textproduct: NWS Phoenix

UPDATE

Updated 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 and this weekend.

SHORT TERM /Today through Tuesday/

Upper level water vapor satellite imagery and streamline analysis show a cut-off low starting to move on shore in central California early this afternoon. This cut-off low will slowly migrate east/southeastward through the rest of today and tomorrow. As the low migrates into our region it will weaken and eventually become an open wave over Arizona tomorrow. Thick mid and high level clouds ahead of the low has covered our region. This, along with falling heights aloft(decreasing to around 568-574dm this afternoon) will lead to cooler temperatures. Temperatures early this afternoon are mainly in the low to mid 70s across the lower deserts, which is around 20 degrees cooler than this time yesterday (as of around noon). Temperatures are forecasted to top out in the upper 70s to low 80s this afternoon across the lower deserts and in the low to mid 70s across the higher terrain. Temperatures of this magnitude are around 8-12 degrees below normal for this time of year. In addition to the cooler temperatures, breezy to locally windy conditions will continue today. Although, the thick mid to high level clouds will help to inhibit wind speeds getting as strong as they were yesterday. However, wind gusts are still expected to be around 15-25 mph across south-central Arizona and much of southwest Arizona this afternoon and evening. Wind gusts upwards of 25-35 mph are expected across southeastern California. Some locally higher gusts are possible across western Imperial County die to mountain rotor action. Some occasional gusts could exceed 40 mph across the typical wind prone areas. However confidence is not high enough that wind gusts in excess of 40 mph will be common enough this evening to warrant an additional Wind Advisory.

Another aspect of this weather system moving through the region will be increased chances for light showers and sprinkles over portions of our CWA. PWATs early this afternoon remain on the lower side (around 0.4-0.5"). However, as the low moves into our area it will bring an increase in subtropical moisture, as models continue to show PWATs peaking around 0.7-1.0" during the overnight hours. This increase in moisture in combination with the large forcing for ascent from the low will result in an area of light showers and virga to develop this evening through the overnight hours, mainly across portions of southeastern Arizona and across the foothills and higher terrain east of the Phoenix Metro. However, slight chances do exist across the Phoenix Metro (~15-25%), but most activity over Phoenix will be virga or sprinkles and no accumulations are expected. Minimal accumulations of generally less than 0.20" are expected across the higher terrain to the east of Phoenix. While rain chances will come to an end early tomorrow morning across the Phoenix Metro, they will linger into the early afternoon across the higher terrain to the east as the system progresses eastward.

It will quickly dry out (PWATs dropping back down to 0.4-0.5") behind the core of the system by tomorrow afternoon with skies becoming partly cloudy/mostly clear. Despite the decrease in cloud cover tomorrow afternoon temperatures are still forecasted to be cooler tomorrow as the core of the low moves overhead and H5 heights lower even further (into a 561-566dm range) tomorrow. Due to this, afternoon high temperatures are forecasted to be in the mid to upper 70s to near 80 degrees across the lower deserts and in the upper 60s to low 70s across the higher terrain. Cloud cover will linger longer into the afternoon across the higher terrain tomorrow, which will also help to keep them cooler.

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 2330Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns during the period will be the presence of VFR CIGs this evening and tonight. FEW-SCT bases around 6-8 kft will move over metro terminals through this evening before dropping slightly overnight, closer to 4-6 kft. As this lowering occurs, coverage will also increase resulting in overnight and early morning CIGs, but they are not expected to drop below VFR levels. Main operational concerns due to these conditions will be focused at KPHX. VCSH will accompany these lower clouds overnight, but any rainfall that occurs should be operationally insignificant. Winds will be out of the W/SW through most of the forecast, but a brief shift to the S/SSE cannot be ruled out, mainly at KIWA and KSDL due to their closer proximity to the potential shower activity.

Slantwise VIS/hazy conditions will likely continue to be a concern due to the brush fire in Buckeye. Upper level winds prevail out of the W-SW, 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 to be the main aviation concern over the next 24 hours. Strongest winds will be focused at KIPL where gusts upwards 25-35 kt will be common through early tonight. After the winds relax slightly overnight, gusts 25 kt can be expected once again Tuesday. At BLH, breezy conditions will relax this evening, though sustained winds will remain relatively elevated through the remainder of the forecast. Some occasional afternoon breeziness around 20 kt will make a return Tuesday afternoon. After some clearing takes place tonight, FEW to sometimes SCT lower bases around 6-8 kft will be present over the region starting late Tuesday morning.

FIRE WEATHER

Gusty winds will continue to remain threat through tomorrow (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 early Tuesday afternoon 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 as high pressure starts to build back into our region.

PSR WATCHES/WARNINGS/ADVISORIES

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