Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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339 FXUS61 KPHI 220431 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 1231 AM EDT Sat Apr 22 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 THIS MORNING/... 1130 pm update: Made some changes to the PoPs/Wx grids tonight based on latest hi-res solutions, radar/satellite trends, and objective surface analyses. A band of storms continue from near Seaside Heights to Atco in southern/eastern NJ at this time. Storms appear to be rooted near 900 mb, where marginal but sufficient instability exists for these storms. With the near- surface layer stable, these storms pose little or no risk of severe weather, but they are producing fairly decent rain rates with several rain gauges recording between a quarter to three quarters of an inch as the storms pass. Hi-res guidance is moving these storms off the coast too quickly and generally diminishing these storms too readily. There are hints from the latest simulations that at least isolated storms may occur for the next few hours in southern New Jersey, so raised PoPs to at least slight chance here through the early morning hours. Additionally, latest mesoscale models are bringing light rain showers into Delmarva in the 07Z-11Z time frame, with light rain/showers overspreading much of the CWA near or after daybreak this morning. Given the solid agreement among these simulations, felt the need to raise PoPs substantially late tonight in Delmarva and adjacent portions of far southern PA and southern NJ. Will continue to monitor latest trends, with further updates to the near-term forecast likely. Previous discussion... 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. && .SHORT TERM /6 AM THIS MORNING THROUGH 6 PM SUNDAY/... 1130 pm update: Made some changes to the forecast for Saturday. Latest mesoscale model simulations show light rain/showers overspreading much of the CWA this morning near/after daybreak. Increased PoPs across the area through the day. Suspect tomorrow will not be an all-day soaker by any means, with one round of steadier precipitation during the morning - followed by spottier showers around midday - followed by another round of steadier rain by late afternoon/early evening. However, latest WRF-ARW /WRF-NMM and NAM Nest simulations suggest potential for fairly steady rainfall for most of the CWA with the second batch, and think PoPs were too low during this time frame especially. They may still be too low, especially north of the Mason-Dixon Line. Further updates to the forecast likely once the latest round of simulations are assessed. Previous discussion... 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 /SUNDAY NIGHT THROUGH SATURDAY/... 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 /06Z SATURDAY THROUGH WEDNESDAY/... The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. For the 06Z TAFs...Low-confidence forecast today. MVFR to occasionally IFR CIGs at all TAF sites except KILG through late tonight before CIGs rise to VFR during the morning. May also see occasional fog, especially at KTTN/KABE before daybreak. Light rain or showers are expected to move through the terminals this morning, with potential for occasional MVFR CIGs/VSBYs, especially if heavier rain falls. Some improvement is expected by afternoon, but another round of rain may move in by late afternoon or early evening. Winds should transition to north or northwest by morning with speeds around or below 10 kts. 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. && .MARINE... 1230 am update: Storms occurring east of Barnegat Light are producing occasional lightning strikes, but gusty winds will be limited owing to a stable layer near the ocean surface. Areas of fog may occur through daybreak. Added some fog to the forecast the rest of tonight, but so far, think visibilities will remain predominantly above 1 SM. 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...CMS/Iovino/Johnson Short Term...CMS/Iovino Long Term...Robertson Aviation...CMS/Robertson Marine...CMS/Robertson Climate...Drag

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