Area Forecast Discussion
Issued by NWS Pittsburgh, PA
Issued by NWS Pittsburgh, PA
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261 FXUS61 KPBZ 191812 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 212 PM EDT Thu Sep 19 2024 .SYNOPSIS... Mostly dry weather and above-normal temperatures will continue through Friday. Chances of showers and storms return Saturday, followed by higher chances early next week. && .NEAR TERM /THROUGH TONIGHT/... KEY MESSAGES: - Scattered showers/storms in northern WV ending this evening. - Mostly clear tonight, with patchy fog development overnight. ------------------------------------------------------------------- The main trough along the Atlantic Coast will continue to pull slowly eastward through tonight. Generally drier air has worked mainly into areas near and north of I-70, resulting in a mostly sunny day. To the south, more numerous cumulus have managed to bloom in an environment with 1000-1500 J/kg of surface-based CAPE. Subsidence is working against convective development here as well, but isolated/scattered showers, and perhaps a thunderstorm, will continue to be possible through the afternoon mainly south of the Mason-Dixon Line and where orographic forcing is in play. The pattern transitions to one of transient ridging starting tonight. Cumulus and any showers will quickly collapse by this evening, leaving a mostly clear and calm pattern tonight. Patchy radiation fog is expected overnight with the lingering moisture, most likely in river valleys, as temperatures remain a few degrees above climatology. && .SHORT TERM /FRIDAY THROUGH SATURDAY NIGHT/... KEY MESSAGES: - Dry and quite warm Friday. - Shower and storm chances areawide on Saturday. A few of the storms could be strong. --------------------------------------------------------------------- Friday will feature dry weather and quite warm temperatures as transient ridging passes over the region. Plenty of sunshine and high temperatures of 10 to 15 degrees above seasonal norms can be expected. There continues to be a bit better confidence in shortwave energy riding over the top of the ridge, crossing the Great Lakes Friday night and the Upper Ohio Valley on Saturday. An increase to around 1.4 inch precipitable water values is noted, and lift will be provided by the shortwave, and potentially left exit region dynamics from a 250mb jet dropping from the Upper Midwest. So, PoPs in the chance range certainly appear appropriate at this stage. The main question then becomes the potential for strong convection. The NBM has a 40-60% potential for 1000 J/kg of surface-based CAPE during the afternoon on Saturday over a good portion of the area. 0-6km bulk shear of 30-35 knots is also possible despite weak low-level flow, as is 700-800 J/kg of DCAPE. If these ingredients can come together at a favorable time, then a low- end threat of damaging wind gusts and perhaps hail could be realized in the stronger storms. However, there remains some timing uncertainty regarding cloud cover/precip arrival (which would impact potential SBCAPE levels), and some model soundings also point to large amounts of dry air aloft that could hinder updraft development. The potential bears watching, but the threat level remains fairly low for now. Rain chances taper off Saturday evening as the wave passes to the east, and as subsidence and drier air settle into the region. Patchy fog will remain possible yet again, particularly if rain does occur. && .LONG TERM /SUNDAY THROUGH THURSDAY/... KEY MESSAGES: - Dry and warm Sunday. - Rain chances increase starting early next week, with temperatures moderating closer to seasonable levels. ------------------------------------------------------------------- Most model scenarios show a brief return to ridging on Sunday, lending high confidence to a forecast of dry weather and quite warm temperatures. Values pushing 90 degrees cannot be ruled out in eastern Ohio (10-30% chance according to the NBM). Uncertainty starts to increase markedly thereafter. There continues to be disagreement regarding how quickly the ridge axis gets pushed east Monday into Tuesday, which has implications for the start time for increasing PoPs. From here, although there is a wide discrepancy with detail regarding individual waves, there is still at least medium confidence in a midwestern trough setup, which could lead to increased moisture flow and precipitation chances during the mid- week period - which could have a positive impact on the ongoing drought. With the increased potential for clouds and rain, temperatures will likely show less of a diurnal range than is typical for late September, with climatologic maximums and above- normal minimums. && .AVIATION /18Z THURSDAY THROUGH TUESDAY/... Lingering CU is expected to dissipate from north to south through the late evening with increase mid-level subsidence. Winds will continue to remain light to variable from the north/northeast. Patchy early morning fog is possible Friday, especially for FKL/DUJ, with radiational cooling and light wind. Otherwise, VFR is expected Friday under high pressure. .Outlook... Low chances for restrictions in thunderstorms are possible Saturday with a crossing shortwave trough. VFR returns Sunday under high pressure before restriction potential returns Monday with an approaching warm front. && .PBZ WATCHES/WARNINGS/ADVISORIES... PA...None. OH...None. WV...None. && $$ SYNOPSIS...CL NEAR TERM...CL SHORT TERM...CL LONG TERM...CL AVIATION...Hefferan