textproduct: NWS Phoenix

KEY MESSAGES.

- Temperatures will heat up several degrees above normal through the week, with lower desert highs climb above 110 degrees most days.

- Extreme Heat Warnings will be take effect Monday and continue through Friday, with widespread Major HeatRisk.

- Thunderstorm activity through the majority of the upcoming week will be mostly confined to the Arizona high terrain and southeast Arizona.

SHORT TERM /TODAY THROUGH TUESDAY/

A weak shortwave trough moved through this morning, within the southwest flow, and helped drive some virga showers across the area. Midlevel water vapor shows dry air moving in on the back side of this feature, which will continue to spread across the area through tonight and add a dry subsident layer at and above 500mb heading into Monday. Convection this afternoon will mostly be limited to the high terrain of northern and eastern AZ, with relatively weak updrafts due to minimal instability. Heading into Monday a low pressure feature slowly moving through Chihuahua, MX looks to come just close enough to shift mid-level steering winds to more of a NE component, albeit weak, across southeast AZ, including the White Mtns. This change, in addition to slightly better instability, may be enough for gusty outflow winds to move west/southwest out of the White Mtns toward South-Central AZ in the late afternoon and evening. All members of the latest HREF show an outflow, of varying strength and timing, moving through southern Gila, Pinal, and Maricopa counties Monday evening. A trend of evening outflows into the lower deserts may continue Tuesday (and beyond) as moisture and instability nudge up slightly. Synoptically, mid-level steering winds become more easterly across all of southern AZ Tuesday as the low pressure feature drops southwest through Sonora, MX and the subtropical anticyclone positions near/over the AZ-NM border.

Unseasonably hot and extreme temperatures will be the primary sensible weather impact through the start of the workweek as high pressure strengthens over the area through Monday. Current objective analysis shows 500mb heights are around 594-595dam, but will rise up to 596-597dam by Tuesday, which is at or above the 97th percentile of climatology for this time of the year. High temperatures today will be around 1-3 degrees above daily averages, with lower deserts reaching 105-109 degrees. Temperatures then warm a few degrees into Monday and Tuesday, increasing up to 4-6 degrees above averages and coming within a few degrees of daily records. This does mean a return of temperatures reaching or exceeding 110 degrees across the lower deserts. These hot afternoon temperatures combined with early morning lows in the mid 80s to 90 degrees will result in scattered to widespread coverage of Major HeatRisk starting Monday, which is when an Extreme Heat Warning will take effect.

LONG TERM /WEDNESDAY THROUGH SATURDAY/.

The subtropical high will remain entrenched across the region through at least the end of the week, with 500 mb height fields remaining steady between 595-597dam. Therefore, temperatures will continue to run a good 4-7 degrees above normal as afternoon highs across the lower deserts will range between 108-113 degrees. There will also be little overnight relief as an increase in low- level moisture will cause overnight lows to only bottom out between the mid 80s to low 90s with the low 90s expected in the Phoenix area. Therefore, widespread Major HeatRisk will continue with Extreme Heat Warnings currently in effect through Friday evening. Extension of this warning may be warranted through next weekend as a weakening and slight re-positioning of the high further away may not come until Sunday-Monday next week.

The latest guidance does show the high eventually moving northeastward into the Four Corners region by the end of the week into next weekend, putting the region under a more favorable moisture advection pattern as the east to southeast flow increases. Therefore, an increase in monsoonal activity is more likely during this timeframe, mostly across the higher terrain areas. Although, it will certainly be possible for convective activity to impact the south-central AZ lower deserts at some point as well, it is still too far out to know what days will be most active as it will be dependent on mesoscale processes such as outflow evolutions and/or any easterly waves, which are difficult for models to resolve several days out. As of right now, NBM PoPs across the south-central AZ lower deserts starting next Thursday range between 10-30%.

AVIATION

Updated at 1720Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are anticipated through the period. Winds will continue to exhibit diurnal tendencies, settling into a W-NW direction this afternoon with speeds generally aob 8 kts. The typical easterly shift will likely occur later than usual at KPHX again tonight. Extended periods of light and vrb can also be anticipated during the onset of any directional shifts. SCT-BKN high clouds will progress over the region this afternoon before clearing from W to E later this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected at the SE California terminals through the forecast period. Winds will fluctuate from SE to W at KIPL and remain predominantly southerly at KBLH through this evening with periods of light and vrb at both terminals expected overnight and into early Monday morning. FEW high clouds will gradually clear through this evening.

FIRE WEATHER

Near to slightly above normal temperatures are expected this afternoon and then will rise another few degrees into the coming workweek. Most lower desert communities will reach or eclipse the 110 degree mark each day this week. Minimal monsoon activity is expected through the first half of the week, with only a few isolated thunderstorms expected across the far eastern districts. Thunderstorm chances increase somewhat, mainly for south-central AZ, by the latter half of the week as moisture increases. Afternoon MinRHs through most of the week will 15-25% and overnight recoveries will be around 35-50%, highest in the Imperial Valley to Yuma, AZ. Outside of thunderstorm winds, the overall winds will follow the typical diurnal tendencies with some modest afternoon upslope gustiness.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Monday to 8 PM MST Friday for AZZ530>544-546-548>551-553>555-559.

Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Friday for AZZ560.

CA...Extreme Heat Warning from 10 AM Monday to 8 PM PDT Friday for CAZ562-565>567-569-570.