textproduct: Cleveland

WHAT HAS CHANGED

Rainfall coverage has continued to trend higher tonight and Thursday afternoon/evening, especially from north central Ohio through NW PA. The forecast Thursday night through Saturday pertaining to lake effect showers, mixing with snow at times, remains mainly the same.

KEY MESSAGES

1) Widespread rain tonight into early Thursday morning.

2) A second wave of widespread showers Thursday afternoon/evening transitioning to more localized lake effect showers Thursday night through Saturday, mainly over north central and NE Ohio and NW PA. Snow will mix in at times away from Lake Erie, especially Thursday night and Friday night, but the risk for impactful accumulations remains low.

3) Drying out Sunday through Wednesday and slowly warming.

DISCUSSION

KEY MESSAGE 1... After a very pleasant Fall, the coldest air of the season is finally set to invade the Great Lakes, Ohio Valley, and Northeast tonight through the weekend as a deep mid/upper trough digs into the eastern CONUS. Satellite and water vapor loops this afternoon show a highly amplified pattern developing as sharp mid/upper ridging strengthens over the western CONUS, with a downstream trough digging into the Upper Midwest. Clouds have already thickened up across the region ahead of this upstream trough and developing surface low, with regional radar showing an expanding area of showers near Chicago. As the mid/upper trough continues to dig into the Great Lakes and Ohio Valley tonight, coupling between a 50-70 knot H5 jet rounding its base toward the Tennessee Valley and a 50 knot H5 southern stream jet offshore of the Carolinas will help the surface low to rapidly deepen as it tracks across central/southern Ohio tonight then offshore of southern New Jersey by Thursday evening.

An initial cold front will settle south across Lake Erie this afternoon and through the rest of the region this evening, with minimal impacts other than a wind shift to light northerly. The main impact will come with the deepening surface low that tracks just south of the CWA tonight and early Thursday morning. Strengthening mid-level frontogenesis on the north and northwest side of the low track beneath upper divergence will lead to continued expansion of the upstream rain, and a modest 850 jet response to the forcing could advect in enough mid- level instability for some weak convective elements to support briefly heavier rain. With this being said, expect scattered light showers this evening to become a widespread, steadier rain after 04Z, with rain then lasting much of the night and tapering off from west to east in the 12-15Z Thursday timeframe. The steadiest rain and biggest risk area for some heavier convective downpours will be from north central Ohio through NE Ohio and NW PA in closer proximity to the strengthening dynamics. Overall, this system will be a soaker, but rainfall amounts will remain very manageable in the 0.25 to 0.60 inch range given the fast movement.

KEY MESSAGE 2... The real change to much colder air will come in the wake of the low Thursday as the center of the mid/upper trough settles over the Ohio Valley and Great Lakes bringing a pool of 0 to -3 C 850 mb air overhead. This will set up a raw, damp day as the tightening pressure gradient and cold air advection lead to N winds gusting up to 30 mph at times and highs only in the upper 40s falling a bit further in the afternoon. There will be a lull in the rain Thursday morning in most areas, but expect widespread showers to rotate back into the region for the afternoon and evening ahead of a mid- level shortwave and associated surface trough dropping southward coupled with deep wraparound moisture and growing lake to 850 mb delta T's. This will set up round two of fairly steady rain, with maximum coverage in the 18-00Z timeframe. The greatest amounts will occur over the central highlands as well as inland portions of the primary and secondary snowbelts of NE Ohio and NW PA where lake enhancement and upslope flow will boost totals. These areas could see an additional 0.25 to 0.50 inch of rain.

By Thursday night, even colder air in the wake of the shortwave/surface trough and continued northerly flow will transition the precip to pure lake effect, which will continue at varying coverages and intensities through Saturday as weak shortwave impulses rotate through. An average boundary layer flow near 360 degrees coupled with sufficient wraparound moisture and strong lake induced instability will set up a Lake Huron band from the Lake Erie Islands to the central highlands Thursday night and Friday morning, with scattered, lighter showers across NE Ohio and NW PA given the short fetch. Locally heavy downpours will accompany this band, with graupel within the strongest convective cores. The warm lake and strong northerly flow will advect the marine layer inland, so expect temperatures to be too warm in most areas for snow flakes Thursday night/Friday morning, however, the higher elevations of the central highlands as well as interior NE Ohio and NW PA will likely see some wet snow. Accumulations likely won't amount to more than a slushy dusting, but will need to watch for wet bulbing in the stronger Huron band that could lead to locally more snow (1-2 inches at most).

Precip should transition back to mainly rain during the day Friday, and expect the main Huron band to slowly pivot eastward into NE Ohio and NW PA as the boundary layer flow backs to NW. This will lead to a more traditional, multi-band lake effect set up Friday evening through Saturday over the primary and secondary snowbelts. Graupel and wet snow will be possible during the day Friday in the heaviest convective bursts, mainly in the highest elevations, with better chances for snow flakes again Friday night away from the lake and over the higher elevations given the continued marine influence.

Lake effect showers will continue Saturday as a final shortwave rotates through the NW flow, gradually ending Saturday night and Sunday morning as high pressure building from the west brings drier air and a lowering inversion, but it will remain cold through Sunday with temperatures a solid 10 degrees below normal.

KEY MESSAGE 3... Surface high pressure will continue to build over the Ohio Valley Sunday and Monday, sliding into the Appalachians and Mid Atlantic by late Tuesday and Wednesday as the eastern CONUS mid/upper trough gradually gets replaced by a building mid/upper ridge ahead of a strong series of troughs progressing into the western CONUS. This will support a pattern change back to warmer and drier weather, with highs in the 50s likely returning by Tuesday and Wednesday.

AVIATION /00Z Thursday THROUGH Monday/

VFR conditions to start the period will lower overnight as low pressure over Indiana deepens across southern Ohio. Thunderstorm activity across southern Indiana is expected to remain south of the local area while rain expands as a cold front is pulled south overnight. Conditions will deteriorate with a trend towards widespread MVFR ceilings and occasional reduced visibilities in the steadier rain. Otherwise, widespread rain will tend to spread east across the area through Thursday morning, then become more showery for the afternoon. A trough will swing south across the area between 20-00Z bringing another round of more organized showers. Some locations may see a period of IFR behind this trough on Thursday evening.

Winds will start out as northeasterly at 10 knots or less, back to northwesterly by Thursday morning with some gusts to 20 knots at times during the afternoon. Winds will set up out of the north behind the trough passage during the afternoon and evening with some locations gusting between 20-30 knots, especially near the lake.

Outlook...Non-VFR will linger across Northeast Ohio and Northwest Pennsylvania through the weekend. Some wet snow showers may also be possible Friday night into Saturday morning.

MARINE

Winds will increase on Lake Erie tonight and especially Thursday as a deepening low tracks across the Upper Ohio Valley and into the Mid Atlantic region. Expect N to NE winds to increase to 15-20 knots tonight, becoming N at 20-30 knots Thursday. This will build wave heights to 6-9 feet. Issued Small Craft Advisories late tonight into Friday. The winds will start to die down Thursday night, but it will take longer for waves to subside. After a lull of NNW winds averaging 10-15 knots most of Friday, NW winds could near 15-25 knots again Friday night through Saturday night, so additional Small Craft Advisories will likely be needed. Winds diminish Sunday and Monday as high pressure builds overhead.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...Small Craft Advisory from 4 AM Thursday to 10 AM EST Friday for LEZ142-143-148-149. Small Craft Advisory from 4 AM Thursday to 1 PM EST Friday for LEZ144>147.