textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Small Craft Advisory has been issued for the Delaware Bay and a portion of the Atlantic coastal waters for tonight into tomorrow morning.

KEY MESSAGES

1. Trending warmer today after a cold night. Some rain showers also move in for tonight.

2. A return to above average temperatures briefly later this week before cooling down again over the weekend. Widespread rainfall possible over the weekend.

DISCUSSION

KEY MESSAGE 1...Trending warmer today after a cold night. Some rain showers also move in for tonight into Wednesday.

After a cold night across the area, we start to warm up today. Freeze warnings remain unchanged through mid-morning before we see temperatures climb through the day. This will be due to our high pressure system moving offshore today and allowing for return flow to develop with a south to southwest wind. Warm air advection takes place today into tonight allowing for this warm up. High temperatures reach into the 50s for many.

In the wake of our high pressure system, a weak low pressure system approaches the area from the Great Lakes region tonight resulting in rain showers developing across the area. This system slowly clears the region later in the day Wednesday. Lows tonight are in the mid 30s to mid 40s with highs Wednesday in the upper 50s to upper 60s.

KEY MESSAGE 2...A return to above average temperatures briefly later this week before cooling down again over the weekend. Widespread rainfall possible over the weekend.

In the wake of Wednesday's system, warm air advection and rising heights will result in temperatures climbing back above average Thursday through Friday. Highs for most of the area are forecast to be in the 70s for Thursday. By Friday, a backdoor cold front may arrive which pushes temps back down a few degrees, though uncertainty here is high and if the front is potent, it could be more than just a few degrees. A low pressure may then arrive Friday night into Saturday with some showers, and with the air mass behind the backdoor front becoming more firmly established, Saturday now looks 10-15 degrees cooler than Friday, possibly even more.

In terms of rainfall, the next low pressure over the weekend has the potential for widespread showers or a period of rain. The strength and timing of the involved features for the weekend however is lower confidence. The pattern that is currently indicated among the model guidance however would result in perhaps up to a half inch of very beneficial rainfall. Uncertainty remains high, however.

AVIATION /10Z TUESDAY THROUGH SATURDAY/

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

Today...VFR with increasing clouds, particularly for the afternoon. A north wind in the morning, transitions to southwest around 5-10 kt in the afternoon. Toward evening, winds turn more southerly at 5-10 kt. High confidence.

Tonight...Mainly VFR. Ceilings continue to lower overnight, but were kept above MVFR. Rain showers mainly look to move in after around 06Z and MVFR conditions are possible if any showers go over a terminal. This was too low confidence to include in the current TAFs for tonight. Winds remain out of the south at 5-10 kt. KACY/KMIV see winds pick up out of the south after around 06Z with gusts upwards of 20 kt.

Outlook...

Sub-VFR conditions possible Wednesday with showers. VFR likely returns by Wednesday night and continues through Friday. Sub-VFR then likely returns Friday night and especially Saturday.

MARINE

A north wind in the morning gradually shifts to be out of the south- southeast this afternoon at around 10 knots with gusts up to 15 knots. Winds increase out of the south tonight at 15-20 knots with gusts to 25 knots. A Small Craft Advisory has been issued for the Delaware Bay from 2AM to 8AM Wednesday. For a portion of the Atlantic coastal waters, a Small Craft Advisory has been issued from 2AM to 11AM Wednesday. Seas through the period are 2-4 feet.

Outlook...

Sub-SCA expected Wednesday night through Friday night. Marginal SCA conditions possible Saturday with gusts up to 25 kts and seas up to 5 feet.

CLIMATE

Record low temperatures are possible at some climate sites for this morning, April 21st. Below are the daily low temperature records for 4/21:

Daily Record Low Temperatures April 21 Site Record/Year Allentown (ABE) 28/1925 & 1956 & 2018 AC Airport (ACY) 25/1981 AC Marina (55N) 26/1875 Georgetown (GED) 27/1961 Mount Pocono (MPO) 11/1908 Philadelphia (PHL) 27/1875 Reading (RDG) 26/1982 Trenton (TTN) 30/1907 & 1925 Wilmington (ILG) 28/1925

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Warning until 9 AM EDT this morning for PAZ060>062-070- 071-101>106. Freeze Warning until 10 AM EDT this morning for PAZ054-055. NJ...Freeze Warning until 9 AM EDT this morning for NJZ007>010- 012>023-027. Freeze Warning until 10 AM EDT this morning for NJZ001. DE...Freeze Warning until 9 AM EDT this morning for DEZ001>003. MD...Freeze Warning until 9 AM EDT this morning for MDZ012-015-019- 020. MARINE...Small Craft Advisory from 2 AM to 8 AM EDT Wednesday for ANZ430-431. Small Craft Advisory from 2 AM to 11 AM EDT Wednesday for ANZ450>455.