textproduct: NWS Phoenix

KEY MESSAGES

- An unsettled weather pattern will carry us through Saturday, with temperatures cooling near to slightly below normal this weekend and chances for a few rounds of showers across South Central and Eastern Arizona.

- Some convective showers capable of producing small hail and lightning will be possible Saturday afternoon into the evening.

- Dry conditions return on Sunday, with temperatures gradually warming next week.

SHORT TERM /TODAY THROUGH SATURDAY/

Water vapor imagery show the closed low diving down the Northern Baja Coast moving southeastwards and is expected to traverse just south of the state through Northern Mexico over the next couple of days. The position of the low has already began to advect moisture in to our region with Thursday's 03Z radiosonde launch showing PWATS already at 0.6" up from 0.41" from the 00Z launch. Model guidance suggest PWATs climbing to a peak of 0.75-0.9" by this evening into Saturday across much of South Central AZ and to the east in the higher terrain areas. With moisture already in place with more to come as the low progresses, this afternoon can expect to see spotty virga to light showers across much of the east valley and east of the Metro.

By Saturday the closed low will begin its journey eastwards across Northern Mexico. As mentioned above PWATs will continue to increase as the system moves, with the NAEFS mean values peaking around the 90th percentile of CFSR climatology across the forecast area and even exceeding the 98th percentile in the southeastern corner of AZ later today. However, GFS bufr soundings project the moisture to be mostly contained in the midlevels, generally above 600 mb. In conjunction with the low passing to our south another disturbance will be diving south along the Interior West passing along Northern AZ. This will help facilitate showers to become more widespread across the eastern CWA Saturday. This disturbance has lead HREF mean MUCAPE values to be between 100-250 J/kg across S.Central AZ in the afternoon, expanding eastwards by the late evening hours. This is enough to produce convective activity resulting in the possibility of small hail and lightning in the affected areas, most notably in the evening and bleeding into the overnight hours as vorticity peaks during this time, providing extra fuel for shower activity to occur.

This second disturbance will also be responsible for temperatures cooling to near normal today and below normal starting Saturday. Today's afternoon highs will be in the low to mid 70s across the lower deserts with some areas in the Phoenix Metro seeing highs just under 70 degrees. Saturday can expect morning lows in the low to mid 50s in the Phoenix Metro, and in the mid to high 40s in the western portions of our CWA, and in the higher terrain areas. Afternoon highs tomorrow will be in the mid to high 60s in central AZ, and in the low 70s out west.

LONG TERM /SUNDAY THROUGH THURSDAY/

The poorly defined cold front that sweeps the area from the north late Saturday into Sunday will usher in a cooler and much drier air mass, ending precipitation chances by early Sunday morning. Temperatures will drop noticeably from Saturday to Sunday, from near normal into a 2-5 degree below normal range. Morning lows are forecast to range from the mid 30s to mid 40s starting Sunday, with some of the typically colder rural, low-lying areas potentially flirting with freezing temperatures (32F or less) into early next week. NBM probabilities for freezing temperatures peak Sunday night/Monday morning around 20-50% in those rural and sheltered river valley locations, except slightly higher (50-80%) in the Tonto Basin.

Ensembles remain in excellent agreement that ridging off the West Coast will slide eastward and build over the Western US during the first half of next week, promoting a gradual warming trend. However, WPC cluster analysis reveals discrepancies on how strong the ridge will become, and whether any disturbances will undercut or weaken the ridge during the latter half of next week. Regardless, after the unsettled weather Friday-Saturday, expect quiet, dry weather to return Sunday and persist through at least the middle of next week.

AVIATION

Updated at 1846Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Lowered CIGs, rounds of VCSH/SHRA, shifting winds, and isolated TS will be the primary aviation impacts and forecast challenges through Saturday. There is currently a break in shower activity, but showers will return by this afternoon/evening. Winds through this afternoon will favor a SE-S component with speeds around 5-10 kt. CIGs prior to the next round of showers will stay up around 10K ft AGL. With the next round of shower activity winds will be light (aob 5 kt) and favor a E component with some variability and CIGs will lower down to around 6-7K ft AGL. CIGs will be lowest Saturday morning, likely after midnight, down to around 4-6K ft AGL with odds of staying above 4K ft at 80%. A break in shower activity is likely again later Saturday morning through early to mid afternoon. Toward late afternoon another round of scattered showers are expected and this round will have the potential for an isolated thunderstorm with gusty winds and small hail. Winds turn W-NW Saturday afternoon with sustained speeds up to 8-13 kt. CIGs in the afternoon will be around 5-7K ft AGL Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns will exist through the current TAF period under periods of thick mid/high level cloud decks. Winds will favor a southerly component during the day at KBLH and shift from SW to SE at KIPL by this afternoon. Expect speeds to remain light, generally aob 6 kts at both terminals with extended periods of nearly calm conditions amongst typical diurnal wind shifts.

PSR WATCHES/WARNINGS/ADVISORIES

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