Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 250553 AFDCTP Area Forecast Discussion National Weather Service State College PA 1253 AM EST Sun Feb 25 2018 .SYNOPSIS... Periods of rain will continue late tonight through mid-day Sunday. The rain could be heavy at times. Saturated ground and swollen streams will support an elevated risk for flooding through the weekend. A break in the wet weather pattern is expected early next week. Above average temperatures are expected to continue through much of next week before a relative cooling trend toward climatology into early March. && .NEAR TERM /UNTIL 6 AM THIS MORNING/...
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Deep layer moisture increasing over PA late tonight with PW over 1" surging north of the Mason Dixon line and moderate rainfall blossoming over western and central PA. The area of rain is expanding rapidly as expected and will cover all of central PA by 07z. Heaviest rainfall based on the latest HRRR and SPC HREF of about 0.75-1.00" to fall across the Western Mtns of PA through 11Z Sunday and across the Central part of the CWA through 13Z window, and over the East between 08-16Z. Some locations will see an additional 1.5 inches of rain by later Sunday morning (west) and early afternoon (East). Temps won`t move much overnight from their early evening Low- Mid 40s levels, but a deg F or two of rise is possible through the rest of the night as winds increase and readily break any weak llvl inversion that exists. Based on regional MRMS (Radar + Gauge Bias Correction) data, that shows 0.75 to 1.25 inches over the past 48 hours across much of Central and Northern PA (with only 0.10-0.40 in the south), we`ve already received about half of our rainfall for this prolonged event. This should bode well for flooding concerns, which should not increase from what we advertised for the past few days. See hydro section near the bottom for additional details on the potential for primarily small stream and creek flooding. Stability decreases across wrn PA late tonight but then skirts around most of the CWA as it is confined to S of the MD border through the rest of the morning. Will not mention T at this point. While the air will be drying out Sunday night, the wind won`t be all that gusty, and temps don`t crash. High builds over the OH vly through the night, and gradient slackens. 8H temps of 0 to -3C are still rather mild for Feb. Mins of u20s NW and 30s elsewhere look solid.
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&& .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM MONDAY/... Air dries out quickly after 9 or 10 AM (14-15Z) in the west and 17-19Z (east), as colder air pushes in from the west on a moderately gusty west wind before noon. Residual SHRA over the Laurels will dissipate about the same time as the main batch of showers exits to the east with drying in between beforehand. Again, the sfc instability stays just south of the MD border through the morning. Can`t rule out an isold Tstorm in the south in the morning, but probably not worth mentioning at this point. Temps do rise 5-10F through the day, esp if some breaks occur in the aftn, but this could be squelched over the west as the cold air arrives there first. && .LONG TERM /MONDAY NIGHT THROUGH SATURDAY/... The wet pattern looks like it will take a break during the first part of next week before precip risk increases next Wed-Fri. Mild and dry for Mon through Tue night as high pressure ridge will be in control. Model and ensemble guidance show a low pressure system tracking east-northeast from the TX/OK panhandle across the Central Plains/Midwest into the Great Lakes/Ohio Valley region by Thursday. The ECMWF and GFS 12z runs beginning to converge on a similar overall solution of strength and timing. First up will be a warm front lifting through Thu night which could bring a period of moderate rain to the area, and have raised pops further during this period. Then attention turns to development of a secondary low to the south of PA from the southern Mid Atlantic piedmont that potentially settles in near the NJ coast for a 12-24hr period Fri into Fri night. This is starting to look more and more like we`ll have potential ptype issues or wintry wx - esp over the northern half of CWA as colder drier air wraps in from the NE. Could see accum snows in those areas, and likely breezy conditions for the weekend. Something definitely to watch at this range. Temperatures will continue to run above average next week with signs of trending cooler/closer to daily climate normals into early March. && .AVIATION /06Z SUNDAY THROUGH THURSDAY/... We`ll have a several hour lull in the steady rain in most places this evening as one wave of weak low pressure moves quickly east to Southern new England. A second wave of low pressure, associated with a plume of a high moisture values spreading NE from the Ohio River Valley, will takes aim at Central PA overnight and Sunday morning. Expect any MVFR or low end VFR this evening across parts of the Middle Susq Valley and Central Mtns to be fleeting and drop steadily into the IFR/LIFR category late this evening through the overnight hours. Conditions will return to quickly MVFR then VFR from west to east across most or all of the region Sunday afternoon/evening, though some intermittent MVFR cigs are possible at KJST and KBFD during that period as shallow cooler air ascends the Alleghenies. Winds aloft will increase to 50 kts at 2,000 AGL so LLWS is possible overnight. These winds will make it to the surface with gusts to 20 kts at times. Outlook... Sun...Widespread restrictions likely in periods of rain. Mon-Wed...No sig wx. Thu...Restrictions possible in periods of rain. && .HYDROLOGY... Plume of moisture from Pac and GOMEX continues to flow overhead. Forcing comes in many waves with a very weak concentration at any one point. Instability will remain limited due to all the clouds and E/SE sfc wind flow. Wet ground, already-high streams and the anticipated rain will push many locations above their caution stages, and a few will approach and perhaps exceed flood stage. However, rain does look a little less in some places than prev forecasts. It looks fairly evenly distributed from this point on. Biggest risk remains for a widespread rise on all the small creeks and streams. The larger creeks will be a slightly lesser worry, but will be the biggest worry for any river forecast points. The mainstem and larger river flooding is the least of the worries. && .CTP WATCHES/WARNINGS/ADVISORIES...
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Flood Watch through this evening for PAZ004>006-010>012- 017>019-024>028-033>037-041-042-045-046-049>053-056>059- 063>066.
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&& $$ SYNOPSIS...Dangelo/Lambert NEAR TERM...DeVoir/Lambert SHORT TERM...Dangelo/Lambert LONG TERM...RXR AVIATION...Lambert/Gartner HYDROLOGY...

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