textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion

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, Heat Risk.

- 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 to dry the region out, limiting further rain chances, while also providing near normal temperatures and breezy conditions during the back half of the week and into the weekend.

SHORT TERM /Today through Wednesday/

Early morning RAP analysis shows broad troughing/quasi-zonal flow, spread over the eastern 2/3rds of the CONUS, all while an eastern Pacific ridge tries to nudge its way over the western tier of the country. Closer to home, the Desert SOuthwest finds itself under unorganized flow as a shrinking area of low pressure continues to linger just off the coast of Southern California. Elevated moisture, responsible for the convection that has been observed over parts of the state the last few days, will continue to have some influence on regional conditions for a little while longer. In previous forecasts, it seemed as if rainfall potential would diminish noticeably, for at least our area, after Monday, and while most locations should not anticipate showers or storms this afternoon, there are some very slight chances for parts of Southwest Arizona and Southeast California. Some hi-res guidance is picking up on localized convection over parts of the Kofas and along near the mountains in the close proximity to I-10 in Riverside County. These potential terrain influenced cells will have very little synoptic support, so anything that does come to fruition likely will not last long and produce little in the way of impacts, other than some gusty winds and occasional lightning. Due to the limited spatial expanse, unfavorable setup, and disagreement amongst the CAMs, max PoPs for these area is only around 25%. Convective activity will quickly cease around sunset.

As we slowly dry out through the middle portion of the week, it will be become harder and harder to see any rainfall activity across the our forecast area, though PWATs will remain near 175% of normal through Wednesday. Though the NBM does not seem confident, which is fair because I am not too confident about further rain chances either, CAMs do show more localized activity for Wednesday afternoon. Now, PoPs are generally less than 10% at this time, and most activity across the state should be confined to the southeast and high country, but perhaps we could see a storm or two in our CWA. The HRRR actually showing more widespread activity across Pima and southern Pinal Counties, so maybe an approaching outflow could spark some activity. Otherwise any convection would likely be anchored to terrain features once again. If this guidance continues to point towards this signal, PoPs may need to be bumped a bit in subsequent forecasts.

In terms of temperatures, it will basically status quo from what we have seen since this past weekend across the region. Afternoon readings will be around 5-8 degrees above normal for the middle of June, which equates to observations ranging from 105-113 for lower desert areas. Unfortunately overnight lows will not offer much in the way of relief, especially around population centers, as elevated moisture, combined with the Urban Heat Island, will keep readings mostly in the upper 70s and 80s. This mix of mild overnight, and hot daytime temperatures will result in widespread Moderate, to even pockets of Major HeatRisk. Proper heat precautions should be used if plans take you outside for extended periods during the next few days.

Even though the upper-level evolution does not reflect a favorable pattern for strong winds, guidance is picking up on some breezy to locally windy conditions Wednesday afternoon and evening, mainly for the Lower Colorado River and Imperial Valleys, along with the high terrain of Southern Gila County. This may be due in part to a minimal enhancement in the stubborn low sitting off the West Coast, but even that will only increase flow aloft to near 25 mph. Nonetheless, there is agreement that surface winds could reach upwards of 25-35 mph for the areas mentioned above, with the higher end of that range focused over the western most locations. Perhaps this breeziness is more terrain driven rather than synoptically influenced, but we do not typically see such relatively weak flow aloft associated with gusts to this magnitude at the surface.

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 1115Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Winds will be the main forecast challenge through Wednesday morning under a few mid/high cloud decks. Confidence remains low regarding timing of wind shifts, and particularly the expanse and duration of east winds this morning. Confidence is much better that either a light east component or variable direction will quickly become westerly by late morning. A few gusts ~20kt will be possible late in the afternoon. 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.

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

FIRE WEATHER

Lingering moisture will help keep very isolated thunderstorms in the foreast, mainly for areas around enhanced terrain features of Southwest Arizona and Southeast California, but rainfall coverage should be noticeably lower regionwide compared to the last few days. Any potential cells that do pop will likely contain little rainfall, so dry lightning will be a fire weather concern. Thunderstorm coverage/potential will continue to diminish through the remainder of the week, but more very isolated activity cannot be ruled out once again Wednesday. Winds will begin to pick up during the middle of the week, with daily breezy to locally windy conditions persisting into the weekend, mainly for the Lower Colorado and Imperial Valleys, along with the high terrain of Arizona. MinRHs will fall from 10-15% toward 5-10% as winds increase, combining to generate daily instance of 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.