Area Forecast Discussion
Issued by NWS State College, PA

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000 FXUS61 KCTP 211128 AFDCTP Area Forecast Discussion National Weather Service State College PA 728 AM EDT Mon Oct 21 2019 .SYNOPSIS... This week will feature more dry days than wet days with rain expected on Tuesday. Seasonably mild temperatures on Monday will trend modestly cooler through midweek and remain near average through the weekend. && .NEAR TERM /THROUGH TONIGHT/... Low clouds and fog this morning should give way to a partly to mostly sunny afternoon. Sfc obs and RWIS data indicate areas of dense fog/lowest visby AOB 1/4SM being observed over the higher terrain from the Laurel Highlands into the Endless Mountains. An SPS may be issued through the morning commute. Lower elevations to the east of the Allegheny Plateau are primarily dealing with low clouds with some patchy fog in spots. The main forecast issue today will be timing low cloud dissipation. HREF data indicates the south central ridge and valley region will take the longest to erode and not fully break out until after 16-18Z. The earlier an area breaks out of the clouds, the more upside they will have in terms of maxT. Overall, expect the mildest readings in the mid to upper 60s on the northwest and southeast fringes of the CWA with the coolest temps (around 60F) over the interior high elevations along the Allegheny Front. Fcst soundings suggest the potential for a few sharp dewpoint drops given mixing of very dry air just above the inversion layer. This is mostly likely to occur over the northwest mtns where skies will be mostly sunny. Clouds will increase into tonight with an increasing south southeast flow ensuring very mild minimum temps running +10 to +15 degrees above average for late October. 00Z HREF shows the leading edge of frontal rains reaching the far western zones by 12Z Tuesday. && .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/... Confidence remains very high in a band of rain moving west to east across CPA on Tuesday. The strong south-southeast flow will transport 1-1.5 inch PWAT air (+2-3 standard deviations above the mean) into the region and support widespread soaking rain. Instability (MUCAPE) appears to be negligible (so no mention of thunder) but the deep moisture available should allow for locally heavy downpours. NBM/WPC blended QPF amounts are still in the 0.50 to 1.00 inch range with the highest totals most likely over the favored southeast flow/upslope areas across east-central PA. A secondary low developing over the Delmarva and tracking to LI may enhance rain should bring the last round of rain to far eastern/northeastern zones btwn 00-06Z Wed before pcpn shuts off west to east across the CWA by the predawn hours Wednesday. Flash flooding is not expected given the recent dryness (3hr FFGs 2-4+ inches) and limited rain rates in the absence of deeper convection. However, can`t rule out some very minor nuisance type street flooding or ponding in urban areas due to leaves clogging storm drains. It will turn mostly sunny, breezy and cooler on Wednesday behind the departing frontal system. High pressure will provide dry wx through Wednesday night with some potential frost/freeze risk for southeast zones still active in the extended growing season. && .LONG TERM /THURSDAY THROUGH SUNDAY/... There is reasonable consensus among the guidance in showing some light rain/showers skirting across the eastern Great Lakes and possibly clipping the northern tier of CPA on Thursday. However, pattern evolution uncertainty grows quickly heading into the weekend with very low confidence in the forecast at this time. The global model guidance continues to offer 2 possible solutions by this weekend: 1) a less amplified GFS with weaker, faster system with little to no rain; or 2) a stronger and slower system with a much higher probability of rain (later Sunday into Sunday night) advertised by the ECMWF/UKMET/CMC. Until there is a convergence/trend toward a common solution, the wide range of outcomes results in a very low confidence forecast which leans on gridded data from the National Blend of Models. && .AVIATION /11Z MONDAY THROUGH FRIDAY/... IFR conds in low clouds and areas of fog, especially along the hier elevation taf sites across the north and west, will give way to improved conds by mid morning. Elsewhere VFR conds will continue through the day. A return to wet conditions on Tuesday as a cold front crosses the airspace from west to east. Then improving conditions after Tuesday, as weak high pressure builds into the region. .Outlook... Tue...Rain/low cigs possible. Wed and Thu...No sig wx expected. Fri...Some showers possible, especially west late. && .CTP WATCHES/WARNINGS/ADVISORIES... None. && $$ SYNOPSIS...Steinbugl NEAR TERM...Steinbugl SHORT TERM...Steinbugl LONG TERM...Steinbugl AVIATION...Gartner/RXR

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