textproduct: NWS Phoenix

UPDATE

Updated 06Z Aviation Discussion.

KEY MESSAGES

- Scattered showers and thunderstorms will affect the Arizona high terrain through this afternoon.

- Near normal temperatures early this week will cool to below normal levels by midweek with afternoon high in the mid to upper eighties across the western deserts to lower nineties across the south-central Arizona lower deserts.

- Breezy to locally windy conditions will materialize across southeast California on Tuesday and then areawide on Wednesday.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The latest water vapor satellite imagery indicates a pronounced shortwave trough centered across central Arizona with the associated upper-level forcing in the form of strong divergence aloft centered over the northeastern 2/3rds of the state. The combination of this forcing along with sufficient moisture and instability will result in afternoon showers and thunderstorms across the Arizona high terrain to the north and east of Phoenix. Meanwhile, across the rest of the region, drier air and subsidence moving in on the southern and backside of the trough will result in mostly clear skies. With the activity developing over the higher terrain areas to the north and east of Phoenix, a southward propagating outflow boundary is likely to move into portions of the Phoenix metro area late this afternoon/early evening resulting in some gusty winds. Afternoon high temperatures today will once again be right around seasonal levels with readings topping out in the mid to upper 90s across the lower deserts.

The next weather maker will be in the form of a strong Pacific low that will move in from the Pacific Northwest into northern/central CA and western Nevada Tuesday through early Wednesday and will meander across these locations through the latter half of the week. Strong height falls and a tightening pressure gradient will lead to breezy to windy conditions developing across portions of southeast California on Tuesday with peak afternoon/evening gusts in the order of 25-35 mph. Across the western half of Imperial County, mountain rotors will lead to higher gusts that will likely exceed 40 mph. As a result, wind advisories have been hoisted across the western half of Imperial County, including the Imperial Valley for Tuesday evening into the first part of the overnight. The strong winds will also be capable of resulting in areas of blowing dust. The strong winds aloft from the low will then spread into Arizona on Wednesday, resulting in breezy to locally windy conditions materializing across most of the region as peak afternoon/early evening reach 20-35 mph, with stronger gusts expected across the western half of Imperial County once again. With the gusty winds will come an elevated fire threat as well.

As the upper-level low settles to our northwest through the latter half of the week, temperatures will cool to below normal levels. Afternoon highs on Wednesday will likely remain in the mid to upper 80s across the western deserts, or around 10 degrees below normal for late May. For the south-central Arizona lower deserts, afternoon highs on Wednesday will top out mostly in the lower 90s, with central Phoenix topping out near 95 degrees.

LONG TERM /THURSDAY THROUGH SUNDAY/

Model guidance continues to trend toward a slower progression of the Pacific low later this week with the low gradually filling beginning Thursday before finally lifting northeastward through the Great Basin on Friday. The close proximity of low on Thursday and probably even Friday will continue to keep temperatures below normal across our area with highs at most in the lower 90s either day. Thursday is expected to be another breezy day across south- central and eastern Arizona, but gusts should mostly stay below 25 mph.

The weather pattern going into next weekend is likely to result in an upper level ridge building across at least eastern portions of the Southwestern U.S. leading to warming conditions. Models favor another Pacific low, but staying mostly off the Pacific Northwest coast allowing ridging to build over the Central U.S. and likely extending into our region. NBM forecast temperatures reflect this building ridge by calling for highs back into the normal range for the coming weekend and potentially even above normal with the start of June.

AVIATION

Updated at 0540Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant aviation weather impacts are expected through Tuesday under occasional high clouds. Light variability early tonight should give way to prevailing easterlies by 09-11Z. Winds late morning through mid afternoon Tuesday will favor a SSE-SSW component with speeds around 5-10 kts. W-SW winds will increase late afternoon and evening with gusts reaching as high as 20-25 kts.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will be the main aviation weather impact during the next 24 hours, with ongoing 25-30 kt westerly gusts at KIPL. These winds should gradually subside after midnight. Winds will increase again Tuesday afternoon at both terminals with peak gusts around 30-35 kts at KIPL and around 30 kts at KBLH. Wind directions will be out of the west through the period at KIPL and favor a S-SW at KBLH. The winds will likely generate blowing dust enough to create some slantwise visibility impacts with a low chance for surface visibility reductions. Mostly clear skies will be common through Tuesday morning before high clouds move in.

FIRE WEATHER

A mostly dry weather system will exit the region later today, but it will allow for continued chances for showers and isolated thunderstorms over the Arizona high terrain through this afternoon. There is a 20% thunderstorm threat across Gila County and far northeastern Maricopa County, but with limited rainfall potential the threat for new wildfire starts due to lightning strikes will be heightened. MinRHs will mostly stay between 10-15% across the lower deserts to 15-20% over higher terrain areas. A second much larger weather system will then dive southward into the Southwestern U.S. by mid week creating breezy to locally windy conditions. Elevated fire weather conditions will become a concern starting Tuesday as winds pick up, but a dip in temperatures and a slight increase in RHs will somewhat help to curtail the threat. The gusty winds will be the most pronounced on Tuesday and Wednesday for the western districts and Wednesday and potentially Thursday for the eastern districts. As winds die down late week and through the weekend, temperatures are forecast to rise to above normal while afternoon RHs fall to around or even below 10%.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory from 3 PM Tuesday to 5 AM PDT Thursday for CAZ562.

Wind Advisory from 5 PM Tuesday to 3 AM PDT Wednesday for CAZ566- 567.