Area Forecast Discussion
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039 FXUS61 KPBZ 231739 AFDPBZ Area Forecast Discussion National Weather Service Pittsburgh PA 139 PM EDT Fri Jun 23 2017 .SYNOPSIS... Downpours are possible through tonight with a tropical airmass in place. A cold front sweeping through early Saturday will return comfortable humidity levels by the weekend. Below normal temperatures greet us early next week. && .NEAR TERM /THROUGH TONIGHT/... Widespread area of rain continues to impact the northern part of the forecast area. The forecast has not changed much with the 12Z NCEP suite. Heaviest rain axis has shifted slightly north into southwestern PA mostly along and south of US 40 where potentially upwards of 3.5" of rain could fall. The remaining part of the hydro discussion including rivers can be found in the hydro section near the end of this product. Severe threat remains a concern as a dry slot is working its way up the Ohio river into parts of southeastern Ohio and northern West Virginia. This will allow the atmosphere to destabilize and potentially foster development of bowing segments that are capable of producing damaging winds. Forecast soundings illustrate wind as the primary threat. Hodographs are not too impressive given mostly speed shear, however if a storm deviates to become a right mover then a weak tornado is possible. Reviewing CIPS analogs for this scenario, they portray a non zero tornado threat due to several of the top analogs showing 1-2 tornadoes happened. This is further supported by updraft helicity fields from experimental NCAR 3km CAM. At this time, any severe weather should be along and south of the clearing that will be working into northern WV and southern PA. Pops will be categorical most of the night as a slug of rain moves through. Very little change to the grids other than to speed up timing of the back edge. && .SHORT TERM /SATURDAY THROUGH MONDAY NIGHT/... Dry and less humid air will be welcome news for many this weekend as dewpoints drop into the 50s! Northwest winds behind the baroclinic zone will clear out the sky during the morning, however moisture will be on the increase as a fast moving shortwave trough crosses during the evening hours. The column is fairly dry, so no measurable QPF is foreseen Saturday. Dry weather continues for the second half of the weekend despite less sunshine. Yet another passing short wave will bring clouds and given its stronger than the one Saturday isolated showers are possible north of the I-76 corridor in the late afternoon / early evening hours Sunday. Mid level heights continue to fall as we kick off a new work week. Most of the energy will reside along the lakes, so precip chances are small over northern WV and western MD when compared to northwest PA. Any shower will be brief. The bigger story is the spring like feel as daytime high temps do not leave the 60s Monday! This will be almost 15 degrees below normal. && .LONG TERM /TUESDAY THROUGH FRIDAY/... Highlights: - Cool start - warm end temp wise - Unsettled weather returns Friday - No heat waves or high water threat Mid level heights increase with a ridge building into the eastern United States. This will bring temps back to normal levels by Thursday and above normal by a week from now. && .AVIATION /18Z FRIDAY THROUGH WEDNESDAY/... Tropical moisture will continue to stream northward ahead of an approaching cold front this afternoon. Interaction with the aforementioned front and digging shortwave will support periods of rain and an increasing chance for thunderstorms through the afternoon. Confidence in widespread MVFR and brief IFR visibility restrictions is high for the remainder of the day in periods of heavy rain, with the expectation that IFR cigs will lift over most terminals this afternoon. Some thunderstorms may be severe, with strengthening shear/jet support, which could result in strong/severe gusts at terminals this afternoon. Restrictions will likely continue tonight as the remnants of Cindy pass along the PA/WV border. Cigs may fall back to IFR after sunset with some fog possible with saturated conditions. But, improvement is expected by Saturday morning as surface ridging builds overhead. WSW wind will remain gusty through the afternoon and again tomorrow. .OUTLOOK... Upper trough may bring occasional restrictions Sun and Mon in afternoon showers/storms. && .HYDROLOGY... The flash flood watch remains on track. The axis of highest QPF has shifted a little north to far southern PA where 24 hour amounts in excess of three inches are possible. HRRR shows a several hour period of moderate to heavy rainfall thankfully it is across a region that was not impacted by the nearly 4-6" of rain that fell in parts of Indiana county last evening. Warm rain process and PRE setup remain in place. PWATS are pushing two inches while warm cloud depths are in excess of 13kft. The low level jet continues to pump moisture from Cindy into our region. All of these point to enhanced convergence ahead of the front. River forecasts have been tweaked upward across Mon and headwaters of Ohio river. We still do not have any forecast points going to flood, but Pittsburgh, Elizabeth, and Charleroi are predicted to reach action stage. && .PBZ WATCHES/WARNINGS/ADVISORIES... MD...Flash Flood Watch through late tonight for MDZ001. OH...Flash Flood Watch through late tonight for OHZ057>059-068-069. PA...Flash Flood Watch through late tonight for PAZ021>023-029-031- 073>076. WV...Flash Flood Watch through late tonight for WVZ002>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.