Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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000 FXUS61 KPHI 140731 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 331 AM EDT Sat Oct 14 2017 .SYNOPSIS...
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As high pressure is centered near and south of the Canadian Maritimes through tonight, a weak system moves up the coast today before lifting to our north and east tonight. A strong cold front crosses our region Sunday night, then high pressure builds in for much of next week. However, a weak and dry cold front should quickly move through late Tuesday.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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High pressure will remain over the western North Atlantic today with an inverted surface trough located off the Middle Atlantic coast. There were low clouds, areas of rain and drizzle, and patchy fog in our region early this morning. The areas of rain should continue to drift northward. As a result, the chance of rain is expected to decrease gradually through the day. Meanwhile, the low clouds are forecast to lift slowly. While there may be some breaks of sunshine this afternoon, the day is anticipated to remain mostly cloudy. The areas of drizzle and patchy fog will likely diminish as the low clouds lift. A light northeast to east wind is forecast. A relatively mild start to the day should allow temperatures to rise into the lower and middle 70s in much of our region during the afternoon.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SUNDAY/...
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The inverted trough is forecast to dissipate tonight and a light south to southwest surface flow should develop in our region. The cloud cover is expected to lower again as the night progresses. Temperatures will likely remain quite mild with lows anticipated to favor the upper 50s and lower 60s.
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&& .LONG TERM /SUNDAY THROUGH FRIDAY/...
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Summary...Turning much warmer and breezy Sunday; strong cold front moves through Sunday night; significant cooling early next week as high pressure arrives, followed by some warming mid to late next week. Synoptic Overview...An upper-level ridge will shift more into the western Atlantic as an upper-level trough tracks from the Midwest to Central Plains to the Great Lakes and eventually into the Northeast through Monday. This trough amplifies some Monday into the East before lifting out during mid to late next week. At the surface, a strong cold front moves through Sunday night which looks to be followed by a weak/dry cold front late Tuesday. Overall, high pressure looks to dominate much of next week with cooler temperatures before some moderation takes place during the mid to late week timeframe. We used a model/continuity blend for Sunday through Monday night, then blended in mostly the 00z WPC Guidance. For Sunday...A drastic change is expected as we start the morning with low clouds, some fog and/or drizzle. An upper-level ridge though shifts more off the Southeast U.S. coast along with surface high pressure, therefore allowing for a southwesterly flow to increase across our region. As this occurs, warmer air will advect into the area as a warm sector ahead of a Great Lakes low pressure system expands northward. As improved vertical mixing occurs through the morning and especially the afternoon, increasing sunshine should occur. The forecast soundings overall show this occurring, and they also indicate that around 25 knots of wind is available to mix down. Assuming that we effectively mix in the afternoon, a gusty southwesterly wind up to 30 mph is anticipated. Given the expected mixing and also the anticipated improving sky conditions, afternoon temperatures are expected to surge into the low to perhaps mid 80s for many places. In addition, dew points should favor the 60s therefore it will feel a bit on the humid side. This will all be short-lived though as a strong cold front arrives at night. An upper-level trough moving across the Great Lakes and Ohio Valley will drive surface low pressure well to our north Sunday night. This will sweep a strong cold front across our area during Sunday night, with a sharp wind shift to the northwest with its passage. The guidance shows that the bulk of the large scale forcing shifts to our north, however enough convergence with the cold front along with some instability should allow for a band of showers to arrive into our western zones. The question is how much does this weaken with an eastern extent. The organization of the showers should be on the decline with an eastern extent given the timing and little instability in place. As a result, held off on adding thunder and continued with the highest PoPs (likely) from near the I-95 corridor on westward then tapered down to chance (scattered) farther south and east. Much of the model guidance hints that the showers occur behind the cold front/wind shift, and this characteristic could allow some more organized showers to continue farther east. There may also be some increase in the winds for a time right behind the cold frontal passage. For Monday and Tuesday...A strong cold front is forecast to be offshore as we start Monday, however a mid level jet streak may keep some showers early near coastal southeastern New Jersey down to southern Delaware. Overall, the bulk of Monday is anticipated to be dry. Decent cold air advection in the wake of the front will result in a much cooler day, and there may be a gusty breeze as well. High pressure builds in from the southwest later Monday night and Tuesday with cool/chilly temperatures. The winds should drop off enough later Monday night into early Tuesday, resulting in temperatures dropping into the mid to upper 30s for portions of northwestern New Jersey and Northeastern Pennsylvania. This could result in some frost. Despite high pressure building in, a strong upper-level trough moving across New England Tuesday pushes a secondary weak cold front through much of our area. This front looks to be moisture starved and therefore we are carrying a dry frontal passage. For Wednesday through Friday...As a gradually building ridge approaches from the west with rising heights, surface high pressure is forecast to be nearly right over our area through Friday. This will translate to some moderation in the temperature department during this timeframe.
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&& .AVIATION /08Z SATURDAY THROUGH WEDNESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Less than ideal aviation weather conditions will continue for today and tonight. Conditions were IFR this morning with areas of rain and drizzle along with patchy fog. Ceilings should lift into the MVFR range for this afternoon with some locations possibly going VFR for a time. However, conditions are anticipated to lower back to IFR tonight. A light northeast to east wind today is forecast to become light and variable for this evening. A light south to southwest wind is expected to develop late tonight. OUTLOOK... Sunday...Low clouds and/or fog with local drizzle gives way to mainly VFR conditions by late morning. A cold front arriving at night will bring some showers, however the coverage is less certain especially farther east. Southwest winds increase to 10-15 knots with gusts up to 25 knots, then becoming northwest behind the front at night. Monday and Tuesday...VFR. Northwest winds 10-15 knots with gusts up to 20 knots Monday, then diminishing at night and Tuesday. Wednesday...VFR. Light westerly winds.
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&& .MARINE...
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An easterly wind around 6 to 12 knots is expected for today. The wind direction is forecast to veer toward the south tonight. Wave heights of 6 to 8 feet on our ocean waters are anticipated to subside gradually to 4 to 5 feet for late tonight. A Small Craft Advisory is in effect for today and tonight. Waves on lower Delaware Bay should be 2 to 4 feet today, and 1 to 3 feet tonight. Waves on the upper part of the bay are expected to be 2 feet or less. OUTLOOK... Sunday...A Small Craft Advisory may be needed as southwesterly winds increase and gusts may reach to around 25 knots for a time. This will also build the seas with time on the ocean, although given it is a southwest wind direction we did not quickly increase the seas. A sharp wind shift to the northwest occurs later Sunday night as a cold front moves through. Monday and Tuesday...The conditions will be close to Small Craft Advisory criteria especially due to a gusty northwest wind. The winds and seas then diminish during Tuesday. Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria.
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&& .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 6 AM EDT Sunday for ANZ450>455.
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&& $$ Synopsis...Gorse Near Term...Iovino Short Term...Iovino Long Term...Gorse Aviation...Gorse/Iovino Marine...Gorse/Iovino

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