textproduct: NWS Phoenix

UPDATE

Updated Aviation

KEY MESSAGES

- Above normal temperatures will occur again today while winds increase in advance of an incoming weather system.

- A slow moving weather system over the weekend into early next week will result much cooler temperatures, breezy to windy conditions, and rain chances focused over higher terrain areas.

- High pressure will eventually settle back into the region by the middle of next week leading to warmer and drier conditions.

SHORT TERM /Today through Sunday/

Upper level ridging over the Desert Southwest will gradually give way to a large upper level trough slowly moving its way into the Western U.S. through the weekend. The first disturbance is currently centered off of northern California and it is expected to quickly dissipate as it moves inland later today into early Saturday. It will however help to bring increased winds today across much of the area, particularly across southeast California where afternoon/evening gusts in excess of 35 mph will be possible. The warm air mass in place across the Desert Southwest will also stick around helping to bring another day of highs above 90 degrees across the lower deserts.

A second even stronger shortwave trough is then anticipated to quickly dive southward along the backside of the large scale trough later today into Saturday reaching the California coast by Saturday afternoon. This disturbance will have better upper level jet support and thus it will remain quite potent as it moves onshore into central/northern California. The track of the low center is still forecast to be well to our north as it moves into Nevada on Sunday with windy conditions being the main impact for our region Saturday and Sunday. The strongest winds are expected to occur on Sunday with Advisory level winds very possible across southeast California into portions of the Arizona high terrain.

Moisture across the region will improve today, but it will largely be aloft before another batch of dry air spreads through the region on Saturday. The second stronger disturbance is likely to be close enough to pull better moisture northeastward into our region starting Sunday, but again much of the moisture will be aloft. PoPs this weekend mostly stay below 10% areawide with at most a few virga showers possible across the area.

LONG TERM /Monday through Thursday/

As the second shortwave trough weakens over Nevada on Sunday, a third shortwave is shown to move southeastward along the California coast Sunday night into Monday eventually merging with the leftover Nevada shortwave energy. Guidance is in good agreement showing this combined shortwave energy moving through the northern 2/3rds of Arizona later on Monday. This should provide our best rain chances as some moisture is likely to pool along a weak cold front moving west to east across Arizona Monday afternoon/evening. NBM PoPs are a bit higher than what was shown 24 hours ago, but chances are still at most 10-20% in the Phoenix area to 25-40% over the higher terrain northeast of Phoenix. Any showers that do develop should provide little accumulating rainfall.

Monday will also bring our coolest temperatures of the period with highs likely only topping out in the mid to upper 70s, or 6-8 degrees below normal. As skies clear out Monday night/Tuesday morning overnight temperatures will dip into the 40s for rural areas to as cool as 50 degrees within the Phoenix metro. Starting Tuesday and potentially lasting through the rest of next week, quasi-zonal dry westerly flow is favored over our region. This should lead to an initial slow warming trend through mid week before temperatures settle at or just above normal later next week.

AVIATION

Updated at 1700Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind directions and timing of wind shifts will be the main weather issue through Saturday afternoon under periods of thicker mid/high cigs. A brief period of early afternoon southerly cross runway directions (140v220) will be likely today followed by a few late afternoon/early evening gusts around 15kt. The nocturnal switch to easterly may be delayed into the overnight, or locally not occur at all resulting in low forecast confidence beyond this evening.

Southeast California/Southwest Arizona including KIPL and KBLH: The primary weather issue will be strong gusty winds, particularly at KIPL this evening under periods of thick mid/high cloud decks. Winds should maintain a W/SW direction through the period with gusts most pronounced late afternoon through the evening. Confidence is good that gusts 20-30kt will be common with KIPL potentially peaking over 30kt at times this evening. Lofted dust and slantwise vsby issues may arise this evening, with greater uncertainty whether sfc vsby would be affected.

FIRE WEATHER

The weather pattern will become more active through the weekend, but overall dry conditions will still prevail. The biggest impacts will come from an increase in winds starting as early as this afternoon across the western districts. MinRHs today will range from 10-20% before gradually increasing this weekend and peaking on Monday at 25- 35%. As a weather system pushes through the region Sunday into Monday, winds will become breezy to windy across the entire area with gusts 25-35 mph quite common on Sunday. Due to the lower RHs today and even Saturday, elevated fire weather conditions may become an issue. Scattered showers will be possible mainly over the higher terrain of southcentral AZ on Monday, but CWR will remain low <10%. High pressure will then settle back over the region going into the middle part of next week leading to dry and warm conditions once again.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory from 5 PM this afternoon to 5 AM PDT Saturday for CAZ562.