National Weather Service Mount Holly NJ
1018am EDT Wednesday Jun 19 2024
Synopsis
High pressure remains in control. A back door cold front may pass through the region Friday night. A stronger cold front will pass through the region Sunday night through Monday, and that front may hang over the area through Tuesday.
Near Term - Through Tonight
The main adjustment to the forecast this morning is an increase in cloud cover through the morning hours as some lo level cloud cover has developed across southeast Pennsylvania, southern New Jersey, Delaware, and eastern Maryland as morning mixing allowed for some moisture to get trapped near the top of the low level inversion. As the day continues to warm, the inversion will mix out and lift, so the lower clouds will dissipate. There is higher level clouds across the northern half of the area, and the higher clouds will continue at times through today.
The Heat Advisory continues for today for most of the region, and although temperatures have come down a touch, the impacts remain the same. Limit outdoor time today and if you have to be outside, take frequent breaks and stay hydrated!
A strong 597-598 dam ridge will remain overhead for today. The result will be large-scale subsidence and hot temperatures continuing. Guidance has come down slightly, and it does look like dew points will mix out a bit, resulting in lower heat indices. However, the cumulative effect of the heat will continue, and no changes to the headlines were made through tonight. Temperatures will range in the upper 80s/low 90s. With dew points mixing out, heat index values will be close to the air temperature. Max apparent temperatures are currently forecast to be in the low to mid 90s.
For tonight, there actually could be some relief as clear skies and light winds will result in favorable radiational cooling conditions. Temperatures will get down into the low to mid 60s. The exception being within the urban corridor, where the urban heat island effect will keep temperatures in the upper 60s/low 70s.
Short Term - Thursday Through Friday Night
Overall, the trend is for somewhat lower temperatures and somewhat lower humidity levels. In fact, highs will generally be in the upper 80s to low 90s on Thursday along with surface dew points starting out in the mid to upper 60s, lowering to the low to mid 60s in the afternoon. This results in max heat index values in the low to mid 90s, which would be just under Heat Advisory criteria. However, given that this will be the third day of heat, feel comfortable converting the Excessive Heat Watch that is in effect for Thursday to a Heat Advisory based on the cumulative impacts of the daytime heat along with the lack of relief that due to relatively warm overnight low temperatures.
By Friday, Bermuda high pressure becomes entrenched off the Mid- Atlantic coast. Increasing southerly flow will usher a warmer and more humid air mass into the region. Highs on Friday should get into the low to mid 90s, perhaps in the upper 90s along the I-95 corridor, including Philadelphia. Surface dew points rise into the upper 60s to low 70s, resulting in max heat index values in the upper 90s to low 100s. Based on current forecast, the max heat index values look to fall just below
Excessive Heat Warning...iteria, but since this would now be the fourth consecutive day of high heat and now increasing humidity, will keep the Excessive Heat Watch in effect for Friday, but it may be converted to a Heat Advisory.
The other aspect for Friday is that a back-door cold front will sag in from the north, sparking off afternoon and evening showers and thunderstorms. These storms may have an impact on high temperatures Friday, but it is far too soon to determine timing and placement of those storms and what impacts those storms would have on the temperature forecast. Will follow NBM and carry low-end likely Probability of Precipitation for the southern Poconos and far northern New Jersey, and chance Probability of Precipitation down to just south of the Fall Line, down to Philadelphia. For areas north and west of the Fall Line, PWATs (Precipitable Waters) will be up around 1.75 inches and 0-6 km Bulk Shear will be less than 20 kt. SB CAPE values should range from 1500 to 2000 J/kg. Localized flooding possible due to potentially slow-moving thunderstorms producing heavy rain.
Warm and muggy both Thursday night and Friday night, though given any thunderstorms, humidity will be elevated Friday night. Lows will be in the upper 60s to low 70s, though lows will be a couple of degrees warmer Friday night compared to Thursday night. Patchy fog may develop Friday night as well.
Long Term - Saturday Through Tuesday
Excessive Heat Watch will remain in effect for Saturday and Sunday, however, the overall trend is for slightly lower high temperatures. As a result, it is looking more and more likely that the Watch could be converted to Heat Advisories, and even in some cases, Heat headlines might not be needed at all for some locations. Will keep the Excessive Heat Watch in effect for now, mainly based on the cumulative impacts have based on several days of heat and humidity with little, if any, relief at night due to warm overnight low temperatures have.
While high temperatures seem to be trending a bit lower than originally forecast, surface dew points are trending on the higher side given persistent southerly flow allowing low level moisture to build into the Northeast and Mid-Atlantic.
Back-door cold front through the northern half of the forecast area Friday night remains nearly stationary on Saturday. As a result, highs will be in the upper 80s to low 90s for the northern portion of the forecast area, and even along the coasts, highs will be in the low to mid 80s due to flow coming off the cooler ocean waters. Just inland, including the I-95 corridor from Trenton to Wilmington and areas west, as well as Delmarva, highs will get in the low to mid 90s. Surface dew points will be in the upper 60s to low 70s. Max heat index values in these areas will be in the upper 90s to around 100.
A thermal trough sets up over central Pennsylvania and some approaching shortwave energy may spark off some afternoon and evening showers and thunderstorms, with the highest Probability of Precipitation north and west of the Fall Line. Again, heavy rain and localized flooding possible.
A cold front approaches on Sunday. Southerly flow ahead of the front ushers warm and humid air with highs in the low to mid 90s and surface dew points in the lower 70s. Max heat index values look to be in the upper 90s to low 100s, but for now look to remain below 105. Will keep an eye on potential severe weather on Sunday. Ahead of the front, SB CAPE values rise to around 1500 J/kg and 0-6 km Bulk Shear will rise to 35 to 40 kt in the afternoon and evening. DCAPE values will be up around 600 to 800 J/kg. PWATs (Precipitable Waters) will be up around 2 inches. Damaging winds and heavy rain possible Sunday afternoon and evening.
Cold front comes through on Monday and may get hung up over the area into Tuesday. With the front over the area, additional scattered showers and thunderstorms possible Monday afternoon. Highs will be in the upper 80s to around 90, with surface dew points in the mid and upper 60s. Max heat index values will not be much higher than the actual surface temperatures. Tuesday looks to be dry with temperatures a few degrees above normal, topping off in the upper 80s to low 90s.
Marine
No marine headlines expected through tonight. Winds will be out of the south around 10-20 kt with 2 to 3 foot seas.
Outlook... Thursday through Saturday...Sub-SCA (Small Craft Advisory) conditions, though persistent 15 to 20 kt winds may develop at northern NJ ocean waters each afternoon.
Sunday...SCA (Small Craft Advisory) conditions may develop with S winds 15 to 20 kt with 25 to 30 kt gusts and Seas building to 3 to 5 feet.
Rip Currents... Wednesday...With winds around 10 MPH or less and breaking waves around 2 feet or less, all coastal zones have a LOW risk for the development of rip currents.
Thursday...Winds will be a bit stronger on Thursday, with waves slightly higher. Part of the NJ coast will have an onshore component to the wind. For this reason, kept a MODERATE Risk for all New Jersey beaches except Monmouth County. For the Delaware Beaches and Monmouth County, continued with a LOW risk of dangerous rip currents.
Rip currents occur often in the vicinities of jetties and piers. Utilize any guarded beaches if venturing out into the water. For specific beach forecasts, visit weather.gov/beach/phi
Climate
Record high temperatures for today. Reading and Mount Pocono are the only climate sites with a forecast high within 2 degrees of the record. Highly unlikely any other sites match or break a record.
Location Record High (6/19)
Philadelphia, PA 100/1994 Allentown, PA 96/1994 Reading, PA 95/1929 Mount Pocono, PA 86/1929 Trenton, NJ 96/1994 AC Airport, NJ 96/1994 AC Marina, NJ 93/1952 Wilmington, DE 100/1994 Georgetown, DE 96/1952
Record high temperatures Thursday.
Location Record High (6/20)
Philadelphia, PA 98/1931 Allentown, PA 100/1923 Reading, PA 101/1923 Mount Pocono, PA 89/2012 Trenton, NJ 98/1923 AC Airport, NJ 95/2012 AC Marina, NJ 90/1908 Wilmington, DE 97/2012 Georgetown, DE 98/2012
Record high temperatures Friday.
Location Record High (6/21)
Philadelphia, PA 99/1923 Allentown, PA 100/1923 Reading, PA 99/1923 Mount Pocono, PA 90/1953 Trenton, NJ 97/1923 AC Airport, NJ 97/1988 AC Marina, NJ 94/2012 Wilmington, DE 98/2012 Georgetown, DE 99/2012
Record high temperatures Saturday.
Location Record High (6/22)
Philadelphia, PA 100/1988 Allentown, PA 95/1941 Reading, PA 96/1921 Mount Pocono, PA 90/1908 Trenton, NJ 99/1988 AC Airport, NJ 100/1988 AC Marina, NJ 92/1949 Wilmington, DE 98/1988 Georgetown, DE 97/2012
Record high temperatures Sunday.
Location Record High (6/23)
Philadelphia, PA 97/1888 Allentown, PA 95/1965 Reading, PA 96/1908 Mount Pocono, PA 90/1908 Trenton, NJ 97/1894 AC Airport, NJ 98/1988 AC Marina, NJ 91/1909 Wilmington, DE 100/1894 Georgetown, DE 100/1988
NOAA Mount Holly NJ Office: Watches - Warnings - Advisories
PA...
Heat Advisory until 6am EDT Friday for PAZ054-055-060>062-070- 071-101>106. Excessive Heat Watch from Friday morning through Sunday evening for PAZ054-055-060>062-070-071-101>106. NJ...
Heat Advisory until 6am EDT Friday for NJZ001-007>010-012-013- 015>020-027. Excessive Heat Watch from Friday morning through Sunday evening for NJZ001-007>010-012-013-015>020-027. DE...
Heat Advisory until 6am EDT Friday for DEZ001. Excessive Heat Watch from Friday morning through Sunday evening for DEZ001. MD...None.
Marine
None.
