textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- A weather system will bring scattered light showers today with the best coverage and rainfall amounts over the eastern Arizona high terrain.

- Dry and warm conditions are expected this weekend with highs mostly in mid 70s across lower deserts.

- A stronger weather system for next Monday and Tuesday should bring even better rain chances, breezy to windy conditions, and noticeably cooler temperatures.

SHORT TERM /TODAY THROUGH SUNDAY/

Current water vapor imagery shows modest moisture streaming into the Desert Southwest ahead of an elongated and fairly weak trough. Moisture advection mainly within a 700-350mb level will continue through around early afternoon with peak PWATs of around 0.8" mainly across south-central Arizona. Low level moisture will be slow to increase and will largely happen from top down saturation once the shower activity gets going by this afternoon. Models continue to show the trough moving through later today with much of the energy missing our region to the south. The best upper level forcing looks to be early this morning, disconnected from the best moisture and any forcing in the low and mid levels which will peak in the afternoon.

CAMs generally agree on two bands of mostly light showers forming later this morning, one very narrow band along the Lower CO River Valley and the other from Tucson north northeastward into Gila County. By mid this afternoon, both of these bands are likely to diminish while slowly pushing eastward, but additional isolated to scattered shower activity is likely to develop across portions of south-central Arizona into the Arizona high country. Unfortunately, guidance has mostly backed off any decent area of showers across the Phoenix area which may leave most people without measurable rainfall today. PoPs have been reduced to between 30-40% across the lower deserts with expected amounts generally under a 0.10". More persistent rainfall should fall over the higher terrain east of Phoenix where upwards of a 0.25" is likely in some spots. We also can't rule out a few rumbles of thunder this afternoon, but the chances are under 10% and any thunderstorms will be weak.

The trough is still forecast to quickly exit the region tonight with any lingering rain chances mainly across eastern Arizona in the evening. Fairly strong ridging will push into the region Saturday morning bringing in drier air and leading to sunny skies for much of the day Saturday. Temperatures will warm a couple degrees from today's readings with highs 72-74 degrees in the Phoenix area to as warm as the upper 70s across southeast California. Sunday will bring increasing clouds ahead of the next weather system, but temperatures will warm further across the south-central Arizona lower deserts as the warmer air from the ridging finally mixes down into the boundary layer.

LONG TERM /MONDAY THROUGH THURSDAY/

A large Pacific trough will develop off the West Coast over the weekend and quickly become mature by Sunday as it drifts southward just off the California coast. The main system moisture and dynamics will impact California late Sunday into Monday with some weakening of the system already occurring by Sunday night. Despite gradual weakening through Monday, an upper level jet streak is expected to strengthen Monday into Monday night as it moves into our region. Guidance shows a modest IVT plume developing west of Baja within the base of the trough Sunday night into Monday before moving into southern California Monday afternoon and into Arizona by Monday evening. This IVT plume is likely to have at least some sub-tropical moisture connection resulting in PWATs increasing to between 0.8-0.9", or around 200% of normal later Monday through Monday night.

Even with the trough weakening as it moves into our region on Monday, it will still be fairly strong as southwesterly mid level flow increases to between 30-50kts. Guidance shows a fairly strong cold front tracking through the area later Monday through Monday night providing scattered showers across the western deserts to as much as a near full band of light to moderate rain across central and eastern Arizona Monday night. Breezy to locally windy conditions are also expected to develop on Monday with the strongest gusts potentially occurring along the cold front later in the day into Monday night. Given the fairly short duration of this rain event, forecast rainfall amounts are not very high with amounts anywhere from 0-0.25" across the lower deserts of southeast California and southwest Arizona to 0.25-0.50" into the Phoenix area. Higher amounts are likely to occur across higher terrain areas with average amounts more into a 0.50-0.75" range. Even though this system will be a bit colder, snow levels are likely to mostly stay above 7000 feet. Tuesday may bring some isolated shower activity, but models mostly show a break in the activity after the first disturbance moves through. A second shortwave trough may clip the area on Wednesday bringing additional precipitation chances, but chances are most of the energy will bypass us to the north.

Temperatures next week will easily be the coolest we have seen so far this month, but the NBM only shows readings falling a few degrees below normal starting Tuesday. Lower desert forecast highs from Tuesday-Friday are mostly in the upper 60s. Once we see drier air and calmer winds later next week, some rural desert areas may see overnight lows dip into the 30s.

AVIATION

Updated at 1122Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Light showers, maybe an isolated thunderstorm, and some gusty winds will be the primary aviation weather impacts today, with prevailing VFR CIGs. Best shower chances in the Phoenix area will be this afternoon (40%), with a low chance for a thunderstorm (10%). CIGs should lower this afternoon to as low as 6-8K ft AGL, which could cause some slantwise visibility impacts at KPHX on approach. Most of the day though cloud bases will be around 10K ft or higher. E'rly winds this morning will veer S'rly around midday and then SW'rly early to mid afternoon. An increase in wind speeds to 7-12 kt with gusts to around 20 kt are anticipated from late morning through this afternoon. Winds subside this evening and skies gradually clear tonight.

Southeast California/Southwest Arizona including KIPL and KBLH: A band of light showers has developed this morning in southeast CA and is forecast to slowly move east through noon before falling apart and/or fully shifting east of KBLH. A single lightning strike has been detected within the band and additional rogue strikes cannot be ruled out, but the TS probability is too low to include in the TAF. VFR conditions are expected to prevail, with cloud bases staying mostly at or above 8K ft AGL. Winds at both terminals will favor a W to NW direction most of the TAF period, with speeds mostly below 10 kt.

FIRE WEATHER

A weather system moving through the area today will bring rain chances mainly across the eastern districts and temperatures closer to normal. MinRH values today will rise to 30-40% for much of the area before drying conditions over the weekend lowers MinRHs back to 20-30%. Occasional breeziness is expected through the weekend, especially across the western districts and the Arizona higher terrain. After the warm and dry conditions over the weekend, more unsettled weather is expected for at least the first half of next week bringing precipitation chances, breezy to windy conditions, and elevated humidities.

PSR WATCHES/WARNINGS/ADVISORIES

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