Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 290025 AFDCTP Area Forecast Discussion National Weather Service State College PA 825 PM EDT Fri Apr 28 2017 .SYNOPSIS... A frontal zone will be near the Keystone state this weekend. A strong trough and cold front will move across the region on Monday, followed by much cooler temperatures. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/... Airmass across central PA late this afternoon is quite dry at low levels. A few showers are making it to the ground at BFD as of late aft. Did up POPS some from 23Z onward. Also adjusted POPS across the south later tonight. While activity to the west should turn to the right a little, given low dewpoints in place and thickness fcst, slightly higher POPS fit better with others and current activity to the west. Not expecting strong or severe storms at this point, but will continue to look situation over. Earlier discussion below. Satellite shows high clouds streaming into the region out of decaying convection over the midwest. We will remain dry today, but the chance for rain will increase this evening and overnight. Guidance indicates that an MCS will form over the Ohio Valley later today and stream NE into the region overnight. ECMWF/GFS as well as The SREF and GEFS all show the MCS decaying as it enters Central PA, while the 12Z NAM and latest HRRR are more aggressive sliding the convection through the area between about 03-10Z. I used a blend of POPs overnight which is not as wet as the HRRR, but wetter than the other models that break up the showers as they approach. I favored the north with the best POPs. Overnight, lows will range from the mid 50s to mid 60s, or about 15-20 deg above normal. && .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... As per above in Near Term section above, did up POPS some prior to early aft on Saturday, mainly across the south, for any lingering activity that moves in from the west. Earlier discussion below. Guidance agrees in bringing the warm front northward late tonight and Saturday, but differences exist as to how far north it manages to progress. Warm and muggy air will pool along and just to the south of the boundary. Models develop a fair amount of CAPE, they just differ on whether the most unstable air will favor the Maryland border areas or extend up into the Central Mountains. SPC has the region under a marginal risk for severe storms, and with moderate deep layer shear expected, this looks reasonable. Look for the best chance of showers and storms to be from mid day into the afternoon. Highs will vary from around 70 along the NY border to the mid/upper 80s over the SE. If we end up with more sunshine than currently expected, I would not rule out a high temp near 90 in a couple of places. With dewpoints well up into the 60s over at least the southern half of the CWA, it will begin to feel humid. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/...
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Upper level ridge tries to builds in for Saturday night through Sunday but continued southerly flow/instability and a weak warm front lifting through the Ohio Valley and W PA will lead to continued chances for showers and even a tsra - mainly in the NW half of the area. Temps remain very warm into Monday. A massive and deepening cyclone lifting into the western Great Lakes Sun night into Monday will push a strong cold front through PA Mon into Mon night, accompanied by a round of potentially potent showers and thunderstorms (likely reaching western half of CWA in the afternoon and eastern half during the evening). Once this front passes by much chillier air will advect into PA on cyclonic flow with unsettled light showery weather persisting mainly for the northern part of the state right into Wednesday. Chance for a more widespread light rain arrives Thu into Fri as a low progged to develop along the southern Appalachians and lift northward. Models showing strength/timing issues so not getting to specific this far out, but looks like unsettled weather pattern continues.
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&& .AVIATION /00Z SATURDAY THROUGH WEDNESDAY/...
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Complex weather pattern across the region. Radar and short term models indicate several dying areas of convection moving in from the west overnight. Have included mention of VCTS in western and central TAFs overnight, with just showers in eastern areas. A wavering frontal boundary is expected to set up across the region Saturday. Thinking right now for aviation purposes is to lean towards northern areas to be in the cool sector, with occasional showers and lower ceilings and less chance of thunder. Central areas are in the battleground region. Scattered showers and thunderstorms possible right through the period. Reluctantly, have included VCTS for large blocks of time in the forecasts, as timing very difficult. Southeastern areas may be in the warm sector Saturday. While there is a risk of thunder here as well at KMDT and KLNS, activity may be more isolated than across the KJST/KAOO/KUNV corridor. Have therefore left thunder out of these (KMDT/KLNS)TAFs for now. Outlook... Sat-Sun...Sct showers/Tstorms. Areas of sub-VFR north, and also associated with any thunderstorms. Mon...Breezy. Showers/thunderstorms likely with periods of sub- VFR. FROPA. Tue-Wed...Breezy with a chance of showers NW 1/2.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...La Corte/Martin NEAR TERM...La Corte/Martin SHORT TERM...La Corte/Martin LONG TERM...RXR AVIATION...Jung/La Corte

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