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 Sunday 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/

This evening and tonight remains to look promising with thunderstorm and showers likely developing in the eastern AZ high terrain and in Southern AZ. The subtropical ridge has promoted easterly winds across the region and a gulf surge has lead an increase in moisture with current PWATs between 1.5-1.6" for most of south central AZ. This is a notable increase from 24 hours ago where PWATs were generally between 1.2-1.3" across south central. This moisture is expected to stay throughout today and tomorrow as mixing ratios start to improve by this evening ranging between 10-12 g/kg. Current mesoscale analysis is already showing that the high levels of CIN from this morning's 12Z sounding are starting to erode to near or below 100 J/kg with forecast models continuing to show further eroding by this evening to mostly below 100 J/kg. Additionally, MUCAPE forecasted to climb to at least 1000 J/kg across all of southern and most of central Arizona to as high as 2000-2250 J/kg across southeast Arizona by early afternoon. Models are in great agreement in scattered thunderstorms starting to develop along the Mogollon Rim into the White Mtns and over portions of southeast Arizona. With these storms outflows are very likely and it is very plausible we will have colliding outflows somewhere over the Phoenix metro late this evening giving rise to additional storm development. SPC has upgraded Pinal County, portions of southern Maricopa County, and the southern tip of Gila County into a slight risk for severe storms and a Marginal risk still remains across the remainder of Gila, and 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, but WPC has kept our region only in a Marginal risk for excessive rainfall for today and tomorrow.

In addition to the chances for thunderstorms, another major impact will be strong gusts and localized areas of dense blowing dust. With the strong to severe storms likely tonight damaging winds will be a concern, with DCAPE values forecasted up to 1600, strong outflows are projected for tonight. HREF currently shows a 50-70% chance of gusts above 35 mph by this evening in eastern Maricopa County and Pinal County. Due to these conditions a Blowing Dust Advisory remains in place until 10PM MST tonight.

Models are continuing to show Thursday being 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, depending on how active tonight ends up being the atmosphere may be too worked over by tomorrow evening to produce much in terms of severe storms, and lingering clouds well into the morning hours may also inhibit heating, 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.

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 1750Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main aviation concerns this TAF package will be the potential for a strong southerly outflow, blowing dust with reduced vsby, and potential TS impacts at the metro terminals. Winds are now shifting out of the W-SW across the region with occasional gusts in the upper teens to around 20 kt expected to materialize by this afternoon. Later this evening, convection over the higher terrain of southcentral and southeastern AZ will likely send multiple outflows into the lower deserts. There may be an initial NE outflow that arrives at KSDL and KDVT, however high-res guidance suggest the southerly outflow will be more dominant and should arrive into the Phoenix Metro around 03Z. This outflow could spark additional SHRA/TSRA in the Phoenix Airspace. Although, chances for SHRA/TSRA remain around 20%, there was high enough confidence to include a TEMPO for TS at KPHX and KIWA between 03Z-06Z tonight. In addition to the potential for TS, strong gusty winds will likely result in blowing/lofted dust and temporary surface VIS or slantwise VIS restrictions down to 3-5 SM. Any linger storm activity should clear west of the terminals after 06Z.

Southeast California/Southwest Arizona including KIPL and KBLH: No aviation weather concerns will exist through the next 24 hours under FEW-SCT high cloud decks. Winds at KIPL will favor a southeasterly component with speed remaining aob 10 kts. Winds at KBLH will be southerly with occasional gusts to around 20 kts through this afternoon. There is a low possibility of an easterly outflow from distant thunderstorms reaching KBLH late tonight.

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 Sunday 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 Sunday for CAZ562-565>567- 569-570.