Pittsburgh forecast discussion

What Has Changed

Marginal Risk for severe storms today includes most of western PA and northern WV. Probabilities for advisory level wind gusts (outside of convection) have also decreased. No other significant changes at this time.

Key Messages

frost possible again Sunday night

3) Dry and warmer next week

Discussion

KEY MESSAGE 1... Showers and isolated thunderstorms in warm advection will continue to cross the area this morning. Elevated instability and a low level jet should also enhance some of this activity until just before sunrise.

A digging upper trough is expected to advance out of the Midwest today, as a deepening surface low tracks across Southern Ontario to New England. The low will pull a strong cold front across the area from mid morning into the afternoon. Increasing flow with a jet aloft will result in increasing shear, with building instability east of the front. Enough heating/instability for strong storms appear unlikely for much of Ohio, with an earlier FROPA. Further to the east, building instability and the shear should result in a potential for storms to produce damaging wind gusts as the front crosses. Winds at 10kft are progged to be around 60kt at the time of FROPA across wrn PA, with around 50 kt further to the south.

There is a potential for damaging winds as a line of showers and embedded thunderstorms develops along the front later this morning into the afternoon. There is some veering in the lower levels, with some limited potential for brief rotation should parameters briefly align, though the main threat should be from damaging wind gusts. Gusty winds are also expected outside of any convection, with a tight pressure gradient and mixing. Probabilities of advisory level gusts have decreases according to the latest model data and BUFKIT momentum transfer procedures. Still, gusts from 30 to 35 mph will be likely thorough tonight, with gusts around 40 mph across the higher terrain. The highest elevations of eastern Tucker county could see gusts around 45 mph, but held off on a wind advisory at this time with the recent downward trend in expected wind gusts.

The front should exit to the east by 4-5 PM, ending the severe storm potential. The deepening upper trough is then progged to track across the Upper Ohio Valley region later today into tonight, with some lake enhancement also possible as cold advection occurs. The precipitation should be tapering off by the time the coldest air arrives Saturday morning, so other than a potential for a few snowflakes mixing in north of I-80 and in the ridges, no snow is expected.

KEY MESSAGE 2... The upper trough should exit the East Coast by late Saturday/Saturday night, as a low deepens/closes off the Carolina coast. Surface high pressure is expected to build across the Upper Ohio Valley region, with light wind and mainly clear skies. This should result in efficient radiational cooling, with a frost/freeze potential across the area. Frost advisories/freeze warnings may be needed. Some frost will be possible again Sunday night with surface high pressure overhead.

KEY MESSAGE 3... Model ensembles indicate the closed low/trough should persist off of the SE Coast, with another trough over the Western CONUS. Areas from the Midwest to the Upper Ohio Valley region should be under a ridge, with dry weather expected from Sunday into late next week. Temperatures are also expected to moderate back to near or just above seasonable levels by mid week.

Aviation /06Z Friday Through Tuesday/

Scattered showers continue to develop in warm advection, and under a low level jet. A thunderstorm is also possible with elevated instability in place, though the probability was too low to include in any TAF sites.

Improvement to VFR is expected as the warm front moves north, and the wind veers from SE to SW. Strong surface low pressure is expected to track across southern Ontario to New England today, pulling a strong cold front across the region. A line of showers is expected to develop this morning as the front moves across Ohio. Building shear and instability should result in the line intensifying as it moves east later this morning into the afternoon. Damaging wind gusts are possible in some of the stronger showers/storms that are able to mix down some of the strong wind aloft (10kft wind from 50-60kt.) Included a TEMPO mention for thunder east of a ZZV-PHD line as FROPA occurs. Cold advection and a crossing upper trough should maintain showers across the area into tonight, with MVFR cigs expected. Gusty SW wind this morning should shift to the WNW after FROPA, with gusts from 20-30kt.

Outlook... Rain showers and MVFR cigs should continue into Friday night as the upper trough crosses, and some lake enhancement occurs. VFR and diminishing wind is expected Saturday under building high pressure. VFR should then continue under the high through at least the middle of next week.

Pbz Watches/Warnings/Advisories

PA...None. OH...None. WV...None.

DISCUSSION...WM AVIATION...WM