textproduct: NWS Phoenix

UPDATE...Updated Aviation Discussion

KEY MESSAGES

- Dry conditions with above normal temperatures will prevail across the region through the end of this week

- An approaching weather system will result in increased cloud cover, breezy conditions, and cooling temperatures by this weekend

- A follow on system early next week will result in further cooling with temperatures falling below normal Monday and Tuesday

SHORT TERM /Today through Friday/

Current GOES-18 wv imagery and 500 mb streamline analysis reveals a broad, low-amplitude ridge centered over the Desert Southwest with a weak embedded shortwave progressing harmlessly through N Mexico. Meanwhile, a cutoff low is positioned over the E Pacific well off the coast of N California. H5 hghts will remain in a 576-579 dam range over the forecast area today with H8 temperatures again exceeding 20C. This will result in high temperatures across the lower deserts reaching the mid 90s or around 10-12 degrees above daily normals. The only noticeable difference today will be an influx of high-lvl cirrus as a plume of Pacific moisture begins to stream into the region ahead of the approaching low. Due to the tightening of the 7H-5H gradient, there will also be enhanced breeziness across SE California this afternoon along with a bout of gusty sundowner winds in Imperial County this evening.

On Friday, the upper-lvl ridge axis will shift farther east into the S Plains, while the aforementioned cutoff low reaches the California coast and quickly transitions to an open wave. As this occurs, we will begin to see increasing SW flow aloft over the Desert Southwest along with H5 hghts falling to around 570-574 dam. Consequently, temperatures will cool by a few degrees, but will still remain above normal with lower desert highs in the upper 80s to lower 90s. Breezy conditions can be anticipated yet again across SE California and SW Arizona Friday afternoon and evening, especially around sunset in the Imperial Valley where an enhanced mountain wave signature will be present.

LONG TERM /Saturday through Wednesday/

The cooling trend will continue into this weekend as large scale troughing becomes established over the Intermountain West. Temperatures will cool from slightly above normal on Saturday to right around seasonal averages on Sunday. The first in a series of shortwaves embedded in the large scale trough will sweep across the Great Basin region on Saturday, but will be too far north of our region to provide any appreciable moisture and lift to generate showers across southcentral AZ. A majority of the moisture will be focused well east of the region into E New Mexico and W Texas. Therefore, NBM PoPs late Saturday into early Sunday have decreased dramatically and are now only around 10-15% at most, even in the higher terrain areas NE of Phoenix. The main weather impacts heading into this weekend will be winds as the mid-lvl hght gradient remains compact across the entire region. Gusts will range from 20-25 mph across the lower deserts and upwards of 30-35 mph in the higher terrain areas, especially at mountain peak level. The strongest winds look to be on Sunday as the next shortwave trough begins to approach from the west. Winds on Sunday may in fact reach low end advisory criteria across portions of SE California and the high terrain of S-C Arizona.

Ensemble members and deterministic guidance are in good agreement that a deeper shortwave trough will progress through the Desert Southwest Monday into Tuesday, with H5 anomalies reaching a minimum on Monday. This will be the coolest day of the forecast period with lower desert highs mainly in the low to mid 70s and lows in the 50s. Increasing cloud cover and even a few passing showers will be possible across the northern fringes of the forecast area Monday into early Tuesday as the trough axis passes overhead. Drier air will begin to filter into the region behind the departing weather system late Tuesday. As H5 anomalies transition from negative to neutral, temperatures will rebound from slightly below normal on Tuesday to near normal by Wednesday.

AVIATION

Updated at 1055Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No significant aviation weather impacts are expected through the next 24 hours under increasing high clouds. Early to mid morning easterly winds will shift to a light southerly wind by late morning and persist between into early afternoon before prevailing west southwest winds takes hold. Late afternoon/early evening winds up to 8-12 kts with gusts to 20 kts are expected. Diminishing west winds late evening will eventually turn easterly after midnight.

Southeast California/Southwest Arizona including KIPL and KBLH: No significant aviation weather impacts are expected through the next 24 hours under increasing high clouds. Winds will favor a W'rly component through the TAF period at KIPL. Winds are likely to gust up to 20-25 kts at KIPL in the afternoon and evening. Winds at KBLH will continue to follow familiar diurnal and nocturnal wind patterns and will also see gusty SW winds develop in the afternoon, peaking around 20-25 kts.

FIRE WEATHER

Dry conditions and well above normal temperatures will persist through the end of this week. MinRHs will range from 10-15% today before increasing above 15% starting on Friday. Overnight recovery will generally range from poor to fair across the region over the next couple nights, however low lvl moisture will trend upward by this weekend resulting in much better recovery up to 50-70%. Winds will follow typical diurnal tendencies, however enhanced upslope gustiness can be anticipated especially across the western districts beginning this afternoon. A weather system will move into the region this weekend, resulting in continued breezy to locally windy conditions and much cooler temperatures. Scattered showers will be possible mainly over the higher terrain of southcentral AZ, but CWR will remain low <10%.

PSR WATCHES/WARNINGS/ADVISORIES

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