textproduct: NWS Phoenix

KEY MESSAGES

- Shower and thunderstorm chances will continue today, especially over the Arizona high terrain. Isolated storms and gusty storm outflow winds can also be expected into the south-central Arizona lower deserts.

- Drying conditions starting Wednesday will mostly end monsoon storm chances by Thursday.

- Extreme Heat Warnings are in effect for all of the lower deserts for the latter half of the week as hot and humid conditions will develop over the next couple of days.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The inverted trough can be seen on GOES mid-lvl WV imagery along the AZ/NM border. This feature will progress through northeastern AZ this afternoon/evening bringing positive vorticity's embedded within, aiding in storm ascent. This system will help promote another round of thunderstorm activity in the eastern higher terrain, very similar to yesterday's activity. Current mesoscale analysis shows divergence aloft in western NM within the cyclonic flow of the inverted trough, with additional divergence aloft in southern NM. Additionally, PWATs across the region remain between 1.5-1.7" in the eastern portions of the CWA with PWATs upwards of 2" in the western lower deserts. While the western lower deserts have higher PWATs than the eastern higher terrain, forecasted MUCAPEs out west are between 100-500 J/kg, while the eastern portions will range between 750-1500 J/kg, due to this, a majority of activity will be confined in the eastern portions of the CWA. Between the moisture, CAPE, divergence aloft, positive vorticity, and the natural lift of the terrain, much of the Arizona high terrain has been placed under a Flood Watch, with localized rainfall amounts of greater than 2" possible.

Again, similar to last night, gusty winds and patchy blowing dust will be the main concerns over the Phoenix metro and lower deserts with HREF members showing a 50-70% chance of wind speeds above 35 mph this evening, and the HRRR again optimistic of an outflow from the higher terrain moving through with speeds near 35-40 mph. A few storms may be able to survive for a short period of time before diminishing, with max PoPs between 30-40% late tonight, but most areas are not likely to receive more than 0.25" and many areas may not receive anymore than a few hundredths of an inch.

By Wednesday winds aloft are expected to shift out of the south to southwest which will aid in the advection of drier air into the region. Due to this shower and storm chances drop considerably with PoPs in the higher terrain between 15-30% and less that 10% across the lower deserts. With that abrupt shift, the region will also begin to warm, with H5 heights forecasted to climb between 591-594 dam across the Desert SW starting Wednesday, pushing high temperatures in south central AZ into the low to mid 100s and then into the mid to upper 100s to locally higher across SE CA and SW AZ. This has lead to the Extreme Heat Watch to be upgraded to an Extreme Heat Warning for SE CA starting Wednesday. Please ensure to take proper heat safety precautions.

LONG TERM /THURSDAY THROUGH MONDAY/

Extreme Heat is expected to impact much of the area late this week through at least the weekend as the subtropical ridge strengthens while the center gradually shifts over the region Friday into Saturday. Record or near record climatological H5 heights are forecast across New Mexico starting Thursday, eventually moving into Arizona Friday into Saturday with H5 heights potentially reaching 598-600dm over Arizona. Major HeatRisk is expected to impact all of the lower deserts starting Thursday, becoming even more widespread Friday into the weekend as localized areas of Extreme HeatRisk may develop. The forecast highs of 110-116 degrees Thursday through next Monday (below records) is masking the potential severity of this heat wave as dew points and humidities are expected to remain elevated. Heat indices are likely to reach 113-120 degrees over the lower deserts starting Friday with the highest readings across southwest Arizona and southeast California. Overnight lows will also become very warm with readings not likely falling much below the upper 80s. Lower 90s can be expected for much of the urban core of Phoenix starting Thursday night. If we do end up mixing out more of the boundary layer moisture, the higher end of NBM guidance shows highs potentially reaching 116-118 degrees in the Phoenix area to as high as 117-120 degrees for portions of southeast California.

The hottest days are likely to be Friday-Sunday, but there is more forecast uncertainty by Sunday as some guidance indicates some moisture return this weekend and the potential for more convective activity. For now, we are not expecting much if any high terrain showers or thunderstorms Thursday and Friday, but that could change starting Saturday or Sunday. Any more extensive convective activity may eventually disrupt the extreme heat, at least over eastern and possibly into central Arizona by Sunday or Monday. If we don't get relief from storm activity, guidance at least heavily favors some weakening of the ridge early next week while also shifting it farther to the east.

AVIATION

Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty outflow winds and modest chances for SHRA/TSRA this evening are the primary weather issues under periods of mid/high cloud decks. TSRA forming over higher terrain to the north and east should send gusty outflows and an abrupt wind shift towards the Phoenix terminals. Chances for outflow gusts exceeding 30 kts will be around 30-50% across the Phoenix terminals. New shower and thunderstorm development may occur along the outflow boundaries with chances of SHRA around 30-40%. Any thunderstorms that develop will create gusty, erratic winds. Outside of this, winds will continue to veer toward the W heading into this afternoon with a few gusts into the teens.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Wednesday morning under a few passing mid/high cloud decks. Winds will generally favor a south direction at KBLH, while directions will predominantly favor the west at KIPL. Periods of variability will be possible at KIPL through the afternoon before gusty sundowner winds are expected to pick up this evening, with gusts to around 20-25 kts at times.

FIRE WEATHER

Much of the shower and thunderstorm activity will be over the Arizona high terrain today while gusty storm outflow winds will be the main concern today for the south-central Arizona lower deserts. Chances for showers and storms will quickly drop off Wednesday with little if any activity expected Thursday as hotter and drier conditions settle into the region. Humidities will remain elevated today with MinRHs of 30-50% across the eastern districts, while the western districts will dip to 15-25%. MinRHs will then dip to 15-20% across all of the lower deserts starting Thursday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Wednesday to 8 PM MST Monday for AZZ530-532.

Flood Watch until 10 PM MST this evening for AZZ556-560-562-563.

Extreme Heat Warning from 10 AM Thursday to 8 PM MST Monday for AZZ531-533>555-559.

CA...Extreme Heat Warning from 10 AM Wednesday to 8 PM PDT Monday for CAZ562>570.

Extreme Heat Warning from 10 AM Thursday to 8 PM PDT Monday for CAZ560-561.