textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Aviation section updated for 18Z TAFs.

KEY MESSAGES

1. Mainly fair and dry weather is expected through Monday.

2. Showers and thunderstorms return Tuesday into Wednesday with the potential for severe weather and flash flooding.

DISCUSSION

KEY MESSAGE 1...Mainly fair and dry weather is expected through Monday.

Today is shaping up to feature sunshine with both lower temperatures and lower humidity levels as a high pressure system builds in. Generally expect highs ranging from the 70s to near 80 over our northern zones over NE PA into NW NJ with low to mid 80s near the urban corridor and mid to upper 80s over portions of our eastern MD shore counties and southern Delaware. Dew points will be much lower compared to Saturday so the heat indices will be close to the actual air temperatures. High pressure remains in control for Monday with temperature and humidity levels remaining similar to Sunday. It remains mainly sunny on Monday with light winds.

KEY MESSAGE 2...Showers and thunderstorms return Tuesday into Wednesday with the potential for severe weather and flash flooding.

Unsettled weather returns Tuesday into Wednesday. For Tuesday, a warm front lifts northward throughout the day. As this warm front lifts northward, winds turn more southerly with moisture being transported northward. Temperatures on Tuesday reach the mid 70s to upper 80s with increasing humidity as dew points reach into the 70s for many.

By early Tuesday morning, isolated showers and thunderstorms may already be developing. The coverage of these showers and thunderstorms will be increasing throughout the day and peak during the afternoon/evening hours. Heading into Tuesday night, a cold front will be approaching the region and cross through our area into Wednesday. This will keep the activity going into Tuesday night and Wednesday morning. Beyond Wednesday morning it is a bit more uncertain as it depends on the placement of the cold front. If the cold front takes longer to clear our area, then showers and thunderstorms will linger into the second half of Wednesday. However, the general trend currently looks to be drier as Wednesday progresses, especially by late day.

For Tuesday, there is the risk for severe weather and heavy rain leading to flash flooding. In terms of the set-up, the exact extent of instability that builds remains a bit more uncertain among model guidance with variations. However, the general consensus shows values that are supportive of severe weather. Also, lapse rates will be supportive along with increasing shear values for storm organization. This looks to be another event with multiple rounds. The first being the showers and thunderstorms in the morning, the second being the more widespread coverage in the afternoon and evening, and another round into Tuesday night with the cold front. Activity in the afternoon and evening looks to pose the greatest and most widespread risk for severe weather with the primary hazard being damaging wind gusts. Currently, the Storm Prediction Center has our whole area outlooked in a SLIGHT (2 out of 5) risk for Tuesday. On the heavy rainfall side of things, the moisture transport on Tuesday will result in PWATs getting near or over 2 inches along with warm cloud layer processes. All of this supports showers and thunderstorms being able to produce heavy rain. There is also a SLIGHT (2 out of 4) risk for excessive rainfall outlooked for a large portion of our area Tuesday by the Weather Prediction Center.

On Wednesday, the Storm Prediction Center has portions of Delmarva and southern NJ outlooked for severe weather and also a MARGINAL (1 out of 4) risk for excessive rainfall for most of our area by the Weather Prediction Center. Part of this set-up will depend on the placement of the front and timing. After Wednesday, we are drier for the end of the week.

AVIATION /18Z SUNDAY THROUGH FRIDAY/

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

Rest of Today...VFR. Northwest winds around 10 kts with gusts up to around 20 kts. Gusts begin to drop off by around 21-22Z. High confidence.

Tonight...Mainly VFR. Patchy mist can't be ruled out at the more rural terminals, but overall unlikely. Winds around 5 kts or less, favoring a northerly direction, but some variability is likely, particularly at more sheltered terminals. High confidence.

Monday...VFR. Winds remain light, around 5 knots or less but a bit variable with high pressure overhead. Generally, winds should favor a north-northeast direction in the morning, and a south-southeast direction by late in the afternoon. High confidence in VFR conditions.

Outlook...

Monday Night...VFR. No significant weather.

Tuesday through Wednesday...Sub-VFR conditions possible in SHRA/TSRA.

Thursday through Friday...VFR. No significant weather.

MARINE

Sub-advisory conditions will prevail through Monday. Winds around 10 kts or less with seas of 2-3 feet. A few gusts up to 15-20 kts remain possible through this afternoon, but will be decreasing by this evening.

Outlook...

Tuesday through Wednesday...Winds and seas likely approach SCA criteria by late day Tuesday and could linger into Wednesday night.

Thursday through Friday...Conditions are expected to remain below SCA criteria.

Rip Currents...

For today, winds turn offshore, becoming northwesterly up to 10 MPH. A medium period swell with wave heights in the surf zone around 2 feet or less. All of this will result in a LOW risk for rip currents at all beaches.

For Monday, winds turn back onshore, but remain around 10 MPH. Medium period swell with wave heights around 2 feet or less continuing. As a result, the rip current risk will remain LOW for Monday at all beaches.

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

EQUIPMENT

KDIX suffered a failure earlier this afternoon due to a lightning strike. Technicians have done some initial troubleshooting but the radar is likely to stay down until at least later today.

PHI WATCHES/WARNINGS/ADVISORIES

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