textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes to the forecast.

KEY MESSAGES

1. A strong cold front passes through the region into this morning leading to below normal temperatures. Frost and freeze headlines remain in place due to these below normal temperatures.

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

DISCUSSION

KEY MESSAGE 1...A strong cold front passes through the region into this morning leading to below normal temperatures. Frost and freeze headlines remain in place due to these below normal temperatures.

After a chillier night with frost and freeze headlines, we see temperatures today reach into the mid 40s to mid 50s for many. Some mid-level energy rotates through the region today allowing for the potential for isolated showers to develop mainly southeast of the I- 95 corridor. Generally, these showers will be in the form of light rain but the cold air aloft may allow the potential for some graupel to mix in.

Behind the cold front, a high pressure system moves east out of the Great Lakes region and overhead tonight. This high pressure system allows for a good opportunity for radiational cooling with a clearing sky and light winds. A widespread freeze looks to occur tonight into early tomorrow morning and a Freeze Warning is now in effect for the whole area except for the immediate coast. All of our counties now have an active growing season due to the recent excessive warmth. Blooms/vegetation have quickly initiated and in some cases are ahead of schedule. Fruit trees and other cold sensitive plants already planted are of the most concern. Frost formation might be somewhat limited given a much drier low-level air mass in place tonight. Lows tonight generally range from the mid 20s to low 30s with mid to upper 30s near the coast.

KEY MESSAGE 2...A return to above average temperatures later this week before cooling down again over the weekend. Some showers expected on Wednesday morning with more widespread rainfall possible over the weekend.

It is not anticipated to be as cold Tuesday night as the air mass continues to modify and clouds increase with high pressure now well offshore. A return, southerly, flow will also become established Tuesday and continue Wednesday. This along with an increase in warm air advection and rising heights will result in temperatures climbing back above average Wednesday through Friday. Highs for most of the area are forecast to be in the mid/upper 60s Wednesday, then into the 70s for Thursday and Friday. A front may arrive Friday Night into Saturday with some showers, and with the low-level flow more onshore it will bring in some cooling starting Friday especially closer to the coast. If the marine influence ends up being stronger Friday into Saturday, then more low clouds may come into play along with even cooler temperatures.

In terms of rainfall, a weak area of low pressure slides by Wednesday morning bringing some showers. Rainfall amounts generally up to a tenth of an inch are expected. Another area of low pressure may arrive during the weekend, especially for Sunday, bringing 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 temperatures dropping to average or below average over the weekend, with an increased chance for rainfall.

AVIATION /15Z MONDAY THROUGH FRIDAY/

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

Today...VFR. A few light/brief showers or sprinkles possible during the day. BKN ceilings around 5000-6000 feet. West- northwest wind gusting to around 20 knots during the afternoon. High confidence.

Tonight...VFR. A north wind around 5 knots with periods of light and variable. High confidence.

Outlook...

Tuesday Night...VFR. No significant weather.

Wednesday...MVFR/IFR conditions expected especially in the morning with showers and low clouds around.

Wednesday Night through Friday...VFR. No significant weather.

Friday Night through Saturday...Sub-VFR conditions likely at times with showers and low clouds moving through.

MARINE

Winds increase through this morning and into the afternoon out of the northwest. During the afternoon, gusts look to reach 15-20 knots. Tonight winds turn out of the north with gusts continuing around 15-20 knots. Seas of 2 to 4 feet are expected through the period.

Outlook...

Tuesday Night/Wednesday Morning...Small Craft Advisory conditions possible (30-40%) with wind gusts near 25 kt.

Wednesday Afternoon through Saturday...No marine headlines expected.

CLIMATE

Record low temperatures are possible at some climate sites tomorrow, April 21st. Here 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 from midnight tonight to 9 AM EDT Tuesday for PAZ054-055-060>062-070-071-101>106. NJ...Freeze Warning from midnight tonight to 9 AM EDT Tuesday for NJZ001-007>010-012-013-015>023-027. DE...Freeze Warning from midnight tonight to 9 AM EDT Tuesday for DEZ001>003. MD...Freeze Warning from midnight tonight to 9 AM EDT Tuesday for MDZ012-015-019-020. MARINE...None.