textproduct: NWS Phoenix

UPDATE

Updated Aviation

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 Warnings are in effect through Friday evening with daily major to extreme HeatRisk.

- Thunderstorms will primarily favor higher terrain areas through early next week, with drier and less favorable conditions next week.

SHORT TERM /TODAY THROUGH MONDAY/

Extreme heat will be the primary weather hazard through the short and long term forecast. Early morning objective analysis shows a 596dm high pressure centered over CO/NM. Models show that this high will slowly progress eastward through the beginning of next week. Despite the center of the high moving away from our region, H5 heights over our region will remain in a 594-597dm range. With heights of this magnitude, the NBM continues to show afternoon highs (morning lows) of 110-116 (83-91) degrees across the lower deserts and 100-110 (70-80) degrees across the higher terrain areas. Temperatures of this magnitude are 5-8 degrees above daily normals and some locations could tie or break their daily records (see Climate section below). These temperatures will lead to widespread high-end moderate to major HeatRisk across much of the CWA and therefore the Extreme Heat Warning remains in effect.

The best thunderstorm chances will exist across the higher terrain areas through the beginning of next week with only slight chances for some isolated activity across the lower deserts. Thunderstorm chances across the lower deserts for this afternoon are around 10- 20%. While some hi-res models (HRRR and RRFS) are trying to pick up on some more scattered activity across south-central AZ (including the Phoenix Metro), they are likely overdoing the coverage. Models show limited moisture today (PWATs of 1.0-1.3"), mixing ratios only around 6-7 g/kg, MUCAPE values less then 500 J/kg, and around 25-50 J/kg of CIN. The hi-res models showing scattered to widespread activity for this evening are likely picking up on some upper-level divergence and colliding outflows. While there will likely be multiple outflows moving off the higher terrain this evening not much activity (other than some isolated showers and maybe a few isolated storms) is expected even if they do collide due to all the limiting factors mentioned earlier. Strong to locally severe wind gusts and areas of blowing dust will be the primary hazard with any storm this afternoon and evening, with high DCAPE values (1800-2000 J/kg).

Models are in decent agreement that there will be a slight increase in moisture on Sunday and Monday (PWATs increase to around 1.1-1.6" across the area) with the highest moisture expected on Monday. Instability will be about the same on Sunday as today, but will increase to around 1000-1500 J/kg on Monday. Additionally, mixing rations will increase to around 10 g/kg on Monday. Despite the increase in moisture, instability, and mixing ratios models show an increase in CIN (100-200 J/kg). Activity each day will depend on how the day prior plays out. But right now, Monday looks to have slightly better chances than Sunday. Either way, most of the lower deserts are expected to remain dry with the best chances (and coverage) of thunderstorms expected across the higher terrain areas to the east of the Phoenix Metro.

LONG TERM /TUESDAY THROUGH NEXT FRIDAY/

Ensemble members are in good agreement that by Tuesday drier air will start to filter back into the region as the subtropical high starts to retrograde back over our region. By the middle of the week the center of the high will be straddling the AZ/NM border and by the end of the week the center of the high will be over AZ. As the high moves overhead, PWATs will drop into a 0.8-1.2" range across our region and steering flow will be out of the S/SW. The combination of these factors will lead to poor chances for thunderstorm development across the region. The NBM shows that Tuesday and Wednesday there could be enough moisture around to support isolated thunderstorm chances for the higher terrain areas. But by the end of next week thunderstorm chances for our area shut off and will mainly be relegated to the Mogollon Rim.

Unusually hot temperatures will be the main story next week. As mentioned above the subtropical high will slowly retrograde back over our region beginning on Tuesday, which will result in a gradual warming trend for our area. 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) are forecasted to 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 forecast for the majority of the CWA by Wednesday. There remains high confidence in the heat forecast for next week. So, the Extreme Heat Warning remains in effect through next Friday and will likely need to be expanded to more areas by the middle of the week and may eventually need to be extended into next weekend.

AVIATION

Updated at 1100Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Uncertainty in TSRA/SHRA coverage and corresponding gusty outflow winds/wind shifts will be the primary forecast challenge through Sunday morning under periods of mid/high cloud decks. Confidence is good that light east winds will prevail through early/mid afternoon with a slow transition to W/SW by late afternoon. TS development over higher terrain areas may send gusty outflow winds towards the Phoenix terminals during the early evening with a S/SE direction most likely. While direct TS impacts are not likely, briefly gusty winds and decaying SHRA could affect operations mid evening. If more concentrated storms can materialize along with multiple colliding outflow boundaries, better chances for isolated TS development in lower elevations will be enhanced with stronger and more prolonged wind gusts.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Sunday morning under mostly clear skies. Trends in winds should be similar to the past 24 hours, generally varying between SE and SW with extended periods of nearly calm conditions in between. TS activity over the Baja spine late this afternoon may send an outflow and decaying SHRA towards KIPL prior to sunset. Chances for direct TSRA impacts are too low to include in this TAF package, however gusty SW winds justify a continued mention through the early evening.

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 be around 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 Monday, but they will mostly favor the 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 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.