textproduct: NWS Flagstaff

SYNOPSIS

Above normal temperatures and mainly dry conditions will continue through Friday for most of the region, while isolated showers and thunderstorms remain in forecast for eastern portions of Arizona through Thursday. This weekend and into early next week, a colder and much windier pattern develops, along with the potential for a significant rainfall event, as tropical moisture moves back into the southwest.

DISCUSSION

The weak shortwave trough is now over northeast Arizona this afternoon will continue to meander southeastward through Thursday. This will keeps the ongoing potential for high- based and isolated convection, mainly for the eastern Arizona. The trough is moving around a ridge that is southwest of northern Arizona, which is close enough to provide us with above normal temperatures for the next few days.

By the end of the week, the ridge moves a bit eastward and then collapsing this weekend as a much stronger trough enters the interior Pacific Northwest. This next trough will then dig south or southwestward, strengthening and possibly cutting off by Sunday or Monday. This will likely allow for significant tropical moisture transport into Arizona, along with the remnants of Hurricane Rachel. However, the GFS and ECMWF does not eject the trough inland until next Tuesday or Wednesday, so this moisture stream could go on for awhile.

There are still many things that could change and shift this forecast. The Canadian ensemble has a faster eastward moving trough, which phases better with the tropical moisture from Hurricane Rachel moving into Arizona and is more favorable for more widespread rainfall across all of Arizona Sunday into early Wednesday then compared to the GFS and ECMWF ensembles. Meanwhile, the GFS and ECMWF ensembles have a slower moving trough, likely related to a low cutting off within the trough by Sunday or Monday. This favors the potential for heavier rainfall more over western Arizona as moisture is pulled northward further west, and shifting where the greatest plume of tropical moisture will setup. There is still an level of uncertainty in the forecast that should be monitored closely. Nonetheless, this is potentially a very impactful pattern.

For now, there is higher confidence in a windy, colder and wet pattern developing as early as Saturday and lasting well into next week. There is still lower confidence in QPF amounts and the potential for intact tropical circulation remnants actually moving into the state.

AVIATION...Wednesday 07/18Z through Thursday 08/18Z

VFR conditions, a few isolated showers and thunderstorms along the Arizona/New Mexico border this afternoon. Winds variable 5-15kts daytime, light and variable or terrain driven overnight.

OUTLOOK...Thursday 08/18Z through Saturday 10/18Z...VFR conditions, a few isolated showers or thunderstorms in the White Mountains Thursday and Friday afternoon. A chance of showers begins moving in over most of the area starting around 12Z Saturday as a weather system approaches. Winds variable 5-15kts Thursday, becoming S-SW 10-15kts Friday.

FIRE WEATHER...Thursday and Friday

Expect mainly dry conditions and continued seasonably warm temperatures. A slight chance of high- based showers and thunderstorms remains possible for Thursday and Friday afternoons, primarily for the eastern zones. Chances for wetting rains are near zero. Winds light and variable 5-10 mph Thursday, becoming S-SW 10-15 mph on Friday.

Saturday through Monday...Unsettled conditions move in Saturday morning with scattered to numerous showers and thunderstorms possible all weekend and into Monday. Wetting rains are likely across the whole region. Winds S-SW 10-20 mph with gusts to 30 mph on Saturday, S-SW 15-30 mph with gusts 40-45 mph on Sunday, S-SW 15- 25 mph with gusts 35-40 mph on Monday.

FGZ WATCHES/WARNINGS/ADVISORIES

None.