textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Increased confidence in the timing of the front and the line of showers and thunderstorms that will accompany it on Sunday.

Low temperatures for the first few days of next week are a little cooler. Some concern for early growing season activities.

KEY MESSAGES

1. Showers and isolated thunderstorms are possible overnight, and then more widespread showers and storms are expected on Sunday as a cold front tracks through the area.

2. Cold temperatures Wednesday morning may affect the beginning of the growing season.

DISCUSSION

KEY MESSAGE 1...Showers and isolated thunderstorms are possible overnight, and then more widespread showers and storms are expected on Sunday as a cold front tracks through the area.

As the backdoor cold front today advances further south, a short wave trough will ride along that boundary and may trigger more late day showers and possible thunderstorms due to elevated instability.

A sequence of fronts will cross through the area on Sunday as low pressure tracks through eastern Canada. First, the backdoor cold front today will lift back north as a warm front during the early morning hours on Sunday. A few showers may develop behind this front.

A lull in activity is then expected before the cold front approaches. The cold front is forecast to cross from west to east between roughly 14Z/10AM EDT and 20Z/4 PM EDT. Showers are expected with some isolated thunderstorms possible as a narrow corridor of instability may creep up into the coastal plains.

At this point, the risk for severe storms is very limited. Any convection will be elevated, not surface based. The only locations that bear watching are southern Delaware and Cape May County, which will be the last to see the cold front, and thus may have a very narrow window that although the convection will be elevated, a few stronger wind gusts above the inversion may mix down. Any shower and thunderstorm activity will end by mid afternoon once the front is off shore.

High temperatures on Sunday will push into the mid 60s to low 70s during the morning hours (with the exception of the Poconos), before temperatures take a tumble in the afternoon in wake of the cold front. Winds will also be quite gusty, especially in the morning, as southerly flow will be enhanced ahead of the approaching cold front. Gusts may push upwards of 30-35 mph before diminishing in the afternoon.

KEY MESSAGE 2...Cold temperatures Wednesday morning may affect the beginning of the growing season.

High pressure will build across the area Monday through Wednesday. A reinforcing surge of colder air will arrive later Tuesday with temperatures dropping well below normal for the midweek period. Low temperatures for Mon/Tue morning will be near normal with low 40s for Delmarva and South NJ while 30s for the NW counties (30 for Mount Pocono). By Wednesday morning, the lows will be around 10 degrees below normal, so lows below freezing everywhere (save the shore) and close to 20 for the far N/W. These temps will lead to a widespread frost. While the growing season has just started across Delmarva, any early season activities for other areas could be affected. It will remain below normal Thursday morning, but Wednesday morning looks the coldest at this time.

AVIATION /18Z SATURDAY THROUGH THURSDAY/

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

Through the rest of today...VFR for most of the remainder of the day. After 21Z, marine layer low stratus could start to move onshore, resulting in lowering ceilings. Less confidence now on the timing of when that stratus will develop, but latest guidance trended slightly later. Current thinking is that with the exception of KACY, IFR ceilings are unlikely before 00Z. Some showers possible through 00Z, but coverage is expected to be very limited, so confidence that any one TAF site will see direct impacts is too low to include in the TAFs. E to SE winds 5 to 15 kt. Low confidence.

Tonight...Low clouds should continue to spread over the region. By 03Z, widespread IFR with possible LIFR restrictions will develop from the low ceilings. Some visibility restrictions in BR or showers are possible, but ceilings are likely to be the controlling factor. E winds around 10 kts. There is also a concern for non-convective low level wind shear, particularly between 06 and 12Z. Low confidence.

Sunday...Will likely start with ceilings IFR or MVFR for most TAF sites. A line of SHRA or TSRA is expected to move through the region from W to E, arriving at KRDG and KABE between 14 and 18Z, KPHL, KILG, KPNE, KTTN between 15 and 20Z, and KMIV and KACY between 17 and 21Z. Once the line of SHRA and TSRA moves by, conditions should return to VFR quickly. Winds will start S or SW around 10 to 15 kt, but with the line of SHRA and TSRA, expect an abrupt shift to W or even NW winds around 10G20KT. Moderate confidence.

Outlook...

Sunday night... Except for any lingering showers across southern NJ or Delaware during Sunday evening, mostly VFR is expected. Patchy rural fog possible Monday morning.

Monday thru Thursday... VFR expected much of the time.

MARINE

Winds will increase later this afternoon and tonight above Small craft advisory conditions. SCA winds possible Saturday evening across the northern ocean zones with E winds gusting to around 20-25 kts. Overnight, the frontal boundary is expected to lift northward again with winds turning SW and ramping up to around 20-25 kts with seas building to 4-6 feet.

SCA conditions are expected to continue through the day on Sunday.

Outlook...

Generally a period of sub-SCA conditions and Fair weather from Sunday night through the midweek. There is a small possibility of low-end SCA conditions on Tuesday as a cold front passes.

CLIMATE

A very warm airmass Saturday may challenge record high temperatures as well as record warmest low temperatures for April 4th. As of 2 PM, it appears that preliminarily, PHL and ACY have broken their daily record highs for today.

Record High Temperatures for April 4th:

SITE...................RECORD...YEAR(S) AC Airport (ACY).......78.......2017 Philadelphia (PHL).....80.......1892 Wilmington (ILG).......80.......1950 Allentown (ABE)........79.......1928 Trenton (TTN)..........82.......1892 Reading (RDG)..........81.......1921 Georgetown (GED).......81.......2023/2011/1963 Mount Pocono (MPO).....78.......1928 AC Marina (55N)........77.......1999

Record Warmest Low Temperatures for April 4th:

SITE...................RECORD...YEAR(S) AC Airport (ACY).......56.......1974 Philadelphia (PHL).....60.......2025 Wilmington (ILG).......60.......2025 Allentown (ABE)........60.......1974 Trenton (TTN)..........62.......1981 Reading (RDG)..........58.......2025 Georgetown (GED).......60.......2025/1950 Mount Pocono (MPO).....58.......1981 AC Marina (55N)........56.......2025

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 6 AM to 2 PM EDT Sunday for ANZ430- 431. Small Craft Advisory until 6 PM EDT Sunday for ANZ450-451. Small Craft Advisory from 11 PM this evening to 6 PM EDT Sunday for ANZ452>455.