textproduct: NWS Phoenix

KEY MESSAGES

- Breezy conditions into the middle of the week will combine with low humidity and very dry fuels to result in elevated fire danger, primarily for the eastern Arizona high terrain.

- Below normal temperatures this week will warm to near normal heading into the weekend then above normal next week, resulting in increasing coverage of Moderate Heat Risk.

SHORT TERM /TODAY THROUGH THURSDAY/

Confidence remains excellent that broad cyclonic flow will be maintained over the Western CONUS through at least Thursday, albeit with negative midlevel height anomalies gradually deteriorating and retreating to the north. A quick-moving, dry shortwave can be seen in water vapor satellite imagery currently rounding the base of the longwave upper level trough and already ejecting northeastward into Utah early this afternoon. This has acted mostly to reinforce the stronger SW'rly flow aloft, though as it departs, midlevel flow has already begun to relax. As a result, afternoon/early evening gusts across the CWA will peak at slightly lower magnitudes than what was observed yesterday, followed by notably weaker gusts Wednesday and during the latter half of the work week (returning to much more typical afternoon breeziness for this time of year).

As noted in previous forecast updates, the atmospheric column is exceptionally dry compared to late June/early July climatology. Further drying is anticipated heading into the latter half of the week, with widespread ensemble mean PWATs dipping below 0.4" to as low as 0.15" over the eastern half of the state. Meanwhile, negative midlevel height anomalies will remain in place through the middle of the week, with ensemble mean H5 heights fluctuating between 580-584 dam. Height rises are then expected starting Thursday, increasing to as much as 589-591 dam late Thursday, closer to climatological median values. As a result of these conditions, expect afternoon highs around at least 5F below daily normals today and Wednesday, in the upper 90s to lower 100s across the lower deserts, with gradual warming starting Thursday. Overnight lows as much as 12F below normal seem likely for some spots across the lower deserts, with efficient radiative cooling under clear skies and very dry conditions. This translates to widespread lows in the 60s for more rural valley locations and out towards SW AZ and SE CA, and 70s in more urban areas and the typically warmer spots.

LONG TERM /FRIDAY THROUGH MONDAY/

Ensembles remain in good agreement that broad Western CONUS troughing will be displaced as a subtropical high begins to build closer to the region over the weekend into early next week. As the high builds, H5 heights aloft will start to increase leading to a gradual warming trend. The latest NBM continues to advertise temperatures returning to near normal by Independence Day then above normal by Sunday-Monday. During this warming trend, Moderate Heatrisk will return and increase in coverage, becoming widespread over the weekend into next week. With the high pressure building, more tranquil weather conditions are expected with only typical, modest afternoon breeziness for early July expected.

The pattern shift over the weekend and into next week will also shift the flow aloft out of a southerly direction, allowing moisture to increase across the region. A familiar, gradual day- to-day increase in thunderstorm coverage may take place during the second week of July; at first, showers and dry thunderstorms over the far eastern/southeastern AZ high terrain develop, then as conditions moisten further, more vigorous convection over the eastern/southeastern AZ mountains develops the next day, and after several days, chances for storms may be introduced to the South- Central AZ foothills and even potentially the lower deserts. One complicating factor for this typical evolution would be the possibility for an inverted trough to hasten the import of better quality moisture and serve as a synoptic lifting mechanism mid- late next week. The latest GFS deterministic reveals this possibility, but solutions vary widely between the suite of ensembles and their individual members. Regardless of the details, an increase in thunderstorm activity, especially over prominent terrain features across the eastern half of the state, seems likely to take place next week.

AVIATION

Updated at 1751Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns under clear skies can be expected throughout the TAF period. The overall wind pattern will follow the typical diurnal tendencies with a period of southerly winds during the late morning/early afternoon hours today and tomorrow before the W-SW shift. Some occasional gusts near 20 kts can be expected once this afternoon/early evening, with a slight decrease in wind speeds for tomorrow.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under clear skies can be expected throughout the TAF period. At KIPL, winds will generally be out of the west while at KBLH, winds will fluctuate between the south-southeast to southwest. Another round of afternoon/early evening gusts between 20-25 kts can be expected, strongest at KIPL.

FIRE WEATHER

Elevated and localized near critical fire weather conditions will persist into the middle of the week due to stronger than usual southwesterly gusts, primarily over the high terrain of Southern Gila County and Tonto NF foothills. Winds will generally return to terrain-driven tendencies and exhibit typical afternoon upslope/upvalley breeziness with gusts mostly 15-25 mph late this week into the weekend. Afternoon minimum humidities will range between 5-15% areawide, with the driest conditions on Friday and Saturday. Poor to fair overnight recoveries will drop solidly into a poor category (15-30% areawide) Thursday night into the weekend. Despite the decrease in winds later this week, seasonably elevated fire danger will persist through the weekend due to very dry conditions, seasonably warm temperatures, very dry and receptive fuels, and the typical upslope/upvalley breeziness each afternoon into the early evening.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.