textproduct: NWS Flagstaff

SYNOPSIS

Increased monsoon activity forecast through the next few days. Shower/thunderstorm coverage look to decrease Tuesday onward, but remain possible primarily across the higher terrain. Above normal temperatures forecast for today, becoming cooler Sunday through at least mid-week.

DISCUSSION

A persistent line of showers/storms has been lingering from the Bellemont area to Gray Mountain since about 11 PM MST. Outside of this line of thunderstorms, the rest of our CWA remains mostly quiet. This weekend is shaping up to be rather active in terms of monsoon activity, so let's dive into the details.

High pressure will shift eastward over the next couple of days, along with a trough pushing down from the Pacific Northwest. This synoptic pattern will allow for increased monsoon moisture across the state. This moisture increase is shown in the elevated PWAT values. Many locations along and south of the Rim are showing values greater than an inch, with areas elsewhere between half and inch to an inch. Following the higher PWAT values and the Slight Risk of excessive rainfall from WPC, we've issued a Flood Watch for Yavapai County, Gila County, and Oak Creek and Sycamore Canyons for 5 PM MST today through 5 AM MST Sunday. Be sure to have a way to receive warnings, and never drive through a flooded roadway. Heavy rainfall will not be the only concern with activity the next few days, but also hail, frequent lightning, and gusty/erratic winds.

Not only are we looking to receive widespread activity throughout the afternoon/evening hours, but convection is forecast to persist overnight Saturday and Sunday as well.

We'll start to see a slight decrease in moisture Tuesday onward, but there is uncertainty with how much our daily chances for showers/storms will drop off. For now, the NBM shows most activity becoming limited to the higher terrain, but things could slightly change depending on how much moisture funnels up from Tropical Storm Karina and how that plays with a shortwave that looks to push across the Great Basin.

Model guidance seems to think the potential tropical storm behind Karina could be slightly more impactful to the Southwest, but that's beyond our forecast period, so confidence is low at this time.

AVIATION...Saturday 29/12Z through Sunday 30/12Z

SHRA/TSRA expected through the TAF period. Isolated activity along a KPRC- KPGA line expected through 16Z, becoming more widespread after 18Z. MVFR/IFR conditions likely in heavier showers/storms. Outside of gusty storm driven winds that could reach near 40 kts, look for W-SW winds 10-20 kts. Light/variable winds forecast overnight.

OUTLOOK...Sunday 30/12Z through Tuesday 01/12Z...SHRA/TSRA expected through the TAF period. Greatest coverage will be between 18Z-02Z, but expect activity to persist overnight as well. MVFR/IFR conditions likely in heavier showers/storms. Outside of gusty storm driven winds that could reach near 40 kts, look for south through west winds 10-20 kts. Light/variable winds forecast overnight.

FIRE WEATHER...Saturday and Sunday

Scattered to widespread showers and thunderstorms expected over the weekend. Greatest coverage forecast for the afternoon hours, but activity expected to persist overnight as well. Localized heavy rain may lead to flash flooding, especially over burn scars. Outside of gusty/erratic winds around/in storms, look for southwest winds 10-20 mph each afternoon, becoming southerly 5-10 mph overnight.

Monday through Wednesday...Widespread showers and thunderstorms look to continue through Monday, before activity decreases for the rest of the week. Localized heavy rain may lead to flash flooding, especially over burn scars. Outside of gusty/erratic winds around/in storms, look for southwest winds 5-15 mph each afternoon, becoming variable overnight.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch from this afternoon through late tonight for AZZ008- 018-037-038.