textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation section.

KEY MESSAGES

1. Record breaking warmth continues through today, with above normal temperatures into the first half of the weekend. Possible showers tonight and Friday.

2. Elevated fire weather potential today.

3. A strong cold front will cross through the area on Sunday resulting in a period of increased showers and some thunderstorms. Much cooler temperatures will follow into early next week, potentially frost and/or freeze concerns.

DISCUSSION

KEY MESSAGE 1...Record breaking warmth continues through today, with above normal temperatures into the first half of the weekend. Possible showers tonight and Friday.

With high pressure situated over the Atlantic Ocean, a return flow remains across the area, and ridging aloft will allow keep warm air across the area through today. The warm air aloft coupled with warm air at surface levels will allow temperatures to be as much as 15 to 30 degrees above normal through the end of the week.

Temperatures have climbed into the mid to upper 80s already, and will likely reach the low 90s for many areas. Dewpoints will mix out a bit more today compared to Wednesday, and have already dropped into the mid to upper 50s for many areas. This would normally support even warmer temperatures, however thicker cirrus could limit heating a bit more. In any case, still expecting several high temperature and warmest low temperature records to fall today. See the Climate Section below for temperature records stats.

As is typical in spring though, temperatures along/near the coast will be significantly cooler due to the colder sea surface temperatures and diurnal sea breeze. While a weak surface front passes through early Friday morning, temperatures will stay well above normal into Saturday with highs mainly in the mid 70s to mid 80s.

With the approach of the cold front tonight, there will be a chance of scattered showers. The first round will be possible between sunset and midnight for portions of northeast Pennsylvania and northern New Jersey as an initial vorticity impulse moves across the area. It would not be surprising for a few lightning strikes to occur as well. The second round of showers will be overnight with the frontal passage. On Friday, there may be a few additional showers as the trough aloft moves across the area and some daytime instability may lead to some weak convection.

KEY MESSAGE 2...Elevated fire weather potential today.

A period of fire weather conditions supportive of fire spread is forecast today, as very warm and dry conditions continue. Min RH values will drop into the 25-35% range for many locales across eastern PA, NJ and Delmarva. This will be accompanied by southwest winds around 10-15 mph with gusts up to 20 mph in the afternoon. Due to lack of recent rainfall, there is some potential for fire spread. A Special Weather Statement will be warranted for some areas.

This is of elevated concern for ongoing drought/abnormally dry conditions over much of the area, which will likely only get worse after this week. While there are a few instances of showers over the next couple of days, any rainfall totals will be minimal.

KEY MESSAGE 3...A strong cold front will cross through the area on Sunday resulting in a period of increased showers and some thunderstorms. Much cooler temperatures will follow into early next week, potentially frost and/or freeze concerns.

A backdoor cold front arrives Friday night into Saturday across parts of the area and guidance is now keen on having this backdoor front pushing completely south of our region by Saturday afternoon. This would lead to cooler temperatures expected on Saturday, where highs are currently forecast to be mainly in the 70s, cooler along the coast and warmest further inland. This backdoor front will then move back north as a warm front by Saturday night as a strong upper level trough begins to approach the area.

A strong cold front will precede this trough and slide across the region late Saturday night into Sunday morning. A weak area of low pressure may also develop along the front in our vicinity. As the main trough axis hangs back farther to the west, much of the shower activity may occur behind the actual front. Given the strength of the incoming upper-level trough, forcing for ascent should be strong enough to result in increasing shower coverage for a time. The thunder risk at this time looks rather low given the timing of the front, however some rumbles of thunder cannot be ruled out. This will be beneficial rain, and it will also result in a significant cool down into early next week. A gusty wind will also occur especially in the wake of the cold front for Sunday afternoon into Sunday night, and this should limit frost formation into early Monday morning. Much lighter winds and a colder air mass with high pressure settling overhead should set the stage for frost and/or freeze conditions Monday night into early Tuesday morning. Temperatures then rebound Tuesday through Thursday.

AVIATION /00Z FRIDAY THROUGH TUESDAY/

The following discussion is for KPHL, KPNE, KTTN, KABE, KRDG, KILG, KMIV, KACY and surrounding areas.

Tonight...Generally VFR. Isolated showers tonight may lead to brief lower conditions, but probability too low to even include VCSH in TAFs. Wind gusts drop shortly but may briefly increase with cold frontal passage overnight. Winds shift to the northwest overnight behind a cold front. High confidence.

Friday...VFR conditions expected. Northwest winds 5-10 knots, with gusts 15-20 knots during the day. A few showers may develop through the day, but not enough confidence to place VCSH in TAFs yet. High confidence.

Outlook...

Friday night through Saturday...VFR. No significant weather expected.

Saturday night through Sunday night...Sub-VFR conditions likely at times. Widespread showers likely with perhaps an isolated thunderstorm. Winds will become increasingly gusty by Sunday afternoon with gusts up to 25 kt.

Monday through Tuesday...VFR. Wind gusts up to 25 kt possible on Monday, otherwise no significant weather expected.

MARINE

South to southwest winds 10-15 knots, with gusts 20-25 knots through this evening and overnight. Winds overall should remain below advisory levels, but occasional gusts may gust around 25 knots. Winds shift to west to northwest overnight into Friday around 5-15 knots.

Outlook...

For Delaware Bay Waters...A period of Small Craft Advisory conditions probable on Sunday and possibly into Monday due to wind gusts around 25-30 kt. Otherwise, no marine headlines are expected.

For Atlantic Coastal Waters...A period of Small Craft Advisory conditions probable on Sunday and possible again on Monday due to wind gusts around 25-30 kt. Otherwise, no marine headlines are expected.

For Atlantic Offshore Waters...No marine headlines expected through Tuesday. Aside for some gusty winds possible on Sunday, winds should remain below 34 kt during this period.

CLIMATE

Record breaking heat is expected to continue today, including potential for some sites to experience monthly record warmest low temperatures for April.

Below are record highs and record high minimum temperatures for April 16th and monthly warmest low temperature records for April.

Record High Temperatures April 16 Site Record/Year Allentown (ABE) 90/2012 AC Airport (ACY) 89/2002 AC Marina (55N) 88/2002 Georgetown (GED) 89/2002 Mount Pocono (MPO) 85/2002 Philadelphia (PHL) 90/2002 Reading (RDG) 90/2012 Trenton (TTN) 91/2012 Wilmington (ILG) 92/1896

Record Warmest Low Temperatures April 16 Site Record/Year Allentown (ABE) 60/1941 AC Airport (ACY) 62/2002 AC Marina (55N) 64/2002 Georgetown (GED) 65/2012 Mount Pocono (MPO) 56/2002 Philadelphia (PHL) 62/2002 Reading (RDG) 65/1941 Trenton (TTN) 62/2002 Wilmington (ILG) 63/2002

Record Warmest Low Temperatures Entire Month of April Site Record/Date (Year) Allentown (ABE) 64/19th (1985 and 2019) and 30th (1983) AC Airport (ACY) 70/26th (2009) AC Marina (55N) 67/26th (2009) Georgetown (GED) 71/29th (2017) Mount Pocono (MPO) 65/25th (1960) Philadelphia (PHL) 70/8th (1929) and 19th (1896) Reading (RDG) 68/25th (1960) Trenton (TTN) 70/19th (1896) and 20th (1896) Wilmington (ILG) 74/19th (1896)

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...None.