textproduct: NWS Flagstaff

SYNOPSIS

Showers and thunderstorms will continue through much of the day with moisture from the remnants of Tropical Storm Rachel over Arizona. Expect cooler, windier, and wetter conditions to continue through at least the first half of the week.

DISCUSSION...Today

Moisture from Hurricane Rachel has moved into much of northern Arizona this morning, with PWAT values near or exceeding daily record levels. Several areas of showers and thunderstorms, with embedded heavy rainfall, are moving across northern Arizona this morning. The heaviest of which is to the west over Mohave County. As the vort max from Rachel moves northeastward into Utah, the upper-level jet over Arizona begins to increase. This should lead to a further increase in coverage of showers and thunderstorms into the afternoon hours, before gradually diminishing later this evening. Gusty southerly winds are also expected today, with gusts upwards of 45 to 55 mph expected. Some locally higher gusts will be possible downwind of the higher terrain.

Latest HREF and REFS guidance highlight the greatest potential for heavy rainfall to be through this afternoon, and mainly from western Coconino county, down to Gila and Yavapai counties. However, with storm motions of 50-60 mph, the overall residency time of any one storm has been limited so far today. Thus, the greatest flash flood threat will exist in any rain sensitive locations (burn scars, slot canyons, and urban areas) and where storms tend to train over one area for an extended period of time. A Flash Flood Watch remains in effect until 5 AM MST Monday to cover this threat.

Given the high shear environment, 40-60 kts in the 0-6 km layer, an isolated strong to severe thunderstorm is not out of the question. The limiting factor to this will be the lack of day time heating, thereby limiting the instability going into this afternoon. The main threat with any storm will be damaging winds, however an brief isolated tornado can no be totally ruled out. The greatest risk area looks to mainly be across northern Gila and Yavapai counties through the early afternoon hours.

Monday and Tuesday...As the remnants of Rachel lift to the north, a strong upper-level low dives southward into the Great Basin. An enhanced upper-level jet over Arizona will keep showers and thunderstorms in the forecast each day. However, model soundings show a much more shallow moisture profile as drier air moves in aloft. Thus, the greatest likelihood for precipitation will be in the higher terrain where orographic effects will aid in vertical motion. Given the more shallow moisture profile, the flash flood threat look to be lesser and more localized.

Winds look to remain gusty given the jet in place, however, not nearly as strong as today. The highest gusts will mainly be found immediately downwind of the Mogollon Rim into the Little Colorado River Valley, where gusts of 40-50 mph will be possible. Given the more limited coverage of the stronger winds, a Wind Advisory does not appear necessary at this time. Cooler conditions look to set in for the start of the work week as well.

Wednesday through Saturday...By the middle of the week, the trough begins to lift out of Arizona and into the northern Plains. Remnant moisture will leave the potential for a few isolated showers Arizona the higher terrain of eastern Arizona, but dry conditions are otherwise expected for the day. Lighter winds and slightly warmer conditions are also expected.

Guidance seems to have come into a bit more agreement with the low breaking off from the jet, and briefly becoming a closed-low over the southwest. Therefore, temperatures look to warm a few degrees but remain cooler than normal. Gusty northeast winds look to set in for Thursday and Friday, with the strong pressure gradient in place with a surface low to the southwest and surface high pressure over Colorado.

Drier air will keep dry conditions in the forecast for Thursday. However, as the upper-level low begins to retrograde over Arizona, some moisture does look to work it's way back into eastern Arizona on Friday and spreading westward into Saturday. Of the ensemble guidance, the EPS members tend to favor a better chances for showers, given that they have maintained a stronger low, while the GEFS members favor the drier solution with the low being weaker and further south. Therefore, uncertainty does still remain in the exact details of the extended forecast period.

AVIATION...Sunday 11/18Z through Monday 12/18Z

Mainly MVFR with brief IFR in heavier showers and thunderstorms this afternoon. MVFR with IFR at the higher terrain terminals overnight. Numerous showers and thunderstorms will continue throughout the TAF period. Winds S-SW 20-30kt with gusts 40-50kts this afternoon, tapering off to S-SW 10-20kts with gusts 25-30kts overnight.

OUTLOOK...Monday 12/18Z through Wednesday 14/18Z...MVFR in the higher terrain, VFR lower terrain. Brief IFR possible near heavier showers and thunderstorms. Expect scattered to numerous showers and thunderstorms Monday and most of Tuesday. Showers begin to end west to east Tuesday night into Wednesday morning. Winds S-SW 15-25kts with gusts 30-40kts Monday. SW-W 15-25kts gusts 30-40kts Tuesday.

FIRE WEATHER...Monday and Tuesday

Scattered to numerous showers and thunderstorms on Monday and Tuesday. Periods of heavy rain are possible each day, with the potential for flooding. Showers begin ending west to east Tuesday night into Wednesday morning. Winds S-SW 15-25 mph with gusts 30-40 mph on Monday, W-SW 15-25 mph, gusts 30- 40 mph on Tuesday.

Wednesday through Friday...Drier conditions are expected for Wednesday and Thursday. A slight chance of showers and thunderstorms may return to the higher terrain Friday. Winds W-NW 5-15 mph Wednesday, N-NE 10-20 mph on Thursday, E-SE 10-25 mph on Friday.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch through late tonight for AZZ004>008-015-016-018-037- 038.

Wind Advisory until 8 PM MST /9 PM MDT/ this evening for AZZ004>018-037>040.