textproduct: NWS Phoenix

KEY MESSAGES

- A large low pressure system will meander across California through the latter half of the week leading to breezy to locally windy conditions and elevated fire weather conditions across the region.

- Temperatures will cool to below normal levels starting Wednesday with afternoon highs in the mid to upper eighties across the western deserts to the low nineties across the south-central Arizona lower deserts.

- Above normal temperatures are forecast to return by early next week with highs topping 100 degrees as early as Sunday.

SHORT TERM /TODAY THROUGH WEDNESDAY/

The latest water vapor satellite imagery as well as streamline analysis show a large, potent upper-level low centered near northern CA. Modest height falls and an increasing pressure gradient will lead to increasing winds this afternoon through this evening, particularly across southeast CA through the western third of Arizona, where gusts between 25-35 mph can be expected. Across the western half of Imperial County, mountain rotors will lead to even higher wind gusts in excess of 40 mph where wind advisories are in effect. With the strong winds will also come the potential for blowing dust, resulting in temporarily reductions in visibilities. Afternoon high temperatures today will top out in the mid 90s across most of the lower desert locations.

The aforementioned upper-level low will slightly migrate into central CA on Wednesday. As it does so, 500 mb height fields will decrease into the 568-576dm range and thus cooler surface temperatures into a below normal category can be expected. Afternoon highs across the western deserts are only expected to top out into the mid to upper 80s, which will be a solid 10 degrees below normal for late May. Across the south-central AZ lower deserts, afternoon highs will be warmer, with readings topping out in the low 90s. Breezy to locally windy will extend areawide as the upper-level jet on the southeast periphery of the trough extends into AZ. Widespread afternoon/evening peak gusts are expected to range between 25-35 mph, with locally higher gusts across the western half of Imperial County once again.

LONG TERM /THURSDAY THROUGH MONDAY/

Model guidance heavily favors the Pacific low staying in place across California into Nevada through Thursday, but it expected to begin filling and lessening the threat for windy conditions. Thursday should be another breezy day, but more muted compared to today and Wednesday. The low is forecast to finally begin shifting more into the Great Basin while continuing to weaken on Friday. NBM forecast temperatures will stay below normal Thursday and Friday with highs anywhere from the mid to upper 80s across the western deserts to around the lower 90s across the south-central Arizona lower deserts.

The upper level weather pattern should weaken across much of the Western U.S. over the weekend with weak ridging to zonal westerly flow taking over across the Desert Southwest. Height rises and warming conditions are expected beginning this weekend, likely persisting through early next week. The latest NBM/WPC forecast temperatures shows highs around 100 degrees by Sunday and as high as 104-108 degrees by next Tuesday.

AVIATION

Updated at 1730Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected throughout the TAF period. Winds will follow diurnal trends with a slower than normal switch to the west which will allow for a window of southerly crosswinds at KPHX and KDVT. Marginal breeziness around 15-20 kt will be observed through the afternoon and evening before speeds relax after sunset. Some passing high cirrus will move over the region, but skies will be mostly clear through most of the forecast.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to windy conditions will be the main aviation concern over the next 24 hours. Gusts upwards of 35 kt are expected at KIPL this evening, with hints of potentially higher gusts through around 09-10Z. However, confidence these higher gusts is low at this time, so updates to the TAF may be needed if gusts 35+ kt are realized. These enhanced winds will increase the potential for blowing dust, but the orientation of the winds should limit extended periods of reduced VIS. At KBLH gusts closer to 25 kt can be anticipated, but some uncertainty exists there as well, as there are signs gusts closer to 30 kt are possible. Again, updates may required if the TAF becomes out of tolerance with observations. Other than some passing high cirrus, skies will be mostly clear during most of the forecast.

FIRE WEATHER

A much larger weather system will dive southward into the Southwestern U.S. over the next couple of days creating breezy to locally windy conditions. Elevated fire weather conditions will become a concern starting this afternoon as winds pick up and MinRHs stay between 10-20%. The gusty winds will continue through at least Wednesday with the strongest gusts of over 30 mph affecting portions of the western districts, while temperatures dip and MinRHs improve slightly (15-25%). Breezy conditions may persist into Thursday before dying down into Friday as the weather system weakens and moves away from the region. High pressure is then expected to build across the region over the weekend into early next week leading to an increase in temperatures and falling RHs, but winds are forecast to be fairly light.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until 5 AM PDT Thursday for CAZ562.

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