textproduct: NWS Phoenix

KEY MESSAGES

- High pressure will stick around for one more day, keeping the dry conditions and above normal temperatures in place. - An unsettled weather regime will lead to periods of light rain from Wednesday afternoon through Thursday night.

- Drier weather should return by the weekend with temperatures still hovering near to slightly above normal.

SHORT TERM /Today through Wednesday/

Upper level ridging is now fully in control across the region, but it won't last long as a large cut-off low to our southwest will start to move toward the area later today into Wednesday. Ahead of this low, we are already seeing strong moisture advection above 20K feet with guidance showing this moisture to gradually lower to between 12-15K feet later today. The ridge overhead has pushed H5 heights to around 580-582dm leading to noticeable warming. The higher clouds today may keep daytime highs down slightly, but NBM guidance still shows readings from the lower 70s across the western lower deserts to the mid 70s in the Phoenix area.

Moisture will continue to improve over the region on Wednesday as the large cut-off begins to move in from the southwest. Forecast PWATs are shown to increase to around 250% of normal by Wednesday morning before peaking around 300% of normal Wednesday afternoon through Wednesday night. Forced ascent will begin to increase during the daytime hours Wednesday with models showing a band of light rain developing along a leading wing of vorticity. There is still some uncertainty how much rain will fall with this first band of rain as there will still be some residual dry air in the lower levels. However, recent guidance has been trending toward a faster top-down saturation and this may lead to much of the area seeing a few hours of steady light rainfall with measurable amounts potentially as high as 0.10-0.20" during the latter half of Wednesday.

LONG TERM /Thursday through Monday/

After the first batch of rain moves through the area later on Wednesday, there looks to be a break in the organized forcing Wednesday night into Thursday morning. However, there should still be enough upslope ascent for some scattered showers focused just to the north and northeast of the Phoenix area. The next round of more organized rain is likely to come from the main shortwave trough as it finally tracks across southern California Thursday morning into central Arizona Thursday afternoon and evening. This should bring another decent batch of showers, first over southeast California Thursday morning and then through southern and central Arizona Thursday afternoon. This additional rainfall should bring the storm total rainfall up to an average of 0.05-0.15" across the western deserts, 0.10-0.25" across the south-central Arizona lower deserts and 0.25-0.50" over the higher terrain northeast of Phoenix. Rain chances will gradually diminish Thursday evening into Thursday night with any lingering chances mainly focused over the Arizona higher terrain after midnight. Upper level ridging and drier air aloft will quickly work into the region by Friday, ending rain chances across the higher terrain by around noon Friday.

Gradual drying is expected to continue through the weekend as troughing remains positioned across the eastern Pacific into the Western U.S. There will likely be another couple of shortwaves moving through the trough through early next week, but the first one should miss our region to the north. By the time the second one potentially gets close to our region early next week, moisture should be much more limited resulting in little if any additional rain chances.

Despite the unsettled weather pattern late this week into next week, temperatures are expected to stay quite mild. The NBM shows daily highs mostly in the upper 60s to the lower 70s with overnight lows staying at least 10 degrees above normal through Friday night. Eventually by early next week, overnight lows will dip lower with readings back into the 40s to lower 50s once some drier air moves back into the area.

AVIATION

Updated at 0531Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation weather concerns expected through the TAF period. Winds will maintain an easterly component throughout the TAF period, with speeds expected to generally be aob 10kts with the exception of elevated speeds and gusts tomorrow afternoon, similar to what we saw today. Currently no westerly shift is expected at any terminals tomorrow afternoon. SCT-BKN mid and high level clouds are expected through the period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period. Winds at KBLH are expected to maintain a northerly component through the period, with speeds generally aob 10 kt, with some elevated wind speeds expected tomorrow afternoon. At KIPL, W to NW winds will prevail with speeds aob 10kts. SCT-BKN mid and high level clouds are expected through the period.

FIRE WEATHER

Slightly above normal temperatures and dry conditions will give way to a rapid increase in moisture Wednesday. Minimum humidity levels in a 20-30% range at lower elevations, and somewhat higher in far eastern districts today will increase closer to 25-40% Wednesday before peaking at 50-70% for Thursday and Friday. Enhanced north to northeast winds will be common again today, particularly across ridge tops of eastern districts where gusts of 20-30 mph will be possible through early afternoon. Speeds should relax by Wednesday as clouds and humidity levels increase. Periods of showers are then expected during the latter half of Wednesday through Thursday with overall light rainfall amounts for much of the lower deserts to 0.25-0.75" in higher terrain areas. Somewhat drier conditions will work back into the region by the weekend, but humidities will remain elevated as temperatures remain 5-8 degrees above normal.

PSR WATCHES/WARNINGS/ADVISORIES

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