textproduct: NWS Flagstaff

SYNOPSIS

Increasing moisture will bring chances for showers and thunderstorms in eastern Arizona today. Precipitation becomes more widespread Wednesday and Thursday as deeper moisture and a low pressure system impact the area. Drier conditions are possible by Friday and the weekend with only slight chances for rain.

DISCUSSION

An upper low centered near Las Vegas early this morning will lift northeastward through the day, leaving behind some weak troughing through southern California down to Baja. Instability ahead of the trough is producing scattered showers and thunderstorms from NW Arizona into Utah this morning but these are likely to mostly end by mid morning. A disturbance over northeast Sonora early this morning is forecast to drift northward along the AZ/NM state line today through Wednesday. Deep moisture will accompany this feature, with precipitable water values forecast to rise dramatically today in eastern Arizona, spreading westward Wednesday to include Yavapai/Coconino counties as well. Latest ensemble forecasts show PW reaching the 95th+ percentile for late September over the eastern third of the state during this period. Shower and thunderstorm chances will be highest in Apache and Navajo counties this afternoon through tonight, with a few pockets of heavy rainfall/flash flooding. By Wednesday - highest rain chances remain over Apache County, but as the moisture spreads west, additional scattered thunderstorms are forecast as far west as Flagstaff and Prescott. Some of these may also produce locally heavy rainfall, and WPC has placed nearly all of our forecast area in a marginal risk for excessive rainfall/flash flooding. On Thursday - the weak trough off the southern California/Baja coast is forecast to lift northeastward across our region. This should provide additional forcing for another round of showers and thunderstorms over much of central/northern Arizona with locally heavy rainfall again the main threat.

Friday through the weekend - most of the guidance indicates drier conditions Friday and especially Saturday as the disturbances move northeast of the state and drier southwest flow develops. We'll need to monitor the possibility of deeper moisture getting pulled northward from a couple of tropical systems well to the south toward Sunday/Monday as a trough develops off the west coast. For now, PoP values move back upward to 20-40% by this time period.

AVIATION...Tuesday 22/12Z through Wednesday 23/12Z

Mainly VFR conditions. ISOLD -SHRA/-TSRA north of KGCN through 14Z. After 18Z, SCT SHRA/TSRA mainly east of KINW. Brief MVFR conditions and gusty winds possible in and around TS. Winds VRB 5-10 kts, becoming S 10-20 kts with gusts 20-25 kts after 18Z.

OUTLOOK...Wednesday 23/12Z through Friday 25/12Z...Mainly VFR conditions. SCT SHRA/TSRA Wednesday afternoon through Thursday much of northern and central AZ. Areas of MVFR over higher elevations east of 0V7-KINW-KPAN through Thursday. Localized/brief MVFR and gusty winds possible in and around TS. Daytime winds E/SE 4-8 kts, becoming light and variable overnight.

FIRE WEATHER...Today through Wednesday

Shower and thunderstorm chances return to mainly eastern Arizona today, spreading west to include Coconino and Yavapai counties by Wednesday. Stronger storms will bring heavy rainfall and gusty/erratic winds. Outside of storms, winds are south through southwest 10-20 mph gusting to 25 mph today, then generally easterly at 5-15 mph on Wednesday.

Thursday through Saturday...Shower and thunderstorm chances continue Thursday area wide, trending downward on Friday and Saturday. Outside of storms, winds will be generally light and variable at 10 mph or less.

FGZ WATCHES/WARNINGS/ADVISORIES

None.