Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 202041 AFDCTP Area Forecast Discussion National Weather Service State College PA 341 PM EST Sat Jan 20 2018 .SYNOPSIS... Moisture will creep into the western mountains tonight. Temperatures will rise above normal today and stay there through mid-week. A cold front will move through the area later Monday night and early Tuesday. && .NEAR TERM /UNTIL MIDNIGHT TONIGHT/... Quite a nice day underway compared to recent days. The sun is a little filtered by the high clouds in the SE and temps are just a few degs slow in meeting the fcst maxes. However, the wind is keeping things well-mixed and very mild. The mixing is only up to about 2-2.5kft. The loss of sunlight/heating will result in the eastern areas decoupling again, and they will get just as cool as the nrn mtns later tonight. && .SHORT TERM /MIDNIGHT THROUGH 6 PM SUNDAY/... The risk of ice jam flooding will continue over the weekend and into early next week. See the hydro section for more details. Clouds do creep in from the SW tonight, but it seems like the models are very aggressive in dropping the wrn counties into the crud. The closest low clouds are clouds around 3kft over far srn WV and ern KY. Nighttime stratification should assist the upslope in making the forecast low clouds appear. Will, however, be less aggressive with the influx of clouds. Will continue to mention the possibility of FZDZ in the grids. but the temps may be just above freezing as the clouds and drizzle materialize. As the clouds arrive I would expect the temps to go up a bit, too. So, no advy at this point. Will allow later shifts to futher assess the situation. By sunrise, about half of the area should be overcast and clouds will creep eastward, but mixing will keep the bases higher to the east of the Alleghenies. No need for POPs until the afternoon when continued influx of moisture and upslope into the eastern ridges makes it possible for a drip or two to fall there. Maxes will likely be challenged by the clouds. Will keep them a little lower than guid. && .LONG TERM /SUNDAY NIGHT THROUGH SATURDAY/... Another January thaw will bring a period of relatively mild weather to Central PA through early next week. Temperatures are not expected to be as warm as the previous thaw (late last week), but departures should reach +10 to +15 degrees above average for mid to late January, peaking Monday in the NW and Mon into Tues in the SE. The progressive pattern will keep the cool down during the middle/late part of next week rather brief before temperatures moderate/trend warmer into next weekend. The start of warm advection Sunday night and Monday ahead of a strengthening Mississippi Valley/Great Lakes cyclone will impinge on a retreating thermal gradient between I-80 and I-90. Forecast soundings indicate moisture will be rather shallow initially with areas of light rain confined mainly to the western and northern parts of the area. Elsewhere expect low clouds to develop with pockets of drizzle/mist and fog. As the cyclone approaches, Monday will see the light showers retreat to the north with the warm front (thermal boundary). The most likely period for widespread rain is Monday night into early Tuesday along/ahead of south-southwesterly LLJ axis and cold/occluded front. A weak secondary low may form in the lee of the Appalachians and support a period of enhanced rainfall over the eastern 1/2 of PA Tuesday morning. At this time, the total rainfall forecast for early next week does not appear to be as heavy as Jan. 11-12. Winds look rather blustery from later Tuesday into Wednesday on the backside of the low pressure system as colder air filters back in. Snow showers are likely downwind of Lake Erie into Wed night. Dry wx with moderating temperatures Thu-Fri under high pressure. Some showers may sneak into the NW Sat as weaker low pressure system lifts across the Great Lakes, with better chances for rain with another low on Sunday. && .AVIATION /20Z SATURDAY THROUGH THURSDAY/... A MVFR stratocu/stratus deck should form or move into the western zones tonight. This deck will become IFR at BFD and JST, and there will likely be some --RA and/or DZ at both sites. Clouds could lower to IFR UNV and AOO, but those latter two airfields will have a bit of a downslope and this should help to keep it dry and just MVFR at UNV/AOO/IPT. The gusty wind will diminish with loss of heating and as the low to our north slides to the NE. As the moisture pools and builds over the area, the threat of DZ could spread into the Poconos. SCT SHRA also possible over the nrn mtns on Sunday. Outlook... Sun PM...SCT SHRA - mainly in the north. Otherwise MVFR S and IFR N. Mon...Reduced flight categories with rain showers associated with an approaching cold front - mainly N. Improvement expected from S-N thru the day. Tue...VFR w/SCT MVFR in SHRA. Tues PM-Wed...IFR SHSN NW. MVFR/VFR SE. Thurs...No sig wx. && .HYDROLOGY... Main concern is watching water levels rise on Susq downstream on Harrisburg. Marietta gage /MRTP1/ continues its slow rise as ice builds up downstream. Gage above action stage and there is some minor flood concerns in Wrightsville ongoing. The Flood Watch for this area has been extended through the weekend, set to expire Monday afternoon. With milder temperatures there is potential for ice movement, as well as slow ice deterioration/thinning with time. All areas near rivers and streams that have significant ice buildup should monitor water levels closely for the next several days. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch through Monday afternoon for PAZ065-066. && $$ SYNOPSIS...Dangelo NEAR TERM...Dangelo SHORT TERM...Dangelo LONG TERM...RXR AVIATION...Lambert/Ceru HYDROLOGY... is the U.S. government's official web portal to all federal, state and local government web resources and services.