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 2315Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Main aviation concern will be breezy conditions until just after sunset this evening. Gusts 20-25 kt will be common over the next few hours before speeds relax during the overnight period. Directions should favor familiar diurnal trends, though the typical overnight/early morning E'rly shift may have a more SE'rly component to it. Winds will begin to veer earlier than usual, which will lead to a window of S'rly crosswinds at KPHX and KDVT, but the typical W'rly shift will take place during a familiar window (19-21Z). High clouds increase this evening, with BKN-OVC skies being common through much of the forecast.

Slantwise VIS/hazy conditions are possible through this evening due to a brush fire in Buckeye. The SW'rly winds should keep and smoke away from KPHX and KIWA, but some operational impacts cannot be completely ruled out at KSDL and KDVT.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will be the main aviation concern during the next 24 hours. AT IPL, gusts 25-35 kts will be common this evening, with perhaps a brief window of gusts nearing 40 kt. Though any areas of blowing/lofted dust should remain clear of the terminal, isolated instances of reduced surface and slantwise VIS cannot be ruled out. Gusts are expected to last through much if not all of the night, though readings should drop closer to 25 kt. At BLH, gusts should remain closer to 25 kt, but isolated higher near 30 kt gusts are not out of the question. Increasing high clouds will result in BKN-OVC skies through Monday afternoon.

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 from 7 PM this evening to 3 AM PDT Monday for CAZ566-567.