This Afternoon:
A slight chance of rain showers after 5pm. Partly sunny, with a high near 77. Northeast wind 0 to 5 mph. Chance of precipitation is 20%.

Tonight:
A slight chance of rain showers before 7pm, then patchy fog. Mostly cloudy, with a low around 59. Southeast wind around 0 mph. Chance of precipitation is 20%.

Monday:
Patchy fog before 10am. Partly sunny, with a high near 78. Southeast wind around 0 mph.

Monday Night:
Patchy fog after 2am. Partly cloudy, with a low around 57. South wind 0 to 5 mph.

Tuesday:
Patchy fog before 8am. Mostly sunny, with a high near 82. Southwest wind 0 to 10 mph.

Tuesday Night:
Mostly clear, with a low around 58.

Wednesday:
Sunny, with a high near 85.

Wednesday Night:
A slight chance of showers and thunderstorms after 8pm. Partly cloudy, with a low around 65.

Extended Forecast

Thursday Chance Showers And Thunderstorms	Thursday Night Chance Showers And Thunderstorms	Friday Sunny	Friday Night Slight Chance Rain Showers	Saturday Chance Rain Showers	Saturday Night Chance Rain Showers
Hi 83 °F	Lo 59 °F	Hi 77 °F	Lo 55 °F	Hi 77 °F	Lo 57 °F
PoP 50%	PoP 30%			PoP 30%	PoP 30%

AREA FORECAST DISCUSSION
National Weather Service Mount Holly NJ
1030 AM EDT Sun May 19 2024

Weather Synopsis:
An area of low pressure moves offshore to our south today. High pressure then builds across our area through Wednesday. A cold front approaches and swings through the area on Thursday into Thursday night. High pressure returns for Friday with another low pressure system approaching by next weekend.

Near Term:
THROUGH TONIGHT - 1030 AM...We are still seeing quite a bit of cloud cover across the area at this time. While some of the early morning mist/fog and stratus has started to lift, areas that have seen some clearing have started to see strato cu develop due to the solar insolation acting on the abundant low level moisture. So expect that the overall trend will be for more clouds than sun through at least around mid afternoon or so. Sky cover was increased some for today with the mid morning update. Even by late this afternoon, it may not get much better than partly sunny across much of the region given the plentiful low- level moisture to work with. Towards the western flank of the marine layer, could even be a pop-up shower, most likely out in Berks County. The insolation and general lack of rain should allow most areas to pop back into the 70s, except near the shore.

Short-term guidance suggests a new push of marine clouds will move into the region tonight, so have another mostly cloudy forecast tonight. If clouds are less widespread, fog may become an issue, but for now have kept it patchy in the forecast. Lows mostly in the 50s again.

Short Term:
MONDAY THROUGH TUESDAY NIGHT - The short term period will be focused mainly on the mid to upper level ridge that approaches and builds overhead through the period. At the surface, broad high pressure over New England will expand southwest and become elongated into the Appalachian region Monday. The high will sink south of the region on Monday night before moving offshore late Tuesday into Tuesday night. During this period, dry conditions are expected with mostly sunny skies during the day and mostly clear skies at night.

With the clear skies and light winds overnight, expect a favorable setup for radiational fog Monday night and possibly again on Tuesday night. Its less clear if there are any more likely areas for fog development, so have a mention of patchy fog across the region Monday night. Have left out a mention of fog for Tuesday night at this time, as there may be some increasing clouds if a prefrontal trough starts to approach our region then.

In terms of temperatures, it is looking like we will return close to normal on Monday with highs in the mid to upper 70s and lows in the low to mid 50s. For Tuesday, winds become more southerly as the high shifts offshore resulting in warmer temps being brought north. Generally looking at the upper 70s to low 80s for Tuesday. However, with rather light surface winds, this should allow a sea breeze circulation to develop each day, so do anticipate cooler high temperatures closer to the coast. Given how cold the water temperatures still are, there is potential for the sea breeze to develop early and then reach far enough inland that highs for most, if not all, of the coastal plains could be slightly lower than the current forecast. However, hard to determine those details this far out, so have stayed close to a blend of guidance for high temperatures both days.

Long Term:
WEDNESDAY THROUGH SATURDAY - Summary: Main focus through the long term is on a cold front which is expected to cross through the region Thursday into Thursday night bringing a chance for thunderstorms. High pressure will return in the wake of the front with another disturbance that approaches by next weekend.

Details:

Wednesday...Upper ridge axis will shift offshore on Wednesday. There continues to be poor run-to-run consistency on if there will be a pre-frontal trough in the region as early as Wednesday afternoon. For now, have kept any mention of thunderstorms (and just a slight chance at that) confined to Berks County, Lehigh Valley, and the southern Poconos through the day, and generally along and west of the 95 corridor Wednesday night.

Thursday...There actually appears to be less model agreement on the timing of the front as compared to previous model runs. Some models (most notably the GFS) depict the cold front passage as early as Wednesday night into Thursday morning. Given how late we are in the season, and the fact that the mid and upper level low should be slowing as the surface front approaches, I think this is the more unlikely scenario. Thus, have stayed close to the previous forecast and a blend of other guidance with the cold front generally arriving from Thursday afternoon into Thursday night. With the location of the mid and upper level trough over the Great Lakes, this keeps the better forcing north and west of the area. However, with enough surface instability aided by diurnal heating, this should support at least scattered thunderstorm develop across the area. This is supported quite well by analog- based guidance. Temps should be above average again and close to Wednesday temperatures, assuming the later timing of the front holds.

Friday and Saturday...The forecast for Friday and Saturday is quite uncertain and depends on how far the front makes it past our area. Unsurprisingly given how quickly it is depicting the arrival of the front, the GFS remains the most aggressive with the progression of the front, bringing in high pressure into the area on Friday and most of Saturday. ECMWF keeps the front stalled just south of our region through Saturday. As a result of the uncertainty in the timing and evolution of the front, have used a blend of guidance, which keeps at least slight chance of showers through the weekend. However...the upcoming weekend will probably not be a washout as almost all guidance shows at least some period of dry weather. However, due to the differences in the timing, it is hard to determine when the dry period could be.

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