textproduct: NWS Phoenix

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- Wind advisories in effect today through Saturday morning across southern Arizona and southeast California, with breezy to windy conditions expected as forecast peak wind gusts reach up to 40-55 mph.

- Strong winds on today will likely lead to widespread lofted dust, leading to hazy conditions, and localized dust channels occasionally reducing visibility below one mile.

- Dry weather with near normal temperatures the next couple days, then slightly cooler with a slight chances for rain showers this weekend. - A Pacific low pressure system moving down the coast early next week is currently forecast to bring regional rain chances, breezy conditions, and cooler temperatures by the middle to latter portions of next week.

SHORT TERM /TODAY THROUGH SATURDAY/

Mid-level WV imagery and RAP40 500mb analysis show the cut off low now developed over southern California and northern Baja, while high pressure continues to strengthen over NW CONUS. The high pressure will be be the driving force for temperatures remaining near normal today. Though the core of the ridge is to the north of the state, H5 heights will still reach between 585-588 dam over the desert SW. As mentioned, near normal afternoon highs can be expected today with temperatures in the upper 80s to low 90s in the western lower deserts and along the Colorado River Valley, while south-central AZ will maintain highs in the mid to upper 80s. The upper level ridge will quickly pass and move into the Plains by Saturday, allowing heights aloft to dampen and be influenced by the lingering cut off low. This will result in Saturday cooling into the upper 70s to low 80s. This will also be in conjunction with increasing cloud coverage and about a 10-20% chances of light showers/virga across south- central AZ and the eastern high terrain as early as Saturday afternoon.

Otherwise, the main weather concern will be winds due to a strong pressure gradient. This may be one of the the strongest easterly gradient wind events of the last decade. With strong winds lofted and blowing dust also poses a threat, especially across dust prone areas. Northerly winds gusts have already developed in the SE CA and along the Colorado River Valley and are under a Wind Advisory through Friday afternoon, where peak gusts between 40-45 mph can be expected. Over the next several hours this morning the surface high will migrate from southern Montana into the southern Plains/southern Rockies region and the pressure gradient will continue to strengthen and shifting the winds from the north to out of the east. Near sunrise this morning the Wind Advisory will expand eastwards into SW and SC Arizona, where gusts between 45-50 mph will be possible, while the Phoenix Metro will be slightly lower with gusts between 35- 45 mph. Winds this strong are likely to pick up a good amount of dust, creating hazy conditions, and will likely lead to some dust channels developing, with reduction in visibilities to under 1 mile at times, depending on land use. Most of the region will be under advisory level by mid afternoon today, while Pinal County and southern Gila County will continue with strong gusts through the overnight periods into late Saturday morning, with locally up to 55 mph over mountain peaks.

LONG TERM /SUNDAY THROUGH THURSDAY/

The strong pressure gradient and resultant strong easterly winds across southern AZ will weaken heading into Sunday as the strong surface high in the Plains weakens and shifts to the Mid-Atlantic. Winds early Sunday morning will remain elevated over south- central Arizona and the higher terrain with gusts between 20-25 in SC AZ, and 30-35 mph in the higher terrain. Past sunrise these winds will quickly weaken as the upper level pattern continues to quickly shift. The ridge will continue to push eastwards, and the cutoff low will begin to weaken and become an open wave, lifting through the region Sunday- Monday. As the open wave moves drifts through, lingering light showers/virga remain in the forecast, 20-35% Sunday, then 10-20% Monday. This will be confined to the higher terrain areas, where with enough extra lift may be possible for showers to develop. However, if any activity does develop total accumulations are expected to be only a few hundredths, or near zero. For the lower deserts temperatures are expected to rebound back into the mid to upper 80s Sunday and into early next week.

By late Monday into Tuesday a troughing feature will begin to dive down the western coastline, however confidence is low in the timing and strength of the feature. This has resulted in a decent amount of spread in temperatures by mid next week. As it stands now temperatures will remain near to slightly below normal Monday- Tuesday then start to fall 6-9 degrees below normal for the later half of the week.

AVIATION

Updated at 1805Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Strong gusty E'rly winds and slantwise visibility reductions due to lofted dust will persist through the rest of the day. E'rly winds will continue to gust consistently up to 20-30 kts, with occasional stronger gusts up to 35 kts, through this afternoon. Strong gustiness should subside tonight at most terminals, but elevated surface speeds in the teens will likely prevail through the overnight hours, with an occasional gust into the 20s. Gusts to 30 kts will still be possible at KSDL after midnight. All terminals will see a resurgence of gusts up to 23-30 kts Saturday morning, but then winds will gradually subside through Saturday afternoon. Slantwise visibility impacts are likely through at least Saturday morning. Thick mid and high cloud decks will spread into the area through the day Saturday.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions through this afternoon will be the main aviation concern. North-northeast flow will be common throughout the period, with periodic gusts upwards of 25 kts (occasionally higher) at KBLH and slightly weaker at KIPL. Mostly clear skies will give way to increasing mid to high clouds through the afternoon at KIPL and by this evening at KBLH. An isolated shower cannot be ruled out overnight, but chances are too low for inclusion in the TAF.

FIRE WEATHER

Drier air will persist over the region over the next couple of days with mostly clear skies and seasonally low humidities. MinRHs will be between 15-30% across the region through Saturday. Winds will turn easterly over the morning, becoming stronger tonight through Saturday across southern AZ. Winds will be strongest over mountain tops during the overnight and early morning hours tomorrow and Saturday, with gusts up to 50-55 mph. Strong gusty winds will spread more to the lower deserts during the daylight hours and be strongest in the morning through early afternoon today, with gusts up to 40-45 mph. These strong easterlies and 20-25% RHs may still create locally elevated fire weather conditions midday through the afternoon tomorrow, but fuels are not the most receptive after recent rains. The easterly breezes will not be nearly as strong during the day Saturday and will trend down further into Sunday. Light showers are possible this weekend, but the chance for wetting rain is low (<10%). A Pacific trough is expected to bring regional rain chances, breezy winds, and cooler temperatures next week.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory until 3 PM MST this afternoon for AZZ531>534- 536>546-548>551-554-559.

Wind Advisory until 11 AM MST Saturday for AZZ547-552-553-555- 557-558-560>562.

Wind Advisory until 2 PM MST this afternoon for AZZ530.

CA...Wind Advisory until 2 PM PDT this afternoon for CAZ564-565- 568>570.