textproduct: NWS Phoenix

KEY MESSAGES

- Very hot temperatures are expected through this week, resulting in widespread Moderate Heat Risk and areas of Major Heat Risk Tuesday through Thursday.

- Due to the expected Major Heat Risk, an Extreme Heat Warning has been posted for the lower deserts of south-central and southwest Arizona, and southeast California, through the middle of the week.

- Outside of an isolated chance of a shower or thunderstorm over higher terrain areas of eastern Arizona, dry conditions will prevail for the majority of our forecast area.

SHORT TERM /Today through Tuesday/

Afternoon upper-air analysis reveals that sub-tropical high pressure now stretches from the Central Plains down through the Desert Southwest as this feature continues its track to be come the dominant weather regime over our corner of the CONUS. However, the high has yet to settle in a favorable position to support the advection of enough moisture to set off widespread showers and storms across Arizona. So with atmospheric heights trending upwards and plentiful sunshine, the hottest stretch of the year so far is likely to be seen through this week. For today, lower desert highs will reach between 108-113 degrees, resulting in widespread Moderate and localized areas of Major HeatRisk. Tuesday is when an Extreme Heat Warning will go into effect as coverage of Major HeatRisk expands due to widespread afternoon temperatures ranging between 110- 115 degrees and, lows only falling into the 80s. Around the Phoenix metro tonight, some spots may barely dip below 90 degrees, offering very little relief from the day time temperatures.

Near to slightly above normal moisture values, with PWATs hovering between 0.7-1.2", are in place across our forecast area and the remainder of Arizona. Although not overly impressive, it will be just enough to help spark some isolated showers and thunderstorms around the White Mountains and other prominent terrain features of southeastern AZ. A stray shower or storm cannot be completely ruled out for far eastern Gila County, but the vast majority of the activity should be confined to the Tucson and Flagstaff CWAs. Similar activity is expected for Tuesday, with maybe some rainfall advancing slightly further to the west, but once again, most locations within our coverage area will remain dry. If convection can sprout far enough into Gila County, maybe even into far eastern Pinal County as well, then perhaps we could see an outflow descend into lower desert areas Tuesday evening.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Hot and overall dry conditions are expected for the latter half of the week with the subtropical high center redeveloping to just off the coast of southern California, but with little change in H5 heights for our region. The shift in the ridge is expected to bring drier air temporarily into at least western portions of our area, but not much change for south-central and eastern Arizona. An even more inhospitable upper level pattern should limit daytime convection further starting Wednesday with PoPs lowering closer to 10% over the Arizona high terrain by Thursday.

Extreme heat will continue to be the main forecast concern through the rest of the week with the peak of the heat likely occurring on Wednesday with highs reaching 112-116 degrees. Once the ridge center becomes more established to our west Thursday it begins to weaken, temperatures are expected to very slowly drop. Friday's temperatures are still very close to Major HeatRisk, especially over the western deserts where highs near 115 degrees are likely to linger through Friday.

Model guidance is still favoring the subtropical ridge to quickly shift back to the northeast over the coming weekend, potentially reaching northern Colorado and Wyoming by Sunday. If and once this occurs, it will turn our winds out of the east southeast as early as Friday night, beginning the process of moisture advection into the region. Uncertainty in how quickly ample monsoon moisture will move into our area is still a issue as it could happen as early as late Saturday into Sunday, but more likely late Sunday into Monday. Shower and thunderstorm chances are expected to increase from east to west as the moisture spreads into the region with the best chances of reaching the lower deserts at some point early next week. We will also be watching for any easterly disturbances that will manage to move across northern Mexico into or near the Desert Southwest. Any of these potential features are likely to enhance storm chances next week.

AVIATION

Updated at 1700Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major weather issues will exist through Tuesday afternoon under a few mid/high cloud decks. Confidence is excellent that wind behavior will be nearly identical to the past 24 hours including limited afternoon westerly gusts, and a later than usual overnight shift back to easterly.

Southeast California/Southwest Arizona including KIPL and KBLH: Occasionally gusty winds will be the only weather issue through Tuesday afternoon under clear skies. Confidence is good that variable wind directions this morning will quickly become S/SE in the afternoon before veering more SW in the evening. A few gusts near 20kt will be possible mid afternoon through the evening before decoupling overnight.

FIRE WEATHER

Hotter conditions, but a slight improvement in moisture is expected for the first half of this week. Lower desert highs will warm to 110 degrees starting today before peaking at around 115 degrees midweek. Minimum afternoon humidities of 10-15% are anticipated each day with overnight recoveries of 25-40%. Winds will follow diurnal upslope/downvalley patterns with modest upslope afternoon breeziness mostly staying below 20 mph, which will continue to result in periods of elevated fire danger. A gradual increase in moisture this week should eventually lead to some isolated storm chances across the eastern Arizona high terrain, but any chances for wetting rains in South-Central AZ is more likely to hold off until next weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Thursday for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Warning from 10 AM Tuesday to 8 PM PDT Thursday for CAZ562-564>570.