textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Highs will return to around 110 degrees today across the lower deserts and continue into early next week before heating up to around 114 degrees during the latter half of next week.

- Extreme Heat Warnings have been extended through next Friday evening due to continued areas of major HeatRisk through early next week and increasing to widespread Extreme HeatRisk during the latter half of next week.

- Isolated thunderstorms are expected to remain confined to the high terrain through at least Saturday.

SHORT TERM /TODAY THROUGH SATURDAY/

The subtropical high is currently centered over the Four Corners region early this morning and models are in good agreement that it will slowly progress eastward through tomorrow and eventually settle over eastern CO/NM. This will cause winds over our region to become more southerly, which will usher in much drier air. PWATs early this morning currently range from 1.0-1.5" over our area and models show PWATs decreasing to 0.9-1.3". Models also show mixing ratios as low as 7-8 g/kg. This will result in dry conditions across the lower deserts and only slight chances for some isolated showers and storms over the higher terrain areas. Models do show slight chances of a weak outflow boundary trying to move into the lower deserts. However, any outflows are expected to wash out as they move off the terrain, similar to last night.

Despite the high shifting eastward over the next couple of days, models show 500mb heights of 593-596dm over our area. Skies will return to mostly clear by this afternoon, which will allow temperatures to heat back up today and are forecasted to be around 110-114 (98-108) degrees across the lower deserts (higher terrain) this afternoon. Similar temperatures are forecasted for Saturday and may be a degree or two warmer than today in some locations. These hot temperatures will result in widespread Major HeatRisk across the lower deserts and in some areas of the higher terrain (specifically the San Carlos area). As a result, the Extreme Heat Warning for the lower deserts and San Carlos area remains in effect. Make sure to practice smart heat safety by drinking plenty of water and electrolytes and limiting your time outdoors, especially during the afternoons.

LONG TERM /SUNDAY THROUGH NEXT FRIDAY/

Model uncertainty remains quite high for the first half of next week as the position of the high is likely to set up somewhere over eastern New Mexico and western Texas by Monday. This position can cause higher uncertainty in moisture levels for our area with the latest guidance trying to advect some moisture into our area by Sunday or Monday, but NBM forecast PoPs are at most 10-15% for the lower deserts. At this point, we could continue to see mostly slight chances favoring the high terrain into early next week, but if moisture does eventually improve enough storm chances are likely to be higher than what the NBM is depicting. Another wildcard will be the potential influence of an upper level trough that may attempt to move into western portions of our region Sunday into Monday. If this occurs, it may be enough to improve convective potential across southeast California and western Arizona for Sunday and/or Monday. By Tuesday, drier air will filter back into the region as the subtropical high begins to retrograde back over our region. This will end limit low end rain chances to the higher terrain areas with the lower deserts remaining dry. By the latter half of next week, the NBM shows PoPs being confined to the Mogollon Rim with no chances for our CWA.

Temperatures are expected to continue to be more influenced by the strong subtropical high as H5 heights hover between 593-596dm across the Desert Southwest through early next week. Daytime highs are not expected to change much from Sunday to Monday, barring any significant change with the convective chances. As mentioned above, by Tuesday the subtropical high will start to retrograde back to the west and center will eventually settle over AZ/NM during the latter half of the workweek. The high will also strengthen to around 595- 597dm during this time. The combination of the center settling over our region and strengthening will result in temperatures heating up to around 10 degrees above normal for this time of year. Afternoon highs (morning lows) will be in the 110-116 (85-95) degree range across the lower deserts and in the 100-110 (75-85) degree range across the higher terrain areas. The increase in temperatures will also result in an increase in HeatRisk, with widespread Extreme HeatRisk forecasted for the majority of the CWA for the latter half of the workweek. Due to these hot temperatures and widespread Extreme HeatRisk expected next week, the Extreme Heat Warning has been extended through next Friday.

AVIATION

Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Saturday morning under occasional mid/high cloud decks. Confidence is good that winds will complete the switch to W/SW early/mid afternoon with minimal gustiness. While TSRA will not directly affect any terminal, a distant traveling outflow could switch winds to S/SE this evening, however confidence is too low to include in this TAF package.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Saturday morning under mostly clear skies. Winds will generally oscillate between SE and SW with limited afternoon/evening gusts, however thunderstorm outflow winds may create an early wind switch to SW at KIPL late this afternoon. Otherwise, periods of variable winds will be common during the early morning hours.

FIRE WEATHER

Drier air will filter into the region today and Saturday with even lower chances for rain while temperatures heat back up to 5 to 8 degrees above normal. Only slight chances for isolated storms exist over the higher terrain through Saturday. MinRHs of 15-25% today decrease to 12-20% tomorrow. MinRh then increases again to 15-25% Sunday and Monday before decreasing back to 10-20% beginning Tuesday. Overnight recovery will generally be in the 30-60% range, with the best night being Sunday night. Winds should overall follow the typical diurnal tendencies with some modest afternoon upslope gustiness.

CLIMATE

Record highs:

Date Phoenix Yuma El Centro ---- ------- ---- --------- Aug 21 114 in 2019 115 in 1969 117 in 1969 Aug 22 113 in 2011 115 in 1969 117 in 1969 Aug 23 114 in 2011 115 in 2011 116 in 1969 Aug 24 115 in 2020 119 in 1985 117 in 1985 Aug 25 113 in 2011 116 in 1962 117 in 1962 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

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530>544-546- 548>551-553>555-559-560.

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