National Weather Service United States Department of Commerce


A look at weather fatality statistics (image below) reveals excessive heat is the leading weather related killer in the United States. This is especially true in the urban centers, where population density, the urban heat island, and building construction exacerbate the effects of excessive heat. A combination of high heat and humidity can lead to heat related illness, including heat cramps, heat exhaustion, and heat stroke. Heat-related illness can occur when the ability of the body to cool itself is challenged, or when there are insufficient levels of fluid or salt in the body due to sweating or dehydration. Heat-related illnesses increase as the combination of temperature and relative humidity increase, but there are other factors involved as well.

Heat Index

The Heat Index (image below), also known as the Apparent Temperature, is a subjective measure of what it feels like to the human body when relative humidity is factored into the actual air temperature. Relative humidity is a measure of the amount of water in the air compared with the amount of water that air can hold at the current temperature. In short, it’s a measure of how close the air is to being saturated with moisture. The body cools itself through the evaporation of perspiration or sweat. However, when the relative humidity is high, the increased moisture content in the air decreases the evaporation of perspiration or sweat.  Therefore, the body feels warmer when it’s humid, and this is why we use relative humidity. For example, in the heat index chart below, a hot and very humid air mass with a temperature of 94 degrees and a relative humidity of 45 percent yields an apparent temperature of 100 degrees . Holding the temperature constant and increasing the relative humidity to 60 percent yields an apparent temperature of 110 degrees.

Excessive Heat Products


The National Weather Service has 122 offices nationwide and its mission is to provide weather, water, and climate data, forecasts and warnings for the protection of life and property and enhancement of the national economy. The Weather Forecast Office in Mount Holly, NJ serves eastern Pennsylvania, New Jersey (excluding the five northeast counties), Delaware, and the eastern shore of Maryland. This area is the second most populous in the nation, encompassing the Interstate 95 corridor between New York City and Baltimore. The Mount Holly Office issues the following excessive heat products:

Hazardous Weather Outlook for Excessive Heat  – A period of excessive heat is possible within the next 3 to 5 days. A heat advisory or Excessive Heat Warning may eventually be needed. Stay informed and be prepared by following the preparedness information on this website in the event excessive heat occurs.

Heat Advisory – Take Action. A period of excessive heat is expected. The combination of hot temperatures and high humidity will create a situation in which heat related illnesses are possible. A Heat Advisory is issued when heat indices are expected to reach at least 100 degrees, except at least  105 degrees over Delmarva and far southern New Jersey (Salem, Cumberland, Cape May, and Atlantic Counties). The aforementioned heat index values must be reached for at least two hours; typically a single day event.

Excessive Heat Watch – Be Prepared. A prolonged period of dangerous excessive heat is possible within about 48 hours.                                         

Excessive Heat Warning – Take Action. A prolonged period of dangerous excessive heat is expected within about 24 hours. The combination of hot temperatures and high humidity will create a dangerous situation in which heat related illnesses are likely. An Excessive Heat Warning is issued when heat indices are expected to reach at least 105 degrees, except at least 110 degrees over Delmarva and far southern New Jersey (Salem, Cumberland, Cape May, and Atlantic Counties). The aforementioned heat index values must be reached for at least two hours per day; typically for a multi-day event.

Preparedness Information

The best advice is to drink plenty of fluids, stay out of the sun, and in an air-conditioned place. If you work or spend time outside, take extra precautions, such as frequent rest breaks in shaded or air conditioned locations.  Also wear clothing that is light weight and loose fitting.  If possible, reschedule strenuous activities for the early morning or evening, when cooler temperatures prevail. Car interiors can reach deadly temperatures in a matter of minutes during hot or warm weather.  Never leave young children and pets unattended in vehicles. Anyone overcome by heat should be moved to a cool and shaded location.  For more preparedness information, including the signs and symptoms of heat exhaustion and heat stroke, visit the NWS Heat Safety Website or click on the image below.

excessive heat events guidebook cover


Questions? Contact

   Winter Weather   

Winter Weather Products

Local Products

Winter Products from National Centers


Watch/Warning/Advisory Terminology & Criteria

  • Warnings:
    A warning is issued to alert the public to imminent dangerous winter weather. Normally a warning is issued after a winter storm watch has been in effect. A winter storm watch may not precede a warning if winter weather develops quickly and unexpectedly. A Winter Storm Warning is issued when heavy snow, significant freezing rain, or heavy sleet is expected to occur. Usually issued 6 to 18 hours in advance of the winter weather. A Blizzard Warning is issued when sustained or gusty winds of 35 mph or more are expected to reduce visibility at or below a quarter of a mile due to falling and/or blowing snow for at least three hours. Wind Chill Warnings are issued when wind chills are expected to be below -24 degrees fahrenheit.
  • Watches:
    A watch is issued to alert the public to the potential for dangerous winter weather. A Winter Storm Watch is issued when conditions exist for the possible occurrence of dangerous winter weather such as a blizzard, heavy snow, significant freezing rain or heavy sleet. Usually issued 12 to 36 hours in advance of the winter weather.
  • Advisories:
    A less severe winter weather event will prompt the issuance of an advisory. An advisory is named specific to the weather event expected and is issued when the event is expected to be widespread. Travel by foot or vehicle may be dangerous during an advisory even if the winter weather is not expected to reach winter storm criteria.
Criteria Maps of Winter Storm Watches, Warnings & Advisories for New Jersey, eastern Pennsylvania, Delaware, eastern Maryland
12-Hour Advisory Snowfall
12-Hour Warning Snowfall
24-Hour Warning Snowfall
Freezing Rain Advisory
Ice Storm Warning
Wind Chill Advisory
Wind Chill Warning

Gradient high wind outlooks, watches, warnings, and wind advisories shall be issued using the following wind speed values
Product Type Sustained Wind ( 1 Hr) Any duration gust
High Wind Outlook >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
High Wind Watch >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
High Wind Warning >= 40 MPH (35 KTS) >= 58 MPH (50 KTS)
Wind Advisory (land) 31-39 MPH (27-34 KTS) 46-57 MPH (40-49 KTS)
Wind Advisory for area lakes 25-30 MPH (22-26 KTS) 40-45 MPH (35-39 KTS)


Snowfall from Past Winters

Seasonal Snowfall Totals from 1979-Present (updated May 2017):


Preliminary Top Ten Philadelphia Snow Storms (updated May 2017):










January 7-8 1996





February 5-6 2010





December 19-20 2009




January 22-23 2016





February 11-12 1983





December 25-26 1909




April 3-4 1915





February 12-14 1899





February 15-18 2003





January 22-24 1935



Winter Weather Awareness and Safety


On September 1st, the Office of the Delaware State Climatologist will kickoff an effort to enlist community volunteers to measure and map rain and snow across the First State. The effort is part of a growing national network of home-based weather buffs known as the Community Collaborative Rain, Hail and Snow Network or CoCoRaHS. CoCoRaHS was launched in Colorado over 10 years ago, and since then many other states have joined, with over 12,000 volunteer observers nationwide. Delaware CoCoRAHS is looking for volunteers to take rain and snow measurements. To join, go to the following website and sign up:

CoCoRAHS observers take daily measurements of precipitation from a set location. These measurements are reported on the CoCoRaHS website by the observer. The data are then displayed and organized and may be accessed by any individual user or organization. All that is needed to participate is an official CoCoRAHS 4" rain gauge (which costs $23 + shipping and can be purchased through several vendors on the CoCoRAHS website), an internet connection, and a yardstick to measure snow depth. Training is provided for CoCoRaHS observers, either through online training modules on the CoCoRAHS website, or if needed, in group training sessions at several locations around the state.

We hope you´ll become a Delaware CoCoRAHS observer. If you have any questions or need additional information, please e-mail us at or call us at (302) 831-6906.

An Opportunity to Participate in a NJ Precipitation Observation Network
Dave Robinson and Mat Gerbush
NJ Community Collaborative Rain, Hail and Snow Network Coordinators
Rutgers University

A new precipitation observing network began in New Jersey on Groundhog Day, 2008. Coordinated by the Office of the NJ State Climatologist at Rutgers University's Agricultural Experiment Station, CoCoRaHS (Community Collaborative Rain, Hail, and Snow network) is a community-based precipitation observing network that has rapidly expanded throughout a number of states. You may sign up by going to

CoCoRaHS observers are trained to collect high-quality daily precipitation data. Observations are entered onto a web form via the CoCoRaHS website, archived, and displayed on the site for end users that include meteorologists, hydrologists, farmers, water resource managers, as well as you! The CoCoRaHS website also allows observers to report hail and intense precipitation events, observations that are immediately relayed to the National Weather Service for use in the issuance of warnings.

All that is needed to participate is an internet connection, a 4" diameter plastic precipitation gauge, and a ruler for measuring snow. Training is provided for CoCoRaHS observers, either through online training modules, or preferably, in group training sessions that will be held at several places around NJ over the coming several months.

Please consider becoming a NJ CoCoRaHS observer! You can contact us with any questions at


Certified/Official Data

Current Climate Products



Daily Information (F6)
Location Month Year

Monthly Climatic Summaries (CLM)
Location Month Year

Temperature Top of page

Historical Weather Information Top of page State Climatologists Top of page
Other Resources   Top of page


Air Quality

The National Oceanic and Atmospheric Administration (NOAA), in partnership with the Environmental Protection Agency (EPA), issues daily air quality forecast guidance as part of a national Air Quality Forecasting Capability. NOAA's National Weather Service (NWS) currently provides forecast guidance for ozone and smoke based on numerical atmospheric predictions updated twice daily. read more ...

Air Quality Forecast Guidance
Air Quality Alerts (AQA)
Air Quality Indexes (AQI)
About the Air Quality Index

The EPA developed the Air Quality Index (AQI) which reports levels of ozone, particle pollution, and other common air pollutants on the same scale. An AQI reading of 101 corresponds to a level that is above the national air quality standard - the higher the AQI rating, the greater the health impact. The AQI is divided into color-coded categories, and each category is identified by a simple informative descriptor. The descriptors are intended to convey to the public information about how air quality within each category relates to public health. 

The table below defines the AQI categories.

AQI AQI Category AQI Color Formulas
Numbers (Descriptor) Color (RGB) (CMYK)
0 - 50 Good Green 0,228,0 224,0,224,30
51 - 100 Moderate Yellow 255,255,0 0,0,255,0
101 - 150 Unhealthy for Sensitive Groups Orange 255,126,0 0,132,255,0
151 - 200 Unhealthy Red 255,0,0 0,255,255,0
201 - 300 Very Unhealthy Purple 153,0,76 0,153,80,102
301 - 500 Hazardous Maroon 76,0,38 0,76,38,179
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* Asterisk indicates that product may not be reliable over northeastern states

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 Rip Current Awareness Week June 7-13, 2015
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Marine Spot Forecast Request - Safety Agencies ONLY

Other Sources of Marine Weather and Forecasts


Northeastern Coast Water Temp     Southeastern Coast Water Temp       Gulf of Mexico Water Temp


Other Useful Marine Links



Submit Marine Wind & Wave Observation Report




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  Surf Zone Forecast  |  Risk Definitions  |  Rip Current Safety  |  Beach Hazards  |  Lightning Safety |  UV Index   

Experimental National Beach Forecast


Latest Rip Current Forecast

(The Surf/Rip Current forecast starts May 24, 2018 and ends September 30, 2018) There is currently an issue with the local graphic, please visit the experimental beach forecast here for the latest forecast.



Low Risk
A low risk of rip currents implies that wind and wave conditions are not expected to support the development of enhanced rip currents. However, Rip Currents are always possible, especially near jetties and other structures.
Moderate Risk
A moderate risk of rip currents implies that individuals planning to enter the surf should check with local beach patrols first. Be sure to swim within sight of a life guard, and never swim alone or at night.
High Risk
A high risk of rip currents means dangerous and potentially life threatening conditions exist for all people entering the surf. 

The Surf/Ripcurrent forecast starts the weekend before Memorial Day weekend and ends September 30 every year








Additional Beach Information from other resources

NJ DEP Cooperative Coastal Monitoring Program (Open/Closed beaches and conditions) 

- EPA Beach Advisories and Find information about your beach

- Delaware Outdoor Recreation

- Delaware River and Bay Authority

- NJ and DE Tide and Current Information

- National Buoy Data Center

Atlantic Coast Buoy and Light List for Navigation

- Maryland healthy beaches app


Observations and Current Conditions

Rainfall and River Reports


HADS (alternate site for Streamflow)

Rainfall Data

Snowfall Data


Precipitation Frequency Data Server

Water Temperature

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Meteorological Model Ensemble River Forecasts (MMEFS)


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Mount Holly Radar, click to enlarge
Latest Infrared Image from GOES8 - Click to enlarge
Weather Map
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Winter Weather

12 hr. Winter Wx (06-18 hr.) 12 hr. Winter Wx (18-30 hr.) Day 2 Winter Wx
12 hr. Winter Weather (6-18 hr.) Graphic 12 hr. Winter Weather (18-30 hr.) Graphic Day 2 Winter Weather Graphic






Advanced Hydrologic
Prediction Services (AHPS)

Advanced Hydrologic Prediction Services
Lehigh and Lower Delaware 

Lower Delaware River
Upper Delaware 

Upper Delaware River


Experimental 4-7 Day Weather Outloook

Severe Weather
  Current Warnings:
   –  Delaware
   –  Maryland
   –  New Jersey
   –  Pennsylvania

Storm Prediction Center Homepage

Tropical Cyclone Potential Impacts (TCI) Website

Watch/Warning/Adviosory Map
Convective Watches
Current Convective Watches Map
Mesoscale Discussions
Storm Prediction Center Mesoscale Discussion Graphic


Convective Outlooks

Day 1 Outlook
Day 1 Convective Outlook Map
Day 2 Outlook
Day 2 Convective Outlook Map
Day 3 Outlook(experimental)
Experimental Day 3 Convective Outlook Map


Extra-Tropical Storm Surge Guidance

North Atlantic Sector      Mid-Atlantic Sector        Delaware Bay              Chesapeake Bay             New York Harbor


Tropical Cyclone Impacts


Tide Predictions

Fire Weather
Additional Useful Information 


Updated December 24, 2015

DroughtMap_Aug 30_2017.PNG
Drought Watches, Warnings and Emergencies are issued by the appropriate State Government Agencies. The National Weather Service is responsible for dissemination of the information provided by the various State Agencies. Click on the State Links below if you have any questions or comments regarding any Drought Declarations.

Drought Information

  Precipitation Departure Maps

  Latest Drought Statement Issued by NWS Mt. Holly, NJ

  State Links
Regional / National Links
  Streamflow (USGS)
  Ground Water (USGS)

Water Sources

Water Sources - Precipitation, Reservoir, Stream, & Groundwater

Indoor Water Usage

Indoor Water Usage pie chart

Miscellaneous Links

  Middle Atlantic River Forecast Center (MARFC)
  Delaware River Basin Commission
  Susquehanna River Basin Commission


Click on an observation site to view current conditions

Click on an observation site to view current conditions

Surface Observations

Upper Air Observations

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