textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- Well above normal temperatures continue today with highs in the upper seventies to lower eighties, resulting in areas of minor HeatRisk across the lower elevations.

- A pattern change mid to late week will lead to cooler temperatures and increasing rain chances, particularly across the eastern half of Arizona on Friday.

- Weather conditions will briefly turn quieter over the weekend before becoming more unsettled once again early next week as another storm system impacts the region, resulting in better chances of more widespread precipitation.

SHORT TERM /TODAY THROUGH WEDNESDAY/

Latest satellite imagery shows a stream mid to high-level cloudiness moving onshore across central and southern CA and through the Great Basin in response to a longwave trough gradually encroaching upon the west coast. The approaching trough is the beginnings of an overall pattern change to a cooler and more unsettled period that is expected to last through the remainder of the week. The trough as makes its approach along the west coast will lower 500 mb height fields to around 570-574dm with mid to high clouds gradually spreading eastward through southern CA and AZ throughout the day. As a result, afternoon temperatures today will lower by 4-5 degrees from the afternoon highs from yesterday, but still remain well-above normal as readings will top out in the upper 70s to lower 80s. These temperature readings will still be sufficient to result in areas of Minor HeatRisk, although of lesser coverage from previous days.

The aforementioned trough will slowly approach the central CA coast on Wednesday, but will be on a weakening phase as it does. Most of the associated PVA and forcing with this trough will remain to the northwest of the region over the Great Basin and thus where the best precipitation chances and coverage will be confined. However, moisture values in the mid to upper-levels will go up later today through Wednesday as PWATs peak upwards of 0.7-0.8", which is about 175-200% of normal. As a result, a few showers in upslope flow may be squeezed out across the higher terrain areas north and east of Phoenix late tonight through Wednesday morning, with little to no accumulations expected. A further lowering of 500 mb heights to 568- 573dm during the day Wednesday will cause afternoon highs to retreat into the mid to upper 70s across the lower deserts.

LONG TERM /THURSDAY THROUGH EARLY NEXT WEEK/

Unsettled weather will remain in place through the end of the week as another troughing feature dives down through the west coast and swings through the Desert Southwest late Thursday into Friday. Model guidance in the last couple of iterations have trended a bit deeper with the trough as it swings through the region, however, the progressive nature will sort of limit any robust moisture advection and thus any precipitation that falls will be limited in coverage, with the greatest coverage expected mostly across the AZ high terrain where NBM PoPs range between 40-70% with considerably lower PoPs of 10-40% across the lower elevations of western and central AZ. With the trough passage, afternoon high temperatures on Friday will cool down to around 70 degrees across the south-central AZ lower deserts (which is right around seasonal norms) to middle 70s across the western deserts.

As the trough quickly exits to the east late Friday into early Saturday, a quieter weather pattern briefly settles in over the weekend as a transient ridge moves overhead with dry conditions and slightly warmer temperatures. Attention then turns to another, more potent longwave troughing feature that is expected to set up along the west coast heading into next week, with guidance showing multiple shortwaves moving onshore and if the overall trajectory is ideal, could lead to more widespread precipitation chances. Latest deterministic and ensemble model suite show the first shortwave moving through early next week, delivering the first widespread chance of precipitation with NBM PoPs ranging between 25-60% areawide. However, given that this potential system is still nearly a week out, lots of uncertainty still remains in the overall details and thus it will probably take until the end of the week to get a better grasp on how things will evolve. Even though the precipitation potential is uncertain, what is a bit more certain is that temperatures are likely to cool down several degrees early next week with the latest NBM deterministic showing highs in the low 70s across the lower deserts (values more typical for mid-February) with the 25th percentile in the upper 60s, which would be more likely if the cloudy/rainy scenario comes to fruition.

AVIATION

Updated at 1745Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns will exist through the TAF period under periods of thicker mid to high cloud decks. Winds will follow a familiar diurnal pattern with speeds generally AOB 8 kts, switching from SE to SW early this afternoon and then back to SE in the evening. Virga and light showers mostly east of the Phoenix airspace will be possible late this afternoon through the overnight hours, with very low confidence on VCSH/-SHRA conditions at any of the terminals. However, while this virga/light shower activity is in the area, temporary CIGS around 7-9 kft AGL are expected to develop.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy conditions during the afternoon and evening hours will be the main aviation impact through the TAF period. KBLH will see S'rly gusts up to 20 kts develop during the afternoon while while KIPL sees occasional W'rly gusts up to 20-25 kt late this afternoon into the evening. BKN to OVC mid and high cloud decks will be common over the region over the next 24 hours. Embedded virga is also likely with the clouds.

FIRE WEATHER

Well-above normal temperatures and dry conditions will persist today before cooler temperatures (although remaining above normal) ensues through the remainder of the week. MinRH values today will range between 20-35% and will continue to be in that range across most of the region through the remainder of the week with good to excellent overnight recoveries. Occasional breeziness, especially across the western districts, will be common during the next several days. A weather system late in the week will bring a 40-70% chance of wetting rains across the higher terrain areas of the eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES

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