Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 230514 AFDCTP Area Forecast Discussion National Weather Service State College PA 1214 AM EST Mon Jan 23 2017 .SYNOPSIS... A multifaceted storm will bring drenching rain, elevation- driven snow and gusty winds to Central Pennsylvania on Monday. High pressure and unseasonably mild conditions will briefly return for midweek before a pattern change brings colder temperatures and lake effect snow to close out the month. && .NEAR TERM /UNTIL 6 AM THIS MORNING/... Low visibilities in stubborn denser fog finally rising a bit from Altoona through State College up toward Williamsport where a swath of fog has been persistent through the day and into this evening. PoPs currently trending upward across the region as moisture and lift increases ahead of the strong storm system tracking northeast across the Southern Appalachians. Band of light rain developed over northern mountains this eve, but QPFs were minimal. PoPs increase from south to north tonight, as latest radar and HRRR progs shows rain continuing to spread north of the Mason-Dixon line overnight. Also, winds will pick up from the east over the lower susq toward sunrise, with speeds rising to 20mph and getting gusty later in the morning. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM TUESDAY/... Rain will increase in coverage and intensity from south to north through daybreak Monday. A tightening pressure gradient between deepening low pressure in the Carolinas and high pressure in eastern Quebec will produce strong/gusty east winds early Monday morning and continue through Monday afternoon. Issued a wind advisory for most of the lower Susquehanna Valley with max wind gusts 45-50mph. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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All model data tracking closed upper low northeast across Virginia Monday. A steady rain will overspread Pa from north to south as strong upper lvl divergence, anomalous easterly low lvl jet/PWATS work into the state. Thermal profiles initially warm enough for rain everywhere. However, dynamic cooling associated with arrival of strongest forcing will likely result in a changeover to wet snow over the higher terrain of central Pa. Forecast soundings suggest the highest elevations of the Laurels/Northern Mtns could mix with or change to wet snow around midday. By later in the day, snow could become more than just a higher elevation threat, with thermal profiles even as far east as AOO/UNV cooling sufficiently for all snow. Limiting factor in terms of accumulation will be marginal boundary layer temps and warm ground. The threat is for several inches of heavy wet snow, especially favoring the higher elevations, across northern Pa. A winter storm watch has been issued for the northern counties, where 6+ inches appears possible, mainly over the higher terrain. Biggest threat across the Lower Susq Valley will likely be gusty winds, the result of tightening pressure gradient between approaching low pressure and high north of New England. Bufkit soundings indicate wind gusts in excess of 40kts are likely across southeast Pa, as low lvl jet swings through Monday. Per coordination with LWX/PHI, have issued a wind advisory for this area. Lastly, still monitoring the potential for minor flooding. Target area for the heaviest rain is across the south central part of the state, where orographic forcing at nose of powerful easterly low level jet will play a role. Mean QPF from both SREF and GEFS max out around 1.5 inches in this region, which would be a beneficial rainfall. However, given FFG/FFH values around 2 inches, can`t rule out some minor flooding. The surface low will reach our latitude between about 6-12Z Tuesday, an old rule of thumb that dictated when the steady precip tends to taper off. Upper ridging will quickly build into the region later Tuesday into early Wednesday, bringing a short period of fair and mild wx. A pattern shift is advertised for the second half of the week as low pressure takes up residence over eastern Canada, and despite a tenacious ridge over the northern Caribbean and Bahamas, models carve out a long wave trough over the eastern US with a return to seasonable cold by the end of the week into next weekend. The ridge in the west and trough in the east is also usually a good one for winter storminess, but the deterministic ECMWF and GFS don`t show much more than a series of clipper type systems that promise an extended period of clouds and scattered mainly mountain snow showers that should continue through next weekend into the week after.
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&& .AVIATION /05Z MONDAY THROUGH FRIDAY/...
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With the showers moving in, and winds beginning to pick up, much of the LIFR conditions have improved, but while visibilities have improved, ceilings continue to lower in response to easterly flow. After several hours of variable cig and vis conditions, expect most areas to settle into mainly IFR conditions late tonight and much of Monday, with a widespread rain event moving into the region. Later in the period across the west and north, conditions expected to deteriorate even more as we approach 20z-00z...with rain mixing with and possibly changing to snow. Extent and degree of changeover still in question, but dynamic cooling may bring some rain/snow mix into most areas except the far southeastern airfields. Additionally, strong gusty winds will impact southern airfields beginning late tonight and Monday. KMDT/KLNS may see gusts approaching 30-35+KT. Low level jet will introduce LLWS at most central and southern airfields late tonight and Monday. Outlook... Tue...Widespread sub-VFR with some improvement by aftn. Rain/snow ending in the morning. Gusty winds from NNW decreasing late. Wed...Low cigs/rain possible western 1/2. Breezy late. Thu-Fri...MVFR/IFR in rain/snow showers west. MVFR to VFR east.
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&& .CTP WATCHES/WARNINGS/ADVISORIES...
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Winter Storm Watch from noon EST today through Tuesday morning for PAZ005-006-037-041-042. Wind Advisory from 5 AM early this morning to 4 PM EST this afternoon for PAZ057-059-064>066.
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&& $$ SYNOPSIS...RXR/Steinbugl NEAR TERM...RXR/Steinbugl SHORT TERM...RXR/Steinbugl LONG TERM...Fitzgerald/La Corte AVIATION...Jung

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