Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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137 FXUS61 KPHI 211546 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1146 AM EDT Sat Apr 21 2018 .SYNOPSIS... High pressure builds over our area through Sunday, then moves offshore on Monday. Low pressure over the Gulf Coast states tracks to the east, and slowly impacts the Mid-Atlantic during the mid-week period. Another area of low pressure may affect the region at the end of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... An upper air analysis showed a lingering trough in the Northeast with a closed low ejecting into the Central Plains. There is some ridging from Hudson Bay Canada toward the Midwest. At the surface, high pressure is centered from the eastern Great Lakes to the Mid- Atlantic region. While surface high pressure is producing some low-level subsidence, a 250 mb jet positioned just to our north is providing enough lift within the fast northwest flow aloft to produce some cirrus. This may thicken a bit at times, but overall lots of sunshine is anticipated. The 12z Sterling, VA raob shows the cirrus level cloudiness between 300 mb and 200 mb. Dry conditions are expected with even some lowering of the surface dew points with ample boundary layering warming and enough mixing. The winds will be less than yesterday, but there will still be a breeze. The hourly temperature, dew point and wind grids were adjusted based on the latest observations/trends. This includes showing a quicker rise in temperatures through at least early afternoon for many places. The dew points were lowered a little for most locales as some lowering as already taken place given mixing and ample boundary layer warming. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/... Northwest midlevel flow will continue tonight as a surface ridge remains over the region. Some perturbations in the midlevel flow will approach the region by morning, but there is little lift with these perturbations. Other than some increased mid and upper-level clouds, not expecting much in terms of sensible weather impacts. This means that temperatures will once again be the primary forecast concern. Could see temperatures flirting with freezing again in portions of the area with the growing season underway, but tonight`s environment will be a little less favorable. For one thing, if increased cloud cover is present, some radiation may be re-emitted to the surface (though the height of the clouds will not hamper nocturnal cooling as much as one may anticipate). This will be especially true in the southern CWA, but how far north these clouds persist may prove critical in how far temperatures fall in more susceptible locations such as the Pine Barrens. At this point, way too uncertain/marginal to issue additional frost/freeze products. My suspicion is that no additional products will be necessary. && .LONG TERM /SUNDAY THROUGH FRIDAY/... High pressure over the area Sunday slowly drifts offshore Sunday night, and remains over the western Atlantic Ocean waters through Monday night before drifting offshore on Tuesday. Plenty of sunshine and mild, though temperatures will generally be a few degrees below normal during the day. At night, with clear skies and light winds, radiational cooling conditions will allow for colder conditions in the mountains and in the Pine Barrens of NJ. During this time, low pressure over the Gulf Coast states will slowly track to the east, and will be over the Southeast U.S by Tuesday evening. A warm front just southwest of the region lifts north through the region Tuesday night as the low tracks north along the coast. Though there are rain chances during the day Tuesday lifting from south to north, the best chances will be Tuesday night as the low lifts to the north. The low then slowly works its way north through Wednesday, will be south of Long Island Wednesday night, and departs on Thursday. Although there may be a period on Wednesday where locally heavy rain is possible at times, not expecting a prolonged period of widespread heavy rain with this system. Weak high pressure builds through the region late Friday and Friday night. Another cold front approaches on Saturday. Temperatures during this time will generally be at or below normal levels for most of the week, but temperatures trend warmer towards the end of next week. && .AVIATION /16Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. This Afternoon...VFR with high clouds. Northwest to west-northwest winds around 10 knots. Tonight...VFR. Clouds at or above 10,000 feet, especially near and south of PHL. Winds becoming light and variable. OUTLOOK... Sunday through Monday night...VFR. Generally light winds. High confidence. Tuesday...Generally VFR. Clouds build from south to north. E-SE winds 10-15 kt. Tuesday night through Wednesday...MVFR/IFR in rain and fog. E-NE winds 10-15 kt. && .MARINE... Fair weather and sub-advisory winds/seas are expected through tonight. Northwest winds 10 to 15 kts (possibly gusting to 20 kts or so) will likely switch to southwest this afternoon before switching back to northwest or north tonight. Seas should remain near or below 3 feet. OUTLOOK... Sunday through Tuesday...Tranquil conditions on the waters with sub-SCA conditions. Tuesday night and Wednesday...Rain, fog, and gusty E-NE winds as low pressure impacts the waters. SCA conditions expected. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...MPS Near Term...Gorse Short Term...CMS Long Term...MPS Aviation...CMS/Gorse/MPS Marine...CMS/MPS

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