Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 210127 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 927 PM EDT Mon May 20 2019 .SYNOPSIS... A cold front moves across the waters tonight, and then high pressure will bring dry and pleasant weather Tuesday and Wednesday. A warm frontal passage is likely Wednesday night, followed by a cold front Thursday night. High pressure will again be nearby Friday and into Saturday. By the weekend, another frontal system will be approaching. A cold front will likely cross the region late Saturday and potentially stall to our south on Sunday. && .NEAR TERM /UNTIL 6 AM TUESDAY MORNING/... A cluster of thunderstorms fired up over southern New Jersey out ahead of the approaching cold front, but have moved offshore. There may be a few lingering showers, and perhaps a thunderstorm, over Delmarva and along the New Jersey coast, but any lingering activity will taper off in the next hour or so. Cold front will be through the region by midnight or so, and cooler and dryer air will filter into the region through daybreak Tuesday. Lows tonight generally in the 40s up north, and otherwise in the 50s. && .SHORT TERM /6 AM TUESDAY MORNING THROUGH 6 PM TUESDAY/... An upper-level trough across the Northeast will keep some cyclonic flow in place, while a ridge begins to build into the central Great Lakes. Surface high pressure centered near the central Great Lakes will build or extend toward our area through the day Tuesday. The combination of some cold air advection, a pressure gradient present and deeper mixing will result in a breezy day. The airmass looks rather dry, therefore while plenty of sunshine is expected there may be some boundary layer heating driven stratocumulus. High temperatures are a MOS/continuity blend, however some of the model guidance 2-meter temperatures are a few degrees colder. Given the stronger offshore flow, a sea breeze is not expected and therefore not much difference in temperatures from the coast to just inland. && .LONG TERM /TUESDAY NIGHT THROUGH MONDAY/... Overview... A rather stagnant big picture pattern remains in place for the duration of this week and into the holiday weekend. It is the familiar beat of "trough in the West, ridge in the Southeast", and the mid-Atlantic sitting near the edge of the ridge. This pattern will continue to favor periodic storm systems lifting out of the Plains and Midwest, with occasional shower and storm chances in our area as these lows lift off to the northeast. Timing the disturbances is tricky given the vast amount of upstream convection which tends to play havoc with the guidance. Tuesday night through Wednesday look to be reliably dry with high pressure in control. Thursday evening stands out as a more likely opportunity for showers and storms, with probably another chance towards Saturday. The Thursday system should be watched, as the environment late in the day Thursday looks rather conducive to severe weather. Shower and storm chances for the weekend currently look more garden variety as the next low center likely passes further away from us, reducing forcing. The other issue will be our temperatures. The expansive Southeast ridge will favor intense, sustained summer heat to our south, but it is less clear cut as to how firm a grasp the warmth will have over us. With multiple frontal passages and a frequently varying wind direction, there are likely to be some ups and downs and some local variations, such as on Saturday when onshore flow will likely keep the coast cooler. Overall, however, we are likely to be above normal for temperatures most of this period. Dailies... Tuesday night-Wednesday... This portion of the forecast is straightforward, as high pressure moves across the area and ensures dry and seasonable weather. Wednesday night-Thursday night... A warm front should move through Wednesday night, setting up what could be a rather active 24 hours of weather. High uncertainty as to how it all plays out, as there will be precipitation risks with both the Wednesday night warm front and the cold front that will approach by Thursday night. For Wednesday night into Thursday morning, looks like scattered showers with possibly some elevated thunderstorms. We should dry out Thursday afternoon, with temperatures getting into the 70s to near 80. Rain chances then go up again for the evening and overnight. Low pressure, with a trailing cold front, will track eastward through the Great Lakes then turn southeasterly as it rides along the top of the ridge. Concern is that if enough instability is present, we could have strong to severe storms given wind fields really intensify as the low pressure makes its turn to southeasterly. An evening or overnight MCS event appears possible. Given it`s still a few days away, will hold off on more detail for now. Friday... Most indications are that this should be a dry day in between systems as we are on the periphery of high pressure. Temperatures near to above normal, except cooler at the coast with an onshore component developing in the wind. Saturday... The daytime period on Saturday looks dry, as retreating high pressure should still lend us protection for most of the day. A cold front will be approaching from the west by late day and evening as another low moving out of the Plains tracks up into Ontario. This may bring a shower and storm risk towards the evening, especially to the west. Not overly concerned about strong storms here, as flow will be onshore Saturday, keeping things stable. This will also keep temperatures Saturday a little cooler than the upper air charts would suggest, especially at the coast, though it should be plenty comfortable with 70s and low 80s. The shower risk will likely increase into the overnight. Sunday-Monday... Saturday`s "cold front" will in fact act to warm temperatures on Sunday by kicking out the onshore flow and turning winds westerly. This westerly wind should also keep the dew points in check, especially if the wind ends up a little north of west. Because of this, Sunday could be quite warm, with strong sensible heating likely in the post-frontal air mass. Widespread 80s look likely with 90s potentially in play as well, though did not go that extreme yet. A caveat, however, is that if the front stalls near or just south of us, a more humid day with afternoon showers and storms would be possible. Went on the drier side for now. Very low confidence by next Monday as another cold front may approach. Could be another warm day if the front is slow enough, but just leaned towards a consensus blend for now. && .AVIATION /01Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Tonight...VFR. Any showers and thunderstorms ending early. West-southwest winds 8-12 knots, becoming northwest. Tuesday...VFR. Northwest winds 12-15 knots with gusts to 20-25 knots. Outlook... Tuesday night-Wednesday night... Mainly VFR. Light north to northwest wind becoming light and variable Wednesday night. Some showers and locally MVFR conditions possible Wednesday night. Thursday-Thursday night... Most of the daytime Thursday should be VFR with a light southwest wind. Showers and thunderstorms possible Thursday evening and night with winds gradually shifting to northwest. Friday-Saturday... VFR expected. Northerly wind initially on Friday will become northeasterly during the afternoon, easterly to southeasterly Friday night, and southerly by Saturday. && .MARINE... South to southwest flow will continue this evening, however, a wind shift to the west and northwest occurs tonight as a cold front moves through. Northwesterly flow continues Tuesday with some gusts to about 20 knots and seas on the ocean will be up to 4 feet. Therefore, the conditions are anticipated to remain below Small Craft Advisory criteria through Tuesday. Some showers and thunderstorms move through early this evening, some of which could produce locally gusty winds. Outlook... Tuesday night-Friday... Winds and seas are expected to remain below SCA criteria. Rip Currents... A northwest wind with no sea breeze expected should result in a low risk. && .EQUIPMENT... The KDIX radar is back online. However, it will be in a test phase through early Tuesday afternoon. Intermittent outages are possible. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...O`Brien Near Term...Gorse/MPS Short Term...Gorse Long Term...O`Brien Aviation...Gorse/MPS/O`Brien Marine...Gorse/MPS/O`Brien Equipment...

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