textproduct: NWS Flagstaff

SYNOPSIS

Warm temperatures, mostly dry conditions and breezy afternoon winds are expected through the rest of the week. Isolated chances for showers or thunderstorms will continue across the higher terrain through Thursday.

DISCUSSION

High pressure aloft will linger over northern Arizona through Thursday before a drier air mass moves across the southwest United States starting Friday and lasting through early next week.

This afternoon through Thursday...The axis of high pressure aloft remained stationed from northwest to southeast across northern Arizona with little change in this general pattern through Thursday. The flow south of the high pressure axis will remain generally south to southwest. Consequently, moisture will continue to linger from around the Mogollon Rim southward with isolated showers and thunderstorms anticipated with daytime heating. Further north, the flow around the high will continue to drag in drier air from the west to northwest resulting in near zero chances for any showers or storms north of the Interstate-40 corridor. Winds will remain surprisingly gusty in response to regional-scale mountain/valley flow that develops with daytime heating (surface winds tend to flow from the lower desert to the Great Basin/Intermountain West with daytime heating). Winds will generally moderate overnight where weak inversions set in. However, downwind of terrain features, where the flow can be disrupted, locally gusty winds will persist through the night. Hot temperatures will continue with many lower elevations stations hovering around 100 degrees. At Phantom Ranch and elevations below 4000 feet in the Grand Canyon, highs of 108-112 degrees are forecast with an Extreme Heat Warning in effect through Thursday.

From Friday into early next week...A weak trough moves over the southwest United States from the west. The arrival of the trough will push a drier west to southwest flow across all of northern Arizona spelling the end of thunderstorm chances. In addition, the trough will deliver a bit cooler temperatures. Pressure gradients associated with the trough and regional diurnal flow will support afternoon breezes of 10-20 mph each day.

AVIATION...Wednesday 17/18Z through Thursday 18/18Z

Mainly VFR conditions. Isolated -SHRA/-TSRA, mainly along/south of a KFLG- KINW-KSJN line. Erratic gusts 30-40 kts in and near TSRA. Outside of storms, Winds W to SW 15-20 kts with gusts 25-30 kts, becoming light 5-15 kts overnight. Overnight winds remaining elevated just northeast of the terrain features.

OUTLOOK...Thursday 18/18Z through Saturday 20/18Z...Mainly VFR conditions. Isolated -SHRA/-TSRA between 18Z-00Z Thursday, mainly along/south of a KFLG-KSJN line. Winds SW to W 10-20 kts with gusts 25-30 kts each day. Overnight winds remaining elevated just northeast of the terrain features.

FIRE WEATHER...Thursday and Friday

Warm temperatures and mostly dry conditions expected. Isolated showers and thunderstorms Thursday afternoon, mainly over the White Mountains. Localized downpours and wind gusts to 40 mph are possible with any thunderstorms. Expect general west to southwest winds at 10-20 mph with gusts 20-30 mph on Thursday, becoming primarily southwest on Friday. Winds remain elevated each night downwind of terrain features. Minimum RH around 10-20% each day. Near-critical fire weather conditions possible across far northern and eastern Arizona each day.

Saturday through Monday...Dry, breezy, and seasonably warm weather expected. Southwesterly winds at 10-20 mph with gusts to 25-30 mph Saturday, decreasing on Sunday and Monday to around 10-15 mph with gusts up to 25 mph. Minimum RH drops to 5-15% each afternoon. Near- critical fire weather conditions possible across northeast Arizona each day.

FGZ WATCHES/WARNINGS/ADVISORIES

Extreme Heat Warning until 8 PM MST Thursday for AZZ006.