textproduct: NWS Phoenix

KEY MESSAGES

- Hot temperatures will continue through the end of the work week resulting in areas of Major HeatRisk. Extreme Heat Warnings remain in effect through this evening across all of the lower desert locations, with the warning extended through Friday across western Imperial County, the Lower Colorado River Valley, and the Phoenix Metro.

- The chances for showers and thunderstorms will continue over the higher terrain areas of the eastern and southeastern third of Arizona through Friday.

- As deeper moisture moves in, the chances for more widespread thunderstorm activity will increase late weekend and early next week.

SHORT TERM /Today through Friday/

Latest objective analysis depicts an elongated subtropical ridge extending from eastern AZ through the eastern Pacific just off the coast of southern CA with 500 mb height fields ranging between 594- 596dm. With the ridging directly overhead, very hot temperatures will continue today across the region with afternoon highs ranging between 110-114 degrees across the south-central AZ lower deserts to 111-116 degrees across the western deserts. These afternoon highs combined with very warm overnight lows in the 80s to around 90 degrees in the Phoenix metro will continue to result in areas of Major HeatRisk. As a result, an Extreme Heat Warning remains in across all of the lower desert locations through this evening. The ridging will weaken slightly into Friday, resulting in slightly lower afternoon highs. However, across western Imperial County and the Lower Colorado River Valley area in particular, temperatures will still top out between 111-115 degrees with areas of Major HeatRisk continuing and thus have elected to extend the Extreme Heat Warning through Friday evening across this region. We also have elected to extend the Extreme Heat Warning through Friday for the Phoenix area as even though afternoon highs will be slightly cooler, ranging between 109-112 degrees, early morning lows will start out very warm near 90 degrees, resulting in areas of Major HeatRisk continuing. With greater subsidence and slightly drier air expected today and Friday, the overall convective coverage will decrease with activity relegated mostly across the White Mountains into the southeastern third of AZ.

LONG TERM /Saturday through Tuesday/

As mentioned in previous discussions, the overall weather pattern heading into the weekend and next week will become more favorable for a more active monsoonal pattern to set up. The subtropical ridge will quickly migrate northeastward into the Rockies over the weekend and then set up over the Central Plains early next week while strengthening in the process. As this whole pattern evolution materializes, the mid-level flow will shift out of the east to southeast. This will introduce strong moisture transport into the Desert Southwest with the latest EPS and GEFS showing PWATs increasing to at least 1.4-1.5" starting as early as Sunday and remaining above 1.5" into next week.

Moisture on Saturday will likely remain fairly limited across south- central AZ with low-level mixing ratios remaining between 9-10 g/kg, with the better moisture and thus the best convective potential remaining relegated to the higher terrain and southeastern AZ. There are strong indications from the latest guidance of a strong convective complex likely to develop over northern Sonora Saturday evening, which will likely send of pool of higher moisture into central AZ heading into Sunday with mixing ratios solidly above 10 g/kg. As a result, Sunday looks to be the first real potential for greater thunderstorm activity to materialize across the south- central AZ lower deserts with NBM PoPs solidly in the 30-50% range. With PWATs values remaining above 1.5" along with mixing ratios above 10 g/kg through the first half of next week, the potential for additional convective activity will remain in place and likely expand further west to include the western deserts as well with NBM PoPs ranging between 20-40% each day. We will also have to be on the lookout for any potential easterly waves that could enhance the convective activity, however, pinpointing the track and timing of these waves this far out is very difficult. Therefore, high uncertainty exists of which particular days next week have the potential to be more convectively active. With the increasing moisture and potential cloud cover, afternoon high temperatures this weekend into early next week will gradually retreat to near to slightly above normal levels with widespread moderate HeatRisk in place.

AVIATION

Updated at 1130Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the TAF period. Winds will trend back towards more diurnal patterns with E/SE early this morning turning west mid to late morning. Westerly winds during the afternoon will have some more gusts generally between 15-20 kts. Skies will remain mostly clear around the terminals.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are expected through the TAF period. Winds at KIPL will mostly be out of the SE with a period of westerly gusts early in the evening. KBLH will be similar to the past several days, remaining southerly. Afternoon gusts are expected at KBLH between 20-25kts into the evening hours. Otherwise clear skies will persist.

FIRE WEATHER

Gusty and erratic thunderstorm winds with isolated lightning over the far eastern districts through Friday will be the main fire weather concern. Outside of any potential outflows, winds should favor diurnal trends with typical afternoon breeziness around 20 mph. Some stronger afternoon gusts between 20-30 mph will be common through Friday along the Lower Colorado River Valley. Afternoon RH values between 10-20% will be common across the region through Saturday. Overnight recoveries will generally range between 30-60% with the upper end of the range across the Imperial Valley and the eastern Districts. Temperatures are expected to run well above normal today, with the lowest elevations reaching between 110-115 degrees before a very gradual cool down takes place starting Friday. More widespread monsoonal activity is likely starting late this weekend and continuing into next week. Moisture levels and humidities should also improve considerably heading into next week, alleviating much of the fire weather concerns.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530-537-540- 542>544-546-548-550-551.

Extreme Heat Warning until 8 PM MST this evening for AZZ531>534- 536-538-539-541-545-547-549-553>555-559-560-562.

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ562-566-567- 569-570.

Extreme Heat Warning until 8 PM PDT this evening for CAZ564-565- 568.