textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- An incoming weather system will begin to cool temperatures and increase rain chances today and Saturday.

- Sunday and Monday will be warm and dry before a series of weather disturbances will bring occasional rain chances and cooling temperatures back to the Desert Southwest by Tuesday.

SHORT TERM /TODAY THROUGH SATURDAY/

The short wave trough that will bring cooler and wetter weather to the Desert SW starting today is currently in the Eastern Pacific just off the southern CA coastline. This system will move quickly, passing through southern AZ and Northern Mexico over the course of today. PWATs will increase to near 200% of normal, which, in conjunction with the energy from the short wave troughing feature rain chances will also increase, with PoPs peaking (30-60%) this afternoon across south-central AZ, then into the eastern higher terrain heading into the evening hours. Most of the expected shower activity will remain relatively light, talking about a few hundredths to at most a tenth of an inch, a few isolated thunderstorms resulting in briefly heavier rainfall rates cannot be ruled out given that there will be a least a few hundredths J/KG of CAPE present.

Behind the short wave just discussed is another short wave that will quickly move in from the northwest. However this next system will remain across northern AZ. This will lead to rain chances being mostly confined to the north with the lower deserts forecasted to be dry, while the higher terrain areas could squeeze out an additional 0.05"-0.10" Saturday.

Outside of rain chances, these systems will also being in cooler temperatures as H5 heights will drop between 564-567 dam on Friday and 570-573 dam on Saturday. Afternoon highs will be in the upper 70s for Friday then as the first short wave passes temperatures will cool into the low 70s across south-central AZ while out west temperatures will remain in the mid to upper 70s. after the first system passes low temperatures will lag in response, resulting in morning lows in the mid to upper 50s starting Saturday morning.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Sunday will be a down day for shower activity with a brief period of shortwave ridging and some slight dry air advection from the northwest. This will lead to considerably less clouds, virtually no rain chances and temperatures climbing back into the upper 70s by Monday. Models remain in good agreement that another northern Pacific waves will continue to be ejected southeastward toward the U.S. West Coast starting early next week. Currently models suggest the next potential system reaching the California coast early Monday before reaching our region Monday night into Tuesday, where additional rain chances will return to the forecast with NBM PoPs peaking between 50-80% in south-central AZ and the higher terrain areas, however this far out this may need to be adjusted based of how the track of this low progresses. By Wednesday models are pointing towards yet again another low system, however larger discrepancies between models are evident for this system. Due to this confidence is low for rain chances by mid to late next week as things are too inconsistent at this time.

Despite if these next systems bring rain to the region or not, a more significant cooling trend can be counted on by the middle of the week as these series of weather systems move in from the northwest. They will likely usher in a cooler air mass with afternoon highs trending more towards the upper 60s to low 70s, the higher or lower end of this range largely being dependent on the depth and position of the systems.

AVIATION

Updated at 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: A period of SHRA with cigs falling 6-8K ft AGL this afternoon will be the initial weather issue, then increased probabilities of cigs developing 4-6K ft AGL Saturday morning. Confidence is excellent that light east winds with increasing mid/upper cloud decks will be common through early afternoon. By mid afternoon, winds becoming 150v210 should precede SHRA, gusty winds, and occasional cigs 6-8K ft AGL in a 21Z-00Z window justifying Prob30/Tempo inclusion. There is also a 10% chance of an embedded TS with the SHRA. Confidence is good that winds will return to an E/SE component after sunset as SHRA exit the PHX vicinity, however cigs redeveloping in a 4-6K ft AGL range appears likely after sunrise Saturday morning.

Southeast California/Southwest Arizona including KIPL and KBLH: Periods of gusty winds will be the main weather issue through Saturday morning under occasional mid/upper level cloud decks. Confidence is good that variable winds under thick mid/upper cigs will become southerly at KBLH and west at KIPL by late morning. Speeds should increase through the afternoon with 20-30kt gusts most pronounced at KIPL after sunset. Gusts should gradually relax overnight with partial decoupling.

FIRE WEATHER

A more unsettled weather pattern will begin to develop starting today and is expected to persist well into next week as a series of weather disturbances moving through the region will bring occasional rain chances and cooler temperatures. Minimum humidity values will increase today to between 30-40%. These higher minimum humidity are expected to remain elevated through much of next week. Expect overall light winds today before increasing Friday through early Saturday, mainly across the western districts, with peak gusts mostly staying under 25-30 mph.

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 have now risen to 3000 cfs and are expected to remain at this release level through the next several days. This 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.