Area Forecast Discussion

WHAT HAS CHANGED

* No significant changes at this time.

KEY MESSAGES

1) Scattered to numerous severe thunderstorms are expected this afternoon through the evening hours today.

DISCUSSION

KEY MESSAGE 1: Scattered to numerous severe thunderstorms are expected this afternoon through the evening hours today.

We are in standby mode for now as the copious amount of energy/lift/strong upper level diffluent flow (associated with the left exit region of a 100+ KT jet) has produced an expansive area of weak convection embedded in light to moderate rain. All of this thick/debris cloud cover will prevent deep convection through the early afternoon, but pockets of fairly quick destabilization via breaks of sun should spread into western PA and remain over our far SE zones to trigger some deeper convection by or shortly after 18Z.

We'll be closely monitoring satellite trends and meso-B stability and shear fields to better hone in on areas under the gun for potential impact of fast-moving TSRA.

Previous Disc...

Thunderstorms are expected to develop ahead of an eastward- moving cold front across the Ohio Valley and along a pre- frontal trough crossing the CWA between roughly 2-9PM. No changes were made to the level 3/5 enhanced risk area from SPC for day 1 with swaths of damaging wind gusts remaining the primary hazard. Diurnal heating within cloud breaks, combined with upper 60s to lower 70s dewpoints, will support moderate surface-based instability across the broad pre-frontal warm sector. The most favorable overlap of this instability and 40-50 kt of effective shear is expected to foster a mix of organized clusters and supercells that should evolve and spread eastward through the day. Severe hail and a few tornadoes will also be possible with any sustained supercells. The enhanced level 3/5 risk favors a higher confidence/coverage in severe storms with a few significant severe storms possible reaching intensity levels (75+ mph wind gusts and/or EF-2 tornado) we may only experience 1x or 2x/year.

WPC has expanded the level 2/4 excessive rainfall outlook to cover the majority of the CWA. However, despite plenty of juice and high PWATs supportive of locally intense rain rates, overall confidence is low/limited by the lack of a hires model signal and relatively fast/progressive storm motions. Opted to pass on a FF watch for this cycle and allow the dayshift to reassess or issue a more short-fused/targeted watch.

Rain showers linger tonight into Wednesday particularly downwind of Lake Erie and over the higher elevations, but for the most part we anticipate a multi-day drying trend with near to slightly below normal temps and comfortably low humidity from midweek into the last weekend of July.

AVIATION /00Z WEDNESDAY THROUGH SUNDAY/

Current SHRA/TSRA stationed just west of BFD could continue to maintain itself over the next hour or two before running into a layer of more stable air and generally go onto a weakening trend. Current forecast outlines no TSRA mentions throughout the 00Z TAF package; however, VCTS could be possible at BFD through 01Z. The bulk of lightning activity is expected to be south of the airfield; however, so no mentions. SHRA mentions retained further east at UNV/IPT where this complex could sustain itself and bring lower ceilings/visibilities but generally not below IFR thresholds. Secondary complex of SHRA is expected at MDT/LNS brining SHRA and lower ceilings/visibilities with MVFR likely the worst-case scenario at this time.

Overnight, HREF/GLAMP guidance outlines lower ceilings and visibilities most likely across the western terminals (BFD/JST) so have continued to outline this potential in the updated forecast package. Elsewhere, guidance paints a more optimistic picture for flying conditions compared to the 18Z TAF package, likely due precipitation not being as widespread as originally forecast. Some pockets of MVFR/IFR will be possible at UNV/IPT as well; however, will mainly be based on precipitation reaching the airfield and a slight decrease in winds so this remains a lower confidence solution at this time. Gradual improvement of the western airfields is expected after sunrise, with widespread VFR conditions expected to prevail in the 14-16Z Wednesday timeframe with high (~70-80%) confidence. These conditions are likely (~80-90%) confidence to continue after prevailing through the end of the 00Z TAF package.

Outlook...

Thu-Fri...Some potential for valley fog across NW PA Friday morning; otherwise, VFR conditions expected.

Sat...Generally VFR conditions with low-end (< 20%) chance of an afternoon shower/storm across SW PA.

Sun...Increasing chances of PM showers/storms, with some restrictions possible.

CTP WATCHES / WARNINGS / ADVISORIES

None.