Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 162351 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 751 PM EDT Sat Mar 16 2024 .SYNOPSIS... Weak high pressure moves offshore tonight. A weak cold front passes through on Sunday followed by a secondary cold front passing through on Monday. A few upper level disturbances will pass north of the area through the mid-week period as surface high pressure builds to the west. Low pressure approaches towards the end of week into next weekend. && .NEAR TERM /THROUGH SUNDAY/...
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Overall, the term forecast remains on track. A zonal flow aloft will back later tonight and especially Sunday as a strong upper- level trough approaches from the west. At the surface, weak high pressure will continue to slide to our south into this evening before shifting offshore during tonight. Much drier air and enough subsidence is resulting in a mainly clear sky which will continue through about the first half of tonight. As the aforementioned upper-level trough gradually shifts south and eastward across the Great Lakes and adjacent Canada, surface low pressure will track well north of our area overnight and Sunday. An associated cold front however will move across our region Sunday morning. The main forcing for ascent is forecast to lift north of our area, however a period of stronger frontal forcing to our west should result in a band of rain or showers with the front. This however should weaken with a southern extent as it shifts eastward overnight and Sunday morning as the main forcing peels off to our north. There may be a secondary area of convergence or lift glancing our far southeastern zones early Sunday morning as a southwesterly low- level jet of 40-50 knots crosses our area. Therefore, some showers are possible later tonight and Sunday morning for mainly the northern to far western areas and near our far southeastern zones. Any rainfall looks to be light. Temperatures should drop the most this evening as winds turn lighter and before more cloud cover starts to arrive. Given the expectation of an increase in clouds overnight and the arrival of a southwesterly low-level jet, temperatures should tend to level off or even rise some overnight especially across the coastal plain. As we go through Sunday, a positive-tilt upper-level trough will gradually be getting closer to our area. This will push the aforementioned cold front offshore during the morning with some cold air advection increasing in its wake. The core of the colder air however hangs back farther west beneath the upper-level trough. While high temperatures will once again be above average, a little more cooling will occur given the cold front that clears the area. A much drier air mass however will advect across the region, and with deeper mixing during peak heating the dew points will drop into the 20s for much of our area. A tightening pressure gradient combined with the cold air advection aloft will result in deeper mixing through the day and therefore a gusty northwesterly wind is expected. The cloud cover should thin out at least some, however the model forecast soundings indicate at least some stratocumulus development possible within the northwesterly cold air advection regime.
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&& .SHORT TERM /SUNDAY NIGHT THROUGH TUESDAY/... Upper level troughing will be slowly pushing into the area Sunday night and Monday with the main trough axis pushing through Monday evening. A secondary shortwave crosses the region later Tuesday but its not nearly as deep. At the surface, low pressure to the northeast and high pressure building in from the west will provide a northwesterly gradient through the period, with cold advection much of the time. With the troughs passing, the chance of some snow showers will exist in the Poconos, particularly Monday night and again late Tuesday. However, the air mass will be rather dry, so it may be hard to squeeze out measurable snow. Winds will be gusty from the northwest on Monday with gusts of 20-30 mph, but by Tuesday the gradient tightens further and we may have gusts of 30-40 mph area- wide. Combined with the much colder temperatures, and we will really feel the chill, even though highs aren`t going to be all that below normal... just much below what we`ve had lately. Lows won`t be that much colder, though, since the gradient and some stratocumulus likely holds them up somewhat. Highs will be near 50 on Monday and mostly 40s Tuesday, with lows in the 30s Sunday night and near 30 on Monday night. && .LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/... An upper level trough will be located over the Northeast and Mid- Atlantic states through Wednesday night. Several impulses embedded in the upper flow will pass north of the area during this time. These impulses may allow for periods of rain/snow showers to occur across the Poconos and northern New Jersey during the Tuesday night and Wednesday timeframe as a cold front crosses the area. Elsewhere, fair weather is expected with seasonable temperatures. High pressure then approaches from the west, building over the Great Lakes region on Thursday before shifting offshore on Friday. Quiet and seasonable weather is expected. Attention turns to Friday night into next weekend where a southern stream low pressure system will be located near the Southeast US. Forecast guidance varies greatly with the details on the track of this system whether it tracks out to sea or up the coast. For this reason, have carried the chance of showers wording into the start of next weekend. && .AVIATION /00Z SUNDAY THROUGH THURSDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Tonight...VFR, with clouds increasing overnight. There is a low chance (about 20-30 percent) for a few showers for KRDG to KABE to north of KTTN after 06z. Southwest surface winds diminishing to mainly less than 10 knots. A southwesterly low-level jet of 40-50 knots arrives overnight and that could lead to some low- level wind shear, however the duration may be limited and therefore opted to not include a mention. Additionally, the arrival of the LLJ may result in a slight uptick in wind speeds to around 10 knots, closer to sunrise. Moderate confidence. Sunday...VFR ceilings should lift and thin some. A few early morning showers possible mainly from KRDG to KABE to north of KTTN. Southwest winds around 10 knots early become west- northwest and increase to 12-15 knots with gusts up to 25 knots. Moderate confidence. Outlook... Monday and Tuesday...VFR overall. Main concern will be gusty NW winds which may reach 20-25 kts Monday and 30-35 kts Tuesday. Winds will be lighter at night and early in the mornings. Tuesday night...VFR likely. SW winds around 5-10 kt. Moderate confidence. Wednesday....VFR likely. SW-W winds around 10-15 kt with gusts up to 25 kt possible. Moderate confidence. Wednesday night through Thursday...VFR. W-NW winds ranging between 10-20 kt. Moderate confidence.
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&& .MARINE... Small Craft Advisory issued for the New Jersey coastal waters late tonight through about mid morning on Sunday. A southwesterly low- level jet is forecast to move across the area overnight and early Sunday morning ahead of a cold front. There looks to be enough mixing beneath an inversion for a period of 25-30 knot gusts. This appears to be more marginal for the Delaware coastal waters and into Delaware Bay, therefore held off on an advisory for here at this point. Seas will also increase for a time, then offshore flow during Sunday will lower the seas some. Outlook... Monday and Tuesday...SCA conditions possible Monday, with gales possible Tuesday. Tuesday night...SCA conditions possible early. W winds of 10-20 kt with gusts up to 25 kt. Seas of 2-4 feet. Wednesday through Wednesday night...No marine headlines expected, although marginal SCA conditions possible late Wednesday night. W-NW winds around 10-15 kt during the day, becoming 15-20 kt at night. Seas of 2-4 feet. Thursday...Marginal SCA conditions possible early Thursday. W-NW winds around 15-20 kt. Seas of 2-4 feet. && .FIRE WEATHER... While some showers may occur late tonight and Sunday morning mainly across northeast PA and northwest NJ, a period of dry and increasingly breezy conditions starts on Sunday and continues through Wednesday. The minimum relative humidity values lower to generally 30 to 35 percent during peak heating each day, with west to northwest winds 15-20 mph and gusts 30-35 mph. The strongest winds look to occur on Tuesday. The region has received a lot of rain over the last several weeks, therefore will have to see how the fuels, especially the fine fuels, dry out. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 2 AM to 10 AM EDT Sunday for ANZ450>453. && $$ SYNOPSIS...DeSilva NEAR TERM...AKL/Gorse SHORT TERM...RCM LONG TERM...DeSilva AVIATION...AKL/DeSilva/Gorse/RCM MARINE...DeSilva/Gorse/RCM FIRE WEATHER...WFO PHI

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