textproduct: NWS Flagstaff

SYNOPSIS

Radar imagery shows stratiform rain and embedded showers are developing in western Arizona and spreading across the rest of northern Arizona this morning. The risk for embedded thunderstorms will increase during the day due to limited daytime heating and as a trough near California continues to move eastward toward the lower Colorado River Valley and interacts with tropical moisture being lifted northward. Heavy rainfall, strong thunderstorms and flash flooding are possible today and Tuesday. A Flood Watch remains in effect through Tuesday evening. Shower and thunderstorm chances will then decrease Wednesday and Wednesday night, with mild and dry conditions to start off October.

DISCUSSION

Moisture from Polo and the remnants of Odalys continue to overspread the area, with stratiform rain and embedded showers spreading across northern AZ as the mid/upper- level trough near California continues to moves into the lower Colorado River Valley, with an closed upper-level low developing at the base of the trough, then slowly moving across the region Tuesday. The risk for embedded thunderstorms will increase later today and into Tuesday due to limited daytime heating, along with improved upper-level synoptic support associated with the trough and closed low. Some of these thunderstorms could become strong to severe at times with heavy rain, strong winds, and large hail. WPC continues to message a moderate risk for excessive rainfall for most of the region for today and then shifting focus for the eastern part of the state Tuesday as the trough and closed upper- level low move eastward. A Flood Watch remains in effect through Tuesday evening. Widespread rainfall amounts of 1 to 2 inches forecast across the high deserts of northeast Arizona have an average return interval of 5 to 10 years, making this at least an uncommon event there. Locally heavy rainfall from thunderstorms, along with upsloping and other terrain-effects could also lead to localized rainfall of 2-3 inches, especially over the heavier terrain and eastern AZ. High temperatures across the region today and Tuesday will be quite cool due to the cloud cover and rainfall, 10 to 20 degrees below average. By Wednesday night, precipitation chances start winding down in the far eastern parts of the state as the trough sweeps east and takes the moisture plume with it.

Continuing note: While the tropical moisture is associated with tropical systems, Odalys has dissipated over the open ocean and the circulation associated with Polo will not actually make it up into Arizona. Polo is expected to make landfall in Baja California today, cross the Gulf of California and break apart to our south when it makes landfall again in mainland Mexico.

By Thursday onward dry air from the west and north will take over and limit the potential for precipitation through the rest of the week. Some ridging will moving in towards the end of the week look for a pleasant start to October as high temperatures recover to a few degrees above average.

AVIATION...Monday 28/06Z through Tuesday 29/06Z

VFR conditions to start the period, lowering to MVFR between 09Z-12Z. Showers and thunderstorms will become more numerous as the night progresses becoming area wide during the day Monday. Winds south 5-15 kts daytime, light and variable overnight. Gusty and erratic winds near storms.

OUTLOOK...Tuesday 29/06Z through Thursday 01/06Z...Expect scattered to numerous showers and thunderstorms area wide through Tuesday afternoon with the focus of precipitation then shifting towards eastern Arizona heading into Wednesday. Look for areas of MVFR conditions with brief IFR conditions in heavier showers and thunderstorms. Daytime winds variable at 5-15 kts Tuesday, west to northwest at 5-15 kts Wednesday. Light and variable at night.

FIRE WEATHER...Today through Tuesday

Precipitation chances will peak today through Tuesday with widespread wetting rain and embedded thunderstorms across the region today and becoming more focus over eastern Arizona by Tuesday evening. This will present a moderate flood and flash flood risk. Winds S 5-15 mph on today, N-NE 10-20 mph on Tuesday.

Wednesday through Friday...Some lingering precipitation chances in far eastern Arizona Wednesday, drying out elsewhere. Dry with no precipitation across the state Thursday and Friday. Winds NW-N 5-15 mph on Wednesday, light and variable 5-10 mph Thursday, light and variable most areas Friday with the exception of some winds E 5-15 mph along the Rim.

FGZ WATCHES/WARNINGS/ADVISORIES

Flood Watch through Tuesday evening for AZZ004>018-037>040.