textproduct: Cleveland

WHAT HAS CHANGED

Expanded the Dense Fog Advisory for northern Ohio as visibility has dropped to less than half a mile. Strong thunderstorms are possible late Thursday night with gusty winds likely during the day on Friday.

KEY MESSAGES

1) Dense Fog Advisory in effect for northern Ohio and northwestern Pennsylvania until 9AM and could impact the morning commute.

2) Above average temperatures and strong thunderstorms possible late this evening into early Friday morning. Strong winds likely along and behind the cold front Friday afternoon.

3) Seasonable temperatures return this weekend with snow showers possible through Monday night.

DISCUSSION

KEY MESSAGE 1... Dense fog has formed along a stationary boundary that has begun to drift southward across northern Ohio and northwestern Pennsylvania. Colder air is moving south behind the boundary that has dropped surface temperatures close to saturation and with winds becoming light and variable, has allowed for fog to form. In the southern portion of the CWA, patchy fog will be possible with an inversion in place and the low levels being saturated from the precipitation earlier today. Fog should begin to dissipate mid morning today though could impact the morning commute.

KEY MESSAGE 2... Temperatures today will rise up into the upper 50s to low 60s as southerly flow takes hold across the region with an approaching low pressure system. This low will enter the Great Lakes region late Thursday evening, tracking northeasterly from the mid-Mississippi Valley. The low will be occluding as it enters the region, so the warm sector influence will be minimal before the cold front sweeps through. Though with that, there will be some instability ahead of the frontal system. This will mainly be confined to the western half of the CWA and lower as the system progress eastward overnight. MUCAPE will be around 300-500 J/kg with decent bulk shear supported by a LLJ of 35-45 knots will allow for an environment conducive of producing small hail. SPC has put the western portion of the CWA within a marginal risk for severe weather, anchored by the hail threat. In addition to the severe threat, there will be a decent amount of QPF across the region. Currently, the forecast has a quarter to half inch of QPF from late Thursday night through Friday afternoon. Within thunderstorms, higher amounts of rainfall are possible. The severe weather threat should diminish early morning on Friday.

After frontal passage, the upper level trough will still be working through the Great Lakes throughout the day on Friday. Temperatures will still be warm, up into the low to mid 50s with westerly flow over the region, but there will be strong pressure gradient to go along with it. A LLJ of 40-50 knots will support gusty winds across the region Friday afternoon. Strongest winds, generally west of the I-71 corridor, will be 20-25 mph sustained with gusts around 40 mph. To the east, winds will be around 15-20 mph with gusts around 30 mph. Winds will begin to diminish late Friday evening as the upper level low moves off to the northeast.

KEY MESSAGE 3... As the low pressure system moves off to the east, flow across the region will shift to be out of the west to northwest bringing more seasonable temperatures to the region. An upper level trough will linger over the Great Lakes through the weekend and into early next week reinforcing the flow. Temperatures will drop down into the low 40s on Saturday before dropping more to be in the low to mid 30s Sunday into next week. Overnight lows will be in the 20s for that time period. Regardless, Saturday should stay dry until a low pressure system moves to the east up the eastern seaboard. Precipitation will return early Sunday morning in the form on snow showers as moisture is pulled across the Great Lakes region. Snow accumulation is likely, mainly in the eastern half of the CWA, though light amounts possible to the west. Accumulation is be dependent on how the low develops and tracks off to the east. The main player for snow accumulation will be with the lake enhanced snow showers within the snow belt that could develop with the wrap around moisture. It is likely that this will continue through Tuesday until ridging starts to build in and precipitation wanes.

AVIATION /06Z Thursday THROUGH Monday/

Lower forecast confidence in the 06Z TAFs this evening in terms of the stratus/fog development for the overnight period through Thursday morning. Also have shower potential moving into with likely two different waves, one during morning/afternoon hours, and a second one after 00Z Friday. In some cases, the showers could be moving into IFR or worse conditions for ceilings and visibilities, and thus, possibly improving conditions in rain. It is a complicated weather pattern with a stationary front in the vicinity, trapped moisture in a stubborn inversion, and convective shower potential. AMDs should be expected.

Outlook...Non VFR potential carries into Thursday night and Friday with a cold front passage, and then with low ceilings from lingering low pressure into the weekend.

MARINE

Colder air has returned over the lake with a stationary front now south of the lake this morning. This colder air has taken advantage of some added low level moisture, courtesy of the initial warm frontal passage on Wednesday, and dense fog has developed on the lake. This fog will last through the morning hours and a Marine Dense Fog Advisory has been issued through Noon. Outside of the fog, the lake should stay relatively steady state with light east flow and cooler temperatures over the lake for much of the day.

For Friday, a low pressure system will advance the stationary front north again with some oomph in a 45 kt low level jet and some warm advection once again to get temperatures into the 50s. This will allow for ice to continue to weaken across the lake and strong southwest winds around 25 to 30 kts will allow for movement of the ice fields. Any ice floes will be hazardous to folks on Lake Erie and may block or close established shipping channels. People are urged to stay off the Lake Erie.

The low pressure system will weaken over the region on Saturday and southwest flow will fall to around 10 to 15 kts. A strong low pressure system will move up the East Coast on Sunday into Monday and enhance the pressure gradient of the trough over the region, allowing for 15 to 20 kts of northwest flow on Sunday and Monday.

CLE WATCHES/WARNINGS/ADVISORIES

OH...Dense Fog Advisory until 9 AM EST this morning for OHZ003- 006>014-018>023-033-089. PA...Dense Fog Advisory until 9 AM EST this morning for PAZ001>003. MARINE...Dense Fog Advisory until noon EST today for LEZ142>149-162>169.