Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 191548 AFDCTP Area Forecast Discussion National Weather Service State College PA 1148 AM EDT Sat May 19 2018 .SYNOPSIS... An extensive plume of moisture with its origin near the equator, will stream north over a nearly stationary frontal boundary located south of Pennsylvania. A weak cold front will pass overnight leading to drier weather for Sunday. The region will remain on the northern periphery of the subtropical ridge through early next week meaning it will remain unsettled. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... Radar shows a chilly rain continuing over the eastern half of the CWA with rain of a more showery nature over my western zones. The steadiest rain will taper off by late morning/early afternoon as the core of the LLJ pushes up into NY stat. SREF/GEFS show the anomalously high PWATs sticking around until the front passes later tonight, so we will stay vulnerable to scattered showers. This will be especially so over my western counties this afternoon where a mix of sun and clouds will result in some modest destabilizing of the atmosphere, and possibly a gusty thunderstorm. SPC has my NWRN zones in a marginal risk which dopesn`t seem unreasonable. Considering the duration of the rain followed by very little vertical mixing within a region of weak llvl pressure gradient across Central PA, hourly temps today were nudged toward the cooler RAP/NAM. This will lead to high temps only in the upper 50s to around 60F across the Middle and communities along the West Branch of the Susq River. High temps will reach the lower 70s across the southern zones and Alleghenies of Western PA, while the far NW see a max temp in the mid 70s. Anticipated rainfall amounts could be enough to create some minor flooding by this afternoon/early this evening, so will leave the Flood Watch in place, but trim off the 2 western counties of Bedford and Somerset. Given how wet the ground is across southern Pa, and the current plume of high moisture/MDT to HVY rain spreading north into the eastern half of the CWA, we coordinated with WFO LWX and KDIX to trim the western counties from the watch. Otherwise, the Flood Watch was extended out through 00Z Sunday. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... The parent shortwave driving the bulk of the showers is timed through by the latest 00Z model guidance between 00-12Z Sun (tonight). A second 35-40kt 850 mb swrly wind max will push across the state early tonight before gradually decreasing late. Uvvel associated with warm advection and differential PVA just ahead of a relatively weak 500mb short wave will bring a few periods of showers with isolated to scattered TSRA...mainly across the NW Mountains and Laurel Highlands. Min temps early Sunday will be on the mild side, only dipping to the upper 50s to around 60F across the Mountains, and in the mid 60s throughout much of the Lower Susquehanna Valley. && .LONG TERM /SUNDAY THROUGH FRIDAY/... After a showery overnight Sat night, Sunday will turn drier, especially for the afternoon as the exiting upper trough/sfc front leads to rising heights aloft. The timing of the sfc cold fropa is during the mid morning hours over the west, late morning across much of the Susq Valley, and during the late morning/afternoon hours in the Southeast. After being suppressed to our south early next week, the chances for showers will increase once again Monday as moisture on the northern periphery of the subtropical ridge creeps back into the region. I used blended MOS POPs leading to a mention of mainly afternoon showers/thunderstorms. Then as if from the department of redundancy department, the showery forecast sticks around for Tuesday before drier air makes a push for Wednesday. I actually cut back on the blended MOS POPs for Wednesday leaning closer to the GEFS idea of drying behind a weak cold front. From there it looks like the period form Wednesday afternoon through Friday morning will feature some rare rain free conditions before the chance for a pop up shower or storm becomes possible before the day is over Friday. Rainfall to date has already exceeded monthly normals at Harrisburg and Williamsport and is on a pace to be wetter than a normal May at Altoona, Johnstown, Bradford and State College. It looks to stay unsettled at least into early next week. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/...
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Widespread MVFR/IFR will continue with only slow improvement over western sections as partial sunshine leads to some mixing out of the low clouds. Steady rain over eastern edge of the 1/2 airspace will continue to move off to the NE, leaving scattered showers behind over the remainder of Central PA. A few thunderstorms are possible over the western 1/3 of the airspace late this afternoon. Showers are likely to persist into the overnight as a cold front pushes through the area. Model guidance is indicating a wind shift to the west by Sunday morning which should spell improvement at airfields east of the Alleghenies. Outlook... Sun-Wed...Variable conditions with isolated/sct showers and Tstorms. Thu...AM Fog then VFR/no sig wx.
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&& .HYDROLOGY... Additional rainfall amounts 0.50 to 1 inch are forecast across the Susquehanna Valley through Saturday. This will bring small streams and creeks to near bankfull and some may exceed caution levels. No river flooding is currently forecast in the Juniata and Lower Main Stem Susquehanna basins, but risk remains somewhat elevated due to very wet antecedent conditions. && .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch until 8 PM EDT this evening for PAZ035-036-056-057- 059-063>066. && $$ SYNOPSIS...La Corte/Lambert NEAR TERM...La Corte/Lambert SHORT TERM...Fitzgerald/Lambert LONG TERM...La Corte/Lambert AVIATION...Lambert/Steinbugl HYDROLOGY...

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