textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Well above normal temperatures will persist through the end of the work week as lower desert highs top out in the triple digits.

- An Extreme Heat Warning remains in effect for portions of southeast California and southwest Arizona today through Friday as temperatures warm to near record levels, resulting in areas of major HeatRisk.

- Dry conditions will persist through at least the end of the workweek before a much more unsettled pattern arrives by the weekend with much cooler temperatures and increasing rain chances.

SHORT TERM /TODAY THROUGH FRIDAY/

Latest objective analysis shows a broad ridge of high pressure over the Desert Southwest with a very weak disturbance near the AZ and UT border. This disturbance combined with enough mid-level moisture may help spark a few showers mainly over the White Mountains this afternoon and Thursday afternoon as it moves southeastward through the Four Corners. Otherwise, with high pressure in control, dry conditions will prevail through much of the area through the rest of the week.

The main story through the end of the week will be the well-above normal temperatures. 500 mb heights today and Thursday will range between 586-590 dam with 850 mb temperatures peaking between 25-27C. This will translate to surface high temperatures surpassing the triple digits across much of the lower desert communities with readings ranging between 98-103 degrees across south-central AZ and 104-108 degrees across the western deserts. With temperatures 10-13 degrees above normal and nearing daily records in Yuma and El Centro, areas of Major HeatRisk are expected and thus Extreme Heat Warnings are in effect starting today for the Imperial Valley and Yuma with the warning expanded to include the Lower Colorado River Valley and along I-8 in Yuma County for Thursday when the hottest temperatures are expected. By Friday, even though the ridge will weaken as a broad troughing pattern begins to impinge into the west coast, low-level thermal profiles will still remain warm enough for afternoon highs to once again surpass the triple digits, with readings ranging between 98-101 degrees across south- central AZ and 104-107 degrees across the western deserts. With areas of Major HeatRisk continuing in Yuma and the Imperial Valley, the Extreme Heat Warnings will remain in effect for these areas.

LONG TERM /SATURDAY THROUGH TUESDAY/

A significant pattern shift is still anticipated this weekend through early next week as the most of the deterministic and ensemble model guidance continues to show a broad troughing pattern setting up across much of the western third of the CONUS. Guidance continues to show a northern stream trough diving into the Pacific Northwest on Saturday before sinking southward over CA on Sunday. Meanwhile, a more southern stream shortwave trough is likely to move into the subtropical eastern Pacific and pick up the remnants of Hurricane Rachel as it moves northeastward and phases with the west coast trough. As this whole pattern evolution takes shape, the increasing south to southwesterly flow aloft will advect moisture into the Desert Southwest starting Saturday, with most of the moisture at first confined in the mid to upper- levels before better low-level moisture moves in on Sunday as the remnants of Rachel gets pulled in. Coincidentally, rain chances will be on the increase as early as Saturday afternoon across south-central AZ before peaking Sunday into Monday across much of the region with the arrival of better low-level moisture. There continues to be a great deal of uncertainty in rainfall amounts as it will be dependent on the overall track of the remnants of Rachel and how it interacts with the west coast trough. It will likely take at least another couple of days to get a better idea on the rainfall perspectives as guidance comes into better agreement on how the overall pattern shapes up. In addition to the rainfall potential, winds will be another hazard to contend with as the combination of the height falls from the trough and remnant circulation of Rachel will likely result in widespread breeziness.

As 500 mb heights lower with the approaching trough along with the increasing cloud cover and moisture, much cooler temperatures are expected this weekend into early next week. Afternoon highs across the lower deserts will go from mid to upper 90s on Saturday to low to mid 80s by Monday and may potentially drop even lower on Tuesday with many locations stuck in the low 80s.

AVIATION

Updated at 1110Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No weather concerns will exist through the TAF period under a few midlevel cloud decks that will clear this evening. Confidence is very good that the trends in light winds and timing of directional shifts will be nearly identical to the past 24 hours. Periods of light and variable conditions are expected, especially preceding wind shifts.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather concerns will exist through the TAF period under clear skies. Extended periods of light and variable winds will be common with a tendency towards for northerly component backing to a west trajectory after sunset. Wind speeds will be aob 7 kt.

FIRE WEATHER

Dry conditions along well-above normal temperatures will continue through the end of the work week as lower desert highs reach into the triple digits. Winds through Thursday will generally be light and diurnally driven before increasing Friday into this weekend. Afternoon MinRHs through the end of the work week will range between 15-25% with fair to good overnight recoveries (35-60%). A more unsettled weather pattern is expected this weekend through early next week as a weather system affects the area with much cooler temperatures along with increasing moisture and chances for wetting rainfall.

CLIMATE

Record highs: Date Yuma El Centro ---- ---- --------- Oct 7 111 in 2024105 in 1991 Oct 8 107 in 1996 106 in 1996 Oct 9 106 in 2024104 in 1996

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM this morning to 8 PM MST Friday for AZZ532.

Extreme Heat Warning from 10 AM to 8 PM MST Thursday for AZZ530- 536.

CA...Extreme Heat Warning from 10 AM this morning to 8 PM PDT Friday for CAZ566-567.

Extreme Heat Warning from 10 AM to 8 PM PDT Thursday for CAZ569- 570.