textproduct: Cleveland

WHAT HAS CHANGED

Rain showers have trended more widespread this morning.

KEY MESSAGES

1) Warm, humid, and unsettled with periodic showers and thunderstorms through Saturday.

2) Strong to severe thunderstorms are possible Sunday night and Monday then turning progressively cooler and less humid the rest of the week.

DISCUSSION

KEY MESSAGE 1...

An active pattern will remain in place through the weekend due to broad WNW mid/upper flow across the Great Lakes between a broad trough over south central Canada and a broad ridge over the Desert Southwest and southern Plains. Multiple weak mid/upper shortwaves and associated surface waves emanating out of the broad trough will progress through the WNW flow and interact with a wavering quasi-stationary frontal boundary between the Ohio Valley and southern Great Lakes. This will support periods of convection given a seasonably warm and moist environment that will remain in place.

Starting off this morning, one weak mid/upper shortwave is progressing slowly east across northern Ohio. RAP analysis shows a weak surface reflection beneath an area of upper diffluence and mid- level PVA, and this is encouraging broad isentropic ascent and focusing warm air advection near the frontal boundary. As a result, rain has blossomed in coverage the past few hours, with enough elevated instability for embedded convection as well. Expect this area of rain and embedded thunder to continue slowly moving east across northern Ohio early this morning, reaching NW PA by about 11Z. Heavy downpours will occur within any convection in this moist environment (PWATs near 2 inches), but progressive movement should limit any flooding concerns.

Behind this morning's shortwave, the front will stall west-east across the CWA, but confidence is low on exactly how far south it will push since another shortwave and an associated weak surface low will be approaching for tonight. The presence of the boundary overhead, diurnal heating, and the abundant low-level moisture will support another round of scattered convection this afternoon and evening, but confidence is low on coverage and location since this morning's rain and thunder trended higher in coverage. Lingering clouds and showers through late this morning may limit diurnal heating and keep instability a little weaker for the afternoon. Nevertheless, expect at least some afternoon thunderstorms, and the lake breeze boundary as well as differential heating boundaries farther inland may serve as initiation points depending on the exact location of the synoptic front. Locally heavy rainfall possible once again wherever any storms can develop.

The next aforementioned mid/upper shortwave looks to progress east across the southern Great Lakes and Upper Ohio Valley tonight. This will once again have decent mid-level PVA and upper diffluence, and with weak instability persisting overnight again, expect showers and embedded convection throughout the night to be quite widespread in coverage. In fact, coverage tonight may be greater than this afternoon due to the forcing moving overhead. A trailing cold front behind this wave looks to move through Saturday afternoon and overtake the old frontal boundary, effectively pushing everything south for a brief period Saturday night and Sunday, but before that happens, one last round of scattered convection is expected ahead of the front Saturday. Coverage will again be dependent on the amount of instability after the overnight/early morning activity. Areas that see the most frequent convection between this morning and Saturday evening could experience flooding of low-lying, poor drainage, and urban areas, as well as rises on area rivers and streams since the environment will be conducive to heavy rainfall rates (high freezing levels, deep warm cloud layer, PWATs near 2 inches, and tall, skinny CAPE).

KEY MESSAGE 2...

Weak high pressure will briefly bring dry and less humid conditions Saturday night and Sunday, but the front will retreat back north as a warm front Sunday night as the high drifts east ahead of a potent mid/upper shortwave dropping into the Upper Midwest. Scattered convection is possible in the warm air advection near the retreating front, but there will also be an MCS ongoing upstream over the western Great Lakes driven by a 35-40 knot low- level jet and strong warm/moist advection. If this MCS can survive into our region, then damaging winds and heavy rain are possible late Sunday night. The best chance for this would be in NW and north central Ohio and the western half of Lake Erie before it outruns the best support and instability.

The strong shortwave will cross the central Great Lakes Monday, with a trailing cold front dropping across the region by Monday night. Mid-level flow increasing to 40-50+ knots as the shortwave passes will support over 40 knots of deep layer effective shear, so depending on how overnight convection plays out in terms of clouds and outflow boundaries, additional severe convection is possible Monday afternoon and evening, possibly in the form of an organized MCS give a WNW shear vector orientation perpendicular to the convection. If such a system materializes, then all modes of severe weather would be possible, with wind being the biggest hazard in addition to heavy rainfall. There is high bust potential with Monday's forecast since as said, it all hinges on how much lingers from Sunday night. If widespread convection Sunday night leaves abundant cloud cover, showers, and outflow boundaries, then the new convection will develop outside of our area. However, the ceiling is high Monday if sufficient instability can build. Stay tuned for more updates.

The broad trough over southern Canada will slowly deepen into the Great Lakes and Northeast U.S. aided by a series of shortwaves Monday night through the end of the week. This will bring progressively cooler and less humid conditions from Monday night onward as the frontal boundary slowly pushes south of the area, with periodic showers given the broad cyclonic flow and shortwave passages. Highs will be in the 70s by the second half of the week, with 50s at night.

AVIATION /12Z Friday THROUGH Tuesday/

A stationary boundary bisects the state of Ohio from KCLE to KCVG with shower and thunderstorm activity running parallel along the front moving southwest to northeast. Some embedded thunder exists with some of the heavier rain showers, which may try to move into the KCAK and KYNG terminals over the next couple of hours. Otherwise, rain from KCLE to K10G will continue east and bring a mix of MVFR to IFR across Northeast Ohio and Northwest PA through the rest of the morning. There may be a slight reprieve in the shower activity with a stabilizing atmosphere behind the showers. However, with just a little bit of a break and some movement in this boundary along with a slight lake breeze, there should be more shower and storm activity that develops across Northeast Ohio and Northwest PA this afternoon. Coverage with any convection this afternoon will be isolated to scattered at best, which gives low confidence in terminal impacts, adding to the conditional formation threat.

There should be another break in shower and storm activity across the airspace in the evening but remnant shower and embedded TS activity will try to enter later in the evening into the overnight. Low confidence on the coverage of activity that makes it into the area tonight but there is a non-zero chance of non- VFR impacts to terminals, just too low of certainty to put into a TAF. Will throw in some PROB30s for TS to highlight a possible window.

Winds are variable with the line of showers and storms moving through Northeast Ohio. There have been brief instances of winds shifting to the north to northeast. Overall, winds should eventually settle into a general southerly direction and become more southwest through the evening into tonight.

Outlook...Scattered showers and thunderstorms expected Saturday, Monday, and Tuesday and may bring some intermittent non-VFR to the terminals.

MARINE

The warm sector south to southwest flow will continue over the next 36 hours or so across the lake as low pressure over the Hudson Bay will extend a cold front across the Great Lakes region. Some shower and storm activity will be in the area of the lake today and tomorrow with good moisture across the region. The cold front will cross the lake on Saturday night and allow for a brief period of elevated northwest, onshore flow. Winds are unlikely to be strong enough to allow for waves to immediately build and a surface ridge will be quick to enter on Sunday to flip winds to the south again. Another weak low will move through the Great Lakes region on Monday and Tuesday allowing for southwest to west flow over the lake and shower and storm activity. Overall, with mostly offshore flow expected through the forecast period, marine headlines are not expected at this time.

CLE WATCHES/WARNINGS/ADVISORIES

OH...None. PA...None. MARINE...None.