Marine Weather and Tide Forecast for Bethel Park, PA

NEAR TERM /UNTIL 6 AM SATURDAY MORNING/
KEY MESSAGES:

- Convoluted environment today will maintain low-moderate confidence in the presence of storms, but a higher confidence in severe potential given initiation.
- A decaying MCS in possible tonight somewhere in the Appalachians, but confidence in location is low.

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.. 3:20pm Update ..

The tornado risk has increased slightly in the watch as dry air filters into the southern side of the northeast moving convection, heightening the curvature in the wind profile in the lowest 2 km of the storms as winds aloft blow from east west to east while surface winds orient more south to north. Helicity is maximized in right moving (west to east) cells on the backside of the line.

Previous Discussion

The lack of overnight storms south of I-80 completely changes the severe forecast for today. Given CAM guidance before 12Z showed a worked over environment across the area, it poorly represents current conditions. So the forecast will heavily rely on initialization at and after 12Z.

Given a look at the current wind field and satellite, there is some indication of a convergence zone in to low levels settling in across southwest PA, eastern OH, and the northern WV panhandle. In addition, there is a residual outflow boundary from overnight convection in the I-80 corridor.

If an area was favored for convection, it would be along an east-west axis passing near the Pittsburgh area. Looking at the 12 sounding showing ~1400 MLCAPE and ~900 DCAPE, the atmosphere would be primed for severe convection, particularly if updrafts drive into and wet-bulb the 6km to 12km later. But recent cirrus overspread has complicated just exactly how intense these updrafts may become. Any intense updrafts in a high DCAPE environment would have a primary risk of damaging winds and hail. There is a chance the DCAPE is lower later in the day, though this would rely on upstream convection to contaminate the environment, which is still of moderate uncertainty.

After initiation, one would expect the primary storm motion to be to the northeast as outflow combined with synoptic wind. If there is an area to watch for flooding, it would be on the south side of convection, where outflow would be fighting the synoptic wind field, resulting in training. This remains lower probability.

Uncertainty snowballs tonight as convection will rely on two factors: 1) Where and if the environment has been tainted by daytime convection. 2) Where storms fire upstream during the day today. If todays storms put do an outflow, it is very likely overnight convection stays south of it. This boundary will be important in distinguishing the threat as scenarios range everywhere from no outflow to outflow far south of the area. The farther north and/or a lack of an outflow means higher severe chances tonight. Second, there is initiation today. The farther north storms in the northern Ohio Valley initiate today, the higher the chance our region is impacted by a progressive, decaying MCS. With both of these factors together, the best chances of severe tonight increases the farther south of Pittsburgh you go.

SHORT TERM /6 AM SATURDAY MORNING THROUGH SATURDAY NIGHT/
KEY MESSAGES:

- A cold front will cross the area, bringing gusty winds and a cooldown.

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Irrespective of prior weather, there is high confidence of a cold frontal passage in the late morning and early afternoon.
With this and the upper low pulling across the northern Great Lakes. This will pack the pressure gradient. Pre-frontally, there is some indication that there may be a shallow cap as a bit of pre-frontal warm advection rides up the axis of the front. Should this exist, winds will not start the day gusty.
Should this be absent, gusts of 30-40 mph may develop in the morning.

Into the afternoon, winds are expected to peak along the cold front. Gusts could be heightened in showers/storms along the front, mostly in the 40-50mph range, but the chance of severe could not be ruled out completely. After the cold front, low level cold-advection settles in, destabilizing profiles with the potential to mix into 40kt 850mb winds. Winds behind the front will be more likely than ahead of the front.

With daytime gusts a bit higher in the ridges of eastern Tucker County, a wind advisory is in effect from 10am Saturday to 2am Sunday, where gusts up to 50mph are possible. Winds die down a bit overnight with decoupling

LONG TERM /SUNDAY THROUGH FRIDAY/
KEY MESSAGES:

- Cooler and drier pattern returns Sunday through Tuesday.
- Precipitation chances return Tuesday into Wednesday with another low pressure system - Potential for heavy rain mid-week that warrants monitoring -------------------------------------------------------------------

Models have been consistent that troughing over the Great Lakes and northeast CONUS will maintain northwest flow over the local area Sunday into Monday, keeping temperatures seasonable and the weather dry through that time.

Probability of precipitation increases again late Tuesday into Wednesday with a new low ejecting out of the Rockies and tracking east across the Plains. A few model scenarios note a stationary boundary straddling south of Pittsburgh with this passing low. If that scenario plays out, heavy rain could pose a threat for portions of the region around mid-week.

AVIATION /19Z FRIDAY THROUGH WEDNESDAY/
A tough and uncertain forecast lies ahead. At this time it looks likely that much of the TAF period can be VFR. The possible interruptions to this are two separate periods of thunderstorms: one this afternoon and another during the overnight hours.

Latest satellite shows a broad expanse of cirrus overspreading the region originating from convection to our south. This cirrus will act to limit heating across the southern portion of our region and could mitigate some risk to see thunderstorms fire near MGW/ZZV/HLG.
Farther north along a BVI/IDI line there remains a boundary left over from last nights convection, which will likely be the focus for afternoon convection. This boundary has shuffled southward through the day and poses a low threat to allow thunderstorms near PIT/AGC/LBE, this has been included as a PROB30 through the afternoon. BVI/FKL/DUJ have a slightly higher chance to see thunderstorms this afternoon. Any of these storms can bring gusty winds, and briefly lower VIS and CIG.

Storms overnight remain more uncertain as the complex that they are associated with has not yet formed in the MO/IL region. This complex is expected to move NE'ward towards us but models diverge on the exact track as some favor a dive southward along the CAPE gradient and some favor somewhat of a split where storms miss much of our region. At this time I have moved our TEMPO groups back to PROB30 for the overnight period with growing uncertainty in track. A period of MVFR showers may trail behind any MCS-like system tonight.

Outlook... Patchy restrictions in scattered showers are expected Saturday and Saturday night under a crossing upper trough. VFR returns Monday under high pressure. Restriction and rain potential returns with a Tuesday warm front.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...Wind Advisory from 10 AM Saturday to 2 AM EDT Sunday for WVZ514.