textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Small Craft Advisory has been allowed to expire.

KEY MESSAGES

1. Breezy with moderating temperatures today.

2. A potentially strong coastal storm/nor'easter late this week.

DISCUSSION

KEY MESSAGE 1...Breezy with moderating temperatures today.

Low pressure will meander over the Gulf of Maine and Canadian Maritimes today before lifting to the north and departing tonight. Meanwhile, high pressure centered over the Midwest will slowly build east.

Some weak shortwave energy passing through the region early this morning will result in some mid-level clouds which will dissipate after sunrise. With sunny skies and the pressure gradient tightening once again over the area, west winds will increase to 15 to 20 mph with gusts up to 25 mph. Temperatures will moderate somewhat compared to Saturday, with highs mostly in the low 60s. Winds diminish tonight.

KEY MESSAGE 2...A potentially strong coastal storm/nor'easter late this week.

A significant upper-level trough is forecast to evolve across the eastern U.S. later this week. This should support a surface low that initially tracks near the Ohio Valley, however a secondary low should develop in the vicinity of the northern Mid-Atlantic. The model guidance overall is in decent agreement with the development of the strong upper-level trough, however there are some differences on the handling of the embedded shortwaves and thus the surface low. The timing and amplification of the trough will also have an impact on the secondary surface low development and track. This will be important as it will determine where the main forcing for ascent becomes established along with colder air on the west/northwest side of the developing coastal storm/nor'easter.

The strength of the parent upper-level trough would result in a colder air mass moving in with time. This could be sufficiently cold enough for a rain/snow mix or even some snow across our far western to northwestern zones. This would have a greater chance of occurrence if the secondary low develops and takes over instead of the initial low remaining primary and tracking over our area or to our west. Elsewhere, a decent amount of rain is possible. The amount of precipitation (rain and/or snow), and precipitation types for at least portions of our area, will depend on the ultimate development and track of the secondary surface low and the associated thermal profiles that evolve across our region. The coastal impacts, including the potential for stronger winds and also tidal flooding, are less certain because if the surface low tracks over our area that would lessen the residence time of the (stronger) onshore flow. Lots of uncertainty with the details this far out in time (Thursday through Friday night), therefore this time frame will continue to be monitored.

AVIATION /16Z SUNDAY THROUGH THURSDAY/

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

Today...Primarily VFR. CIGs down to 3500 ft or so, though MVFR CIGs down to 2500 ft at KRDG, will scatter out by 13Z to 14Z, then SCT250 or so by late morning. W-NW winds 10 to 15 kt with 20 to 25 kt gusts. High confidence.

Tonight...VFR. W-SW winds 5 to 10 kt. High confidence.

Outlook...

Monday...VFR. West-northwest to northwest winds Monday with gusts to 25 knots probable.

Tuesday and Wednesday...VFR. West-southwest wind gusts to 20 knots possible Tuesday.

Thursday...Sub-VFR conditions possible especially at night along with some rain developing (rain/snow possible near KABE/KRDG late at night).

MARINE

The Small Craft Advisory has been allowed to expire for all waters. Winds have diminished with gusts now below 25 kt and seas below 5 feet. Winds are still expected to continue to decrease slowly into this afternoon, though they may continue to gust to around 20 kt through the day. Seas 2-4 feet.

Winds and seas will increase again tonight, and a new Small Craft Advisory will likely be needed.

Outlook...

Monday...Small Craft Advisory conditions probable. The conditions should improve Monday night.

Tuesday...A period of Small Craft Advisory conditions are possible.

Wednesday...The conditions are anticipated to be below Small Craft Advisory criteria.

Thursday...Small Craft Advisory conditions may start to develop mostly at night.

PHI WATCHES/WARNINGS/ADVISORIES

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