textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation section for 0z TAF.

KEY MESSAGES

1. Freeze/frost conditions expected again tonight into Thursday morning.

2. Elevated risk of rapid fire spread is an increasing concern for areas northwest of the I-95 corridor on Thursday.

3. A dry weather pattern continues for the remainder of the week and potentially most of this upcoming weekend.

4. A significant warm up is expected for the early and middle part of next week.

DISCUSSION

KEY MESSAGE 1...Freeze/frost conditions expected again tonight into Thursday morning.

The center of strong Canadian high pressure is currently located over New England and is expected to shift off the coast of New England tonight. A very dry and seasonably cold airmass will persist through tonight as a result.

With the surface high moving offshore tonight, surface flow should gradually become more onshore, allowing dew points to recover some as low-level moisture slowly penetrates inland. As this occurs, frost formation is expected from east to west during the evening and overnight hours as low temperatures are expected to fall into the mid/upper 20s to low/mid 30s. Efficient radiational cooling conditions should develop with continued clear skies and light winds expected for most of the night. Upgraded the freeze watch for tonight to a warning as inherited. Do not intend to issue frost advisories for the coastal strip which have been left out of the freeze warnings, as potential marine influence and clouds will likely limit frost potential in these areas.

KEY MESSAGE 2...Elevated risk of rapid fire spread is an increasing concern for areas northwest of the I-95 corridor on Thursday.

As high pressure heads offshore, winds are becoming southerly and will start to increase in speed across inland areas, particularly north and west of the I-95 corridor, on Thursday, with gusts up to 20-25 mph possible in the afternoon. However, relative humidity in these areas will remain 30 percent or less during peak heating of the day. This combination will result in an increased risk of rapid fire spread. Coordination with partners is ongoing this afternoon but at minimum plan to issue a special weather statement for our I-78 corridor and Pocono counties for Thursday for enhanced risk of rapid fire spread. This may be needed for adjacent portions of New Jersey as well.

Areas further south and east should see a more favorable combination of lighter winds and slightly higher humidity as the oceanic influence begins to reduce fire risk.

KEY MESSAGE 3...A dry weather pattern continues for the remainder of the week and potentially most of this upcoming weekend.

A warming trend is expected to continue through Friday with the region on the western periphery of high pressure centered off the Northeast coast. This will allow for winds to become more southwesterly by Friday, though they are expected to remain fairly light. By Friday, highs look to be near 70 for much of the area. Despite the return flow, mixing during the daytime hours should allow RH to fall to near 30% in some areas. This could lead to some fire weather concerns, though the fairly light winds will be a limiting factor.

A cold front will move through the region Friday night. A few light showers may accompany the frontal passage, though as of right now the potential for meaningful rainfall appears low. Slightly cooler temperatures will be ushered in for Saturday, with highs generally in the 60s. With the dry air being ushered in behind the front along with breezy northwest winds, Saturday will also bear watching for fire weather concerns, especially if little to no rainfall occurs with the frontal passage.

KEY MESSAGE 4...A significant warm up is expected for the early and middle part of next week.

After a seasonable weekend, a significant warming trend will likely take place across the area early next week. High pressure will initially build back in across the region in the wake of the cold front this weekend, before shifting east and allowing for a prolonged period of return flow. By mid-week, high temperatures could surge well into the 80s across much of the area, with overnight lows only falling into the 60s.

A few weak disturbances could bring a slight chance for a few showers to northern parts of the area on Tuesday. Otherwise, conditions are expected to remain dry until at least Wednesday, when a cold front may begin to approach the area from the northwest.

AVIATION /00Z THURSDAY THROUGH MONDAY/

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

Tonight...VFR this evening. It appears increasingly likely that there will be some low stratus developing and affecting ACY and MIV as well as potentially ILG, PHL, and PNE late tonight into tomorrow morning. At this point have indicated a period of MVFR cigs for these sites focused mainly around the 11-15z time period but this could starts as early as 8-9z for MIV and ACY. Confidence on cigs forecast is moderate at this time. Also worth adding, if this stratus does develop, can't rule out cigs occasionally getting down to IFR. Winds generally SE/E around 5 knots or less. Moderate confidence.

Thursday...MVFR cigs potentially continuing through much of the morning for the sites mentioned above. VFR by afternoon. Southeast to south winds around 5-10 knots. Moderate confidence.

Outlook...

Thursday night through Friday...VFR. No significant weather.

Friday night...Primarily VFR. Brief periods of sub-VFR conditions are possible with a chance of showers, primarily for the Lehigh Valley terminals.

Saturday through Monday...VFR. No significant weather.

MARINE

All Small Craft Advisories have been allowed to expire or cancelled.

East-northeast winds will then continue through tonight around 10-15 kt, gradually shifting to southeasterly with speeds relaxing to around 10 kts Thursday. Seas around 2-4 feet. Fair weather.

Outlook...

Thursday night through Saturday...SCA conditions possible. Winds under 25 kt. However, seas will increase to 4-6 feet Thursday night and continue through Saturday.

Saturday night through Sunday night...No marine hazards anticipated. Winds under 25 kt. Seas under 5 feet.

Monday...SCA conditions possible. Southerly winds gusting near 25 kt. Seas increase to 4-6 feet.

PHI WATCHES/WARNINGS/ADVISORIES

PA...Freeze Warning from midnight tonight to 9 AM EDT Thursday for PAZ060-070-071-101>104-106. NJ...Freeze Warning from 10 PM this evening to 9 AM EDT Thursday for NJZ012>023-027. DE...Freeze Warning from 10 PM this evening to 9 AM EDT Thursday for DEZ001>003. MD...Freeze Warning from 10 PM this evening to 9 AM EDT Thursday for MDZ012-015-019-020. MARINE...None.