textproduct: NWS Phoenix

KEY MESSAGES

- After a brief reprieve from the extreme heat today over south- central and eastern Arizona, highs will return to around 110 degrees by Friday, lasting into early next week.

- Extreme Heat Warnings are in effect through Sunday evening due to continued areas of high-end moderate to major HeatRisk.

- Isolated thunderstorms are expected across the AZ high terrain this afternoon and evening with less than 10% chances for the lower deserts. Chances will likely remain confined to the high terrain through at least Saturday.

SHORT TERM /TODAY THROUGH SATURDAY/

After the biggest monsoon event of the season so far in the Phoenix Metro area, we are not anticipating much if any activity in the lower deserts today due to an overturned atmosphere. Latest visible satellite and composite radar imagery reveals a remnant MCV left over from last night's storm complex which is now progressing through the Yuma area. This MCV is expected to continue bringing an area of light to moderate showers with a few embedded lightning strikes to Yuma and Imperial Counties over the next few hours before finally dissipating. Farther east, skies have cleared out across southcentral AZ allowing temperatures to begin rising, however highs in the Phoenix area will likely top out right around normal due to residual moisture from previous rainfall. Therefore, NBM high temperatures were adjusted down by several degrees this afternoon and overnight lows tonight as well. Latest RAP 13 mesoanalysis across southcentral AZ shows CAPE values are still around 1000-1200 J/kg, but there is a much stronger mid-lvl inversion today with ML CIN on the order -120 to -150 J/kg. Therefore storm coverage will be much more isolated this afternoon, and without a strong outflow, little to no storms are expected across the lower deserts this afternoon and evening.

Deterministic models and ensemble members suggest the subtropical high will shift over Colorado on Friday and then migrate into eastern NM on Saturday. This shift in the upper-lvl pattern will cause winds to turn more out of the south, ushering drier air into our beginning on Friday. Both the GEFS and ECS show PWATs falling to 1.3" or lower and mixing ratios as low as 7-8 g/kg. As such, NBM PoPs for both Friday and Saturday fall below 10% for the lower deserts to 10-20% over portions of the high terrain. Despite storm coverage decreasing substantially, there will still be a chance of a distant outflow from storms along the International Border reaching Maricopa or Pinal Counties, but additional storm development is unlikely. Although the ridge axis will shift ewd into this weekend, overall 500 mb hght fields will remain largely unchanged from previous days. Therefore, we should see a return of above normal temperatures and extreme heat conditions by Friday and persisting into this weekend and the Extreme Heat Warning will remain in effect through Sunday.

LONG TERM /SUNDAY THROUGH WEDNESDAY/

Model uncertainty remains quite high for the first half of next week as the position of the high is likely to set up somewhere over eastern New Mexico and western Texas by Monday with little to no movement into the middle of next week. This position can cause higher uncertainty in moisture levels for our area with the latest guidance trying to advect some moisture into our area by Sunday or Monday, but NBM forecast PoPs are at most 10-15% for the lower deserts. At this point, we could continue to see mostly slight chances favoring the high terrain into early next week, but if moisture does eventually improve enough storm chances are likely to be higher than what the NBM is depicting. Another wildcard will be the potential influence of an upper level trough that may attempt to move into western portions of our region Sunday into Monday. If this occurs, it may be enough to improve convective potential across southeast California and western Arizona for Sunday and/or Monday.

Temperatures are expected to continue to be more influenced by the strong subtropical high as H5 heights hover between 593-596dm across the Desert Southwest through early next week. Daytime highs are not expected to change much day to day from Sunday through early next, barring any significant change with the convective chances. The Extreme Heat Warning is currently in effect through Sunday, but it seems quite likely it will need to be extended again at some point.

AVIATION

Updated at 1818Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: A down day in terms of thunderstorm activity is expected for the Phoenix area, with primarily just outflow passage potential this evening. W'rly winds are expected through this evening, ahead of any outflow winds from the north and/or northeast. Timing of any outflows are most likely between 03-07Z. Outflow gusts to 20-25 kts are possible, but the outflows may just serve as a wind shift, with E'rly winds then prevailing the rest of the night. VCSH/VCTS is not expected at terminals this evening/tonight, but there will remain a 10-15% chance. FEW mid and high clouds are expected through the afternoon, followed by SCT to BKN this evening and tonight.

Southeast California/Southwest Arizona including KIPL and KBLH: A complex of rain showers with embedded lightning is currently slowly moving west into Imperial County. This complex is expected to continue westward through this afternoon, but the rain may gradually dissipate with time. VCSH was added to the KIPL TAF for the afternoon and VCTS cannot be ruled out. Winds will eventual shift more SE'rly as the complex nears the terminal. A shift in the wind to more of a W/SW direction is anticipated this evening as the complex shifts west and storms in the mountains to the west may push outflows to KIPL. At KBLH a S/SW wind component is expected through the TAF period. Both terminals will see wind speeds mostly at or below 12 kts sustained, while KIPL may see gusts up to 20-25 kts this afternoon and evening. FEW-SCT cloud decks will be present through much of the forecast window, with the lowest bases around 12 kft.

FIRE WEATHER

Elevated moisture levels will persist today with a temporary reprieve from the extreme heat across much of the area. Expect mainly isolated showers and thunderstorms this afternoon and early evening over the AZ high terrain, with a less than 10% chance of storms in the lower deserts. Drier air will filter into the region Friday and Saturday with even lower chances for rain while temperatures heat back up to extreme levels. MinRHs of 20-30% today will lower to 15-25% beginning Friday. Winds should overall 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.

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