textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- An Extreme Heat Warning will be in effect for Phoenix and portions of southeast California on Sunday and Monday.

- Moderate HeatRisk will impact the majority of the area through Tuesday with isolated major HeatRisk Sunday and Monday.

- Monday is expected to be the hottest day with lower desert high temperatures peaking between 105 and 110 degrees.

SHORT TERM /TODAY THROUGH MONDAY/

Upper level ridging is now fully in control across the Southwestern U.S. providing hot temperatures and dry conditions. The center of the ridge will remain offshore today and for the first part of Sunday before moving directly overhead late Sunday through the first part of Monday. The current H5 heights of 581-583dm along with an already very warm boundary layer will allow for even hotter daytime temperatures today with readings between 101-104 degrees in the Phoenix area to 103-106 degrees across southeast California and southwest Arizona. As the center of the ridge begins to move into the region from the west on Sunday, H5 heights will rise to 585-587dm before peaking between 588-591dm on Sunday.

Between now and Monday, guidance indicates H8 temperatures warming another 4C, peaking near 30C on Monday. This warming aloft is expected to easily mix down through the boundary layer with the biggest change in temperatures from Sunday into Monday. Forecast highs have barely changed over the past several forecast packages and still call for 103-107 degrees Sunday and 106-110 Monday. Both days will represent a high-end Moderate HeatRisk for nearly all locations across southeast California through southern and central Arizona with Monday having the highest areal coverage (~25%) of Major HeatRisk. An Extreme Heat Warning has been issued for western portions of Imperial County and for the Phoenix metro on Sunday and Monday.

LONG TERM /TUESDAY THROUGH FRIDAY/

A gradual change in the upper level pattern will help to bring some modest heat relief by the latter half of next week. The first change will be a weak trough that is forecast to develop just west of southern Baja on Sunday before tracking northward along the California coastline on Tuesday. This feature is not expected to bring big changes to our region, but it will lead to increased southerly flow and moisture while also somewhat displacing the ridge to our east. Models show decent moisture advection mainly above 15K feet into our region starting Monday night, but more so Tuesday night into Wednesday. Tuesday may bring some sparse higher level clouds, before thicker and more cloud coverage is likely to move in on Wednesday.

The track of the shortwave trough across California Tuesday and Wednesday is also expected to lower heights across the Desert Southwest, but any cooling will be slow to occur. Tuesday's forecast highs are very similar to Sunday's expected readings, but by Wednesday highs are likely to fall back to just above 100 degrees. A larger, but weakening Pacific low is then expected to reach the California coast sometime Wednesday into Wednesday night before moving east northeast through Nevada and Utah on Thursday and/or Friday of next week. This disturbance should continue to aid in weak height falls across the Desert Southwest late next week potentially dropping daytime highs into the upper 90s, or around five degrees above normal.

AVIATION

Updated at 1124Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No aviation weather concerns under mostly clear skies can be expected throughout the TAF period. The overall wind pattern will continue to exhibit the typical diurnal tendencies with speeds aob 12 kts, although occasional gusts near 20 kts will be common this afternoon through early evening.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns under mostly clear skies can be expected throughout the TAF period. At KIPL, winds will generally prevail out of the west, with the exception of a period southeasterly winds during the early to mid-afternoon hours. At KBLH, winds will generally fluctuate out of the south to southwest during the day and veer north late tonight. Overall wind speeds will be aob 12 kts, although some gusts upwards of 20-25 kts are anticipated at KIPL for a few hours this evening.

FIRE WEATHER

Hot and dry conditions will prevail well into next week with lower desert highs topping 100 degrees through at least Tuesday. With afternoon highs warming 10-15 degrees above normal, minimum humidity levels will mostly fall into the single digits each day. Correspondingly, overnight recovery will only be in a poor to fair 20-35% range. Winds will be very typical for mid May through Monday with some gusts around 20 mph common during mid/late afternoon. The combination of the hot temperatures, very low RHs, dry fuels, and breezy conditions focused during the late afternoon hours should result in elevated fire weather conditions for portions of the area.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Sunday to 8 PM MST Monday for AZZ537-540-542>544-546-548-550-551.

CA...Extreme Heat Warning from 10 AM Sunday to 8 PM PDT Monday for CAZ562-563-566.