Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211128 AFDCTP Area Forecast Discussion National Weather Service State College PA 628 AM EST Sat Jan 21 2017 .SYNOPSIS... Relatively mild, but cloudy and unsettled conditions will persist through the weekend before cooler air makes a return next week. A complex storm system is expected to move across the deep south then swing northeast along the Appalachians Sunday afternoon and night. The storm will then move slowly off the Mid Atlantic coast Monday and Tuesday. Colder temperatures will arrive at the end of next week. && .NEAR TERM /THROUGH TONIGHT/... Plentiful low level moisture and little in the way of cloudiness above have helped create conditions conducive to fairly widespread dense fog. We expanded the previous advisory to cover all but Cambria-Somerset where milder air is in place helping suppress the fog. A diffuse warm front should finally either pass to our north or fall apart altogether, allowing milder air to be enjoyed by most of us in the ridge-valley areas of central PA. Highs today, even though we will remain cloudy, will average some 15-25 deg above normal. Other than some patchy drizzle, we should stay mainly dry and unseasonably mild today under the southerly flow on the back side of the surface high off the Mid Atlantic coast. The damp but mild southerly flow will continue overnight. Near term models splash some very light QPF around the region, but don`t agree on where exactly. Consensus pops favor southern areas with the moist flow so I opted for a small chance of light rain and some patchy drizzle being the most likely outcome. Again it will be unseasonably mild, some 20-30 deg above normal! && .SHORT TERM /SUNDAY/... As the storm system tracks east from Tennessee on Sunday, the local flow will become more SELY and tend to increase. The short term models keep the bulk of the rain associated with the storm still off to our south, but the increasingly moist flow should help support at least some light rain, especially over southern areas. GEFS pops show a good chance of rain everywhere with a near certainty over the south where I painted my highest numbers. The rain will trim a few deg off the high temps, but it will still remain much warmer than normal for this, the climatologically coldest time of the winter. && .LONG TERM /SUNDAY NIGHT THROUGH FRIDAY/... The lustiest GFS/ECMWF as well as the EC ensemble are in pretty good agreement in tracking a surface low east through the Carolinas-southern Virginia before redeveloping it off the Delmarva and tracking it offshore Monday and Tuesday. We start off very warm so it`s still uncertain if or how much snow will fall. The period of most intense ascent/dynamic cooling looks to be Monday morning into the early afternoon. The GFS/ECMWF/GEFS all show very marginal cold air being generated at the peak of the storm. At this stage it looks like it will be a very elevation dependent precip type, which the EC ensemble agrees with, painting something along the lines of 2-4 inches of snow from the Laurels up into the northern mountain. The ECENS is notoriously generous with snow amounts, but I like the portrayal of my higher elevation areas. The GEFS plumes show BFD with the most snowy members, with mostly rain even down into JST. So it all points to a highly uncertain forecast. Another consideration will be the potential for heavy rain. The GEFS develops a strong ESE low level jet of about 50-60kt at 850mb. In the ensemble that figures to be a widespread 5-6 sigma easterly anomaly. The ensemble shows a high likelihood of at least an inch of rain in 24 hours between Sunday night and Monday night, with other features pointing to the Monday morning into afternoon timeframe. RFC guidance suggests rain amounts of around 2 - 2.5 inches in 6 hours will start to cause flooding problems, so as the event nears we will have another thing to focus on. After our early week storm system, the eastern ridge is made to make a rapid rebound, even if for just a short time around midweek. A fast moving shortwave quickly chews the top off the ridge with cyclonic westerly flow by week`s end. Colder air looks to advect into the region bringing in more winter like temperatures late next week. && .AVIATION /12Z SATURDAY THROUGH WEDNESDAY/...
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Made a few adjustments, mainly the later period. 12Z TAFS sent. IFR/LIFR stratus/dense fog will be across most of the area this morning. JST at times will be VFR, as they are in the warmer air west of the mountains. Little improvement expected east of the Appalachians today, as low level moisture remains trapped beneath inversion to the northeast of stalled warm front. Best conditions will almost certainly be at JST, where VFR conditions appear likely west of front. Elsewhere, some modest improvement appears possible by afternoon, but IFR/low MVFR CIGs appear likely to persist through the day. An extended period of rain expected late Sunday into Tue. Outlook... Sun...Low CIGs likely. Rain advances from S-N late. Mon...Rain/low CIGs likely. Tue...AM rain/snow and low CIGs possible. Wed...Reduced CIGs/showers possible NW.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... Dense Fog Advisory until 8 AM EST this morning for PAZ004>006- 010>012-017>019-025>028-034>037-041-042-045-046-049>053- 056>059-063>066. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...La Corte LONG TERM...La Corte AVIATION...Martin

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