textproduct: NWS Phoenix

UPDATE

Updated 06Z Aviation Discussion.

KEY MESSAGES

- Unseasonably strong high pressure over the Southwest will result in very warm temperatures and minor HeatRisk this week with afternoon highs more than 15 degrees above normal.

- Daily record highs and warm lows will likely be tied or broken in Phoenix, Yuma, and El Centro from Thursday through Monday.

- Dry, tranquil weather will persist through early next week.

SHORT TERM /Today through Thursday/

The upper-lvl pattern remains unchanged from the past 24 hrs, consisting of longwave ridging over the entire western half of the CONUS. 500 mb hghts remain between 584-586 dam over our forecast area, or near the 99th percentile of climatology for late February. Latest visible satellite imagery reveals thin high cirrus clouds cresting the top of the ridge and spilling into the Desert Southwest, but this has done little to hamper warming across our region. Temperatures are again on their way up to the middle 80s across the lower deserts this afternoon which is around 10-12 degrees above normal for this time of year. Dry and tranquil weather will continue into tonight with lows ranging from the mid 50s to lower 60s across the lower deserts and upper 40s to low 50s for the higher terrain areas.

The strengthening of the upper ridge and increasing mid-lvl hghts/thickness will promote a steady warming trend through mid- week. Highs across the C AZ deserts are expected to reach the upper 80s and slightly higher into the lower 90s across the SW AZ and SE CA deserts on Wednesday. The lower 90s will become more widespread on Thursday which is forecast to be the first 90 degree day of the year in Phoenix. Thursday will also mark the beginning of a 4-5 day stretch of near record to record breaking highs and warm lows for all 3 of the major climate sites (Phoenix, Yuma, and El Centro). Due to the deeper PBL mixing and tightening of the 500 mb hght gradient over N AZ , enhanced afternoon breeziness can be anticipated with gusts reaching 20-25 mph at times. Otherwise, dry and calm conditions will prevail.

LONG TERM /Friday through Monday/

Essentially nothing will change in the synoptic pattern through the weekend as the stable Conus longwave pattern holds steady. If anything, H5 heights may locally edge higher (closer to 588dm at times) while sfc-H8 thermal profiles continue to warm. Model guidance continues to forecast H8 temperatures peaking around +20C over the weekend easily resulting in afternoon highs above 90F across lower desert communities. Guidance spread also remains unusually narrow with probabilities of exceeding daily records well above 50% over the weekend. Widespread minor HeatRisk will expand even into higher elevations with afternoon readings exceeding 20F above normal. The trend among the vast majority of ensemble membership during the first half of next week shows some form of troughing with lowering heights entering the SW Conus, however specific timing and orientation of any incoming negative height anomalies is very uncertain. Regardless, forecast confidence is moderately good regarding temperatures retreating from record levels as at least minor height falls enter the region.

AVIATION

Updated at 0510Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are expected through the TAF period. Winds will continue to follow typical diurnal tendencies with periods of light variability. Speeds will generally be aob 10 kts, but some occasional gusts into the mid teens are possible tomorrow afternoon. FEW-SCT high cirrus clouds will be passing over the region throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected through the TAF period. Winds will favor the W/NW at both terminals through most to the TAF period, with speeds aob 7 kts. Extended periods of light and variable winds are also expected. FEW-SCT high cirrus clouds will be passing over the region throughout the period.

FIRE WEATHER

Warm and dry conditions will continue through the remainder of the week with temperatures reaching well above seasonal norms. Minimum afternoon humidity levels will generally fall to 15-20% across the lower deserts, and into a 20-25% range at higher elevations. This will follow fair to good overnight recovery of 30-60%. Wind speeds will remain generally 10 mph or less overnight and during the morning hours with modest afternoon upslope gusts up to 15-25 mph. Overall conditions will be favorable for early spring prescribed burning operations.

CLIMATE

Daily High Temperature Records:

Phoenix Yuma El Centro --------- --------- --------- 2/25 92 (1921) 95 (1986) 94 (1986) 2/26 91 (1986) 96 (1986) 95 (1986) 2/27 92 (1986) 95 (1986) 96 (1986) 2/28 89 (1986) 97 (1986) 92 (1986) 3/1 89 (2016) 93 (1986) 91 (2016) 3/2 90 (2016) 94 (1910) 92 (2016)

PSR WATCHES/WARNINGS/ADVISORIES

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