textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Added isolated showers to forecast area for rest of the day today.

Confidence is increasing in potentially dangerous heat late next week.

Updated aviation discussion for 18z TAFs.

KEY MESSAGES

1. Isolated showers and perhaps even a stray thunderstorm thru the rest of this afternoon.

2. Mainly dry conditions expected through the middle of the week with temperatures gradually warming.

3. Dangerous heat will be possible across the region late this week and into this weekend with a few chances for thunderstorms.

DISCUSSION

KEY MESSAGE 1...Isolated showers and perhaps even a stray thunderstorm thru the rest of this afternoon.

A secondary front and associated upper level shortwave is moving through late today, ushering in the cooler and drier airmass. Most areas will stay dry today but spotty showers and even a stray thunderstorm have developed along and ahead of it, with best chance of thunder near the coast. Not expecting much in terms of rainfall or impacts, but anyone expecting a dry and tranquil day may be somewhat surprised.

KEY MESSAGE 2...Mainly dry conditions expected through the middle of the week with temperatures gradually warming.

The region will remain embedded within a belt of somewhat enhanced mid-level flow through Monday as a sharp trough located over New England dives south into the Western Atlantic. Thereafter, mid-level ridging will likely begin to take shape across the region through mid-week. At the surface, high pressure in the wake of a cold front will shift into the area, and generally remain in place through Tuesday.

Easterly flow will result in a notable east-west gradient in temps on Monday, with lower 70s closer to the coast (probably 60s right at the coast) and low to mid 80s well inland. Temperatures Monday night will fall into the low to mid 50s, maybe some 40s in the typical cool spots. The cool down does look to be fairly short lived with high pressure taking shape across the area. Tuesday will be a bit warmer, with temperatures generally climbing into the low to mid 80s.

Dry conditions are expected through Tuesday night.

KEY MESSAGE 3..Dangerous heat will be possible across the region late this week and into this weekend with a few chances for thunderstorms.

In general, mid-level ridging is expected to remain in place across the region into this weekend, though a few disturbances embedded in the flow could clip the area. At the surface, high pressure will largely dominate, though it is expected to begin to weaken as it moves more toward the southeastern US.

The pattern in place will begin to support daily chances for showers and thunderstorms Wednesday through Sunday, primarily in the form of diurnally driven convection. PoPs through this period are generally 20-40%. It is worth mentioning though, that some of the machine learning guidance from CSU is beginning to highlight Friday as potentially a severe weather day. Still a lot of details to tune out between now and then, but just something to monitor at this time.

Of greater concern is that this pattern will also favor increasing heat and humidity across the region. Temperatures beginning on Wednesday are likely to be in the mid to upper 80s across the region, rising into the low to mid 90s on Thursday and into the weekend. With increasing moisture, heat indices could potentially reach or exceed 100 degrees in spots beginning as early as Thursday. There will be limited relief at night, with lows in the upper 60s to low 70s areawide by late the week and into the weekend. Trends will continue to be monitored as this level of heat could ultimately necessitate the need for heat headlines across parts of the region should it materialize.

AVIATION /20Z SUNDAY THROUGH FRIDAY/

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

Rest of Today...Mainly VFR. Inserted VCSH as well given spotty showers have developed across the area, but any impacts should be minimal and brief. TS could occur east of the terminals, but not expected at any terminals as of now. West/northwest winds around 10-15 kt with gusts 20-25 kt. Wind gusts diminish between 23z-02z but go more north/northwesterly around that time. Moderate confidence.

Tonight...VFR. Winds gradually veering as the night goes on, starting the night north/northeasterly, with east/northeast winds expected by sunrise, around 5-10 kt. Moderate confidence.

Monday...VFR. East/northeast winds around 5 to 10 kt. High confidence.

Outlook...

Monday night through Tuesday night...VFR. No significant weather expected.

Wednesday though Friday...Prevailing VFR. A few brief periods of sub- VFR conditions possible with isolated to scattered afternoon thunderstorms each day.

MARINE

Isolated t-storm could result in a special marine warning this afternoon on the waters, but otherwise should generally be sub- SCA conditions through Monday. Winds out of the west this afternoon around 10-15 kt, becoming north/northeasterly tonight around 10-20 kt, then east Monday 10-20 kt. Seas of 2 to 3 feet are expected.

Outlook...

Monday night...No marine headlines expected. Winds generally less 10 kt with seas around 2-4 feet.

Tuesday through Tuesday night...No marine headlines expected. Winds generally between 10-20 kt with seas around 2-3 feet.

Wednesday through Wednesday night...SCA conditions possible mainly due to wind gusts around 25 kt. Seas around 2-4 feet, possibly up to 5 feet.

Thursday through Friday...No marine headlines expected. Winds generally between 10-20 kt with seas around 2-3 feet.

Rip Currents...

Monday, northeast winds in the morning around 15-20 mph with a few gusts to 25 mph, becoming easterly in the afternoon around 10-15 mph. Breaking waves 2 to 3 feet. A light east- northeasterly swell will develop, but have a short to medium period of 6-7 seconds. Given these factors, have maintained a LOW risk for the development of dangerous and life threatening rip currents at all Jersey Shore and Delaware beaches.

Tuesday, light winds in the morning will increase out of the south- southeast to 10-15 mph in the afternoon. Breaking wave heights generally 1 to 2 feet. Light east-northeasterly swell 6-7 seconds in length. These factors lead to a LOW risk for the development of dangerous and life threatening rip currents at all Jersey Shore and Delaware beaches.

Ocean water temperatures are generally in the low 60s for all Jersey Shore and Delaware beaches. These chilly water temperatures can quickly cause hypothermia and physical incapacitation to anyone suddenly immersed in the water.

For specific beach forecasts, visit weather.gov/beach/phi

PHI WATCHES/WARNINGS/ADVISORIES

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