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FXUS61 KPBZ 041813 AFDPBZ

Area Forecast Discussion National Weather Service Pittsburgh PA 213 PM EDT Sat May 4 2024

SYNOPSIS
Intermittent rain and a few storms are possible through the weekend. With clouds and rain, temperatures will be cooler today, but will rebound Sunday as a southerly flow returns. A brief break in the rain is possible Monday.

NEAR TERM /THROUGH TONIGHT/
KEY MESSAGES:

- Showers slowly move across the area, thunderstorms in the afternoon.
- Cooler temperatures today.
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East coast ridge will move very little today and amplify this morning in response to trough digging into the northern Plains.
We will continue to rest on the western side of the ridge where a shortwave will drift northward throughout the day.

Deep moisture will flow northward on the backside of the ridge axis keeping in plenty of clouds and the risk for showers all day. An increasing southeasterly flow at the surface will pump Atlantic moisture into the region aiding in the shower development. For the most part, rainfall should be on the light side. There are some deterministic models today that suggest a 1.40 PWAT leading to the 99th percentile in dealing with climo PWATs. That said, the NBM only gives roughly 20% probability of > 0.75 inches from 8am this morning through 2am tonight. Thus, it will depend on where thunderstorms develop. Clouds, showers and a cool easterly flow will keep temperatures slightly below normal today.

Expect thunderstorms to dissipate by this evening but the shower potential is expected to persist through tonight. This will keep warmer temps around for the low.

SHORT TERM /SUNDAY THROUGH MONDAY/
KEY MESSAGES:

- Unsettled pattern remains with rain chances continuing on Sunday. Thunder possible on Sunday.
- Temperatures push back above normal Sunday and Monday.

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East coast ridge will flatten and drift eastward on Sunday. The shortwaves riding northward on the western flank of the ridge will also shift to the east. Shower coverage looks to dissipate Sunday morning. A weak cold front will slowly cross Ohio Sunday. Models are hinting that scattered storms could develop ahead of the front Sunday afternoon. The air mass during the afternoon is certainly conditional and with any breaks in cloud cover or WAA at the surface will be enough for convective development. In fact, PWATS another day being in the 1.20 to 1.40 range with skinny CAPE will make for a heavy rainfall threat. However, there are some dry layers in the model soundings with DCAPE values between 400 J/Kg and 600J/Kg may lead to a few strong storms with downburst potential. Temperatures will warm on Sunday as the low-level flow veers to the southwest ahead of the front which may be enough to kick start the event tomorrow afternoon.

Ensembles have been consistent in showing a shortwave trough over the Middle Ohio Valley approaching, but weakening, on Monday as it interacts with a weak ridge over our region. A south-to-north gradient in PoP values still seems appropriate for the Monday/Monday night period. The pattern does continue to coincide with development each day with day time heating.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/
KEY MESSAGES:

- Rain chances continue next week but more uncertainty lends to lower confidence.
- Temperatures favored to remain above normal.
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Uncertainty still reigns after Monday. Most guidance depicts a ridge centered over the Great Lakes at 12Z Tuesday, along with a deep closed upper low in or near the Dakotas. The upper low appears likely to fill during the midweek period, and as it does so, shortwaves rotating around it appear to flatten out the ridge as it moves across the Upper Ohio Valley, finally eroding it almost completely in the northeast CONUS. Some strength and timing issues remain with the details of this process, which in turn could impact precipitation amounts and timing.

Nevertheless, a warm front is likely to cross on Tuesday as the ridge progresses eastward. This will lead to the persistence of a warm and moist airmass, with precipitable water values at or above the 90th percentile in the climatology. Along with the previously mentioned shortwave activity, this will keep an active weather pattern in place for our region, with decent daily precipitation chances through Friday. Deep-layer shear will increase as well behind the departing ridge, so severe weather chances will need to be monitored as well. According to CSU machine-learning guidance and NBM CWASP probabilities, Wednesday and Thursday may be the days to watch.

Rain chances then continue to show additional activity on Friday with the post frontal trough passing across the area.
There is little confidence on this occurrence though.

AVIATION /18Z SATURDAY THROUGH THURSDAY/
Shower coverage will continue to increase through the afternoon as a shortwave rides up the back side of a ridge just east of our region, and as diurnal heating peaks. MVFR ceilings will dominate this afternoon for the most part, with brief drops to IFR visibility possible in the heavier showers. Instability is best to the south and west of PIT; thus, thunder chances were confined to the ZZV/HLG/MGW TAFs for now.

Any threat of thunder will end with sunset, but fairly widespread shower activity is forecast to continue well into the night. Southeast wind will continue as well and may gust up to 20 knots in some cases, particularly along west-facing slopes near LBE. Ceiling restrictions will continue, with widespread IFR/low MVFR ceilings forecast. Patchy drizzle/mist can also be expected between any more sustained rain showers. Modest improvement is expected after 12Z, but restrictions will continue.

Outlook
Restriction ease a bit Sunday afternoon, but thunderstorm potential builds during the afternoon and evening. Periodic restrictions may continue through early next week as multiple disturbances pass through the region.

PBZ WATCHES/WARNINGS/ADVISORIES
PA...None.
OH...None.
WV...None.

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