textproduct: NWS Flagstaff

SYNOPSIS

Widespread rain and cool temperatures will continue today, with periods of moderate to heavy rainfall possible. Widespread showers, along with increased thunderstorm activity, continue Tuesday, bringing a heightened risk of flooding. A Flood Watch remains in effect for northern Arizona through Tuesday evening. Chances for showers and thunderstorms continue across eastern Arizona on Wednesday, before warmer and drier weather returns Thursday and Friday.

DISCUSSION

Current satellite imagery show a plume of moisture originating from the remnants of Odalys moving across northern Arizona. Meanwhile, Hurricane Polo is centered of the west coast of Southern Baja California. Moisture associated with these two features will interact with a closed low approaching northern Arizona, which is currently centered over Central California. This active weather pattern is forecast to bring a period of impactful weather to the area through Wednesday.

Radar imagery shows a band of primarily stratiform precipitation draped across northern Arizona from the southwest to northeast. Rain rates are mostly light, with some embedded showers producing moderate rainfall rates. With the cool and cloudy conditions, we are not expecting robust storm development today, but some isolated storm activity cannot be ruled out this afternoon. The main concern is for flooding in areas that receive prolonged periods of moderate to heavy rainfall. Otherwise, today's forecast calls for light winds with daytime temperatures around 10 to 20 degrees below normal.

From late tonight through Wednesday morning, the low is forecast to move across northern Arizona. As it does so, additional atmospheric moisture from Hurricane Polo will be entrained into the low. With increased synoptic-scale forcing associated with the passing low, greater storm activity and higher rainfall rates are forecast. High-resolution model guidance highlights the eastern Mogollon Rim and White Mountains as the area with the highest flood risk with 24 hour rainfall totals up to 3 inches. We will also see higher 0-6km Bulk Wind Shear, with values ranging from 40-60 kts. Despite the strong shear, forecast CAPE values at or below 600 J/kg may limit the overall severe thunderstorm threat, though isolated severe storms cannot be ruled out given the benefit of forcing from the low. So, all things considered, we are looking at a moderate/high risk of flooding/flash flooding, with a lower risk of strong storms producing large hail and severe wind gusts. A Flood Watch remains in effect for northern Arizona through midnight Tuesday.

On Wednesday, the low center moves into New Mexico, with chances for showers and storms primarily remaining across eastern Arizona. High pressure is forecast to bring a return of dry weather, with daytime temperatures warming to near average on Thursday and Friday.

AVIATION...Monday 28/18Z through Tuesday 29/18Z

MVFR conditions will be common within bands of steady stratiform rain and showers moving across the region. Isolated thunderstorms likely become embedded this afternoon and continue at times into Tuesday. Expect brief IFR conditions in heavier showers and thunderstorms, or patchy fog. KPRC-KSEZ-KFLG and surrounding areas will be on the edge of activity this afternoon and again overnight, seeing at least brief breaks in rainfall. Winds south 5-15 kts daytime, light and variable overnight. Gusty and erratic winds near storms.

OUTLOOK...Tuesday 29/18Z through Thursday 01/18Z...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 afternoon, west to northwest at 5-15 kts Wednesday. Light and variable at night.est to northwest at 5-15 kts Wednesday. Light and variable at night.

FIRE WEATHER...Tonight through Wednesday

Precipitation chances will peak now through Tuesday with widespread wetting rain and isolated embedded thunderstorms across the region, becoming more focused over eastern Arizona by Tuesday evening. This will present a moderate flood and burn scar flash flood risk. Some precipitation chances linger in far eastern Arizona Wednesday, drying out elsewhere. Winds N-NE 10-20 mph on Tuesday, NW-N 5-15 mph on Wednesday.

Thursday through Saturday...Dry with no precipitation across the state, minimum RH drops to the 20s and 30s percent by Saturday. Winds light and variable 5-10 mph Thursday, light and variable most areas Friday/Saturday 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.