textproduct: NWS Phoenix

UPDATE

06Z Aviation Discussion.

KEY MESSAGES

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

- A couple 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/

Mid level water vapor imagery and 500mb RAP40 analysis shows upper level ridging over the desert SW this morning, with upper level troughing to the west, currently centered just off the coast of Northern California. This troughing feature is expected to move onshore by late this evening but looks to quickly degrade as it traverses over northern California and into The Great Basin area. While the core of this system will be well to our north it will help increase winds, especially in southeast California where gusts in excess of 35 mph will be possible late tonight into Saturday morning. Afternoon highs today across the lower deserts will still remain above normal, with most areas staying in the low 90s with localized areas in the upper 80s.

Trailing close behind this initial troughing feature is a second, stronger system that will dive down along the NW coast. This second system is expected to reach the northern California coast by Saturday afternoon and continue to move inland over the weekend. Again the core of this system will be will to our region's north, however with better upper level jet support it will not degrade as quickly as the first system. This will lead to increased breezy to windy conditions starting Saturday afternoon, but more notably Sunday afternoon where advisory level winds are very possible across southeast California into portions of the Arizona high terrain. Meanwhile in the Phoenix Metro winds wont reach advisory levels Sunday afternoon, but gusts near 20 mph will be common.

Along with both of these troughing systems upper level moisture will increase with PWATS already increased today to near 150% of normal. However, after the first system degrades over land drier air will filter back into the region Saturday morning/Afternoon before the following system can reintroduce moisture into the region from the southwest starting Sunday. PoPs continue to stay fairly low over the weekend with most of the region at or below a 10% chance of precipitation. Any activity that does develop will likely be virga showers.

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 0550Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Wind directions and timing of wind shifts will be the main weather uncertainty through Saturday afternoon. The typical nocturnal switch to easterly at KPHX is expected to be delayed overnight, and instead there will likely by periods of calm and VRB. If easterly flow does become establish, it will be short lived and winds will return out of the W/SW by 15Z-17Z. Gusts up to 20 kts are expected to materialize at all terminals Saturday afternoon. A few weak showers may develop and pass by the NW periphery of the Phoenix Metro Saturday morning between 10-14Z, with little to no impacts expected. FEW to SCT mid-high clouds will progress over the region through Saturday morning.

Southeast California/Southwest Arizona including KIPL and KBLH: The primary weather issue will be strong gusty winds through Saturday evening, particularly at KIPL. Winds should maintain a westerly direction and KIPL and south to southwest at KBLH through the period. Gusts will continue overnight at KIPL, but will likely subside for several hours around sunrise. Confidence is high that gusts 20-30 kt will become common at both terminals again Saturday afternoon. There is even a moderate chance of gusts exceeding 35 kts at KIPL by Saturday evening.

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 afternoon/evening winds. MinRHs today will range from 10-20% before gradually increasing by the end of the weekend and peaking on Monday at 25- 35% then returning mostly between 15-20% Tuesday. 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 until 5 AM PDT Saturday for CAZ562.