textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures around 3 to 8 degrees above daily normal will result in widespread Moderate Heat Risk with isolated pockets of Major Heat Risk at times, through the middle of the week.

- Chances for showers and thunderstorms remain in the forecast for at least one more day, with the best potential focused over foothill and high terrain locations, though lower desert storms cannot be ruled out.

- An eastern Pacific area of low pressure will help to dry the region out while also providing cooler temperatures during the back half of the week and into the weekend.

SHORT TERM /Today through Tuesday/

Current RAP40 500mb analysis show region today under H5 heights between 590-592dam with the core of the subtropical high over Northwestern Mexico/Central Baja Peninsula. An area of low pressure remains over Central California and extending into the Eastern Pacific with broad ridging in the Pacific NW coast line. The interaction between the subtropical high and the lower pressure over CA are helping keep moisture more or less trapped here in the lower deserts, with this morning's 12Z sounding seeing even a slight increase compared to yesterday morning's 12Z sounding with a PWAT value of 1.54", or near 200-225% of normal for early June. Morning MUCAPE was 672 J/kg with the GFS computed MLCAPE projected to be between 750-1000 J/kg to some areas near 1500 J/kg. Additionally, guidance continues to point towards flow aloft increasing across central and eastern Arizona, this would set up more favorable conditions to promote and sustain updrafts. Like the past few days orographic lift will continue to be the main trigger for storms to begin their ascent, however with the conditions mentioned earlier, any storms that do develop in the higher terrain have a better chance of survival and can move further down into the Valley. Winds aloft this afternoon have already begun to shift from the west to out of the northwest, due to this outflow boundaries are likely to push further down where PoPs today range between 20-30% across the western and southern Maricopa County and between 10-20% across eastern Maricopa County, northern Pinal County and into the eastern higher terrain. While most areas today won't see much in terms of accumulations, localized areas where storms crop up may see a few hundredths of an inch. Otherwise outside of rainfall potential, other impacts will be the chance for lightning and blowing dust in the usual dust prone areas.

By Tuesday the moisture will begin to slowly dissipate with PWATs expected to drop to 1.00-1.25", although even those values are 150- 180% of normal. In addition to losing some of the moisture, the region will begin to be taken over by stronger ridging leading to more subsidence as the low over California degrades, this will severely limit potential for any convective activity for tomorrow afternoon. The higher terrain areas might be able to squeeze an isolated shower out, however, currently most CAMs show very little to nothing in terms of activity even in the higher terrain areas.

Temperatures for today and Tuesday aren't nearly as exciting. Afternoon highs today's will be between 105F-111F and then between 107F-113F for Tuesday as ridging builds over the region. Overnight lows will also remain in the mid 80s providing very little relief. Continuing this trend of above normal high and low temperatures keeps widespread Moderate to localized areas of Major HeatRisk in the lower deserts. With that said remember that proper heat precautions should be used if plans take you outside for extended periods during the next couple of days.

LONG TERM /Wednesday through Sunday/

The remainder of the week looks generally unexciting, at least for our area, as dry air filters in from Wednesday onward. There could be just enough left over moisture to squeeze out some showers over southeast Arizona or high terrain areas to our north and east, but the majority of activity should be focused over Tucson and Flagstaff CWAs. Something a bit peculiar is the presence of PoPs and QPF for the Phoenix metro on Friday, even though PWATs will be falling closer toward near and below normal for June. Moisture at those levels would likely not even be enough to get high terrain storms, let alone lower desert rainfall. This could be just an artifact of the ingested WPC rainfall forecast that gets adjusted with time, but we would be hard pressed to get rainfall on Friday with dry air rushing in. Who knows, maybe if we can get enough synoptic lift with an approaching eastern Pacific trough to interact with stubborn moisture, some rain chances cannot be completely ruled out, but as of now, I lean more toward the drier solution.

Speaking of that trough, its migration closer to the Desert Southwest by the latter half of the week will help us "cool" off a bit as temperatures fall closer to normal, with perhaps some areas even seeing below normal readings by the weekend. Now, this does not mean we get a break from the triple digits, but at least daily forecasted highs fall closer to 99-108. Not a massive amount of relief, but enough to back regional HeatRisk down to the lower end of the Moderate category. Heat precautions will still need to remain in place regardless. Lower moisture with those cooler temps will also allow for some more comfortable overnight lows in the upper 60s to near 80 degrees. Something that will have to monitored is the potential for elevated fire weather conditions as this feature will increase winds regionwide. Strength of gusts is still uncertain at this time, but with very dry air expected to be in place, it would not take much wind to increase fire danger.

AVIATION

Updated at 1750Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Thunderstorm activity and associated strong outflow winds this afternoon/early evening will be the main aviation weather concerns for this forecast period. Winds will generally follow diurnal tendencies through the early afternoon. Southerly flow will gradually transition to westerly within the next hour or so and become elevated and gusty by this afternoon. Latest hi-resolution model guidance suggest storms will initially develop to the N and SW of the Phoenix Metro and increase in coverage around 22Z-23Z. Although there is still high uncertainty in the overall coverage of TS, the main focus looks to be west of KPHX this afternoon which will maintain a westerly wind component through this evening. The greatest chance for -TSRA at any of the metro terminals will be between 23Z-01Z. Gusty outflow winds out of the NW (330-350 direction) will be of concern during this timeframe. There is currently around a 50-70% chance of gusts exceeding 35 mph with any outflow that pushes through. FEW-SCT mid-level clouds aoa 10 kft will be common with occasional BKN coverage during periods of SHRA/TSRA.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns will exist for the next 24 hours under FEW mid to high cloud decks. Winds will follow a nearly identical pattern to the last 24 hours, varying between SE during the day and SW/W during the evening at KIPL with some westerly gusts up to 20 kts possible between 03Z-07Z. At KBLH winds will vary between S to SW, generally remaining between 6-12 kts with afternoon gusts to around 20 kts.

FIRE WEATHER

Elevated moisture levels will result in isolated to scattered thunderstorms once again this afternoon and evening, mainly for higher terrain areas, that will be capable of producing gusty and erratic winds and dry lightning. Outside of any thunderstorm outflows, winds will be diurnally driven with the typical afternoon and evening upslope/upvalley breeziness between 15-25 mph. Enhanced moisture will bring some benefit as MinRHs range between 15-20% for the majority of the region, with the exception being SE California where readings will be closer to 10%. For those areas with better moisture, the overnight period will offer at least some modest relief as MaxRH readings rise to 30-50% each night. Those drier spots further west however will only see values increase to around 25%. Moisture scours out during the back half off the week, which will decrease dry thunderstorm potential, but drop RHs closer to 10-15% during the afternoons. By mid to late this week winds will begin to pick up, mostly along the Colorado River Valley, and eastern AZ higher terrain, where gusts between 25-30 mph may occur. This can lead to elevated fire weather, especially as moisture begins to filter out of the region.

PSR WATCHES/WARNINGS/ADVISORIES

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