textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Seasonably hot temperatures can be expected into next week, with the hottest temperatures expected today with lingering Extreme Heat Warnings across some lower desert areas.

- The chance for showers and thunderstorms will be mainly confined across the higher terrain areas of eastern Arizona as well as across southeast Arizona through Saturday.

- Deeper moisture moving into the region through early next week will result in better chances for more widespread showers and thunderstorms.

SHORT TERM /Today through Saturday/

Latest objective analysis depicts the subtropical ridge of high pressure centered near the southern California coast while the eastern edge extends into Arizona with northerly mid-level flow encompassing the state. The high will gradually move east northeastward throughout the day through southern CA and the southern Great Basin with 500 mb height fields expected to hover between 593-594dm, which is slightly lower than the last couple of days. As a result of this slight lowering of the upper-level height fields, afternoon high temperatures today will be a couple of degrees cooler with readings topping out between 109-112 degrees across the south-central AZ lower deserts to between 108-115 degrees across the western deserts. Extreme Heat Warnings will remain in place through this evening across the western half of Imperial County as well as along the Lower Colorado River Valley as these areas will experience the hottest temperatures with readings topping out close to 115 degrees, resulting in areas of Major HeatRisk. An Extreme Heat Warning is also in effect through this evening for the Phoenix Metro Area, mostly due to very warm early morning lows expected to be near 90 degrees making it difficult for the body to recover from the daytime heat. Temperatures will slightly cool even further on Saturday with afternoon highs across the lower deserts generally between 106-110 degrees.

Similar to yesterday, a good deal of subsidence and slightly drier air from the northerly flow will result in limited storm coverage with activity this afternoon into early this evening relegated to the White Mountains and far southeast AZ as indicated by the latest hi-res guidance. Heading into Saturday, the overall pattern will be changing significantly as the subtropical high quickly migrates northeastward towards Utah and the Central Rockies. This will cause the mid-level flow to shift more out of the east, helping to import higher moisture into the region. In addition, a strong convective complex over northern Sonora Friday evening will help boost moisture levels as well. Latest hi-res model guidance shows activity developing over the eastern AZ higher terrain before moving westward, with widespread convective activity likely across much of southeast AZ. Across the south- central AZ lower deserts, convective activity is likely to be much more limited as the latest forecast soundings indicate a good deal of convective inhibition in place. However, there are strong indications from the latest hi-res guidance that a strong outflow or potentially multiple outflows emanating from thunderstorm activity across southeast AZ will migrate northwestward into south-central AZ, producing gusty winds as well as areas of blowing dust. If strong/multiple outflow collisions occur, then it could be enough to generate additional storms. Otherwise, the outflow will likely serve to increase the low-level moisture even more across the region, setting the stage for a better thermodynamic environment heading into Sunday.

LONG TERM /Sunday through Thursday/

Excellent agreement remains in place amongst the guidance of the upper high quickly migrating northeastward into the Plains and Upper Midwest regions through next week. This overall pattern setup will maintain easterly flow in place across the region, helping to transport moisture and transition the Desert Southwest into a more active monsoonal pattern. The latest EPS and GEFS indicate PWATs climbing and remaining above 1.5" through most of next week along with low-level mixing ratios remaining above 10 g/kg.

As mentioned previously, Sunday will offer the first real shot this monsoon season for more widespread convective activity to affect the south-central AZ lower deserts, given the more favorable thermodynamic environment that will be in place and this is reflected in the latest NBM with PoPs solidly in the 40-60% range by the early evening hours. The chances for additional convective activity will continue each day through next week and will expand further westward to include the western deserts with daily variations in the overall coverage. There are indications from guidance that a rather organized easterly wave/inverted trough may move in from the east and affect the region sometime towards the latter half of the week. However, given that the synoptic models are notoriously poor in the overall handling of these easterly waves/inverted troughs, high uncertainty exists in the overall forecast. If the easterly wave/inverted trough scenario pans out, then there is a good chance for enhanced convective activity to materialize across much of the region. This is something that will have to be monitored during the next several days as it could be highly impactful.

With the elevated moisture levels and more cloud cover that will be in place, temperatures through the much of next week will remain near to slightly above normal with readings across much of the lower deserts in the upper 100s to around 110 degrees for afternoon highs and overnight lows in the 80s. This will maintain the overall HeatRisk levels solidly in the moderate category.

AVIATION

Updated at 1140Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: No major aviation concerns are expected through the forecast period. Gusty winds and dust/haze associated with an outflow boundary have now subsided and winds will return to normal diurnal patterns through the rest of today. The typical westerly shift is expected to occur by 17Z-18Z this morning. By the early afternoon, intermittent gusts into the upper teens to around 20 kt can be anticipated at all terminals. Winds will likely remain elevated out of the SW (10-15 kts) after sunset. The chances of any S-SE outflow from distant thunderstorms is much lower this evening. Skies will remain mostly clear with only FEW high clouds expected during the morning hours.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation concerns are anticipated through the TAF period under clear skies. At KIPL, winds should remain SE through this afternoon. Besides a brief period of elevated winds this mornings, speeds should remain aob 10 kts. At KBLH, winds are expected to remain elevated out of the S-SE through the period with gusts up to 20-25 kts becoming common this afternoon.

FIRE WEATHER

Seasonably hot temperatures will prevail through the next several days as readings will be near to slightly above normal. Dry conditions will prevail today before thunderstorm chances increase Saturday across the higher terrain areas of south-central AZ. More widespread monsoonal activity is likely starting Sunday and continuing through next week. Afternoon humidity levels today will range between 10-20% across the western districts and 15-25% across the eastern districts. Afternoon humidity levels Saturday increase to 15-25% areawide. Starting on Sunday and persisting through much of next week, afternoon humidity levels will increase even further and bottom out above 20% as moisture levels increase, and thus alleviating much of the fire weather concerns. Outside of any potential outflows/thunderstorm winds, winds should favor diurnal trends with the typical afternoon breeziness around 20 mph. Some stronger afternoon gusts between 20-30 mph will be common along the Lower Colorado River Valley today.

PSR WATCHES/WARNINGS/ADVISORIES

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

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