textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes have been made to the forecast.

KEY MESSAGES

1. Aside from potential for nocturnal fog development tonight and Tuesday night, generally tranquil weather is expected to prevail through the middle of the week.

2. The next chance for rain returns late this week and into the weekend.

DISCUSSION

KEY MESSAGE 1...Aside from potential for nocturnal fog development tonight and Tuesday night, generally tranquil weather is expected to prevail through the middle of the week.

High pressure will remain in place within the vicinity of our area through the middle of the week. Dry weather is expected to continue through Wednesday amid warming temperatures each day.

Scattered to broken high cloud cover will persist through the middle of the week despite surface high pressure. Temperatures are expected to increase back to above normal values, warming each day through Wednesday. High temperatures look to be in the upper 60s to low 70s Tuesday, and in the low to mid 70s Wednesday. Overnights will becoming increasingly milder (no frost/freeze potential). Dry weather is expected to persist through Wednesday.

There is potential for areas of fog development both tonight and Tuesday night. Dewpoints will also be on the rise each day. Given mostly clear skies, light winds, and long nights, we anticipate some fog development across the area during the overnight periods. The latest hi-res guidance suggests the lower visibilities (and thus higher dense fog probabilities) will be along and southeast of the I-95 corridor and across the coastal plain. Confidence remains low on any dense fog, but trends will continue to be monitored. Where fog does develop, it will likely be slow to mix out after sunrise Tuesday and Wednesday mornings. Light southerly flow will promote dewpoint advection and the solar insolation is relatively weak until closer to midday, which will limit mixing earlier in the morning.

KEY MESSAGE 2...The next chance for rain returns late this week and into the weekend.

The ridging that has be in place across the area for the past several days will finally begin to break down by Wednesday night into Thursday as a potent upper trough over central CONUS cuts off and lifts northeastward into portions of the Great Lakes and southern Canada by the end of the week. As this occurs, broad troughing is expected to take shape across the eastern CONUS as a few lobes of upper level energy will pivot through the region Thursday and over the weekend. At the surface, low pressure over the Midwest is forecast to track northeast into Canada as it weakens into Thursday with a trailing cold front back to the southwest. After this time, there is still considerable uncertainty as to how this system will evolve to impact our local area.

At the very least, broad low pressure looks to lift well to the north and west of the area Thursday into Friday. This is expected to bring rain chances back to the region, as a cold front slowly approaches the area. Latest guidance indicates that the frontal progression has slowed, meaning precipitation now looks to occur Thursday afternoon into Friday. PoPs are generally in the 50-70% range for most of the area with greatest PoPs further north and west. However, the better upper level support as depicted by the NAM (in its last days in operation) and other global guidance remains displaced to the N+W of the area, it should be noted that these PoPs may in fact be a bit too high.

Heading into this weekend, ensemble guidance indicates negative anomalies and lowered surface pressure across the region. This indicates that the pattern may remain a bit unsettled through the weekend and into early next week. This is supported by NBM PoPs which as a 20-30% chance for showers on Saturday, less than 10% of precipitation on Sunday, and 30-40% PoPs returning on Monday.

AVIATION /18Z MONDAY THROUGH SATURDAY/

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

Rest of today...VFR. South-southwest winds 5-10 kt. High confidence.

Tonight...VFR to start, with fog development likely after about 06Z. Some fog is likely to impact all terminals, but the greatest potential for IFR restrictions is expected to be at KILG/KMIV/KACY. Winds becoming light with calm periods expected. Moderate confidence.

Tuesday...Restrictions in fog are expected to continue through around 14Z, with conditions improving to VFR thereafter. South- southwest winds 5-10 kt. High confidence.

Outlook...

Tuesday night...Primarily VFR. Patchy to areas of fog possible which may cause sub-VFR conditions at times.

Wednesday through Wednesday night...VFR. No significant weather expected.

Thursday through Saturday...Sub-VFR conditions probable. Rain chances daily with a slight chance of thunderstorms on Thursday.

MARINE

No marine hazards through Tuesday. South-southwest winds generally 5-10 kt through tonight, becoming more southerly or south-southeasterly at around 10 kt on Tuesday. Seas 1-3 feet.

Outlook...

Tuesday night through Wednesday night...No marine headlines expected. South winds generally around 5-15 kt with seas around 2-3 feet. Fair weather.

Thursday through Saturday...SCA conditions possible. While winds and gusts are expected to remain below 25 kt, seas around 3-5 feet are expected. Daily showers possible.

PHI WATCHES/WARNINGS/ADVISORIES

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