textproduct: NWS Flagstaff

SYNOPSIS

Dry and warmer conditions will continue today. A series of storm systems will bring rain and snow along with gusty winds to northern Arizona through much of the coming week.

DISCUSSION...Today

High clouds are on the increase today as southerly flow ahead of an approaching storm system pulls moisture into the region. Mild temperatures and breezy southerly winds are expected, with a ridge of high pressure to our east still holding on for one more day.

Monday and Tuesday...A strong low ejects off the Pacific into northern California early Monday, eventually transitioning into a negatively titled trough as it passes through Arizona.

Strong southerly flow develops out ahead of the trough on Monday, leading to gusty winds and increased moisture advection into the region. While winds aloft increase well in excess of 50 kts, a mid- level inversion will limit how much of this will be able to be mixed down. Winds at the top of the inversion look to support surface gusts upwards of 40-50 mph, with some locally gustier conditions along and downwind of the higher terrain. A lack of decoupling overnight may also keep winds elevated through the overnight, especially downwind of terrain features.

With the first plume of moisture reaches Arizona late Monday evening, an area of rain and snow is expected to develop from west to east overnight shortly thereafter. Snow levels may initially start out around 6500-7000 feet, however with increasing cold air advection and surface wet-bulbing, snow levels look to quickly fall to 5500-6000 feet by Tuesday morning. Given strong frontogenetic forcing traversing the area Tuesday morning, a 1-2 hour period of moderate to heavy rain/snow is expected to occur. 12Z HREF guidance has a 60-90% likelihood for a period of >1" per hour snowfall rates between 12 AM and 7 AM MST Tuesday, mainly above 6500-7000 feet.

Behind the front, low-level moisture looks to remain in place. However, with the absence of large-scale forcing, any activity through the remainder of the day on Tuesday will primarily be upslope-driven.

Overall QPF amounts look to largely favor the upslope areas along and south of the Mogollon Rim, where upwards of an inch of liquid are forecast. Across the lower elevations, upwards of 0.10-0.30 inches are forecast. Snow accumulations look to largely be focused above 6000-6500 feet, where 3-6 inches is most common. However, upwards of 8-12 inches are possible in the higher elevation upslope areas; namely the Kaibab Plateau, highs points of the Mogollon Rim, and the San Francisco Peaks.

Given the potential for travel impacts with moderate to heavy snow and blowing snow in the high country, a Winter Weather Advisory has been issued for Monday evening through Tuesday. The Wind Advisory has also been extended through Tuesday for areas outside of the winter headlines.

Wednesday through Saturday...Winter weather conditions look to continue into the extended period with the longwave trough still in place over the west. Even colder air looks to set in by Wednesday, ahead of the next round of precipitation, thus potentially brining accumulating snow down to 4000-5000 feet. While QPF amounts are not too dissimilar from the previous, the colder temperatures should result in better snow accumulations (higher snow-liquid ratios) for the higher terrain. Given continued southerly flow, the usual upslope locations may see a more prolonged period of rain/snow, and thus higher amounts. Strong, gusty winds are also expected to continue into Wednesday, thus additional headlines will likely be needed once the potential need for winter headlines is addressed.

A third and final blow looks to move through late Thursday and Friday, with another round of rain and snow possible. Confidence however with each system gets progressively lower, as each will be dependent upon the track of the previous. Nevertheless, an cold and unsettled pattern looks to continue through at least Friday.

AVIATION...Monday 16/00Z through Tuesday 17/00Z

VFR expected. S-SW winds 5-15 kts gusts 15-25 kts through 02Z, then light and variable with locally gusty terrain driven winds overnight. S-SW winds 10-20 kts gusts 20-30 kts after 15Z, then increasing to 20-30 kts gusts 30-40 kts after 18Z.

OUTLOOK...Tuesday 17/00Z through Thursday 19/00Z...MVFR/IFR in RA/SN from west to east and lasting through much of the period. Periods of LIFR in +SN/BLSN over the higher terrain late Monday through early Tuesday. S-SW winds 15-25 kts gusts 30-40 kts each day, remaining elevated overnight.

FIRE WEATHER...Monday and Tuesday

Windy and dry during the daytime on Monday, but rain and snow showers begin spreading from west to east by late evening into the night. Snow levels start around 7000-8000 feet by the onset of precipitation, then fall to 5000-6000 feet by midday Tuesday. Heaviest rain/snow accumulations are anticipated late Monday night through Tuesday morning. Winds are SW 15-25 mph with gusts 35-45 mph through the period, remaining elevated overnight.

Wednesday through Friday...Periods of widespread rain and snow showers continue as a series of weather disturbances pass through. Accumulating snow or wetting rains are likely through the period, with snow levels continuing to drop. Gusty conditions again Wednesday with southwest winds 15-25 mph gusting 35-45 mph. Winds decrease Thursday and Friday, becoming southwest through west 10-15 mph gusting to 25 mph.

FGZ WATCHES/WARNINGS/ADVISORIES

Wind Advisory from 11 AM to 8 PM MST Monday for AZZ004-015>017.

Winter Weather Advisory from 8 PM Monday to 5 PM MST Tuesday for AZZ004-015>017.

Wind Advisory from 11 AM Monday to 8 AM MST Tuesday for AZZ006>008-038.

Wind Advisory from 11 AM Monday to 5 PM MST Tuesday for AZZ012>014-039.