Area Forecast Discussion
Issued by NWS State College, PA

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157 FXUS61 KCTP 281900 AFDCTP Area Forecast Discussion National Weather Service State College PA 300 PM EDT Wed Sep 28 2016 .SYNOPSIS... A multi-day heavy rain event will commence tonight and continue through Thursday night and Friday. Minor flooding impacts are likely across the southern half of central PA...but impacts should be lessened to some extent by dry antecedent conditions. Unsettled weather with occasional lighter rain showers will persist into the weekend with a gradual drying trend by early next week. && .NEAR TERM /UNTIL 6 AM THURSDAY MORNING/...
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*Flood Watch in effect for the Laurel Highlands, South Central Mountains and southern portions of the Central Mountains midnight tonight through Friday morning. *Heavy rainfall event probable over far south-central Pennsylvania on Thursday *Flooding is likely however high impacts may be mitigated by dry antecedent conditions Increasing southeast flow aiding expansion of lower clouds from the Mason Dixon line northward into the Laurel Highlands and parts of the South Central and Central mountains and Ridge and Valley region at mid afternoon. Deep easterly flow with long over water fetch from the Western Atlantic is pushing low clouds westward from the Hudson River Valley into eastern PA as well. Showers are breaking out over the ridge and valley region and lower Susq this afternoon...and expect them to become more persistent and heavy as we get into the evening hours...as per CAM solutions. Clouds will continue to increase from south to north throughout the mid and late afternoon as southeast flow increases and boundary layer moisture deepens. Model guidance still shows the main surge in rain coverage and intensity later tonight into Thursday which corresponds with arrival of stronger dynamical forcing and strengthening E-SE upslope low level flow. Showers with locally heavy banded and orographics will increase by late evening and overnight across the southern third to half of central PA.
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&& .SHORT TERM /6 AM THURSDAY MORNING THROUGH FRIDAY/...
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Heavy rain event is expected to be ongoing over south-central PA on Thursday. An enhanced convergence axis/frontal zone is progged to develop on the east side of an upper low meandering over the OH/TN Valley, tapping into deep moisture/high PW air off the Atlantic Gulf Stream via anomalous east/southeast low level jet. The heavy rain axis is progged to gradually pivot to the southwest with time oriented within moderate excessive rain outlook area from southwest PA near the Laurel Highlands southeast into Northern VA/D.C. area. The strength of the upslope flow and high PW transport along with some elevated instability should provide an environment for efficient rainfall processes. WPC QPF nudge employed this afternoon but overall staying the course from previous forecasts...despite a downtick in some deterministic solutions in the 12z cycle. Dry antecedent conditions may limit more significant flooding/runoff issues. Still expect minor flooding to result from long duration continuingthroughout Thursday. event...and am maintaining Areal Flood Watch for Laurel Highlands, South Central Mountains and southern portions of the Central Mountains for late tonight through Friday morning. Will continue to highlight potential flood risk in HWO elsewhere...but heaviest rain should fall across the southern half of the area. The upper low is fcst to drift back to the west/NW into the OH Valley on Friday before slowly moving to the ENE across the Lower Great Lakes through the weekend. We should continue to see periods of showers on Friday but rainfall amounts will be much lower and less organized.
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&& .LONG TERM /FRIDAY NIGHT THROUGH TUESDAY/...
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The upper level low will continue to slowly move through the Eastern Great Lakes region and into Southern Canada which should pull the moisture to the north. Some lingering showers should continue through Eastern PA Saturday afternoon. There is some disparity on the timing of the exit of this low and whether or not it opens up into a wave. The model guidance still suggests unsettled conditions over the weekend with a gradual decrease in the chance for showers by Sunday. Temps still holding close to seasonal normals as we turn the calendar to October.
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&& .AVIATION /19Z WEDNESDAY THROUGH MONDAY/... VFR conditions slowly retreating from south to north this afternoon as deep southeast flow increases. Reductions expand northward tonight and impact all sites Thursday with widespread ifr developing late tonight and lasting through Friday. Outlook... Thu-Fri...Widespread showers/cig reductions. Sat-Sun...Reductions possible with a chance of showers. Mon...Improving conditions. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch from 2 AM EDT Thursday through Friday morning for PAZ024>028-033>036-056-063>065. && $$ SYNOPSIS...DeVoir NEAR TERM...DeVoir SHORT TERM...DeVoir LONG TERM...Ceru/Steinbugl AVIATION...DeVoir/Gartner/Martin

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