Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 261421 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 921 AM EST Sun Feb 26 2017 .SYNOPSIS... High pressure builds south of the region today and moves offshore by Monday afternoon. Low pressure approaching from the west will lift a warm front through the region on Tuesday. The aforementioned low will track from the Great Lakes region into eastern Canada. The associated cold front will move through the East Coast by Thursday morning. An upper trough builds into the Northeast for the end of the week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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930 am update: Only change to the forecast was to add some flurries to the southern Poconos and portions of Sussex County, NJ, as some northwest flow light snow showers occasionally make a push into these areas. Otherwise, forecast is in good shape. For the 630 AM update, increased the sky cover for much of the area faster at least for awhile this morning given a wealth of stratocumulus advecting southeastward. The hourly temperature, dew point and wind grids were tweaked based on the latest obs. A much colder day today as we get back to reality following a stretch of very warm temperatures (away from the immediate coast). A strong upper-level trough will continue to lift out of New England this morning with cold air advection in its wake. This cold air advection pattern will weaken especially this afternoon as the flow begins to back toward the west. A trailing strong short wave will become more channelized vorticity, therefore this combined with cold air advection mostly this morning results in any lingering isolated snow showers/flurries across the northern areas ending this morning. Surface high pressure will be sliding to our south later today, however its northern extent reaches into our area allowing for the pressure gradient to relax with time. Until this occurs, efficient mixing will occur especially after sunrise and therefore a breezy day is anticipated with gusts to around 30 mph. The winds are expected to drop off as we go through the afternoon due to incoming high pressure and waning cold air advection. Given the cold pool aloft for awhile, stratocumulus enhanced by the eastern Great Lakes will get pulled southeastward allowing for more cloudiness across much of our area through about early afternoon. These clouds should tend to thin/dissipate as gradual warming starts aloft this afternoon and some increasing subsidence occurs. High temperatures were mostly a MOS/continuity blend. A much colder day especially with the added wind, however temperatures will be much closer to where they should be for this time of the year.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM MONDAY/... High pressure centered to our south will gradually start to shift offshore through the overnight. As this occurs, the flow will continue to back more from the west and southwest. Some warm air advection aloft combined with low pressure tracking north of the Great Lakes should promote some high level clouds overnight. The winds are expected to quickly become light or even locally calm, setting the stage for a colder night. Low temperatures were mostly a MOS blend. && .LONG TERM /MONDAY THROUGH SATURDAY/... Unsettled weather on tap for most of the new week. High pressure centered just off the Mid-Atlantic coast Monday morning will continue to drift offshore during the day. Upper trough over the Northeast moves offshore as well, and upper flow flattens out. Return flow sets up during the day, and temperatures warm back up to above normal levels with highs in the mid 40s in the Poconos, and in the mid and upper 50s for the rest of the CWA. From there, low pressure organizes and develops over the central U.S. on Tuesday. A warm front develops ahead of this low, and lifts north through the Mid-Atlantic and Northeast during the day. Some light rain will develop with the passage of the warm front, but think the bulk of the rain will hold off until the late afternoon and evening when weak low pressure passes north of the region. Stronger low pressure over the Midwest then lifts into the Great Lakes on Wednesday, and then tracks towards northern NY State, and then into eastern Canada Wednesday night. There are some differences between the GFS and the ECMWF in terms of the timing and placement of the low, and a cold front tracks across the region behind the departing low by Thursday morning. With deep SW flow and WAA on Wednesday, temps soar back into the 50s and 60s, and possibly around 70 across the Delmarva. With several shortwaves passing through the region ahead of the upstream low, this may touch off some showers across the region, but low confidence on timing and placement of any showers. Will follow guidance and carry likely PoPs for Wednesday afternoon and Wednesday night with the approach and passage of the cold front. Will carry isolated thunderstorms as well. GFS indicating marginal instability. Cold front will be through the region by Thursday morning, and deep upper trough builds into the Northeast. Several strong shortwaves will pass through the region Thursday afternoon and Friday, and this will keep at least chance PoPs in the forecast during this time. Temps should be warm enough for rain on Thursday, and then cold enough for snow Thursday night through Friday morning. Strong CAA will be underway. Max temps will fall into the 40s and 50s on Thursday, which is still above normal, and then back to normal on Friday with highs in the 30s across the Poconos and in the low to mid 40s elsewhere. Canadian high pressure builds into the region by Saturday. Cold and dry conditions on tap with highs a few degrees below normal, in the 20s in the Poconos and in the upper 30s/low 40s elsewhere. && .AVIATION /14Z SUNDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with a ceiling around 4000 feet, which should scatter out this afternoon. Northwest winds around 15 knots with gusts to around 25 knots, then diminishing and turning locally westerly toward early evening. Tonight...VFR. Southwesterly winds 5-10 knots early, becoming locally light and variable to calm. Outlook... Monday...VFR. SW winds 5-10 KT. Moderate confidence. Monday night through Tuesday night...Scattered showers with MVFR conditions. S-SW winds 5-10 KT. Low confidence forecast. Wednesday through Wednesday night...Better chance for showers and isolated thunderstorms. SW winds 10-15 KT. IFR and lower conditions. Low confidence forecast. Thursday...Scattered showers. Winds become W-NW 10-20 KT with 20-30 KT gusts. Low confidence forecast. && .MARINE... Cold air advection occurring (into this afternoon) is allowing the boundary layer to cool early this morning. This is creating an improved vertical mixing environment, with gusts up to 30 knots. A Small Craft Advisory is in effect through the day, except through early this evening for the northern two Atlantic coastal waters zones. The winds are expected to diminish from south to north this afternoon and especially this evening as the pressure gradient relaxes and the cold air advection wanes. Seas have lowered some given the gusty offshore flow. Outlook... Monday through Monday night...Sub-SCA conditions on the waters. Tuesday through Wednesday night...SCA conditions. S-SW winds 15-20 KT with 25-30 KT gusts. VSBY restrictions in rain/fog, especially Wednesday and Wednesday night. Isolated thunderstorms possible Wednesday afternoon/evening. Locally dense fog possible Wednesday night. Thursday...Wind become W-NW 15-20 KT with 25-30 KT gusts. Scattered showers. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ430- 431-452>455. Small Craft Advisory until 9 PM EST this evening for ANZ450- 451. && $$ Synopsis...MPS Near Term...CMS/Gorse Short Term...Gorse Long Term...MPS Aviation...Gorse/MPS Marine...Gorse/MPS

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