High pressure over the Desert Southwest allowed for temperatures to climb to dangerous levels on the 18th and 19th of August. Four heat-associated fatalities (three direct and one indirect) were reported by the Maricopa County Department of Public Health.
Every event with a place to put it; 4 filed by county or forecast zone are drawn at its center, in a lighter ring. Tap one for its entry below.
Deaths and injuries are direct and indirect together, as the offices filed them. Damage is property and crops in the dollars of the year, not adjusted for inflation, and only where an office estimated it.
The episode as NWS PSR wrote it up.
High pressure over the Desert Southwest allowed for temperatures to climb to dangerous levels on the 18th and 19th of August. Four heat-associated fatalities (three direct and one indirect) were reported by the Maricopa County Department of Public Health.
The local office's own words before the first event, as it sent them, from the Iowa Environmental Mesonet's archive of National Weather Service text.
NWS Phoenix, AZ wrote its last area forecast discussion before the first event at Aug 18, 8:45 AM MST, 1 hour 15 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 845 AM MST Sat Aug 18 2018 .SYNOPSIS... Very isolated thunderstorms will be possible today over the higher terrain north and east of Phoenix. High pressure centered over Arizona will keep most of the region dry for Sunday and Monday as temperatures over the lower deserts approach 110 degrees. Moisture returns to the region on Tuesday to increase thunderstorm chances and gradually decrease in temperatures back closer to normal for the second half of next week. && .DISCUSSION... Very quiet across the area this morning with skies mostly clear per latest IR satellite imagery. Just a few mainly high clouds floating around. 12z plot data indicated upper high situated near the Mexican border with a light westerly flow aloft in place over southern Arizona. This west flow confirmed by the morning Phoenix sounding. Still rather moist with PWAT near 1.8 inches in Phoenix and surface dewpoints over the deserts were running 65 to 70. Latest high res models suggest no convection in the area through the afternoon hours; steering flow will be very light and becoming mostly light north by this evening so an outside chance of an isolated storm drifting into higher terrain areas north and east of Phoenix after 5 pm but we don't expect storms moving into the lower deserts this evening. Current forecasts look to be in good shape and no updates are planned. .PREVIOUS DISCUSSION... Another quiet night has settled across the region as a ridge of high pressure over the Pacific coast merges with high pressure centered over Sonora. Temperatures are a few degrees warmer than last night in the upper 80s to lower 90s across the lower deserts under mostly clear skies, with high clouds streaming in from the south into far eastern Maricopa and Gila Counties. Significant drying continues to occur at midlevels and upper levels in response to west-northwest flow associated with the ridge. However, surface dew points in the mid to upper 60s with healthy boundary layer moisture continues to keep PWAT values around 1.5-1.7 inches across the lower deserts and 1.2-1.5 inches over the higher terrain. Moisture should continue to decrease today as the ridge consolidates over southeast California with 5-10 knot winds above 700 mb becoming more north-northwest this afternoon. Hi-res models develop isolated thunderstorms along the Mogollon Rim with the lingering moisture in place, but the lack of strong steering flow should keep these storms out of the lower deserts. The north-northwest steering flow should bring isolated showers and thunderstorms into Gila County later this afternoon and early evening, but the flood threat will be lower than it has been over the last several days. High temperatures today may approach 110 degrees closer to the center of the ridge in southeast California, with mid 100s over the lower deserts of Arizona. Temperatures will increase at least a few more degrees and PWAT levels will drop another 0.3-0.4 inches on Sunday and Monday as the ridge slowly pushes to the east in response to a trough moving into the Pacific Northwest. Although the H850 ridge will remain around 5940 dam, 850 mb temperatures should increase another 3 deg C today to around 30-31 deg C for the Phoenix metro. This will support high temperatures approaching 110 degrees for Phoenix and 111-113 over the lower deserts of southwest Arizona and southeast California for both days. Although these temperatures are just below excessive heat thresholds, people will need to exercise caution during outdoor activities considering these will be the hottest days we have seen in over ten days. These dry conditions combined with weak steering flow should keep the entire region dry for Sunday and most likely for Monday as well unless the center of the ridge is able to push far enough east to allow storms to develop over the higher terrain of Gila County. Models are still consistent in showing a surge of Gulf moisture Monday night into Tuesday as the ridge becomes centered over New Mexico. Although models appear to be backing off a bit on a weak shortwave rotating around the southern edge of the ridge, decent 10-15 knot southeast steering flow should support at least isolated thunderstorms. The GFS has merged a bit towards the ECMWF in keeping the ridge centered to our east which places the region in a persistent southeasterly flow aloft. This would support a gradual decrease in temperatures back closer to normal and at least isolated thunderstorms over the higher terrain and perhaps the lower deserts. At the current moment, it is difficult to pick out a specific day or two for the most elevated thunderstorm chances through the end of next week, but it does appear at least lower grade monsoon thunderstorm activity will return through the remainder of the work week besides possibly Tuesday. && .AVIATION... South-Central Arizona including KPHX, KIWA, and KSDL: Weak flow will allow for little downslope east winds this morning. Drier air should keep any isolated storms today over the high terrain north and east of Phoenix. The Phoenix metro, especially across north Phoenix, could see modest outflow winds from the north or northeast between 00-03Z, but at this point confidence is not high enough to include in TAFs. Southeast California/Southwest Arizona including KIPL and KBLH: Light winds with just few/sct mid and high clouds through Saturday. No significant impacts expected to area terminals. Aviation Discussion not updated for amended TAFs. && .FIRE WEATHER... Monday through Friday: An increase in available moisture during the first half of next week brings a chance of isolated thunderstorms back to the lower deserts in addition to increasing minimum relative humidity values back above 20 percent over the lower deserts. The best chances for storms across the entire region currently appears to be on Tuesday, but thunderstorms will be possible over higher terrain locations nearly each afternoon next week. Wind speeds will be typical for mid-summer with the usual afternoon breezes. Temperatures will remain slightly above normal through the extended period. && .SPOTTER INFORMATION STATEMENT... Spotters should follow standard reporting procedures. && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...CB PREVIOUS DISCUSSION...Hopper AVIATION...Kuhlman FIRE WEATHER...Wilson/Hernandez
The national radar mosaic for the moment the first event began.
4 heat. Local standard time, as filed.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
One indirect fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
One direct fatality was reported by the Maricopa County Department of Public Health, with their details, such as age, gender and circumstances unavailable.
As the offices recorded each death: direct deaths were caused by the weather itself, indirect ones by something it set in motion.
| Event | Date | Age | Sex | Where | Kind |
|---|---|---|---|---|---|
| Heat, Cave Creek/New River | 2018-08-18 | Unknown | Direct | ||
| Heat, Central Phoenix | 2018-08-19 | Unknown | Direct | ||
| Heat, Buckeye/Avondale | 2018-08-19 | Unknown | Indirect | ||
| Heat, Northwest Valley | 2018-08-19 | Unknown | Direct |
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2018Every state in 2018This day in weather historyWarnings in Arizona, August 2018
NOAA National Centers for Environmental Information, Storm Events Database, compiled from the National Weather Service’s monthly Storm Data. Complete through 2026-06; NCEI adds each month about 75 days after it ends and revises past years a few times a year. Rebuilt 2026-09-24. Each event’s entry at NCEI: 867269, 867271, 867272, 867273.