textproduct: Cleveland

SYNOPSIS

High pressure slides through the region today, before a weak low pressure dives through the northern Ohio Valley tonight. After high pressure briefly slides through on Thursday, another low pressure tracks into the upper Ohio Valley on Friday.

NEAR TERM /THROUGH THURSDAY/

High pressure slides through the region today, giving a brief break between systems locally. Between lower-level stratus, especially across Northeast OH and Northwest PA, and higher-level clouds spreading in from the west it will not be the cleanest high pressure, though will be dry. Highs will range from the upper 30s to lower 40s.

A low-amplitude shortwave dives out of the western Great Lakes and into the upper Ohio Valley overnight tonight. There will be enough lift and low to mid-level moisture ahead of the shortwave for showers to accompany it across the area, especially across the southwest half or so of our area. There will be just enough elevated instability that showers may have a bit of a convective component tonight. Lows will range from near 30 in far Northeast OH and Northwest PA to the upper 30s closer to Findlay/Marion. Those sub-freezing lows in our northeast corner will occur early tonight and should modestly rise overnight, limiting the concern for any mixed precipitation should any very light precip reach into far Northeast OH or Northwest PA.

Another ridge axis slides through during the day Thursday, quickly drying out any lingering sprinkles/showers and leaving a mix of sun and clouds for Christmas Day. Highs are expected to range from the upper 30s in the higher terrain of Northeast OH and Northwest PA to the low to mid 40s across the rest of northern Ohio.

SHORT TERM /THURSDAY NIGHT THROUGH FRIDAY NIGHT/

-Increasing confidence in impactful mixed precipitation, including freezing rain, across Northwest PA on Friday. A shorter duration of freezing rain is possible across northern OH on Friday, particularly near Toledo and in far Northeast OH.

Much of Thursday night will be chilly and quiet ahead of the next low-amplitude shortwave and weak low pressure that will dive out of the Midwest and into the Ohio Valley on Friday. Lows Thursday night will range from the lower 20s in interior PA to the lower 30s towards Findlay and Marion, another tick cooler as has been the recent trend.

Shifting into Friday, there's high confidence in precip spreading into the entire area during the day. There remains 6 or so hours of difference in the onset timing of precipitation from west to east among various guidance, especially across Northeast OH and Northwest PA where there will be a dry east flow behind strong high pressure over New England. A quicker onset of precipitation would give less time for surface temperatures to warm ahead of it, increasing the concern for impactful mixed precipitation, whereas a slower onset would allow more of our area to warm above freezing before precip starts. The heaviest swath of QPF is becoming better-agreed-upon to track from SE Michigan across Lake Erie and into far Northeast OH and Northwest PA, with a swath of 0.40-0.75" likely, trending towards or under 0.25" to the southwest towards Findlay-Mt Vernon. The heaviest precip likely will occur between the late morning and afternoon from west-northeast to east-southeast across the area. This precip then exits to the east-southeast Friday night.

The main forecast difficulty for the Friday system remains potential for mixed precipitation across at least portions of our forecast area. The Arctic high pressure pushing into New England Thursday night into Friday will push a shallow dry/chilly low-level airmass into the area as temperatures aloft remain warmer. Where surface temperatures warm above freezing before precipitation arrives, just rain should result. It may be chilly/dry enough aloft for some initial snow across far Northeast OH and Northwest PA, though in general some combination of rain/freezing rain (with perhaps some sleet) is currently favored for the bulk of the event, even across Northwest PA. That makes the timing of surface temperatures warming above freezing (in conjunction with the timing of precip onset and how much QPF occurs before warming) critical. Temperatures should warm fairly quickly across most of Ohio on Friday, with two exceptions...near Toledo, where the low may track just far enough southwest to maintain an ENE wind off the icy waters of western Lake Erie and slow any warming, along with far Northeast OH where better proximity to the cold/dry airmass and more terrain may support a slower warming. Guidance is getting into better agreement regarding Northwest PA taking until later Friday afternoon or evening to warm more substantially, giving a more confident and concerning window for mixed precipitation/ice. Highs on Friday will likely occur during the late afternoon or evening, struggling to get above freezing in Northwest PA but likely spiking well into the 40s south of US 30.

Overall, Northwest PA should plan on at least several hours of wintry mixed precipitation on Friday with impacts to travel, especially later in the morning through the afternoon. If the bulk of the precip falls as freezing rain (with limited snow/sleet), ice accretion may exceed a quarter-inch, bringing tree/power-outage concerns into play. A Watch (driven by icing concerns, not snow/sleet amounts) was considered for Northwest PA with this update, though for now was held off on. At the least, an advisory will be needed there and we can still put out a watch today if trends hold. Potential is tricker in Ohio, though the Toledo area and far Northeast OH appear to have higher confidence (over 50%) in at least a brief window of freezing rain at precipitation onset. Confidence in freezing rain decreases across the rest of northern Ohio, though as the prior discussion mentioned nearly all of the area does have at least a modest probability of seeing a bit. After the recent/ongoing milder weather, a brief window of marginal freezing rain likely wouldn't be impactful, though a more solid period of it could lead to some consideration for Winter Wx Advisories into at least some of our Ohio counties as we get closer. Overall, would say concern in Ohio will be highest where precipitation arrives quicker, limiting ability for the air/ground to warm.

We dry out through Friday night with lows ranging from the upper 20s/lower 30s in far Northeast OH and Northwest PA to the mid-upper 30s elsewhere across the forecast area.

LONG TERM /SATURDAY THROUGH TUESDAY/

Aloft, ridging will briefly build Saturday night and Sunday ahead of a longwave trough that will wrap in a lobe of the tropospheric polar vortex and drop into the upper Midwest on Sunday and the Great Lakes Sunday night and Monday. This trough then shifts into New England towards Tuesday. At the surface, a cold front will cross on Sunday as low pressure develops and deepens over and east of the Great Lakes. Low pressure will likely develop and takeover near the New England coast Monday into Monday night.

Quiet and relatively mild weather is expected Saturday and most of Saturday night. Rain chances ramp up on Sunday with the cold frontal passage. While we may get brushed by wrap-around snow as low pressure intensifies to our northeast Sunday night, most guidance (outside of the 0z CMC) currently suggests the low will intensify too far to our northeast to get into that. What is confident is a period of quickly falling temperatures and gusty winds late Sunday and Monday as lake effect snow sets up amid the deep cold airmass that gets pulled in under the heart of the upper trough. While there is disagreement on specific details (such as wind direction, temperature profiles, moisture, and duration), a majority of solutions presented by operational models and ensembles would support impactful/headline- worthy lake effect snow and blowing snow into at least the primary snowbelt region of Northeast OH and Northwest PA Monday into Tuesday. Elsewhere, it will be a return to much colder weather with potentially some passing flurries/snow showers, but likely not much snow outside of the lake effect. Highs in the low-mid 20s and lows in the 10s are expected to return for Monday and Tuesday, with wind chills potentially approaching or dipping below 0 at times.

AVIATION /06Z Wednesday THROUGH Sunday/

Skies are mostly clear as MVFR stratus has moves off to the east with the high pressure's entrance. Patchy lower visibilities may develop in the clear skies. This should largely be a hazy 4-6 SM, though IFR or lower visibilities could be lower out west, especially given the 1/4 SM visibilities that have developed to the west of our forecast area (such as Van Wert).

An area of stratus will southward across the region, first reaching KERI area in the next couple hours before expanding southwestward across the area through the rest of the morning before dissipating early Wednesday afternoon. VFR is expected thereafter with mid-level cloud cover lingering.

Current light northerly winds veer with time becoming east by noon, and then south by sunset.

Outlook...Non-VFR conditions possible in periods of rain Wednesday night and Thursday night into Friday.

MARINE

Changing wind directions through Thursday as high pressure moves across Lake Erie west to east, followed by a warm front in the vicinity of the lake for Friday and low pressure passing just south of the lake Friday night. This will translate to wave heights less than 2 feet through early Thursday, but increasing to 2-4ft Thursday night into Friday as waves become northerly around 10-20kts, and then easterly 10-20kts. Winds variable less than 10kts Friday night through Saturday night and wave heights less than 2ft, followed by strong offshore flow early Sunday increasing to 20-25kts. Strong cold front brings northwest winds 30-35kts late Sunday through early Monday and wave heights likely in the 6-10ft range.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...Small Craft Advisory until 4 AM EST early this morning for LEZ146>149.