textproduct: NWS Flagstaff

SYNOPSIS

An active monsoon pattern extends across northern Arizona with scattered to numerous showers and thunderstorms developing across the region. The main threat will be flash flooding, but gusty winds and hail will be possible with the strongest storms. A Flash Flood Watch remains in effect through this evening. Monsoon conditions are expected to continue Thursday, with a downtrend in Monsoon activity possible by the weekend, as drier air moves into the region.

DISCUSSION

Plenty of Monsoon moisture extends across northern Arizona as the high pressure system as moved eastward into the southern plains and southerly flow and transported moisture northward. Right now a trough at 850 mb is supporting the showers and thunderstorms in northwestern Arizona, with showers and thunderstorms also developing along the rim and higher terrain down to the White Mountains. The UA WRF model shows this active pattern continuing through 6 PM MST/7PM MDT, and then decreasing as the potential area of development shifts southward. However, due to the north-northeast storm motion, it is possible for rain to move into areas near and south of I-40 overnight and early Thursday morning. The UA WRF model also shows and active monsoon pattern for Thursday afternoon and evening, though the 12 and 15Z runs show a slight decrease in overall coverage. The Flash Flood Watch may need to be extended into Thursday if shower and thunderstorm coverage is still expected to be extensive enough to warrant a watch.

A mid-level trough is currently sitting off of the west coast and will attempt to move inland. This could bring drier, mid-level area over northern Arizona and reduce shower and thunderstorm activity across the region. However, if this trough fails to move inland or moves farther north, then the active monsoon pattern may continue into the weekend. Right now forecast trends does support the trough moving inland and an overall decrease in monsoon activity this weekend, but these trends will be monitored.

AVIATION...Thursday 13/00Z through Friday 14/00Z

Mainly VFR conditions away from thunderstorms. SCT SHRA/TSRA and ISO +TS through the period, with the highest coverage through 03Z and again after 18Z. Stronger storms may produce brief MVFR/IFR and wind gusts to 45 kts. Outside of storms, daytime winds W-SW 10-15 kts.

OUTLOOK...Friday 14/00Z through Sunday 16/00Z...Mainly VFR conditions away from thunderstorms. SCT SHRA/TSRA and ISO +TS through around 03Z Fri and again 18Z Fri to 03Z Sat. Decreasing storm coverage Saturday, mainly affecting eastern AZ. Stronger storms may produce brief MVFR/IFR and wind gusts to 45 kts. Outside of storms, W-SW winds 10-15 kts becoming light and VRB overnight.

FIRE WEATHER...This afternoon through Friday

Cooler temperatures with active Monsoon conditions expected each day. Numerous showers and thunderstorms through Thursday with an eastward push in activity on Friday. Outside of thunderstorms, expect southwest winds around 10-15 mph.

Saturday through Monday...Eastward shift in monsoon activity through the weekend with some drier conditions expected. Temperatures will gradually warm to near normal by early next week. Expect southwesterly winds at 10-15 mph each afternoon.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch until midnight MST /1 AM MDT/ tonight for AZZ004>018- 037>040.