textproduct: NWS Phoenix

KEY MESSAGES

- Above normal temperatures this weekend will briefly cool into a below normal range early next week.

- Breezy to locally windy conditions will materialize early next week with modest rain chances across Arizona higher terrain areas.

- A rapid warming trend with above normal temperatures is likely to return during the latter half of next week.

SHORT TERM /Today through Monday/

Early afternoon WV imagery depicts a weak vorticty center over the four corners propagating SE while shortwave ridging builds directly over the CWA. Deeper negative height anomalies upstream over the East Pacific are in the process of cutting off west of the California coast indicative of hemispheric pattern amplification and blocking development (common pattern evolution in May). While amplified blocking typically provides increased ensemble spread and reduced forecast confidence, only minor differences are noted affecting timing and depth of energy moving through the region next week. As such, there is good confidence of temporary shortwave ridging with above normal temperatures this weekend giving way to gradual height falls and positively tilted troughing with below normal temperatures slowly progressing through the region early next week.

The aforementioned four corners shortwave and associated cold air aloft has supported deeper convection over the White mountains this afternoon. While a shower could conceivably clip eastern Gila Co, the greater influence of this activity will be to reestablish the enhanced easterly wind gradient with increased overnight/morning gusts over ridge tops, eventually mixing into lower elevations though with little to no adverse impacts. Otherwise, with H5 heights in a 574-578dm range, narrow ensemble guidance spread yields excellent confidence of temperature 4F-8F above normal continuing Sunday. As the closed low approaches the Southwest Sunday afternoon/evening, the combination of midtropospheric height falls, enhanced jet energy, an expansive and deepening marine layer in San Diego County, and a frontal passage will support intensifying downslope flow and mountain rotors across western Imperial County. While there remains some model discrepancy regarding the extent and magnitude of wind gusts, pattern recognition and several high resolution models suggest solid wind advisory criteria with some modeling indicating a higher end advisory event.

Height falls and cyclonic flow within a positively tilted trough will slowly migrate inland Monday with H5 readings in a 568-574dm range resulting in rather abrupt cooling and high temperatures falling below normal Monday some 10F-15F cooler than Sunday. Increased wind speeds though the depth of the troposphere will translate into widespread gusts Monday afternoon; and while well short of advisory criteria could yield some localized blowing dust and regional hazy skies. Global models remain consistent in advertising a plume of midlevel moisture being pulled into the SW flow over southern Arizona Monday evening/overnight along an elevated front. While PWAT anomalies associated with this feature may reach 200% of normal, typical moisture levels are so low this time of year, raw total column PWATs only appear to reach near 0.75" and largely packed above 600mb with low level mixing ratios only 5-7 g/kg. Synoptic forcing looks quite robust at this time, however the amount of sub-cloud dry air and model trends towards focusing this moisture plume farther to the south near Tucson should preclude much of the CWA from receiving accumulating rainfall. Have trimmed the mandated NBM POPs in expanse and magnitude given the appearance of the typical model artifacts with only a 10-20% chance of accumulations over higher terrain locations southwest of Phoenix heading into Tuesday morning.

LONG TERM /Tuesday through Friday/

As the the upper low moves through the Desert SW Tuesday, temperatures will cool further with afternoon highs only reaching the upper 70s/lower 80s across the lower deserts. This will be a solid 10 degrees below normal for early May, and quite possibly the coolest temperatures across the forecast area for the next 6 months. Breezy conditions will also remain in place across much of the region. The low will finally exit east by midweek with upper level ridging building along the west coast. There are indications from guidance that a piece of energy left behind from the departing low could develop into a weak cutoff low over the Baja Peninsula during the latter half of the week, but as of right now, it looks to be too far to the south to have any sensible weather impacts for our region. With 500 mb height fields rapidly rising to around 580dm from the building ridge, temperatures by the latter half of the week will be on a rapid warming trend. The latest NBM is showing afternoon highs across the lower deserts rapidly warming from the middle 80s on Wednesday to middle 90s on Thursday. Additional warming into the triple digits, which would be the first occurrence since the unprecedented early season heatwave from late March, is being shown starting Friday.

AVIATION

Updated at 1755Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Occasionally gusty southeast winds and lower than usual confidence on directions this afternoon to around sunset will be the main weather issues under increasing mid and high cloud decks. Gusts to around 15-21 kts will subside within the next hour or so, with an easterly wind component continuing to be favored through at least Sunday morning. A period of variability or even a brief NW switch cannot be ruled out late afternoon through around sunset. E/SE winds will increase once again overnight, with another period of gusts to around 20 kts expected shortly after sunrise Sunday morning. Gusts will then decrease late morning as winds veer out of the south, leading to a period with a southerly cross runway component at KPHX starting midday, before a more pronounced SW wind takes hold later Sunday afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the next 24 hours under increasing high clouds. NE winds at KBLH are expected to decrease over the next few hours. After that point, winds at both terminals are expected to vary between SE and SW, with speeds AOB 10 kts. Extended periods of variability are likely.

FIRE WEATHER

Dry conditions and above normal temperatures will be observed through the weekend. A low pressure system will gradually approach the CA coast late this weekend, resulting in widespread breezy to locally windy conditions into early next week and temperatures cooling into a below normal category Monday-Tuesday. Gusty afternoon winds combined with low humidities will likely produce elevated fire weather conditions Sunday for portions of the western districts, including the Lower Colorado River Valley. As the low pressure system moves through the Desert Southwest early next week, the chance of showers will increase late Monday into the first part of Tuesday across the far eastern districts, however, the probability of wetting rains will remain on the low side. Afternoon MinRHs between 8-15% will be common today, increasing slightly into a 10- 20% range Sunday and 15-30% range early next week.

PSR WATCHES/WARNINGS/ADVISORIES

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