textproduct: NWS Phoenix

KEY MESSAGES

- A weather system passing our region to the north will result in marginally breeziness conditions this afternoon followed by locally windy conditions and elevated fire weather concerns Friday for portions of Southeast California.

- A Wind Advisory has been posted from early Friday morning until the early afternoon for an area stretching from Joshua Tree NP to along the Lower Colorado River Valley.

- After a brief stint of near and below normal temperatures over the next few days, readings will rebound with widespread afternoon highs in the 90s expected by the end of the weekend.

SHORT TERM /TODAY THROUGH FRIDAY/

Current WV imagery and 500mb analysis reveals the Desert Southwest caught in the middle of two approaching areas of low pressure, each of which will impact conditions through the end of the work week. The southern most system, currently located off Baja Coast, will underhand upper-level moisture over the region, providing some decent cloud cover overhead. The other, more potent disturbance, currently spinning over the Northern Rockies, will slide further southeast through the day today, imparting at least some influence on the region this afternoon. Although not directly over us, the two troughs will help to tighten up the regional pressure gradient at least slightly which will help to generate some marginally breezy conditions this afternoon. Gusts should range generally between 15-25 mph for the majority of the region, with the higher end of that range focused over higher terrain areas and the Lower Colorado River Valley. Locally higher gusts can be expected in the typically breezier spots of Western Imperial County. Lower desert highs will be a degree or few warmer than yesterday, with readings in the middle to upper 80s being common.

Stronger winds can be expected as the northern most storm slides through the Great Basin and Intermountain West tonight into Friday, dragging a cold front along with it. This boundary will help increase our thermal and pressure gradients even further, helping to push gusts upwards of 35-45 mph, mainly from an area extending from Joshua Tree NP toward the Lower Colorado River Valley. Locally higher gusts will be possible around enhanced terrain features and gap wind prone areas. These strong winds will present difficult travel conditions, especially for high profile vehicles along portions of I-10 around and west of Blythe, CA, and some blowing dust channels cannot be ruled out. Due to the high confidence for gusts exceeding 40 mph, a Wind Advisory has been posted for the stretch of area mentioned above, valid from 3 AM through 1 PM MST/PDT Friday. Other breezy spots will be the Imperial Valley and portions of wester Yuma and La Paz Counties. However, gusts for these areas should range closer to 25-35 mph, though an isolated advisory-level gust would not be surprising.

The passage of the cold front will provide the region with at least a brief cool down to end the work week. Lower Desert temperatures will hover near to below normal, with the greatest departure from typical values this time of year being observed over western portions of our forecast area. Putting those words into numbers, Friday's afternoon highs will range in the lower to middle 80s.

LONG TERM /SATURDAY THROUGH WEDNESDAY/

Ensembles advertise the overall pattern stagnating somewhat for a few days late this weekend into early next week, with upper level ridging building over the West-Central CONUS and another relatively potent upper low diving southward from the Gulf of Alaska and settling off the West Coast. The influence of high pressure over the region will allow temperatures to rebound over the weekend, with lower desert highs once again reaching the 90s and in a decidedly above normal category by Sunday. Something that is becoming more clear in the global model guidance is that a strong surface high will shift from the Intermountain West to the Southern Plains by Sunday, allowing another E/SE'rly gradient wind event to take shape Sunday morning. This will mostly impact Southeastern AZ, but likely extend into South-Central AZ higher terrain east/southeast of Phoenix.

Forecast uncertainty increases considerably heading into the middle of the upcoming workweek, when the upper low off the West Coast is expected to move inland over the Great Basin or even over the Desert Southwest. The uncertainty is reflected in the probabilistic NBM temperatures, as IQRs for the forecast highs/lows increase to 5F or greater Tuesday onward. Overall, temperatures should retreat closer to or even slightly below seasonal normals during the middle of next week. Another uncertainty is whether the forcing from the incoming upper low will combine with meager moisture (mostly in the mid levels) to produce light shower activity over portions of AZ. However, the vast majority of global guidance shows the area remaining dry, with PoPs below 10%. From experience, the track of this low is also not promising to produce anything more than light precip totals favoring upslope areas and higher terrain.

AVIATION

Updated at 1745Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No significant weather issues will exist through the forecast period under mid to high cigs. Timing of directional wind shifts should be similar to the past 24 hours, although west winds will be maintained around the Phoenix metro longer into Thursday night than usual. Wind speeds from the mid afternoon through early evening will be stronger than the past several days with occasional gusts 15-20kt across the region. For KIPL and KBLH expect winds to pickup this afternoon with a WNW component and gusts reaching up to 20-25kts. Expect a period of increased gustiness at KBLH tomorrow morning with velocities reaching up to 20-25 kts sustained and gusts up to 30kts.

FIRE WEATHER

Dry and occasional breezy conditions will prevail through the next week. Temperatures will cool from near normal today to slightly below normal Friday, then warm above normal over the weekend. A weather system passing the region to the north will send a cold front down the Colorado River Valley and produce gusty winds Friday morning, with gusts to 30-45 mph for portions of Southeast CA and Southwest AZ. Winds will gradually relax heading into the afternoon as humidity drops into the single digits. Elevated and locally critical fire weather conditions are expected to materialize for portions of the western deserts Friday as a result, particularly along the Lower Colorado River Valley. Afternoon MinRHs below 15% and at times in the single digits will be common through the next 7 days, with minor day to day variations. Overnight recoveries between 30-50% tonight will drop into 15-30% range Friday and Saturday nights.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory from 3 AM to 1 PM MST Friday for AZZ530.

CA...Wind Advisory from 3 AM to 1 PM PDT Friday for CAZ560-561-564- 565-568>570.