textproduct: Cleveland

WHAT HAS CHANGED

Forecast, including QPF, POP's, and snowfall, remains valid per latest trends in obs and NWP model guidance at 6:45 PM EST. Widespread snow associated with moist isentropic ascent and frontogenetical convergence/moist ascent releasing potential instability in a TROWAL will exit our region generally from west to east this evening through about the first hour of Monday morning. This snow will be heavy at times with snowfall rates up to 1" per hour as the the aforementioned forcing for ascent and release of instability result in strong, maximized ascent in a cloudy DGZ about 1 km deep. Additional snow accumulations from this widespread snow are expected to be 1-3" at most in our CWA. Note: the forcing for ascent within the TROWAL and resulting snow should begin to weaken beyond the 8 PM hour this evening as an older surface low weakens in vicinity of southwestern PA at the expense of a newer, strengthening surface low still expected to wobble NE'ward from south of Long Island toward Nantucket the rest of this evening.

KEY MESSAGES

1) Widespread snow will continue this afternoon and evening before tapering off tonight. Lake enhanced snow showers are expected to linger in northeastern Ohio and northwestern Pennsylvania Monday with additional light snow accumulation expected.

2) An Extreme Cold Watch has been issued for wind chill values near - 15F and below -20F for some locations on Tuesday as arctic air is ushered in with high pressure.

3) Prolonged cold with occasional light snow is expected through the end of next week creating elevated risks for cold exposure and damage to infrastructure.

DISCUSSION

KEY MESSAGE 1... Widespread snow accumulation will continue through the evening before tapering off tonight. A low pressure system, currently located over the Tennessee Valley will track northeastward up the Appalachians this evening and off the east coast by tonight. Overrunning precipitation due to broad moisture advection and isentropic ascent driving the snowfall will persist until the low moves off to the east of the region. Additional snow accumulations across the region will range from 3 to 5 inches for areas west of I- 71 and around 5 to 8 to the east with the higher amounts in far eastern Ohio and northwestern Pennsylvania. Winds will also be a factor this evening as gusts of around 20mph are possible with winds shifting to be out of the northwest and cold air advection moves in. As mentioned, the snow will begin to taper off from west to east this evening as the low pushes off the east coast.

On the back end of the low pressure system, there will be some lingering moisture that will generate some lake enhanced showers across northeastern Ohio and northwestern Pennsylvania. Though, with most of the moisture off to the east, additional accumulations will be limited. Other limiting factors will be that Lake Erie being almost completely ice covered and there will decent low level shear in place over the region through mid-morning Monday. With the ice coverage, there may be some breaks with the shifting winds that could allow for areas of stronger lake enhanced showers. Regardless, an additional 1 to 2 inches are expected across the snowbelt with locally higher amounts near 3 inches. Snow showers will end as high pressure builds in just south of the region and flow backs to be more southwesterly Monday night.

KEY MESSAGE 2... A large upper level trough will be in place across eastern Canada reaching down into eastern CONUS that provide support for an arctic surface high pressure to move south along its western periphery. This will bring much colder air to most locations east of the Rockies to include the Great Lakes region. Combined with an ice covered Lake Erie, northwesterly winds moving across the lake, and a fresh snow pack across the region, overnight temperatures will drop to below zero for much of the region starting on Monday night. Temperatures have continued to trend down for Monday night/Tuesday morning in particular and accompanied with southwest winds gusting 15 to 25mph and clearing skies, wind chills will be down to -15F to below -20F for some locations. A Extreme Cold Watch has been issued for that time frame as there will be impacts with prolonged exposure.

KEY MESSAGE 3... The previously mentioned upper level trough will be stubborned to depart and will be in place over the region through the end of the week. This will ensure that temperatures will continue to be well below average with daytime highs barely reaching into the mid-teens. Overnight lows will be down in the low single digits and below zero for some locations as well. Wind chills as well will be between -10F and -20F periodically throughout the week, with the coldest times during the overnight and morning hours. This prolonged cold stretch will have elevated risks for cold exposure and infrastructure damage across the region. Take precautions and limit time outdoors if possible. Throughout the week, there will be frequent shortwave system moving across the region that will reinforce the cold air mass and provide occasional light snow fall across the region with periods of possible lake effect snow showers. Further details on these systems will come closer to the event.

AVIATION /00Z Monday THROUGH Friday/

At the surface, a low wobbling NE'ward in vicinity of the Upper OH Valley early this evening dissipates by 05Z/Mon in vicinity of southwestern PA as a stronger low wobbles NE'ward from south of Long Island toward Nantucket. The latter low is then expected to strengthen further as it wobbles NE'ward to Atlantic waters south of Nova Scotia by 00Z/Tues. Accordingly, a trough lingers over our region through about 05Z/Mon and then a ridge builds from the north-central United States through 00Z/Tues. Our regional surface winds continue to back from NE'erly to W'erly through the TAF period and remain around 5 to 15 knots in magnitude. Gusts up to 20 knots are possible between ~15Z/Mon and ~23Z/Mon.

Scattered to widespread low clouds with bases between 700 ft and 3kft AGL are expected through the TAF period. Widespread snow, moderate to heavy at times, is expected to exit our region generally from west to east this evening through ~06Z/Mon. Visibility will range between primarily MVFR and LIFR in this snow. Primarily dry weather is then expected behind the widespread snow. However, light lake-effect snow (LES) originating over Lake Huron and originating over mainly ice- covered Lake Erie should impact NE OH and NW PA at times through 00Z/Tues as mean low-level flow backs from N'erly to W'erly. Visibility should vary between mainly VFR and MVFR in this LES.

Outlook...During Monday night through Friday, additional periods of snow with non-VFR are possible. Greatest chances exist in NE OH and NW PA, where periodic lake-effect snow downwind of Lake Huron and mainly-ice covered Lake Erie should occur.

MARINE

Northeast winds gradually shift north and northwest at 10-20 knots through tonight. Winds gradually shift west Monday and southwest Monday night, increasing to 20-30 knots Monday night and Tuesday ahead of the next cold front. This cold front crosses Tuesday afternoon, shifting winds more west at 15-25 knots Tuesday night. Winds shift southwest Wednesday into Wednesday night at 15-20kt ahead of the next cold front, which crosses early Thursday and shifts winds more westerly at 15-20kt.

Ice will continue to thicken through next weekend as several bouts of cold air impact the region. Stronger southwest winds on Tuesday may break up and shift the ice northeastward away from the southwestern shoreline of Lake Erie.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Winter Storm Warning until 7 AM EST Monday for OHZ003-006>008- 017. Extreme Cold Watch from Monday evening through Tuesday afternoon for OHZ003-006>014-017>023-027>033-036>038-047- 089. Winter Storm Warning until 10 AM EST Monday for OHZ009>014- 018>023-027>033-036>038-047-089. PA...Extreme Cold Watch from Monday evening through Tuesday afternoon for PAZ001>003. Winter Storm Warning until 1 PM EST Monday for PAZ001>003. MARINE...None.