textproduct: NWS Phoenix

UPDATE

18Z Aviation Discussion.

KEY MESSAGES

- Temperatures will remain around 5 to 10 degrees above daily normals through Tuesday.

- A passing weather system will result in periods of breezy to locally windy conditions and cooler temperatures during the latter half of this week.

SHORT TERM /TODAY THROUGH TUESDAY/

Latest mid-level water vapor imagery shows upper level ridging building over the Desert SW, sandwiched between two large upper level troughs. One trough is to the region's east spanning across much of the Central Plains, and the second is to the region's west, currently in the eastern pacific off the NW coast. With these systems in place, tightening of the pressure gradient has resulted in strong easterly winds across the high terrain of southcentral AZ this morning. The stronger wind gusts will relax to sub advisory levels for the afternoon, however wind gusts between 20-30mph can still be possible in the higher terrain areas. Models continue to hint at the chance of virga showers this evening in SE AZ with the increase in cloud coverage throughout today. Despite the increasing cloud cover, upper-lvl ridging will continue to bring above normal temperatures today with highs in the low to mid 90s across the lower desert region.

By Monday the ridge will begin to shift eastwards into the Plains, however H5 heights will continue to be between 577-580 dam over the Desert SW. This will result in temperatures remaining in the low to mid 90s across the lower deserts. Models are pointing towards Monday afternoon having 100-300 J/kg of MU CAPE in eastern AZ, and enough mid level moisture for the potential of a few convective showers developing, mainly along the Mogollon rim and in the White Mountains, while the lower deserts are expected to remain dry.

Temperatures start to trend a few degrees cooler by Tuesday with highs mostly in the lower 90s across the lower deserts, with localized areas in the Western portions of the CWA in the upper 80s. This is in response to the trough west of the region beginning to approach northern CA, while simultaneously the ridging further moves eastwards out of the region. Otherwise, ahead of the system moving over the Desert SW, winds will begin to increase in the afternoon, especially in SE CA where gusts could reach 20-30 mph.

LONG TERM /WEDNESDAY THROUGH SATURDAY/

By the middle of the workweek, troughing over the West Coast will finally push inland over the Intermountain West, albeit in a weakening phase. Ensembles members are in good agreement on the evolution of the shortwave trough which is expected to remain well north of our forecast area. However, the Desert Southwest will still be under the influence of negative hght anomalies which will result in cooler temperatures (likely closer to seasonal levels, in the 80s across the lower deserts) beginning on Wednesday. Periods of breezy to locally windy conditions can also be anticipated across the entire forecast area due to the tightening of the 500-700 mb hght gradient. The most widespread breezy conditions look to be on Wednesday and mainly across eastern AZ on Thursday as the trough axis passes north of the forecast area. Quasi-zonal flow aloft will return by Friday and into next weekend ahead of another potential shortwave trough. This will allow for a slight boost in temperatures to a few degrees above normal.

AVIATION

Updated at 1816Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Gusty morning winds will gradually subside heading into the afternoon and earlier lofted dust will continue to settle with improving slantwise visibility. As winds subside, directions will tend to veer S/SW toward mid-afternoon and some light variability may also develop as wind speeds dip to 7 kts or less. Most guidance supports a W/SW shift around 01-02Z this evening, but only lasts for a few hours before returning easterly. Confidence is good that spotty virga showers will develop this evening south of the terminals and may spread into the metro. Any shower this evening will be capable of producing locally brief gusty and erratic winds. SCT-BKN clouds will persist through tonight before clearing, with lowest bases around 12-13K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH: No significant weather issues will exist through the next 24 hours, with SCT-BKN high cirrus decks that will clear tonight. Confidence in the wind forecast is moderate with a E/NE component favored at KIPL this afternoon followed by a W component this evening and light variable winds at KBLH turning out of the S/SW this afternoon into the evening. Extended periods of nearly calm conditions will be common.

FIRE WEATHER

Dry conditions with above normal temperatures will continue over the next few days before cooler and breezy weather arrives mid-week. Elevated fire weather conditions will persist across south- central AZ through the afternoon, improving by the evening hours. Winds will weaken on Monday before breezy to locally windy conditions return on Tuesday with widespread elevated fire weather conditions. Afternoon humidity levels are expected to remain below 15% and at times in the single digits over the next several days, with only minor day to day variations. Overnight recoveries will also vary through the week, but remain mostly in the 30-50% range. Due to the breezy and dry conditions, periods of elevated fire weather conditions can be expected during the middle to latter half of this week.

PSR WATCHES/WARNINGS/ADVISORIES

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