textproduct: Cleveland

WHAT HAS CHANGED

The forecast swath of precipitation associated with a disturbance aloft continues to shift southward this Sunday night into Monday. As a result, very little or no snow accumulation is expected in our CWA during that time period with this forecast update.

KEY MESSAGES

1.) Mainly dry and relatively-mild weather persists through Saturday.

2.) Snow is expected Saturday night. Total snow accumulations should be mainly one inch or less.

3.) After a brief period of quiet weather during the day on Sunday, periods of unsettled weather are expected to return Sunday night through this upcoming Friday.

DISCUSSION

1.) A high pressure ridge at the surface and aloft continues to exit E'ward through Saturday as cyclonic W'erly flow aloft becomes established over our region. In addition, a surface cold front starved of low-level moisture and exhibiting a subtle slope should sweep SE'ward through our region Saturday morning. Behind the front, a weak surface ridge should nose into our region from the north-central United States and vicinity. Mainly dry weather is expected through Saturday, including during the cold front passage itself. However, ahead of the front, a nocturnal SSW'erly low-level jet of ~40 to 60 knots at/near 925 mb should develop, undergo moist isentropic ascent, and trigger isolated to scattered rain showers during the predawn hours of Saturday morning, especially east of our I-75 corridor counties. Lows are expected to reach mainly the mid 30's to near 40F overnight tonight. On Saturday, late afternoon highs should reach the upper 30's to lower 50's amidst peeks of sunshine and very weak low-level CAA behind the front. A notable S'erly gradient in forecast high temperatures exists due to expected Lake Erie lake breeze development during the late morning through early evening, amidst a weak synoptic MSLP gradient, and the fact that ice-free lake surface temperatures are ~34F.

2.) During Saturday night, cyclonic W'erly flow aloft and embedded shortwave disturbances affect our region as the aforementioned surface ridge continues to nose into our region. The cold air mass deepens as the upper-reaches of the aforementioned cold front sweep SE'ward through our region, which should be accompanied by a frontogenetical deformation zone. Moist isentropic ascent ahead of the shortwave trough axes and associated with the frontogenetical convergence zone should trigger a fairly brief period of precip, mainly in the form of snow, across our region. However, snow may mix with rain initially roughly along and south of U.S. Route 30 before the atmospheric column cools sufficiently via nocturnal cooling, the wet-bulb effect, and CAA at the surface and aloft for precip type to become all snow. A sufficiently-cold/moist low/mid- level atmospheric column and NNW'erly mean low-level flow over/downwind of the ~1C ice-free waters of Lake Erie, weak lake-induced CAPE, and the seeder-feeder process should permit a few hours of lake-enhanced snow (LEnS) to occur generally south of Lake Erie, especially the central and eastern portions of the lake, before much drier air at the surface and aloft overspreads our area. Total snow accumulations are still expected to be mainly 1" or less in our CWA, but localized totals of 2-3" are not out of the question due to the LEnS. Overnight lows should reach mainly the upper teens to mid 20's around daybreak Sunday.

3.) Stabilizing subsidence and dry weather are still expected to impact our region on Sunday as W'erly flow aloft becomes anticyclonic briefly as a shortwave ridge moves E'ward across our region and the surface ridge continues to build from the Upper Midwest and vicinity. Late afternoon highs should reach only the 20's in NW PA and mainly the mid 20's to mid 30's in northern OH amidst continued low-level CAA. Note: normal highs are near 40F and normal lows are near 25F this time of year in our CWA. During Sunday night through Monday night, mainly cyclonic W'erly flow aloft and embedded shortwave disturbances should affect our region as we remain within the cold sector, the aforementioned surface ridge continues to affect our CWA, and the embedded high pressure center moves from near the central Great Lakes toward the Gulf of Maine. Primarily below- normal air temperatures are expected. Moist isentropic ascent ahead of a stronger shortwave trough axis may allow periods of light precip, mainly in the form of snow, to impact our region Sunday night through Monday. However, the latest trends in NWP model guidance continue to depict a S'ward shift in the strongest forcing for ascent and greatest precip amounts. Based on these latest model trends, very little or no snow accumulation is expected in our region. During Monday night, a warm front should approach from the TN and OH Valleys. Moist isentropic ascent along the upper-reaches of the front should trigger precip. This precip may change from snow to freezing rain to plain rain as strengthening low-level WAA with height causes an elevated melting layer to form, deepen, and eventually become surface-based. However, forecast confidence is low regarding precip types and amounts. Stay tuned to continued forecast updates for Sunday night through Monday night.

Weather pattern evolution at the surface and aloft remains less certain this Tuesday through Friday given sizable spread in NWP model guidance. In general, cyclonic W'erly to SW'erly flow aloft and embedded shortwave disturbances should affect northern OH and NW PA. A warm front should sweep generally N'ward through our region on Tuesday and allow near-normal to above- normal high temperatures to return. Near-normal or above-normal temperatures should then affect our region Tuesday night through Friday as the aforementioned front potentially wavers between the Great Lakes and roughly the OH Valley as multiple mid-latitude cyclones develop and move generally E'ward along the front, yet primarily WAA at the surface and aloft affects our region. Periods of precip, mainly in the form of rain, are expected Tuesday through Friday due, in part to moist isentropic ascent along the upper-reaches of the front and ahead of shortwave trough axes.

AVIATION /00Z Saturday THROUGH Wednesday/

The main aviation weather concern for this 00z TAF update will be for some non-convective low level wind shear between 03z and 10z overnight. Mainly VFR conditions and ceilings are expected for this TAF period. Ceilings will generally be 10K or above tonight through Saturday afternoon. Winds will be from the south-southwest and gradually ramp up to 12-15 knots across the area with gusts of 20-25 knots possible overnight. As a cold front moves closer to the area tonight, a strong LLJ of 40-50 knots will develop. Have included a period of LLWS at all terminals due to the magnitude of the jet within the period of 3-10Z Saturday. As the cold front pushes east Saturday morning, winds will become west-northwesterly at 5-10 knots.

Outlook...Non-VFR possible in snow Saturday night into Sunday and again Sunday night into Monday, mainly along and south of US-30. Periods of non-VFR conditions are possible throughout next week as an active pattern becomes established.

MARINE

With mostly clear skies today, there was an excellent view from satellite of the remaining ice across Lake Erie. Much of the central basin is now open with the western basin ice quickly diminishing. In the eastern basin, the vast majority of ice still exists, however it is important to note that significant ice cracks are occurring, especially near the lakeshore. As an active pattern continues through next week, multiple periods of gusty winds will continue to shift the ice and fracture it even more.

The first system will occur tonight as a low pressure moving across the region pushes a cold front east across Lake Erie. Southwest winds this afternoon will increase to 15-20 knots before backing to westerly by Saturday morning. High pressure will nudge over the area Saturday night, shifting winds to become north-northwesterly at 10-15 knots. This high will remain dominant into Tuesday. It is worth noting that Small Craft Advisories remain suspended at this time, but waves within open waters may build to 2-4 feet at times.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...None.