textproduct: NWS Phoenix

KEY MESSAGES

- A slow moving weather disturbance will continue to bring periodic rain showers with a few isolated thunderstorms mainly across southern and central Arizona through Wednesday night.

- A Flood Watch has been issued for northern Maricopa County and is in effect through much of today.

- Another weather system will then bring very good chances for moderate rainfall Thursday night and Friday across southeast California and southwest Arizona with light rain chances extending through the rest of southern Arizona on Saturday. - Temperatures through the rest of the workweek will be around 10 degrees below normal before getting closer to normal over the weekend.

SHORT TERM /TODAY THROUGH THURSDAY/

Active weather will continue today and likely into tonight across southern and central Arizona as a slow moving upper level low drifts eastward across the region. Rainfall amounts yesterday definitely exceeded forecasted amounts for portions of the area with amounts anywhere from 1-3 inches across northwest Maricopa County. The low center is currently near San Diego and is forecast to only move to over the Lower CO River Valley by tonight. Abundant low and mid level moisture continues to stream northward centered across central Arizona just ahead of the low. Upper level forced ascent has weakened over the past 12 hours, but at least marginal forcing will stay present through the bulk of today while low level moist upslope forcing persists.

Scattered shower and isolated thunderstorm activity is expected to persist through at least this evening mainly affecting south- central Arizona and to a lesser degree over eastern Arizona. Additional rainfall amounts of 0.5-1.5" will be possible across south-central Arizona as PWATs stay near 200% of normal through this evening before 'drier' air (125% of normal) finally starts to push in from the west. Given that moisture doesn't drop off through much of today, the gradually weakening forcing should still be enough to bring at least instances of moderate rainfall to the area. We will not have as much instability as we had on Tuesday, but HREF still shows a large area of 100-250 J/kg of MUCAPE for today. Because of the already saturated soils and the good chances for additional moderate rainfall for today, we have elected to issue a Flood Watch for northern and much of western Maricopa County. CAMs eventually show the rain shifting more into the eastern Arizona higher terrain during the overnight hours Wednesday night with lingering chances through at least Thursday morning across Gila County. By Thursday afternoon, the bulk of the energy from the system is expected to move into New Mexico with the next disturbance quickly approaching the region from the northwest.

Temperatures today and Thursday will be even cooler than the early part of the week with highs only averaging in the mid 60s across the lower deserts. Overnight temperatures will also be noticeably cooler with much of the area dipping into the 40s for lows.

LONG TERM /FRIDAY THROUGH TUESDAY/

The last of the Pacific weather systems will quickly take shape across northern and central California early on Thursday with the low really wrapping up Thursday evening and Thursday night across southern California. Guidance shows additional moisture advection just ahead of the system reaching southeast California with PWATs near 200% of normal by Thursday evening. Upper level jet forcing will also be ramping up quickly during the latter half of Thursday with the strongest forcing likely focused across southeast California Thursday night into Friday. The combination of the jet forced ascent, multiple vort lobes rotating through the area around the low center, and the abundant moisture should give rise to a large area of rain developing across southeast California by Thursday night before expanding through southwest Arizona on Friday.

The latest guidance shows average rainfall amounts of 0.5-1.0" across southeast California and far southwest Arizona Thursday night and Friday. Locally higher amounts of more than an inch are likely to occur, especially over higher elevation areas of southeast California and where any banding of heavier showers occurs. It seems fairly likely this will cause some flooding issues on Friday for the typical flood prone areas. A Flood Watch may end up being needed.

The track of the Friday and Saturday system is still shown to move south southeastward to over northern Baja Friday night into Saturday before shifting to the east later Saturday into Sunday. Guidance is still a bit uncertain with the latter half of the track and how close the low center will be to the Arizona/Mexico border. Rain chances should extend through the rest of southern and to a lesser degree across central Arizona later Friday into Saturday, but the potential rainfall amounts are much less certain. The current forecast for south-central and eastern Arizona mainly keeps rainfall amounts less than 0.25", but any track farther to the north would likely bump up those amounts.

Models then favor the weather system exiting to the east on Sunday with ridging gradually spreading in from the west on Monday. This should allow for drier and much quieter weather to settle in across the region by next Monday, likely lasting for most if not all of next week. NBM forecast highs are also shown to rise back into the normal range by early next week with readings around or just over 70 degrees and lows in the 40s to low 50s.

AVIATION

Updated at 0556Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Periods of SHRA, lower cigs and visibilities, variable wind directions, and a lower chance for TS will all be weather issues through Wednesday night. There will be chances for isolated to scattered SHRA throughout the TAF period. Exact timing of rounds of SHRA is low confidence, but there are a couple time periods when SHRA impacts are more favored, after midnight tonight through Wednesday morning and Wednesday night. In general, the greatest impacts with lower cigs, reduced vsby, and wind shifts will occur with individual rounds of showers. VFR conditions with cigs 040-060 will be the most likely outcome through the day Wednesday, then higher probabilities of MVFR cigs arrive Wednesday evening, with low chances (20-30%) for IFR cigs. Winds will favor a W component while showers persist to the west. Then a S/SE direction will follow during the morning, however directions become far more uncertain Wednesday afternoon as a west or north component starts to become more likely.

Southeast California/Southwest Arizona including KIPL and KBLH: Weather issues through Wednesday morning will be slight chances (20%) for SHRA, with occasional lower cigs down to around 050 and variable winds. Overall, VFR conditions are expected to prevail. Winds will favor a westerly direction at KIPL and southwest veering to northerly at KBLH. Variability in direction and speed will be common near any robust SHRA.

FIRE WEATHER

Periodic showers along with a few isolated thunderstorms will affect much of Arizona through tonight providing very good chances for wetting rains. Thursday will bring lingering chances for wetting rains over the eastern AZ higher terrain in the morning with rain chances increasing by Thursday evening across the western districts. Below normal temperatures and elevated moisture will remain in place keeping MinRHs in a 40-70% range following excellent overnight recovery greater than 80%. Locally gusty winds upwards of 20 mph will be possible at times, though weaker wind speeds will be more common through the period. Another weather system is expected to move mainly across the western districts on Friday leading to very good chances for wetting rains with more scattered shower activity across the eastern districts lasting through Saturday. Temperatures will mostly remain below normal through the weekend with humidities staying elevated.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Flood Watch through late tonight for AZZ541-542-545-547-557.

Flood Watch through this afternoon for AZZ534-537-538.

CA...None.