textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion

KEY MESSAGES

- Much cooler temperatures will materialize over the region the next couple days.

- Breezy to locally windy conditions will be common the first part of the week with modest rain chances across Arizona high terrain areas.

- A rapid warming trend with temperatures into an above normal territory will arrive the latter half of the week.

SHORT TERM /Today through Tuesday/

Shortwave ridging over the area was quickly becoming dampened as troughing with intensifying jet energy and height falls slowly advance into the SW Conus. The increased momentum imparted by this system combined with seasonally deep mixing depth will promote regionally gusty afternoon winds the next couple days, although the strongest impactful winds will occur in the typical locations of the far western CWA. With a front moving onshore this afternoon deepening the windward marine layer and optimally timed robust height falls edging inland, mountain rotors and hydraulic jumps will be favored this evening over the western half of Imperial County where solid advisory level wind gusts 40-50 mph appear likely. Localized blowing dust and downstream lofted dust will be possible overnight before surface gusts weaken slightly.

Troughing in the form of a closed low will slowly migrate inland Monday with a continuation of modest height falls spreading into the forecast area. With H5 heights retreating into a 568-574dm range, midlevel temperatures will fall abruptly while thicker high clouds restrict better insolation such that afternoon highs should be 10F- 15F cooler than today (or 5F-10F below normal for early May). While stronger winds aloft and continued height falls will support another round of gusty winds Monday afternoon/evening, thick clouds may retard mixing depths and the ability to tap higher momentum air, limiting lower elevations winds with more pronounced gusts relegated to mountain peaks. Even the windiest far SW Imperial County locations may only flirt with advisory criteria as height falls will have already moved east and winds through the tropospheric depth weakening quickly.

The greatest forecast challenge and uncertainty is the potential for showers in the eastern CWA Monday night and Tuesday. Models continue to advertise a plume of better subtropical moisture absorbed into the stronger SW flow advecting into southern and eastern Arizona. While a large component of the moisture will be above 600mb, trends in modeling suggest better availability of 6-7 g/kg mixing ratios in the H8-H7 layer resulting in total column PWATs near 1.00" (or better than 200% of normal) by Tuesday morning. There are indications of a subtle shortwave combined with a midlevel front along the cold core allowing favorable saturated ascent early Tuesday morning. This is a time of reduced low level T/Td spreads, so the influence of sub-cloud evaporation should be reduced. Ensemble output is widely varying though does argue for better rainfall chances in foothill and mountain orographic upslope regions south and east of Phoenix, though a few showers in the eastern parts of the metro cannot be discounted. Otherwise, as the cold core moves directly overhead on Tuesday afternoon, high temperatures will be 10F-15F below normal with lower desert communities struggling to even reach 80F resulting in possibly the coolest day in the forecast area for the next 6 months.

LONG TERM /Wednesday through Saturday/

The main energy associated with the upper low will exit to the northeast on Wednesday with upper-level ridging building along the west coast. However, model guidance is showing a trailing piece of energy left behind that will likely develop into a cut-off low somewhere to the south of the region with differences noted with respect to the positioning and speed as it gradually progresses eastward through the latter half of the week. Nevertheless, given that this feature will be positioned far enough south, it will likely not have much in the way of sensible weather impacts for the region. With upper-level height fields steadily rising from the building ridge over the west coast, temperatures during the latter half of the week will rapidly warm from the middle 80s on Wednesday to middle 90s on Thursday. Additional warming into the triple digits is forecast as early as Friday and will likely be the start of an extended stretch of triple digit highs as the upper-level ridge gradually builds across the western CONUS.

AVIATION

Updated at 0520Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected during the TAF period. Winds will follow familiar diurnal trends, though the typical turning of the winds during the late morning will commence early than normal, around 14Z or so. The turn will more gradual as well, which should result in at least a few hours of S'rly cross-runway winds at KPHX and KDVT. Though no prevailing include gusts at this time, occasional gusts in the mid-teens to around 20 kt are likely to be observed from mid-morning into the evening hours. Cloud levels will slowly drop over the next 24 hours, with lower bases around 5-6 kt entering the picture toward the end of the foreast window. A few showers will accompany these lower clouds, but should remain mostly to the east of the airspace. The most likely terminal to any rainfall will be KIWA so mention of VCSH has been added to the TAF. It is not out of the question the other terminals may see some weak echoes/virga, but chances are too low to include mention of any VCSH/SHRA at these sites at this time.

Slantwise VIS/hazy conditions will continue to be a potential concern due to a brush fire in Buckeye. The nightly E'rly wind shift will keep any smoke away from the terminals. However, the usual afternoon switch to the W/SW, lofted smoke will shift more toward the metro, so operational impacts, mainly at KSDL and KDVT cannot be ruled out.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will continue be the main aviation concern during the next 24 hours. At KIPL, Gusts 35-40 kt will be possible through about 09Z before winds relax, though gusts 20-25 kt should continue overnight. Another window of gusts 30-35 kt will be possible Monday evening, but confidence surrounding gusts reaching that level is medium at best. Areas of blowing/lofted dust generated by these enhanced winds should remain clear of the terminal, but isolated instances of reduced surface and slantwise VIS cannot be ruled out. AT BLH, gusts should abate overnight, but reemerge late Monday morning, reaching near 25 kt once again. BKN-0VC skies will be common through most of the period.

FIRE WEATHER

Dry conditions along with above normal temperatures will continue today. An approaching low pressure system will result in widespread breezy to locally windy conditions through the first part of the week and temperatures cooling into a below normal category Monday- Tuesday. Gusty afternoon winds combined with low humidities will likely produce elevated fire weather conditions today and Monday. As the low pressure system moves through the Desert Southwest, the chance of showers will increase late Monday into the first part of Tuesday across the far eastern districts, however, the probability of wetting rains will remain on the low side. Afternoon MinRHs between 10-20% will be common today before increasing into a 15-25% range Monday and into a 20-35% range Tuesday. Lighter winds as well as much warmer temperatures and lower humidities are then forecast for the latter half of the week.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until 8 AM PDT Monday for CAZ562.

Wind Advisory until 3 AM PDT Monday for CAZ566-567.