textproduct: NWS Phoenix

UPDATE

Updated 12Z Aviation Discussion.

KEY MESSAGES

- Dry conditions along with temperatures around 10 degrees above normal will persist today.

- An Extreme Heat Warning remains in effect for western Imperial County and Yuma through this evening.

- A much more unsettled weather pattern is expected this weekend through early next week as a series of weather systems will affect the region resulting in much cooler temperatures, breezy to windy conditions, and heightened rain chances.

SHORT TERM /TODAY THROUGH SATURDAY/

Latest objective analysis shows a ridge of high pressure still prevailing across the region. However, the ridge will be in a weakening phase throughout the day as a troughing pattern begins to materialize along the west coast. Under the influence of the ridge, another day of dry conditions along with well-above normal temperatures can be expected as lower desert highs once again reach into the triple digits with readings ranging between 99-103 degrees across south-central AZ and 103-107 degrees across the western deserts. El Yuma and El Centro will once again be within a couple of degrees of daily records, with areas of Major HeatRisk still continuing. Therefore, Extreme Heat Warnings remain in effect for the Imperial Valley and Yuma areas through this evening.

Big changes are then on tap starting on Saturday as a large northern stream trough dives into the Pacific Northwest while, across the eastern Pacific, Tropical Storm Rachel will recurve northeastward towards the northern Baja Peninsula as it is picked up by a cutoff low. South to southwest flow aloft will advect significant moisture into the region as PWATs surge above 200% Saturday afternoon/evening according to the EPS and GEFS. This moisture surge in addition to increasing upper-level forcing from the approaching trough will result in areas of scattered showers and isolated thunderstorms breaking out starting Saturday afternoon and continuing through Saturday evening through the overnight. Latest hi-res guidance shows activity breaking out first across central and southern AZ with another area of activity materializing further west across portions of southwest AZ and southeast CA. Gusty winds and brief periods of moderate to locally heavy rainfall will be the main threats. With the increase in cloud cover and heights aloft lowering from the approaching trough, afternoon high temperatures will be about 10 degrees cooler than today as readings top out in the low to mid 90s across much of the lower deserts.

LONG TERM /SUNDAY THROUGH THURSDAY/

The more impactful weather is expected on Sunday as the remnants of Rachel move through. According to the latest official forecast track from the National Hurricane Center, Rachel is expected to accelerate north-northeastward along the vicinity of the Lower Colorado River Valley. An area of heavy rainfall is likely to follow along and just to the west of where Rachel tracks. Even though the official NHC forecast has the system tracking along the vicinity of the Lower Colorado River Valley suggesting that the heavy rainfall may fall across portions of southeast CA, there is a lot of spread amongst the guidance in the track as some solutions have Rachel tracking near the southern CA coast whereas other solutions have the system tracking as far east as southwest AZ. Therefore, the rainfall forecast is still highly volatile and could still significantly shift depending on the eventual track. The greater impact with Rachel will be the potential for strong winds as a belt of strong 850 mb winds in excess of 40-50 kts is likely to set up along the eastern quadrant of Rachel with much of the guidance showing gusts exceeding 40-50 mph across much of southwest into south-central AZ, especially early Sunday morning through Sunday afternoon. Wind gusts this high could certainly result in areas of blowing dust across the dust prone areas. Given the strong wind potential, a wind advisory has been hoisted from eastern Riverside and Imperial Counties through all of southwest and south-central AZ. In addition to the wind threat, there will also be the potential along the eastern quadrant for multiple rounds of widely scattered showers and storms to materialize. There is a potential for some of these storms to reach severe levels given that strong vertical shear in excess of 50 kts will be present, however, the severe potential will be dependent on how much instability will be present.

Even though the remnants of Rachel will be well north of the area by Sunday evening, unsettled conditions will continue right through early next week as the main west coast trough moves through the region bringing additional chances for showers and isolated thunderstorms, with the highest chances across the foothills and higher terrain areas to the north and east of Phoenix from upslope flow. Thereafter, drier and quieter weather is expected by the middle of the week as the main trough axis lifts to the northeast.

Under the presence of the troughing pattern, well-below normal temperatures are expected during the first half of next week with lower deserts highs going from the low to mid 80s on Sunday to mostly 70s Tuesday and Wednesday. Early morning lows will also take a tumble with the coolest morning expected on Wednesday as temperatures are expected to bottom out in the 50s across much of the region with even some 40s across the higher terrain areas.

AVIATION

Updated at 1140Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant weather concerns will exist through the current TAF period as midlevel cigs gradually develop. Confidence is excellent that east winds will prevail well into this afternoon with potentially a few late morning gusts 15-20kt, albeit spatially and temporally limited. Very low confidence exists regarding wind directions later this afternoon and early evening where some terminals may obtain a light southerly/southwesterly cross runway component, or potentially become light and variable for a short time. Areas of virga and possibly a few isolated SHRA are expected to develop, further complicating wind directions. Regardless, directions should quickly switch back to E/SE by the mid evening timeframe.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through the current TAF period under gradually increasing midlevel cloud decks with bases aoa 10 kft. Wind speeds will be aob 10 kt at both terminals. At KIPL, current westerly winds will go southerly this afternoon then back westerly this evening. At KBLH, current northwesterly winds will go southerly late this morning, southwesterly this evening, then back southerly overnight.

FIRE WEATHER

Dry conditions along well-above normal temperatures will continue today as lower desert highs reach into the triple digits. Afternoon MinRHs today will range between 15-25%. Winds today will remain mostly light across much of the area. A much more unsettled weather pattern then develops over the weekend as increasing moisture associated with the remnants of Tropical Storm Rachel brings increasing rain chances. The chances for showers and storms increase starting Saturday afternoon/evening and continues into Sunday with a greater than 50-70% chance of wetting rainfall area wide. Winds will also increase significantly, especially late Saturday night through Sunday with widespread gusts exceeding 30-40 mph. With the increasing moisture and cooler temperatures, MinRH values will increase from 25-40% Saturday to 45-70% on Sunday along with good to excellent overnight recoveries. Another weather system will bring additional chances for wetting rainfall early next week, mainly for the eastern districts, before quieter weather settles in by the middle of the week.

CLIMATE

Record highs: Date Yuma El Centro ---- ---- --------- Oct 9 106 in 2024104 in 1996

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ532.

Wind Advisory from 2 AM to 5 PM MST Sunday for AZZ530>533-535- 536.

Wind Advisory from 8 AM to 5 PM MST Sunday for AZZ534-537>563.

CA...Extreme Heat Warning until 8 PM PDT this evening for CAZ566-567.

Wind Advisory from 2 AM to 5 PM PDT Sunday for CAZ564-565-569- 570.