textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

The Freezing Fog Advisory was replaced with a Dense Fog Advisory in Monroe County until 6 PM.

For marine zones, Small Craft Advisories have been issued for all Atlantic Coastal waters beginning Saturday night.

KEY MESSAGES

1. Patchy dense fog is expected to develop tonight through early Saturday morning with an interval of light rain/showers.

2. Warmer air gradually overspreads the region later this weekend into early next week, with a couple chances for showers and fog.

DISCUSSION

KEY MESSAGE 1...Patchy dense fog is expected to develop tonight through Saturday morning with an interval of light rain/showers.

Dense fog remains in place across the higher elevations in Monroe County, mainly along the Pocono Plateau. With temperatures now above freezing, the Freezing Fog Advisory was allowed to expire, but was replaced by a Dense Fog Advisory until 6PM. Further extensions may be needed with fog potentially extending overnight.

High pressure over eastern Canada continues to wedge in from the northeast across there region, providing a reinforced shot of cooler temps and cloudy conditions, acting as a backdoor front in many ways. Overnight, another weak wave of low pressure may bring more showers/light rain to the region. As this system moves through, warm air advection aloft will begin to intensify with the Canadian high providing a ample cold air damming (CAD) setup. Luckily the only major impacts this CAD setup will bring is low stratus and fog. Temperatures at the surface are expected to stay above freezing, so freezing rain is not expected at this time. Fog could be dense at times and headlines may be needed at some point tonight into early Saturday morning. Fog will not be as dense as we go through Saturday, but likely linger into the early afternoon. A surface warm front ahead of our next system will very slowly lift north across the region by mid to late afternoon to eventually break the CAD pattern, but this front will likely stagnate across the Delmarva and South Jersey for most of the day. Areas across southern Delmarva may be the only locations that break the low status deck and warm into the low 60s by late afternoon.

KEY MESSAGE 2...Warmer air gradually overspreads the region later this weekend into early next week, with a couple chances for showers and fog.

An upper-level disturbance tracks well to the north Saturday night into Sunday, with a trailing weakening cold front moving through the region. This should bring a decaying line of showers and possibly a thunderstorm to our region into early Sunday morning. As of now, did not make any changes to the NBM PoPs for Saturday night into early Sunday which may still be on the high side. We become more embedded within the warm sector by early next week with surface high pressure anchored in the western Atlantic and a south to southwest flow. This should result in a much warmer air mass surging into the region. Highs for Sunday and Monday are forecast to be in the 60s for much of the area, then into the low to some mid 70s for Tuesday and Wednesday for many areas. The flow may be light enough which would support sea breeze circulations to occur daily, resulting in significant cooling along the coast where many coastal areas will be stuck in the 50s.

The much milder airmass and higher dew points noted above adjacent to the cold ocean over the weekend and early next week will create opportunities for fog, perhaps dense fog. These conditions will be more enhanced closer to the coast and around Delaware Bay.

Shower and thunderstorm chances return once again late in the day on Wednesday into Wednesday night and perhaps lingering into Thursday. Guidance varies on timing, but both deterministic and ensemble guidance show signals of a rather strong cold front that will track through the area during this time period. Following the frontal passage, the warmth will cease and we'll welcome the return of more seasonable weather towards the end of next week. Depending on how quickly everything evolves and progresses, some shower chances may linger into late week, but overall should come to an end in wake of frontal passage.

AVIATION /20Z FRIDAY THROUGH WEDNESDAY/

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

Rest of today...IFR conditions persist due to low clouds. A few showers possible, mainly late.

Tonight...IFR/LIFR continues due to low cigs, with some scattered showers and possible reductions in vsby as fog attempts to develop.

Saturday...IFR conditions due to low clouds and fog, although visibilities may improve slightly by the afternoon.

Outlook...

Saturday night through Sunday...Sub-VFR conditions likely with a chance of showers and thunderstorms. Conditions may improve to VFR by Sunday afternoon.

Sunday night through Wednesday...VFR expected. Localized sub-VFR conditions possible at times with fog. A chance for showers Tuesday night into Wednesday, otherwise, no significant weather.

MARINE

Marine conditions are expected to stay below SCA criteria thru Saturday. Fog may develop Friday night into Saturday morning.

Outlook...

Saturday night through Sunday...A Small Craft Advisory is in effect for all Atlantic Coastal waters due to winds up to 25 kt and seas between 3-7 feet. A chance for rain showers.

Sunday night through Tuesday night...No marine headlines expected. Winds generally less than 15 kt and seas around 2-4 feet.

Wednesday...Small Craft Advisory conditions likely. Wind gusts up to 25 kt and seas building up to 6 feet. Showers possible.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Dense Fog Advisory until 6 PM EST this evening for PAZ055. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory from 7 PM Saturday to 6 PM EST Sunday for ANZ450>455.