textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Above normal temperatures will continue over the next several days, with some lower desert locations reaching 110 degrees by this weekend.

- An increase in moisture by the end of the week and weekend will lead to slight chances of showers and storms, mainly during the early morning and overnight periods.

SHORT TERM /Today through Friday/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals a broad trough of low pressure encompassing much of the interior western and central CONUS while a ridge of high pressure begins to expand over TX and NM. A Pacific low pressure system is also situated off the coast of the Baja California which will provide a focus for enhanced moisture and potential shower activity by this weekend. At least for the near term, conditions will remain hot and dry across the Desert Southwest as ridging aloft continues to expand westward and 500 mb hghts over the forecast area remain around 588- 590 dam. These positive hght anomalies will result in lower desert highs topping out around 103-108 degrees this afternoon, or between 3-5 degrees above normal. 500 mb hghts are not expected to change much through the end of the week, and thus there will be very little day-to-day variation in temperatures.

By the end of this week, the aforementioned weak upper-level low will continue to drift northward just off the coast of the Baja Peninsula while the ridge of high pressure strengthens over the Southern Plains. The positioning of both of these features will cause the flow aloft over our forecast area to shift out of the south, drawing moisture into the region Thursday night into early Friday. In response, PWAT values are expected to increase above 1.0" across much central and southern AZ. In addition to the increasing moisture, a vortmax moving out of N MX into AZ will provide enough upper-level ascent to produce isolated to widely scattered elevated showers across portions of southwest and south-central AZ on Friday morning. NBM PoPs still range from 15-20% across the lower deserts and given the lack of deep moisture in place, most of the showers that develop will high-based and thus rainfall accumulations will be very minimal (upwards of 0.10" at best).

LONG TERM /Saturday through Tuesday/

Moisture levels will remain well-above normal (200-250% of normal), with PWATs hovering between 1.0-1.4", during the weekend. The combination of the moisture and daytime heating will favor afternoon convection across the AZ high terrain. The limited instability with large T/Td spreads and dry sub-cloud layer will favor dry lightning and gusty outflow winds versus heavy rainfall, as is typical with convective activity in June. There are some indications from guidance of some elevated showers and isolated storms materializing and affecting portions of the lower deserts Saturday morning, likely due to another lobe of upper-level vorticity moving through. Heading into early next week, as another longwave trough builds across much of the central CONUS, west to northwest flow will usher in much drier air into the region and scour out most of the moisture.

With upper-level heights remaining stagnant throughout the weekend and early next week, temperatures are expected to remain steady state with afternoon highs each day in the upper 100s across most of the lower desert communities, with some areas, especially the western deserts, touching 110 degrees. Overnight lows will be above normal with most locations bottoming out in the upper 70s and low 80s.

AVIATION

Updated at 2310Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather issues will exist through Thursday evening with a gradual increase in thin cirrus decks. Wind speeds and timing of directional shifts will follow a persistence type forecast with gusts 15-20kt limited in time and space Thursday afternoon.

FIRE WEATHER

Temperatures will remain around 3-5 degrees above normal over the next several days with lower desert highs approaching 110 degrees by this weekend. Dry conditions will continue through Thursday with relative humidity bottoming out around 5-15%. Low level moisture will improve beginning Friday and through this weekend with minimum humidity largely above 15% and overnight recoveries improving from poor to fair. With the increasing moisture will also come increasing chances for at least isolated thunderstorms across the AZ high terrain over the weekend, with gusty outflow winds and dry lightning potentially leading to natural fire starts being the main hazards. The overall wind pattern will remain diurnal with speeds at or below 15 mph and limited afternoon upslope gustiness.

PSR WATCHES/WARNINGS/ADVISORIES

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