textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- An Extreme Heat Warning is in effect for portions of the western deserts today and for the Phoenix Metro area through Tuesday. - Today will be the hottest day of the week with lower desert highs reaching 105-112 degrees, followed by a gradual cooling through the remainder of the week.

- Dry conditions will prevail this week under generally clear skies most days. Wednesday will be the only day with partly to mostly cloudy skies.

SHORT TERM /TODAY THROUGH TUESDAY/

A strong upper level ridge is currently moving eastward through the region with H5 heights expected to peak later today between 588- 590dm, or near the 99th percentile of climatology for the period. The higher heights will help to push temperatures even hotter today with lower desert highs of 106-110 degrees, or around 15 degrees above normal. The forecast high in Phoenix has nudged up to 109 degrees today which is only one degree shy of the daily record.

A weak upper level disturbance has also formed just west of southern Baja, but there is currently no moisture connection or clouds (other than marine stratus). However, as the disturbance expands and the flow turns southeasterly across inland Mexico, it should result in some convection today across Chihuahua and eventually some mid to upper level clouds working their way into southern Arizona tonight. Before this higher level moisture advection occurs, a shallow low level east southeasterly jet will affect eastern and southern Arizona this morning, bumping surface dew points upward by around 20 degrees by mid to late morning. Gusty easterly winds will also affect southeast Arizona into south-central Arizona this morning with gusts over the higher terrain upwards of 25-30 mph in some spots to 15-20 mph into Phoenix. By mid to late afternoon, much of this boundary layer moisture will get dispersed as much drier air mixes down. However, some of the boundary layer moisture will remain and with the southerly mid-level flow returning on Tuesday, some afternoon Cu and potentially some isolated shower activity may develop across southeast Arizona to as far north as eastern Pinal and southern Gila Counties. Even if some showers do manage to develop, we are not anticipating any measurable rainfall in our area.

The Baja disturbance is forecast to move northward later today through Tuesday reaching southern California Tuesday afternoon. Some mid and upper level clouds will be possible as this happens along with height falls across southern California and western Arizona. The height falls and increased gradient will help to drive a decent push of southerly winds for Tuesday afternoon across far southwest Arizona and southeast California. Wind gusts may briefly reach 30 mph for some of these locations late Tuesday afternoon. Temperatures Tuesday will react to the falling heights mainly across southeast California and southwest Arizona where highs will fall back to between 102-106 degrees. The Phoenix area will only dip a couple of degrees from today's highs with readings topping out 104-107 degrees.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Wednesday will be a pattern transition day for the Desert Southwest as upper level troughing from a much larger Pacific trough nudges southeastward into the region while a sub-tropical upper level jet comes on shore across northern Mexico into Arizona. The jet will drive increased higher level clouds across at least the eastern half of Arizona for much of Wednesday, while the lowering heights will allow for cooling conditions. Forecast highs Wednesday range from the upper 90s to around 100 degrees across the western deserts to around 100 degrees in the Phoenix area.

The main Pacific shortwave is set to miss our region well to the north on Thursday, but the broader upper level troughing is still favored to move through Thursday into Friday. This will drive heights even lower while dropping highs more into a 95-99 degree range for both Thursday and Friday. The pattern for the upcoming weekend is likely to support a weak ridge moving through giving a slight boost in temperatures as readings may top 100 degrees again for some of the lower deserts. The westerly dry flow late this week and through next weekend should provide for clear to mostly clear skies.

AVIATION

Updated at 1710Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Uncertainty in timing of wind shifts and directions will be the primary weather issue through Tuesday afternoon under clear skies. Confidence is good than an easterly component will prevail through mid afternoon, then attempting to switch to a westerly component late afternoon. However, extended periods of variability are possible late afternoon/early evening with directions potentially 260v030 until settling on a W/NW trajectory beyond mid evening. A west component may hold longer into the overnight before making the typical nocturnal easterly switch prior to sunrise.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather issues will exist through Tuesday afternoon under clear skies. Confidence is fair that wind directions will oscillate between an early morning/daytime SE component and an evening SW direction with speeds remaining under 12kt.

FIRE WEATHER

Hot and dry conditions will prevail through Tuesday with lower desert highs topping out 10 to 15 degrees above normal. Minimum humidity levels will bottom out in the single digits each afternoon with overnight recoveries remaining poor to fair, averaging 20-35%. After a brief period of elevated easterly winds across the eastern districts this morning, winds will become light in the afternoon. Tuesday will bring more of a predominant southerly wind, particularly across the western districts where afternoon gusts of 25-30 mph will be possible. These stronger winds coupled with very dry conditions will result in elevated to near critical fire weather. The weather pattern will then shift for the latter half of the week bringing temperatures down, but still remaining above normal while dry conditions continue to prevail.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST this evening for AZZ530-532.

Extreme Heat Warning until 8 PM MST Tuesday for AZZ537-540- 542>544-546-548-550-551.

CA...Extreme Heat Warning until 8 PM PDT this evening for CAZ567-569- 570.

Extreme Heat Warning until 8 PM PDT this evening for CAZ562-563- 566.