textproduct: NWS Phoenix

KEY MESSAGES

- Very hot temperatures will return over the next few days creating Moderate to Major Heat Risk by Tuesday and lasting through at least Thursday.

- An Extreme Heat Watch has been issued for Tuesday through Thursday across the lower deserts, including Phoenix, Yuma, and El Centro. Forecast highs are currently 111 to 116 degrees.

- Dry conditions will prevail much of the coming week, although isolated storm chances are expected to return over the Arizona high terrain by Tuesday or Wednesday.

SHORT TERM /TODAY THROUGH MONDAY/

Extensive cloud cover on Saturday kept much of the area below normal, but that is expected to change today as dry air aloft will move in from the southwest throughout the day. Much of the area remains quite cloudy early this morning and it is leading to very warm overnight temperatures. After the warm start to today, it will not take much sunshine to warm daytime temperatures to above 100 degrees with highs of 110 degrees likely possible for some locales. The western lower deserts are expected to see clearing skies first this morning with much of south-central and eastern Arizona likely hanging on to some partly cloudy skies through at least sunset.

The subtropical high will again become the dominant weather feature starting today with the center of the high just to our east southeast. The center is still forecast to slowly drift westward into Monday, likely setting up over southeast Arizona while raising heights even further across the region. Monday looks to be a clear day across the western lower deserts to mostly clear across the rest of Arizona. However, lower level moisture will continue to gradually improve through at least Monday with surface dew points rising well into the 40s to even the lower 50s in southwest Arizona. The rising heights and more sunshine should help to push daytime highs on Monday to over 110 degrees for the bulk of the lower deserts with readings topping out between 109-113 degrees, or just below Major HeatRisk.

LONG TERM /TUESDAY THROUGH SATURDAY/

The main forecast concern for the upcoming week is still the potential for Extreme Heat across the region starting as early as Tuesday. Guidance remains very confident in the strengthening and repositioning of the subtropical high directly over Arizona for Tuesday and Wednesday before shifting more to the west late week. Forecast H5 heights are shown rising to above the 90th percentile later on Tuesday and lasting through Wednesday, while boundary layer moisture slowly improves. Daytime temperatures are expected to reach to 110-114 degrees on Tuesday before likely peaking at 112-116 degrees Wednesday. The slightly higher moisture will also help to keep overnight temperatures very warm with lows on average in the mid 80s to as warm as the low 90s in the urban core of Phoenix. Forecast confidence continues to increase for a period of 2-4 days of Extreme Heat later this week with the core days being Wednesday and Thursday. Friday may also need to be included depending on how quickly and how far west the high center moves later in the week. For now, the Extreme Heat Watch remains in effect for Tuesday-Thursday.

The gradual increase in moisture early this week should eventually bring some isolated shower and storm chances, but the strong subsidence under the ridge will definitely hold back the potential convection through midweek. Low end PoPs of 10-15% are mainly forecast for the higher terrain east of Globe through Thursday with little if any chance of anything nearing the lower deserts. Once the high shifts far enough to the west by Friday, guidance does show some additional moisture advection across southern and central Arizona, but how much and exactly when is still unknown. A good portion of the ensemble members then show the high center drifting back to the north northeast next weekend potentially setting up over Utah or western Colorado. If this occurs, it should be quite favorable for monsoon storm activity to increase across much of our area, either at some point next weekend or during the first part of the following week. The subtropical ridge is also expected to strengthen again as it shifts somewhere near the Four Corners area. This would keep higher than normal heights over the Desert Southwest and likely lead to a continuation of above normal temperatures through at least next weekend.

AVIATION

Updated at 0520Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No significant weather concerns will exist through the forecast period under periods of thick mid-to-high lvl cloud decks. Although cigs should remain aoa 10 kft, expansive areas of virga and potentially isolated SHRA/sprinkles will remain possible through early Sunday morning. Winds will follow diurnal trends, with a later than usual easterly shift anticipated at KPHX.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major weather concerns will exist through the TAF period under periods of thick mid-to-high clouds which are expected to clear out late Sunday morning. Winds will follow familiar diurnal trends, with extended periods of calm and VRB conditions expected at both terminals.

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 over 110 degrees as early as Monday 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 Watch from Tuesday morning through Thursday evening for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Watch from Tuesday morning through Thursday evening for CAZ562-564>570.