textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

SHORT TERM /Today through Thursday/

Early this afternoon, water vapor satellite imagery and objective analysis show the subtropical ridge stretched across the southwestern CONUS with H5 heights of 592-594 dm. The SPC mesoanalysis shows that PWATS across the region are in the 1.4-1.8" range across our area. The subtropical high in combination with the increased moisture trapped under it will continue to lead to hot and humid conditions across the region over at least the next couple of days. The increased moisture (120-130% of normal) will also lead to daily shower and thunderstorms chances, mainly across the higher terrain areas.

With the high pressure still overhead afternoon high temperatures are still forecasted to be at least a few degrees above normal today and tomorrow. Afternoon high temperatures are forecasted to be in the 107-112 degree range across the lower deserts and in the upper 90s to low 100s across the higher terrain. Temperatures early this afternoon are very similar to that of 24 hours ago, so afternoon high temperatures will likely be similar to that of yesterday, especially with the cloud cover hanging on across much of the CWA like yesterday. This cloud cover is expected to clear by the late afternoon/early evening hours. If there is enough breaks in the clouds this afternoon I wouldn't be shocked to see afternoon highs a few degrees warmer than yesterday. With the increased low level moisture dew points are mostly in the 60s across the CWA, with some locations seeing dew points in the low 70s. These high dew points are leading to hot "feels like" temperatures with max "feels like" temperatures forecasted to be in the 110-120 degree range across the lower deserts today and tomorrow. Due to these hot temperatures paired with the hot "feels like" temperatures, the Extreme Heat Warning remains in effect. Similar conditions are expected again tomorrow.

While convective potential remains high across the higher terrain in eastern AZ with storms already firing up along the Mogollon Rim. Activity has been slower to fire up in SE AZ. Convective potential, however, remains low across the south-central lower deserts. And with the lingering cloud cover this afternoon convective potential continues to decrease for this evening across the lower deserts. However, the CAMs continue to show at least some potential for showers and storms to develop across the lower deserts of south- central AZ lower deserts mainly between 03-07Z this evening. CAMs continue to show MUCAPE values around 1000-1500 J/kg, however they also show CIN around 100-200 J/kg. The storms across the Mogollon Rim and potential storms across SE AZ are expected to send multiple outflows into the lower deserts. Confidence is high on an outflow from the E/NE. However, with the slower development across SE AZ confidence in an outflow from that direction is lower. If we do get an outflow from the SE, it would be stronger and produce areas of blowing dust and reduced visibility. If we get multiple outflows it may be enough to break the cap and fire up some storms, especially if outflows collide. Despite the high amount of MUCAPE, overcoming the CIN will be the main issue for storm development across the lower deserts this evening.

Tomorrow, the subtropical high will start to strengthen again, with H5 heights increasing to around 595-597 dm, and the center will shift to be more over northern Arizona. As a result some drier air will move into the region, with PWATs forecasted to decrease from around 1.4-1.8" today down to around 1.2-1.5" tomorrow. Therefore, there will be a slightly lower chance of showers and storms across the higher terrain in eastern AZ, with little to no chance across the lower deserts.

LONG TERM /Friday through Tuesday/

Strengthening of the ridge is forecast through Friday before gradually weakening this weekend into Monday. Guidance agrees H5 heights will rise to 596-598dm on Friday before dropping back to 594- 596dm by Sunday. The strength of this ridge will easily be around the 99th percentile of climatology across the region on Friday, dropping back to 90-97th percentile on Sunday. Due to the strength of the ridge and some slight drying, temperatures are forecast to peak on Friday and/or Saturday with highs 110-115 degrees. Surface dew points should fall back into the upper 50s to lower 60s during this time, but it will still feel somewhat humid as heat indices could reach as high as 115-120 degrees across the lower deserts of southeast California. There was enough confidence in guidance to also extend the Extreme Heat Warning through Sunday as the convective potential should be fairly limited. The strength of the high and slight dip in moisture is expected keep CIN values quite high across the area, especially over the lower deserts. Higher terrain areas of eastern Arizona will keep daily 15-30% chance PoPs, while the Phoenix area mostly stay between 10-15%.

By early next week, models show the ridge weakening again, while most likely staying centered to our north. This should allow for better monsoon storm chances with models leaning toward some improving moisture and better upper level support. NBM/WPC PoPs seem too high for Sunday at 30-40% over central and eastern Arizona, but those chances may be more reasonable for Monday and/or Tuesday of next week. Temperatures will also drift lower early next week due to the weakening of the ridge and with more convective activity in the area. The latest NBM shows temperatures back into the normal range by around Monday or Tuesday.

AVIATION

Updated at 0019Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Uncertainty in strong, gusty outflow winds and the potential for scattered TSRA this evening/tonight are the main forecast challenges. Confidence is very good that west winds will prevail through early evening with the potential for some 15-20kt gusts. TSRA has formed well east and north of the terminals, but has struggled to develop, so far, southeast of the terminals. Outflow boundaries focused towards the metro this evening are still anticipated, but timing may be delayed later than currently shown in the TAF, especially with any boundaries from the south. Model indications suggest an initial easterly/northeasterly wind shift followed by a southerly outflow boundary. The secondary outflow may allow scattered TSRA to develop mid evening - early tonight with additional erratic wind directions and lowered vsby due to imported BLDU. Confidence in this outcome is only low to moderate with prob30 appropriate for this scenario.

TSRA Thursday is forecast to be focused primarily north-northeast of the terminals, with low chances (5-10%) at terminals. Gusty outflow winds from the north will be favored.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather issues will exist through Thursday under periods of mid/high cloud decks. Trends in winds will be similar to the past 24 hours with a preference towards a southerly direction and modest afternoon and evening gusts.

FIRE WEATHER

Hot temperatures will continue through the weekend 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 today with a 10-30% chance of storms. MinRHs will remain elevated at 20-30% through Thursday before dropping back into the teens over the lower deserts Friday into Saturday. Overnight recoveries will remain fair to good at 40-60%. Outside of storm outflows, winds will mostly follow diurnal patterns, with upslope afternoon gusts of 15-20 mph at times.

PSR WATCHES/WARNINGS/ADVISORIES

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

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