884 FXUS61 KPHI 311808 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 210 PM EDT Sat Jul 31 2021 .SYNOPSIS... Weak high pressure will move offshore this evening. Late Sunday into early Monday a coastal low will move northeast just offshore of the NJ coastline. A cold front will then cross the region Monday morning. Another coastal low is possible Wednesday. && .NEAR TERM /THROUGH TONIGHT/... Surface high pressure located in the Great Lakes and the Ohio River Valley early this morning will build eastward across our region today and tonight. The air mass is particularly dry for this time of the year. Dew point readings are expected to favor the upper 40s and lower 50s today. River valley fog developed in parts of the Pocono Region, the Lehigh Valley and northwestern New Jersey due to the cool temperatures, light wind and clear sky. The fog should dissipate quickly this morning. An area of middle to high level clouds approaching from the west overspread far southeastern Pennsylvania, eastern Maryland, Delaware and southern New Jersey early this morning. The clouds are forecast to clear our region by afternoon, leaving mostly sunny conditions. High temperatures should be mainly in the upper 70s and lower 80s. A north to northwest wind 5 to 10 MPH is expected to back to the west and southwest. Tonight should begin under a mostly clear sky. The return flow on the back side of the area of high pressure will likely bring a slow return of moisture to our region. An increase in cloud cover is likely across the southern part of our forecast area late tonight. There is a chance of showers in eastern Maryland and Delaware toward daybreak. Tonight's minimum temperatures are expected to range from the lower 50s in the Poconos and far northern New Jersey to the middle 60s in eastern Maryland, and in central and southern Delaware. && .SHORT TERM /SUNDAY THROUGH SUNDAY NIGHT/... A potent upper level low will be diving southeast out of Canada Sunday morning helping to reinforce the upper level trough axis across the eastern United States. The mid-level low will then trigger surface cyclogenesis across central NC with a coastal low heading northeast Sunday night/ early Monday morning. The coastal low is forecast to track just off the coast of NJ with precipitation moving over the region. This strong DCVA (and accompanying height falls) will be slightly offset though by the dual surface lows (one across upstate NY along with the NJ coastal low). This will really not allow for substantial moisture return, but nevertheless most of the region will observe precipitation Sunday night into Monday morning. Due to the approaching wave, high temperatures will mostly be in the upper 70s Sunday. && .LONG TERM /MONDAY THROUGH SATURDAY/... No significant changes were made to the long range forecast per the latest model guidance. The coastal low will be rapidly heading northeast away from the region on Monday. As this occurs, a cold front will sweep across the region with another day of wind gusts up to 20 MPH. On Tuesday, a weak surface cold front will stall just offshore as another piece of energy dives south and breaks off from the primary low over the Hudson Bay. Overall, the upper level pattern here looks rather messy and fractured. The long wave trough axis over the eastern United States/ Canada has two jet streaks, with PA/ NJ just on the divergent side of the trough axis. Surface high pressure Tuesday will be located over the PA/ NY border, but this will be battling increased pressure falls from the approaching mid-level low. This means the chance of precipitation will be on the rise Tuesday. The caveat to this is the substantial amount of dry air deposited across the region Tuesday thanks to Monday cold front. As of current, the best chance of precipitation will be along the coast, with more of just a thick cirrus shield across eastern PA. Wednesday into Thursday, the upper level low over the Ohio Valley will be under increasing influence from an approaching wave entering the Great Lakes. This will cause the Ohio Valley low to start to open out and shear out with the vorticity advecting northeast. As this occurs, higher PWATs will continue their approach from the southeast. Higher chances of precipitation will also move further inland, with precipitation expected across the entire area Thursday. By Friday, the upper level low will also be ejecting northeast and start to take on a negative tilt. This means another round of showers and thunderstorms will be possible Friday into Saturday. && .AVIATION /12Z SATURDAY THROUGH THURSDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR. North to northwest wind 5 to 10 knots, becoming west to southwest. High confidence. Tonight....VFR. Variable wind 5 knots or less. High confidence. Outlook... Sunday... VFR conditions lowering to MVFR (especially towards coastal NJ/ DE). Some showers and isolated thunderstorms are expected in the afternoon and evening. Southeast winds around 10 knots, becoming northwest overnight. Light patchy fog possible Sunday night ahead of an approaching cold front. Moderate confidence. Monday-Monday night...Mostly VFR. Northwest winds 5-10 knots gusting 15 to 20 knots during the day. Winds light and variable overnight. Moderate confidence. Tuesday through Thursday...Mostly VFR. A chance of showers and thunderstorms which may temporarily lead to lower conditions (esp towards coastal NJ and DE). Low confidence. && .MARINE... High pressure is forecast to build over the coastal waters of New Jersey and Delaware from the west for today and tonight. A north wind around 10 knots this morning is expected to veer to the east and south at 5 to 10 knots today. The wind should settle into the southeast and south at 5 to 10 knots for tonight. Wave heights on our ocean waters should be 2 to 3 feet. Waves on Delaware Bay are anticipated to be 2 feet or less. Outlook... Sunday... Surface high pressure will exit to the east allowing southeast winds 10 to 15 knots. Wave heights of 2 to 4 feet expected. Monday... A weak coastal low pressure will form late Sunday night/ early Monday morning and move northeast just offshore. Winds turning from the northwest 10 to 15 knots. Seas 3 to 5 feet. Tuesday... Weak high pressure moving will be moving east across the NY/ PA border with winds veering from the east over the waters. Speeds of 10 to 15 knots again with seas 2 to 4 feet. Wednesday and Thursday...East to northeast winds around 10 knots. Gusts approaching SCA criteria. Wave heights also approaching 5 feet. Rip currents... The risk of rip currents is forecast to be LOW for today and Sunday. The wind should be mainly onshore around 10 MPH. Breaking waves are expected to be 1 to 2 feet with a medium period swell. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Haines Near Term...Iovino Short Term...Haines Long Term...Haines/Franklin Aviation...Haines/Iovino Marine...Haines/Iovino