textproduct: NWS Phoenix

UPDATE...Updated 06z Aviation Discussion

KEY MESSAGES

- Extreme heat will persist through the end of the week with temperatures hovering near to several degree above normal.

- Shower and thunderstorm chances will favor east and southeast Arizona the remainder of the week with gusty outflow winds and blowing dust the most likely impacts for south-central Arizona.

SHORT TERM /Today through Thursday/

Elongated subtropical ridging was meridionally bisecting Arizona this afternoon with a H5 594dm anti-cyclone center over western New Mexico. This configuration was confining shortwaves in enhanced easterly flow over northern Sonora with very weak flow and more neutral ascent structure closer to the high pressure core covering the CWA. Despite strong thunderstorm outflows importing 11-12 g/kg boundary layer mixing ratios into the majority of the forecast area this morning, exceptionally warm air at the top of the mixing depth has contributed to strong inhibition with forecast CinH in excess of 100 J/kg the remainder of the day. As a result, it would require multiple deep outflow boundaries to release instability this afternoon/evening, and little to no modeling suggests more than residual, isolated midlevel showers/virga. Instead, another round of gusty outflow winds emanating in far southern Arizona will be possible mid/late evening across south-central Arizona, though the magnitude and extent of impacts appears less than Monday.

The synoptic trend over the next 72 hours is towards the migration of the anti-cyclone center into southern Utah while increasing in both magnitude and breadth as the H5 core approaches 600dm. While this northward shift would tend to support increasing convective chances with cooler lower/middle tropospheric temperatures and increased easterly flow, the strengthening anti-cyclone will generally negate these tendencies imparting growing subsidence and expansion of the warm core aloft. This will create an ebbing effect on both temperatures and convective potential. Afternoon highs should retreat closer to daily normals Wednesday with only minor to moderate HeatRisk, but then quickly resume a warming trend Thursday as areas of major HeatRisk re-emerge. Similarly, thermodynamic conditions appear slightly more favorable for thunderstorm development across lower elevations Wednesday afternoon/evening as CinH likely drops below 50 J/kg where multiple, colliding outflows could breach this inhibition. Surprisingly, nothing in the HREF suite supports lower elevation storms resulting in very low POPS, but it wouldn't be unexpected if somewhat better chances materialize.

LONG TERM /Friday through Monday/

Little will change with the weather pattern for the rest of this week, and likely well into next week as the high pressure ridge is expected to remain centered over the Desert Southwest. The center of the ridge is forecast to somewhat shift farther to the north by Friday which could help to bring better rain chances, but guidance shows the ridge also strengthening which will likely reinforce the subsidence over much of our area. As of now, Friday is expected to follow the same pattern as today and Wednesday with mostly eastern Arizona high terrain storms and very conditional 5-15% PoPs into the south-central Arizona lower deserts. As stated in the short-term discussion, even though it will be a day-to-day low chance environment for the lower deserts, it would not be surprising to have a day where the elevated instability is managed to be tapped into causing some scattered storms to fire. Hot and humid conditions will continue to prevail with daytime highs likely nudging upward again late week as the ridge restrengthens. The Extreme Heat Warning currently goes through Friday which is very reasonable, but it will be possible to have a day in there where it fails to reach criteria over south-central Arizona if convection ends up being more widespread one evening/overnight.

For the weekend into early next week, ensembles still favor the ridge basically staying stationary with the center somewhere just to our north. Some weakening of the ridge is likely to occur by early next week and depending on how much moisture will be available we could be looking at a further uptick in monsoon activity. The GEFS is more optimistic with rain chances by early next week with activity expanding into central and northern Arizona, but the EPS holds off until later next week. If convection does eventually become more widespread and impacts the lower deserts, temperatures are expected to dip closer to seasonal normals.

AVIATION

Updated at 0522Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; No major aviation concerns are expected through the TAF period. The outflow mentioned in previous discussions looks to remain to the south of the terminals through the overnight period, however a few rouge gusts may still manifest early tomorrow morning. Otherwise westerly to northwesterly winds will persist through the overnight periods, with an easterly shift unlikely. Afternoon gusts look to re-materialize again tomorrow, with speeds generally between 17-22kts. Models are pointing towards another outflow tomorrow evening between 04-06Z, with current models showing a 30-50% chance of speeds above 30kts. FEW-SCT high clouds will persist through a majority of the TAF period, becoming BKN near the end of the package.

Southeast California/Southwest Arizona including KIPL and KBLH: Breezy to gusty conditions, mainly at KBLH, will be the main aviation concern during the TAF period. Winds at KIPL will persist out of the SE, while KBLH will be southerly. Winds at KBLH will remain elevated (near 15kts or more) with gusts between 25-30kts tomorrow afternoon. Winds at KIPL will be much weaker, generally ranging 7-15 kt with a period of some gusts up to 20kts possible tomorrow afternoon. FEW to occasionally SCT high level clouds will be present through the majority of the forecast window.

FIRE WEATHER

Hot temperatures will continue all week with fairly elevated humidities, but showers and thunderstorms will mostly remain over far eastern and southeastern Arizona. Gusty outflow winds are likely to impact the south-central Arizona lower deserts again late this evening. MinRHs will continue to improve, climbing to around 25-30% by Wednesday, while overnight recoveries range between 40-70%. Outside of storm outflows, winds will mostly follow diurnal patterns, but southwesterly winds will be dominant much of the time with afternoon gusts of 15-25 mph at times.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530>544-546- 548>551-553>555-559.

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ560>570.