textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion

KEY MESSAGES

- High temperatures reach or exceed 110 degrees nearly every day through the next week and will be within a few degrees of daily records, while morning lows remain unusually warm.

- Extreme Heat Warning in effect through next Friday evening with daily Major to Extreme HeatRisk.

- Isolated thunderstorms will primarily favor higher terrain areas through this weekend, with drier and less favorable conditions next week.

SHORT TERM /TODAY THROUGH SATURDAY/

Extreme heat will be the primary weather hazard through the short, and long, term forecast. Latest objective analysis shows a 599dam high centered near the Four Corners region, with 596-598dam heights over the local area. Heights of this magnitude are at or above the 99th percentile of sounding climatology. So, it is no surprise that forecast high temperatures this afternoon, and through this weekend, will be within a few degrees of daily records, topping out around 110-116 degrees. Morning low temperatures will also remain very warm and near daily record warm lows, in the mid 80s to low 90s, offering little to no relief from the daytime heat. This combo will lead to widespread Major HeatRisk through the weekend and an Extreme Heat Warning remains in effect.

The thunderstorm chances for the lower deserts this afternoon are not great, due to the warm air aloft and drier air that moved in aloft as well. However, surface dew point temperatures remain seasonally elevated, ranging from the mid-50s to mid-60s. This is contributing to high SBCAPE values early this afternoon, up to and in excess of 1500 J/kg. This setup was resulting in cu development over prominent terrain features as of 1 PM MST and strong storms were already going over southeast AZ where mesoanalysis was showing an uncapped environment. The cap over much of south- central AZ and points westward, although relatively weak (SBCIN between -20 to -40 J/kg) will likely keep convective development reserved to the prominent terrain features, like the Table Top Mtns, Kofas, and perhaps Pinal Mtns. Instability is also expected to decline through the rest of the afternoon as the PBL continues to mix out. This will inhibit updraft strength with time. Any storm that does go up this afternoon will be capable of producing strong to severe wind gusts, due to high DCAPE values up to 1800-2000 J/kg. An outflow may move up into south-central AZ later this evening from southeast AZ storms, but it will likely take a very strong outflow to trigger additional activity in northwest Pinal and Maricopa Counties.

Guidance shows boundary layer moisture will drop into tomorrow, with afternoon dew point temperatures across the lower deserts mostly in the mid-50s. This will result in lower SBCAPE values, but surface temperatures will be slightly hotter and hi-res models show weaker inhibition, if not uncapped, and slightly steeper mid-level lapse rates. This may support slightly better coverage of afternoon convection tomorrow versus today, but still focusing primarily over the prominent terrain features. Strong to locally severe wind gusts and blowing dust will be the primary hazard with any storm tomorrow afternoon, with high DACPE values again. It still may take one good outflow or multiple outflows and outflow collisions to trigger storms near/in the Phoenix area.

LONG TERM /MONDAY THROUGH NEXT FRIDAY/

Model uncertainty remains for the first half of next week, primarily with respect to thunderstorm chances, as the position of the high is likely to set up somewhere over eastern New Mexico and western Texas by Monday. There is good global ensemble consensus in a brief increase in moisture and instability Sunday evening into Monday, most notably across southwest AZ and southeast CA, but NBM forecast PoPs are mostly under 15% for the lower deserts both days. 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. By Tuesday, drier air will filter back into the region as the subtropical high begins to retrograde back over our region. This will limit low end rain chances almost exclusively 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 the center will eventually settle over AZ/NM during the latter half of the workweek. The high is also expected to strengthen to around 596-598dam 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) ware forecast 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 forecast for the majority of the CWA by Wednesday. There is high confidence already in the heat forecast for next week. So, the Extreme Heat Warning was been extended through next Friday and will likely need to be expanded to more areas by the middle of the week.

AVIATION

Updated at 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period. Winds will follow light and diurnal trends with speeds generally aob 10 kt. There remains a slight chance (~20%) of an outflow from distant convection moving through this evening, but the potential remains too low to include mention of a boundary in the TAFs at this time. SCT cloud decks will be present through much of the forecast window, with the lowest bases around 10-12 kft.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through Saturday afternoon. Typical diurnal trends, along with overnight and early morning VRB conditions, can be anticipated at the terminals, with westerly flow switching to the southeast at KIPL, while KBLH fluctuates between southwest and south-southeast. A decaying outflow is possible at KIPL this evening, but the only impact looks to be a reinforcement of westerly flow. Other than a FEW mid and high level cloud decks, skies will be mostly clear.

FIRE WEATHER

Hot and seasonally dry conditions are expected nearly every day, through next week. Aside from a brief increase in moisture Sunday- Monday, minimum RH values each afternoon will be around 12-18% (15-25% Sun-Mon). Temperatures will range 5-10 degrees above normal through the next week, with lower desert highs eclipsing 110 degrees most afternoons. There will be slight chances for storms each afternoon through this weekend, but mostly favoring higher terrain areas. Drier conditions, with lower storm chances are expected by the middle of next week. Outside of thunderstorm outflow winds, winds will 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>555-559- 560.

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