textproduct: NWS Flagstaff

SYNOPSIS

Shower and thunderstorm chances continue through Sunday evening as a weather system approaches. This active pattern continues through most of the week with continued daily shower chances, occasional gusty winds, and below normal daytime temperatures. The highest chance of rain will be on Wednesday and Thursday.

DISCUSSION...For remainder of Sunday through Monday

Low pressure located over southwest Arizona Sunday afternoon will slowly track northeastward across the state, weakening as it goes. The low will deliver scattered showers and perhaps a stray afternoon thunderstorm each day. However, there are a few factors that will limit precipitation amounts with this low. First, the low is weak and will grow weaker. Second, the low-level flow and thus orographic lift will be minimal. Third, mainly cloudy skies will limit daytime heating and associated instability. As a result, generally light precipitation is anticipated with totals ranging from trace amounts to 0.20 inches through Monday (the highest mountain peaks could see as much as 0.50 inches). In any case, this is a warm system so snow levels are expected to remain primarily above 11,000 feet. Light and variable winds on Sunday will turn more southerly on Monday as another Pacific low approaches. There will be a cooling influence from the light precipitation and clouds with high temperatures dropping by around 5 degrees on Sunday and Monday compared to Saturday.

On Tuesday...The current weak low will move to the northeast in response to a stronger low pressure system dropping southward from the Gulf of Alaska. Moisture will continue to linger across Arizona in advance of this stronger low with slight chances for showers or a stray thunderstorm continuing. Activity will mainly be confined to the afternoon and early evening associated with instability induced by daytime heating. Southerly winds will strengthen to 10-20 mph as the low draws closer to Arizona. High temperatures will warm a bit as southerly flow pushes a mild air mass across Arizona.

From Wednesday onward...Forecast models continue to show the Pacific low diving southward then moving across the western states including Arizona, tapping into moisture of subtropical (or even tropical) origins. The result, widespread showers and likely a few thunderstorms are forecast, especially on Wednesday and Thursday. The most substantial moisture will likely move across Arizona from about Flagstaff eastward where local rainfall totals ranging from 1 to 3 inches will be possible. The area of the highest rainfall totals includes the White Mountains, Mogollon Rim, Navajo Nation and Gila County. Further west looking at lighter amounts of 0.25-0.75 inches. The snow level will remain elevated for much of the storm due to the subtropical to tropical nature of the moisture. The snow level could drop as low as 8500 feet as the coldest temperatures aloft move over Arizona on Friday and Saturday (when shower chances will be rapidly diminishing). Also, Pressure gradients will strengthen on Wednesday and Thursday with south to southwest winds of 15-25 mph gusting to 35 mph developing. Later on Friday and on Saturday a weak low will linger over Arizona and would not be suprised if at least a slight chance of showers lingers. High temperatures will be on the decrease under the influence of perception, clouds and cooler air associated with the low.

AVIATION...Sunday 18/18Z through Monday 19/18Z

Mainly VFR with localized MVFR possible in heavier showers. SCT -SHRA with ISO TS diminishing after 02Z. Variable winds 5-10 kts, becoming light overnight.

OUTLOOK...Monday 19/18Z through Wednesday 21/18Z...Mainly VFR with brief MVFR in heavier showers. SCT -SHRA/-TSRA along the higher terrain on Monday afternoon, becoming ISO on Tuesday. Daytime winds S-SW 5-15 kts on Monday, increasing to 10-20 kts on Tuesday. Expect light and variable winds during the overnight period.

FIRE WEATHER...Monday through Tuesday

Cool conditions expected to continue through the period. South winds 5-15 mph on Monday, increasing to 10-20 mph on Tuesday. Scattered showers and thunderstorms again on Monday, with a slight chance of showers and thunderstorms on Tuesday.

Wednesday through Friday...Cool temperatures continue. Showers and thunderstorms likely on Wednesday and Thursday with most areas seeing wetting rains, then scattered activity expected on Friday. South winds 15-25 mph with gusts 30-40 mph on Wednesday and Thursday, becoming south through southwest 10-20 mph with gusts 25- 30 mph on Friday.

FGZ WATCHES/WARNINGS/ADVISORIES

None.