Area Forecast Discussion
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000 FXUS61 KPBZ 210512 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 1212 AM EST Tue Feb 21 2017 .SYNOPSIS... Dry and warm weather will be briefly interrupted by some showers late Tuesday as a weak front crosses the region. && .NEAR TERM /THROUGH TONIGHT/...
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A fairly long fetch of elevated RH values in the layers generally above 300 mb extends across the entire CWA already very early this morning. This is well out in advance of a mid and upper level system currently splitting off from the upper flow in the Mississippi Valley. The vast majority of the moisture and lift will remain with the cut off low that will meander into the southeastern portions of the country. The remnant upper level wave in the northern stream will take its sweet time crossing the Great Lakes region on Tuesday, only to edge as far eastward as our area by very late in the day. Deep saturation with this system remains generally north of our area. In addition, as the H5 wave shears off to the north through Tuesday night, lift along the boundary as it shifts through the CWA on Tuesday night is looking fairly paltry. Beyond that, deep moisture is entirely lacking. That said, PoPs were trended back below likely threshold for the vast majority of the area with the boundary passage on Tuesday night. In fact, some guidance (the new 00z NAM) is trending toward a basically dry passage of the system. Regardless of the chances of rain, high clouds will likely keep a lid on insolation driven upward temperature mobility on Tuesday, however warm advection will continue to do its thing, resulting in another day with highs straddling 60 across the region. Fries
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&& .SHORT TERM /WEDNESDAY THROUGH WEDNESDAY NIGHT/... The front will enter the region Tuesday night, but it is questionable whether it will survive the trek across as the temperature gradient slackens with time. There is some modest right entrance region support from the 300 mb jet overnight, but much of the moisture remains to the south and there is little isentropic help ahead of the front. Will continue with likely PoPs with the expectation of a light QPF event. A few showers may linger southeast of Pittsburgh after 12Z Wednesday before ending by midday. Flat ridging follows for Wednesday afternoon and evening, with a dry interlude. By late Wednesday night, developing low level southwest flow begins to induce isentropic lift and a slow increase in moisture. This may be enough to produce a touch of light rain or showers after 06Z Thursday, and have slight chance PoPs for this. Little change in airmass will result from the front, and have continued with temperatures well above climatology. && .LONG TERM /THURSDAY THROUGH MONDAY/... Not sure how much precipitation will be across the region on Thursday with a front north of the region. Have continued chance pops through this period, as well as Thursday night along the warm front associated with strong low pressure in the central plains. As warm as this week will be, Friday will likely be the warmest day of the week, with many locations possibly seeing 70 degrees. A cold front will bring showers along with a chance of thunderstorms Friday night into Saturday morning, as well as much more seasonable temperatures. Some scattered showers could persist into Saturday night, and depending on the timing, may end as a few snow showers. Expect dry and seasonable weather Sunday before another chance of rain comes with a system racing across the Tennessee Valley. && .AVIATION /05Z TUESDAY THROUGH SATURDAY/...
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VFR can be expected through much of Tuesday although extensive high cloudiness will mar the sky. Sfc wind will veer to the south by daybreak as sfc high pressure gives way to an advancing trough. Some restrictions will start to edge in from the north on Tuesday night as a weak system shifts through the Great Lakes. High uncertainty exists on exactly how much shower activity will remain as it gets to our region as well as the degree to which ceilings and visibilities may fall as it passes. .OUTLOOK... Restrictions are likely with a Friday night/early Saturday cold front.
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&& .PBZ WATCHES/WARNINGS/ADVISORIES... MD...None. OH...None. PA...None. WV...None. && $$

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