The area of high pressure which brought some short-lived relief to hot conditions just a few days ago is now going to become our foe. It will turn into a Bermuda High, pumping in a southwesterly flow of hot and humid air. Sunday, temperatures will rise into the lower nineties with increasing moisture. Heat index values will be in the mid-nineties.
On Monday, widespread mid-nineties are expected. A weak cold front will begin to sag southward into our region. This front should prompt the development of cumulus clouds and scattered thunderstorms later in the afternoon. Plenty of instability will build up and therefore any thunderstorm that can develop has the potential to become severe. The 12z NAM has most of the action (quite intense) coming through after 6 p.m. and lingering with us right through midday Tuesday) with the southern counties spared the worst of the convective line. The Storm Prediction Center has placed much of the region (except the south) under a slight risk designation for severe thunderstorms on Monday in the Day 3 convective outlook. The GFS and EURO vary a bit on the timing of the convection….but the bottom line is a period of potentially active thunderstorms from Monday Afternoon into Tuesday Morning.
The picture for Tuesday is becoming clearer, but with some details still missing. It appears thunderstorms will be ongoing early in the period…perhaps lingering into midday at worst with extensive cloudiness when most wake up. Clearing may not happen until early afternoon in portions of the area. If the NAM is correct, the thunderstorms and convective debris cloud could be with us for so long that temperatures rise only into the upper eighties once the sun reappears…potentially temporarily busting the heat wave. For now, I will go with 90 degrees. Some areas could be dealing with flash flooding if 1 to 2 inches of rain occurs in a short period of time and the NAM is correct about the slow nature of the convective line. During the afternoon, the front will settle into the area and stall out. Depending on how fast we can recover from the morning convection…some additional pop-up thunderstorms may develop along and south of the boundary.
The front will still be in our vicinity on Wednesday, before moving back northward as a warm front on Wednesday Night into Thursday Morning. Temperatures and the dew points during this period will be very dependent on where this boundary settles. The boundary could also act as a trigger for a few isolated thunderstorms which could impact the amount of heating which takes place. At this point, lower nineties still appear attainable across much of the area on Wednesday. If portions of the area end up on the northern side of the front, the humidity levels could be somewhat in check.
By Thursday Afternoon, we will be within the warm sector with a building heat ridge from the Midwest. There are a few issues though that may impact how high we go in the temperature department...keeping the brutal heat potentially at bay. First, will be the amount of rain that could fall on Tuesday. This could soak portions of the region. Wet grounds usually shave off a few degrees in the temperature department. Second, the GFS shows some troughs impacting the area…especially on Friday Morning. If convection is ongoing or develops on Friday…even a few hours of clouds will be enough to prevent a run at 100 degrees. The ridging looks strong though and may eventually end up keeping much of the area out of the “Ring of Fire”.
I have been biting my nails (expression) on inserting a “100” in the graphic this early out…especially with the GFS showing some convective chances. As we often say here on the site, whether it is 98 vs. 100 degrees makes no true difference to the danger that will develop with the excessive heat expected. My choice to go with 100 degrees is that I expect that at least some location in the area that avoids any thunderstorms will make a run for it and strike a home run. We already had some 100-103 degree highs earlier this year in our area (Philadelphia fell short)…and truth be told…on paper Friday looks hotter than the day we had those highs in the 100’s recorded. If the model data is correct about Dew Points in the lower and mid-seventies from Thursday into Saturday…heat index values will range between 105 and 110 degrees. Last year when we did hit 100 and even earlier this year, it was a dry heat. See this is another potential fly in the ointment…studies suggest that we struggle to hit the Century Mark when the air is loaded with moisture.
The all-time high temperature for Philadelphia is 106 degrees.
Already this year, we have seen a few heat related deaths…especially in the urbanized areas where there is low income residences who cannot afford proper cooling devices or who have them…but cannot afford to keep them on. It is in these areas where crime is also high and many then also fail to open their windows to get at least some circulation flowing through the hot infrastructure. The other area we commonly find issues is when careless individuals leave young children inside a closed vehicle. So be careful and here are a few pieces of advice that we pull out from time to time.
Heat exhaustion may develop when fluids and salt that are lost through sweating are not replaced. Primary symptoms include extreme weakness, fatigue, giddiness, nausea or a headache; other symptoms may include clammy or moist skin, a pale or flushed complexion and a slightly higher-than-normal body temperature. Someone experiencing heat exhaustion should rest in a cooler place, with the feet raised and tight clothing loosened, and slowly drink salted liquids. Heat exhaustion may rapidly turn into heat stroke, a potentially fatal condition. If symptoms persist or worsen, seek immediate medical attention. Heat stroke is a serious and potentially fatal condition that requires immediate medical attention. Heat stroke occurs when the body's heat-regulating system breaks down, sweating stops, and body temperature rises significantly.
Signs of heat stroke include:
Mental confusion, delirium, chills, dizziness, loss of consciousness, convulsions or coma , a body temperature of 105 degrees F or higher, Hot, dry skin that may be red, mottled or bluish , and a strong, fast pulse. If you suspect someone is suffering from heat stroke, call an ambulance immediately. Until medical help arrives, move the victim from the heat and into a cool place, soak the victim's clothes with water and use a fan or ice packs.
Close all drapes/blinds on the sunny side of the house.
Remember to drink plenty of fluids, espeically water.
If a family member appears overheated, use cool compresses to cool skin.
Remember to check on elderly or home-bound neighbors.
Spend as much time as you can in cool surroundings. Use fans and air conditioners. During the warmer, daytime hours go to air-conditioned malls, libraries, movie theaters or any public place that is air conditioned if you don't have A/C.
Slow down and take it easy. AVOID Physical activity.
Wear light-weight, light-colored, loose-fitting clothing made of a breathable fabric, such as cotton.
Wear a hat or use an umbrella.
Another reminder is that unusual heat like this can lead to blackouts. Some long lasting outages can cause heat to build up in homes that normally have A/C units.
Transformers can easily fail from overheating. Transformers are built to dissipate their heat, but in extreme weather conditions such as we’re experiencing, there is no ability to cool because temperatures remain high throughout the night (we are forecasting 80 degree lows around 3 a.m. with 82-88 most of the night at the end of the week). Problems are also magnified in the confined spaces of an underground electrical system (which we have in Atlantic City-Trenton-Allentown-Camden-& Philadelphia). If there is a flaw or crack in the cable insulation, a short circuit could occur as the cables expand from the heat. Increased demand for air conditioning means more electricity flowing through power lines. This causes them to heat up and expand or sag, and in some cases they sag into tree branches, causing a short circuit. Electricity loads combined with high temperatures cause transformers to heat up, sometimes reaching critical levels that if uncorrected would permanently damage the equipment. The equipment will automatically and safely shut down to protect itself and other equipment. High current causes stretching of cables, switches and other equipment and can increase the size of minor flaws in insulation or connections. Electric equipment can be weakened by lightning strikes and circuit failures, making it more susceptible to an outage as it can no longer withstand the increased flow of electricity during periods of high demand.
We will be watching a disturbance along the Southeastern United States coast for tropical development. There is a 20% chance of development in the next 48 hours...but a potentially higher chance beyond that time. What impact, if any, this will have remains to be seen...could cause more humidity and perhaps an uptick in pop-up cells sometimes.
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