textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

A Marine Dense Fog Advisory has been issued for all marine zones until 10 AM this morning.

A Dense Fog Advisory has been issued for the coastal zones of New Jersey and Delaware until 10 AM this morning.

KEY MESSAGES

1. Patchy dense fog through this morning is followed by a warm front and cold front late today into tonight.

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 through this morning is followed by a warm front and cold front late today into tonight.

Canadian high pressure has continued to usher in cooler air from the northeast which has acted like a backdoor cold front for the area. Our high pressure system starts to move offshore through the day today which will open up the opportunity for a warm front and cold front to move through.

We see warm air advection in the low-levels today. This will be followed by the surface temperatures later today and into tonight as a warm front moves through. This warm air advection in the low- levels has a steep low-level inversion which has moisture trapped beneath it. This moisture along with a saturated ground and relatively light winds have resulted in plenty of stratus but also dense fog in spots. A Dense Fog Advisory remains in effect for Monroe county and the coastal zones of New Jersey and Delaware until 10 AM this morning. Additional Dense Fog Advisories may be needed this morning depending on how widespread the dense fog becomes. The reduced visibility should improve some through the day today but the clouds stick with us.

Today will be another cooler day with highs for most in the mid 40s to low 50s. Parts of Delmarva see highs in the upper 50s to low 60s as the warm air advection moves south to north. Temperatures will actually warm overnight as we continue to see that warm air filter in with a more southwest wind, so our low temperatures happen early.

This increase in temperatures overnight is helped by the warm front moving northward through the area. A cold front follows this warm front tonight into tomorrow morning. Ahead of this cold front is a line of showers and potentially embedded thunderstorms that will weaken as they pass through our area from west to east late this evening into tomorrow morning.

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

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 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 Thursday. Guidance varies on timing while becoming overall slowed a little, but both deterministic and ensemble guidance show signals that 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 see 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 /12Z SATURDAY THROUGH WEDNESDAY/

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

Today...IFR/LIFR conditions due to low clouds and fog. Visibility restrictions improve after 16-18Z. Low ceilings persist through the day at all terminals. Winds become more southerly through the morning. High confidence in prevailing IFR/LIFR due to ceilings but low confidence on exact timing of visibility improvements.

Tonight...IFR/LIFR with low ceilings. Rain showers move in from west to east between 00-02Z for the Lehigh Valley terminals and I-95 terminals leading to visibility restrictions at times. Due to the line of showers weakening, mention of -SHRA was not included for KMIV/KACY. LLWS also looks to develop around 00Z out of the southwest at around 45 knots at all terminals. After 09Z, the LLWS looks to end and shower coverage lessens. Ceilings continue to remain at IFR/LIFR. Moderate confidence.

Outlook...

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

Sunday night through Tuesday night...VFR prevails. Localized sub-VFR conditions possible at times with fog.

Wednesday...Shower chances increase with more potential for sub-VFR.

MARINE

Marine conditions are expected to stay below SCA criteria through today. Marine dense fog has developed leading to a Marine Dense Fog Advisory being issued through 10 AM this morning.

A Small Craft Advisory goes into effect this evening through tonight for all the Atlantic coastal waters for wind gusts up to 25 knots and seas increasing to 5-7 feet.

Outlook...

Sunday...A Small Craft Advisory is in effect for all Atlantic Coastal waters due mainly to seas of 5-7 feet, though winds may also gust up to 25 kts. 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 30 kt and seas building up to 7 feet. Showers possible late.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Dense Fog Advisory until 10 AM EST this morning for PAZ055. NJ...Dense Fog Advisory until 10 AM EST this morning for NJZ013-014- 020-022>027. DE...Dense Fog Advisory until 10 AM EST this morning for DEZ003-004. MD...None. MARINE...Dense Fog Advisory until 10 AM EST this morning for ANZ430-431- 450>455. Small Craft Advisory from 7 PM this evening to 6 PM EST Sunday for ANZ450>455.