A strong and cold upper level low pressure system was in place over the desert southwest on October 20th. The low was associated with elevated levels of moisture, instability and wind shear and as a result, scattered thunderstorms developed across south central Arizona, starting in the early morning hours and continuing throughout the day. Due in part to cold temperatures in the upper atmosphere, some of the stronger thunderstorms produced large hail with diameters greater than one inch. Funnel clouds were observed in the greater Phoenix area. Some storms also produced locally heavy rainfall which led to episodes of urban flooding as well as flash flooding. At 0800MST flash flooding occurred in far north Phoenix, in the town of Anthem, and resulted in a water rescue in Skunk Creek.

Hail in MARICOPA, ARIZONA
From 20-OCT-15 12:08:00 to 20-OCT-15 12:32:00 (MST-7)
Location: SUNNYSLOPE
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Scattered thunderstorms moved across the greater Phoenix metropolitan area, including the community of Glendale, during the late morning hours on October 20th. Due in part to cold temperatures aloft, the stronger storms were able to generate large hail. At 1132MST a trained spotter just west of the Metro Center Mall estimated hailstones up to one inch in diameter at the intersection of 35th Avenue and Peoria Avenue. About 15 minutes earlier, another spotter 3 miles northeast of the Glendale Sports Complex estimated hailstones with diameters up to nearly 0.90 inches. Finally, at 1208MST another trained spotter estimated one inch diameter hail at the intersection of 75th Avenue and Bethany Home Road in Glendale. None of the spotters reported any damage due to the large hail.

Funnel Cloud in MARICOPA, ARIZONA
From 20-OCT-15 10:58:00 to 20-OCT-15 11:00:00 (MST-7)
Location: PHOENIX TURF ARPT
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Scattered thunderstorms developed across south central Arizona, including the greater Phoenix area, during the morning hours on October 20th. Due in part to elevated levels of wind shear and cold temperatures aloft, some of the thunderstorms actually produced funnel clouds. According to a report from the public, a cold air funnel cloud was seen near the intersection of Interstate 17 and Greenway Road. The funnel cloud was not long lasting and never reached the ground.

Funnel Cloud in MARICOPA, ARIZONA
From 20-OCT-15 09:30:00 to 20-OCT-15 09:35:00 (MST-7)
Location: MORRISTOWN
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Public

Scattered thunderstorms developed across the greater Phoenix metropolitan area during the morning hours on October 20th. Due in part to the presence of a cold upper level low pressure system with elevated upper level winds, isolated stronger storms produced funnel clouds. One such funnel was reported near the town of Morristown. According to a public report, a cold air funnel was spotted near the intersection of Highway 60 and Highway 74, about 1 mile northwest of Morristown. The funnel cloud did not last for long and never touched the ground.

Hail in MARICOPA, ARIZONA
From 20-OCT-15 11:15:00 to 20-OCT-15 11:15:00 (MST-7)
Location: NEW RIVER
Magnitude: 1.00 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms developed across the far northern fringes of the greater Phoenix metropolitan area during the morning hours on October 20th, and due to the cold nature of the air mass, isolated stronger storms generated large hail. Some of the largest hailstones fell near the community of Anthem. One trained weather spotter 4 miles southeast of Anthem estimated hailstones as large as one inch in diameter. At the same time, a second spotter 2 miles east of Anthem estimated hailstones that were three quarters of an inch in diameter. Neither spotter reported damage associated with the large hail.

Hail in MARICOPA, ARIZONA
From 20-OCT-15 12:05:00 to 20-OCT-15 12:10:00 (MST-7)
Location: PHOENIX
Magnitude: 0.75 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms moved across the greater Phoenix area during the late morning and early afternoon hours on October 20th and some of them affected downtown Phoenix. Due in part to cold temperatures aloft, the stronger thunderstorms produced large hail. According to a trained weather spotter, at about noon large hail fell about 3 miles northwest of the Arizona State Fairgrounds in downtown Phoenix. The largest hailstone diameters were estimated to be three quarters of an inch. No damage was reported due to the large hail.

Hail in MARICOPA, ARIZONA
From 20-OCT-15 10:35:00 to 20-OCT-15 10:40:00 (MST-7)
Location: PHOENIX DEER VLY ARP
Magnitude: 0.88 
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Scattered thunderstorms moved across the northern portions of the greater Phoenix metropolitan area during the afternoon hours on October 20th, and due to cold temperatures aloft some of the stronger storms produced moderate to large hail. According to a trained spotter 6 miles northeast of the town of Peoria, large hail fell just north of Happy Valley Road, near 43rd Avenue. The largest hailstones measured nearly one inch in diameter. No damaged was reported due to the large hail however.

Heavy Rain in MARICOPA, ARIZONA
From 20-OCT-15 10:00:00 to 20-OCT-15 11:45:00 (MST-7)
Location: PHOENIX DEER VLY ARP
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Thunderstorms moved across the northern portions of the greater Phoenix metropolitan area during the late morning hours on October 20th and due to elevated levels of moisture, instability and wind shear, the stronger storms produced locally heavy rainfall with peak rain rates in excess of one inch per hour. Locally heavy rain fell in the communities of north Phoenix and Deer Valley. A trained weather spotter 6 miles to the northeast of Peoria measured 1.24 inches of rain within a 20 minute period ending at 1035MST. The heavy rain fell just north of Happy Valley Road and near 43rd Avenue. The heavy rain led to significant urban street flooding in the area with water ponded to the top of the curbs. A Flash Flood Warning was issued for the area during the time of the street flooding but no flash flooding actually occurred in the area.

Flash Flood in MARICOPA, ARIZONA
From 20-OCT-15 07:00:00 to 20-OCT-15 09:30:00 (MST-7)
Location: NEW RIVER
Flood cause: Heavy Rain
Property damage: 10.00K
Crop damage: 0.00K
Reported by: Broadcast Media

Scattered thunderstorms developed across the northern portions of the greater Phoenix area during the early morning hours on October 20th, and they affected communities along Interstate 17 such as Anthem and New River. Due to elevated amounts of moisture in the atmosphere, some of the storms produced very heavy rainfall with peak rain rates in excess of 1.5 inches per hour. According to local broadcast media, at 0745MST flash flooding occurred along Skunk Creek, about 2 miles southeast of Anthem. The flooding resulted in a water rescue near 19th Avenue and Desert Hills Drive; the vehicle became trapped in Skunk Creek which was swollen with excessive runoff. The driver was rescued and no injuries were incurred. A Flash Flood Warning was not in effect at the time however a Flood Advisory was issued for the area beginning at 0538MST and it ran through 0930MST.

Flash Flood in MARICOPA, ARIZONA
From 20-OCT-15 11:30:00 to 20-OCT-15 13:30:00 (MST-7)
Location: NEW RIVER
Flood cause: Heavy Rain
Property damage: 0.00K
Crop damage: 0.00K
Reported by: Trained Spotter

Scattered thunderstorms moved across the far northern portions of the greater Phoenix metropolitan area during the late morning and early afternoon hours on October 20th, and they affected areas surrounding the community of Anthem. Due to elevated amounts of moisture in the atmosphere, the stronger storms produced very heavy rainfall with peak rain rates in excess of 1.5 inches per hour. The heavy rain produced episodes of small stream flooding as well as flash flooding. According to a trained weather spotter 3 miles west of Anthem, at 1215MST water up to one foot deep was flowing across New River Road. A Flash Flood Warning was in effect for the area at the time of the flooding, starting at 1123MST and running through 1330MST. No injuries were reported due to the flash flooding.