Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 231757 AFDCTP Area Forecast Discussion National Weather Service State College PA 157 PM EDT Mon Oct 23 2017 .SYNOPSIS... A strong frontal system will push colder air into the region overnight Monday into Tuesday. A second shot of cold air is expected this weekend. Overall most of the coming 6-8 days the region will be in a mean trough thus cooler weather will be the norm for awhile. && .NEAR TERM /THROUGH TONIGHT/... A strong upper-level low to our west is headed our way. Most mesoscale guidance keeps the more organized rain out of the region through about 8 PM. The GEFS 3-hour data and the HRRR suggest most of the rain will come in a north-south band between about 9 PM in the west and by 5 AM in the east. Meso models imply renegade shower potential could affect NW areas this afternoon and evening. But most of the rain will be overnight with showers and perhaps some isolated thunderstorms. The winds along this line are about 50 to 60kts at 850 hPa so it will be breezy and any strong convective cores could easily bring 35 to 50 mph winds to the surface. The v-winds are about 4 to 5 sigma above normal ahead and along the frontal boundary. Most areas will have a good 1-3 hour window with the rain. In the HRRR and the GEFS winds this has a classic NCFRB look so most of the rain will be close to the frontal boundary. Rapidly improving west to east behind the line. Most of the rain should be to our east by 8 AM. Some areas patch fog in east and a few isolated showers. && .SHORT TERM /TUESDAY/... Improving day weatherwise as the front pushes farther to our east. After 15Z the GEFS has no QPF in our CWA. It will be a cold advection day with potential for some self- destruct cumulus in the mountains. Strong westerly winds at 850 hPa should easily mix down behind the front. So gusty winds likely. The coldest air does not filter in until Wednesday but Tuesday will be the start of a cooler period. Enjoy would could be one of the warmest day for some time to come. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Surface ridging indicated over central Pa by med range guidance late Tuesday through Friday, indicating dry weather for most of the forecast area. The exception will be late Wed, when passage of shortwave could produce a few showers across the northwest mountains. Ensemble mean 925/850 temps are slightly below normal Wed/Thu, likely translating to max temps from the upper 40s over the Alleghenies, to the upper 50s across the southeast counties. This cooler stretch will be short lived as heights and 850 temps rise quickly into next weekend. Another chance for precipitation will arrive at the end of the period when a cold front is anticipated next Sunday, bringing rain to much of the CWA, while colder air and a few waves of low pressure riding NNW along the front brings the chance of a light to moderate, and elevation dependent snow event. && .AVIATION /18Z MONDAY THROUGH SATURDAY/... After a prolonged period of largely unrestrictive/VFR flying conditions, the weather is about to become rather tumultuous over the next 24 to 30 hours. A steady dose of thickening high clouds will continue to blanket the airspace. Beneath the cirrus canopy, a moist east-southeast flow will result in MVFR/IFR conditions this morning over the east-central airspace. High confidence at the southeast airfields KLNS/KMDT based on current satellite, observational and guidance trends. Still not totally convinced in significant improvement during the day at the eastern TAFs and have hedged toward the low end of the guidance spread which keeps MVFR cigs through the afternoon/eve. Winds from 140-180 degrees will increase through the period with surface gusts 20-30kts this evening into tonight. LLWS is expected tonight as low level jet reaches 50+kts ahead of cold front sweeping east across the airspace 00-12Z Tue. A band of moderate to heavy rain is likely along the front late tonight into early Tuesday morning which may be accompanied by strong, gusty winds or embedded thunderstorms. Models are in good agreement in shifting the frontal rain band east of the airspace by mid-day Tuesday with conditions improving to VFR. Outlook... Wed-Thu...Sct showers/low cigs possible especially KBFD/KJST. Fri...Mainly VFR with chance of showers wrn 1/2 Fri night. && .CLIMATE... Through 10/22/17, the average monthly temperatures at Harrisburg and Williamsport are 63.8F and 61.8F. When compared to the maximum 1-month mean avg. temperature for previous Octobers, both would rank as the warmest on record. Computing a daily avg. temperature when only taking into account the first 22 days of the month and comparing to the previous Octobers, the rankings are #2 at IPT and #3 at MDT. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Fitzgerald/Lambert NEAR TERM...Grumm SHORT TERM...Grumm LONG TERM...Lambert/Gartner AVIATION...Grumm CLIMATE...

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