textproduct: NWS Phoenix

UPDATE

18z Aviation Discussion.

KEY MESSAGES

- Well below normal temperatures expected today as afternoon highs struggle to reach eighty degrees across the lower deserts.

- Shower activity will persist through this morning, particularly across the foothills and higher terrain areas east of Phoenix.

- As high pressure builds across the western United States through the end of the week, a rapid warming trend to above normal temperatures is expected with triple digit highs materializing as early as Friday across the lower deserts.

SHORT TERM /Today through Thursday/

Latest water vapor satellite imagery shows an upper-level low centered across central CA. This upper-level low will continue to slowly trek east-southeastward throughout the day, reaching AZ early this evening. Out ahead of the low, a large moisture plume with subtropical connection is currently enveloping the eastern half of AZ with the latest SPC mesoanalysis showing PWAT values ranging between 0.7-1.0 across central and southern AZ. The combination of the moisture in place and the large scale forcing for ascent associated with the low has led to an area of light showers to break out across portions of southeast AZ, with activity extending northward to include the foothills and higher terrain areas just east of Phoenix. This activity is expected to persist throughout the morning hours across these areas. A few scattered showers may also develop across the Phoenix metro throughout the morning hours as well. For the most part, rainfall amounts should remain on the light side, with most of the Phoenix area seeing little to no accumulations while amounts of upwards of 0.25", locally higher in the most persistent bands, are likely across the higher terrain areas east of Phoenix. Activity will come to an end across most of the region by this afternoon as drier air gradually filters in.

With cold core of the low approaching the area heading into this afternoon, high temperatures today will be well-below normal as readings struggle to reach 80 degrees, in what will likely be the coolest day for the next 6 months. With some jet energy lingering overhead, breezy conditions will also continue today with afternoon/early evening gusts ranging between 15-30 mph, with the strongest gusts expected across Imperial County.

The main energy from the low will exit to the northeast on Wednesday and will be absorbed by another larger scale trough that will encompass most of the central and eastern CONUS. Meanwhile, a trailing piece of energy is expected to become cutoff from the main jet stream and form a new upper-level low across northern Sonora as a ridge of high pressure builds across the west coast. This feature will continue to gradually progress eastward through northern Sonora through Thursday with no sensible weather impacts expected for our region. As 500 mb height fields steadily rise with the building ridge over the west coast, temperatures will be on a rapid warming trend, warming into the middle 80s on Wednesday to middle 90s on Thursday across the lower deserts.

LONG TERM /Friday through Monday/

The main story heading into the long term period will be a prolonged heat episode that will materialize as triple digit highs will be in place for several days. As the aforementioned ridge continues to gradually build across the western CONUS, temperatures will continue to gradually warm with lower desert highs reaching the low 100s as early as Friday with widespread highs in the low to mid 100s continuing through the weekend. Heading into early next week, ensembles show the ridge intensifying a bit more as 500 mb height fields near 590dm. This will result in additional warming, with the latest NBM showing widespread lower desert highs in the mid to upper 100s. With temperatures heating up into the triple digits by the end of the week and beyond, widespread Moderate HeatRisk will be in place across most of the area. Thus, any vulnerable communities and those participating in outdoor activities will need to take the necessary heat precautions to avoid any heat-related illnesses.

AVIATION

Updated at 1720Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Aviation weather concerns will remain minimal through the TAF period. Much of the shower activity will remain confined to the far eastern periphery of the Phoenix Metro where cloud bases could remain around 5-6 kft for the next hour or two. Otherwise, expect generally a SCT to BKN CU deck with bases aoa 7 kft through this afternoon before eventual clearing out this evening. A west wind is favored through much of the forecast period, with intermittent afternoon and early evening gusts up to 20 kts. A later than normal easterly shift is expected at KPHX tonight.

Dependent on smoke generation by the wildfire in Buckeye, W-SW winds today may pull more smoke into central portions of Phoenix and could impact slantwise visibility, especially this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: West to southwest winds will be favored at both terminals through this evening, with intermittent gusts up to 20-25 kts during the afternoon and evening. A few gusts may reach 30 kts at KIPL later this evening. FEW to SCT cumulus clouds based around 7-8K ft AGL are expected through the day and will clear this evening.

FIRE WEATHER

Below normal temperatures will prevail today and Wednesday across the region as readings across the lower deserts will top out in the upper 70s today and middle 80s Wednesday. Scattered shower activity will continue through this morning, particularly across the higher terrain areas east of Phoenix. Total rainfall amounts will generally average under 0.25" across most areas, with locally higher amounts in the more persistent rain bands. Breezy conditions will continue for today with afternoon/early evening gusts peaking at 15-30 mph. MinRHs for this afternoon will remain elevated with values bottoming out between 20-40%. Lighter winds as well as much warmer temperatures and lower humidities are then forecast for the latter half of the week and beyond as high pressure builds back into our region.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.