Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 262041 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 341 PM EST Sun Feb 26 2017 .SYNOPSIS... High pressure will move off shore tomorrow. Low pressure approaching from the west will lift a warm front through the region on Tuesday. That low will track from the Great Lakes region into eastern Canada on Wednesday. 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 AM MONDAY MORNING/... Water vapor imagery depicts the strong vort max affecting our region yesterday moving into the Canadian Maritimes with the trailing end becoming elongated zonally by the upper-level jet streak encompassing much of the eastern half of the U.S. Cold air advection is waning as a surface high approaches the East Coast. Stratocumulus deck is eroding from southeast to northwest as northwest flow weakens. As the surface high reaches the coast this evening, surface winds will begin to decrease. With the clearing skies and light winds, should see a fairly decent drop in temperatures this evening. However, low-level isentropic ascent will commence by late tonight as return flow on the upstream side of the surface high moves in. Clouds will begin to increase late tonight, especially in the southern CWA, which may curb more substantial cooling in this area. As a result, I stuck close to guidance given the competing factors in place -- but it is possible the places most susceptible to radiational cooling could be cooler than what is forecast. These trends will be monitored this evening to see if temperatures need to be lowered a little bit. && .SHORT TERM /6 AM MONDAY MORNING THROUGH 6 PM MONDAY/... As the surface high moves farther east into the Atlantic, southwest surface winds will become established across the area on Monday. Substantial near-surface warm air advection will contribute to a much warmer day Monday, with temperatures returning to well above average values. A perturbation in the west-southwesterly upper-level flow will approach the Mid-Atlantic by 00Z Tuesday, with cloud cover continuing to increase. However, residual dry air in the low levels and generally weak large-scale ascent should prevent much if any precipitation from occurring before sunset. Notably, model guidance has been all over the place in the handling of this system for days, rendering confidence much below average in the details -- even for a 12-24 hour forecast. There are at least some indications lift may become sufficient to produce light precipitation to the west of the area (generally the Appalachians westward in southern PA and adjacent MD/VA/WV) by late morning or early afternoon. However, the aforementioned limiting factors seem too much to overcome for generating precipitation in the CWA by the end of the short term period. Thus, reduced PoPs on Monday to non-mentionable levels. Guidance has struggled mightily with temperatures in warm air advection patterns this past month. Went slightly above guidance for highs based on the expected cloud cover present -- otherwise, I would have gone well above guidance. However, would not be at all surprised to see highs several degrees warmer than forecast, especially if the models are overdoing the moist air advection in the 900-700 mb layer. && .LONG TERM /MONDAY NIGHT THROUGH SUNDAY/... A very active pattern continues through the long term. Monday night through Tuesday night...warm front will lift north through the region. Some weak lift is expected with the front followed closely by a local vorticity maxima associated with the low lifting into the Great Lakes Region. It isn`t exactly an impressive set up for widespread precip, but models continue to depict QPF across the region through this period. It looks like the best chance through this period would be Tuesday afternoon and evening, when we still have a slight onshore component to the low level flow. Wednesday and Wednesday night...This is the period of greatest focus as it looks like our region will once again be solidly in the warm sector as a pre-frontal trough slides offshore and the cold front approaches from the west. With continued southwesterly flow, should see temperatures once again well above normal, approaching record highs (see climate section below). The combination of the very warm boundary layer (resulting in a relatively unstable profile with modest CAPE values) and a mid and upper level southwesterly jet (resulting in bulk shear values above 50kt) means there is once again a risk for strong or severe storms. The biggest source of uncertainty right now is the timing, primarily of the cold front. There are considerable differences with the GFS showing the most progressive solution, bringing the cold front through Wednesday evening, while most of the rest of the guidance shows a cold frontal passage late Wednesday night. The GFS solution would be the highest risk as the warmest conditions would be coincident with the best lift. Even with the slower solutions, there remains some risk for severe storms, it would just be a more limited period. As for the hazards, it looks like the primary hazard would be strong winds. Current model soundings show limited instability in the hail growth region, limiting the threat of large hail. If there is widespread rain on Tuesday leading in to the event, then the risk for poor drainage flooding could increase for Wednesday. Thursday and Friday...strong cold air advection with breezy northwesterly winds. At this point, it looks like we will have at least 2 consecutive days of below normal temperatures. A fast moving low may dig across the region, though there remains considerable uncertainty with the track. Saturday and Sunday...High builds south, keeping us in the cold air for a few more days, although there may be a modest warming trend by Sunday as winds shift more westerly. && .AVIATION /21Z SUNDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. VFR through Monday afternoon, with SCT-BKN stratocumulus deck around 5000 feet dissipating through early evening. Northwest winds will diminish quickly by 00Z, becoming mostly light westerly or even variable by late evening. After a period of mostly clear skies through about 09Z, clouds will increase with CIGs of 8-15 kft expected after 12Z. Southwest winds will develop tomorrow, but should generally remain below 10 kts. Outlook... Tuesday...Should begin as VFR, but ceilings could lower to MVFR later in the day as rain begins to move in. Wednesday and Wednesday night...Thunderstorms are likely, primarily Wednesday afternoon or Wednesday night. With any storms or showers, MVFR or even IFR conditions are expected. There will be an abrupt shift to breezy northwesterly winds with the cold front which should arrive Wednesday night. Thursday and Friday...Mostly VFR conditions. There is a small chance of lower conditions with rain and snow showers Thursday night into Friday. Very breezy northwesterly winds are possible both days. && .MARINE... Seas are beginning to subside in the coastal waters, and winds are slowly diminishing. Small craft advisory conditions should end by early this evening, as expected. Sub-advisory conditions are forecast thereafter through Monday afternoon. Outlook... Tuesday through Wednesday...southwesterly winds at or above 25 kt likely, especially on the coastal waters. Periods of showers and thunderstorms possible, especially on Wednesday. Wednesday night...Thunderstorms and showers possible. An abrupt shift to northwesterly winds is expected with a cold front either late Wednesday night or Thursday morning. Thursday and Friday...Northwesterly winds gusting above 25 kt are likely through out the period. There is also a chance for gale force gusts, primarily Friday afternoon and Friday night. && .CLIMATE... Record max temps for Wednesday March 1. 1972 was the year for most except GED ACY 72-1972 PHL 76-1972 ILG 75-1972 ABE 67-1972 TTN 74-1972 GED 73-1976 RDG 74-1972 MPO 67-1972 && .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...Johnson Near Term...CMS Short Term...CMS Long Term...Johnson Aviation...CMS/Johnson Marine...CMS/Johnson Climate...Drag is the U.S. government's official web portal to all federal, state and local government web resources and services.