textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

No significant changes.

KEY MESSAGES

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

2. Dangerous heat is likely during the latter portion of the week.

3. There are multiple chances for thunderstorms Wednesday through Monday.

DISCUSSION

KEY MESSAGE 1...Mainly dry conditions expected through the middle of the week with temperatures gradually warming.

Mid- level ridging will begin to take shape across the region tonight through mid-week. At the surface, high pressure will be in place tonight, then gradually build off the coast on Tuesday. In large part thanks to the broad area of high pressure, there aren't any significant rain chances through Tuesday.

Winds will become light and variable under the high tonight, with temperatures falling into the low to mid 50s, with some 40s in the typical cool spots.

The cool down will be short lived, as by Tuesday, low level flow will shift to southerly, kick starting a warming trend.

KEY MESSAGE 2..Dangerous heat is likely during the latter portion of the week.

There is increasing concern for the potential for dangerously hot conditions during the latter portion of this week. A warm front is expected to cross through the region Tuesday night into Wednesday which will increase the warming trend that begins on Tuesday. Thursday currently looks to be the day with the highest chance for dangerously hot conditions, with maximum hot air advection in the wake of the warm front. There is more uncertainty on Friday - some deterministic models have shortwave ridging over the region, which would mean warmer conditions than Thursday. However, there is also model solutions depicting a mid-level shortwave trough over the eastern seaboard which would result in cooler conditions compared to Thursday both due to lower thicknesses and increased cloud cover. Right now, the high temperatures on Friday are similar to Thursday given the uncertainty.

When discussing heat impacts, it is not only a factor of the temperature but also humidity. Regardless of the pattern that the models are split between, this pattern favors higher dew points, thanks in large part to the persistent southerly return flow.

The net result is widespread temperatures in the 90s and maximum heat index values near or above 100 degrees on Thursday and Friday.

Beyond Friday, the risk for extreme heat is expected to decrease over the weekend. A set of cold fronts are forecast to move through the region this weekend. High temperatures for many on Saturday and Sunday are near or in the 90s with heat index values being close to the air temperature as dew points are lower from the cold fronts moving through.

KEY MESSAGE 3...There are multiple chances for thunderstorms Wednesday through Monday.

The pattern in place will begin to support daily chances for showers and thunderstorms Wednesday through Monday. While there are a few features to focus on for the highest potential of storms, there will be chances every day just from diurnally driven convection developing off the sea breeze or orographic lift.

The higher chances for widespread precipitation come first with the potential mid level trough on Friday. As noted previously, 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.

Recent deterministic guidance has trended a bit drier for the weekend. However, there remains a large amount of uncertainty. A series of cold fronts are forecast to move through the area this weekend into Monday. The air mass is drier during this timeframe compared to Wednesday through Friday, so the exact extent of the precipitation is more uncertain with PoPs generally 20-40% during parts of this period.

AVIATION /20Z MONDAY THROUGH SATURDAY/

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

Rest of Today...VFR. Winds east 5-10 kts. Moderate confidence.

Tonight...Prevailing VFR. Winds should gradually shift to southeasterly and may eventually shift to southerly, but likely with some light/variable to calm periods. Moderate confidence.

Tuesday...VFR. Winds shifting to south-southwest 5-10 kts. High confidence.

Outlook...

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

Saturday... Mainly VFR. No significant weather.

MARINE

Winds and seas should stay below Small Craft Advisory criteria through Tuesday.

Outlook...

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 with wind gusts upwards of 25 kt and seas building to 3-5 feet.

Thursday through Saturday...No marine headlines expected. Winds generally between 10-20 kt with seas around 2-4 feet.

Rip Currents...

On Tuesday, light south winds in the morning will increase to 10 to 15 mph with gusts up to 20 mph in the afternoon. Breaking waves will average 1 to 2 feet with a light easterly swell with a period around 7 seconds. As a result, there is a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore and at Delaware Beaches.

On Wednesday, south winds increase to 15 to 20 mph with gusts up to 25 mph. Breaking waves will be 1 to 2 feet with a light easterly swell around 8 seconds. This will result in a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore in Monmouth county and Delaware Beaches, and a MODERATE risk at the Jersey Shore in Ocean, Atlantic, and Cape May counties.

Ocean water temperatures are gradually increasing, but remain mostly in the 60s.

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

PHI WATCHES/WARNINGS/ADVISORIES

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