textproduct: NWS Flagstaff

SYNOPSIS

Overall dry and seasonably warm conditions will continue into Friday, with a isolated showers and slight chance of thunderstorms mainly over the higher terrain. Rain chances will start to increase Saturday afternoon and continuing into early next week, as tropical moisture moves back into the region, bringing cooler and windy conditions as well. There is the potential for a significant rainfall event.

DISCUSSION

Visible satellite imagery today shows cumulus developing over the higher terrain areas of norther Arizona, which will likely lead to some isolated showers and possibly a thunderstorm or two in areas with locally higher dewpoints. Similar conditions are expected for Friday as a ridge of high pressure tries to build into the area. The ridge will be weak and doesn't really get established as a trough starts to develop over the Pacific Northwest and digs southward.

Starting Saturday, there will be a shift in the weather across the Desert Southwest as the Pacific Northwest trough starts to dig to the south. As the trough digs south, it will interact with what will become the remnants of TS Rachel. Model runs continue to drag that moisture up into the Desert Southwest over the weekend and into early next week. The trough looks to become cut off by late in the weekend and models are slow to push the low off to the north and east. With the potential for a prolonged period of tropical moisture being pulled northward into the region through, it looks like we could have a very active and wet period ahead of us. QPF ranges are fairly widespread at this time but the potential for 1-3" with locally higher amounts remain possible. This could lead to flood/flash flooding concerns, but exact impacts will depend if most of the rain falls as heavy showers and thunderstorms with high rain rates with a lot of rain in a short period of time, or if this is more of a stratiform rain event with light to moderate rainfall over a couple of days, with some embedded areas of heavier rainfall. The former would support more of a flash flooding threat while the latter would lead to high water in streams and rivers affecting low water crossings or poor drainage areas, leading to ponding of water on roads.

Current projections have western areas seeing the greatest potential for heavy rain around the Sunday into Monday time period but any slight shifts in the track could push things to the east. As Rachel weakens and the trough starts to dig south, we should start to see a better picture of just where the greatest impacts will be expected. On top of the potential for heavy rainfall, we will see increasing south to southwest winds with gusts 30-45 mph on Sunday. Keep any eye on the forecast as we get more refined over the next day or two.

AVIATION...Friday 09/00Z through Saturday 10/00Z

VFR conditions. Increasing clouds Friday afternoon, with isolated -SHRA/-TSRA developing. S-SW winds mostly 10-15 kts Friday afternoon, except gusts up to 30 kts near showers.

OUTLOOK...Saturday 10/00Z through Monday 12/00Z...Mainly VFR through 18Z Saturday, with periods of MVFR possible thereafter. Isolated -SHRA/-TSRA through 12Z Saturday, then scattered coverage of SHRA/TSRA possible after 12Z Saturday. SHRA/TSRA becoming widespread after 00Z-06Z Sunday. Periods of MVFR/IFR possible Saturday night into Sunday in +RA. S-SW Winds increasing to 10-20 kts with gusts 25-30 kts on Saturday, then 20-25 kts with gusts 30-40 kts Sunday.

FIRE WEATHER...Friday and Saturday

Mainly dry conditions on Friday, outside of a slight chance for isolated high-based showers and thunderstorms over the higher terrain. Cooler, and wetter conditions set in through the day Saturday, and especially into the overnight. Winds south 5-15 mph on Friday, increasing to 10-20 mph on Saturday.

Sunday through Tuesday...Cool conditions with numerous to widespread showers and thunderstorms on Sunday, becoming scattered Monday and Tuesday. South winds 15-25 mph with gusts 35-45 mph on Sunday, subsiding to 10-20 mph with gusts 30-40 mph on Monday. Winds becoming south/southwest 10-15 mph with gusts 20-30 mph on Tuesday.

FGZ WATCHES/WARNINGS/ADVISORIES

None.