textproduct: NWS Phoenix

KEY MESSAGES

- Above normal temperatures with moderate HeatRisk will prevail throughout the week before retreating closer to normal by the end of the weekend.

- Other than a slight chance of a shower or thunderstorm in eastern Arizona during the next few afternoons, dry conditions under mostly sunny skies will prevail through the weekend.

- Locally breezy conditions will develop late in the week and this weekend, particularly across the lower Colorado River Valley and higher terrain communities.

SHORT TERM /Today through Friday/

Latest midday objective analysis shows very weak flow over the region, with a bit of a col overhead. The weak coastal low is now just off the central Baja Peninsula coast and should begin pushing eastward this afternoon. H5 heights over the area are around 587dam, which is around the 75th percentile of climatology for this time of year. This higher than normal height field and pressure will result in above normal surface temperatures this afternoon and the next few afternoons with limited change in the synoptic pattern as the low slowly progresses east across northern Mexico through the end of the week.

High temperatures this afternoon are forecast to reach up to 104-107F across the lower deserts, under sunny skies. These temperatures will be around 4-6 degrees above daily averages. Latest NBM forecast has increased high temperature forecasts for tomorrow by 1-2 degrees over previous forecast packages and now has some areas flirting with 110F, including in the Phoenix area and Imperial Valley. High tomorrow are now forecast to reach 106-109F across the lower deserts. While it may still seem a little early to see 110F it would not be uncommon. Daily records are in the 112-116F range for early June. Forecast high temperatures for Friday have also come up slightly from previous forecasts and is now expected to be similar to today. These temperatures will lead to widespread Moderate HeatRisk.

While most of the region will remain very dry and mostly sunny the next few days, some low level moisture has moved into southeast AZ. This moisture contributed to some convective showers in the White Mountains yesterday and westward-propagating outflows from these showers and storms in NM have pushed moisture a little further into AZ for today. This moisture will again aid convective development this afternoon and a few isolated storms had already developed over predominant terrain features as of noon. Latest mesoanalysis show an area of high SBCAPE (>1000 J/kg) across portions of southeast AZ, that drops off quickly westward to 0 J/kg in the lower deserts of south-central AZ. With modest instability over portions of southern Gila County a few convective showers and storms may develop, with best chances over features like Pinal Peak near Globe and the Hilltop area. Rainfall will be very limited with any activity that develops, mostly less than 0.10". So, the greatest risks will be lightning generating new fires and strong gusty outflow winds. The 12Z HREF and REFS runs show around a 60-70% odds of thunderstorm wind gusts >35 mph in southern Gila County. Decaying outflows may eventually make there way toward the lower deserts later this evening with locally gusty winds. The convective activity today will be diurnally driven and should dissipate with the loss of heating. There will be a chance for convection again tomorrow afternoon, but hi-res models are showing less instability tomorrow and overall less coverage.

LONG TERM /Saturday through Tuesday/

As we head into the weekend, ensembles point towards another trough moving over western portions of the CONUS, which will eventually become more amplified and stretch from British Columbia down the California coast. However, uncertainty remains regarding the strength and positions of this potential disturbance. The increasing temperature spread through the weekend and into the start of next week between the NBM 25th and 75th percentile reflects this uncertainty. Nonetheless, even with the cooler air associated with this potential system, it appears widespread triple digits are here to stay. Regardless of which ensemble solution comes to fruition, the continuation of breezy, to perhaps locally windy conditions appears likely. The main question will be how strong gusts may become, which will be dependent on how tight the regional pressure gradient becomes. With little moisture flux, any breeziness will keep the fire weather risk elevated at least through Sunday.

Forecast confidence does not improve for the start of next week as model clusters show a wide variety of outcomes, with some showing continued troughing, while others favor the return of high pressure. The return of ridging across the western CONUS appear to be most likely outcome at this time, but how amplified this feature becomes, its placement, and if we remain under some influence of a lingering area of low pressure remains uncertain at this time. One thing that does appear certain though, other than our high terrain rain chances today and Thursday, dry conditions are likely to prevail over the next week at least for most of the region.

AVIATION

Updated at 1725Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT; and Southeast California/Southwest Arizona including KIPL and KBLH:

No significant weather issues will exist through Thursday evening under passing cirrus decks and a few afternoon CU/CB developing over the mountains east of Phoenix. Confidence is very good that trends in wind speeds and timing of directional shifts will be very similar to the past 24 hours. However, the late evening/overnight shift back to an easterly direction around the Phoenix metro may occur a few hours earlier than the past couple days due to decaying outflow descending into the valley from storms over mountains.

FIRE WEATHER

The threat for a isolated dry thunderstorms over southern Gila County today and Thursday is the main fire weather hazard over the next few days. Winds will follow typical diurnal tendencies with typical afternoon upslope breeziness the next couple of afternoons. Gusts begin to pick up Friday and into the weekend, mainly across the Lower Colorado River Valley and high terrain areas of the eastern districts. With daily MinRHs hovering close to 5-10%, even marginal breezes will result in periods of elevated fire weather conditions. Isolated instances of near critical to critical conditions cannot be ruled out. Overnight recovery will offer very little in terms of relief as MaxRHs run between only 15-45% for most areas. Breezy, to locally windy, conditions are likely to continue into the weekend, potentially lingering into the start of next week, resulting in a prolonged period of daily occurrences of elevated to near critical fire weather conditions starting on Friday.

PSR WATCHES/WARNINGS/ADVISORIES

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