Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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379 FXUS61 KPHI 270716 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 316 AM EDT Mon May 27 2024 .SYNOPSIS...
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A warm front lifts north through the region this morning, followed by a strong cold front tonight. Weak high pressure builds through the region Tuesday. Low pressure passes through Wednesday and Wednesday night. High pressure returns to close out the week.
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&& .NEAR TERM /THROUGH TONIGHT/...
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A warm front lies through southeast Pennsylvania and Delmarva, and will continue to track north through New Jersey as the morning progresses. There are some showers and thunderstorm associated with this front that will lift north through the region through daybreak. In other news, areas of dense fog remain in place along the New Jersey coast, but that fog will lift and visibilities will improve as the warm front lifts north. Dense Fog Advisory remains in effect through 6 am. A brief lull in the convection will then take place during the morning hours. It will be warm and quite humid. Southerly flow will usher surface dew points well in the upper 60s to low 70s along with high temperatures in the upper 70s to low 80s, and in the mid 80s in Delmarva. A pre-frontal trough approaches by early afternoon, and this will trigger the second round of convection of the day, mainly north and west of the Fall Line. The cold front approaches late in the afternoon, and then the third and most significant round of convection develops. SB CAPE values will be upwards of 2000 J/kg by this evening, and even up to 1500 J/kg of Downdraft CAPE. Highest instability values will be over Delmarva and into portions of southeast Pennsylvania. 0- 6 km Bulk Shear will generally be around 30 to 40 kt, though in the evening, Bulk Shear values will be 20 to 30 kt in the southern Poconos and northern New Jersey before rising to 30 to 40 kt with the approach of the cold front. It does look like an area of 40 to 50 kt of 0-6 km Bulk Shear will pass south of Delmarva. PWATs will be up around 2 inches. Strong shortwave energy just ahead of the front will track from Maryland and southeast Pennsylvania northward towards the southern Poconos and northern New Jersey. Since the shear will be lower in those areas, heavy rain could result in localized flash flooding, especially in the Lehigh Valley. Although heavy rain is a threat throughout the region, given the lower shear values across northern areas, there is a higher potential for bands of heavy rain to develop across areas north and west of the Fall Line. In these areas, the Weather Prediction Center has a Slight Risk (2 out of 4) for Excessive Rainfall. The Storm Prediction Center now has the whole region in a Slight Risk (2 out of 5) for severe weather. The strongest storms will be capable of damaging wind gusts and even large hail. Although given the relatively warm boundary layer, the risk for hail is not as high as the risk for damaging wind gusts. Cannot rule out the tornado threat, especially in the vicinity of the cold front, but if the instability is elevated, that should help to limit the tornado threat. The bulk of the activity should be well east of the region before midnight tonight, and then the initial cold front will pass through the region in the predawn hours.
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&& .SHORT TERM /TUESDAY THROUGH WEDNESDAY NIGHT/...
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Initial cold front will be offshore Tuesday morning, and then a secondary cold front passes through by midday. Although the air mass will not necessarily be cooler behind the secondary cold front, there will be a noticeable drop in humidity levels as surface dew points drop from the upper 60s/low 70s on Monday to the upper 50s/low 60s on Tuesday. Some shortwave energy passes through the region in the afternoon as the base of an upper trough sets up over the Great Lakes/Ohio Valley/Mid-Atlantic. This may touch off isolated showers and thunderstorms Tuesday afternoon, mainly for the southern Poconos and Lehigh Valley. PoPs will mostly be confined to slight chance, though PoPs may touch low end chance in far northwest portions of Carbon and Monroe counties. Highs will be a touch above normal levels, generally in the upper 70s to low 80s. That upper trough will be over the Northeast/Great Lakes/Ohio Valley/Mid-Atlantic for the mid-week period. Shortwave energy will dive into the base of the trough Tuesday night, and surface low pressure develops over the Appalachians. This low will the pass through the region on Wednesday and Wednesday night. Showers will become likely along with scattered thunderstorms for most of the area Wednesday. With highs generally in the mid to upper 70s and dew points mainly in the mid to upper 50s, SB CAPE looks to be minimal, generally up around 500 J/kg and highest 0-6 km Bulk Shear values will be 35-45 kt, mainly over southern New Jersey and Delmarva. So while thunderstorms are possible, there does not look to be a widespread severe weather outbreak at this time. Showers taper off Wednesday night as low pressure departs.
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&& .LONG TERM /THURSDAY THROUGH SUNDAY/...
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Another shortwave passes through the region on Thursday, but the area will be fairly moisture-starved, so not expecting much more than isolated showers or even a thunderstorm. The Long Term period should mostly be dry as surface high pressure builds over the area. Upper trough departs over the weekend and will be replaced by mid- level ridging. Conditions should remain dry into the weekend with the next system approaching early in the new week. Cooler Thursday and Friday with below normal temperatures, and then temperatures return to normal levels over the weekend.
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&& .AVIATION /07Z MONDAY THROUGH FRIDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas... Today...Mostly IFR CIGs this morning, with improvements to MVFR and even VFR by midday for some TAF sites. For KACY, VLIFR VSBY through the early morning hours. IFR at KACY otherwise. Several rounds of SHRA/TSRA will impact the terminals throughout the day, with stronger convection by this afternoon and evening. SE winds 5 to 10 kt, increasing to 10 to 15 kt with gusts up to 20 kt this afternoon. Severe thunderstorms will be capable of damaging wind gusts and large hail. Low confidence on details. Tonight...SHRA/TSRA continue through 06Z. Conditions improve to VFR thereafter. S winds around 10 kt, become W after 06Z. Moderate confidence on the overall pattern, but low confidence on details. Outlook... Tuesday through Friday...Mostly VFR, but cannot rule out a SHRA/TSRA at KABE Tuesday afternoon. Sub-VFR conditions Wednesday in SHRA/scattered TSRA. VFR Thursday and Friday.
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&& .MARINE...
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Marine Dense Fog will continue on the NJ ocean waters through this morning, then patchy fog continues on the waters into this evening. S winds 10 to 15 kt, but will issue a Small Craft Advisory for the NJ ocean waters for this afternoon and the first half of tonight for as winds will increase to 15 to 20 kt with gusts up to 25 kt. For DE ocean waters and DE Bay, S winds will average 15 to 20 kt. Winds turn W around 10 kt late tonight. Thunderstorms will impact the waters with potentially damaging winds and large hail later today and tonight. Outlook... Tuesday through Friday...Sub-SCA conditions expected through the week. VSBY restrictions in showers and scattered thunderstorms expected on Wednesday. Rip Currents... S to SE winds will increase to 15 to 20 kt with gusts to 25 kt along the NJ coast. This will result in a MODERATE risk for the development of dangerous and life threatening rip currents for NJ beaches. Since winds will be a bit lighter at DE beaches, the rip current risk there remains LOW. For Tuesday, winds will shift to more of a W to SW flow. There will continue to be a MODERATE risk for dangerous rip currents at NJ beaches and a LOW risk at DE beaches. As always, rip currents can still develop, and often occur in the vicinities of jetties and piers. Utilize any guarded beaches this holiday weekend if venturing out into the water.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...Dense Fog Advisory until 6 AM EDT early this morning for NJZ013-014-020-022>027. DE...None. MD...None. MARINE...Dense Fog Advisory until 8 AM EDT this morning for ANZ450>455. Small Craft Advisory from 3 PM this afternoon to 1 AM EDT Tuesday for ANZ450>453.
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&& $$ SYNOPSIS...MPS NEAR TERM...MPS SHORT TERM...MPS LONG TERM...MPS AVIATION...MPS MARINE...MPS