textproduct: NWS Phoenix

UPDATE...Updated 18z Aviation Discussion

KEY MESSAGES

- Dry conditions with temperatures hovering around 8 to 12 degrees above normal will prevail through this weekend.

- A slight cooling trend is anticipated by early next week with lower desert highs falling from the upper 70s to the mid 70s

SHORT TERM /Today through Saturday/

An unseasonably strong ridge of high pressure located over northern CA has remain intact and unchanged over the past 24 hours. This large scale ridging pattern continues to result in positive hght anomalies overspreading the Desert Southwest with H5 hghts now up to 582-584 dam which have exceeded the 90th percent of climatology for this time of year. The NBM deterministic has been performing poorly w.r.t temperatures over the past couple days as observed highs have been 3 to 5 degrees warmer than forecast. This discrepancy is likely due to the fact there has been a persistent NE downsloping wind component which has lead to compressional warming across the foothills and lower deserts. This may be the case again today as breezy NE winds are anticipated through at least early this afternoon. Therefore, forecast highs were adjusted upward to be more in line with the NBM 75th percentile. Highs are expected to again reach the upper 70s in most lower desert communities this afternoon, although a few locations including Yuma and El Centro could see highs reach the low 80s.

Heading into this weekend, longwave troughing over the central CONUS will retrograde slightly as a result of jet energy digging into the trough base downstream. This will cause the ridge axis to slide farther NW and allow heights aloft over our forecast area to decrease slightly Friday and Saturday. Despite the slight reduction in 500 mb heights, there will not be a noticeable decrease in sfc temperatures as highs remain in the mid to upper 70s across the lower deserts or around 6 to 8 degrees above normal.

LONG TERM /Sunday through Thursday/

Long range deterministic guidance and ensemble members remain in good agreement that the West Coast ridging and central U.S. troughing will continue through at least the first half of next week. There are some signals within the EPS and GEFS clusters that the ridge may begin to break down by the end of next week. Until then, there is still high confidence that daily temperatures will hover well above normal (6-10 degrees). By the Monday-Tuesday timeframe, our forecast area may see a slight cooling trend due to the relaxation of 500 mb heights as lower desert highs fall into the low to mid 70s. With persist NW flow carrying into early next week, dry conditions are expected to continue with rain chances remaining nil across the Desert Southwest.

AVIATION

Updated at 1655Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns under a FEW passing high cirrus cloud decks can be expected through the TAF period. The overall wind pattern will exhibit light diurnal tendencies with speeds aob 7 kts along with extended periods of variable to calm conditions.

FIRE WEATHER

Temperatures will remain well above normal over the next several days with dry weather and mostly sunny skies prevailing. MinRH values of 15-30% and overnight recoveries of 40-70% will continue through the end of the workweek. By this weekend, drier air will filter into the area causing minRHs to fall around 15-25% along with overnight recoveries of 30-60%. Elevated easterly flow will continue across the eastern districts today and to a lesser extent on Friday. Gusts up to 20-25 mph will be possible at times. Winds should relax this weekend and follow typical diurnal patterns.

PSR WATCHES/WARNINGS/ADVISORIES

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