textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

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

- 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 FRIDAY/

Latest RAP40 500MB analysis continues to show high pressure lingering over the Desert SW region. This will lead to one more day of afternoon highs 5F-8F above normal, and dry conditions. By late tonight heading into Friday morning a cut off low will break off from the main low pressure system in the Pacific NW and begin to progress towards the lower deserts. This low will lower afternoon temperatures into the upper 70s Friday. Additionally, with this cut off low inbound and influx of moisture will be advected into the region, going from near to slightly above normal today (~0.50") to between 180-200% of normal (0.80"-0.95"). Isolated showers will be likely as early as Friday afternoon, with activity mostly in southern to southeastern AZ as the core of the cut off low tracks along the Arizona/Mexico border. However as the low moves rain chances will be pulled into south-central AZ and into the eastern higher terrain Friday afternoon/evening with PoPs between 15-30%. While most activity will be light showers, an isolated thunderstorm is not out of the question, but total rainfall amounts will only amount to a few hundredths for any the lower deserts to at maybe 0.10" in higher terrain areas.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

By Saturday a second follow-on shortwave trough will quickly move in from the northwest as early as sunrise Saturday morning, lasting through at least Saturday afternoon. Compared to the short wave on Friday, the track of this next disturbance will remain across northern AZ, bringing rain chances to at least the northern half of Arizona with more doubt for the Arizona lower deserts. Similarly to Friday, rainfall amounts will again be light, however slightly higher in comparison, especially in the higher terrain where amounts between 0.10"-0.25" are likely.

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 with Sunday slotted to be a down day for shower activity with a brief period of shortwave ridging and some slight dry air advection from the northwest and should lead to considerably less clouds and virtually no rain chances. Temperatures will continue to be at to slightly below normal over the weekend and heading into next week.

Models continue to forecast one after another northern Pacific waves being 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. However, 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, so continued monitoring will be needed. 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 1750Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns are expected through the next 24 hours. Winds will retain an easterly component through the TAF period. A period of light and variable winds is expect tonight between 01-04Z and a TEMPO group has been added to both the KPHX and KIWA TAFs with this package. Skies will be mostly clear with FEW high clouds arriving late tonight.

Tomorrow afternoon, winds will go southerly, with VCSH arriving around 22Z. Better chances for RA at the terminals will arrive after 00Z and will likely be included, in the KPHX TAF, with the next package. Occasional gusts in the upper teens to around 20 kt is also possible with any -SHRA tomorrow evening. Lower cloud decks will also arrive with bases generally aoa 10 kft, but as low as 5-6 kft with any shower activity.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected over the next 24 hours. Winds at KBLH will be light and variable (less than 6 kt) through the whole TAF package. At KIPL, there will be extended periods of light and variable to calm conditions, but winds will tend to favor a SE'rly direction this afternoon and a W'rly/NW'rly direction overnight. Wind speeds at KIPL will generally be aob 8 kt. Skies will be mostly clear this afternoon with FEW-SCT high clouds moving in this evening. Then, tomorrow morning FEW clouds with decks aoa 10 kft with SCT-BKN high clouds will move into SE CA.

FIRE WEATHER

The dry conditions and above normal temperatures will persist through the rest of today before chances for mostly light rain begin Friday. Minimum humidity values through today 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.