textproduct: NWS Flagstaff

SYNOPSIS

Mainly dry conditions are expected through much of the week, with the best chances for afternoon showers and thunderstorms across the White Mountains. Above-normal temperatures are forecast, with dangerous heat expected at the lower elevations of the Grand Canyon beginning Monday.

DISCUSSION

High pressure is broadly centered over northern Mexico and southwest New Mexico. This isn't a favorable position for transporting deep monsoon moisture into northern Arizona, but mid-level moisture has increased across the area, largely originating from a former tropical system off the west coast of the Baja Peninsula. Aided by a passing inverted trough, extensive mid- level cloud cover and virga can be seen in satellite and radar data over central and eastern Arizona.

It's not all mid-level moisture though, as surface dew points have increased as compared to 24 hours ago. Dew points this afternoon are forecast to be in the 30s and 40s. While dew points have increased, they remain insufficient to generate enough instability for robust thunderstorm activity. As a result, an extensive mid-level cumulus deck and virga, with perhaps a few light rain showers, is the most likely scenario for today.

On Monday and Tuesday, the high pressure cell is forecast to migrate northward, centering near the Arizona/New Mexico border. As it does so, surface dew points are expected to rise further, but mid-level warming associated with the strong high pressure cell should keep instability limited. The forecast calls for scattered showers and thunderstorms near the White Mountains, with only slight chances for showers (10-20%) over higher terrain elsewhere. Given the dry sub-cloud layer, the primary hazards will be lightning and powerful downdraft winds in the vicinity of any storms that do form.

In addition, heat is a concern at the lower elevations of the Grand Canyon as high temperatures at Phantom Ranch are forecast to exceed 110 degrees. As a result, an Extreme Heat Warning is in effect for the Grand Canyon below 4000 ft beginning 10 AM MST Monday and lasting through 8 PM MST Wednesday.

From Wednesday through the remainder of the work week, the high pressure cell is forecast to shift west of the state, resulting in a dry west to northwest flow. The current forecast calls for only low chances for precipitation near the White Mountains with high temperatures between 5-10 degrees above normal during this time. Heat remains a concern at the lower elevations of the Grand Canyon. In addition to the Extreme Heat Warning in effect through Wednesday, an Extreme Heat Watch remains in effect Thursday through Saturday.

AVIATION...Monday 06/00Z through Tuesday 07/00Z

VFR conditions, MVFR CIGS/VIS possible in FU at KFLG in the afternoon hours and KSEZ during the overnight and early morning hours. Winds light and VRB, becoming W/SW 10-15 kts with gusts 20-25 kts after 18Z. Gusty outflow winds possible in and around ISO -TSRA after 18Z, mainly INVOF KJTC/KSOW.

OUTLOOK...Tuesday 07/00Z through Thursday 09/00Z...VFR conditions, MVFR CIGS/VIS possible in FU at KFLG in the afternoon hours and KSEZ during the overnight and early morning hours. Winds W/SW 10-15 kts with gusts 20-25 kts each afternoon, becoming light and VRB overnight. Gusty outflow winds possible in and around ISO -TSRA each afternoon, mainly INVOF KJTC/KSOW.

FIRE WEATHER...Monday and Tuesday

Expect mainly dry weather and above-average temperatures. There is only a 10-20% chance for high based showers or thunderstorms over the higher terrain, although a 50% chance is forecast in the White Mountains. Aside from the White Mountains, wetting rains are not expected. Winds SW 10-20 mph and gusts 20-30 mph each afternoon. Minimum RH values 10-25% both days.

Wednesday through Friday...Above average temperatures continue. Isolated showers and thunderstorms mainly across the higher terrain in eastern Arizona each afternoon. Winds SW-W 10-15 mph with gusts 20-25 mph each day. Minimum RH values between 10-25% Wednesday, 5-20% Thursday and Friday.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning from 10 AM Monday to 8 PM MST Wednesday for AZZ006.

Extreme Heat Watch from Wednesday evening through Saturday evening for AZZ006.