textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Updated aviation discussion.

KEY MESSAGES

1) Relatively cool and cloudy conditions will prevail today, but there remains a 20 to 50% chance for showers and storms.

2) The next chance for showers and storms will be Thursday through Saturday as a cold front approaches and crosses through the region.

DISCUSSION

KEY MESSAGE 1...Relatively cool and cloudy conditions will prevail today, but there remains a 20 to 50% chance for showers and storms.

The stationary front remains just south of our region. This could continue to serve as a focus for showers and storm development through the day today before it finally starts making more significant progress southward tonight into tomorrow. However, based on the early morning radar and observation trends, I suspect that many models are having trouble resolving the depth and persistence of the marine layer over our region (as evidenced by the persistent and expansive low cloud cover). Given the synoptic scale pattern and the prevailing wind direction that most models are depicting through the day, see little chance for the marine layer to erode.

Therefore, while several models show scattered showers and storms across the region, suspect that most of the area will stay dry, with only some drizzle or light stratiform rain at most. The exception to this is southern Delaware and Talbot and Caroline Counties in MD. The front will stay close to those counties through the day, thus the proximity of convective initiation makes it more likely for showers to persist in to those areas.

KEY MESSAGE 2...The next chance for showers and storms will be Thursday through Saturday as a cold front approaches and crosses through the region.

The next cold front is expected to approach the region Thursday, likely crossing through our region Friday into Saturday. A few things set this apart from the multiple days of severe and flood impacts that we just saw. First, after today there will be limited opportunity for warm air and moisture advection before the front arrives. High temperatures on Wednesday and Thursday will be in the 80s - warmer than today, but a far cry from the widespread triple digit temperatures that we had at the end of last week. Dewpoints will be similarly slow to increase, though dewpoints in the 70s are possible by Thursday.

The other difference is that this looks like a rather progressive pattern. On Thursday, the mid and upper level flow will be mostly zonal allowing a small short wave trough to slide over the region. A long wave trough will dig southeast over the region Friday into Saturday, likely allowing the cold front to make progress further south from the region before stalling.

All that to say, while we can't rule out any thunderstorm hazards (severe or flash flooding) at this point, the risk is lower than what we just saw with the active period over the last 4 days.

AVIATION /12Z TUESDAY THROUGH SATURDAY/

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

Today...No major changes with the TAFs at 12Z. Thanks to a persistent marine layer, low stratus is likely to prevail through the day. There might be some improvement in the ceilings to the lower end of MVFR during the day time thanks to a slightly deeper mixed layer during the day, but a return to widespread VFR conditions is unlikely during this TAF period. There is up to a 20 percent chance for showers through the day, but unlikely to lower conditions from the prevailing IFR or MVFR conditions. Northeast winds around 5-10 kt. Moderate confidence.

Tonight...Low stratus is likely to persist for all or at least most of the night. After 06Z, may see clouds start to erode thanks to some drier air moving in, but confidence in the timing of improvement is low as climatologically this is rare timing for improving conditions.

Outlook...

Wednesday...Once the clouds break up, prevailing VFR is expected.

Thursday through Saturday...Prevailing VFR, but scattered showers and storms could result in temporary restrictions to MVFR or even IFR.

MARINE

Winds at buoy 44065 and wave heights at buoy 44091 show some locally enhanced northeasterly winds (and subsequent increase in wave heights). This isn't being modeled well by guidance, so I have low confidence on when conditions will improve, but given the overall pattern, expect SCA conditions to continue through at least mid morning. Given the uncertainty, will issue the SCA through 18Z, though it may need to be cancelled early. Once winds and waves subside for the waters north of Great Egg Inlet, winds and seas should stay below SCA criteria for the remainder of the day and tonight.

There is a chance for fog development through the day today. However, so far fog has been slow to develop, and where it has developed, visibilities remain well above 1 mile.

Outlook...

No marine headlines are currently anticipated through the rest of the week.

Rip Currents...

For the beaches in Cape May County and Delaware...thanks to a favorable wind direction and relatively low surf height, there is a LOW risk for the formation of dangerous rip currents today and tomorrow.

For the beaches in Atlantic, Ocean, and Monmouth Counties...there is a small area of enhanced northeasterly winds and subsequently higher wave heights in these areas. Based on the current observations at buoys 44091 and 44065, this would result in a MODERATE risk for Ocean and Monmouth Counties and a LOW risk for Atlantic (the bathymetry of Atlantic County makes the NE direction more favorable for Atlantic Co). However, marine conditions in these areas are not being well modeled by guidance, so this will be reevaluated after sunrise so that we can get a better view of current surf conditions.

For tomorrow, winds are expected to shift to more easterly particularly in the afternoon which could result in a MODERATE risk for the formation of dangerous rip currents.

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

PHI WATCHES/WARNINGS/ADVISORIES

PA...None. NJ...None. DE...None. MD...None. MARINE...Small Craft Advisory until 2 PM EDT this afternoon for ANZ450>452.