textproduct: NWS Phoenix

KEY MESSAGES

- Temperatures will continue to hover 5 to 8 degrees above normal through the middle of the week which will result in persistent, widespread Moderate, to locally Major, HeatRisk.

- Lingering moisture will result in very isolated shower and thunderstorm chances today, mainly around enhanced terrain features in Southwest Arizona and Southeast California.

- An eastern Pacific low will help dry the region out, limiting further rain chances, while also providing near normal temperatures and breezy conditions by the end of the week and into the weekend.

SHORT TERM /Today through Wednesday/

Latest mid-lvl wv imagery and 500 mb streamline analysis reveals an area of high pressure situated over the Baja Del Norte while a weak low pressure system meanders over the eastern Pacific, several hundred miles off the California Coast. The upper-lvl flow is very weak and chaotic over our forecast area today, but there is just enough diffluence aloft and residual sfc moisture in place to help generate isolated showers and storms over the high terrain features of northern and western AZ. The most likely location for storms to develop today will be over the Kofa and Chocolate Mountains. Due to the weak upper lvl flow, any storm that develops will not move much at all and should remain confined generally to any terrain features. The main threats with any storms this afternoon will be strong outflow winds and potential for blowing dust, especially along the I-10 and I-8 corridors in western AZ and southeast CA. Under the influence of ridging and positive hght anomalies, temperatures will soar into the 105-111 degree range this afternoon with some of the lowest elevations and river valleys approaching 112-113 degrees. These high temperatures are around 5 to 8 degrees above normal for mid-June and will result in a localized Major HeatRisk. Therefore, proper heat precautions should be used if working outside for a prolonged period.

On Wednesday, the aforementioned area of low pressure off the coast of California will begin to progress inland and will result in drier air building into the region from W to E. Although PWATs will fall below an inch across the western deserts, they will still be around 150-175% of normal across south-central AZ on Wednesday afternoon. Thus, another round of isolated to widely scattered convection will be possible over the typical terrain features surrounding the lower deserts. Steering flow will be more out of the S-SW on Wednesday which will keep convection from moving toward the Phoenix Metro, however residual outflow boundaries from decaying convection could still reach N Pinal or S Gila Counties. Another result of the upper-lv low moving into SE California on Wednesday afternoon will be an uptick in breeziness where gusts could reach 25-35 mph along and west of the Colorado River Valley. Stronger winds in the 850-700 mb level will also result in localized gusts around 40 mph at mountain peak level, especially in SW Imperial County. 500 mb hghts will begin to decrease slightly on Wednesday, however highs across the lower deserts will still reach upwards of 105-111 degrees resulting in at least one more afternoon with a localized Major HeatRisk.

LONG TERM /Thursday through Monday/

The remainder of the week looks generally unexciting, at least for our area, as rain chances fall to near zero once considerable drying takes place. There could be just enough left over moisture to squeeze out some showers over the White Mountains on Thursday, but that looks to be the only remaining precip potential statewide through at least the start of next week. This drop in regional moisture will be thanks to the migration of an eastern Pacific trough toward the Great Basin, imparting dry southwesterly flow upon the region. We may lose the moisture, but there is some good news. This wave will erode at positive height anomalies, which will aid in a downtrend in temperatures with readings falling toward seasonal levels. Now, this does not mean we get a break from the triple digits, but at least daily forecasted highs fall closer to 100-108. Not a massive amount of relief, but enough to tamp 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. Exact 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 1728Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: The main impact today will be winds. Winds are expected to gust this morning out of the west with gusts near 15-20 kts. Later in the evening the gusty conditions are likely to subside, however, elevated wind speed will linger through the late evening hours. TS development in higher terrain should be less prevalent than the past couple days with very low chances of activity or outflows descending into lower deserts. FEW mid to high level clouds will be passing through the region today, expecting to clear by tomorrow morning.

Southeast California/Southwest Arizona including KIPL and KBLH: No major weather concerns will exist through the TAF period with only a few building Cu expected this afternoon. While isolated afternoon thunderstorms are possible this afternoon over terrain features, chances of direct impact to a terminal location is very limited. However, outflow winds could conceivably cause abrupt wind shifts during the late afternoon, but odds remain low at this time to preclude any mention in the TAF package. Outside of this possibility, winds should oscillate between SE and SW with some modest late afternoon/evening gustiness, with speeds between 10-15 kts likely.

FIRE WEATHER

Lingering moisture will help keep isolated thunderstorms in the foreast mainly over the high terrain features of Southwest Arizona and Southeast California today and south-central AZ on Wednesday, however chances of any wetting rainfall remain low. The main concerns with any storms that do develop will be dry lightning and strong, gusty outflow winds. Outside of any storms, winds will follow diurnal trends will with breezy to locally windy conditions developing Wednesday afternoon, mainly for the Lower Colorado and Imperial Valleys, along with the high terrain of Arizona. Breezy conditions will likely persist through this weekend. Along with increasing winds, MinRHs will fall from 10-15% toward 5-10% by mid- week, generating daily widespread elevated to locally near critical, fire weather conditions. MaxRHs will offer less and less relief over in the coming days as values fall from 30-50% toward 15-35%.

PSR WATCHES/WARNINGS/ADVISORIES

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