textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Temperatures will warm heading into weekend, and continue warming heading into next week, reaching above normal levels by around Monday. - As the heat builds, it will lead to increasing coverage of Moderate Heat Risk and highs eventually reaching 110 degrees next week.

- Dry conditions will prevail through the weekend, although a sprinkle cannot be ruled out Saturday into Sunday, before isolated storm chances return over the Arizona high terrain during the first part of next week.

SHORT TERM /TODAY THROUGH SATURDAY/

A broad upper level trough still has influence over the greater Southwest, but a shortwave is lifting off to the northeast and the broad trough is gradually weakening across the West. H5 heights are currently around 588dam and are forecast to rise to approx 592dam into the weekend as subtropical high pressure builds back into the region. Current PWATs are near 0.2-0.3 in across the region, contributing to the clear skies and very dry conditions today. Seasonal surface winds, with afternoon breeziness will continue today through the weekend with directions and speeds following typical diurnal and topographical variations.

Temperatures today will remain similar to yesterday, with below normal readings as lower deserts reach the low 100s. However, temperatures will begin to rise a couple of degrees into the weekend, back to normal, with most lower deserts reaching 105F for highs and good chances (60-70%) of reaching 107-109F in the hottest communities, including Phoenix.

Mid and upper level moisture will increase into the region from the southwest this weekend, shedding off from TC Douglas well to the southwest in the E Pacific. Latest model guidance is highlighting PWATs rising to 0.9-1.1 in by Sunday morning. Scattered to broken mid and upper level clouds will spread into the region this weekend, with cloud bases mostly staying above 11-12k feet. In addition to the cloud cover, some embedded virga showers and maybe a very light rain shower are possible Saturday into Sunday, but the potential for any measurable rain (>0.01 in) is very low across the lower deserts (10% or less).

LONG TERM /MONDAY THROUGH THURSDAY/

The not so bad temperatures to start off July will unfortunately not last any longer as the subtropical high is expected to gradually become more of a dominant feature heading into next week. We will also have to begin to contend with increasing boundary layer moisture and higher dew points making it feel more uncomfortable as early as Sunday, but the higher humidities will be more noticeable going into the middle of next week. Ensembles have begun to shift where the center of the subtropical high is most likely to set up early next week with it more likely shifting directly over southern and central Arizona instead of to our northeast. This should not last long however, as the high is then favored to shift farther westward, potentially even settling off the coast of California by next Wednesday. The exact positioning of the high will not stop it from getting hotter as H5 heights are heavily favored to rise more into a 592-595dm range starting Monday and likely staying there through at least Tuesday and possibly Wednesday before lowering slightly again. Temperatures and humidities are expected to rise at the same time early next week with daytime highs peaking on Tuesday and/or Wednesday between 110-114 degrees across the lower deserts. This will lead to a widespread Moderate HeatRisk with potentially even some localized Major HeatRisk. Overnight temperatures will react to the increasing moisture and higher daytime temperatures with lows rising into the 80s nearly everywhere and potentially to near 90 degrees for portions of the Phoenix area by Tuesday.

Even with the increase in moisture during the first part of next week, we are not expecting much convective potential. Lower level moisture will still be very marginal with afternoon surface dew points still mostly in the mid to upper 40s. The marginal moisture will also have to contend with a high center directly over or close to our area creating a decent amount of subsidence. We may get some isolated Arizona high terrain showers or storms starting Monday or Tuesday, but PoPs are barely reaching 10-15%. For the latter half of next week, guidance is hinting at a further increase in moisture, but nothing too drastic. It may be enough to increase shower and storm coverage somewhat over higher terrain areas, but for now storm chances for the lower deserts still look to mostly remain below 10%.

AVIATION

Updated at 0455Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns are expected through Friday evening under gradually increasing mid to high clouds. The overall wind pattern will exhibit the typical diurnal tendencies with overall speeds aob 10 kts, with some occasional afternoon gusts in the mid to upper teens possible.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns are expected through Friday evening under gradually increasing mid to high clouds. At KIPL, westerly winds will persist into the overnight period, with southeast winds expected Friday morning through the afternoon before shifting out of the west once again Friday evening. At KBLH, winds will generally fluctuate between the south-southeast to southwest. Overall speeds will remain under 12 kts with some occasional gusts in the mid to upper teens possible during the afternoon/early evening hours.

FIRE WEATHER

High pressure will gradually move into the region over the next few days allowing winds to return to normal patterns with only the typical afternoon upslope/upvalley 15-20 mph gusts. Temperatures will warm up further, rising into the normal range starting Friday. Afternoon minimum humidities will continue to range between 5-10% through at least Saturday with overnight recoveries only reaching 15-30%. Despite the decrease in winds, seasonably elevated fire danger will persist through the weekend due to very dry conditions and very dry and receptive fuels. Moisture is likely to begin to increase over the region during the first half of next week allowing minimum humidities to improve to 10-15%, but temperatures will also heat up further with lower desert highs likely reaching 110 degrees.

PSR WATCHES/WARNINGS/ADVISORIES

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