Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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338 FXUS61 KPHI 250716 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 316 AM EDT Mon Jun 25 2018 .SYNOPSIS... High pressure located in central Ontario early this morning will build to the southeast. The center of the high is forecast to pass off the coasts of southern New England and Long Island on Tuesday. The air mass is expected to influence our weather into early Thursday. A weak frontal boundary approaching from the west is anticipated to arrive in our region on Thursday. Another area of high pressure should follow for Friday and the coming weekend. && .NEAR TERM /UNTIL 6 PM THIS EVENING/... The pattern today reminds me more of a pattern we would see in late April, not late June. Behind the cold front that arrived last evening, high pressure will build south form Canada through the day. As it does so, the pressure gradient will slowly relax through the day. With the high building in, expect dry conditions through the day. There are two uncertainties with our forecast today, the sea breeze and the depth of the mixing layer. A sea breeze should develop this afternoon, but due to the relatively strong northwesterly flow, do not expect the sea breeze to make much progress inland, possibly staying right along the coast. The question is the depth of the mixing layer. With this similar pattern in the Spring, models tend to underestimate the depth of the mixing layer. Consequently, depicted dew point temperatures are often too high, and depicted temperatures are often too low. However, since this is an unusual pattern for this time of year, I don`t have as much confidence that these biases will be true today. Therefore, I stayed close to the warmest and driest guidance for temperatures and dew points today. && .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM TUESDAY/... As the pressure gradient continues to decrease, and with the loss of diurnal mixing, winds will subsequently decrease as well. This, along with the clearing skies, will set the stage for prime radiational cooling conditions. With the dry air in place, minimum temperatures could be 5 to 10 degrees below normal. && .LONG TERM /TUESDAY THROUGH SUNDAY/... A mid level ridge is forecast to extend from the southeastern states up over Ontario on Tuesday morning. The feature will progress eastward with its axis expected to pass overhead on Tuesday night. Surface high pressure is anticipated to pass off the coasts of southern New England and Long Island on Tuesday. The air mass should bring dry conditions to our region for Tuesday and Tuesday night. A mid level trough is expected to extend from the Great Lakes down to the middle Mississippi River Valley on Wednesday morning. The trough is forecast to move to the east and it should pass over our region on Thursday. As the trough approaches, we are anticipating an increasing chance of showers and thunderstorms on Wednesday and Wednesday night. The potential for showers and thunderstorms will continue into Thursday as a surface front associated with the mid level feature arrives in our region. Precipitable water values are expected to increase to greater than 2 inches, so there is the potential for some locally heavy rain at that time. Heat and humidity will be on the increase for Friday, Saturday and Sunday. A mid level ridge is forecast to build eastward from the lower Ohio River Valley on Friday. It is expected to settle over our region for Saturday and Sunday, limiting the potential for precipitation even as the heat and humidity levels rise. It appears as though heat index values will be near or a bit above 100 on Saturday and Sunday. && .AVIATION /07Z MONDAY THROUGH FRIDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Today...VFR conditions are expected with few, if any clouds. Winds, westerly early this morning will slowly shift to northwesterly this morning. Gusts to 20 kt are possible this afternoon. The one caveat is that a sea breeze is expected to develop this afternoon. However, due to the relatively strong northwesterly flow, do not expect this sea breeze to reach even ACY. Moderate confidence on the sea breeze, high confidence on all other aspects of the forecast. Tonight...VFR conditions will continue. Winds will slowly shift from northwesterly to northeasterly, but wind speeds after sunset should be less than 10 kt. High confidence. OUTLOOK... Tuesday and Tuesday night...Mainly VFR. East wind less than 10 knots becoming southeast. Wednesday...Mainly VFR. A chance of afternoon showers and thunderstorms. Southeast wind around 10 knots becoming south. Wednesday night...Showers and thunderstorms are likely. Conditions are expected to lower to MVFR and perhaps to IFR at times. South wind 5 to 10 knots. Thursday...Conditions varying from MVFR to VFR with a chance of showers and thunderstorms. Southwest wind 5 to 10 knots. Thursday night and Friday...Late night and early morning visibility restrictions are possible, otherwise mainly VFR. West wind 5 to 10 knots becoming northwest. && .MARINE... Winds and seas are expected to remain below small craft advisory criteria. However, northwesterly gusts near 20 kt will be possible, especially this morning. OUTLOOK... Tuesday through Wednesday evening...No marine headlines are anticipated. Late Wednesday night through Thursday evening...Wave heights on our ocean waters may build around 5 feet due to a persistent southerly wind. Late Thursday night and Friday...No marine headlines are anticipated. RIP CURRENTS... The risk for the formation of dangerous rip currents is forecast to be low today thanks to offshore winds (with the exception of a weak sea breeze for a period this afternoon) and wave heights 2 ft or less. The wind is forecast to become onshore around 10 MPH on Tuesday. However, a medium period swell should keep the risk for the development of dangerous rip currents at low for Tuesday. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Iovino Near Term...Johnson Short Term...Johnson Long Term...Iovino Aviation...Iovino/Johnson Marine...Iovino/Johnson

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