textproduct: NWS Phoenix

UPDATE...Updated 00z Aviation Discussion

KEY MESSAGES

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

- Chances for showers and thunderstorms will exist through the remainder of today and into the start of the upcoming week, with the best chances focused over high terrain areas and portions of Southeast Arizona.

- Brief gusty winds from distant outflows and low probabilities for a thunderstorm or two over the foothills of Maricopa County cannot be ruled out today and again Monday during the afternoon and evening hours.

SHORT TERM /Today through Monday/

Current objective analysis continues to show a more complex upper level pattern over the Desert SW with the subtropical high still pushing westwards over the lower deserts with H5 heights between 590- 592 dam, which puts them in the 90th percentile of climatology. Ridging remains over the Eastern Pacific, with a closed low that has developed over Northern California. This low over CA and the subtropical high to our SE are working together to promote SW winds aloft and continuing to advect moisture into Southern Arizona. Ensembles keep PWATs between 1.25-1.50" today and Monday, with this morning's 12Z sounding backing up the models with a PWAT value of 1.40". Even though MUCAPE this morning was only near 500 J/kg, very little to no CIN was present so the natural orographic lift of the mountains near Table Top were able to produce a few isolated storm early this morning. These storms were able to squeeze 0.01-0.08" of rainfall in areas near Buckeye.

The early morning activity quickly dissipated by the late morning hours. Current satellite imagery shows the bulk of the activity now in the Northern AZ high terrain and some in southeastern AZ. The storms to our north can create outflow boundaries this afternoon where wind gusts are likely to reach between 25-35mph, with the HREF showing a 50% chance of seeing wind speeds upwards of 35 mph in Northern Maricopa County and the Northern Foothills later this afternoon into the evening hours tonight. The HRRR bufr sounding has MUCAPEs between 500-750 J/Kg this afternoon/evening so similar to this morning any outflow boundaries over terrain can be enough to sustain the development of an isolated shower/thunderstorm. Due to this PoPs for tonight are between 10-15% in the northern portions of our CWA, then extending down into Pinal County by roughly 7PM MST tonight. Some localized areas of blowing dust cannot be ruled out if storms do pop along the border of southern Maricopa and Pinal Counties.

For Monday Hi-res guidance continues to point towards small areas of precipitation early in the morning yet again. By late afternoon/ evening the northern Foothills and eastern high terrain of Gila County can expect greater PoP chances, 15-30%, where the main driver of development looks to be orographic lift, as atmospheric conditions don't stray too far from what what observed today. One notable difference however will be in the direction of flow aloft. Southwest winds will be shifting out of the northwest by Monday afternoon which should create a more favorable pattern for potential outflows over high terrain areas to descend toward the lower deserts. This can trigger more convection, which is why chances for Phoenix are better for Monday as well, but still remain low (10-15%) due the highly dependent nature of where storms may develop.

Otherwise, afternoon high temperatures will stay 3F-6F degrees above normal with the lower deserts ranging between 105F-110F. Overnight lows will also stay consistent in the upper 70s to mid 80s, or about 5F-8F degrees above normal. Due to this widespread Moderate to localized Major Heatrisk remains in place.

LONG TERM /Tuesday through Saturday/

Models indicate that moisture will not completely scour out through the middle of the week, allowing for at least some diurnally driven shower and thunderstorm activity during this window across the southeastern portion of Arizona and some high terrain areas. However, guidance continues to show eastern Pacific ridging stretching into our forecast area, generating a broad area of subsidence aloft and therefore limiting near-future rainfall for at least most of our forecast area. This area of near to slightly above normal height anomalies will help to keep temperatures around 3-8 degrees above normal through at least Wednesday. Beyond that, we begin to flip the script as an eastern Pacific trough develops in conjunction with the northward migration of a sub- tropical jet streak. This feature will increase winds regionally as the subtropical jet imparts deep southwesterly flow, decrease heights aloft, and substantially scour out the low level moisture across the region. As a result, anticipate elevated fire weather concerns, especially for Southeast CA and Southwest AZ, temperatures moderating closer to daily normals, and the diurnally driven shower/storm chances over AZ high terrain to end.

AVIATION

Updated at 2340Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT: Latest convective and model trends have backed off on a strong northerly outflow affecting the area terminals early this evening. As a result, the overall wind pattern into Monday afternoon will follow the more typical trends with westerly winds through this evening shifting out of the east during the late evening/overnight and back out of the west late Monday morning. Some occasional gusts near 20 kts will be possible through early this evening and once again Monday afternoon. Latest guidance for late Monday afternoon/early evening is aggressive in showing thunderstorm activity and strong northerly outflows affecting the area terminals and thus a PROB30 has been introduced for TSRA for this TAF package. FEW-SCT mid to high decks will be common throughout the TAF period.

Southeast California/Southwest Arizona including KIPL and KBLH: No major aviation weather concerns under FEW mid-level cloud decks during the day Monday can be expected throughout the TAF period. At KIPL, current southeasterly winds will temporary shift out of the west early this evening before shifting back out of the southeast during the overnight period. At KBLH, winds will fluctuate out of the south to southwest. Some occasional gustiness near 20 kts will continue during the next couple of hours at KBLH and will be possible early this evening at KIPL.

FIRE WEATHER

ELevated moisture levels will result in isolated convection the next few afternoons, 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, MaxRHs will offer at least some modest relief as 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% during the afternoons.

PSR WATCHES/WARNINGS/ADVISORIES

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