textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- The chances for showers and thunderstorms will continue through tonight, with the highest potential mostly focused over the foothills and higher terrain areas north and east of Phoenix.

- After drying out temporarily this weekend, rain chances will return to the region late Sunday into early next week as tropical moisture gets pulled northward into the Desert Southwest.

- Near to slightly above normal temperatures will persist through the weekend before noticeably cooling early next week.

SHORT TERM /Today through Friday/

An extensive area of showers and storms was ongoing through much of the morning hours, especially to the south and west of the Phoenix Metro Area across much of western Maricopa county extending into portions of La Paz and Yuma Counties. All of this activity was associated with a mid-level low currently spinning over southern AZ. This activity should gradually weaken heading into afternoon hours. The mid-level low is expected to move northward into central AZ by this evening. However, despite there being good ascent, the extensive cloud cover and rainfall activity from earlier has overworked the atmosphere to the point that it is likely that little to no activity, with the exception of portions of Gila County, will materialize through the rest of this afternoon through early this evening as depicted by the latest runs of the hi-res guidance. By late this evening into the overnight period, however, as the mid-level low migrates into central AZ, the orographic and synoptic lift will combine to lead to an area of showers and storms forming mostly across the foothills and higher terrain areas to the north and east of Phoenix with only isolated coverage across the lower deserts. As the mid-level low lifts to the northeast on Friday, westerly flow will encroach much of the region and advect much drier air, essentially ending rain/storm chances.

Given the extensive cloud cover still in place, afternoon high temperatures across the south-central AZ lower deserts, in particular, are likely to struggle to reach 90 degrees with many locations staying in the 80s. Across the western deserts, lesser cloud cover with more sunshine will cause readings to top out in the mid to upper 90s. Mostly clear skies on Friday should allow temperatures across south-central AZ to rebound to more seasonal levels, in the mid to upper 90s, with slightly warmer readings into the lower 100s across the western deserts.

LONG TERM /Saturday through Wednesday/

Dry westerly flow is expected to persist through at least Saturday with large scale troughing remaining over the Pac NW while the subtropical ridge slowly shifts southwestward from east TX into the interior of MX. Due to the presence of the ridge to our east, 500 mb hghts are expected to peak around 586-588 dam Saturday afternoon. This will result in highs topping out between 100-105 degrees across the lower deserts (4-6 degrees above normal) under mostly sunny skies and zero chance of rain. From Sunday into early next week, there does look to be a significant degree of cooling as tropical moisture arrives and rain chances increase. Highs will likely fall below 100 degrees across the lower deserts on Sunday and continue to cool to the upper 80s and lower 90s Monday through Wednesday.

Our attention then turns to the tropical Pacific Sunday into early next week where potential moisture from two weakening hurricanes (Polo and Odalys) will come into play. There is still a high degree of uncertainty as to a) how far north the residual moisture will be shed out ahead of these decaying storms, and b) where the plume(s) of moisture will set up. Another major question mark will be just how deep and progressive a developing trough of low pressure will be over the Intermountain West. All of these factors will have to line up perfectly for our forecast area to get significant rainfall. Both the GEFS and EPS are telling a different story with varying degrees of moisture and timing and intensity of said trough which is really complicating things. The latest NHC track for Hurricane Polo shows the storm making landfall along the coast of the Baja California by Monday which if aligned with the passage of the aforementioned trough would draw a large plume of moisture into interior MX and and much of AZ. NBM PoPs have already increased to around 20-30% with an initial band of moisture on Sunday, but with the main lift arriving on Monday, PoPs are now widespread 30-60% across our forecast area. The remnant tropical moisture may linger into Tuesday before fully exiting the region on Wednesday. It is also worth pointing out that some ensemble members are showing significant rainfall totals in excess of 1-2" across southcentral AZ Monday-Tuesday but there is still significant spread between members. Therefore, we will likely have to wait until this weekend for things to become more clear.

AVIATION

Updated at 0005Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Cloudy conditions with 6-12 kt westerly winds are expected through the next few hours. Forecast confidence degrades heading into the overnight hours. An area of low pressure will move through tonight and may generate additional SHRA with embedded TSRA, but confidence is low. Any rain development will likely influence the wind directions. Otherwise, a NW-N wind component is favored through the night. Any rain should dissipate and move off to the east by 12-15Z Friday morning, after which conditions will return to a more traditional diurnal tendency, with light winds veering to W-SW in the afternoon. Brief CIGs down to 6K ft AGL are possible in SHRA/TSRA, with mid and high CIGS more common through the night. FEW to SCT cumulus around 7K ft AGL are expected Friday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather impact are expected during the next 24 hours. A 5-10 kt SW wind is expected for the next few hours at KIPL before turning VRB and light SE heading into Friday. At KBLH, a SSW-SSE wind is favored through most of the period, with speeds mostly 5-10 kts and periods of VRB. SCT to BKN skies will be present over the region through early tonight, followed by clearer skies heading into Friday.

FIRE WEATHER

Widely scattered showers and thunderstorms will be possible through tonight, mainly focused over the higher terrain of the eastern districts. Localized gusty and erratic winds will be possible in the vicinity of any storm that develops. Rain chances will decrease Friday into this weekend before much better chances for wetting rainfall arrives early next week. MinRHs will range from 25-60% today with a gradual decrease to around 15-30% region-wide Saturday. Significant moisture return is expected across the eastern districts by Monday which will keep RH values above 40% with excellent overnight recoveries. Winds will generally follow diurnal patterns with speeds around 10-15 mph with typical afternoon gusts in the upper teens.

PSR WATCHES/WARNINGS/ADVISORIES

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