textproduct: NWS Phoenix

KEY MESSAGES

- Dry conditions with temperatures remaining 3 to 5 degrees above average across the lower deserts through Friday

- A strengthening ridge of high pressure over the Desert Southwest this weekend will promote the hottest temperatures of the year thus far.

- An Extreme Heat Watch is in effect from Saturday morning Monday evening for high temperatures ranging from 106 to 115 degrees across the lower deserts.

DISCUSSION

Forecast concerns for Extreme Heat will take shape by this weekend with lower desert highs climbing to above 110 degrees by Sunday. A strong sub-tropical ridge has set up off the coast of Baja with H5 heights as high as 595dm. This ridge is currently providing H5 heights of 590-592dm over our area which is near the 90th percentile of climatology. For our region, little will change through Friday as the center of the ridge slowly shifts eastward into northern Mexico, but it will undergo some slight weakening. Heights aloft over our region will basically stay stable albeit with a slight dip to between 588-590dm. NBM forecast highs for today through Friday undergo little to no change with readings topping out between 104-108 degrees each day, or 3-5 degrees above normal. Overnight lows will follow a similar pattern of slightly above normal.

By Saturday, the sub-tropical ridge is forecast to start strengthening again as it recenters itself just to our southeast. Ensembles show H5 heights within the center of the ridge reaching 595-596dm on Sunday with 592dm heights building over southeast CA to 594dm heights over the southeastern half of AZ. H8 temperatures over our area are also seen rising from around 28C over the next few days to as high as 32C on Sunday and Monday. This warming will translate down to the surface for Saturday- Monday with highs nearing 110 degrees Saturday before likely peaking between 110-115 degrees on Sunday and Monday, resulting in areas of Major HeatRisk. An Extreme Heat Watch remains in effect for all of the lower deserts for Saturday-Monday. Overnight low temperatures will also climb during this time with most lower desert readings between 75-80 degrees to 80-85 degrees within the Phoenix Metro.

Model guidance then shows a dry trough quickly approaching the California coast later Monday before likely tracking across our region Tuesday into Wednesday. There is still a good deal of model uncertainty with the strength and the exact track of the trough, but there is enough evidence to point toward a slight cooldown starting Tuesday. This should push lower desert highs to just below 110 degrees and likely eliminate the areas of Major HeatRisk, but there is still a chance this may not happen and we could still keep temperatures at or just above 110 degrees through the rest of next week. The temperature forecast for the middle of next week currently assumes the trough will be enough to bring high temperatures down to between 105-109 degrees. We should have a better idea on this potential cooldown within the next few days. No matter the eventual solution, dry conditions and clear to mostly clear skies are expected through at least the middle of next week.

AVIATION

Updated at 0527Z.

South Central Arizona including KPHX, KIWA, KSDL, KDVT; No major aviation concerns through the TAF period. KPHX may have some see some VRB winds during wind shift tomorrow morning while the northern terminals will see prolonged VRB conditions through the overnight period. By late tomorrow morning / early afternoon winds will shift back out of the west, with potential for gusts in the afternoon generally aob 20kts. FEW high clouds will persist through the TAF period. Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns through most of the TAF period. KIPL continues to hold SE'rly winds throughout the period, and KBLH will continue to hold a S to SSW direction. Tomorrow afternoon gusts are expected with speeds between 20-25 kts at KBLH, while KIPL can expect some elevated wind speeds near 16kts during this time as well. FEW high clouds will persist through the TAF period.

FIRE WEATHER

Above normal temperatures and dry conditions will prevail through the remainder of this week. Winds will continue to follow typical diurnal tendencies with periods of modest afternoon upslope breeziness (gusts of 20-25 mph at times). Minimum humidity will bottom out between 10-15% over the next few days with poor to fair overnight recovery between 20-50% region-wide. Temperatures are forecast to spike well above normal this upcoming weekend with afternoon highs reaching 110 or hotter as early as Saturday across the lower deserts as Min RHs lower in the 5-10% range.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Watch from Saturday morning through Monday evening for AZZ530>544-546>556-559>562.

CA...Extreme Heat Watch from Saturday morning through Monday evening for CAZ562>567-569-570.