Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 160318 AFDCTP Area Forecast Discussion National Weather Service State College PA 1018 PM EST Thu Feb 15 2018 .SYNOPSIS... A complex frontal system will move through the region overnight and early Friday. Cooler and drier weather will move in for Friday before a new frontal system brings more inclement weather for late Saturday through early Sunday. && .NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...
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The nose of the low level jet is surging through SRN PA resulting in a shot of strong warm advection and potent moisture convergence. RAP shows the LLJ continuing eastward and settling south along or just south of the MD border after midnight. Locally heavy rain is falling from Somerset east into the Lower Susq Valley. We got a call earlier of some minor road flooding in Somerset and with the convective-type moderate to heavy rain, we have issued a couple of advisories for minor flooding. The deep and extensive moisture plume that extends all the way from the tropical Pacific south of Baja Mexico will yield a high precipitation efficiency into the overnight. Add in an upslope/orographic component, and we`ll see some heavy storm total rainfall (2+ inches) tonight and early Friday over Cambria and Somerset counties, which remain in a flood watch. Am a little concerned about the potential for flooding over Bedford and Blair where the HRRR wants to bring some local storm totals of around 2 inches, but for the most part the meso models are consistent with confining the biggest rain totals to the higher elevations. The latest HRRR shows a stripe of 1 to 1.5" rainfallsfrom northern Cambria all the way to the Harrisburg area and into northern Lancaster county. Details are in the Hydro section below. Min temps tonight will be very mild and in the 50s in the SE, but in the lower 30s in the far NW where an early morning cold FROPA will send temps tumbling just before sunrise.
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&& .SHORT TERM /6 AM FRIDAY MORNING THROUGH 6 PM FRIDAY/... A strong cold front pushes SE through the region Friday morning. The mild weather will be erased (albeit just for a rather brief 48 hour period) as a cold front sends temperatures falling slowly but steadily through the daylight hours on Friday. The dry air will also kill off the rain before noon in many places - except the Laurels. There will likely be a transition zone from rain to snow across the northwest 1/2 of the area with a slushy accumulation possible over the higher terrain as the colder air catches up with the back edge of the frontal precip. But, the drying occurs so quickly and temps mild enough over the south that no snow is expected SE of UNV/AOO/IPT. Clearing and good CAA will bring sfc temps down into the lower teens in the NW, and uTeens and l20s elsewhere. && .LONG TERM /FRIDAY NIGHT THROUGH THURSDAY/... Period starts off with high pressure moving quickly west to east across the state. Weak and fast moving low pressure center is forecast to develop over eastern NC Saturday afternoon, an move to off the NJ coast overnight into Sunday morning. This could bring a swath of 2-4 inches of snow to much of central counties with a little less to the north and a little more to the south and east. Of some concern is the air and ground temps at the start of pcpn...this may limit accumulations til sfc temps can cool off. System clears out quickly for Sunday with a mild pattern resuming next week with rounds of rain targeting the northwest 1/2 of the area. Temps will be back into the 50s and 60 or so by Tues and remain mild into mid- week. && .AVIATION /03Z FRIDAY THROUGH TUESDAY/... 00Z TAFS sent. 00Z TAFS close to earlier package. Main thing was to add more detail later on Friday. A moist southwest flow ascending the Allegheny Mountains will result in persistent MVFR cigs at KBFD/KJST through dusk, This will be followed by quickly lowering cigs spreading across the region this evening, as an area of low pressure approaches from the midwest and tracks across Pennsylvania tonight, resulting in rain of varying intensity and deteriorating cigs/vsbys. Cold front moving faster now...than what models had several days ago. Expect clearing from northwest to southeast later on Friday. Some snow may occur on the back side of the cold front across the northwest. Outlook... Sat and Sat night...Snow spreading northeast across the state late Sat and continuing into early Sunday with widespread IFR and LIFR restrictions. Sun...Clearing. Mon and Tuesday...Periods of Rain/low cigs possible, especially NW Mtns. && .HYDROLOGY... PWATs climb to 30mm - nearly 5 standard deviations above normal. Upslope and prolonged time of rain will result in 2-3 inches of rain in the Laurels and 1-2 inches across the middle third of the area. The greatest threat for flooding exists in the Laurels, but some minor problems may crop up in the central mtns. At this point, not enough to worry about in the central mtns for a flood watch. Much of the snow is melting, but the pack is dense, now. 50 dewpoints and strong SW wind will help melt quite a significant amount away today and tonight in the W. Streamflows are already well above normal (>75th percentile) in the southern half of PA right now. So, the rain will be excessive, and flooding is almost likely in the Laurels. The WPC outlook of a SLGT risk of excessive rainfall matches up nicely with the area covered by the watch. && .EQUIPMENT...
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The radar is down with a malfunctioning motor. Techs are in the process of trying to install a replacement.
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&& .CTP WATCHES/WARNINGS/ADVISORIES... Flood Watch through Friday evening for PAZ024-033. && $$ SYNOPSIS...La Corte NEAR TERM...La Corte SHORT TERM...Dangelo/Lambert LONG TERM...Dangelo/Gartner AVIATION...Martin HYDROLOGY...La Corte EQUIPMENT...La Corte is the U.S. government's official web portal to all federal, state and local government web resources and services.