Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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188 FXUS61 KPHI 201418 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1018 AM EDT Fri Apr 20 2018 .SYNOPSIS... High pressure will build in from the west today and remain in the area through the weekend before sliding offshore on Monday. Low pressure developing over the southeastern United States will move up the Mid Atlantic coast, affecting our area through the mid week period. && .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Low pressure was located near the Canadian Maritimes this morning while high pressure was centered over the Midwest states. A relatively tight gradient in between both systems has resulted in a breezy start to the day with northwest winds 15-20 mph gusting 25-30 mph. Winds will relax ever-so-slightly this afternoon owing the presence of a weak surface trough over the area. Cold-air advection stratocu originating from Lake Ontario continues to break apart downstream past the Poconos owing to downsloping flow and mid-level subsidence in wake of the exiting mid-level trough. However, a CU field should be present through the afternoon with strong boundary-layer mixing underneath the subsidence inversion. High temperatures today in the 40s in the southern Poconos and far northwestern NJ and low to mid 50s elsewhere are close to what climo would be for March 20th but generally 10-15 degrees below normal for April 20th.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/... The center of the surface high is forecast to slide into the eastern Great Lakes Region and the upper Ohio River Valley tonight. We are anticipating a mostly clear sky with perhaps an increase in cirrus late tonight. The northwest wind is expected to diminish to less than 10 mph. We continue to issue frost and freeze products only for locations from the counties of Berks, Montgomery, lower Bucks, Mercer and Middlesex southward. We will begin frost and freeze products for much of the remainder of our forecast area next week. Based on the anticipated low temperatures for tonight (mostly in the 30s) and the decreasing wind, we may need to put some areas under a Frost Advisory. Another Freeze Warning is possible for the same locations as the current one. We will look at the next full suite of guidance before making a final decision during the day. && .LONG TERM /SATURDAY THROUGH THURSDAY/... Saturday Through Monday... Surface high pressure will build over the region through this period along with an associated upper level ridge. This will bring fair weather with sunshine and gradually warming temperatures. Forecast models are in excellent agreement with this scenario so a high confidence forecast for this period. In terms of the day to day specifics, each day will feature plenty of sunshine but there will still be a bit a NW breeze Saturday near 10 mph with highs generally in the upper 50s to low 60s (except cooler in the southern Poconos). This is still a little cool for this time of year. However winds will be lighter for Sunday and Monday with temperatures warming a couple degrees each day so by Monday, highs will be well into the 60s for much of the region. Lows each day will be chilly due to the clear skies and light winds...generally in the 30s with western and northern zones in the CWA likely dipping to near or below freezing. Tuesday through Thursday... Overall, no major changes to this part of the forecast as general thinking remains the same. A low pressure system will move across the Mississippi Valley and into the southeastern United States early next week. As the low pushes towards the coast, it starts to move northward towards the Mid-Atlantic states. While the forecast models agree that there is some form of a coastal low that develops and impacts our area, there are still differences regarding timing and evolution that lead to a relatively low confidence forecast at this time. The system will bear watching as it will have good moisture associated with it and the potential for some heavy rain will exist. Strong onshore flow could also bring some coastal flooding concerns and will also need to be monitored. Still a long way out and plenty of time to see how the models come together on this system over the coming week. && .AVIATION /14Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR with predominately few to sct CU with bases 4-6 kft AGL. NW winds 10-20 kt with gusts to 25 kt, weakening a bit mid to late afternoon. Tonight...VFR with a mostly clear sky. NW wind diminishing to less than 10 knots. OUTLOOK... Saturday...VFR conditions with northwest winds around 10 knots. High confidence. Sunday...VFR conditions with light winds. High confidence. Monday...VFR conditions expected along with continuing light winds. Moderate confidence. Tuesday...Mainly VFR conditions expected. East to southeast winds around 10 to 15 knots. Increasing cloudiness through the day. Moderate confidence.
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&& .MARINE...
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Today and tonight...NW winds have weakened slightly this morning but widespread gusts of 20-25 kt are still occurring as of 10 AM. Seas are currently around 5 ft. The 2 PM expiration time for the current SCA still looks reasonable as the diminishing trend for winds and seas will continue through the rest of the day. OUTLOOK... Friday night through Monday....Sub-advisory conditions are expected on the the area waters. Tuesday...Winds and seas increase in advance of an approaching coastal low with SCA conditions likely be late day.
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&& .FIRE WEATHER...
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We are expecting a northwest wind of 10 to 15 mph with gusts of 20 to 25 mph for today. Relative humidity values are forecast to drop around 30 percent in much of northeastern Maryland, Delaware, New Jersey and southeastern Pennsylvania. We will be coordinating with our fire weather partners later this morning regarding fuel moisture levels to determine if any additional fire weather products need to be issued for today.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ430- 431-450>455.
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&& $$ Synopsis...Fitzsimmons Near Term...Klein Short Term...Iovino Long Term...Fitzsimmons Aviation...Fitzsimmons/Iovino/Klein Marine...Fitzsimmons/Klein Fire Weather...

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