National Weather Service Mount Holly NJ
352am EDT Sunday Jun 30 2024
Synopsis
Showers and thunderstorms early this morning and then again this afternoon and evening prior to a cold front moving across the area. High pressure builds in Monday through Tuesday before moving offshore Wednesday. A surface trough arrives on Thursday as a cold front may approach from the northwest Friday.
Near Term - Through Tonight
Very warm/hot and humid air mass today. Severe thunderstorms possible this afternoon and evening, roughly from 4-10 PM. Drying and cooling tonight as dew points lower especially overnight.
An active day is anticipated especially this afternoon and early this evening. Our region becomes more situated within a warm sector and this will boost high temperatures into the lower 90s for many places. This occurs once areas of lower clouds lift, although at least some clouds are anticipated to persist. A cold front then works its way through the region tonight. The high dew points advecting over the cooler ocean waters should result in some marine fog along the coast this morning.
A cluster of showers and thunderstorms will continue to slide eastward from the I-95 corridor and also parts of our Delmarva area early this morning. The southern end of this is stronger and this is where thunder is occurring. Very heavy rain for a time with this especially across parts of southern New Jersey into Delmarva. Locally gusty winds possible with the stronger storms.
Deep southerly flow will be maintained today ahead of a cold front. This will strengthen some and as the boundary layer warms, a gusty southerly breeze should commence especially across the coastal plain this afternoon. The surface dew points will be in the 70s this morning for much of the area. There may be enough mixing in the afternoon for the dew points to drop a little. Heat index values will be in the upper 90s to low 100s. No changes to the Heat Advisory as peak heat indices this afternoon should be around 100 degrees within the urban I-95 corridor (lower advisory criteria through today) and around 105 for our eastern shore of Maryland counties. If more cloud cover prevails and/or convection gets going sooner, than high temperatures and therefore heat indices will be impacted (lower).
While low pressure tracks well to our north, an incoming upper-level trough will push a cold front across our region late today and this evening. Some showers and thunderstorms are forecast to develop, however a pre-frontal trough may focus much of the convective development along and south/east of the I-95 corridor. Given the heat and high humidity in place coupled with ample instability (MLCAPE up to 2000 J/kg) and effective shear of 40 knots will support some discrete storms although these should organize into more of a linear mode. Severe thunderstorms are certainly possible, especially the more organized they become, with damaging straight- line winds and some hail the main hazards. The downburst potential could become enhanced especially given the high precipitable water environment and with some model forecast soundings showing an inverted-V low-level profile. This would increase the downdraft instability or DCAPE. The environment looks conducive for thunderstorms that have a taller and stronger core to produce frequent cloud to ground lightning and stronger outflow winds. The low-level flow is also forecast to veer some and therefore the 0-1km SRH decreases with time. The precipitable water values may start to lower later in the afternoon although this will depend on the eastward progression of the trough/cold front, however locally very heavy rain will occur with any stronger convection. Convection will be moving and therefore the flash flooding threat looks more limited. It will then dry out by later tonight in the wake of the cold front, and dew points will also be on the decrease especially overnight.
Short Term - Monday Through Tuesday Night
High pressure will be the name of the game during the short term forecast period. This will bring a dry and pleasant start to the new month across the region. Ushered in by breezy north- northwest winds, temperatures on Monday will top out in just the upper 70s to low 80s across the region. This is 5 degrees or so below normal for the beginning of July. Dew points will be lower as well, in the 50s, making conditions quite comfortable. Lows Monday night look to be in the upper 50s to low 60s.
Highs on Tuesday will be closer to normal, mainly in the low- mid 80s. However, with dew points forecast to remain in the 50s, another pleasant day looks to be on tap. Lows Tuesday night will be a touch warmer as well, mainly in the low-mid 60s.
Long Term - Wednesday Through Saturday
Summary...Less humid to start then the heat and humidity spikes Thursday, followed by a little cooling but remaining humid. Some convection possible late in the week. Few changes from the previous forecast.
Synoptic Overview...A mid/upper level ridge remains in place Wednesday, then some influence from a Canadian upper-level trough will push the ridge southward some Thursday and Friday. At the surface, a warm front lifts northward Wednesday then a trough arrives Thursday with a cold front approaching from the northwest Friday.
Wednesday...Surface high should remain the dominant feature for one more day, leading to one more day of tranquil conditions. As the high shifts further off shore though, southwesterly flow will develop, leading to increasing dewpoints, although, guidance still shows the dew points in the lower 60s even late on Wednesday, which is humid, but not oppressively humid.
Thursday (Independence Day) through Saturday...Southerly flow becomes more established leading to hot and humid conditions all three days (though Saturday is dependent on if a cold front will stay northwest of our region. The influence of a Canadian upper-level trough will start to approach during Thursday, however the timing and amplitude of this trough is less certain. As of now, the main trough is more toward the Midwest and therefore a cold front may be slow to approach our area late in the week. There may be a pre-frontal trough in our vicinity Thursday into Friday and this may provide enough focus amid a destabilizing air mass to initiate some convection.
Marine
Southerly flow will be maintained today ahead of a cold front with some increase as the low-level flow also increases. Mixing over the cooler waters will be limited some. Will maintain the Small Craft Advisory for the New Jersey and Delaware Atlantic waters into early this evening for now as some gusts up to 25 knots and seas up to 5 feet are still possible. Some showers and a thunderstorm early this morning, then additional showers and thunderstorms later this afternoon and tonight with locally strong winds. Some fog may occur through this morning especially nearshore with visibility restrictions. The conditions improve overnight as a cold front shifts out to sea.
Outlook... Monday through Thursday...Conditions are forecast to be below Small Craft Advisory criteria.
Rip Currents... Today...South-southwest winds 10-20 mph with breaking waves of 2-3 feet are expected. Swell periods are expected to be up to 6-7 seconds in length. Due to winds and a longer swell period, have gone with a MODERATE risk for the development of dangerous rip currents for both the Jersey Shore and Delaware Beaches.
Monday...North-northeast winds around 10 mph with breaking waves 1-2 feet. As winds and breaking waves are lower, have gone with a LOW risk for the development of dangerous rip currents for both the Jersey Shore and the Delaware Beaches.
For specific beach forecasts, visit weather.gov/beach/phi
NOAA Mount Holly NJ Office: Watches - Warnings - Advisories
PA...
Heat Advisory from 11am this morning to 7pm EDT this evening for PAZ070-071-102-104-106. NJ...
Heat Advisory from 11am this morning to 7pm EDT this evening for NJZ010-012-013-015-017>020-027. DE...
Heat Advisory from 11am this morning to 7pm EDT this evening for DEZ001. MD...
Heat Advisory from 10am this morning to 7pm EDT this evening for MDZ012-015-019-020.
Marine
Small Craft Advisory until 7pm EDT this evening for ANZ450>455.
