textproduct: NWS Phoenix

KEY MESSAGES

- Extreme Heat Warnings remain in effect through this evening as afternoon high temperatures approach the 110 degree mark across most of the lower desert communities, resulting in areas of Major HeatRisk.

- Shower and thunderstorm activity will once again develop across the higher terrain areas as well as across southern Arizona later this afternoon, with additional activity possible across the lower deserts this evening.

- Deeper moisture will provide a better opportunity for more widespread shower and thunderstorm activity during the first half of the week, along with cooler temperatures.

SHORT TERM /Today through Monday/

Current objective analysis depicts the subtropical high centered near the Four Corners Region with the region situated under modest easterly flow of around 15-20 kts along the southern periphery of the high. Similar to the last several days, thunderstorms are expected to develop later this afternoon across the Mogollon Rim and White Mountains and then migrate westward into south-central AZ, with the likelihood of another storm complex developing across southern AZ, especially in Pima County according to the latest hi-res guidance. With DCAPE values expected to exceed 1500 J/KG, there is a high potential of strong outflows to materialize and affect the lower deserts with gusty winds exceeding 30-40 mph along with areas of blowing dust, especially with the southern outflow from the storm activity that develops in southern AZ. Forecast soundings for this evening does still show a decent amount of convective inhibition and thus it will take a strong outflow/multiple outflow collisions to overcome this convective inhibition to spark thunderstorms across portions of the south- central AZ lower deserts, including the Phoenix Metro. This scenario is being depicted by some of the hi-res guidance and thus NBM PoPs for this evening across the south-central AZ lower deserts are a bit higher than the previous couple of days, ranging from 15-25%.

Environmental conditions heading into Monday will become more favorable for more widespread storm activity to materialize with the latest NBM showing widespread PoPs on the order of 50-70% across much south-central AZ and southeast AZ. The subtropical high will remain positioned near the Four Corners Region, resulting in better moisture advection as PWATs exceed 1.5" along with low-level mixing ratios exceeding 11 g/kg, providing higher instability and weaker convective inhibition. In addition, guidance is indicating an increase in upper-level divergence as a weak easterly wave moves into northwestern Chihuahua in northern Mexico, which will likely aid in higher thunderstorm coverage and sustenance. Storms are likely to develop across the higher terrain areas of eastern AZ as well as across southeast AZ, with activity moving westward with strong outflow/multiple collisions resulting in additional storm development across the lower deserts. Strong downburst wind gusts, locally heavy rainfall, as well as areas of blowing dust in the typical dust prone areas will all be likely.

Afternoon high temperatures today will still approach the 110 degree mark across the majority of the lower desert communities, with areas of Major HeatRisk. Thus, an Extreme Heat Warning remains in effect through this evening. Heading into Monday, due to heights aloft further lowering, afternoon highs will be 2-3 degrees cooler, which will be enough for HeatRisk levels to drop into the moderate category and thus ending the extreme heat episode.

LONG TERM /Tuesday through Saturday/

Conditions will remain favorable through the middle of the week for additional monsoonal activity. Depending on how active Monday turns out, Tuesday could actually be more of a down day given a worked over atmosphere and thus even though there is still potential for storm activity, especially across the higher terrain areas, NBM PoPs for Tuesday are lower, mostly ranging between 30-50%. Another more active period appears to be in the cards for late Wednesday into the first half of Thursday. The flow by Wednesday is forecast to shift out of the south as the subtropical high shifts into Texas and a upper-level low moves off the coast of California. This southerly flow is likely to bring additional moisture northward from Mexico, with projected PWATs increasing to 1.7-2.0" and low-level mixing ratios increasing to 12-13 g/kg. In addition, there will likely more favorable upper-level forcing as both the GFS and ECMWF do indicate an upper-level wave moving into the region from Mexico, which will likely enhance the convective activity with flash flooding becoming more of a threat given the deeper moisture profiles that will be in place. The latest NBM PoPs for late Wednesday through the first part of Thursday currently range between 50-60% across much of south- central and southeast AZ.

Heading towards the end of the week and next weekend, the guidance is in good agreement in showing the subtropical high shifting towards the Gulf Coast Region while the aforementioned upper- level low remains situated off the west coast. This pattern configuration will cause the flow to shift more out of the southwest, bringing in drier air as PWATs drop under 1.2-1.3". As a result, an overall downtrend in storm activity is likely.

With the lowering heights aloft and as well as an increase in convective activity and cloud cover, temperatures throughout the upcoming work week are expected to gradually cool with afternoon highs expected to fall to near seasonal levels by Tuesday and potentially a few degrees below normal by the latter half of the week. Temperatures do eventually trend slightly back up again by next weekend, but to near seasonal levels with no extreme heat in sight.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Strong outflow winds, blowing dust, and VCTS/TS at the terminals will be the primary forecast challenge and potential impacts today. There is good confidence that one or multiple outflow boundaries will move through the terminals Sunday evening, with wind gusts up to 20-30 kts anticipated and around 50% chance for peak gusts greater than 30 kts. The outflow winds will be capable of bringing a wall of dust through the metro. There will also be slight chances (20%) for VCTS/TS. Timing of activity Sunday is favored between 02- 05Z.

Before this evening, winds should generally be light (AOB 10 kts), with no strongly preferred direction this morning before shifting westerly in the afternoon. Confidence in winds is then very low due to the potential outflows moving through this evening, however, southerly directions look preferred, with a tendency towards southeast late evening into the overnight hours.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns are expected through the next 24 hours under periods of FEW-SCT mid to high cloud decks and otherwise mostly clear skies. At KIPL, winds will primarily stay southeasterly. At KBLH, winds will generally fluctuate between SE and SSW. Overall, wind speeds should generally remain AOB 12 kts. A distant thunderstorm outflow reaching KBLH this evening cannot be ruled out, which would result in an abrupt wind shift and potentially some VIS restrictions due to lofted/blowing dust.

FIRE WEATHER

Hot temperatures with afternoon highs around 110 degrees can be expected across the lower deserts today, before gradual cooling to more seasonal levels takes place during the upcoming week. Elevated moisture levels with maintain afternoon MinRHs throughout the upcoming week above 20% along with good to excellent overnight recoveries. Shower and thunderstorm activity will become more widespread through the first half of the week. The chances of wetting rainfall will also increase significantly with the increasing convective coverage. Outside of gusty and erratic winds due to thunderstorms, winds will follow the familiar diurnal trends, with typical afternoon upslope breeziness around 20 mph.

PSR WATCHES/WARNINGS/ADVISORIES

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

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