textproduct: Pittsburgh

SYNOPSIS

Upper ridging and surface high pressure keep the weather dry through the weekend as temperatures rise through Sunday. A stalled boundary provides an unsettled pattern next week with daily rain chances and temperatures returning back towards normal.

NEAR TERM /THROUGH TONIGHT/

KEY MESSAGES:

- Isolated showers and thunderstorms possible mainly north of I-80 late this afternoon. - Quiet overnight with low temperatures trending warmer than the past few nights. ---------------------------------------------------------------

Temperatures have crept into the mid to upper 80s across most of the region this afternoon under building high pressure. Expect to tack on a few more degrees over the next few hours, with high topping out in the upper 80s and low 90s.

Meanwhile, a scattered diurnal cu field will continue to percolate through the afternoon, with the latest visible satellite imagery already showing a few showers forming along the lake breeze in far northwest PA. The vast majority of the area will remain dry and mostly sunny, though can't rule out a stray shower or rumble of thunder north of I-80 through this evening (~20 percent chance). Convection wanes and the cu field dissipates after sunset with the loss of daytime heating. Quiet weather is expected overnight with low temperatures remaining in the mid to upper 60s, a few degrees above seasonal norms.

SHORT TERM /SUNDAY THROUGH MONDAY NIGHT/

KEY MESSAGES:

- Building heat through Sunday and Monday. - Showers and storms return Monday. ----------------------------------------------------------------

Ridging will start to break down and turn flatter on Sunday in response to an approaching trough from the Great Lakes. Stronger warm and moist advection will ensue as southerly low level flow strengthens a bit which will also mitigate a lake breeze and keep the day dry across the board. Plenty of subsidence and a dry atmosphere will allow for efficient solar insolation, and it will be hot with an 80-90+% chance of highs reaching 90 in the lowlands and a 60-70% chance in the ridges. Combined with increased dew points in the mid to upper 60s, heat indices will top out in the upper 90s. Heat Advisory criteria doesn't appear to be reached, but that doesn't mean that heat impacts are null as the Heat Risk jumps up to major category with compounding days of 90s heat indices and low temperatures only in the 60s and low 70s. Those especially susceptible to heat-related effects should take proper precautions.

Clouds increase subtly overnight Sunday as lows continue to hold quite warm up into the low 70s for most. Warm overnight temperatures will provide little break from the heat and continue Major Heat Risk into Monday.

The upper trough arrives across the region Monday and brings with it a weak cold front draping south from a low pressure system expected to track across southern Canada. Continued warm air advection looks to give us another shot at 90 degrees across much of the region (50- 80% south of I-80). Modest shower coverage may occur in the morning helped along by weak convergence, but more widespread coverage of showers and thunderstorms is expected in the afternoon with diurnal heating trends.

Shear looks rather weak overall with model soundings indicating not more than 15-20 knots deep layer. This could hurt our chances to see deep organized convection but support a heavy rain threat. Column moisture increases and spurs our PWATs up towards 1.5" with light cloud bearing layer wind and slow downshear vectors oriented parallel to the boundary which all suggests a potential flooding threat as slow moving thunderstorms grow upscale along the front. Ensemble probabilities for >1" of rain remain very low at this time, but that's likely to change once we get the hi res guidance in. Our entire region is currently in a Marginal Risk (1/4) of excessive rainfall from WPC.

LONG TERM /TUESDAY THROUGH SATURDAY/

KEY MESSAGES:

- Unsettled pattern next week with daily rain chances along a stalled boundary. - Temperatures right around normal. -------------------------------------------------------------------

The boundary is expected to stall somewhere south and east of Pittsburgh on Tuesday keeping rain chances in the forecast well into next week, highest south of Pittsburgh in proximity to the boundary. Behind it, temperatures will moderate some as we move into midweek and are expected to fall back to near normal for the remainder of the forecast period.

Just how far south the front stalls is dependent on how deep the parent trough is, but for now ensembles peg it somewhere near the WV ridges. The highest coverage and probability of precip will be in the afternoon and evening coincident with diurnal trends, highest south and east of Pittsburgh. Deep layer moisture will remain elevated with ensemble PWAT values between 1.25-1.5", so any showers and storms will likely be efficient rainfall producers. A developing surface low across the Ohio Valley looks to drag the boundary back north late this week continuing the unsettled pattern and increasing rain chances back across more of the area.

AVIATION /18Z SATURDAY THROUGH WEDNESDAY/

High confidence of prevailing VFR conditions at all terminals through the TAF period. An ongoing diurnal cu field with cigs around 5-7kft AGL will continue to percolate through the afternoon. Already seeing a few showers forming along a lake front in far northwest PA, but latest hi-res guidance suggests low probabilities for impacts at FKL/DUJ due to very isolated coverage and uncertainty regarding how far inland they advance before dissipating. Therefore, opted to remove PROB30s from those terminals since probabilities are closer to 20% or lower. Elsewhere, mostly sunny skies and light winds prevail with high confidence.

Outlook... VFR conditions and dry weather are forecast through Sunday. Daily thunderstorm chances (and associated restrictions) return Monday through next week, likely following a diurnal pattern with peak probabilities occurring each afternoon and evening.

PBZ WATCHES/WARNINGS/ADVISORIES

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