textproduct: NWS Flagstaff

SYNOPSIS

Scattered showers and thunderstorms will continue into this evening, with drier conditions returning for the middle of the week. Additional showers and thunderstorms are likely again by Friday through the weekend.

DISCUSSION

A shortwave lifting northeastward ahead of the large west coast trough is focusing convection in northwest Arizona up into Utah early this afternoon. This area also started the day sunny, so additional instability was able to build. This is where the highest flash flood threat will be (north/west Coconino County) into this evening, with WPC upgrading the area to a moderate risk for flash flooding. Elsewhere, the large area of showers and thunderstorms that moved northward through much of the region left overnight behind a cooler and more stable boundary layer with surface temperatures mostly in the 60s. So the threat of stronger storms outside of north/west Coconino County has lowered. However, with deep moisture in place and some redevelopment still possible, will leave the Flash Flood Watch in place into this evening. Tuesday through Thursday, southwest flow aloft will increase as the western US trough moves closer, bringing some drier air into our region but not completely scouring out the low level moisture. As a result, there is still a chance for some isolated showers and thunderstorms each afternoon, but intensity appears to be less than what we have seen the last several days. Daytime high temperatures will be a few degrees below normal through the period. Southwest breezes will also increase due to the trough, reaching 15-20 mph and gusting up to 30 mph at times.

Friday into the weekend - high pressure nudges back westward as the west coast trough retreats a bit. This should allow for a more southerly flow with moisture returning to the area. The timing of the moisture return, and the influence of a possible tropical system off the coast of Baja remain uncertain. This will impact just how much moisture we end up seeing. For now, storm chances rise to the 30-60% range for Friday through Sunday.

AVIATION...Tuesday 01/00Z through Wednesday 02/00Z

Mainly VFR conditions expected tonight, outside of isolated SHRA/TSRA creating localized areas of MVFR conditions. Isolated SHRA/TSRA are expected to linger through 06Z and mainly found along and northwest of a line extending through KPRC-KINW. Gusty/erratic winds possible near storms, otherwise SE to SW 10-15 kts winds will continue through 06Z. After 06Z, light and variable winds or terrain driven winds will to return. Isolated SHRA/TSRA across the higher terrain are expected to start along the higher terrain starting around 18Z Tuesday, with SW winds of 10-20 kts.

OUTLOOK...Wednesday 02/00Z through Friday 04/00Z...VFR conditions expected. Look for SW winds 10-20 kts each afternoon, becoming light and variable overnight. There will be a slight chance for SHRA/TSRA each afternoon, with main impacts being gusty/erratic winds.

FIRE WEATHER...Rest of today through Wednesday

Shower and thunderstorm activity is mostly in northwestern Arizona today, while a thick layer of clouds that was across most northern Arizona this morning is helping to reduce day time heating and the development of showers and thunderstorms. This cloud cover is expected to decrease the evening and overnight, and should allow for isolated showers and thunderstorms over the terrain on Tuesday. Heavy rain leading to flash flooding, especially over recent burn scars, will continue to be a main concern. Storms today will also be capable of producing hail, gusty/erratic winds, and frequent lightning, though this risk should decrease tonight through Wednesday. Outside of storm driven winds, look for SW winds 5-15 mph today, increasing to 10-20 mph Tuesday and Wednesday. Expect daytime highs 5-15 degrees below normal.

Thursday through Saturday...A brief drying trend is expected to continue into Thursday, although an isolated hi-based shower is not out of the question. Friday and Saturday appears to be more active across central/northern Arizona in terms of showers/storms. Temperatures look to slowly warm through the period, becoming closer to seasonal norms. Expect southwest winds 10-20 mph each afternoon, becoming light and variable overnight.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch until midnight MST /1 AM MDT/ tonight for AZZ004>018- 037>040.