Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 240717 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 317 AM EDT Mon Jun 24 2019 .SYNOPSIS... High pressure loses its grip over the area today as it moves offshore. Low pressure will move across the Great Lakes and then into Canada today through Tuesday. Its associated fronts will move across the Middle Atlantic region. High pressure will build back in from the south for the mid to late week period. Another low will move towards the region next weekend dragging a cold front southward through the area. && .NEAR TERM /THROUGH TODAY/... High pressure off the Mid-Atlantic coast continues to drift out to sea. Meanwhile, a warm front approaches from the west. With clear skies, light winds, and slowly increasing low-level moisture with dewpoints creeping up to around 60/low 60s, some patchy fog will develop through the pre-dawn hours. That fog should burn off quickly after sunrise, and the day starts out sunny. High clouds out ahead of a warm front lifting through the Ohio Valley and Appalachians will spread into the region during the day, resulting in filtered sunshine by late afternoon. Some weak mid-level shortwaves may spark off some afternoon showers and thunderstorms across western zones, and those storms could make it as far east as the I-95 corridor. However, with H5 riding building in from the west, would not expect activity to become widespread or well organized. Will keep PoPs capped at chance for far western portions of the forecast area, and slight chance as far east as Philadelphia. Southwest flow will usher a more humid airmass into the region with surface dewpoints climbing well into the 60s throughout the day. Temperatures will be a bit warmer than Sunday, generally in the mid to upper 80s. && .SHORT TERM /TONIGHT THROUGH 6 PM TUESDAY/... H5 ridge moves over New Jersey early in the evening, and then moves offshore shortly after midnight. Low pressure passes north and west of the region late tonight, and as it does, will drag a warm front through the region after midnight tonight. With the support of 500 mb shortwaves, showers and thunderstorms will form to the west, and pass through the region tonight. Some showers and thunderstorms are possible in the evening, but the bulk of the activity will hold off until after midnight and into Tuesday morning. Surface-based CAPE values will generally be less than 200 J/kg, but MU CAPE values at 0-1 km will be as high as 1500 J/kg. So there is some support for convection, but the main threat will be for heavy rain. With surface dewpoints well in the 60s and low 70s, PWATs will be over 2 inches, and given the flooding that occurred last week, the ground remains saturated, and it will not take much rainfall for flooding to occur. However, with winds aloft at 25-35 kt, storms should be moving quickly enough to limit widespread flash flooding. Still cannot rule out localized flooding in heavier showers and thunderstorms. Since the main threat will be in the pre-dawn hours, it will be important to check the roads Tuesday morning before your morning commute. Low pressure departs Tuesday morning, and showers and thunderstorms taper off late. Some wrap-around precip may keep some lingering activity across northern and eastern zones into the afternoon, but most of the region should dry out during the day. Winds shift to the west behind the departing low, and it will take some time for appreciably dryer air to filter into the region. Highs on Tuesday top off well into the mid and upper 80s. && .LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/... Tuesday night through Friday... A summer pattern expected with building H5 heights and sfc high pressure across the western Atlantic. This will help to pump above average temperatures and increasing humidity to many areas of the East. Guidance is showing several days in a row of max temperatures right around 90 for much of the region. This would be the first `heat wave` by definition, but a day in the upper 80s would stop the stretch. Nonetheless, we haven`t had a week like this yet this summer, so getting ready for the heat would be advised. A couple scattered showers or a tstm possible Thu, but well keep the chc low since no organized system will be present and the weather will otherwise be precip free with skies generally mainly clear to partly cloudy. Next weekend...Many of the longer range models are showing an deep upper low across Ontario/Quebec dropping southward into New England by early next week. An associated sfc low and sharp cold front are depicted sweeping N to S across our area Saturday night and Sunday. This will likely put an end of the early season heat and bring a refreshing dry/cool air mass of the last day of June and into July. We`ll have more details as the week progresses. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Patchy morning fog, otherwise VFR. Some late day SHRA/TSRA possible at KRDG, but confidence not high enough to include in the TAF at this time. SW winds less than 10 kt. Tonight...Scattered SHRA/TSRA possible in the evening, but the bulk of the activity will hold off until after 06Z Tuesday. Sub-VFR conditions, possibly IFR or lower in the heaviest rainfall. VSBY restrictions in patchy fog as well. Light south winds. Tuesday...Lingering SHRA/TSRA taper off Tuesday morning, then generally VFR for the rest of the day. West winds less than 10 kt. Outlook... Tue night thru Fri night...Mostly VFR. Patchy morning fog and also some haze possible. && .MARINE... Sub-SCA conditions today through Tuesday. Showers and thunderstorms with locally heavy rain will develop late tonight through Tuesday morning. VSBY restriction in fog possible as well late tonight. Outlook... Tue night thru Friday...sub-SCA. Mostly fair thru the period. Rip Currents... There will be a low risk for the development of dangerous rip currents today with seas running 2-3 feet and southerly winds around 10-15 kts this afternoon. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Fitzsimmons Near Term...MPS Short Term...MPS Long Term...Fitzsimmons/O`Hara Aviation...Fitzsimmons/MPS Marine...Fitzsimmons/MPS is the U.S. government's official web portal to all federal, state and local government web resources and services.