textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion.

KEY MESSAGES

- Scattered showers and thunderstorms will develop over the high terrain of southcentral AZ this afternoon with much higher chances for storms surviving into the lower deserts. There is also a slight risk for severe thunderstorms in Maricopa and Pinal Counties this evening.

- With high pressure shifting into the Great Plains, daily shower and thunderstorm chances will continue over the Desert Southwest through much of the upcoming week.

- Seasonably hot temperatures will persist through the next several days resulting in widespread Moderate Heat Risk.

SHORT TERM /Today through Monday/

Upper-air analysis reveals that the sub-tropical high has progressed even further to the north, now centered over eastern Wyoming and the Northern Plains. This northerly progression has resulted in a more traditional monsoon setup for the Desert Southwest over the past day or so, with a lot of southeastern Arizona seeing strong storms and even flash flooding yesterday evening. With easterly/southeasterly flow now firmly in place, shower and thunderstorm chances do not appear to be going anywhere anytime soon.

Starting with this afternoon and evening, the environment looks ripe for widespread convective activity, not only for our high terrain areas, but for the lower deserts east of the Colorado River as well. The typical evolution will take place with storms firing over mountainous areas before descending toward the lower elevations later in the afternoon and evening as cells ride with the easterly flow aloft. Once those storms move off the high terrain, the forecast becomes a bit more complex as further convection over the lower deserts will be highly conditional on the strength of associated outflows, and whether or not multiple boundaries can collide. Areas in south-central Arizona around the Phoenix metro will see their best chances (30-40%) for rainfall so far this summer, but it is highly likely that not everyone will see rain based on the hit and miss nature of monsoonal storms and the unknown of where storms will collide. There has been a consistent signal there will be a boundary interaction somewhere over the western half of Maricopa County, which would help set off a chain of further storms and outflows that could stretch into La Paz and Yuma Counties further into the evening.

Looking at model soundings for the lower deserts, potential boundaries will likely have to overcome some MLCIN to the tune of 50-75 J/kg, but if they can, the environment supports strong to potentially damaging thunderstorms. In fact, the SPC has placed an area along the I-10 corridor under a slight risk of severe weather, indicating a 15% chance to see winds in excess of 58 mph at a given point. Forecasted DCAPE values supports such probabilities as 1300 to potentially 1700 J/kg is forecasted, indicating a very favorable setup for strong to damaging outflows. Thankfully, not everyone will see winds reach severe magnitudes, but enhanced gusts at or above 35 mph could be much more common across Gila, Maricopa, and Pinal Counties. HREF neighborhood probabilities give a 70-90% chance of winds reaching this threshold within a 25 mile radius of any point in the counties listed. Given the high confidence of enhanced winds over dust prone areas of Pinal and southern Maricopa County, a Blowing Dust Advisory has been posted for these locations for this evening. If you plan to travel along I-8 or I-10, prepare for hazardous driving conditions as visibility may drop to 1 mile and below at times. Though chances are less than 5%, some small hail cannot be ruled out with the strongest updrafts, as there is some CAPE located within the hail growth zone thanks to some relatively steep lapse rates. Monday looks to be a bit less active in terms of convection, especially for lower desert areas, but that is not unusual in the wake of more widespread storm coverage the day before. As of now, typical mountain and foothill areas east of the Phoenix metro will see the best chances for rain thanks to orographic influences. Terrain will also play a factor in sparking some activity over the near Joshua Tree NP and potentially the Kofas as well during the afternoon and evening timeframe as these areas get in on some decent instability. As for the lower elevations, primarily of Maricopa and Pinal Counties, there are conflicting signals on what may occur as some guidance points towards another active evening, while others point toward almost nothing. Updated PoPs lean toward the latter outcome as values have dropped from where they were 24 hours ago, but if activity tonight is not as robust as expected, its not out of the question that we could destabilize enough to see more convection sprout up tomorrow.

In terms of temperatures, daily highs will hover near or just above normal, translating to readings between 104-109 degrees. Plentiful moisture (by desert standards) will make insolation less efficient at heating us up, but in turn, the increased humidity will make it feel hotter, with heat indices climbing toward 110-115 degrees. Moderate HeatRisk will remain widespread through the next few days, so if plans take you outside, be sure to exercise heat precautions.

LONG TERM /Monday through Friday/

There is still excellent agreement within the EPS and GEFS members regarding the placement of the upper high over the northern Plains and Upper Midwest through midweek before retrograding over the central Rockies by the latter half of the week. The overall position of the 500 mb high will maintain deep easterly flow across the Desert Southwest, helping enhance moisture transport. Latest EPS and GEFS continue to show PWATs hovering around 1.5"-1.8" through the entire week with low-level mixing ratios remaining between 10-12 g/kg. Therefore, conditions will continue to remain conducive for daily thunderstorm activity with variations in the overall coverage. Both the mean of the EPS and GEFS show an uptick in QPF across the region by the end of this week due to an easterly wave/inverted trough approaching the area by Thursday-Friday. If this occurs, this troughing feature will likely enhance convective activity potentially introduce a risk for heavy rainfall across portions of AZ. This will have to be monitored closely in the coming days.

Temperatures through the first half of the workweek will generally remain steady state at near to slightly above normal with highs generally between 102-110 degrees, resulting in the continuation of widespread Moderate HeatRisk. The NBM continues to indicate temperatures cooling to well below normal by the end of the week with highs falling into the 90s to around 100 degrees across the lower deserts by Friday. This is likely due to the increased signal for thicker cloud cover and the potential for more widespread rainfall.

AVIATION

Updated at 0028Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Outflow boundaries are moving through the terminals, as of 00Z, with NE'rly winds up to 30 kt. Reinforcing outflow winds from an E'rly direction are expected through the next few hours. It is still uncertain if storms will develop in the Phoenix area this evening, but will maintain a PROB30 in the TAFs for the 01-05Z hours. Strong gusty winds and sporadic wind shifts will accompany any storms that do develop. Storm activity is expected to diminish and move off to the west before midnight tonight. Another round of potential storms are expected Monday afternoon, with outflow winds anticipated from the east/southeast. Hazy skies from lofted dust will continue to impact slantwise visibility through this evening and may persist into Monday morning. Cloud bases will mostly stay at or above 10K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH: Winds at KIPL will remain SE'rly with winds generally between 8-14 kts, with a period of possible gusts in the upper teens near 10-13Z tomorrow morning. KBLH will maintain generally a southerly flow with gusty conditions over the overnight hours out of the ESE, otherwise continuing teetering between SSW and SSE with speeds hovering around 10 kts. There is support for an area of high-based showers with an embedded storm to progress across portions of southeast CA Monday morning, with best chances for VCSH/SHRA at KIPL. This may lead to some gusty erratic winds. SCT- BKN clouds, with bases mostly above 12 kft AGL will develop late this evening and persist through Monday morning.

FIRE WEATHER

Seasonably hot temperatures will prevail through the next several days as readings will be near to slightly above normal. Scattered showers and thunderstorms will be possible this afternoon and evening bringing a threat of strong winds. Daily thunderstorm activity will be possible through this week with the potential for wetting rainfall increasing across the high terrain later in the week. Due to increasing boundary layer moisture, afternoon humidity levels will remain in a 20-30% range which will keep any fire weather concerns at a minimum. Overnight recoveries will be fair to good, or between 40-70%. Outside of any thunderstorm driven outflow, winds should favor diurnal trends with the typical afternoon breeziness around 20-25 mph.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Blowing Dust Advisory until 8 PM MST this evening for AZZ539-553- 554-559.

CA...None.