textproduct: NWS Phoenix

UPDATE

00Z Aviation Discussion.

KEY MESSAGES

- A mostly dry weather system moving through the region over the weekend will bring breezy to windy conditions, near to below normal temperatures, and perhaps a few showers over higher terrain areas.

- Temperatures will warm early next week, rising to slightly above normal starting midweek. Hotter temperatures with lower desert highs well into the nineties look possible by next weekend.

- A potential weather system late next week may bring chances for showers to the area, but widespread rainfall is not anticipated.

SHORT TERM /TODAY THROUGH SUNDAY/

Quasi-zonal flow is currently stretched out across much of Southwestern and South- Central CONUS, while a positively tilted trough linger just off the California Coast. Considerable mid and upper-level moisture advection over the Desert Southwest, provided by the Eastern Pacific disturbance, has provided our forecast area plentiful cloud cover this morning, but the at least some thinning/clearing should take place through the remainder of today. These cloud will suppress insolation which should provide the region slightly "cooler" temperatures compared to yesterdays highs, with readings this afternoon mainly in the middle 80s for the lower deserts. An associated jet aloft, resulting from an enhanced regional pressure gradient, will start to see some of its higher momentum winds reach the surface this afternoon and evening once convective mixing can initiate. The highest gusts will be focused over SOutheast California where peak readings should reach upwards of 25-30 mph. The cloud cover will have some say in how much mixing occurs, but with skies clearing from west to east, those western locations can expect those higher gusts. Locations east of The Colorado River will see more limited gusts thanks to shallower momentum transfer, but gusts 20-25 mph, with locally higher values in Gila County, should be common.

Heading into this evening, the jet will strengthen and interact with the Peninsular Ranges that split the Southern California Coast from the desert, generating even stronger winds. BUFR soundings for Imperial, CA indicate winds just above the surface will approach 50kt by around sunset. This is likely thanks to the channeling of winds through an increasing stable layer of the atmosphere over the mountains to the west, accelerating what will already be enhanced winds down the terrain toward the desert floor. We lose the mixing, but this terrain interactions will likely provide many locations, from and area stretching from Joshua Tree NP down through most of Imperial County, with gusts exceeding 40+ mph. It would not be surprising too see isolated gusts 50+ mph as mountain rotors will also be in play. In response, a Wind Advisory has been posted for tonight for the area mentioned above.

As the trough moves on shore, it will drag a decaying cold front along with it which will interact with some mid-level moisture that could set off some shower activity for parts of the Arizona high terrain early Sunday. However, limited forcing and a dry boundary layer will inhibit most, if not all, rainfall activity for our forecast area. Its not impossible that some communities near the border of Maricopa and Yavapai Counties see a light shower, but the best chances will remain over the Flagstaff CWA. Most of us will miss out on the rain, but some very comfortable temperatures will be observed behind the frontal boundary, with highs Sunday in the upper 70s to right around 80 degrees, a good 5-10 degrees below normal for this time of year.

LONG TERM /MONDAY THROUGH FRIDAY/

Once the weekend system exits on Sunday, it will leave behind a drier air mass which will slowly modify and warm Monday into Tuesday. Skies will remain clear to mostly clear through Tuesday with high temperatures warming back into the low 80s Monday and the upper 80s Tuesday. Model uncertainty is still an issue for later next week as another Pacific weather system is forecast to develop well west of southern California early in the week before moving through or near our region at some point during the latter half of the week. The latest model guidance does indicate a slightly later timing of the system, now favored more on Thursday instead of Wednesday. There is also a good deal of uncertainty with the strength and the amount of moisture that will be available, but the potential rain chances definitely look better than this weekend's system. The latest NBM/WPC PoPs have risen across south-central Arizona to 20-30%, while the rest of the lower deserts are more in a 10-15% range.

Temperatures are still likely to warm above 90 degrees during the latter half of the week, but the uncertainty with the weather system is providing a wider range of potential highs for Thursday and Friday. For now, highs for much of the lower deserts should top out somewhere in the upper 80s to the lower 90s through Friday before warming up even more next weekend.

AVIATION

Updated at 2350Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns through the forecast period will be periods of gusty SW-W winds and the potential for hazy conditions and slantwise visibility restrictions from lofted dust, primarily Sunday morning. Winds have not been as gusty as models have indicated this afternoon, most likely due to extensive mid-lvl cloud cover, however gusts in the upper teens to around 20 kts will still be possible over the next few hours. Gusts should subside between 01-03Z this evening, and confidence is good that winds will maintain a prevailing westerly component overnight. A cold front will progress through the Phoenix Metro early Sunday morning, allowing winds to become elevated near sunrise. Winds will increase further by mid-morning, with gusts peaking during the afternoon around 20-25 kts, slightly stronger than what is expected today. CIGs AOA 15 kft will prevail through this evening and through most of tonight. Confidence is increasing that CIGs will fall to around 7-8 kft early Sunday morning followed by gradually clearing skies by the afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: Strong, gusty SW-W winds and associated slantwise and sfc visibility restrictions will be the primary aviation concern through this evening under mid to high level CIGs. Winds are expected to be stronger at KIPL, remaining westerly through the entire period, with gusts peaking around 30-35 kts this evening. These strong gusts may bring a period of hazy conditions from localized blowing dust channels, potentially reducing visibilities to around 5-6 SM. Extended periods of gusty SW-W winds are likely to continue at KIPL through the overnight hours. At KBLH, winds will also peak this evening with gusts reaching 30-35 kts, but confidence is better that gusts will eventually subside later tonight. Both terminals will experience a resurgence of gusty winds Sunday morning, but only peaking around 20-30 kts.

FIRE WEATHER

An approaching weather system will bring increased winds today, while lingering through Sunday. Wind gusts will peak late this afternoon and through the evening, commonly reaching 20-25 mph in many locations to as high as 35-50 mph across portions of southeast California. Winds Sunday will peak in the afternoon with gusts between 20-30 mph. Expect MinRHs this afternoon 15-20% before increasing further Sunday to 20-30%. Overnight recoveries will continue to improve, rising to 40-60% tonight before dropping off again early next week. A mostly dry weather system passing through the region tonight may bring some high terrain showers, but CWR is less than 10%. Seasonably breezy afternoon winds and drying conditions are forecast for early next week, but winds will fall short of creating widespread elevated fire weather concerns.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until 5 AM PDT Sunday for CAZ560-563>568.

Wind Advisory until 11 PM PDT Sunday for CAZ562.