textproduct: NWS Phoenix

KEY MESSAGES

- Scattered thunderstorms are expected this afternoon and evening across eastern and south-central Arizona. Strong gusty winds, blowing dust and locally heavy rainfall will be possible.

- Temperatures are forecast to remain several degrees above daily normals through the rest of the week with lower desert highs ranging between 107-113 degrees and overnight lows generally in the mid 80s to low 90s.

- Extreme Heat Warnings are in effect through Friday evening due to continued areas of major HeatRisk.

- Thunderstorm chances will continue through Thursday before decreasing in coverage by Friday or Saturday.

SHORT TERM /TODAY THROUGH THURSDAY/

Today is potentially shaping up to be a big weather day with guidance finally coming together to suggest scattered thunderstorms (some strong to severe) affecting portions of southern and central Arizona. A strong Gulf moisture surge is currently underway with 70-75 degree surface dew points in the Yuma area to the mid to upper 60s now as far north as Phoenix. Even though this is shallow, it should greatly improve upon last evening 8-9 g/kg mixing ratios, with guidance indicating 10-12 g/kg across the area by late afternoon.

As stated yesterday, the subtropical high is reforming across northern Arizona allowing for easterly mid-level flow across southern Arizona while allowing for Gulf moisture surges to recommence. The overall lack of convection yesterday has allowed for the atmosphere to heat up with MUCAPEs improving to around 500 J/kg. The added moisture from the ongoing Gulf surge is forecast to improve MUCAPEs to at least 1000 J/kg across all of southern and most of central Arizona to as high as 2000 J/kg across southeast Arizona by early afternoon. The strong instability will also coincide with some upper level forcing as southeast and south-central Arizona is forecast to fall within the right entrance region of a weak upper level jet max associated with the weak disturbance over northwest Mexico.

Forecast soundings also show high DCAPEs of 1400-1800 J/kg over the lower deserts this afternoon/early evening. The high instability and weakening CIN this afternoon are expected to allow for scattered thunderstorms to develop along the Mogollon Rim into the White Mtns and over portions of southeast Arizona. A modest 5-10 kt east northeasterly steering flow this afternoon should allow for storms and storm outflows to track to the west southwest toward the south-central Arizona lower deserts by 5-6 PM. A second stronger cluster of storms is likely to form across Pima County with indications of a north northwestward outflow propagating into Pinal and Maricopa Counties. It is very plausible we will have colliding outflows somewhere over the Phoenix metro early this evening giving rise to additional storm development. Modest 0-6km shear of 20-25kts should help to maintain some of these storms with a few becoming strong to severe. The biggest threat with any strong to severe storms will be damaging winds due to a high DCAPE environment which should also result in localized dense blowing dust. SPC has included a Marginal Risk for severe storms across Gila, Pinal, and much of Maricopa County for today. We also can't rule out the threat for localized heavy rainfall today, but storm movement should be enough to keep most storms from producing more than an inch or so over any particular location. The latest HRRR suggests storms will make their way to near the Maricopa/Yuma-La Paz border late this evening while also weakening as they encounter an increasingly capped environment.

Thursday may bring another fairly active weather day as moisture will remain plentiful across the area and the subtropical high center moves to over the Four Corners area. However, it seems fairly likely the storm coverage this evening will be widespread enough to at least somewhat overturn the atmosphere. Lingering clouds well into Thursday morning may also inhibit heating a bit on Thursday, keeping instability lower than today. That being said, if today is not as active as anticipated, Thursday is likely to be the biggest storm coverage day. As of right now, PoPs today are higher than Thursday.

Hot and humid conditions are expected today with lower desert afternoon highs between 108-112 degrees, but much higher heat indices are forecast for locations across southeast California through the Lower CO River Valley. Expect late afternoon heat indices of 113-120 degrees in the aforementioned areas. Temperatures are more uncertain for Thursday due to potential impacts from storms this evening and lingering clouds, but NBM guidance indicates very similar highs and heat indices again breaching 110 degrees over the majority of the lower deserts.

LONG TERM /FRIDAY THROUGH TUESDAY/

Hot and somewhat humid conditions are expected to prevail through the upcoming weekend with a high probability of the Extreme Heat Warnings being extended soon. Forecast uncertainty has been an issue for late this week into the weekend as storm chances were higher with model runs earlier this week. However, it now seems more likely than not drier air will move into the area beginning Friday leading to much more limited shower and storm chances through the upcoming weekend. The lower storm coverage and fairly consistent upper level heights should keep daily highs right around 110 degrees or even a couple degrees above through the weekend. Guidance does hint at some better moisture advecting into the area early next week, but the latest trends show the ridge center drifting back toward our region. If that holds true, our convective potential should remain on the lower side with little to no relief from the hot temperatures.

AVIATION

Updated at 0915Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns this TAF package will be the potential for strong gusty winds, blowing dust with reduced visibility, and thunderstorm activity this evening. Winds at KSDL, KDVT, and KIWA will follow their typical patterns this morning with light and variable at KSDL and KDVT and SE'rly at KIWA prior to the development of westerly winds this afternoon. At KPHX, westerly winds are expected to go light and variable during the mid morning hours prior to redeveloping westerly winds this afternoon. Occasional gusts in the upper teens to around 20 kt is possible this afternoon.

By Wednesday evening, conditions will be more favorable for strong, gusty outflows to survive into the lower deserts. Multiple outflows are possible, but confidence is highest in an outflow from the south/southeast. But an outflow from the northeast could move in an hour or two prior to the south/southeast outflow. These outflows could spark additional SHRA/TSRA in the Phoenix Airspace. Chances for SHRA/TSRA remain around 20%. Additionally, the strong gusty outflow winds from the south or southeast could bring blowing/lofted dust and result in temporary surface VIS or slantwise VIS restrictions.

Southeast California/Southwest Arizona including KIPL and KBLH: No weather concerns will exist through the next 24 hours under FEW-SCT high cloud decks. Winds at KIPL will favor southeasterly with speeds AOB 10 kts sustained. Winds at KBLH will be southerly with occasional gusts to around 20 kts, mainly this morning and afternoon.

FIRE WEATHER

For today, expect above normal temperatures with increasing moisture and rain chances. Scattered thunderstorms producing gusty winds are likely to impact the eastern districts from late afternoon through this evening. Elevated moisture levels will persist through Thursday with additional chances for scattered showers and storms before some slight drying and lower rain chances occurs Friday into the weekend. MinRHs of 20-30% are anticipated through Thursday before lowering to 15-25% beginning Friday. Outside of gusty and erratic winds near any thunderstorm, overall winds will follow the typical diurnal tendencies with some modest afternoon upslope gustiness.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Friday for AZZ530>544-546- 548>551-553>555-559-560.

Blowing Dust Advisory from 5 PM this afternoon to 10 PM MST this evening for AZZ538>540-550-551-553-554-559.

CA...Extreme Heat Warning until 8 PM PDT Friday for CAZ562-565>567- 569-570.