textproduct: NWS Flagstaff

SYNOPSIS

Showers and thunderstorms will increase through the day as tropical moisture lifts across the state in response to an approaching trough interacting with Tropical Storm Rachel. Expect cooler, windier, and wetter conditions to continue into next week.

DISCUSSION

The weekend is here and we are already starting to feel the changes coming our way. Tropical Storm Rachel has been pushing to the northeast at a good pace and is starting to interact with a trough/cut-off low over the Pacific. Additionally, a deepening trough is pushing down from the Pacific Northwest and will become a factor in the weather through the next several days. These features will all move towards southern California, with Rachel/trough moving into the SoCal coast through today, likely making landfall late tonight. The PacNW trough will then continue to dig further south, eventually moving over the Great Basin by early next week. The trough is slow to eject and may remain near the region through at least the middle of the week, potentially longer. Overall, an active weather pattern remains in play for the coming days.

Today through Wednesday...Models have trended slightly west with the landfall of Rachel and the track of the remnants. This doesn't mean that we will be spared from the impacts, just that some of the higher impacts will shift westward. Moisture is already starting to stream into the region on the strengthening south to southwest flow. Some isolated showers and thunderstorms have developed and will continue to move towards the northeast through the night and into the morning hours. As we head through today, moisture will continue to increase and showers and thunderstorms will become more scattered to widespread. As moisture steadily increases, coverage of storm activity will also increase with Sunday and Monday looking to be the most active days, especially across western and southern areas where we currently have a Flood Watch in place.

QPF continue to be largely in the 1-3" range, with locally higher amounts are possible. With the path of Rachel shifting west, the best chances for the higher amounts mainly along and south of terrain features, mainly from the Grand Canyon down through the Mogollon Rim. There is still considerable uncertainty with how this event will unfold. Latest model runs show a bit more dry air being dragged into the mid-levels, which could potentially limit the heavy rainfall potential and keep storm activity more scattered and flooding more localized. But with cold air aloft, we may end up seeing some enhancement of rainfall rates, especially across higher terrain. Hi-res models continue to show multiple convective bands moving through the region over the next few days, with the potential for some to have some very heavy rainfall. Storms may be moving pretty quickly which could help to limit some potential flash flooding but will bear watching. Another thing to keep in mind is there will be decent instability available as the trough pushes into the Desert Southwest. Combined with the ample moisture and deep shear there will be the potential for some supercells to develop with strong/damaging winds being the main hazard.

Winds will also be an issue with these systems. Expect increasing south to southwest winds as the gradient tightens up in advance of Rachel's landfall, then further tightening as the remnants/trough move across the area. Winds look to be strongest on Sunday and Wind Advisory is in effect for the entire area. Winds may remain elevated on Monday and the advisory may need to be extended for portions of the forecast area. Winds on Sunday will be south to southwest 25-35 mph with gusts 40-50 mph with some locally higher gusts possible. Winds remain strong on Monday and Tuesday, mainly across the higher terrain but really begin to taper off later Tuesday.

There is some conflict in the models on just what transpires with the PacNW trough in the midweek time frame. Will it eject out around Wednesday or become a cut off low that stalls nearby through the end of the week? Only time will tell and hopefully the models will come to an agreement in the coming days.

AVIATION...Saturday 10/12Z through Sunday 11/12Z

Initially VFR, becoming MVFR in SHRA/TSRA moving from the southwest to the northeast. Periods of IFR or lower possible in +RA and low CIGs, especially during the overnight period. S-SW winds 10-20 kts with gusts to 30 kts.

OUTLOOK...Sunday 11/12Z through Tuesday 13/12Z...Mainly MVFR conditions in SHRA/TSRA through the period. Periods of IFR possible through Sunday in +RA and low CIGS. S-SW winds 20-30 kts with gusts to 35-50 kts on Sunday, decreasing to 15-25 kts with gusts 25-35 kts on Monday.

FIRE WEATHER...Today and Sunday

Showers and thunderstorms are developing from the southwest to northeast this morning and will continue today through Sunday. Periods of heavy rain are possible , especially Saturday night into Sunday. South winds 10-20 mph today, increasing to 20-35 mph with gusts 35-50 mph on Sunday.

Monday through Wednesday...Scattered showers and thunderstorms continue on Monday and Tuesday, with isolated activity expected on Wednesday. South winds 15-25 mph on Monday, becoming south to southwest on Tuesday. Light west to northwest winds are expected for Wednesday.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch from 11 AM MST /noon MDT/ this morning through late Sunday night for AZZ004>008-015-016-018-037-038.

Wind Advisory from 8 AM MST /9 AM MDT/ to 8 PM MST /9 PM MDT/ Sunday for AZZ004>018-037>040.