Area Forecast Discussion
Issued by NWS Mt. Holly, NJ

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023 FXUS61 KPHI 280730 AFDPHI Area Forecast Discussion National Weather Service Mount Holly NJ 330 AM EDT Fri Apr 28 2017 .SYNOPSIS...
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A cold front will wash out as it moves to our south this morning. A backdoor cold front will move across the area Saturday into Saturday night. This front will remain near the Delmarva and southern New Jersey on Sunday, then return as a warm front on Sunday night. Another cold front is expected on Monday night as an area of low pressure moves into the Great Lakes region. This low will drift northeast through southeast Canada through Thursday, with a couple of weak surface troughs moving across the area Tuesday and Wednesday. An area of low pressure may affect the Mid Atlantic region late next week.
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&& .NEAR TERM /UNTIL 6 PM THIS EVENING/...
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Cold front is expected to propagate off shore rather quickly this morning, and with it, any remaining showers should also move out of the region. Once that happens, expect the rest of the daytime hours to be dry across the region. In the mid and upper levels, our region will be on the northern periphery of a strengthening long wave ridge. In addition, clouds are forecast to dissipate quickly behind the front, leading to mostly sunny conditions through the day. Thus, despite the passage of the cold front this morning, temperatures today will likely be slightly above yesterday. We are forecasting highs to be about 15 degrees above normal, ranging from the lower 70s to lower 80s across the region.
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&& .SHORT TERM /6 PM THIS EVENING THROUGH 6 AM SATURDAY/...
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A few showers and thunderstorms may move in to portions of NJ and SE PA as a surface trough digs south through the region as it is filling and weakening. Once again it looks like there should be some meager elevated instability - enough to support some thunderstorms across the region. Lows will likely be near the morning dew point temperatures - generally in the upper 50s to upper 60s. However, winds are expected to shift from south southeasterly to southwesterly after midnight. This subtle wind shift combined with increasing mid level clouds may be enough to inhibit any fog development overnight.
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&& .LONG TERM /SATURDAY THROUGH THURSDAY/...
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A backdoor cold front will move into the area on Saturday and sink southward through Saturday night. High temperatures Saturday could be quite warm, but will be highly dependent on how fast the front moves through the area. If it waits until the late afternoon or evening, temperatures will be able to warm quite significantly. However, if the front moves through quicker, high temperatures may not be as high as currently forecast. This would be more likely across portions of northeast Pennsylvania and northern New Jersey where the front may cross sooner. A couple of short wave/vorticity impulses are forecast to move across the area Saturday through Saturday night, so there will be a chance for isolated/scattered showers and thunderstorms. If enough instability builds on Saturday, a few storms could become strong with gusty winds. But there could be a strong enough cap to prevent much activity until late in the day or evening. The front will likely stall across the Delmarva and southern New Jersey during the day Sunday. With the front near the area, this could help create some additional lift to interact with any short wave/vorticity impulses that move across the area and create some scattered showers. Sunday`s highs are forecast to be markedly cooler than Saturday, about 15 degrees cooler for many areas. The front will not stay stalled out for very long as it is expected to lift back northward as a warm front Sunday night/Monday morning. As the front lifts across the area, there will be a chance of showers Sunday night into Monday morning. Temperatures Monday will warm once again as we enter into the warm sector ahead of the approaching cold front and return flow sets up. There could also be some showers and thunderstorms developing during the day Monday ahead of the approaching cold front. However, the best chance for showers and thunderstorms is for Monday night as the cold front moves across the area. Being we should enter into the warm sector during the day, we should warm quite nicely, and in turn some instability should build ahead of the front. Therefore there will be a chance of thunderstorms Monday afternoon and Monday night. The front will move offshore by Tuesday morning, as an area of low pressure moves through the Great Lakes region. This low will drift through southeast Canada through Thursday, with a couple of weak surface troughs possibly moving across our area Tuesday and Wednesday. There is a slight chance of showers across northeast Pennsylvania and northern New Jersey during each day, but chances are low at this time. By Thursday into Friday, an area of low pressure is forecast to move up the east coast and potentially bring a period of steady rainfall to the area. There is some timing and placement differences, which is typical this far out, but they do agree on Thursday into Friday as the likely period.
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&& .AVIATION /07Z FRIDAY THROUGH TUESDAY/...
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The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas. Radar derived winds show approximately 20040kt at 1000 ft AGL. Thus, have included mention of low level wind shear for the first few hours. However, expect wind shear to lessen once the cold front moves through later this morning, resulting in westerly or northwesterly winds through the low and mid levels. Wind speeds at the surface are generally expected to be light through the TAF period. Mostly VFR conditions are expected through the TAF period. There is a chance for showers and thunderstorms, primarily after 06Z tonight and primarily for KTTN and KABE. MVFR conditions will be possible with any showers or thunderstorms. OUTLOOK... Saturday...Becoming VFR during the morning, then a chance of showers during the afternoon. Conditions may temporarily be reduced with any showers. Gusty westerly winds 15-20 knots. Saturday night-Sunday night...Low clouds and fog may develop overnight Saturday and continue into Sunday night leading to reduced conditions. Small chance of showers and thunderstorms. Conditions may temporarily be reduced with any showers. Monday...Low conditions in the morning, becoming VFR during the day. A chance of showers thunderstorms during the day. Lower conditions possible during the day with any showers or storms, more likely lower conditions overnight. Gusty southwest winds around 25 knots. Monday night...MVFR CIGS possibly developing. Showers and thunderstorms likely overnight Monday could briefly lead to IFR conditions. Tuesday...VFR conditions. Gusty southwest-west winds 25-30 knots.
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&& .MARINE...
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Seas are slowly starting to drop near 5 feet. Once seas drop further this morning, Winds and seas are expected to remain below SCA criteria through the remainder of today and tonight. OUTLOOK... Saturday-Sunday night...Seas may approach 5 feet at times, and winds may gust near 20 knots, but conditions expected to remain below advisory levels. Monday-Tuesday...Winds likely to gust 25-30 knots, and seas likely to exceed 5 feet as well leading to Small Craft Advisory conditions.
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&& .CLIMATE... **Record or number 2 warmest April on record expected** Presuming our forecast temps these last 4 days of April are accurate, we are assured of a top 2 warmest April on record in much of our forecast area. Sunday is probably the critical day for determining record or not. Below: April projected within the top April average temps, the normal for April and the period of record (POR). This includes todays high and low temperatures through 4 PM. PHL normal 54.0 POR 1874 59.4 1994 59.4 2017? projected tied warmest ever 58.5 1921 58.4 2010 57.9 1941 ABE normal 49.9 POR 1922 56.8 projecting record 56.4 1941 54.7 1994 ACY normal 51.7 POR 1874 57.2 projecting record 56.3 2010 56.1 2011 && .PHI WATCHES/WARNINGS/ADVISORIES...
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PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory for hazardous seas until 1 PM EDT this afternoon for ANZ450>455.
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&& $$ Synopsis...Robertson Near Term...Johnson Short Term...Johnson Long Term...Robertson Aviation...Johnson/Robertson Marine...Johnson/Robertson Climate...Drag

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