522 FXUS61 KPHI 151326 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 926 AM EDT Tue Aug 15 2023 .SYNOPSIS... A cold front crosses the area later today. High pressure then builds in Wednesday into Thursday. The next cold front is scheduled to move through later Friday with high pressure arriving for Saturday. && .NEAR TERM /THROUGH TONIGHT/... Update... The new SPC Day1 outlook has adjusted the Slight risk for Severe weather into our CWA more. It now has Slight risk for much of central and southern NJ metro Philadelphia and out Delmarva areas. This seems to align with the better heating which will take place in those areas the next few hours. Areas to the north are in the thicker clouds attm. They will tend to diminish later on. We have made some adjustments to temps/dew points and winds for the update. A mid level low was located over southwestern Michigan early this morning. The low is expected to progress to the east, reaching Lake Erie this afternoon and evening before becoming an open wave over New York State tonight. A surface low is forecast to follow the mid level feature. A secondary surface low was located near Raritan Bay around 6:00 AM. The low will move out to sea this morning. It will likely leave a trailing frontal boundary in our region for today. There should be a break in the precipitation in our region for this morning along with a decrease in cloud cover. A mid level short wave trough is forecast to approach from the west and southwest this afternoon with its axis passing overhead this evening. As a result, we are expecting another round of showers and scattered thunderstorms at that time. The lingering frontal boundary will act as a triggering mechanism and it should focus the convection along and to the southeast of the Interstate 95 Corridor. Precipitable water values in those areas should remain around or slightly above 2 inches, so locally heavy rain is possible. Mixed layer CAPE values may rise into the 1000 to 1500 J/kg range with the potential for some organized convective development so strong wind gusts may occur with some of the thunderstorms. The showers and thunderstorms are expected to pass off the coast tonight, leaving some lingering clouds and the possibility of patchy fog wherever heavy rain occurs. Today's maximum temperatures are forecast to range from the mid to upper 70s in the elevated terrain up north to the lower 90s in southern Delaware. Tonight's lows should favor the 60s and lower 70s. && .SHORT TERM /WEDNESDAY THROUGH THURSDAY NIGHT/... Cold front stalls just off the coast on Wednesday, with an inverted trough extending back to the northwest across New York City and the upstate. Meanwhile, upper trough axis will remain to our west in the morning, shearing out slowly in the afternoon, but not without some vorticity advection. Thus, the depiction by some models (notably the GFS) of some shower activity over northern NJ doesn't seem unreasonable, so included some slight chance pops into the forecast. Elsewhere, dry weather should prevail, with temps in the mid 80s and dew points dropping into the 60s. The stalled front then starts to move back to the northwest as a warm front as another upper trough approaches and tries to induce cyclogenesis along it Wednesday night through Thursday night, by which point another cold front will be dropping southeastward from Canada. Thus, have mostly sub-slight chance pops Wednesday night, but have widespread slight chance on Thursday as the warm front backs inland, then some chance pops in the northwest Thursday night as the next cold front approaches. None of this precip looks like a big deal, but enough to slightly dampen the forecast on occasion, potentially. Severe threat looks low, especially given the cold front's arrival late at night/early in the morning Friday. Temperature-wise, lows will be in the 60s Wednesday night, with highs back in the 80s Thursday, but dew points will be creeping back up during the day. Lows Thursday night as the cold front approaches will be close to 70. && .LONG TERM /FRIDAY THROUGH MONDAY/... Cold front pushes though the region early Friday, with pops subsiding through the day. Temperatures will be several degrees cooler than on Thursday, but still mostly 80s, but dew points will be dropping back into the 50s by late in the day. Canadian high pressure will dominate Friday night through Saturday night, with dry and relatively cool air and mostly clear/sunny skies. Many cooler spots will end up in the 50s for lows both nights, while highs will struggle to reach 80 during the day. Dew points will remain deep into the 50s through this period. High pressure then modifies as it slides off the coast Sunday, with temps rising back into the mid-upper 80s under continued mostly sunny skies. Dew points will creep back into the low 60s, but still not bad for this time of year. Monday we're back near 90 in many areas as southwest flow maximizes ahead of the next cold front, which looks to arrive Monday night. However, at this time there remains a lot of uncertainty about any significant weather with it, so have kept pops sub-slight chance. Dew points will not likely have recovered into the 70s just yet, but should be well into the 60s by then. && .AVIATION /14Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...Mainly VFR. A chance of showers and thunderstorms late this afternoon which may lower conditions briefly to MVFR or IFR. Westerly wind around 10 knots with gusts of 15 to 20 knots. Medium confidence. Tonight...A chance of evening showers and thunderstorms, mainly from around KPHL south and eastward. The precipitation may briefly lower conditions to MVFR or IFR. Lingering clouds and patchy fog are possible overnight with additional MVFR/IFR ceilings and visibility values. Variable wind 5 knots or less. Medium confidence. Outlook... Wednesday...Mainly VFR. Isolated shower may result in a brief reduction in vsby, but this looks pretty unlikely at the terminals. Winds mostly westerly 5-10 kts. Moderate confidence. Thursday...Mainly VFR. Again, an isolated shower may result in a brief reduction in vsby. Winds becoming southerly 5-10 kts. Moderate confidence. Friday...Mainly VFR. Once again, an isolated shower may result in a brief reduction in vsby. Winds westerly 10-20 kts. Moderate confidence. Saturday...VFR. Winds west-northwesterly at 10-15 kts. High confidence. && .MARINE... A south to southwest wind around 10 knots is forecast for today. The wind is expected to shift into the northwest to northeast quadrant tonight. Waves should be 2 to 4 feet on our ocean waters, and 2 feet or less on Delaware Bay. There is the potential for showers and thunderstorms from late this afternoon into this evening. Outlook... Wednesday...No marine headlines expected. Winds generally northwesterly then becoming southerly 5-10 kts. Seas 2-3 ft. Thursday...No marine headlines expected. Winds southerly around 10 kts. Seas 2-4 ft. Friday...Small Craft Advisory conditions possible. Winds westerly 10- 15 kts with gusts possibly up to 25 kts. Seas building 3-4, possibly to 5 ft. Saturday...No marine headlines expected. Winds westerly around 10 kts. Seas 2-4 ft. Rip currents... A south to southwest wind around 10 MPH is anticipated for today along the coasts of Delaware and New Jersey. Breaking waves should be around 2 feet with a long period (around 10 seconds) east southeast swell. The expected conditions suggest that there will be a LOW risk for the development of rip currents. A variable wind 5 to 10 MPH on Wednesday morning is expected to become onshore around 10 MPH on Wednesday afternoon. Breaking waves are forecast to be 1 to 2 feet with a medium period southeast to south swell. There is again a LOW risk of rip currents. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ SYNOPSIS...RCM NEAR TERM...Iovino/po SHORT TERM...RCM LONG TERM...RCM AVIATION...Iovino/RCM MARINE...Iovino/RCM