textproduct: Philadelphia/Mt Holly

WHAT HAS CHANGED

Thunderstorm threat has ended for tonight.

The Small Craft Advisory was canceled.

There remains an increasing risk for patchy fog overnight into Sunday morning.

KEY MESSAGES

1. Fog is possible across the region overnight into Sunday Morning.

2. Several opportunities for much needed rainfall from late Sunday through next week.

DISCUSSION

KEY MESSAGE 1...Fog is possible across the region overnight into Sunday Morning.

The threat for showers and thunderstorms has ended for the evening. No additional activity is expected through tonight, although an isolated shower is possible north of I-80 early Sunday morning.

With light winds tonight and some residual ground moisture from rain today, some areas of fog development is anticipated. Many of the model soundings depict fog, especially northwest of the I-95 corridor. Have included a mention of patchy to areas of fog across the area through early Sunday.

Right now, the risk for dense fog or widespread fog is relatively low. However, cannot rule out some locally dense fog is the usual spots.

KEY MESSAGE 2...Several opportunities for much needed rainfall from late Sunday through next week.

An upper-level trough is forecast to dominate across much of the East to end this weekend and continue right through next week. Some guidance is much more potent with the trough amplification later next week with a closed low developing in the vicinity of the Mid- Atlantic and then moving off to the northeast. This upper-level pattern will keep the extended portion of the forecast unsettled.

Our first system brings a cold front through the area tomorrow night into Monday morning. Rain showers start to develop tomorrow afternoon into the evening with some isolated thunderstorms possible given some instability present. Overnight Sunday into Monday morning, some guidance shows more a stratiform band of rain developing ahead of the front with the best coverage being near and southeast of the I-95 corridor. An isolated thunderstorm will remain possible into early tomorrow night as instability decreases into the overnight. Behind the front, we trend drier into Monday afternoon.

After a brief dry period late Monday into Tuesday, the active weather pattern looks to reload as another upper-level trough quickly replaces the first one across much of the East. This feature may become closed off in the vicinity of the Mid- Atlantic Wednesday through Friday. Beyond Friday, some guidance moves the closed off upper low off to the northeast into Saturday.

As the pattern turns unsettled again, rain showers develop and increase in coverage late Tuesday night into Wednesday with a surface low advancing into the region. These showers continue through Wednesday night. In terms of any isolated thunderstorms, this will be dependent on how much instability is present. For Thursday into Friday, if the upper trough closes off and we get a surface low off the coast of the Mid-Atlantic, then this would lead to more showers across the area and lower temperatures due to the onshore flow. Uncertainty remains for the end of the week as we get towards the end of the extended forecast period.

AVIATION /00Z SUNDAY THROUGH THURSDAY/

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

Tonight...VFR conditions to start. There is an increasing risk for fog overnight, particularly after 06Z. There is some risk across the region, but the highest risk for IFR and even LIFR conditions is at RDG, ABE, TTN, and ACY. Winds quickly diminishing to light and variable by 01-03Z with calm periods likely overnight. Moderate confidence overall, low confidence in the extent of restrictions from low stratus or fog.

Sunday...Once any morning fog clears out by 15Z, prevailing VFR conditions likely. 30-50% chance for SHRA and TSRA after 18Z. If any SHRA or TSRA move over a TAF site, ceilings and visibilities could briefly drop to MVFR. Given the increasing risk of SHRA/TSRA, went for prevailing VCSH with PROB30 for TSRA. Winds out of the southwest to west 5-10 kts through much of the day, however winds will likely shift toward the northwest behind any organized SHRA/TSRA between 19-21Z or so. Moderate confidence in the overall pattern, low confidence in any one TAF site being directly affected by SHRA or TSRA.

Outlook...

Sunday night through Monday...A period of sub-VFR conditions probable Sunday night into Monday morning with showers. A few thunderstorms possible into early Sunday night. Conditions should improve through the day Monday.

Tuesday...VFR.

Wednesday through Thursday...Sub-VFR conditions possible along with showers.

MARINE

The Small Craft Advisory is remains was canceled for all NJ and DE Atlantic coastal waters and the lower Delaware Bay. Winds and seas will continue to lessen overnight. There is a threat of some fog overnight, but confidence on this is low.

Conditions are forecast to remain below advisory criteria through Sunday night. A line of showers and storms may impact the nearshore coastal waters after 4 PM, with brief gusty winds possible. Showers are likely Sunday night, which may lower visibility at times.

Outlook...

Monday...A brief period of Small Craft Advisory conditions possible.

Tuesday...The conditions are anticipated to be below Small Craft Advisory criteria.

Wednesday...A period of Small Craft Advisory conditions possible.

Thursday...The conditions are anticipated to be below Small Craft Advisory criteria.

PHI WATCHES/WARNINGS/ADVISORIES

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