textproduct: NWS Phoenix

UPDATE

18Z Aviation Discussion.

KEY MESSAGES

- A dry front will sweep the region from the northwest leading to locally windy conditions and elevated fire weather concerns, primarily for portions of Southeast California later this morning.

- A Wind Advisory will be in effect from early this morning until the early afternoon for an area stretching from Joshua Tree National Park to along the Lower Colorado River Valley.

- Temperatures near to slightly below normal today will warm back into an above normal category over the weekend, with widespread lower desert highs in the nineties likely by Sunday.

SHORT TERM /TODAY THROUGH SUNDAY/

A core of strongly negative midlevel height anomalies sits over North-Central Montana extending into Southern Canada early this morning, with a shortwave trough axis attached to it and swinging through the Great Basin and into Utah. Clues from surface analysis and station observations, midlevel wv imagery, and early morning RAP analysis indicate that a low-level front and associated area of tight pressure/temperature gradients is moving southward through Southern NV. Surface winds are picking up at several sites in the CA/AZ/NV tri-state area, but the main surge of more widespread windy conditions will not occur until after sunrise for our western deserts. A Wind Advisory remains in effect through 1 PM MST/PDT this afternoon for an area extending from Joshua Tree NP toward the Lower Colorado River Valley, where gusts to between 30-45 mph will become common after sunrise. These strong winds will present difficult travel conditions, especially for high profile vehicles along portions of I-10 around and west of Blythe, CA. Some blowing dust channels cannot be ruled out. 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. As local pressure/temperature gradients relax during the afternoon, so too will the winds.

Ensembles remain in excellent agreement that this initial shortwave will quickly eject eastward, with upper level ridging shifting over the Western US in its wake and building over the West-Central CONUS late this weekend into early next week. Meanwhile, an upper level low dives southward off the Pacific Northwest Coast and eventually settles off the NorCal coast. Temperatures today, thanks in large part to the front passing over the region, will be near to slightly below normal, with the below normal readings more common out west. The influence of upper level ridging will allow temperatures to rebound into an above normal category over the weekend. This will translate to lower deserts highs near 90F by Saturday. Forecast highs from the latest NBM maintain Sunday as the warmest of the next 7 days, with lower desert highs likely attaining the middle 90s. The influence of upper level ridging will maintain highs in the 90s into early next week.

As the initial shortwave ejects eastward over the next couple days, an attendant area of surface high pressure currently over the Great Basing will shift over the Rockies, then slide south southeastward over NM/Western TX by Sunday morning. NAEFS mean MSLP in this area will in fact exceed the 90th percentile and locally upwards of the 97th percentile of climatology. This will set up a strong ESE-WNW regional pressure gradient by Sunday morning. As a result, another round of breezy to locally windy conditions are expected to develop for the southeastern portion of AZ. For our forecast area, the strongest winds will be focused over higher terrain to the east/southeast of Phoenix. This southeasterly fetch will moisten the midlevels of the atmosphere modestly, and even allow dewpoints across South-Central AZ to reach the 30s F from their much drier values in the teens Saturday night.

LONG TERM /MONDAY THROUGH THURSDAY/

Early next week, the upper level pattern with West-Central CONUS ridging and a broad upper low off the West Coast will be maintained, however, shortwaves rotating around the broad upper low to our northwest will bring sensible weather changes for the forecast area as we head into the middle of the week. Forecast uncertainty remain moderate to high, with WPC cluster analysis revealing discrepancies in timing and the N/S displacement of the upper low as it eventually makes its way inland. The uncertainty is still reflected in the probabilistic NBM temperatures, as IQRs for the forecast highs/lows increase to 5F or greater Wednesday 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 shortwaves rotating about the broad 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%. Regardless, this pattern evolution will almost certainly result in another widespread breezy to locally windy period during the middle of the upcoming work week.

AVIATION

Updated at 1808Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No major aviation concerns throughout the TAF period. Winds will follow typical diurnal tendencies with wind speeds mostly aob 10kts. Winds will pick up slightly this afternoon into the evening hours but no major gusts are anticipated. However, early tomorrow afternoon gusts between 15-20kts are possible between 16-18Z. Otherwise, clear skies will continue through most of the period, with FEW high clouds filtering into he region by the end of the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH:

Gusts will continue to be the main aviation concern this TAF period. These strong northerly gusts will continue into the early potions of the afternoon, where then KIPL will relax to aob 10kts by 22-23Z and KBLH will relax to aob 10kts by 03-04Z. Otherwise, clear skies will continue through most of the period, with FEW high clouds filtering into he region by the end of the TAF period.

FIRE WEATHER

Dry and occasionally breezy conditions will prevail through the next week. A dry cold front is currently moving southward down the Colorado River Valley, which will produce gusty winds later this 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 as a result, particularly along the Lower Colorado River Valley. Winds will be much lighter, generally below 15 mph, on Saturday. 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 will offer little relief this weekend, with values commonly between 10-30% (on the lower end of that range for the western deserts).

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Wind Advisory until 1 PM MST this afternoon for AZZ530.

CA...Wind Advisory until 1 PM PDT this afternoon for CAZ560-561-564- 565-568>570.