Plaincast

What has changed

Significant wildfire smoke is expected to continue through Friday, and this will keep high temperatures several degrees cooler than the previous forecast.

Messages

Wildfire smoke will produce poor air quality and reduce visibilities through Friday.

Periodic showers and thunderstorms are expected Friday afternoon through Saturday and again Tuesday into Wednesday. The storms Saturday afternoon and evening could be severe.

Very warm temperatures will persist through Saturday before cooler weather arrives Sunday through next week.

Discussion

KEY MESSAGE 1. Today has been an incredibly rare day across northern Ohio and Northwest PA as dense wildfire smoke continues to funnel across the region, originating from hundreds of active fires burning in NW Ontario Province. Mid afternoon visibilities are averaging 0.5 to 1 mile, with the worst visibilities near Lake Erie and across Northeast Ohio and Northwest PA. The mid/upper ridge currently elongated from the corn belt through the Tennessee Valley will remain largely in place through Friday to the west of mid/upper longwave troughing over eastern Canada and New England. The associated northwest flow aloft will keep the smoke plume funneling into our area through Friday. The latest the high-res rapid-refresh model smoke plume forecast shows similar conditions to today for much of Friday, so expect another day of poor visibilities and air quality. Additionally, the smoke kept temperatures a solid 5 degrees cooler than forecasted this afternoon, and expect a similar outcome Friday, so lowered high temperatures to generally be mid/upper 80s.

A warm front will lift across the region Friday evening through Friday night in response to a strong mid/upper shortwave progressing into the Upper Midwest and northern Great Lakes. This will turn the low-level flow southerly and start to scour out the smoke, so expect slow improvement Friday night.

KEY MESSAGE 2. A major pattern change will take place this weekend as the mid/upper longwave trough over eastern Canada and New England deepens into the Great Lakes and retrogrades the large mid/upper ridge back into the Plains and Intermountain West. This trough will be deepened in part by a strong shortwave dropping from the Upper Midwest and northern Great Lakes Friday night through the southern and eastern Great Lakes by Saturday night. This system will have plenty of dynamics when combined with the heat and humidity to support severe weather.

A quasi-stationary frontal boundary over the Ohio Valley Friday will retreat northeastward across the region Friday evening and Friday night in response to the approaching shortwave trough. This will usher the 70 plus degree dew points back into the area. Strong warm/moist/theta e advection on the nose of a 30 knot west-southwest low-level jet will generate scattered convection late Friday afternoon through Friday night from west to east along and ahead of the warm front, where isentropic ascent will be maximized. Generally do not expect severe weather with this round due to limited shear, but enough instability will be in place where a few stronger storms with gusty winds and small hail cannot be ruled out.

Any lingering showers should quickly move out Saturday morning as the region becomes entrenched in the warm sector. This will set up a hot and humid day and allow for at least moderate instability ahead of the shortwave and associated strong cold front. Depending on any lingering smoke or convective debris cloudiness, surface based storm energy could push 3000 J/Kg in the afternoon, and this combined with deep layer shear increasing to 30 to 35 knots will support organized severe convection. Timing wise, it looks like convective temperatures will be reached by 19Z to allow for scattered cells to begin developing, and then a broken line or QLCS could drop across Lake Erie and much of northern Ohio and NW PA during the evening ahead of the cold front. This timing and evolution is supported by the latest runs of the HREF and RRFS. The wind profile looks to be unidirectional, and with shear vectors oriented NW to SE (normal to the line of convection), there could be surges and bows to enhance the wind risk. Low-level SRH is unimpressive, but cannot rule out a brief spin up QLCS tornado given the potential for surges/bows in the line. The latest SWODY3 Slight Risk continues to look good, with the primary hazard being damaging winds.

Rapid drying is expected behind the front Saturday night, with dry conditions Sunday and Monday as Canadian high pressure builds across the Great Lakes. However, the mid/upper longwave trough over the eastern CONUS/Great Lakes will continue to deepen through mid week as a couple of shortwaves drop through it, and expect another cold frontal passage Tuesday into Wednesday. This will bring the next potential for showers and thunderstorms.