textproduct: NWS Phoenix

KEY MESSAGES

- Very hot temperatures are expected all week creating at least a Moderate Heat Risk and areas of Major Heat Risk for Tuesday through Thursday.

- An Extreme Heat Warning has been issued for Tuesday through Thursday across the lower deserts, including Phoenix, Yuma, and El Centro. Forecast highs are currently 111 to 116 degrees.

- Dry conditions will prevail much of the coming week, although isolated storm chances are expected over the eastern Arizona high terrain.

SHORT TERM /TODAY THROUGH TUESDAY/

The subtropical high is again becoming the dominant weather feature across the Desert Southwest and as it strengthens over the next couple days will bring our hottest temperatures so far this year. Current objective analysis shows drier air aloft slowly working in from the southwest, while at the same time improving moisture in the lower levels as southerly flow has developed across the Gulf of California. Soundings also still show some moisture remaining between 15-20K feet which is helping to bring some overnight high based CU.

As the subtropical high continues to slowly drift westward over the region early this week, H5 heights are expected to rise from the current 591-593dm to 594-596dm for late Tuesday into Wednesday. The higher heights and the continued warming aloft will easily help to push daytime highs to around or just over 110 degrees today and closer to 115 degrees starting Tuesday. Extreme Heat Warnings go into effect on Tuesday for much of the area with forecast highs mostly between 111-115 degrees and overnight lows in the low to mid 80s for most of the lower deserts to as warm as 90 degrees in the Phoenix area.

Marginal moisture will also seep westward into eastern Arizona today, likely enough to bring some isolated convection focused more over the White Mtns to as far west as eastern Gila County. Slightly better moisture, even extending through most of southeast Arizona, is forecast for Tuesday. However, this marginal moisture will have to overcome subsidence under the high pressure ridge which is likely to limit convection. The HRRR does show some convection potentially reaching as far west as central Pinal County, but other hi-res models are not as enthusiastic. Gusty outflow winds will be of a higher likelihood, potentially reaching the Phoenix area sometime later Tuesday evening.

LONG TERM /WEDNESDAY THROUGH SUNDAY/

Hot and overall dry conditions are expected for the latter half of the week with the subtropical high center redeveloping to just off the coast of southern California, but with little change in H5 heights for our region. The shift in the ridge is expected to bring drier air temporarily into at least western portions of our area, but not much change for south-central and eastern Arizona. An even more inhospitable upper level pattern should limit daytime convection further starting Wednesday with PoPs lowering closer to 10% over the Arizona high terrain by Thursday.

Extreme heat will continue to be the main forecast concern through the rest of the week with the peak of the heat likely occurring on Wednesday with highs reaching 112-116 degrees. Once the ridge center becomes more established to our west Thursday it begins to weaken, temperatures are expected to very slowly drop. Friday's temperatures are still very close to Major HeatRisk, especially over the western deserts where highs near 115 degrees are likely to linger through Friday.

Model guidance is still favoring the subtropical ridge to quickly shift back to the northeast over the coming weekend, potentially reaching northern Colorado and Wyoming by Sunday. If and once this occurs, it will turn our winds out of the east southeast as early as Friday night, beginning the process of moisture advection into the region. Uncertainty in how quickly ample monsoon moisture will move into our area is still a issue as it could happen as early as late Saturday into Sunday, but more likely late Sunday into Monday. Shower and thunderstorm chances are expected to increase from east to west as the moisture spreads into the region with the best chances of reaching the lower deserts at some point early next week. We will also be watching for any easterly disturbances that will manage to move across northern Mexico into or near the Desert Southwest. Any of these potential features are likely to enhance storm chances next week.

AVIATION

Updated at 0900Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

No significant aviation weather concerns will exist through the forecast period. Winds will mostly follow typical diurnal trends, aside from some extended periods of light and vrb prior to the onset of diurnal wind shifts. At KPHX, there will be a later than usual easterly shift again on Tuesday morning (~10Z). FEW to SCT clouds will remain through this morning before becoming just FEW this afternoon.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns will exist through the TAF period under mostly clear skies. At KIPL, current W'rly winds will go SE'rly this afternoon and then back W'rly this evening. Some occasional gusts into the upper teens to around 20kt is possible this evening from some sundowner winds. At KBLH, a period of light and variable to calm winds is expected at KBLH this morning. Then winds will develop a S-SW component by this afternoon through the remainder of the TAF period. Speeds will be around 10 kts with gusts up around 20 kts during the afternoon and early evening hours.

FIRE WEATHER

Hotter conditions, but a slight improvement in moisture is expected for the first half of this week. Lower desert highs will warm to 110 degrees starting today before peaking at around 115 degrees midweek. Minimum afternoon humidities of 10-15% are anticipated each day with overnight recoveries of 25-40%. Winds will follow diurnal upslope/downvalley patterns with modest upslope afternoon breeziness mostly staying below 20 mph, which will continue to result in periods of elevated fire danger. A gradual increase in moisture this week should eventually lead to some isolated storm chances across the eastern Arizona high terrain, but any chances for wetting rains in South-Central AZ is more likely to hold off until next weekend.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Extreme Heat Warning from 10 AM Tuesday to 8 PM MST Thursday for AZZ530>534-536>551-553>555-559-560-562.

CA...Extreme Heat Warning from 10 AM Tuesday to 8 PM PDT Thursday for CAZ562-564>570.