Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 161321 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 821 AM EST Tue Jan 16 2018 .SYNOPSIS... A ridge of high pressure will weaken across the area today. A low pressure system and front will approach from the Great Lakes region tonight. Another low will develop off the coast and affect the weather tonight and early Wednesday. More high pressure will build towards the area late this week and remain for the weekend. Low pressure and a cold front will move towards the Middle Atlantic region for the start of next week. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... 800 AM...Sent a minor update that included adding flurries for the I-95 corridor this morning (which is being reported at KPHL right now). The biggest issue with the forecast at this time for this winter event is timing. While the previous shift trended in the right direction with slowing down the eastward progression of the snow today, our forecast still appears to be too fast. We will address this in later updates this morning after taking a look at some of the incoming 12Z guidance. Yesterday`s guidance indicated the potential for an impact to this evening`s rush hour (especially in northeastern PA). Now it appears to be pushed back so much that tomorrow morning`s rush hour is the one to be concerned about with a signal for heavier snow bands to potentially move through the northern half of the area during that time. Previous discussion from early this morning... Weak low pressure over the Great Lakes will push a cold front toward our region today. Meanwhile, a secondary low is forecast to begin developing off Cape Hatteras this afternoon. We continue to expect snow today in parts of eastern Pennsylvania and northern New Jersey. The remainder of our forecast area should remain mostly cloudy with no precipitation during the daylight hours. An initial shot of light snow will affect Berks County, the Lehigh Valley, the Poconos and the northwestern edge of New Jersey early this morning. Any accumulation should be around an inch or less. The more substantial snow is expected to move into those areas from the northwest during the course of the afternoon. We have made some adjustments to the timing of the Winter Weather Advisory, delaying the start time in all but Berks County, the Lehigh Valley and the Poconos. The wind is expected to remain fairly light today. High temperatures should favor the 30s in eastern Pennsylvania and northern New Jersey. Readings are forecast to rise into the lower 40s on the coastal plain. && .SHORT TERM /6 PM THIS EVENING THROUGH WEDNESDAY NIGHT/... The secondary low is forecast to strengthen gradually as it moves northward off the coasts of Delaware and New Jersey tonight, then over the coastal waters of New England on Wednesday. The system will likely throw some precipitation back over our region for tonight and Wednesday morning. The precipitation type will favor snow. However, the boundary layer is expected to be warm enough for some rain on the coastal plain during the first half of the nighttime period. We continue to expect a substantial snow in the northern part of our forecast area. Amounts of 4 to 6 inches are anticipated for the Poconos with totals tapering down to perhaps an inch or two in the Philadelphia metropolitan area and southern New Jersey. Little or no snow accumulation is expected for the Delmarva south of the canal and for far southern New Jersey. The precipitation is expected to be mainly off our coast by Wednesday afternoon with some clearing late in the day. A light wind for much of tonight should become northwest around 10 MPH toward daybreak on Wednesday. The northwest wind is forecast to increase to 10 to 15 MPH on Wednesday with some gusts near 20 MPH. Low temperatures tonight should be mainly in the 20s. Readings should recover only slightly on Wednesday with highs mostly in the upper 20s and lower 30s. && .LONG TERM /THURSDAY THROUGH MONDAY/... The upper low that affected the weather in the near/short term parts of the forecast will be moving though the Tidewater area and it will take the last of the precip with it. We only has a few lingering showers Wed evening across the ern/srn most parts of the area. Sprawling high pressure from the southern Mississippi Valley will begin to move into the area. Dry weather is expected for Wed night and into Thu/Fri as the high builds. Temperatures will be below normal until Friday, when readings will be near normal. The high continues to affect the weather this weekend, so more fair weather is expected. The airmass will moderate as the upper ridge continues to build. Temperatures will be closer to 10 degrees above normal by Saturday and the near 15 degrees above normal by Sunday. The next low pressure system will be rather intense as it moves from the Plains states to the Great Lakes area early next week. We will be on the warmer side of the system, so mostly rain is expected at this time. Temperatures will still be much above normal Mon before returning closer to normal Tue. High chance and low likely pops (srn Poconos) are in the fcst at this time. Pops decrease back to slgt chc for Tuesday after the cold front crosses the area. && .AVIATION /13Z TUESDAY THROUGH SATURDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...MVFR and VFR ceilings today. Snow around KRDG and KABE may briefly reduce conditions to IFR early this morning and again late this afternoon. Tonight...Snow developing with conditions lowering to IFR. Wednesday...The snow is expected to end in the morning with conditions improving to VFR for the afternoon hours. OUTLOOK... Wed night...VFR. Fair with W to NW winds 5 to 10 knots. Thu thru Sat...VFR. NW/W winds Thu/Fri and SW winds Sat. && .MARINE... A Small Craft Advisory will remain in effect for our ocean waters from Manasquan Inlet to Fenwick Island until 6:00 PM. Wave heights on our outer waters are expected to be around 5 feet due to the residual onshore flow. There should be a lull early tonight. Low pressure off the coasts of Delaware and New Jersey tonight should strengthen as it moves northeastward on Wednesday. Wind speeds and wave heights are forecast to increase gradually from late tonight into Wednesday. OUTLOOK... Wed night through Thursday: SCA conditions on the ocean with sub-SCA across Delaware Bay. Fair weather. Thursday night: SCA conditions diminishing. Fair weather. Friday through Saturday: Sub-SCA conditions. Fair weather. && .HYDROLOGY... An ice jam continues along the Delaware River at Trenton, and flooding has been reported adjacent to the river in Bucks and Mercer Counties. Several road closures are in place between Morrisville and Yardley in PA and along NJ State Highway 29 in Trenton. The ice is having an impact on the ability to accurately forecast the river level in the Trenton vicinity. Please use any forecast levels with caution. If you live near the Delaware River in the Trenton and Yardley vicinity, pay special attention to any additional information that is issued regarding the Delaware River. Additional ice jams may form this weekend when milder conditions arrive. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...Winter Weather Advisory until 6 AM EST Wednesday for PAZ054- 055-060>062. Winter Weather Advisory from 4 PM this afternoon to 6 AM EST Wednesday for PAZ101-103-105. NJ...Winter Weather Advisory from 4 PM this afternoon to 9 AM EST Wednesday for NJZ008>010. Winter Weather Advisory until 9 AM EST Wednesday for NJZ001- 007. DE...None. MD...None. MARINE...Small Craft Advisory until 6 PM EST this evening for ANZ451>455. && $$ Synopsis...O`Hara Near Term...Iovino/Klein Short Term...Iovino Long Term...O`Hara Aviation...Iovino/O`Hara Marine...Iovino/O`Hara Hydrology... is the U.S. government's official web portal to all federal, state and local government web resources and services.