Timberline Mountain

Summary

SYNOPSIS

... Seasonable warm weather is expected through Wednesday before the first in a series of upper level disturbances promote periods of showers and thunderstorms. Severe potential appears highest Wednesday afternoon and evening, though impacts can't be ruled out through the weekend.

NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES:

- Well-above normal temperatures into the overnight. _____________________________________________________________

Broad eastern CONUS ridging and surface high pressure will continue to promote well above normal temperature this evening. Diurnal heating through the day and orographic assist was lacking this evening in the ability to produce convection across the area. Thus, pops were removed for the evening.

Increasing cirrus overnight ahead of an upper shortwave and its associated nocturnal convection should further buoy overnight temperature. Low readings are likely to be 15 degrees above the daily average and could approach record values for high minimum temperature (Zanesville/New Philadelphia/Wheeling favored).

SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... KEY MESSAGES:

- Strong to severe thunderstorms possible Wednesday afternoon into Thursday morning. - Damaging wind is the primary threat, while tornadic threat favors northwest PA. - Showers and thunderstorms are likely to continue ahead of a cold front Thursday. _____________________________________________________________

Shortwave movement ahead of the main trough axis will push a decaying line of showers and thunderstorms towards the region Wednesday morning. The stable airmass should prevent this convection from continuing/maintaining east, but its residual outflow boundary appears to be the key for afternoon convective initiation within an increasingly unstable environment (upper level shortwave associated with this convection will weaken and result in less convective support). Mean SBCAPE values between 1250-2000 J/kg combined with 25-30kts shear offer heightened probabilities for damaging wind and large hail; a smaller corridor of enhanced low-level helicity around NW PA could also favor isolated tornado development. This appears to be a "if storm initiation can occur" severe threat environment where convection won't be widespread through the early evening hours as the main upper trough remains too far west.

Overall convection coverage is likely to increase overnight into Thursday morning as a more well-defined upper trough lifts through the Great Lakes and pushes a surface cold front eastward. Though surface based instability will wane with the loss of heating, increased shear with residual elevated instability could maintain the damaging wind and hail threat during this period. As the upper trough lifts NE Thursday morning, the surface boundary will stall in a WSW-ENE orientation through the middle of the forecast area; this residual boundary combined with afternoon heating should favor additional thunderstorms south of the boundary until the front drops south of the area Thursday night with additional shortwave movement.

Though forward prorogation of storms and lack of stronger forcing should limit flooding hazards, elevated PWAT values and potential for some training during the day Thursday (as the boundary becomes more parallel to the upper flow) could lead to localized flooding.

LONG TERM /FRIDAY THROUGH TUESDAY/... KEY MESSAGES:

- Variability remains high on long term forecast and may be predicated on prior day's convective outcomes. - Overall, periodic showers and thunderstorms with slightly above normal temperature is favored through the holiday weekend. ____________________________________________________________

Ensembles favor high pressure north of the region establishing more seasonable and dry weather to at least start the day Friday in the wake of Thursday's shortwave passage. However, global models suggest the potential for a weak shortwave to lift northeast out of the TN River Valley through Friday evening to promote showers and thunderstorms. Either way, the overall pattern will usher additional rounds of shortwave crossings through the Upper Ohio River Valley as it remains in between broad ridging over the SE CONUS and troughing over the northern Great Plains. Expect periods of showers and thunderstorms with near to slightly above normal temperature, with potential for severe hazards depending on evolution of prior day's convection.