Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 220145 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 945 PM EDT Fri Apr 21 2017 .SYNOPSIS... An area of low pressure will move across southeast Canada tonight and Saturday as a cold front pushes south of the area. This front will stall to our south over the weekend while an area of low pressure is forecast to move along the boundary to our south. This low will strengthen as it moves off the southeast coast late Sunday, then move north offshore of the east coast through early next week. A cold front is expected to move through the Great Lakes region Wednesday and approach our area Thursday. && .NEAR TERM /UNTIL 6 AM SATURDAY MORNING/...
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Isolated showers and thunderstorms continue generally in and south of Philadelphia (where clearing occurred earlier today). However, expect the coverage of these storms to wane over the the next few hours as the surface low slides off shore. A cold front approaching from the northwest is expected to pass through our region late tonight. The arrival of some drying with the front should help to break some of the low cloud cover at that time. The wind should remain from the east and northeast in much of far eastern Pennsylvania and New Jersey into tonight. A varying wind direction is anticipated elsewhere in our forecast area. Wind speeds should remain less than 10 MPH except perhaps in the vicinity of any thunderstorms that develop. Minimum temperatures are forecast to favor the 40s in the north and the 50s in the south.
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&& .SHORT TERM /6 AM SATURDAY MORNING THROUGH 6 PM SATURDAY/... Some moisture is forecast to override the low level cold air in the wake of the frontal passage as the mid level flow remains from the west southwest. While there may be some break over our northern counties, our central and southern counties are anticipated to remain mostly cloudy on Saturday. Also, some light rain is possible mainly across northeastern Maryland, Delaware and southern New Jersey. Maximum temperatures are expected to favor the lower 60s, except in the elevated terrain up north where readings should get no higher than the 50s. The wind is forecast to be from the northwest at 5 to 10 MPH on Saturday. && .LONG TERM /SATURDAY NIGHT THROUGH FRIDAY/... For Saturday night into Sunday, the front is expected to remain stalled to our south while an area of low pressure moves along the boundary well to our south across the southeast states. Several short wave/vorticity impulses are expected to move across the area this weekend north of the frontal boundary and low pressure system. This will lead to a chance of showers for portions of the area, especially across southern New Jersey and the Delmarva areas. Sunday looks like the shower activity may become less widespread as we lose some of the enhanced moisture/lift combination. However, showers chances increase Sunday night across southern New Jersey and southern Delmarva again. By Sunday night into Monday the low pressure to our south is expected to move offshore of the southeast coast, then begin lifting northward offshore of the east coast into the middle of the week. There is some timing differences in how fast the model guidance lifts this low up the coast, but there is a general consensus for a enhanced chance of showers for Monday through Tuesday for much of the area. Depending on how fast this system lifts north of the area and it`s placement off the coast will depend on where shower activity will occur. By Wednesday, the low should be lifting to our east then northeast and bring shower activity to an end for Wednesday. This will then start a warming trend for the end of next week. A cold front is forecast to approach the area Thursday, with showers approaching as well. These showers may dissipate as they approach. Even behind this frontal boundary, return flow develops and thicknesses begin to increase for the end of the week, so temperatures may warm Thursday into Friday several degrees above normal. && .AVIATION /02Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. MVFR ceilings, lowering to IFR at some sites, are expected to continue through at least 06Z. After 06Z, confidence is low as to how quickly we will see improving conditions. A wind shift (from easterly now to northerly late tonight), may start the improving conditions as early as 06Z. However, climatologically, it is rare to see improving conditions between 06 and 09Z, especially given how extensive the low cloud deck is across the region. Earlier thunderstorms should continue to wane through 03Z. Showers are possible for KPHL/KPNE and areas south after 12Z, but timing and coverage is uncertain at this time. Rain should not be heavy enough to impact the visibility. Winds are expected to back out of the northwest by 12Z. OUTLOOK... Saturday night-Sunday night...Chance for showers and lower conditions over the weekend, mainly southern New Jersey and Delmarva areas. Areas farther north may remain dry and VFR through the weekend. Monday-Tuesday night...MVFR and IFR conditions likely with periods of showers. Wednesday...Improving conditions. MVFR CIGS possible early, but return to VFR during the day.
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&& .MARINE... The wind should favor the east to north quadrant tonight and the northwest on Saturday at speeds of 15 knots or less. Wave heights on our ocean waters are forecast to favor the 3 to 4 foot range. Waves on Delaware Bay are expected to be 1 to 3 feet. Areas of fog will persist on our ocean waters into tonight. OUTLOOK... Saturday night-Sunday...Conditions expected to remain below advisory levels. Winds shift from a west-northwest direction to a northeast direction overnight Saturday. Sunday night...Winds and waves begin to increase to advisory levels late Sunday night into early Monday morning. Monday-Tuesday night...Small Craft Advisory conditions likely. Wednesday...Winds expected to drop below advisory levels, but seas may remain elevated. && .CLIMATE... Overall projections today were identical or slightly warmer than yesterdays. Confidence is above average on the info below. April will probably be a top 10 warmest in the period of record for multiple long term climate stations in our forecast area. Depending on the warmth of this afternoon and Friday and how cold it is on Sunday or Monday when a chilly rain may occur, we appear to be on our way for a top 2 warmest April on record. The usual analysis process first 19 days done, the 20th-26th per our 330 am fcst, the 27-30th from FTPRHA. PHL projects #2, 4.9 above normal and 0.5degs from record. POR 1874 ABE projects #2, 6.1 above normal and 0.4degs from record. POR 1922 ACY projects rer 5.0 above normal,0.4F above prev 2010 56.3 POR 1874 So, there could be some slippage but its unlikely that any of these locations can slip below #10. && .PHI WATCHES/WARNINGS/ADVISORIES... PA...None. NJ...None. DE...None. MD...None. MARINE...None. && $$ Synopsis...Robertson Near Term...Iovino/Johnson Short Term...Iovino Long Term...Robertson Aviation...Iovino/Johnson/Robertson Marine...Iovino/Robertson Climate...

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