textproduct: NWS Phoenix

UPDATE...Updated 12z Aviation Discussion

KEY MESSAGES

- Scattered showers and isolated thunderstorms will continue to be possible for portions of the area today as the remnants of Tropical Cyclone Rachel lifts northward into Nevada. Locally heavy rainfall will be possible along with breezy to windy conditions.

- Additional chances for mostly light rain will continue for portions of the region, especially across South Central Arizona Monday into Tuesday. - Below normal temperatures are anticipated through the middle of the week with a drier and quiet weather pattern settling into the region by Wednesday.

SHORT TERM /TODAY THROUGH MONDAY/

The remnants of TC Rachel are quickly lifting northward across southern California early this morning with moderate to heavy rainfall diminishing from south to north. Localized flash flooding will continue to be a concern over the next few hours before much of the rain moves out of the area by sunrise. Isolated to scattered showers and thunderstorms are also expected early this morning across south-central Arizona with a broken line currently over western Pima and Maricopa Counties drifting northeastward.

Strong gusty winds have also developed across portions of the area with gusts as high as 50-55 mph across Imperial and Yuma Counties since midnight. Wind gusts of 40-50 mph should be quite common through sunrise across southeast California and southwest Arizona. The windy conditions will eventually shift eastward through south-central Arizona later this morning with gusts of 35-45 mph developing. Additional showers and isolated thunderstorms should develop across south-central Arizona by this afternoon with a focus more across the high terrain driven by strong south southwesterly upslope flow. The remnants of Rachel will be completely out of our area by this afternoon, but we will remain under the influence of a large Pacific trough and broad upper level ascent going into Monday. A break in the shower activity is expected tonight with only widely isolated showers possible. Monday should be much of the same with upslope forcing waining and drier air gradually working in from the southwest ahead of the main shortwave. We expect some occasional isolated showers and maybe a few thunderstorms on Monday, but overall not much additional rainfall for most areas.

Rain chances are likely to improve again going into Monday night as guidance shows the main shortwave clipping our area as it tracks to the northeast, as well as a weak cold front moving across the area. Hi-res CAMs are beginning to show some shower activity developing across the western deserts as early as Monday afternoon before pushing into Arizona Monday evening into Monday night. Given that moisture is expected to be fairly limited, rainfall amounts should be light with lower desert areas mostly less than 0.10" to at most 0.25-0.50" over the high terrain north and northeast of Phoenix.

The temperature forecast likely brings some good news with a substantially cooler air mass settling in over the region. Daytime temperatures today will barely budge with afternoon highs only reaching into the low 80s across the western deserts to around 85 degrees in the Phoenix area. Further cooling is anticipated for Monday with highs in the upper 70s to the lower 80s, even before the cold front moves through the area.

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. We should also have another period of gusty easterly winds develop across eastern and south-central Arizona by next Friday or Saturday.

AVIATION

Updated at 1125Z.

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

A band of showers and storms is likely to move through during the early morning hours, sometime between the 14z to 16z timeframe with brief visibility reductions. Otherwise, dry conditions are expected through the remainder of the day with strong wind gusts the main issue through this afternoon. Wind directions early this morning will favor the southeast between shifting out of the south by the mid to late morning hours and more out of the south- southwest to southwest by the late afternoon hours. Peak wind gusts during the late morning through the afternoon hours will likely be in the 25-35 kt range, which could lead to areas of lofted/blowing dust causing slantwise visibility reductions. Wind gusts will taper off after sunset, with speeds returning to 8-12 kts and directions shifting out of the southeast by the mid to late evening hours. SCT-BKN cloud bases between 5-7 kft will be common throughout the period and could briefly drop to as low as 3 kft with any thunderstorms.

Southeast California/Southwest Arizona including KIPL and KBLH:

VCSH will linger mainly for KBLH through the early morning hours before mainly dry conditions prevail throughout the rest of the period. Strong winds will be the main issue through this afternoon as gusts could peak upwards of 30-35 kt. Winds will generally favor a west to southwest component at KIPL and south to southwest component at KBLH. Wind gusts will taper off after sunset, with speeds returning to 8-13 kts. SCT-BKN cloud bases as low as 7-8 kft will be common throughout the period.

FIRE WEATHER

Active weather will continue through the early part of the week with the remnants of Tropical Cyclone Rachel affecting the area today followed by trough of low pressure for Monday and Tuesday. Periods of rain and windy conditions will affect the area today with locally moderate to heavy rainfall possible. More scattered shower and isolated thunderstorm activity is then anticipated for Monday and Tuesday with a focus over the Arizona high terrain. Humidities will remain very elevated through Tuesday with MinRH values mostly between 40-60%, while temperatures fall to well below normal. Drier conditions will gradually settle back into the region during the latter half of the week with rain chances ending by Wednesday.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory until 5 PM MST this afternoon for AZZ530>533-535- 536.

Wind Advisory from 8 AM this morning to 5 PM MST this afternoon for AZZ534-537>563.

CA...Wind Advisory until 5 PM PDT this afternoon for CAZ560>570.

Flood Watch through this afternoon for CAZ560-561-568.