textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation section for 12z TAFs.

A Flood Watch has been issued for a large portion of the area from around the urban corridor northward beginning this afternoon as we are growing increasingly concerned about flash flooding this afternoon through Monday.

KEY MESSAGES

1) Multiple rounds of heavy showers and thunderstorms are expected to impact the area late today and continuing through Monday bringing the threat for flash flooding. A Flood Watch is in effect from 2 PM this afternoon until 8 PM Monday for areas from around the urban corridor extending northward.

2) Severe weather remains a threat with showers and storms later this afternoon through this evening with the greatest threat existing for areas near the I-78 corridor southward.

3) Impacts from prolonged heat and humidity will continue today even though the high temperatures and max heat indicies will not be as high as recent days.

DISCUSSION

KEY MESSAGE 1... Multiple rounds of heavy showers and thunderstorms are expected to impact the area late today and continuing through Monday bringing the threat for flash flooding. A Flood Watch is in effect from 2 PM this afternoon until 8 PM Monday for areas from around the urban corridor extending northward.

The showers and thunderstorms from this past evening have diminished however a diffuse frontal boundary remains situated across the area. This may continue to bring a few isolated showers through this morning but no severe weather or flooding is expected through midday. However as we get into the mid to late afternoon expected storms to bubble up once again in response to diurnal heating plus weak impulses moving through aloft. The column will be more saturated compared to yesterday with PWATs progged to be over 2 inches. At the surface the front will stalled roughly over Delmarva into southern NJ while aloft the area will be under the favorable right jet entrance dynamics of a a jet streak over New England extending into the Canadian Maritimes. This pattern looks to lock in place not just for today but likely right through Monday. The upshot will be heavy showers/storms becoming quite widespread across the area by early this evening. Rain rates of over 2 inches per hour are likely at times and model guidance indicates there will be areas likely to see 3-4+ inch rainfall amounts in just a matter of a few hours within the heaviest storms. This will certainly be enough for flash flooding and given these recent trends we've gone ahead and issued a Flood Watch for flash flooding that encompasses our forecast zones from around the urban corridor extending northward as these are the areas likely to see the heaviest rainfall amounts. Timing wise, there could be some heavier scattered showers/storms around mainly over NE PA into NW NJ as early as the mid to late afternoon but it really looks to be the evening period when heavy storms will be quite widespread.

Getting into the overnight period of Sunday night, showers/storms should temper down at least somewhat due to the loss of daytime heating however there will still be plenty of frontal forcing at the surface and jet support aloft to at least keep some showers and possible storms around. This is not a setup where convection will be completely dying after sunset. Lingering elevated instability will mean even overnight lightning will be possible.

Unfortunately, very little change is likely into Monday. Expect showers/storms to linger over the area and potentially become quite widespread and heavy by the afternoon period once again leading to more instances of flash flooding.

Impacts from flash flooding could be significant over the next couple days. Areas facing the greatest threat from flash flooding will be urban and lower lying areas and areas around streams and creeks as these are likely to exceed their banks in spots.

The heaviest of the rain should diminish overnight Monday night but even into Tuesday there are likely to be some more showers and storms around even though they are not likely to be as widespread and intense.

KEY MESSAGE 2... Severe weather remains a threat with showers and storms later this afternoon through this evening with the greatest threat existing for areas near the I-78 corridor southward.

The storms discussed above will also have the potential to produce severe weather late this afternoon through this evening. ML CAPE values could once again exceed 2000+ j/kg with modest shear. Expect multi-cell clusters to be the dominant mode with damaging winds being the biggest threat. The Storm Prediction Center has the majority of our area in a SLIGHT risk for severe storms meaning scattered severe storms will be possible. The highest threat for severe weather looks to be areas near and south of the I-78 corridor where it will be more unstable closer to and south of the front.

The severe weather threat will diminish by mid to late evening as the lower levels start to stabilize and instability becomes more elevated.

KEY MESSAGE 3...Impacts from prolonged heat and humidity will continue today even though the high temperatures and max heat indicies will not be as high as recent days.

Today will not be as hot as recent days due to a front that has moved southward into our area. However it will remain quite muggy with most area seeing high temperatures ranging from the upper 80s to mid 90s. While this is not as hot as recent days this will still be enough to result in continuing heat impacts due to the long duration of these high temperatures and humidity. We have a Heat Advisory in effect for today that includes all areas except the Poconos and Sussex County NJ. Further cooling can be expected for the new work week so we don't expect heat headlines being needed beyond today.

AVIATION /12Z SUNDAY THROUGH THURSDAY/

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

Today...VFR through most of the day although there's the chance showers/storms could affect RDG and ABE as early as the 20-22z time frame. And if that happens these sites could see restrictions at least down to MVFR or lower. Winds variable but generally favoring a SW to SE direction at 4-7 knots. Moderate confidence.

Tonight...Showers and storms will affect most terminals this evening with a good chance for vsby restrictions to at least MVFR. Most of the lightning activity diminishes overnight but showers linger and most sites should see at least times of IFR cigs late at night. East to northeast winds around 5 knots. Moderate confidence overall.

Outlook...

Monday through Monday night...Scattered to widespread showers and thunderstorms with sub-VFR conditions expected at times.

Tuesday...Still some showers around that could bring sub VFR conditions.

Wednesday...Mainly VFR.

MARINE

A few showers may linger over the waters through this morning along with the potential for some areas of mist and fog. Another round of showers and thunderstorms is likely to impact the waters this evening and could produce localized wind gusts over 40 knots.

Outlook...

No marine headlines are currently anticipated for Monday however by later Tuesday into Wednesday seas could reach 4 to 6 feet.

Rip Currents...

For today, winds will be from the east around 10 mph with gusts up to 15 mph in the afternoon. Breaking waves will be around 1-2 feet or less. There will be a weak southeast swell with a period around 8 seconds. This results in a LOW risk for the development of dangerous and life threatening rip currents at the Jersey Shore and at Delaware Beaches.

For Monday, winds remain east around 10 to 15 kt, with gusts to 20 kt in the afternoon. Resulting increasing NE wind wave could drive an elevated MODERATE Rip Current Risk along the Jersey Shore, with LOW risk persisting over the Delaware Beaches.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...Heat Advisory until 8 PM EDT this evening for PAZ060>062-070- 071-101>106. Flood Watch from 2 PM EDT this afternoon through Monday evening for PAZ054-055-060>062-070-071-101>106. NJ...Heat Advisory until 8 PM EDT this evening for NJZ007>010- 012>027. Flood Watch from 2 PM EDT this afternoon through Monday evening for NJZ001-007>010-012-013-015>019. DE...Heat Advisory until 8 PM EDT this evening for DEZ001>004. Flood Watch from 2 PM EDT this afternoon through Monday evening for DEZ001. MD...Heat Advisory until 8 PM EDT this evening for MDZ012-015-019- 020. MARINE...None.