textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated Rip Current Section for Wednesday and Thursday.

KEY MESSAGES

1. Dry conditions expected through much of tonight, however a few isolated showers or storms may arrive by around dawn Wednesday.

2. Dangerous heat is likely on Thursday and Friday.

3. There are multiple chances for thunderstorms Wednesday through Friday. The weekend has trended drier.

DISCUSSION

KEY MESSAGE 1...Dry conditions expected through much of tonight, however a few isolated showers or storms may arrive by around dawn Wednesday.

Broad upper ridging will build through tonight. At the surface, high pressure is sliding offshore, beginning a transition to a warm advection regime which will ramp up late tonight as a warm front lifts north. A mid level shortwave trough associated with upstream convection will approach the area by dawn Wednesday.

Following a warmer afternoon, lows tonight will be upward of 10-15 degrees warmer than this morning was, mainly in the mid 50s to mid 60s under increasing cloud cover. We'll have to keep an eye on the remnant convection approaching from upstream overnight. Current indications remain that instability will weaken considerably toward the east as the remnant activity moves in overnight into our area. This will likely result in some isolated decaying showers and embedded rumbles of thunder moving in around dawn or so across the western half of the forecast area.

KEY MESSAGE 2...Dangerous heat is likely on Thursday and Friday.

In general, mid-level ridging is expected to build into the region during the middle and latter part of the week. However, guidance has been trending southward with placement of an upper-low over Canada and associated troughing over the CONUS, and therefore featuring a slightly weaker ridge axis through our region. At the surface, the region will largely be under the influence of high pressure centered over portions of the Southeast.

Despite this, dangerous heat is still expected across the area on Thursday and Friday. Temperatures on both days look to climb into the low to mid 90s across most of the area. With dewpoints generally in the low 70s, heat indices are expected to range between 95 to 104 degrees across the majority of the area, outside of the Poconos. The greatest threat for heat indicies over 100 will be found across southeast PA, southern NJ and the Delmarva. This level of heat and humidity can become dangerous quickly for sensitive individuals and those outdoors for extended periods of time. Heat headlines will likely be necessary during this time period to cover this threat.

A cold front is forecast to move through the region late Friday into Saturday, which will is expected to knock temperatures and dewpoints down several degrees. Though it will still be hot with highs upper 80s to low 90s over the weekend, dewpoints will return to more comfortable levels, minimizing the threat for additional heat headlines.

KEY MESSAGE 3...There are multiple chances for thunderstorms Wednesday through Friday, some which may be severe. The weekend has trended drier.

The pattern in place will become increasingly conducive for precipitation chances across the region beginning on Wednesday. Much of this activity looks to be in the form of diurnally driven convection, though some guidance is beginning to indicate a few better opportunities, especially on Friday.

The first opportunity comes on Wednesday, with a weak shortwave and surface trough moving through the region. Given marginal instability and shear around the region, the Storm Prediction Center now has our entire forecast area in a MARGINAL Risk (Level 1/5) for severe weather. As of right now, PoPs are around 40-60% areawide. The next opportunity comes on Thursday, however large scale forcing and shear are expected to remain weak. However, hot temperatures and high dewpoints will likely trigger at least some diurnally driven convection, so the Storm Prediction Center has the entire region in a MARGINAL risk once again. PoPs are generally in the 30-60% range.

On Friday, the region is expected to begin feeling the influence of the upper trough to the west of the region, in addition to a cold front that will be approaching from the west. Scattered showers and storms may focus near and ahead of this boundary, and with strong destabilization and slightly better wind fields aloft, there is concern that some severe threat could materialize. This will need to be monitored in the coming days as the SPC now has areas northwest of the I-95 corridor outlooked in a 15% chance of severe weather area.

Guidance has trended considerably drier for much of the weekend in wake of the cold front, so it now appears that much of the weekend will be dry. However, another front may approach towards the end of the weekend and into early next week, with more chances of showers and storms returning next week.

AVIATION /20Z TUESDAY THROUGH SUNDAY/

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

Rest of Today...VFR. Generally SW winds near 10 kts. Some occasional gusts up to 20 kt are possible. SCT clouds around 4-6 kft AGL, otherwise, increasing high clouds late. High confidence.

Tonight...VFR until near dawn. By 09Z or so, a few isolated showers and SCT to BKN MVFR ceilings will start to develop, but right now it looks more like most terminals stay VFR until after dawn. Southerly winds near 5-10 kts may become light and variable at times. High confidence in VFR through 09Z, then low confidence on timing/coverage of any restrictions from stratus or showers.

Wednesday...MVFR cigs likely envelop most of the region during the early-mid morning hours with scattered showers. These may break during the afternoon with cigs lifting back to VFR, with another round of showers/t-storms possible late in the day. Winds SSW 5-10 kts. Moderate confidence in pattern, low confidence in details/timing.

Outlook...

Wednesday night through Friday night...Prevailing VFR expected through the period. Brief periods of sub-VFR conditions are possible, with isolated to scattered showers and thunderstorms during the afternoon and evening hours.

Saturday through Sunday...VFR. No significant weather expected.

MARINE

No marine hazards expected through Wednesday. Southerly winds increasing to 10-15 kts with gusts up to 20 kts and seas 2-3 feet. May try to touch SCA gusts on the waters late Wednesday, but confidence is low at this time.

Outlook...

Wednesday night...SCA conditions possible due to wind gusts up to 25 kt and seas around 3-5 feet.

Thursday through Sunday...No marine headlines anticipated. Winds will generally remain between 5-15 kt through Saturday, with gusts up to 20 kt possible on Sunday. Seas generally around 2-3 feet. Isolated to scattered showers and thunderstorms possible on Thursday and Friday. Fair weather expected for Saturday and Sunday.

Rip Currents...

For Wednesday, southerly winds increase to 10 to 20 mph with gusts up to 25 mph, especially in the afternoon. Breaking waves will vary between 2 to 3 feet. While there will be a light easterly swell in the morning, a more dominant southerly swell around 7 to 8 seconds should propagate northward in the afternoon. Given these conditions, have opted to go with a MODERATE risk for the development of dangerous rip currents for all beaches.

For Thursday, southwesterly winds diminish to around 10 to 15 mph. Breaking waves around 1 to 2 feet with a southerly swell around 6 to 7 seconds. Given the lighter conditions, have opted to go with a LOW risk for the development of dangerous rip currents for all beaches.

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.