Area Forecast Discussion

SYNOPSIS

A dry front moving into the area from the east will result in windy conditions across much of Southeast Arizona today. Although the strongest sustained winds may be blocked in some locations by the terrain, east to southeast aligned valleys such as the Gila River Valley are the most likely to experience impactful winds. Wind gusts to 45 mph across the Gila River and San Simon valleys may result in areas of blowing dust. In addition to the winds, modest mid-level moisture moving into the region will result in a slight chance of mainly dry thunderstorms this afternoon and early this evening. Warm and breezy conditions are anticipated for much of the upcoming work week.

DISCUSSION

The upper-level weather pattern this morning is defined by a shortwave ridge axis extending from the Big Bend in Texas NW to the Four Corners region and a weak trough axis extending along the southern California and Baja Peninsula coast. The surface high pressure system that built down the front range of the Rockies into eastern New Mexico/northern Texas has since setup a strong pressure gradient/frontal boundary over the eastern half of Southeast Arizona this morning. This backdoor front won't stick around for too long though, as the gradient will rapidly relax this afternoon into this evening as the surface high shifts east.

Although the strongest sustained winds may be blocked in some locations by the terrain, those east to southeast aligned valleys are the most likely to experience impactful winds today. In general, expect east to southeast winds 20-30 mph with gusts to 35-40 mph. The strongest winds will be across the Gila River and San Simon valleys, where southeast winds of 25-30 mph with gusts to 45 mph are possible. Areas of blowing dust will accompany these winds, especially across the more dust-prone areas within the San Simon Valley which impact portions of Interstate-10 between Willcox and San Simon.

In addition to the potential for blowing dust, this ELY low-mid level flow will import just enough mid-level moisture into the eastern portions of Southeast Arizona for a slight chance (10-15 percent) of mainly dry thunderstorms this afternoon into the early evening. These storms will produce little to no rainfall and are capable of producing erratic and gusty outflows to 40-45 mph due to the evaporating downdrafts.

Otherwise, the GEFS and ECMWF ensemble members are in good agreement with the evolution of the upper pattern next week. It looks like a trough of low-pressure will develop along the West Coast through the middle of next week, then as a high- amplitude ridge to the west of this trough builds into the Pacific Northwest, a more progressive and open mean trough develops across the Great Basin and Desert Southwest late next week into next weekend. This pattern forces individual shortwaves to rapidly pass to our north, keeping us dry along the southern periphery as they zip on past with periods of breeziness.

AVIATION

Valid through 20/12Z. Increasing mid-to-high level clouds this morning with FEW-SCT clouds 12-15k ft AGL and SCT- BKN 20k ft AGL. SFC winds east-southeast 15-20 kts with gusts up to 30 kts through 19/22Z gradually decreasing to around 10 kts with gusts to 20 kts this evening. Areas of the Gila River Valley including KSAD will see the strongest winds through this afternoon with southeast winds of 22-26 kts and gusts to 40 kts. KSAD may also see localized BLDU with visibility down to 3-5SM. A period of LLWS possible at KTUS through 19/14Z before surface winds increase as southeasterly wind at 1500-2000 ft AGL increases to 40 kts. Aviation discussion not updated for TAF amendments.

FIRE WEATHER

A dry front moving into the area from the east will result in windy conditions across much of Southeast Arizona today. Although the strongest sustained winds may be blocked in some locations by the terrain, east to southeast aligned valleys such as the Gila River Valley are the most likely to experience impactful winds. Expect east to southeast 20-foot winds 20-25 mph with gusts up to 40-45 mph, with strongest winds in areas exposed to east-southeast flow (especially through the Gila River Valley), mountain gaps, and the lee side of the higher terrain. The pressure gradient will loosen with winds diminishing through the late afternoon and evening hours. Although minimum RHs between 15-20 percent are anticipated in the valleys east and northeast of Tucson Sunday, we may see brief near critical Fire Weather conditions develop.

In addition to the winds, a modest increase in mid-level moisture will result in a slight chance (10-15%) chance for mainly dry thunderstorms over the higher terrain this afternoon into the early evening. Little- to-no rainfall is expected. A stray lightning strike combined with gusty and erratic outflow winds could result in a new wildfire start and rapid growth with abundant dry fuel. Much lighter winds are expected Monday with a lingering chance of thunderstorms in the White Mountains in the afternoon. Passing systems to the north will keep southeastern Arizona dry but breezy each day through the remainder of the work week.

TWC WATCHES / WARNINGS / ADVISORIES

Wind Advisory from 3 AM to 1 PM MST Sunday for AZZ503>507. Wind Advisory until 1 PM MST Sunday for AZZ508-509.