A strong thunderstorm complex known as a Mesoscale Convective System developed across southern Arizona and migrated westward into southern California during the evening and overnight hours on the 30th-31st. The mesoscale convective system developed in an environment characterized by MLCAPE of 1000-1500 J/KG as well as around 30 knots of deep-layer shear from an inverted mid-level trough that was…
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The episode as NWS PSR wrote it up.
A strong thunderstorm complex known as a Mesoscale Convective System developed across southern Arizona and migrated westward into southern California during the evening and overnight hours on the 30th-31st. The mesoscale convective system developed in an environment characterized by MLCAPE of 1000-1500 J/KG as well as around 30 knots of deep-layer shear from an inverted mid-level trough that was situated over northern Sonora in Mexico. Isolated damaging winds were reported in the Yuma area as well as a lightning induced fire in a tree farm located southwest of the City of Maricopa.
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 Jul 30, 4:53 PM MST, 3 hours 37 minutes earlier.
Area Forecast Discussion National Weather Service Phoenix AZ 453 PM MST Sun Jul 30 2023 .Update...Updated 00Z Aviation Discussion .SYNOPSIS... As high pressure shifts to the east away from the region today, an area of low pressure will approach from Mexico. This will result in temperatures retreating somewhat closer to normal as moisture levels increase. Today will bring an increase in shower and thunderstorm chances to much of the area, particularly across southwest Arizona. The unsettled weather pattern will continue into Monday with eastern and central Arizona likely seeing the best chances for showers and thunderstorms. While strong gusty winds and dense blowing dust will be the primary weather hazards, some locations could experience heavy rainfall. This wetter pattern will be short lived as abnormally hot and dry weather is expected to return during the latter half of the week. && .DISCUSSION... Today/Tonight... Latest water vapor imagery and streamline analysis reveal a well- defined inverted trough across northern Mexico. Ahead of this system, conditions are considerably cooler and more moist across the Desert Southwest than they were 24 hours ago. Earlier this afternoon, surface dewpoints reached the lower 60s across central Arizona and as high as the lower 70s across the Imperial Valley of southeastern California. Temperatures across the lower deserts have also struggled to rise through the lower 100s. Clouds have been slow to clear across the Phoenix metro area, likely in response to weak ascent associated with an MCV in the vicinity of Coconino County. The steering flow is also stronger than normal between the stubborn Monsoon High across northern New Mexico and the approaching trough, with 20 kt noted in the KPHX ACARS soundings. This is yielding 0-6 km shear of 30 kt across Pinal/Pima Counties. Mesoanalysis indicates some drier air has worked its way into eastern Arizona. Nevertheless, isolated convection has already initiated across the White Mountains. Latest HREF depicts a strong signal for an MCS developing tonight near the Maricopa/Pinal/Pima triple point, before spreading westward into southwestern Arizona and ultimately southeastern California after midnight. Conceptually, this seems reasonable given the presence of deeper moisture and stronger deep layer shear closer to the inverted trough. Any cells within this complex will be capable of producing strong to severe wind gusts, blowing dust, and localized heavy rain. Across central Arizona, variability in the CAMs suggests the forecast is more uncertain. Latest ACARS soundings still show abundant CIN associated with some drying near 700 mb. Rainfall in the Valley largely hinges on the development of activity further upstream across the Mazatzal and Superstition Mountains. There is some potential for at least isolated activity, per the latest runs of the HRRR and U of A WRF-GFS. However, latest trends in these CAMs are not nearly as bullish in these areas and more closely resemble this morning’s NSSL WRF. One other low-probability scenario is the organized complex of storms across Pima County produces an outflow boundary that triggers additional development further north across the Valley later this evening. && .PREVIOUS DISCUSSION... For Monday, the inverted trough is forecast to track north northwestward through the western half of the region, while moisture levels continue to improve. Depending on the extent of the convection later today and tonight, Monday may actually be the better day for showers and storms across eastern and south-central Arizona. The latest hi-res guidance shows higher instability on Monday vs today with forecast CAPEs in a 1000-1500 J/kg range across south-central Arizona to 500-750 J/kg over the eastern Arizona high terrain. The better quality moisture and higher instability could result in more widespread storm coverage during the afternoon across southeast Arizona northward through the Mogollon Rim as long as there isn't too much leftover morning debris cloud to inhibit insolation. This scenario could then present an optimal pac-man collision of outflows over the Phoenix area with outflows coming from the Tucson area and from the high terrain east of Phoenix. Shear will be lower on Monday, but with the higher CAPE and the possibility of significant outflows colliding over the south-central Arizona lower deserts, right now it seems Monday evening may be the best chance for decent rain over the Phoenix metro. Looking farther west over southwest Arizona and southeast California on Monday, it very well could be a fairly quiet day as it seems likely the atmosphere will be convectively overturned from this evening/early overnight convection. By Tuesday, the inverted trough is forecast to have ejected well to our north with southwesterly flow overtaking the region. This will result in a gradual drying and likely less shower and thunderstorm chances on Tuesday with the best focus of convection likely over the eastern Arizona high terrain. Temperatures should also be the coolest we have seen since late June with forecast highs on Monday and Tuesday right around normal readings. The rest of the coming week will see a resurgence of the sub-tropical high first across northern Mexico and then into the Desert Southwest late in the week into next weekend. The positioning of the high to our south is expected to continue to bring a drying flow during the latter half of the week with any residual boundary layer moisture likely getting scoured out. This should nearly completely end any storm chances, even over the high terrain, starting Thursday. As the sub-tropical high takes over across the region again later this week and we dry out, temperatures will also start climbing to above normal readings. The latest NBM forecast highs show readings back to around 110 degrees across the lower deserts during the latter half of the week and possibly back to around 115 degrees for some areas by next weekend. && .AVIATION...Updated at 2350Z. South-Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main concerns over the next few hours will be line of showers and thunderstorms approaching from the east. The arrival time is expected by 02Z-03Z at the metro terminals. The best chances for storms will be between 03Z-05Z as well as gusty northeasterly winds up to 30-35 kts. Storm chances will wane by 06Z tonight. Winds are expected to return back to west as activity moves out of the region with a late easterly shift expected early tomorrow morning. Southeast California/Southwest Arizona including KIPL and KBLH: A complex of thunderstorms is expected to develop across SW AZ and move west into SE CA late tonight. This activity looks to reach the TAF sites generally after the 07-08z timeframe where VCTS is expected with gusty outflows up to 35kts. There is a risk that visibilities could come down both in blowing dust and heavy rainfall, something that will be monitored for future updates. Otherwise, a general SSE wind and SCT/BKN mid to high clouds. && .FIRE WEATHER... An unsettled weather pattern will be seen over the area through Monday with much better shower and thunderstorm chances areawide. Storms today are more likely to be seen across western Maricopa Co. westward through the Colorado River Valley. For Monday, the likely best area for storm activity will be across the eastern and south-central Arizona. Gusty erratic outflow winds are the greatest concern with these storms, though some beneficial wetting rainfall is likely for some areas. Minimum afternoon humidity levels will fall into a 15-25% range today and 20-30% on Monday, while temperatures fall back closer to normal readings by Monday. Starting Tuesday, a drying flow will overtake the region bringing decreasing shower and storm chances. For the latter half of the week, storm chances will completely come to an end, while temperatures once again warm to above normal readings. Minimum humidities later this week will also dip back into a 10-20% range by Wednesday and possibly even into the single digits by Friday. && .CLIMATE... Active Streaks: PHOENIX 1. Consecutive days of high temperatures 110F or greater: longest on record at 30 days (previous record: 18 days in June 1974) 2. Consecutive days of no measurable precipitation: 4th longest on record at 129 days YUMA 1. Consecutive days of low temperatures 85F or greater: 2nd longest on record at 19 days && .PSR WATCHES/WARNINGS/ADVISORIES... AZ...None. CA...None. && DISCUSSION...Hirsch PREVIOUS DISCUSSION...Kuhlman AVIATION...Salerno FIRE WEATHER...Kuhlman
Special Weather Statement
National Weather Service Phoenix AZ
351 PM MST Sun Jul 30 2023
AZZ547-556-558-563-302315-
Southeast Gila County AZ-Tonto Basin AZ-Rio Verde/Salt River AZ-
Pinal/Superstition Mountains AZ-
351 PM MST Sun Jul 30 2023
...A strong thunderstorm will impact portions of Gila and Maricopa
Counties through 415 PM MST...
At 351 PM MST, Doppler radar was tracking a strong thunderstorm 10
miles northeast of Roosevelt, moving west at 10 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Roosevelt, Roosevelt Dam, Tonto National Monument, Tonto Basin, and
Roosevelt Estates.
This includes AZ Route 188 between mile markers 235 and 257.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Frequent cloud to ground lightning is occurring with this storm.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
If on or near Roosevelt Lake, get out of the water and move indoors
or inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.
&&
LAT...LON 3379 11113 3376 11099 3365 11092 3355 11116
3380 11131 3385 11120
TIME...MOT...LOC 2251Z 088DEG 9KT 3374 11096
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSSpecial Weather Statement
National Weather Service Phoenix AZ
436 PM MST Sun Jul 30 2023
AZZ547-549-552-555>558-310015-
Fountain Hills/East Mesa AZ-Mazatzal Mountains AZ-Tonto Basin AZ-
Apache Junction/Gold Canyon AZ-Superior AZ-Rio Verde/Salt River AZ-
Pinal/Superstition Mountains AZ-
436 PM MST Sun Jul 30 2023
...Strong thunderstorms will impact portions of Gila, Maricopa and
Pinal Counties through 515 PM MST...
At 435 PM MST, Doppler radar was tracking strong thunderstorms along
a line extending from 6 miles southeast of Tonto Basin to near
Superior. Movement was west at 15 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Apache Junction, Superior, Gold Canyon, Sugarloaf Mountain,
Ballantine Trailhead, Roosevelt, Round Valley, Sunflower, Gold Camp,
Roosevelt Dam, Lost Dutchman State Park, Goldfield, Top-Of-The-World,
Florence Junction, Queen Valley, Canyon Lake, Superstition Mountains,
Tonto National Monument, Four Peaks, and Apache Lake.
This includes the following highways...
US Highway 60 between mile markers 199 and 241.
AZ Route 87 between mile markers 197 and 218.
AZ Route 79 between mile markers 146 and 150.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
Frequent cloud to ground lightning is occurring with these storms.
Lightning can strike 10 miles away from a thunderstorm. Seek a safe
shelter inside a building or vehicle.
These storms may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
If on or near Roosevelt Lake, get out of the water and move indoors
or inside a vehicle. Remember, lightning can strike out to 10 miles
from the parent thunderstorm. If you can hear thunder, you are close
enough to be struck by lightning. Move to safe shelter now! Do not
be caught on the water in a thunderstorm.
&&
LAT...LON 3384 11119 3380 11115 3376 11100 3329 11089
3317 11141 3353 11158 3389 11163
TIME...MOT...LOC 2335Z 092DEG 15KT 3377 11121 3333 11108
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSSpecial Weather Statement
National Weather Service Phoenix AZ
650 PM MST Sun Jul 30 2023
AZZ552-553-555-558-310215-
Northwest Pinal County AZ-Apache Junction/Gold Canyon AZ-Superior AZ-
Pinal/Superstition Mountains AZ-
650 PM MST Sun Jul 30 2023
...A strong thunderstorm will impact portions of Gila and Pinal
Counties through 715 PM MST...
At 650 PM MST, Doppler radar was tracking a strong thunderstorm over
Boyce Thompson Arboretum, or near Superior, moving west at 10 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Superior, Florence Junction, Queen Valley, Boyce Thompson Arboretum,
Top-Of-The-World, and Gold Camp.
This includes the following highways...
US Highway 60 between mile markers 206 and 234.
AZ Route 79 between mile markers 139 and 150.
AZ Route 177 between mile markers 159 and 167.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 3316 11106 3306 11121 3310 11141 3318 11148
3346 11136 3333 11097
TIME...MOT...LOC 0150Z 106DEG 9KT 3325 11115
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSSpecial Weather Statement
National Weather Service Phoenix AZ
758 PM MST Sun Jul 30 2023
AZZ554-559-310345-
Sonoran Desert Natl Monument AZ-West Pinal County AZ-
758 PM MST Sun Jul 30 2023
...A strong thunderstorm will impact portions of Maricopa and Pinal
Counties through 845 PM MST...
At 757 PM MST, Doppler radar was tracking a strong thunderstorm near
Kaka, or 36 miles east of Ajo, moving west at 10 mph.
HAZARD...Wind gusts up to 50 mph.
SOURCE...Radar indicated.
IMPACT...Gusty winds could knock down tree limbs and blow around
unsecured objects.
Locations impacted include...
Kaka.
PRECAUTIONARY/PREPAREDNESS ACTIONS...
If outdoors, consider seeking shelter inside a building.
This storm may intensify, so be certain to monitor local radio
stations and available television stations for additional information
and possible warnings from the National Weather Service.
&&
LAT...LON 3276 11247 3276 11205 3273 11205 3272 11207
3272 11214 3268 11215 3268 11220 3250 11221
3251 11252 3252 11252
TIME...MOT...LOC 0257Z 091DEG 7KT 3252 11226
MAX HAIL SIZE...0.00 IN
MAX WIND GUST...50 MPH
INSThe Phoenix radar (KIWA), 53 km away, was scanning. The volume nearest the first event began at 03:28 UTC.
1 lightning, 1 thunderstorm wind. Local standard time, as filed.
A lightning strike sparked a fire in a tree farm located in the area of Ralston and Peters & Nall Roads southwest of Maricopa. The fire burned for nearly 24 hours after the lightning strike. No property damage nor injuries were reported with this fire.
A large uprooted tree caused a shed to bank upward at Cindy Rose Alterations in the Yuma Foothills. Wind gusts were estimated at between 50-55 mph based on nearby observations. Timing based on radar. No injuries were reported.
After NWS Directive 10-1605, the rules offices file Storm Data by.
Every storm in Arizona in 2023Every state in 2023This day in weather historyWarnings in Arizona, July 2023
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: 1121446, 1121447.