textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Much cooler temperatures with below normal readings will prevail during the next couple of days.

- Breezy to locally windy conditions will be common through Tuesday with modest rain chances across the Arizona high terrain areas.

- A rapid warming trend to above normal temperatures is likely by the latter half of the week.

SHORT TERM /Today through Tuesday/

The latest water vapor satellite imagery as well as streamline analysis show a rather potent cut-off low situated just off the central CA coast with a large stream of mid to high-level cloudiness moving through the Desert Southwest. The cut-off low will continue to slowly migrate inland later today through Central CA before moving southeastward through southern CA and AZ during the day Tuesday as an open wave. As the low continues to slowly approach the region, 500 mb height fields will continue to decrease into the 568-574dm range and combined with thick mid to upper-level cloudiness, limiting the solar radiation, afternoon high temperatures will be a good 10-15 degrees cooler compared to yesterday as readings across most of the lower desert communities only top out in the low 80s. These temperatures will be a good 5-10F below normal for early May. The additional height falls and enhanced jet energy will continue to enhance the lower tropospheric winds. However, the thicker cloud cover may temper the overall mixing depth and thus the ability for the higher momentum air to fully mix down to the surface. Thus, even though some gusty winds are likely to materialize this afternoon/evening, it will likely not be as strong as yesterday with many areas likely observing gusts between 20-30 mph. Some locally higher gusts in excess of 30-35 mph will once again be possible across western portions of Imperial County due to mountain rotor action. Cannot rule out temporary gusts exceeding 40 mph across the wind prone areas of southwestern Imperial County.

As the low continues to slowly migrate eastward from the eastern Pacific, a plume of subtropical moisture out ahead of the feature will be advected into southern and eastern AZ later today. The latest model guidance has continued the uptrend in moisture levels as PWATs are now shown to peak to between 0.8-1.0". This moisture combined with the large forcing for ascent from the low will result in an area of light showers to break out this evening through the overnight period across portions of southeast AZ as well as across the foothills and the higher terrain areas to south and east of Phoenix as depicted by the latest hi-res guidance. It is not inconceivable to even see some rain drops making it to the surface across the greater Phoenix area. Activity will continue to affect the higher terrain areas to the north and east of Phoenix into the first part of Tuesday. Overall rainfall amounts should remain on the light side, with most areas observing less 0.10". Otherwise, as the cold core moves directly overhead on Tuesday afternoon, high temperatures across most of the lower desert communities will struggle to reach 80 degrees with many areas topping out in the upper 70s, which will be a solid 10-15F below normal.

LONG TERM /Wednesday through Saturday/

The primary energy from the low will exit to the northeast and get absorbed by another broad trough encompassing most of the central and eastern CONUS on Wednesday. Meanwhile, a trailing piece of energy will develop into a weak cut-off low just south of the International Border in northern Sonora as an upper-level ridge of high pressure builds along the west coast. Although there continues to some uncertainty with respect to the speed progression of this feature as it cuts off from the main jet stream energy, latest trends has been for a faster eastward progression through the latter half of next week with no sensible weather impacts expected for our region.

Otherwise, the main weather story heading towards the end of the week and beyond will be the rising temperatures with an extended stretch of triple digit highs. As the upper-level ridge gradually builds across the western CONUS by the latter half of the week, temperatures will be on a rapid warming trend with highs back up in the 90s on Thursday and into triple digits as early as Friday and beyond. As afternoon highs climb into the triple digits, the overall HeatRisk level across most of the area will increase into the moderate category.

AVIATION

Updated at 1126Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. Wind gusts have calmed considerably compared to yesterday, but sustained winds will remain elevated, in the mid teens, throughout the the period. While no prevailing include gusts, periodic gusts can still be possible around 20kts, mostly late this afternoon into the evening hours. Westerly to southwesterly winds will be dominant today. Cloud levels will slowly drop throughout the period, however should remain above VFR conditions. There is the possibility of showers developing by late tonight into Tuesday morning, but are expected to remain mostly to the east of the terminals. 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 likely continue to be a concern due to the brush fire in Buckeye. This continues to be a concern as overnight winds took an unexpected shift out the west and is expected to prevail, 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 between 25-35 kts are expected to continue throughout the TAF period with sustained wind speeds between 15-25 kts, from the west. With these winds, blowing/lofted dust around the KIPL terminal may be possible, leading to concerns of reduced surface and slantwise VIS. AT BLH, gusts will be slightly lighter in comparison, however, sustained winds will remain elevated and gusts between 20-25 kts will develop by late this morning, lasting through the afternoon and evening. BKN-0VC skies will be common through most of the period.

FIRE WEATHER

Some gusty winds will continue to remain threat through Tuesday as an area of low pressure approaches and moves through the region, with only a locally elevated fire danger threat expected as higher humidities will limit a greater risk. Some modest rain chances will be in place, mainly across the far eastern districts, late today through Tuesday morning with the chances for wetting rains remaining on the low side. Afternoon MinRHs between 15-25% will be common today before increasing into a 20-35% range Tuesday along with good overnight recoveries. 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 this morning for CAZ562.