textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion

KEY MESSAGES

- Extreme Heat Warnings remain in effect through Saturday across much of the area.

- Lower desert highs in excess of 110 degrees and overnight lows in the 80s to lower 90s will be common this week, resulting in Major to Extreme Heat Risk.

- Monsoon storm activity will remain isolated in coverage through Friday before a significant increase in moisture arrives this weekend, promoting cooler temperatures and better overall rain chances.

SHORT TERM /TODAY THROUGH THURSDAY/

Current GOES wv imagery and 500 mb streamline analysis reveals an unseasonably strong ridge of high pressure situated over the AZ/NM border. 500 mb hghts are now up to 598 dam which is at the climatological maximum for late August. Latest ACARS soundings present a well mixed boundary layer (up to 600 mb) under full sunshine across southcentral AZ which is causing temperatures to soar above 110 degrees in most desert locales. Temperatures will peak around 113-117 degrees across the lower deserts this afternoon. If Sky Harbor reaches the forecast high of 117 degrees, it would tie the record high for today's date last set in 2011. Farther west across SE California and SW Arizona, cloud cover left over from earlier shower activity has stunted warming slightly, but high temperatures are still expected to reach around 110-116 later this afternoon. Storm chances will remain minimal through the rest of today and tonight with only around a 10% chance of an isolated storm or two in S Gila County and far SW Imperial County. Some mid-lvl moisture from the E Pacific is beginning to advect into the region which will cause cloud cover to increase tonight and into Thursday morning. If clouds are thick enough to prevent ample radiational cooling, then Phoenix may set a new record warm low (current record is 91 degrees).

On Thursday, the robust subtropical high will still be stationed over the AZ/NM border with only a slight decrease in 500 mb hghts to around 595-596 dam. This will allow temperatures to decrease by a few degrees, but most lower desert communities will still see highs around 108-116 degrees, or near record levels. Moisture levels will remain quite low on Thursday afternoon with PWAT values ranging from 1.2-1.4" and mixing ratios around 6-8 g/kg. The overall lower moisture content will keep convection isolated and mainly confined to the AZ high terrain, although high-res models do indicate a slight uptick in shower/storm activity across E and SE AZ Thursday afternoon. If enough convection develops over the higher terrain, there may be a more well defined outflow that descends into the lower deserts. Latest HREF probabilities for winds greater than 35 mph is around 10-30% in Maricopa County and 30-50% in Pinal County. Other than a potential outflow, the chances for any additional storm activity in the lower deserts will be very low (10% or less).

LONG TERM /FRIDAY THROUGH TUESDAY/

The subtropical ridge is still expected to weaken and shift back eastwards by Friday according to ensembles. This is due to a troughing pattern pushing into the NW CONUS and along the West Coast. As the trough pushes eastward, PWATs will begin to improve, reaching near 1.5"-1.7" by Saturday and lasting through at least the weekend. Mixing ratios will also significantly improve going from mid week's 6-8 g/kg to 10-12 g/kg by this weekend, generating better support for storm formation in the lower deserts. With that being said NBM/WPC continue to show PoPs over the weekend between 20-35% across South-Central AZ, and now even up to 50% in the eastern high terrain. WIth these PoPs the NBM/WPC QPE totals over the weekend are forecasted between 0.10"-0.25" to locally higher in the higher terrain areas. Continued monitoring of this system will be needed but models continue to show support for activity developing this weekend. In other good news, temperatures are forecast to drop closer to late August normals by Sunday and into early next week as falling midlevel heights and an increase in moisture/cloud cover over the eastern CWA support a cooling trend (more pronounced across South-Central AZ).

AVIATION

Updated at 0505Z.

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

No major aviation concerns will exist through Thursday evening under SCT-BKN cloud decks. Winds are expected to follow light and diurnal trends with periods of VRB conditions during the overnight hours. Some VCSH cannot be ruled out during the mid to late morning timeframe, but forecast uncertainty remains too high to warrant inclusion of any rainfall mention in the TAFs. If any SHRA were to occur, operational impacts should be minimal.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected through Thursday afternoon. Winds will follow familiar diurnal trends with perhaps some moments of VRB conditions overnight. Some VCSH cannot be ruled out during the mid to late morning timeframe, mainly for KBLH, but forecast uncertainty remains too high to warrant inclusion of any rainfall mention on the TAF. For KIPL, there is a slight chance (10-30%) of a gusty outflow impacting the terminal during the early evening hours, but nothing is currently reflected in the TAF as, much like morning SHRA activity, forecast uncertainty remains high.

FIRE WEATHER

Unseasonably hot temperatures will continue through the remainder of this week with some relief in store by this weekend. Overall temperatures will remain well above normal through Saturday until falling to more seasonal levels by Sunday. Isolated showers and storms will be confined to the AZ high terrain through the end of this week with a much better influx in moisture and rain chances anticipated area-wide by this weekend. Humidity levels will bottom out around 10-15% today and increase to above 15% on Thursday. Overnight recoveries will be poor to fair, increasing to good across the eastern districts on Friday night. Outside of distant thunderstorm outflows, expect overall light winds (below 15 mph) following typical diurnal tendencies with some modest afternoon upslope gustiness.

CLIMATE

Record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 26 117 in 2011 115 in 2020 115 in 1981 Aug 27 114 in 2023 120 in 1981 117 in 1981 Aug 28 117 in 2023 118 in 2023 117 in 2009 Aug 29 116 in 2023 117 in 1954 117 in 2005

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Saturday for AZZ530>555-559- 560.

Extreme Heat Warning until 8 PM MST Friday for AZZ556-561-562.

CA...Extreme Heat Warning until 8 PM PDT Saturday for CAZ562-565>567- 569-570.

Extreme Heat Warning until 8 PM PDT Friday for CAZ561-563-564- 568.