textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures will cool trend through the weekend reaching below normal levels for several days early next week.

- Unusually strong winds will impact the region through Sunday resulting in areas of blowing dust and critical fire weather conditions.

- More tranquil weather conditions and a slow warming trend will arrive during the middle of next week.

SHORT TERM /Today through Sunday/

Seasonally strong midlevel height falls were surging into the western Conus early this afternoon as increasing deep SW flow quickly scours away boundary moisture across the forecast area. Despite this loss of low level moisture, a sheared shortwave with the last vestiges of mid/upper moisture was lifting into northern Arizona resulting in virga/light showers exiting the region. While the lead shortwave carving out troughing over the Pacific NW is already ejecting eastward, upstream energy will continue dive southeast intensifying and amplifying troughing over the Great Basin such that negative height anomalies nearly 4 normalized standard deviations below normal will become established this weekend. With H5 heights locally retreating as low as a 582-585dm range, forecast confidence is excellent that temperature will fall 5F-10F below normal heading into the first part of next week.

The greatest impact from this very unusual late June system will be a prolonged stretch of gusty winds through the weekend. The depth of the troughing and magnitude of height falls entering the region will promote enhanced jet winds readily mixed through the boundary layer. U-wind anomalies as measured by an ensemble mean are near seasonal maximums with ECMWF EFI output suggesting gusts very near all-time highs by late June standards. In terms of raw data, 30-40kt speeds frequently within the sfc-H7 layer will be tapped during daytime mechanical mixing, and further aided by mountain wave activity around larger terrain features. Wind advisories continue along the corridor of strongest winds aloft, in addition to the typical wind prone areas where difficult travel for high profile vehicles and localized dense blowing dust may be common. Otherwise, the combinations of these enhanced wind gusts, low humidity levels, and very dry fuels receptive to fire could result in extreme fire behavior and uncontrolled wildfire growth resulting in highly elevated to critical fire weather conditions.

LONG TERM /Monday through Friday/

The large pacific trough that will begin to push inland over the weekend will remain over the Western CONUS through much of next week. With negative height anomalies remaining in place, temperatures will remain a few degrees below normal through midweek, with lower elevation highs in the upper 90s to lower 100s. NBM guidance shows very little spread between the 25th and 75th percentile with respect to high temperatures before ensembles shows the troughing feature beginning to be displace by the subtropical high trying again to build over the Desert SW. As the high begins to build back over the region, temperatures will begin to warm back towards normal (generally 105F to 110F). Otherwise, while the wind advisories will expire by the end of the weekend, breezy conditions are likely to persist into early next week.

AVIATION

Updated at 1750Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns will be breezy conditions this afternoon into the evening hours today, with gusts around 20-25 kt. Familiar directional patterns can be expected, with winds likely taking a little longer than usual to fully turn out of the W/SW, leading to a few hours of S'rly cross winds. SCT mid-level clouds will stick around through the morning hours before skies slowly clear out and become mostly clear by this afternoon. Expect gusty winds to return tomorrow and are forecast to be around the 20-25 kt range.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions this afternoon and evening will be the main aviation concern. Gusts out of the W and SSW/SW at KIPL and KBLH respectively will reach upwards of 25-30 kt. KIPL readings could reach upwards of 35 kt at times. Although not included in the TAF at this time due to low confidence, it is not out of the question that these enhanced winds may result in reduced VIS due to BLDU. Mid-level clouds through the morning hours will give way to mostly clear skies for the remaining TAF period.

FIRE WEATHER

Elevated to critical fire danger will continue today due to low humidity, very warm temperatures, and afternoon upslope/upvalley breezy conditions. Red Flag Warnings have been issued today through Sunday for much of the area. Expect MinRHs closer to 5-15% starting today, then staying in this range for several days. Winds will increase this evening with gusts into a 20-35 mph range and locally higher over higher terrain areas. Winds are likely to peak on Saturday with gusts commonly reaching 25-40 mph. These windy and dry conditions will combine with the very dry fuels to create a risk of extreme fire behavior. Temperatures will cool this weekend reaching slightly below normal levels starting Sunday. Winds are expected to gradually diminish next Monday into Tuesday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Red Flag Warning until 8 PM MST Saturday for AZZ131.

Wind Advisory from 11 AM to 11 PM MST Saturday for AZZ530-533.

Red Flag Warning until 8 PM MST Sunday for AZZ133.

CA...Red Flag Warning until 8 PM PDT Saturday for CAZ231.

Wind Advisory from 11 AM to 11 PM PDT Saturday for CAZ564>567- 569-570.

Wind Advisory from 5 PM this afternoon to 11 AM PDT Sunday for CAZ562.