Area Forecast Discussion

UPDATE

Updated 18Z Aviation Discussion.

KEY MESSAGES

- Above normal temperatures will continue through the forecast period with Extreme heat Warnings in effect for portions of the area through mid week.

- Typical monsoon conditions are expected into next week with daily thunderstorm chances favoring Northern Arizona high terrain and Southeast Arizona and low chances in the South Central Arizona lower deserts.

- After a slight drop in temperatures during the first half of the coming work week, high pressure will strengthen over the region once again late in the week, resulting in another period of unseasonably hot temperatures and widespread Major Heat Risk.

SHORT TERM /TODAY THROUGH THURSDAY/

GOES mid-lvl WV imagery and RAP-40 500mb analysis shows southeasterly flow aloft as the subtropical high is positioned near the Four Corners region. The activity from the past couple of days has helped cap the atmosphere, as the latest 12Z sounding showed only around 200 MUCAPE but almost 600 CIN. Today will be another quiet day with very little activity expected. Moving forward, throughout the first half of the week south to southeasterly flow aloft will remain in place, with PWATs staying above 1.6" keeping chances for thunderstorms in the forecast, however storms will be mostly confined in Northeastern AZ. Meanwhile the chances for thunderstorm and showers to develop in south-central AZ and the lower deserts are very limited, with current guidance pointing towards Tuesday morning as the best chances for any development in south-central AZ, to include the Phoenix metro.

Outside of any storm chances, dangerously hot temperatures with little overnight relief will be the main impact as we head into the first half of the work week. With that said, the widespread Extreme Heat Warning will remain in effect through this evening as morning low temperatures today will be in the upper 80s to lower 90s, and afternoon highs will be between 108F-115F. By Tuesday, temperatures in south-central AZ fall by a 1-2 degrees, however highs will remain 4F-6F above normal as H5 heights will only dampen to near 594-596 dam. While most of the region will fall out of the Extreme Heat Warning Monday evening, the Phoenix metro, Imperial Valley and the Lower Colorado River Valley will remain under the effect of the Warning through at least Wednesday evening. This is driven largely due to overnight lows remaining well above normal leading to very little relief in these areas. More expansive headlines will likely be needed again by late week as the subtropical high moves closer and restrengthens. This is expected to drive temperatures back in the upper teens, with the lower deserts between 112F-118F, flirting with record highs yet again. H5 heights near the end of the work week will climb to between 595-597 dam, or in the 99th percentile to near max for climatology for this time of year.

LONG TERM /FRIDAY THROUGH MONDAY/

By the end of the of the week and heading into the weekend, most global ensembles continue to support the strengthening of the high pressure, with H5 heights up to 600dam and the center of the anticyclone shifting to over northern AZ/southern UT. These heights are near or at the max of NAEFS percentile for climatology for this time of year, which are quite frankly impressive. The peak of the extreme heat is expected to be Friday and Saturday, where the chances of Phoenix Sky Harbor at least tying the record high (116F) will be 65% on Friday and 50% Saturday. As mentioned previously, an additional widespread Extreme Heat Warning will be likely near the end of the workweek. Additionally, this setup will likely add more subsidence over the area and subdue afternoon convection. Global ensembles also show a slow downtrend in PWATs, falling under 1.5" by Thursday- Friday. So, this is not great for the prospects of seeing storms push into the lower deserts. However, the NBM keeps slight PoPs focused in the AZ high terrain.

AVIATION

Updated at 1805Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Aviation concerns will remain low through the forecast period. Somewhat elevated westerly winds are expected through the majority, if not all of the upcoming TAF period. Gusts in the upper teens to around 20 kt are expected this afternoon/early evening and again tomorrow afternoon. There is low confidence in an easterly shift tomorrow morning. Currently, only KIWA is anticipated to go SE'rly during the overnight and early morning hours tomorrow. FEW-SCT mid and high level clouds are expected throughout the period.

Southeast California/Southwest Arizona including KIPL and KBLH: Aviation concerns will remain low through the forecast period. Current SE winds at KIPL will go SW'rly this evening, then back SE'rly early tomorrow morning. Wind speeds are anticipated to mainly be aob 10 kt. At KBLH, winds will stay southerly the whole period with some gusts up around 20 kt expected this afternoon and early evening. FEW-SCT mid and high clouds will persist.

FIRE WEATHER

Typical monsoon conditions are expected through much of the forecast, with thunderstorm activity mainly favoring the high terrain of northern AZ and southeastern AZ and low chances (<10%) in the lower deserts of south-central AZ. Above normal, temperatures will contribute to seasonally dry afternoon conditions each day through the first half of the week, before temperatures once again heat up during the second half of the week. Minimum RH values of 15-30% will be common through the first half of the week before dropping into the 10-20% range late in the week as temperatures heat up again. Overnight recoveries will be fair most nights with RH values mostly in the 35-50% across lower deserts to 45-65% across southern Gila County. Wind speeds should be fairly light through the period with only local afternoon gusts 20-25 mph.

PSR WATCHES / WARNINGS / ADVISORIES

AZ...Extreme Heat Warning until 8 PM MST Wednesday for AZZ530-532-537- 540-542>544-546-548-550-551.

Extreme Heat Warning until 8 PM MST this evening for AZZ531- 533>536-538-539-541-545-547-549-552>555-559.

CA...Extreme Heat Warning until 8 PM PDT Wednesday for CAZ567-569-570.

Extreme Heat Warning until 8 PM PDT this evening for CAZ560>566- 568.