Residents of Pittsburgh and surrounding counties woke up to a dense blanket of fog this morning, prompting the National Weather Service to issue a Dense Fog Advisory effective until 9 AM EST. Visibility in some areas has dropped below one-half mile, with the advisory now including Pittsburgh, Wheeling, Washington, and Morgantown after an early morning update extended coverage west of the Laurel Highlands. According to the National Weather Service Pittsburgh PA, the threat for fog will likely rapidly decrease between 9 am and 10 am as diurnal heating promotes boundary mixing.
The probability of rain increases after sunset, and although a weak trough may bring some light rain or drizzle north of Pittsburgh near dawn, a more persistent and substantial rainfall is predicted later tonight as a low-pressure system moves in from the southwest. The amount of rain isn’t expected to be significant, with forecasted totals through midnight capping at a modest 0.3 inches. However, as this disturbance moves through the region, rain is likely to persist beyond midnight into the early hours of Saturday. Precipitation chances diminish rapidly as the cold front sweeps across Lake Erie, signaling drier conditions for Saturday, and seasonable temperatures are anticipated.
Looking ahead, the long-term forecast suggests a dry and mild end to the weekend and start to next week. Sunshine may be sporadic at times due to cold advection persisting over the Great Lakes, but high pressure is expected to thin out cloud coverage by Saturday afternoon. Increasing subsidence in the low and mid levels associated with building high pressure should thin cloud cover by Saturday afternoon, the National Weather Service outlines. Come Tuesday and Wednesday, precipitation chances return as a trough from the Midwest moves into the Great Lakes, bringing potentially limited rainfall. If a dry slot enters the region early Wednesday, the probability of receiving a half-inch of rain within 24 hours stays below 10%.
For aviation, widespread LIFR conditions have been ongoing, with fog and low stratus severely impacting visibility. The forecast indicates that gradual mixing and dissipating of fog should begin in the 14z-16z timeframe, with VFR conditions expected to return Sunday morning under the influence of high pressure, lasting until a new low-pressure system's arrival near Tuesday. The Pittsburgh Weather Service’s aviation outlook anticipates continued challenges tonight into Saturday morning, with MVFR/IFR likely in areas of rain, particularly around and south of Pittsburgh, while FKL/DUJ could experience near VFR as they remain on the edges or just outside the rainy areas. Even with some early drizzle, meaningful rain should hold off until the evening, providing a brief respite to the thick morning fog.
