textproduct: NWS Phoenix

UPDATE

Updated Aviation Discussion

KEY MESSAGES

- Daily chances for showers and thunderstorms will exist through the upcoming week, most favorable in the Arizona high country. - Thunderstorm chances may be more favorable (30-40%) for the lower deserts on Tuesday through Thursday.

- Temperatures will gradually climb to near normal through the upcoming workweek with areas along and west of the Colorado River valley topping out above 110 degrees by mid-week, resulting in a locally major HeatRisk.

SHORT TERM /Today through Monday/

Latest satellite imagery showing well defined MCV circulation moving slowly west across Yavapai County. This has resulted in considerable cloudiness across central and southwest AZ to start the day. Not much rainfall outside of some light showers or sprinkles across portions of Maricopa, La Paz and Yuma Counties. Low level water vapor imagery and 500 mb streamline analysis reveals an elongated area of high pressure encompassing the Intermountain West and the Central Plains. Meanwhile, the Desert Southwest remains to the south of the high pressure center allowing deep easterly flow to prevail with embedded short waves to enhance storm chances at times. Another round of storms will materialize this afternoon, but are expected to again remain relegated to the higher terrain of S Gila and Yavapai Counties with only a 10-30% chance of a weak outflow making it down to the lower deserts. Remnant clouds and maybe sprinkles/light showers expected again across the lower deserts late tonight, moving out to west early Monday morning.

On Monday, the positing of the subtropical high will not change much, remaining centered over the Intermountain West and Southern Rockies. This will allow deep easterly flow to continue over AZ. The most noticeable difference will be a slight shift wwd of an easterly wave/inverted trough which has been sitting over W TX. This feature will continue to slowly progress into far W TX and N MX by Monday afternoon. Ahead of this feature, we could see a more robust vort max progressing wwd into N AZ which will promote another round of convection across the Mogollon Rim and eastern AZ where the highest instability will be present. CAPE values in the lower deserts will still be moderate at best, upwards of 500 J/kg with a capping inversion present so it may be difficult for storms to survive off the higher terrain Monday evening. A longer lived outflow boundary is more likely which could at least foster isolated storms over far E Maricopa and Pinal Counties. Due to the strengthening of the 500 mb high over the Intermountain West and responding low-lvl thermal profiles, temperatures will tick up a couple more degrees Monday afternoon with most lower desert locations reaching the triple digits.

LONG TERM /Tuesday through Saturday/

Deterministic guidance and ensemble members continue to indicate that the subtropical high will shift southeast over the Southern Plains beginning on Tuesday. This will cause steering flow over the Desert Southwest to shift from easterly to more of a southeasterly direction. The afomentioned inverted trough will slowly progress through N MX and into S AZ Tuesday into Wednesday. This feature will enhance large scale lift over the region and promote additional moisture transport from N MX into AZ. In response, shower and thunderstorm activity will likely increase in coverage and intensity with much better chances for the lower deserts to receive measurable rainfall. Currently NBM PoPs are highest during the late evening on Tuesday through the overnight period, peaking around 20-40% across the Phoenix Metro. If convection is more robust on Tuesday, then Wednesday may be a quieter day overall. Confidence decreases in timing and overall coverage of thunderstorm activity later next week as ridging aloft expands over the forecast area and drier air begins to intrude into southeast portions of AZ.

Model consensus indicates an overall expansion and strengthening of the subtropical high, allowing positive height anomalies to build over the forecast area from Thursday into next weekend. The GEFS and EPS indicate mean hghts approaching 594-596 dam which around the 90th percentile of climatology for late July. Thus we will likely see temperatures increasing back above normal starting Thursday. Unfortunately this means the return of Major HeatRisk, especially across SE California and SW Arizona on Thursday and Friday. Temperatures will increase further across the lower deserts by next weekend with good indications that highs will reach 110+F in Phoenix beginning Saturday.

AVIATION

Updated at 0010Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: A fairly typical diurnal wind pattern is expected through Monday afternoon with little to no SHRA impacts anticipated besides perhaps some weak spotty showers during the overnight and morning hours. W winds at 5-10 kts are expected through this evening before shifting E and/or VRB and then winds will veer back W/SW by late morning-noon Monday. There will be better odds for a gusty outflow from the east and/or north Monday evening, but potential for SHRA/TSRA sparking with the outflows will be low (10-20%). FEW to BKN clouds will be common through the TAF period with lowest bases around 8-10K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather impacts are expected through Monday. At KBLH, 7-12 kt SSW-SSE winds will be prevail. At KIPL, winds will follow typical diurnal trends with a period of gusty W winds this evening (G up to 20-25 kts) and then return to a SE wind by Monday afternoon. Spotty VCSH/-SHRA may develop in the terminal areas tonight through Monday morning, mainly between 07-19Z, but confidence on specific timings is low. FEW to BKN clouds aoa 10K ft AGL will be common throughout the period.

FIRE WEATHER

Recent wetting rainfall has resulted in drastic improvements in fuel moisture across south-central AZ where ERC values have fallen below the 25th percentile. Additional rounds of beneficial wetting rainfall will be possible each day through at least the middle of this week, especially over the foothills and high terrain of the eastern districts. Winds will remain light, mostly below 15 mph and follow typical diurnal upslope and downvalley patterns, the main exception being gusty and erratic winds in the vicinity of thunderstorms. Elevated moisture levels will keep minimum afternoon humidity above 20% across the western districts and between 30-40% over the eastern districts. Overnight recovery will range from fair to good across the western districts and very good to excellent for the eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...None. CA...None.