Area Forecast Discussion

WHAT HAS CHANGED

The Aviation section was updated to reflect current trends.

KEY MESSAGES

1. A strong cold front will bring rain showers to the area through early this afternoon.

2. Freeze/frost early this week as much colder air will be settling in, with a widespread freeze potential early Tuesday morning. A return to above average temperatures then occurs later this week.

DISCUSSION

KEY MESSAGE 1...A strong cold front will bring rain showers to the area through early this afternoon.

As of 7 AM, the cold front is crossing through the Lehigh Valley and NW NJ now, and should continue to progress through the region, moving off shore late this morning. Coverage of showers ahead of the front has been quite limited thus far, but still expecting coverage of showers to increase as it gets closer. That being said, overall, rain amounts are still expected to be rather light - ranging from a few hundredths to three quarters of an inch.

The risk for other thunderstorm hazards remains quite low, although thanks to some elevated instability, can't rule out an isolated thunderstorm.

Due to the strong cold air advection behind the front, high temperatures are likely to occur early in the day.

KEY MESSAGE 2...Freeze/frost early this week as much colder air will be settling in, with a widespread freeze potential early Tuesday morning. A return to above average temperatures then occurs later this week.

The big change is that there is increasing confidence that higher terrain areas, particularly the southern Poconos, will see temperatures near or below freezing later tonight into Monday morning. A Freeze Warning has been issued for Carbon and Monroe Counties where there is the highest confidence for below freezing temperatures. For surrounding areas, particularly the Lehigh Valley and NW NJ, if winds diminish quick enough, and if clouds don't build in until after midnight, there is a risk for near freezing temperatures and patchy frost development. However, the risk in these areas is very conditional on the winds and clouds. Therefore, while there is a chance, confidence is too low to issue a frost advisory at this time.

The center of cold surface high pressure will then slide over our region during Monday night before gradually shifting offshore during Tuesday. This combined with a clearing sky, winds becoming very light to calm and low dew points will result in efficient radiational cooling conditions Monday night. A widespread freeze looks to occur early Tuesday morning, and the Freeze Watch has been expanded to include most of our area. 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 the most concern. Frost formation might be somewhat limited given a much drier low-level air mass in place. Outside of the urban city centers and away from the immediate coast, temperatures are expected to drop below freezing. In some cases, well below freezing.

High temperatures both Monday and Tuesday are forecast to be in the 40s and 50s across the region, which is several degrees below average. A few light rain/snow or graupel showers are possible on Monday as the core of the cold air aloft is overhead along with some mid level energy sliding through with the trough axis. The air mass below cloud base looks rather dry and therefore anything that develops could be mostly virga outside of the higher terrain. It will feel much colder Monday with a breeze and the very dry air in place. A return, southerly, flow will then become established Tuesday and continue into Wednesday. This along with an increase in warm air advection and rising heights will result in temperatures climbing back above average Wednesday through Saturday.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

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

Rest of today...Narrow band of rain will move opffshore by 20Z followed by VFR conditions from west to east. Winds will remain out of the northwest, but begin to slowly diminish after 21Z.

Tonight...VFR conditions expected. Westerly winds 10 kts or less.

Monday...VFR. A few light/brief showers or sprinkles possible during the day. West-northwest wind gusts to 20-25 knots, quickly diminishing at night.

Outlook...

Tuesday...VFR.

Wednesday...Areas of sub-VFR conditions are possible at times due to some showers.

Thursday...VFR.

MARINE

Visibility has improved as a cold front moves through and widns have shifted northwesterly. Thus, the Marine Dense Fog Advisory expired at 9 AM.

Winds increase quickly behind a cold front later this morning. Guidance has trended windier near the mouth of the Delaware Bay and downstream, which is not uncommon in these flow regimes due to funneling effects along the bay. Therefore, have issued a gale warning for the lower Delaware Bay, the near coastal areas (out to 20 nm) from Great Egg Inlet NJ to Fenwick Island DE, and the farther marine areas (20 to 60 nm) from Cape May NJ to Fenwick Island DE.

For the rest of the marine areas, winds are expected to stay between 25 and 30 kt during the day time, so a Small craft advisory remains in effect for the rest of the Delaware Bay and near coastal areas (SCAs are not issued for the 20 to 60 nm marine areas).

Once winds diminish by early this evening, winds and seas are expected to remain below SCA criteria through the rest of tonight.

Outlook...

Monday...Wind gusts could be around 25 knots for a time.

Tuesday through Thursday...The conditions are anticipated to be below Small Craft Advisory criteria.

PHI WATCHES / WARNINGS / ADVISORIES

PA...Freeze Watch from late Monday night through Tuesday morning for PAZ054-055-060>062-070-071-101>106. Freeze Warning from 11 PM this evening to 10 AM EDT Monday for PAZ054-055. NJ...Freeze Watch from late Monday night through Tuesday morning for NJZ001-007>010-012-013-015>023-027. DE...Freeze Watch from late Monday night through Tuesday morning for DEZ001>003. MD...Freeze Watch from late Monday night through Tuesday morning for MDZ012-015-019-020. MARINE...Small Craft Advisory until 6 PM EDT this evening for ANZ430- 450>452. Gale Warning until 5 PM EDT this afternoon for ANZ431-453>455- 485.