textproduct: NWS Flagstaff

SYNOPSIS

Isolated thunderstorms are possible this afternoon over the higher terrain, especially over the White Mountains. Otherwise, as high pressure builds over Arizona today, hot daytime temperatures are expected through the weekend, and are expected to reach the warmest readings so far this year. Monsoon moisture is then expected to start moving back into the region during the second-half of next week as the high begins to weaken and shift into a more favorable position.

DISCUSSION

High pressure is building over Arizona today and will help to diminish Monsoon activity as subsidence increases under the ridge and drier air gradually works its way into the region. Observations from this morning still show dewpoints in the low to mid 50s across the higher terrain, especially from Flagstaff southward to the White Mountains. This lingering moisture may still support isolated thunderstorms over the higher terrain this afternoon. Storm motion is expected to be east- northeast around 5 mph, while outflow from thunderstorms may introduced a slight southward drift. The slow storm motion will will keep a low-end flash flood threat in place, especially over burns scars if thunderstorms develop overhead. This somewhat suppressed period of monsoonal activity is forecast to continue through at least the weekend. Showers and thunderstorms will not fully shut off each day, but remain isolated with the best coverage in the White Mountains.

The primary hazard over the next few days will be heat. With the decrease in moisture and above normal heights at 500mb, temperatures will be the warmest of the year so far for all of northern AZ. As a result, a variety of heat headlines will be in effect. An Extreme Heat Warning for the Grand Canyon below 4000 ft will remain in effect until Sunday with daytime temperatures up to 110-117 F. Additional Extreme Heat Warnings will be in effect today through Sunday for Glen/Marble canyon and low elevation areas south of the Mogollon Rim, where temperatures will approach or exceed 110 F. Lower elevations of northeastern Arizona will have a Heat Advisory on Saturday and Sunday, with daytime temperatures up to 100-105 F.

By the early to middle part of next week, ensemble guidance is leaning towards the high weakening and shifting east. This would allow monsoonal activity to increase again. There is still some uncertainty on the exact timing and nature of this transition, and there is potential that heat headlines will be extended past Sunday. Right now the forecast is leaning toward hot temperatures with diminished monsoonal activity continuing into Monday and potentially Tuesday, before Monsoon moisture starts to make a more noticeable return around Wednesday.

AVIATION...Saturday 01/00Z through Sunday 02/00Z

VFR conditions. ISO -SHRA/-TSRA INVOF a KFLG-KJTC line through 03Z, and again after 19Z mainly INVOF KSOW/KJTC. Gusty outflow winds 30-40 kts possible in and around TS. Otherwise, winds VRB 5-10 kts.

OUTLOOK...Sunday 02/00Z through Tuesday 04/00Z...VFR conditions. ISO -SHRA/-TSRA each afternoon INVOF KSOW/KJTC. Gusty outflow winds 30- 40 kts possible in and around TS. Otherwise, winds VRB 5-10 kts.

FIRE WEATHER...Saturday and Sunday

Hot with temperatures 10-15 degrees above average all weekend. Isolated showers and thunderstorms each afternoon/evening over the White Mountains. Winds light and variable 5-15 mph. Minimum RH values as low as 7-15% in the deserts, 15-25% mountains.

Monday through Wednesday...A slight cooling trend but still 5-10 degrees above average. Isolated showers and storms over the White Mountains Monday, with coverage increasing and expanding westward on Tuesday and Wednesday. Daytime winds generally SW-W at 5-15 mph each day. Minimum RH values 10-25% Monday and Tuesday, 10-30% Wednesday.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST /9 PM MDT/ Sunday for AZZ005- 006-018-037-038.

Heat Advisory from 10 AM MST /11 AM MDT/ Saturday to 8 PM MST /9 PM MDT/ Sunday for AZZ009-010-012>014-040.