textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated all sections.

KEY MESSAGES

1. A warm front and associated low pressure will lift across the area today creating unsettled conditions.

2. For the later half of the week, we will have a hot, humid, and at times stormy pattern in place.

DISCUSSION

KEY MESSAGE 1...A warm front and associated low pressure will lift across the area today creating unsettled conditions.

A warm front will continue lifting north through the region this morning. A weak area of low pressure attached to the front will also add some more lift to the synoptic situation this afternoon. Increasing southerly flow thru today will push dew points up into the low to mid 70s this afternoon. With highs in the low to mid 80s, max heat index values will be in the upper 80s to low 90s.

In terms of precipitation, some showers will develop in the morning with the passage of the warm front, and then another round of showers and scattered thunderstorms will develop in the afternoon. The primary concern is for heavy rain leading to flash flooding, but when it comes to a hot and humid airmass, a few strong to severe thunderstorms cannot be ruled out.

The Weather Prediction Center has a Marginal Risk (1 out of 4) for Excessive Rain for today. Rainfall amounts will be light in the morning. While overall basin averages will generally be 1/4 to 1/2 inch of rain, there is the potential for training leading to localized rainfall totals in excess of 1 inch. With most of that rain occurring in the afternoon, that creates the potential for flash flooding.

KEY MESSAGE 2...For the later half of the week, we will have a hot, humid, and at times stormy pattern in place.

Expect a prolonged period of southwesterly flow as our region will be in between a Bermuda High well to our east, and a mid-level long wave trough that will be slowly sliding east over the northern tier of the U.S./southern Canada. As such, it will be hot and humid for the later half of the week and weekend with maximum temperatures each day ranging from the low 80s (Poconos) to the low 90s (metro). However, with dewpoints from 70F to 75F, heat index values at or above 100 degrees are possible for much of the area.

The other aspect of this are the daily storm chances, primarily confined to the afternoon and evening with a typical diurnal pattern. Given the hot and humid conditions that will be in place, we can't rule out the more common thunderstorm hazards of damaging winds and heavy rain/flooding. If an embedded short wave trough crosses our region as the larger trough axis approaches, that could increase the risk, particularly for severe threats, but trying to time that out at this point would be very difficult, given that we are still seeing some differences between the models with the larger pattern.

AVIATION /06Z WEDNESDAY THROUGH SUNDAY/

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

Today...MVFR or some high-end IFR conditions much of the day. SHRA in the morning, then SHRA and TSRA in the afternoon. There could be periods of VFR between the showers. SE winds less than 10 kt. Low confidence.

Tonight...Conditions may return back to VFR behind the batch of showers/tstms in the early evening. Limited confid. Patchy fog may develop towards morning. Low confid.

Outlook...

Thursday through Sunday...Periods of MVFR or lower in afternoon and evening SHRA/TSRA.

MARINE

Sub-Small Craft Advisory conditions today. East winds 10 to 15 kt become southeast less than 10 kt, then winds become south this afternoon at 10 to 15 kt. Seas will average 2 to 3 feet.

Scattered showers are expected this morning with areas of fog too. Showers and thunderstorms will develop again this afternoon and last into the early evening.

Outlook...

Wednesday night through Sunday...Overall, a prolonged period of sub-SCA conditions, however there is a chance for 25+ kt wind gusts Thursday night. Afternoon and evening showers and thunderstorms possible as well.

Rip Currents...

For Today, winds becoming southeasterly near 10 mph. Breaking waves in the surf zone of 1-3 feet are forecast with a medium period swell. Given the more onshore component for most of the Jersey Shore, maintained a MODERATE risk for the development of dangerous rip currents. Breaking waves look to be a little lower for the Delaware Beaches with a more parallel wind therefore went with a LOW risk for the development of dangerous rip currents.

For Thursday, south to south-southwest winds increase to 10-20 mph. Despite the increasing wind and it becoming more parallel to the coast and the breaking waves forecast to be a little lower, a longer period swell may arrive. Opted to go with a MODERATE risk for the development of dangerous rip currents for the Jersey Shore, and a LOW risk for the development of dangerous rip currents for the Delaware Beaches.

PHI WATCHES/WARNINGS/ADVISORIES

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