textproduct: Cleveland

WHAT HAS CHANGED

Confidence in the timing and evolution of heavier lake enhanced snowfall tonight and Monday continues to increase. The Winter Storm Watch for Southern Erie County in PA has been upgraded to a Winter Storm Warning from 10 PM this evening through 7 AM Tuesday. A Winter Weather Advisory has been issued for the Erie County lakeshore where the lower elevation will reduce amounts. Additionally, the Ohio Winter Weather Advisories have been expanded to include Erie and Huron Counties from 6 PM this evening through 7 PM Monday.

KEY MESSAGES

1) Light snow transitions to bands of heavier lake enhanced snow tonight which continues through Monday across portions of north central and NE Ohio and NW PA. The greatest snow amounts and resultant travel impacts will occur in the higher elevations of the snowbelts. The heaviest snow will impact the Monday morning commute.

2) A Clipper system will bring a quick shot of light snow to NE Ohio and NW PA Tuesday night into Wednesday morning, followed by a potentially more impactful system Thursday. Confidence in the precipitation type and track of the Thursday storm is low.

DISCUSSION

KEY MESSAGE 1... The much advertised big East Coast blizzard is starting to organize this afternoon. Water vapor loops and RAP analysis show a digging mid/upper trough over the Ohio Valley and southern Great Lakes, with its axis taking on a negative tilt. This is supporting intense dynamics near the coast characterized by strong upper diffluence helping to strengthen low-level convergence. As a result, surface low pressure is rapidly strengthening offshore of Virginia and will lift north to just offshore of Cape Cod by late Monday afternoon while bombing out to around 970 mb.

For our area, light snow will continue areawide this evening driven by the combination of the mid/upper trough and associated PVA overhead and deep synoptic moisture wrapping back westward beneath the trough. This snow has been low-impact, but as the East Coast cyclone rapidly deepens tonight, much colder air advecting into the region and traversing Lakes Huron and Erie, boundary layer flow becoming well-aligned from the NNW, even deeper wraparound synoptic moisture, and the continued presence of the trough aloft will set up more intense bands of lake enhanced snow. HREF members and the RGEM have come into much better agreement on the timing and evolution of these lake enhanced bands, with HREF probabilities for greater than 6 inches of snow in 24 hours (assuming a 15:1 ratio) now in the 50-60% range for much of the inland primary and secondary snowbelts of north central and NE Ohio and 70-100% across southern Erie County in PA. This makes sense with the expected deep synoptic moisture and upsloping. Probabilities for greater than 8 inches in 24 hours have increased to 25-35% in parts of the north central and NE Ohio primary and secondary snowbelts and 40-70% in southern Erie County, PA, so this will be a classic upslope snow event.

The lake enhanced snow will start to set up after 00Z this evening and will intensify overnight and Monday morning as boundary layer moisture and instability deepens along with strong Omega (lift) into the DGZ. The heaviest snowfall looks to occur Monday morning due to an inverted surface trough hanging back westward from the East Coast storm to the south shore of Lake Erie. There is a strong signal for this trough and associated enhancement of convergence on all HREF members and the RGEM, as well as the RAP and operational NAM12. This boosts confidence that the heaviest snowfall rates will occur from roughly 09-17Z Monday. HREF probabilities for snowfall rates of 0.75 inch per hour have increased to 40-50% across southern Erie County in PA and around 10% in parts of SE Cuyahoga, northern Medina, northern Summit, and Geauga Counties in NE Ohio during the Monday morning commute. This will lead to treacherous travel. The snow will gradually lessen in intensity Monday afternoon and eventually come to an end Monday night from west to east as the convergence weakens and drier air/surface ridging build into the area.

A couple of forecast challenges: First, warning amounts are very possible in SE Cuyahoga and Geauga Counties. If that area of stronger convergence sets up earlier tonight or persists deeper into the afternoon Monday, then 8+ inches of snow could fall in these areas. Capped amounts at 6 to 7 inches for now since am already on the higher end of blended guidance and there is some question as to how much open water is on the central and eastern basins. Second, Ashland and Richland Counties, and to some extent Portage and Trumbull Counties, may get Advisory-level snow amounts as well. This depends on the orientation and inland extent of the snow bands, so kept amounts in the 1-3 inch ranges there for now (highest in northern parts of these counties). Was confident enough to expand the Advisory into Erie and Huron Counties in north central Ohio since there is a strong signal in HREF and RGEM guidance for a Lake Huron band to affect that area for a few hours Monday morning into the afternoon bringing 2-5 inch amounts. The NNW boundary layer flow and a more definite area of open water near the Lake Erie Islands support this idea.

Finally, the tight pressure gradient will lead to NW winds gusting to 30-40 mph at times Monday. This will lead to some minor blowing and drifting impacts where the heaviest snow falls. Wind chill values will fall into the single digits Monday night as the snow ends.

KEY MESSAGE 2... The quieter weather Tuesday will be short-lived as a very active pattern is expected to continue through the week. A fast moving northern stream mid/upper shortwave and associated surface low (Clipper system) will drop through the central and eastern Great Lakes Tuesday night into Wednesday morning. Confidence is increasing that this will put down a strip of light snow in far northern Ohio and NW PA Tuesday night into Wednesday morning, with the greatest amounts falling in far NE Ohio and NW PA closer to the synoptic forcing. Confidence is lower regarding the specific amounts but look to be in the sub Advisory range at this time.

A stronger Clipper system on Thursday still looks to potentially phase with southern stream energy leading to a deepening surface low tracking into the Mid Atlantic or NE CONUS. Guidance continues to significantly differ on the details of this system, with the 12Z ECMWF now leaning toward the more suppressed and lower impact Canadian solution, whereas, the GFS continues to phase it farther NW and bring much greater precipitation into our region. This gives low confidence to the amount of precipitation and the precip types for Thursday.

AVIATION /00Z Monday THROUGH Friday/

A mix of MVFR to IFR conditions across terminals this evening due to both ceilings and visibilities in widespread light to moderate snow showers. Anticipate for widespread IFR visibilities with patchy IFR ceilings along and east of the I-71 corridor as lake enhanced snow spreads across the region. MVFR to IFR conditions are expected to persist through the TAF period lake enhanced snow showers persist through Monday night.

Northwest to north winds 8-12 knots this evening will increase behind a trough Monday morning. Sustained winds increase to 12-18 knots with gusts of 20-28 knots possible.

Outlook...Periodic snow with non-VFR expected through Tuesday night. Non-VFR likely on Wednesday in snow changing to rain/snow with a clipper system. Non-VFR may return again on Thursday as another system moves through the region.

MARINE

Main concern over the next several days will be the increasing north to northwest flow of 20 to 30 knots across Lake Erie (primarily the western and central basin) tonight into Monday as a trough sweeps southeast through the region. This will lead to abrupt southerly shifts of the ice across Lake Erie, especially on Monday. Winds will diminish to 10 knots or less Monday night, before shifting towards the southwest on Tuesday, then west on Wednesday and increasing into the 15 to 25 knot range. Winds appear to briefly increase out of the northeast on Thursday, 10 to 15 knots, as a system passes just south of the Lake.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Winter Weather Advisory until 7 PM EST Monday for OHZ009-019. Winter Weather Advisory until 1 AM EST Tuesday for OHZ010>014- 020-021-089. PA...Winter Weather Advisory from 10 PM this evening to 7 AM EST Tuesday for PAZ001-003. Winter Storm Warning from 10 PM this evening to 7 AM EST Tuesday for PAZ002. MARINE...None.