textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated the aviation section for the 12z TAFs.

KEY MESSAGES

1. Low pressure passing across our region will bring showers and isolated thunderstorms later today through Thursday.

2. Becoming very warm to hot this weekend and early next week.

DISCUSSION

KEY MESSAGE 1...Low pressure passing through the region will bring showers and isolated thunderstorms later today through Thursday.

An upper trough extending from a closed H5 low over central Canada will move through the Great Lakes and into the Ohio Valley tonight. Surface low pressure associated with this low will stay well north of the area, but the closed low will sag down into the Northeast by Thursday. Behind the departure of the surface low, a cold front slides through the region. Unsettled weather on tap during this period.

The timing of precipitation seems to have slowed down a bit, with scattered showers moving into far northern and western zones by midday Wednesday, but the bulk of the showers will hold off until evening.

Thunderstorms are possible later today and tonight, but the latest guidance points to a later start with the rains and CAPE values are rather low, so coverage will not be scattered at best. According the the SPC outlook, severe thunderstorms are not expected.

Storm total QPF continues to trend lower with overall totals of a tenth to a quarter inch. The higher totals will be across the southern Poconos and North NJ. Any tstm will be capable of producing locally higher totals.

It be seasonably mild today ahead of the system with highs reaching the low/mid 70s in many areas with some 60s across the far N/W areas. Readings will be some 5 to 7 cooler on Thursday with highs mostly in the 60s.

KEY MESSAGE 2...Becoming very warm to hot this weekend and early next week.

As a closed low departs to our east on Friday, a ridge starts to build across the East Friday night and especially this weekend into early next week. This along with high pressure becoming centered across the western Atlantic and strengthening some will result in southerly flow advecting in a much warmer air mass across our area. As a result, high temperatures get into the 70s to mid 80s Saturday with widespread 80s on Sunday (some inland areas touching 90 degrees). Given a southerly wind component though, it should be cooler along the coast. The heat looks to build into early next week with even hot conditions. Highs Monday are forecast to be well into the 80s with even some areas reaching the low 90s (again cooler along the coast). Given the presence of the ridge aloft, no precipitation is currently anticipated. Some convection to our northwest and west more removed from the ridge could try and make a run into parts of our area later Monday. On Tuesday, the heat continues to build with highs forecast to reach the upper 80s to low 90s (remaining cooler along the coast). The surface dew points will increase Monday and Tuesday, peaking in the low to mid 60s for much of the area. This will boost the heat indices above the air temperatures some, and the urban I-95 corridor could be very close to Heat Advisory criteria Tuesday (lower heat index criteria starting at 96F through June).

The northwest side of the ridge aloft may start to weaken as an upper-level trough approaches from the west later Tuesday. This may start to allow for some convection to develop as we go deeper through Tuesday. The greater chance for some convection may not occur until after Tuesday with more of a trough arriving along with a cold front. This will all depend though on how quickly the ridge weakens and also the timing of an incoming trough and cold front.

AVIATION /10Z WEDNESDAY THROUGH SUNDAY/

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

Today...VFR with increasing clouds. Some showers and lower ceilings (low-end VFR) for KABE/KRDG for later this afternoon. Increasing south to southwest winds 15-20 knots with gusts 25-30 knots. Winds at KACY/KMIV may turn southeast by late afternoon. Moderate confidence overall.

Tonight...Lowering ceilings then visibilities as showers overspread most areas. MVFR expected, but IFR possible by late evening. A few thunderstorms are possible, but not included in the TAFs given low probability. South winds 10-15 knots, becoming southwest late. Low confidence.

Outlook...

Thursday...VFR ceilings overall. Some lingering showers however could result in times of sub-VFR conditions. Northwest to west-northwest winds 10-15 knots with some gusts 20-25 knots.

Friday...Mostly VFR. An isolated shower possible.

Saturday and Sunday...VFR.

MARINE

No changes to the present SCA flag that's already out. Winds and seas will continue to build thru the morning with gusts reaching 25 to 30 kts and seas on the ocean reaching 4 to 6 ft today. The highest winds and seas will be found close to the northern NJ waters. Fair today and then showers arriving after sunset with a chance for a tstm.

Outlook...

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

Saturday...A period of Small Craft Advisory conditions possible.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 10 PM EDT this evening for ANZ430- 431-450>455.