textproduct: NWS Flagstaff

SYNOPSIS

Shower and thunderstorm chances will increase slightly this afternoon and continue to increase overnight, with widespread showers and embedded thunderstorm Monday. This is associated with an incoming trough from the West Coast that will interact with tropical moisture and potentially bring heavy rain, strong thunderstorms and possible flash flooding. A Flash Flood Watch has been issued for Monday and Tuesday which is the time period when the heaviest rain is likely to occur. Shower and thunderstorm chances will then decrease Wednesday and Wednesday night, with dry and warm conditions to start off October.

DISCUSSION

Moisture from tropical cyclones Odalys and Polo will begin overspreading the area, most likely in the high and mid levels at first which will increase cloud cover today, with some light rain starting this afternoon. The lower levels will be dry at first but start moistening up from these initial rain showers. the potential for showers and thunderstorms will continue to increase overnight as moisture continues to increase across AZ.

By Monday a deep West Coast trough approaches with a closed upper- level low expected to develop at its base, then slowly move across the region Tuesday. This trough will act upon the tropical moisture already in place and lift from the approaching trough will generate some embedded thunderstorms that could become strong to severe at times with heavy rain, strong winds and some large hail. WPC continues to message a moderate risk for excessive rainfall for most of the region for Monday 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 for Monday and Tuesday.Temperatures across the region Monday and Tuesday will be quite cool due to the cloud cover and rainfall, about 10 degrees below average. By Wednesday night precipitation chances should start winding down in the far eastern parts of the state as the trough sweeps east and takes the moisture plume with it.

One thing to note: Despite the fact the tropical moisture is coming from two tropical cyclones to the south, neither one of these circulations will actually make it up into Arizona. Odalys is looping south and will likely die in the open ocean, Polo is expected to make landfall in Baja California, cross the Gulf of California and break apart to our south when it makes landfall again in mainland Mexico. The strong trough and upper-level low moving in from the west and acting on that tropical moisture drawn north will be the source of the active weather Monday and Tuesday.

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...Sunday 27/06Z through Monday 28/06Z

VFR conditions. Winds light and variable overnight. Look for increasing clouds on Sunday with southwest winds 10-15 kts gusting to 25 kts developing after 18Z. A chance of showers and thunderstorms along and south of a KINW-KFLG-KIGM line late Sunday afternoon through the evening. gusty and erratic winds near storms.

OUTLOOK...Monday 28/06Z through Wednesday 30/06Z...Areas of MVFR conditions developing in scattered to numerous SHRA/TSRA. Daytime winds south 10-20 kts on Monday becoming variable at 5-15 kts on Tuesday. Overnight winds generally light and variable.

FIRE WEATHER...Today through Monday

Dry conditions are expected this morning, with a slight chances for showers and thunderstorms this afternoon. Precipitation chances will ramp up overnight tonight with widespread wetting rain and embedded thunderstorms on Monday, presenting a moderate flood risk. Light winds this morning will become S-SW at 10-15 mph gusting to 25 mph this afternoon, and S 5- 15 mph on Monday.

Tuesday through Thursday...Prolonged widespread precipitation chances continue into Tuesday night as an approaching weather system combines with tropical moisture. Precipitation chances decline from west to east Wednesday and Wednesday night. There is a threat of heavy rainfall and flash flooding on Tuesday for all of northern AZ. Winds N-NE 10-20 mph on Tuesday, then NW-N 5-15 mph on Wednesday and Thursday.

FGZ WATCHES/WARNINGS/ADVISORIES

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