textproduct: NWS Phoenix

KEY MESSAGES

- High pressure will continue to maintain dry and tranquil conditions and above normal temperatures in place through Thursday.

- A more unsettled pattern is expected starting Friday and lasting well into next week with occasional rain chances and cooler temperatures.

SHORT TERM /TODAY THROUGH THURSDAY/

Latest objective analysis continues to depict upper-level ridging persisting over the Desert Southwest. This ridge will remain in place through much of Thursday before shifting east late Thursday night into early Friday as a shortwave trough approaches from the west. In the meantime, dry and tranquil weather along with mostly clear skies will remain in place through Thursday. Temperatures will also continue to run about 5 degrees above normal as afternoon highs top out in the low to mid 80s across much of the lower desert communities with overnight and early morning lows remaining mild with 50s to around 60 degrees expected.

LONG TERM /FRIDAY THROUGH TUESDAY/

Model guidance continues to show a significant pattern change starting Thursday and eventually affecting our region by Friday, but a decent amount of spread and uncertainty remains with any rain potential for the first two shortwaves that will brush by our area. The leading shortwave is still slated to approach southern California by Friday morning, but the track should keep the best energy across northern Baja and Sonora Mexico. The system will at least advect a decent amount of moisture into the region later Thursday into Friday pushing PWATs to around 200% of normal by Friday afternoon. Lower level moisture will noticeably improve during this time, but mixing ratios will only top out at 6-7 g/kg.

There is at least some improved optimism for rain chances as models have mostly kept the track of the system not too far away on Friday with the weakening circulation moving along or just south of the Arizona/Mexico border. This track along with the modest moisture should at least allow for around a 12 hour period of rain chances from later Friday morning through mid to late evening Friday. The best focus for the expected shower activity (and maybe a weak thunderstorm or two) should be south of Phoenix earlier Friday before shifting east of Phoenix by the evening. Forecast PoPs have increased to include 25-40% chances in the Phoenix area to 50-70% over the high terrain northeast and east of Phoenix. Rainfall amounts with this first round of rain chances should only amount to a few hundredths for any the lower deserts to at maybe 0.10" in higher terrain areas.

A second follow-on shortwave trough is then shown to quickly move in from the northwest as early as sunrise Saturday morning, lasting through at least Saturday afternoon. The track of this next disturbance will at least bring rain chances to the northern half of Arizona with more doubt for the Arizona lower deserts. The latest NBM PoPs of 40-70% for Phoenix and 60-90% for the high terrain seem too optimistic, but have held off on making any adjustments at this time. Rainfall amounts for Saturday should at least be higher than the first round with forecast soundings pointing at a near saturated mid-level layer, but with a less favorable upslope west southwest wind component we'll have to mostly rely on system dynamics for forcing.

By Saturday evening, the shortwave is expected to push to our east quickly decreasing rain chances and likely ending them all together by around midnight. Sunday will bring brief shortwave ridging and some slight dry air advection from the northwest and this should lead to considerably less clouds and virtually no rain chances. Temperatures this weekend will easily fall into the 70s for highs with most lower deserts likely not surpassing 75 degrees both days.

The high amplitude unsettled weather pattern will continue into next week, but model uncertainty increases even more. Guidance suggests one after another northern Pacific waves will get ejected southeastward toward the U.S. West Coast with the next potential system reaching the California coast early Monday before reaching our region Monday night into Tuesday. This may even be followed by another system during the second half of next week. It is too early to have any good sense on the track of these systems as they could move directly through the Desert Southwest or mostly miss us to the north. NBM/WPC PoPs of 20-60% are still in the forecast for the Tuesday disturbance, but that could easily change depending on the eventual track. So far, any system that may move through is not expected to carry anything more than average moisture, so any rainfall amounts are likely to be on the lighter side. However, the expected northwestward trajectory of the weather systems next week should usher in even cooler temperatures with highs trending more toward the upper 60s to lower 70s during the middle part of the week.

AVIATION

Updated at 1715Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period under mostly clear skies. Winds will favor an E'rly component through much of the period with speeds generally aob 10 kt. Though VRB conditions may yield some W'rly observations this afternoon, the typical full diurnal switch appears unlikely to take place. A short window of marginal breeziness may develop late in the forecast, but any gusts that come to fruition should quickly diminish soon after.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns are expected over the next 24 hours. Winds will continue to favor a W'rly component at KIPL, while KBLH switches between NE and NW flow. Speeds generally aob 7 kt will yield extended periods of VRB conditions. Mostly clear skies will be common through Thursday morning.

FIRE WEATHER

The dry conditions and above normal temperatures will persist through Thursday before chances for mostly light rain begin Friday. Minimum humidity values through Thursday will range between 20-30% for the lower deserts to 30-40% for higher terrain areas, while overnight recoveries stay good to excellent at 40-70%. Expect overall light winds, but also some marginally breezy conditions across ridge tops and terrain gaps of eastern districts during the morning hours. Winds will increase starting Friday, but gusts should mostly stay under 25 mph. Several passing weak weather disturbances will bring occasional showers and maybe an isolated thunderstorm Friday and Saturday and potentially again early next week.

HYDROLOGY

Gila: A Flood Warning remains in effect from Painted Rock Dam through the Dateland area through at least early next week due to water released from the dam. Water release levels are expected to increase during the next couple of days, peaking at 3000 cfs. These increased releases will have the potential to flood farm fields and low-water crossings along the river downstream from the dam.

PSR WATCHES/WARNINGS/ADVISORIES

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