Area Forecast Discussion
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772 FXUS61 KPBZ 210007 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 807 PM EDT Thu Oct 20 2016 .SYNOPSIS... Low pressure and a crossing cold front will generate more rain through Friday. Much cooler weather will follow for the weekend. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/... The special 19Z KPBZ raob went up indicating 1.39 in of precipitable water, which is roughly 200 percent of normal. This is in an environment of deep southwesterly moisture feed as indicated by nearly saturated conditions from the surface up to about 600 mb with strong southwesterly flow through the layer. This is embedded in a deeper layer of shear and a strongly anti- cyclonically curved upper jet over the region. As the mid and upper wave slowly advanced eastward overnight and tilt turns from positive to neutral and eventually negative, the environment will likely remain conducive to heavy rainfall as low level flow right off the deck will likely continue strong isentropic ascent into the slowly SEward moving frontal boundary. All of this is only considering the synoptic portion of the equation. In the more mesoscale, several smaller mesolows are advancing northeastward in the deeply sheared environment ahead of the mid- level wave. Each of these is harnessing a withering amount of surface CAPE. Due to the slow-moving nature of the surface boundary as well as mesoscale elements tracking up it, several successive rounds of heavy rainfall will be possible as these elements move northeastward in a friendly large scale environment even as the threat for more significant convection wanes. The previously issued flash flood watch remains in effect for this. However, as convection tracks farther south and east into the area and an increasing amount of the available surface-based instability is used up, the severe thunderstorm watch has been limited to just a few of the southeastern counties in the CWA at this time. Fries && .SHORT TERM /6 AM FRIDAY MORNING THROUGH SUNDAY/... Showers are expected to continue Friday as the surface low and it`s associated cold front slowly slides east of the area. The upper trough is progged to continue it`s slow approach Friday, with the axis crossing Friday evening. Cold advection in northwest flow, and the proximity of the upper low/trough should keep shower chances continuing Saturday for portions of the area. A few locations especially in the higher terrain could see a few snow showers mix in at times. Building high pressure and lowering inversion heights should result in rapidly decreasing POPs by Saturday evening, with dry weather continuing Sunday. Much cooler temperatures are expected, with readings near or several degrees below the seasonal averages. && .LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/... A fast moving shortwave is progged for an early week passage, with most of the shower chances remaining north of PIT. Ridging is progged thereafter through mid week before another trough advances out of the Midwest by late week. Temperatures should average a few degrees below seasonal levels through the period. && .AVIATION /00Z FRIDAY THROUGH TUESDAY/... All sites should gradually transition to IFR as low level moisture increases and cold advection gradually begins. This will occur as thunderstorm chances increasingly become confined to the SE portions of the area. Guidance continues IFR conditions at all sites through Friday, however there is a chance that as wind gusts increase that a few sites may pop to MVFR for a time during the afternoon. Fries .OUTLOOK /FRIDAY NIGHT THROUGH MONDAY/... Periodic restrictions are expected into Sunday as an upper trough crosses the area. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flash Flood Watch through Friday morning FOR MDZ001. OH...Flash Flood Watch through Friday morning FOR OHZ039>041- 048>050-057>059-068-069. PA...Flash Flood Watch through Friday morning FOR PAZ007>009- 013>016-020>023-029-031-073>076. WV...Flash Flood Watch through Friday morning FOR WVZ001>004-012- 021-509>514. && $$ is the U.S. government's official web portal to all federal, state and local government web resources and services.