textproduct: NWS Phoenix

KEY MESSAGES

- Lingering low pressure will result in continued breezy to windy conditions and below normal temperatures today.

- Temperatures will warm early next week, rising to slightly above normal starting midweek. Hotter temperatures with lower desert highs well into the nineties look possible by next weekend.

- A potential weather system during the latter portion of the upcoming week will increase rainfall chances parts of the region, with the best chances currently focused over the Arizona high terrain.

SHORT TERM /TODAY THROUGH FRIDAY/

Current objective analysis reveals troughing encompassing much of the Intermountain West with a vort max hugging the Arizona-Utah border. This system, after already producing 40-50 mph winds for SE CA and a few sprinkles/light showers for parts of AZ, will continue to influence the Desert Southwest for at least one more day, with the main weather impact being a continuation of enhanced winds. Once we start to convectively mix down higher momentum winds, widespread gusts 20-30 mph can be expected, with the top end of that range favoring the high terrain of South-Central AZ and the typical wind prone area of Imperial and Riverside Counties. Locally higher gusts should be focused over higher ridge top areas and the very southwestern corner of Imperial County. The latter of those locations will still see elevated potential for gusts approaching 50 mph through this evening, therefore, a Wind Advisory remains in effect until 11 p.m. PDT tonight. One other piece of the forecast today that cannot be overlooked is our regional high temperatures this afternoon as the associated cooler air with the above-mentioned disturbance helps to keep readings in the upper 70s to around 80 degrees. We talk about warmer-than-typical temperatures quite a bit, so it is nice to say that our afternoon values should be between 5-10 degrees below- normal for late April.

Heading into the front half of the upcoming workweek, our forecast area will find itself in a bit of a transition zone as subtropical high pressure begins to nudge at the broader negative height anomaly field. As we flip the pattern, the thermal profile will take some time to respond, so temperatures on Monday will only be a few degrees warmer than what is expected this afternoon, with readings in the upper 70s to lower 80s. With the interaction of these two different weather regimes, the regional pressure gradient will remain relatively tight, but not nearly as much as this weekend. Marginal breeziness with gusts 15-25 mph should be the extend of what is seen. The amplifying ridge will slice the stretched out troughing in two, becoming more entrenched across the Desert Southwest by Tuesday. In response, a more noticeable temperature increase will take place, jumping closer to normal with widespread middle 80s for lower desert locations.

LONG TERM /WEDNESDAY THROUGH NEXT SUNDAY/

Earlier in the week a piece of vorticity will come off the main trough moving through Western CONUS and form a closed low in the Pacific Ocean well off the coast of central CA. By the middle to end of the week the closed low will progress eastward and eventually move on shore during the later half of the workweek. As the low approaches our region, models show it becoming an open wave and getting wrapped into a shortwave trough moving through the Great Basin region. While models have come into better agreement on the timing of this system, looking like a Thursday event, they still disagree on the exact strength and placement of this system. The GEFS favors a slightly stronger and further south system whereas the ECMWF ensemble favors a slightly weaker and more northern system. If the GEFS were to come to fruition then that would lead to better precipitation chances and cooler temperatures for our region. Thursday has the largest temperature spread of this coming week and is currently a 9 degree spread between the 25th and 75th percentiles. Either way, it does look like temperatures will cool and PWATs will increase on Thursday. The latest NBM/WPC PoPs are around 10-20% across south-central AZ and 20-40% across the higher terrain and foothills in eastern AZ.

Heading into the weekend the models are in pretty good agreement on the overall synoptic pattern. The aforementioned low pressure system will quickly exit the region on Friday with a low amplitude ridge moving in behind it and building over our region. With ridging building in heights aloft will be on the rise. H5 heights look to go from 570-575 dm on Friday to 576-579 dm on Sunday. Additionally with high pressure overhead skies will be mostly clear. The ample sunshine and building high pressure will allow for temperatures to warm well above normal next weekend. Highs are currently forecasted to be in the mid to upper 90s (mid to upper 80s) across the lower deserts (higher terrain).

AVIATION

Updated at 1740Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The primary aviation concern through Monday afternoon will be periods of gusty SW-W winds under FEW to at times SCT cumulus this afternoon, with bases gradually lifting from around 7K ft to 9K ft AGL. Gusts between 20-25 kts will be common through the afternoon, subside between 01-03Z this evening, and then speeds will continue to relax through the remainder of the evening. Confidence is good in a later than usual switch to E/SE tonight. Then winds will establish back out of the SW-W mid-late morning Monday, with gusts to 15-20 kts developing during the afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH: T The main aviation concerns at the SE California terminals will continue to be gusty winds and lofted dust, particularly at KIPL. Winds are expected to remain SW at KBLH and W at KIPL through the entire forecast period. Gusts reaching up to 30 kts at KIPL and around 25 kts at KBLH will be common through the afternoon, then gusts will retreat closer to 20-25 kts at KIPL and subside at KBLH this evening.

FIRE WEATHER

A weather system will move through the region today leading to another day of increased winds. Wind gusts of 20-30 mph are expected across most locations, with gusts as high as 30-50 mph across portions of SE CA. Wind gusts across SE CA will gradually decrease through the day, but gusts upwards of 25-35 mph are still expected during the afternoon and early evening hours. This system will allow for minRHs to be in the 20-30% range before decreasing back into a 5-20% range during the first half of the week (Tuesday is currently forecasted to have the lowest RHs). Overnight recoveries will be in the 40-70% range tonight, but lower to 30-60% tomorrow and 20-40% on Tuesday night. Winds will return to more seasonable breezy afternoon conditions during the first half of the week and are expected to fall short of creating widespread elevated fire weather concerns. Another weather system looks to move through the region during the later half of the workweek leading to increased RH and slight chances for rain, however CWR remains very low at this time.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...Wind Advisory until 11 PM PDT this evening for CAZ562.