough axis should sweep generally E'ward across our region and be followed by ridging at the surface and aloft building gradually from the west through Sunday night. The widespread snow preceding the shortwave trough's axis should exit our region generally from west to east Saturday evening. The snow should be steady to heavy at times due to the above-mentioned crosshair signature. The widespread snow should total 1-5" outside LES and the greatest of these accumulations should be realized roughly along and south of U.S. Route 30. Once the widespread snow ends, odds favor dry weather through Sunday night, outside lingering LES, as stabilizing subsidence accompanies the ridge. The surface ridge will be associated with a particularly-cold air mass. Accordingly, overnight lows should reach mainly the 5F to 15F range Saturday night and Sunday night, respectively. Daytime highs should reach the 15F to 25F range on Sunday. Note: wind chills as cold as 0F to -10F are forecast around daybreak Sunday and Monday, respectively.

As for the LES, it will be steady to heavy at times and persist across the snowbelt of NE OH/NW PA and vicinity Saturday night through Sunday as mean low-level flow varies between WNW'erly and NNW'erly, weak to moderate LICAPE exists amidst net low- level CAA and 850 mb temps plummeting further to near -20C, upstream moisture connections to Lakes St. Clair and Huron develop and enhance LICAPE over portions of Lake Erie, and a periodic crosshair signature is likely realized. During Sunday night, the LES should shift N'ward to the primary snowbelt and vicinity in our CWA as mean low-level flow backs to W'erly. In addition, the LES should weaken due to synoptic low-level dry air advection and a lowering subsidence inversion accompanying the ridge, which will weaken LICAPE. Between daybreak Saturday and daybreak Monday, fresh snow accumulations may reach 4-12" in/near the snowbelt of NE OH and NW PA due to the combination of localized LES and the aforementioned widespread snow. Again, as mentioned above, would not be surprised if we end up having to issue a Winter WX Advisory for the snowbelt counties outside the current Winter Storm Watch. Figured the watch would be a good starting point since the heaviest and most persistent snow should occur in portions of the watch.

On Monday through Monday night, the ridge at the surface and aloft should crest E'ward across our region and eventually begin to exit toward New England. Thus, dry weather is expected in most of our CWA. However, a shortwave trough aloft should move SE'ward across our region on Monday and temporarily weaken the ridge at the surface and aloft. LES is expected to persist over and downwind of Lake Erie on Monday through most of Monday night amidst at least weak LICAPE and a sufficiently-cold/moist mean low- level flow that should vary between SW'erly and W'erly. Thus, the LES should be transient. Ahead of the shortwave trough axis, moist isentropic ascent may allow scattered snow showers to occur outside the LES, especially in NE OH and NW PA. In addition, the seeder- feeder process may occur ahead of the shortwave trough axis and enhance the LES for a time. Additional snow accumulations of a coating to several inches are possible. The LES should weaken Monday night and end by daybreak Tuesday amidst weakening LICAPE due, in part, to a lowering subsidence inversion behind the shortwave trough axis. Highs should reach the 20's on Monday. Overnight lows should reach the 10F to 20F range Monday night.

LONG TERM /TUESDAY THROUGH THURSDAY/

Current odds favor dry weather this Tuesday through Tuesday night as the above-mentioned ridge at the surface and aloft continues to exit E'ward. In addition, net and strengthening low-level WAA along the backside of the ridge should be accompanied by daytime highs in the upper 20's to mid 30's on Tuesday and lows mainly in the 20's Tuesday evening before temperatures begin to moderate after midnight.

A trough at the surface and aloft should overspread our region from the west on Wednesday through Thursday. In addition, a cold front should approach our region from the Upper Midwest and vicinity on Thursday as net low-level WAA persists in northern OH and NW PA. Daytime highs should reach the upper 30's to lower 40's on Wednesday and the lower 40's to near 50F on Thursday. A low-level return flow of warm and moist air from the Gulf should undergo isentropic ascent aloft, ahead of the front and primary trough axis aloft, and allow periods of mainly rain to affect our region Wednesday afternoon through Thursday. However, enough nocturnal cooling may allow wet snow to mix with the rain at times Wednesday night, especially in interior NW PA.

AVIATION /06Z Friday THROUGH Tuesday/

Remaining lake effect snow showers across Northeast Ohio will continue to weaken in intensity overnight. Lingering snow is mainly focused towards YNG but CAK is also experiencing a little snow at the start of the period. Expecting any additional snow at CLE to be flurries or very light. ERI is seeing a break in snow between bands and any additional snow overnight will be hard to time. Ceilings are mainly VFR except MVFR where light snow is falling. There is some dry air starting to sneak in and could see some breaks in the clouds at MFD/CAK but confidence is low in that. Winds are 10 knots or less at all sites and will tend to back to southwesterly or southerly by Friday morning.

Outlook...Non-VFR is likely in periods of snow as a series of systems cross the area through the weekend with the best chance in Northeast Ohio and Northwest Pennsylvania.

MARINE

The Small Craft Advisory has been allowed to expire as conditions improve on Lake Erie. Should continue to see relatively calm conditions on Lake Erie through the day Friday as high pressure briefly builds in.

Southwest winds will develop late tonight, with the strongest wind speeds of 25-30 knots expected Saturday morning as a cold front crosses the area. These strong southwest winds could result in low water in the western basin of Lake Erie, with water levels at Toledo approaching the critical mark for safe navigation Saturday morning.

Following the frontal passage, winds become westerly, and then northwesterly by Saturday night. Winds with northwest flow will generally be in the 15 to 25 knot range, though could approach 30 knots at times Sunday afternoon/evening, especially in the central basin where wave heights up to 6-9 feet may be possible. An extended Small Craft Advisory for much, if not all, of Lake Erie is likely needed starting early Saturday morning for the southwest flow and through at least Sunday night to capture the west and northwest flow.

Southwest flow of around 20 to 30 knots is expected again on Monday and Monday night when Small Craft Advisories will be needed once again and low water may be possible in the western basin.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Winter Storm Watch from Saturday morning through late Sunday night for OHZ011>014-089. PA...Winter Storm Watch from Saturday morning through late Sunday night for PAZ001>003. MARINE...None.