textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Breezy to locally windy conditions return over the weekend with the strongest gusts across Southeast California and the Arizona high terrain.

- Elevated to critical fire weather conditions this weekend, particularly on Sunday for the Eastern Arizona higher terrain where a Red Flag Warning has been issued.

- Afternoon high temperatures 4 to 8 degrees above normal through Saturday will drop into a near to below normal range Sunday and early next week.

SHORT TERM /TODAY THROUGH SUNDAY/

Mid level WV imagery shows mostly quasi linear flow across the CONUS with a weak ridge over the southern Gulf states, and a weak shortwave trough over the Desert SW. This shortwave trough has been lingering over the region for the past couple of days and has been responsible for temperatures cooling in comparison to the beginning of the week, however afternoon highs remain 4-6 degrees above normal today and Saturday. Forecasted high temperatures today across the lower deserts will mostly be in the upper 90s with areas along the Colorado River Valley reaching triple digits. Saturday will be a case of deja vu with almost identical temperatures, with the exception of the Colorado River Valley cooling to under the century mark.

By Saturday afternoon a stronger troughing feature will dive down the western CONUS, starting from the Pacific NW states, and will extend down into the Great Basin region by Sunday evening, which will help cool the region by 4-6 degrees, or to below normal. Ensembles continue to show small discrepancies in the depth of this next system, while the GEFS and GEPS showed little change from the 00Z to 12Z run, the ECMWF has weakened in strength and depth in comparison to the 00Z run. However, there is enough consistency to be confident that widespread breezy conditions (15-25 mph gusts) will develop by Saturday afternoon, and more locally windy conditions in SW Imperial County where a wind advisory will begin to take effect Saturday starting 2PM PST and lasting through Sunday night. Winds will relax for most of the region during the overnight period before ramping back up Sunday afternoon when peak gusts are expected. Much of the lower deserts can expect peak gusts Sunday afternoon between 20-30 mph, the eastern higher terrain between 30-40 mph, and the SW portion of Imperial County between 45-55 mph.

Elevated fire weather concerns in the eastern higher terrain area will begin to develop Saturday afternoon due to increased wind speeds, reaching critical conditions by Sunday with the peak gusts, in conjunction with MinRH values near 10%. Due to these conditions a Red Flag warning has been issued for Southern Gila County and Tonto National Forest foothills starting 11 AM MST on Sunday.

LONG TERM /MONDAY THROUGH THURSDAY/

The aforementioned second, more potent piece of energy will rotate through just north of the area Sunday night into Monday, with several global models depicting an associated front being sent down the Lower CO River Valley, resulting in locally windy conditions for portions of Southeast CA Monday morning. This is the final anticipated impact from the system that deepens over the Western US this weekend, as negative height anomalies retreat to the north and east heading into the middle of the upcoming workweek. Monday is also shaping up to be the "coolest" of the next 7 days, with afternoon highs potentially struggling to reach 90F across the lower deserts, around 5F below daily normals. Forecast uncertainty remains moderate to high Monday onward, however, as the core of the weekend system departs northeastward, some measure of broad cyclonic flow over the Western US will remain and likely evolve into quasi-zonal flow through the middle of the week. Heights aloft will rebound closer to seasonal averages and so temperatures are expected to warm through the middle of the week, with dry conditions continuing.

AVIATION

Updated at 0500Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Some elevated wind gusts Saturday afternoon under clear skies will be the main aviation weather issue throughout the TAF period. The overall wind pattern will continue to exhibit the typical diurnal tendencies, although a period of southerly crosswinds is likely to materialize late Saturday morning/early afternoon before the eventual westerly shift. Elevated gusts upwards of 20-25 kts is likely to materialize Saturday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Periodic gusty winds under clear skies will be the main aviation weather issue throughout the TAF period. At KIPL, winds will generally maintain a westerly component while at KBLH winds will fluctuate out of the south to southwest. Overall wind speeds through Saturday morning will remain aob 12 kts before gusts pick up during the afternoon hours. At KIPL, peak gusts during the early evening hours may approach/exceed 30 kts.

FIRE WEATHER

Slightly above normal temperatures and generally light winds with typical afternoon upslope/upvalley breeziness will prevail today. A weather system will move onshore along the Pacific Northwest early Saturday and deepen over the Western US resulting in increased winds across the area this weekend. Afternoon/early evening wind gusts will commonly peak between 20-35 mph Saturday, with locally stronger gusts in Southeast CA. The strongest gusts by Sunday will likely be confined to Eastern AZ higher terrain, where gusts between 30-40 mph will be common. This has lead to elevated to locally critical fire weather conditions across the region both days, and a Red Flag Warning has been issued starting Sunday 11 AM MST in response. Afternoon minRHs mostly between 8-12% today will increase by several points this weekend, with values 7-15% areawide Saturday, then 10-20% Sunday. Overnight recoveries ranging from 25- 45% across the area and improving only slightly from there on Saturday and Sunday nights.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Red Flag Warning from 11 AM to 11 PM MST Sunday for AZZ133.

CA...Wind Advisory from 2 PM Saturday to 11 PM PDT Sunday for CAZ562.

Wind Advisory from 4 PM to 11 PM PDT Saturday for CAZ566.