textproduct: NWS Phoenix

UPDATE

Updated 00Z Aviation Discussion.

KEY MESSAGES

- Lingering showers and an occasional storm this afternoon through tomorrow and tomorrow night with breezy south to southwest winds, strongest during the daylight hours. - Temperatures cool through the start of the workweek with below normal reading anticipated through the middle of the week.

- Drier and quieter weather conditions develop by Wednesday and then breezy conditions may develop again by the end of the week.

SHORT TERM /TODAY THROUGH MONDAY/

The remnant circulation of TC Rachel is no longer discernible on satellite, having sheared apart and fused with the large-scale trough across the West. However, showers and a few storms continue to develop across AZ, feeding off elevated surface moisture (dew points in the upper 50s to lower 60s) and modest upslope ascent. A lot of dry air has moved in aloft, especially above 700mb, which is choking the updrafts and, overall, showers are notably less intense than they were last night and early this morning. There has not been much in the way lightning either. Through the rest of this afternoon and evening fast-moving showers and the occasional thunderstorm are expected to continue to favor terrain areas of AZ, mainly north and east of Phoenix, and along a SSW-NNE oriented band mostly between Phoenix and Quartzsite. The threat for localized flash flooding is all but over. With the fast-moving showers and lower intensity, it will be tough to accumulate enough rainfall to lead to flash flooding. However, training of cells over the same areas may still lead to localized impacts. Latest REFS & HREF show the best potential for flooding impacts through this evening being in Yavapai County, associated with the band of continuous rain showers. Areas like Wickenburg have around a 10-20% chance to pick up over 1" of rain this afternoon and evening.

In addition to the lingering rain showers this afternoon, winds have picked up across the region, associated with a strong pressure gradient. Surface wind gusts this afternoon have mostly been hitting 35-45 mph. Any shower, even weak ones, will be capable of mixing down stronger wind gusts to the surface. The gusty winds have also been strong enough to generate blowing dust and hazy skies in some areas. A Wind Advisory remains in effect through 5 PM this afternoon The gustiness should relax this evening with the loss of heating. It will be gusty again Monday, across mainly AZ, but the magnitude of gusts will be around 10-15 kts lower than today.

Spotty showers and an occasional rumble of thunder are likely to continue into Monday, with a persistent southwest flow, especially in the afternoon with surface heating. But again, the better rain chances and coverage look to favor higher terrain areas of AZ and in particular across Yavapai County. Steering winds will still be very fast Monday, with 700-500mb winds around 30-60kts, which will limit rainfall totals. The REFS probability for rainfall Monday >0.25" is <20% south of I-10 to around 30-50% along the southern Yavapai County border. Rain chances are likely to improve again going into Monday night - Tuesday morning as guidance shows a shortwave trough, within the larger Western CONUS trough, clipping through the area. A weak cold front is also shown to move west to east across the area, which may help focus showers and isolated storms into a scattered line/band. Once again, fast steering flow and overall low intensity showers should limit rainfall amounts with this activity Monday night to mostly under 0.25" across the lower deserts.

Temperatures will continue a downward trend through the start of the week, which is welcome news to just about everyone that grinded it out through another hot Summer+. Highs across southeast CA today will mostly stay below 80 degrees while AZ locations have already warmed into the middle 80s. Temperatures are then forecast to cool several degrees into Monday, dropping ~5-8 degrees with the lows and ~2-5 degrees with the highs. This cooling into Monday will be ahead of the weak cold front Monday night. So, further cooling is expected into Tuesday.

LONG TERM /TUESDAY THROUGH SATURDAY/

Ensembles are in good agreement the Pacific low will slowly drift east northeastward across far northern Arizona and southern Utah on Tuesday before most of the energy exits to the northeast on Wednesday. Additional dry air will spread across the region from the northwest during this time with PWATs dropping to 75% of normal and skies clearing out later on Tuesday. Behind the cold front on Tuesday, temperatures will dip further with NBM forecast highs only in the mid 70s Tuesday, or 10-15 degrees below normal. Overnight lows Tuesday night/Wednesday morning are also expected to fall well into the 50s for the bulk of the area to as cool as the mid to upper 40s for rural lower desert and higher terrain locations.

Model guidance is still somewhat uncertain with the eventual placement of the incoming upper level ridge and a likely lingering trough axis and/or cut-off low that should form late week. No matter the eventual evolution, our weather will basically stay the same with dry conditions prevailing late week into next weekend. Temperatures will moderate some late week with highs returning into the 80s, but likely staying below normal. We may end up having another back-door cool front moving into the area from the east by Friday or Saturday and this should either maintain or cool off temperatures going into next weekend. As with any backdoor front, gusty easterly winds are likely to follow as well and with the potential cutoff low in the area, easterly winds in this case may become quite strong. Global models are already showing potential for some very strong, advisory level or higher, winds across southeast AZ.

AVIATION

Updated at 0200Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Gusty cross runway winds and VCSH will be the primary aviation concerns through the TAF period. Wind gusts are tapering off this evening and should stop by 02-03Z. However, winds will remain elevated overnight (8-13 kt). Current westerly/southwesterly winds will slowly go southeasterly overnight, and may have more of a southerly component than usual. By mid-morning tomorrow winds will develop more of a southerly component and start gusting up around 20 kt. By the early afternoon (20-21Z) winds will go more southwesterly with gusts of 20-25 kt expected through sunset. Most of the shower activity has shut off within the PHX Metro this evening, but some lingering showers remain near/just north of KDVT. Those should be moving further north within the next hour (03Z). Dry conditions are expected overnight through tomorrow morning before more VCSH develops around 20-21Z. Periodic showers, with a few embedded thunderstorms possible, will then continue through the evening and overnight hours. CIGs will remain aoa 7 kft through the majority of the TAF period, with FEW-SCT decks as low as 4-5 kft. CIGs are not expected overnight tonight, but FEW- SCT clouds will remain around 4-7 kft.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusty winds will be the main aviation concern through this TAF package. Winds will predominately be out of the west at KIPL and out of the SW at KBLH through the TAF period. Gusts will end by 02-03Z with winds remaining elevated (8-13 kt) overnight. Winds will then start gusting again by late tomorrow morning/early tomorrow afternoon (18-19Z). Wind gusts will be less tomorrow but gusts of 20-25 kt are still expected. FEW-SCT midlevel decks will be common through the period.

FIRE WEATHER

Isolated to scattered showers and a few storms will remain possible across mainly AZ this afternoon through Monday night before a weak cold front moves through and drier air filters in. Winds will be strongest now/this afternoon, with gusts up to 35-45 mph from the S-SW. Gustiness will subside this evening and then pick back up during the day Monday, but with magnitudes around 10-15 mph lower. Winds will then be lightest Tuesday and Wednesday. Although a north to south gradient wind will develop along the Lower Colorado River Wednesday, leading to some gusty northerly winds. Winds then look to become stronger area-wide Thursday and especially Friday into this weekend with a strong E-W gradient potentially setting up. Drier conditions develop through the day Tuesday and likely stay dry through the end of the week with MinRH values mostly between 40-60% the next couple days to then 25-40% by Thursday. Below normal temperatures are expected through at least the middle of the week.

PSR WATCHES/WARNINGS/ADVISORIES

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