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 is on Wednesday and Thursday.

DISCUSSION...Today

A low pressure system currently spinning off the coast of northern Baja California is visible in mid- level water vapor satellite imagery. This is expected to slowly drift northeastward while weakening through Sunday-Monday. A southerly moisture surge is currently underway, somewhat enhanced by continued active tropical cyclone activity in the Eastern Pacific. Combined with synoptic lift from the approaching weather system, we are seeing bands of light showers across Northern Arizona early this morning. Observed rainfall has remained very light thus far due to lingering dry surface conditions, though surface dewpoints are quickly rising. Moisture will continue to stream into Arizona through the day today, with PWAT rising well above normal for mid October. However cloud cover will limit daytime heating, and weak flow will limit orographic influences. As a result, total rainfall accumulations through Sunday evening are expected to remain light, up to around 0.2-0.4 inches. Besides showers, expect continued cool daytime temperatures and light winds.

Monday and Tuesday...A strong low pressure system will rapidly dive along the west coast and approach Arizona. This will reinforce a pressure gradient bringing south-southwesterly flow to our region. We will see gradually strengthening southerly surface winds through the period. Lingering moisture will also lead to continued chances for daytime showers and thunderstorms, especially Monday afternoon. Daytime temperatures will climb a few degrees, but still stay near to below October normals.

Wednesday through Friday...The strong low pressure system will begin to push inland and carry a deeper surge of moisture to northern AZ. Widespread showers and thunderstorms, some strong, are expected on Wednesday and Thursday. The current outlook brings the best moisture and rainfall accumulations across eastern AZ. Stronger low-level flow with orographic influences is also expected. Most areas will see at least 0.25-0.75 inches of rain, with preferred upslope regions across eastern AZ seeing as much as 1.5-2.5 inches. Ensemble guidance still does have some spread in the trajectory and how progressive the trough will be, so there is room for change in total accumulations and where the deepest moisture will land. Activity is expected to trend downward by Friday into the weekend. Also expect even cooler temperatures with gusty south to southwest winds each day, strongest on Thursday.

AVIATION...Sunday 18/12Z through Monday 19/12Z

Primarily VFR, but MVFR conditions possible in heavier showers. Periods of -SHRA will continue across much of northern AZ, diminishing after 02Z. ISOLD -TS also possible after 18Z. Winds are variable at 5-10kts through the period.

OUTLOOK...Monday 19/12Z through Wednesday 21/12Z...Primarily VFR, but brief MVFR possible in heavier showers. SCT -SHRA/-TSRA along the higher terrain on Monday afternoon, then ISOLD on Tuesday afternoon. Winds are S-SW 5-15kts on Monday, then 10-20 kts on Tuesday.

FIRE WEATHER...Today through Monday

Cool conditions through the period. Light and variable winds on Sunday, becoming south 5-15 mph on Monday. Scattered showers with isolated thunderstorms continue through Sunday evening, then scattered showers and thunderstorms again on Monday.

Tuesday through Thursday...Slight chance of showers and thunderstorms on Tuesday, becoming likely showers and thunderstorms on Wednesday and Thursday. Wetting rains are expected for most. South winds 10-20 mph on Tuesday, increasing to 15-25 mph with gusts 30-40 mph on Wednesday and Thursday. Below normal temperatures continue through the week.

FGZ WATCHES/WARNINGS/ADVISORIES

None.