textproduct: NWS Phoenix

UPDATE

12Z Aviation Discussion.

KEY MESSAGES

- Flood Watches cover much of southern and central Arizona today as periods of showers and thunderstorms, capable of producing heavy rainfall, will remain possible.

- Quiet weather under mostly clear skies is expected for Tuesday and Wednesday before potentially another more active period of weather materializes by the end of the week into the weekend.

- Near to slightly below normal temperatures are expected throughout much of the week.

SHORT TERM /TODAY INTO TONIGHT/

Scattered showers and thunderstorms continue to impact portions of south-central and eastern Arizona early this morning, some of which continue to produce gusty (sub-severe) wind gusts and localized moderate rainfall. Much of the available instability that built up yesterday has been exhausted, but a narrow corridor of 500-1000 J/kg of elevated CAPE remains from east of Phoenix northwestward through northern Maricopa County into Yavapai County. Showers and storms should mainly be focused east of Phoenix through the rest of the morning with localized rainfall amounts of an inch or so still a possibility. The Flood Watch has been extended through noon for Pinal and Gila Counties and the eastern half of the Phoenix Metro. Given this activity is expected this morning, it is likely to ruin any chances for organized activity east of Phoenix during the afternoon hours.

Looking more broadly across the region, the main driver of the shower and thunderstorm activity stems from a shortwave trough digging eastward through the southern half of California and a jet streak positioned across northern Arizona through Utah. Moisture levels across most of Arizona remain quite good with low level mixing ratios of 11-13 g/kg and PWATs around 150% of normal. Given the continued broad forced ascent over much of the area persisting through at least this afternoon, additional rounds of showers and thunderstorms are likely. The best area of focus by this afternoon should switch to over western Maricopa County and La Paz County and possibly int northern Yuma County. This area will likely see a decent amount of sunshine later this morning and this afternoon to rebuild the instability with HREF MUCAPEs again reaching between 1000-1500 J/kg for this afternoon. CAMs generally agree scattered thunderstorms are likely to develop from around Tucson through southern/western Maricopa County by mid to late afternoon with more isolated storms across La Paz County. Some of these storms may result in strong gusty winds, but the severe threat remains quite low. Additional rainfall amounts of up to or just over 1" will also be possible in these areas resulting in a renewed localized flash flood threat. Flood Watches have been extended across western Maricopa County through early this evening and also expanded into La Paz and northern Yuma Counties for this afternoon through early evening.

As the shortwave trough lifts northeastward into Nevada this afternoon and into Utah this evening, we will gradually lose our upper level support leaving only slight chances for a few showers during the overnight hours tonight.

LONG TERM /TUESDAY THROUGH SUNDAY/

West southwesterly drier flow aloft will spread over the rest of Arizona by Tuesday with a brief time period of anticyclonic flow aloft. The drier air aloft is expected to mix into the boundary layer by Tuesday afternoon dropping surface dew points into the 40s across southeast California to 55-60 degrees in the Phoenix area. Although we can't rule out a few isolated showers or weak thunderstorms Tuesday afternoon over the more favored higher terrain locations, the chances are only around 10-15%. Temperatures will remain below normal across south-central and eastern Arizona with lower desert highs at around 100 degrees, while the drier western lower deserts should reach closer to 105 degrees.

The drying aloft will continue to a lesser degree into Wednesday as low level mixing ratios drop to 5-6 g/kg in southeast California to 7-9 g/kg across much of Arizona. Chances for any showers and storms should be similar or even less than Tuesday's chances. Temperatures should also warm another couple of degrees under sunny to mostly sunny skies.

Forecast concern is increasing for the potential of tropical moisture surging northward into the region as early as Thursday night into Friday, but more so for the coming weekend. NHC shows a tropical disturbance currently near 10N and 107W with a 90% chance of cyclone formation this week and likely tracking northward off the coast of Baja by Friday into the weekend. There is still a lot of uncertainty with this potential tropical system, but model guidance has been coming to a bit better consensus the last several model runs. Roughly 90% of the GEFS and EPS members now show PWATs increasing to 1.8-2.2" over portions of our area by Friday or Saturday. Given this likely increase in moisture, PoPs have gone up starting Friday and continue through the weekend. It will likely be at least 2 or 3 more days until we have a good idea on what would likely happen late this week. Getting tropical moisture into our region is definitely not unusual, but many times when it happens we struggle to build instability due to extensive cloudiness and poor lapse rates. However, it seems quite likely a Pacific trough will be situated along or just off the West Coast which may provide for enough upper level forced ascent to overcome the likely lackluster instability. We will continue to watch this throughout the week as it very well could lead to another round of heavy rainfall at some point.

AVIATION

Updated at 1000Z.

South Central Arizona including KPHX, KIWA, KSDL, and KDVT:

Current radar mosaic depicts a band of showers with embedded lightning strikes continuing to stream N-NE into southcentral AZ. This trend will continue through sunrise with a potential reinvigoration of SHRA/TSRA for a few hours (mainly between 15Z-18Z). The most likely terminals to see any VCTS or TS will be KIWA, but a few lightning strikes cannot be ruled out at KPHX through the morning hours. By later this afternoon, storm activity should largely come to an end across the Phoenix Metro. Winds will likely maintain an E to SE component through the period with some gusts into the teens to around 20 kts. SCT to BKN mid to high clouds will prevail over the region with gradual clearing anticipated by this evening.

Southeast California/Southwest Arizona including KIPL and KBLH:

No major aviation concerns are expected at the SE California terminals. At KIPL, winds will fluctuate between southeasterly during the daytime and westerly after sunset. At KBLH, winds will maintain a southerly direction through the TAF period. Speeds will range mostly between 10-13 kts with intermittent gusts around 20 kts at KBLH this afternoon. Aside from a few passing hight clouds, skies should remain mostly clear.

FIRE WEATHER

Elevated moisture and periods of showers and thunderstorms will continue today, mainly across the eastern districts. Gusty winds, heavy rainfall, and localized flooding will remain a threat. Drier conditions will move in beginning Tuesday with rain chances mostly ending through midweek. Expect MinRHs of 15-25% across the western districts to 35-50% over the eastern districts today before falling back to 15-25% areawide by Wednesday. Temperatures will range from around normal over western districts to slightly below normal over the eastern districts.

PSR WATCHES/WARNINGS/ADVISORIES

AZ...Flood Watch from noon MST today through this evening for AZZ531- 533-539.

Flood Watch through this evening for AZZ534-537-538-540-554-559.

Flood Watch until noon MST today for AZZ541>553-555>558-560>563.

CA...None.