The National Weather Service has placed the Inland Empire under an Extreme Heat Warning for four consecutive days, forecasting temperatures reaching 110 degrees and warning that heat-related illness rises sharply during events of this length.
The warning covers the San Bernardino and Riverside County valleys and runs from 10 a.m. Thursday through 8 p.m. Sunday. The forecast office describes the conditions as "dangerously hot" and advises residents to stay in air-conditioned spaces, drink fluids, avoid sun exposure, and check on relatives and neighbors.
Two groups carry most of the risk in an event like this, and the second is why this warning deserves more than a weather headline. Older adults living alone regulate heat less efficiently and are less likely to call for help. Outdoor workers cannot leave the heat. And within both groups, a large share are taking daily prescriptions that quietly change how their bodies handle a 110-degree afternoon.
What the Alerts Say and Where They Apply
The Extreme Heat Warning is the more serious of two alerts issued together. It applies to the valley floor across both counties, the corridor that includes Riverside, San Bernardino, Ontario, Corona, Moreno Valley, Fontana, and Rancho Cucamonga.
A separate Heat Advisory covers the San Bernardino County Mountains, where the forecast calls for highs in the 90s to around 100 below 7,000 feet over the same window. Mountain communities are not exempt from this event, and residents who head uphill expecting relief may find less of it than usual.
The duration matters more than the peak number. A single hot afternoon allows the body to recover overnight. A four-day stretch, particularly when overnight lows stay elevated, removes that recovery window and is the pattern most associated with heat deaths in Southern California.
The Medication Question Most Heat Coverage Skips
Standard heat advice tells people to hydrate and stay cool. It rarely mentions that a routine prescription can undercut both.
The Centers for Disease Control and Prevention's clinical guidance on heat identifies several ways medications raise heat risk. Diuretics, ACE inhibitors, and angiotensin receptor blockers can blunt the sensation of thirst, so a person feels fine while becoming dehydrated. Antipsychotics, anticholinergics, and stimulants can interfere with the brain's temperature regulation. Anticholinergics, tricyclic antidepressants, and antipsychotics can reduce sweating, which is the body's primary cooling mechanism.
Beta blockers and aspirin can limit the blood vessel dilation that moves heat to the skin. Diuretics, beta blockers, and tricyclics can cause volume depletion and low blood pressure, raising the risk of fainting and falls in the heat. The agency flags one combination in particular: an ACE inhibitor or ARB taken alongside a diuretic, a pairing common in heart failure and hypertension care, may significantly increase risk.
The list extends to children and adolescents. CDC names non-selective antihistamines such as diphenhydramine, stimulants prescribed for ADHD including methylphenidate, SSRIs, tricyclics, and diuretics as medications to be aware of during hot weather.
None of this is a reason to skip a dose. CDC's clinical materials are explicit that patients should not abruptly stop medications and should take them as directed unless a clinician says otherwise. Stopping a blood pressure medication during a heat wave creates a certain problem to avoid a possible one.
The useful step is a conversation, and it does not require an appointment. A pharmacist can review a medication list against heat risk in a few minutes, at no cost, and can flag whether anything warrants a call to the prescriber. That conversation is worth having before Thursday rather than during the weekend.
Storage is the other overlooked piece. Inhalers, EpiPens, and insulin degrade in high heat. None should be left in a car, and mail-order deliveries should be brought inside promptly rather than sitting on a porch through the afternoon.
What California Law Requires for Outdoor Workers
The Inland Empire's warehouse, logistics, construction, landscaping, and agricultural workforce will be working through all four days, and California's rules for those shifts are more specific than most workers realize.
Under Cal/OSHA's heat illness prevention standard, employers with outdoor workplaces must provide fresh drinking water, access to shade, and cool-down rest breaks whenever a worker requests one, in addition to regular breaks. The state's guidance specifies enough water for each worker to drink about a quart per hour.
Cal/OSHA has stated that the law requires employers to provide outdoor workers "access to shade (which must be in place when temperatures exceed 80 degrees)," a threshold that will be cleared before mid-morning every day of this event. Shade must genuinely block direct sunlight and allow the body to cool. A metal shed or a vehicle interior does not qualify.
When temperatures reach or exceed 95 degrees, additional high-heat procedures apply in agriculture, construction, landscaping, oil and gas extraction, and the transportation of agricultural products, construction materials, or other heavy materials. Those procedures include regular observation of employees for signs of heat illness, effective communication so workers can reach a supervisor, pre-shift meetings, and reminders to drink water throughout the shift. In agriculture at 95 degrees and above, workers are entitled to a minimum ten-minute cool-down period every two hours.
Employers in both indoor and outdoor settings must maintain a written heat illness prevention plan with training. Workers who believe those protections are not being provided can file a complaint with Cal/OSHA.
Who Is Most at Risk and What Symptoms Signal Trouble
Risk in this event is concentrated, not universal. Adults 65 and older, particularly those living alone or without working air conditioning, face the highest mortality risk. Infants and young children cannot regulate temperature or communicate distress. People experiencing homelessness have no reliable cooling. Outdoor workers accumulate exposure across a full shift. People with heart disease, kidney disease, diabetes, obesity, or a psychiatric condition, and those on the medications above, sit at elevated risk regardless of age.
Heat exhaustion typically presents as heavy sweating, cool and clammy skin, weakness, dizziness, nausea, headache, muscle cramps, and a fast but weak pulse. Moving to a cool place, loosening clothing, sipping water, and applying cool cloths usually resolves it. Symptoms that worsen or persist beyond an hour warrant medical guidance.
Heat stroke is different and is an emergency. The signs are a body temperature above 103 degrees, skin that is hot and either dry or damp, a rapid and strong pulse, confusion, slurred speech, and loss of consciousness. Sweating may stop entirely. This requires a 911 call and active cooling while help arrives, not a wait-and-see approach.
What Happens Next
The warning is scheduled to expire Sunday at 8 p.m., but NWS San Diego updates alerts as forecasts shift and has already revised these products once since issuance. Residents should check the current alert rather than assume the end time holds.
Cooling centers in both counties typically expand hours during declared heat events, and county public health and emergency management pages list current locations and transportation options. Utilities in the region operate emergency assistance programs for households at risk of shutoff during heat events, which is worth checking before a bill becomes a crisis.
The confirmed facts are that a four-day Extreme Heat Warning covers the Inland Empire valleys with temperatures forecast to reach 110, and a Heat Advisory covers the San Bernardino County Mountains. The people most affected are older adults without reliable cooling, outdoor workers, and anyone taking medications that impair thirst, sweating, or blood pressure regulation. The most reasonable action is a pharmacist medication review before Thursday and a plan to check on someone who lives alone. The central uncertainty is how long the pattern holds past the weekend.
Frequently Asked Questions
Where and when does the warning apply? The Extreme Heat Warning covers the San Bernardino and Riverside County valleys from 10 a.m. Thursday through 8 p.m. Sunday. A separate Heat Advisory covers the San Bernardino County Mountains over the same period.
Which medications raise heat risk? CDC identifies diuretics, anticholinergics, and psychotropic medications among those that increase risk, and flags the combination of an ACE inhibitor or ARB with a diuretic as carrying added risk. Beta blockers, antihistamines, and ADHD stimulants also appear on the agency's list.
Should I stop my medication during the heat wave? No. CDC guidance is explicit that patients should not abruptly stop medications. Ask a pharmacist or prescriber whether anything needs adjusting.
What are my employer's obligations if I work outdoors? Cal/OSHA requires fresh water, access to shade once temperatures exceed 80 degrees, and cool-down rest breaks on request. At 95 degrees and above, additional procedures apply in agriculture, construction, landscaping, oil and gas extraction, and heavy-materials transportation.
How do I tell heat exhaustion from heat stroke? Heat exhaustion involves heavy sweating, clammy skin, dizziness, and nausea, and usually improves with cooling and fluids. Heat stroke involves a temperature above 103 degrees, hot skin, confusion, and possible loss of consciousness. Heat stroke is a 911 emergency.
Where can I find a cooling center? County public health and emergency management pages list current locations and hours, which typically expand during declared heat events.
Does the mountain advisory mean it is safe to go up there? Not necessarily. The advisory forecasts highs in the 90s to around 100 below 7,000 feet, and officials note that hot temperatures at that level can still cause heat illness.
