textproduct: NWS Phoenix

KEY MESSAGES

- Abundant moisture will remain situated across the eastern half of Arizona providing enhanced chances for showers and thunderstorms through the middle part of the week, especially over mountain locations.

- Although uncertainty remains, there will be potential for some storms to produce strong winds and heavy rainfall over the next several days.

- Near to slightly above normal temperatures are expected throughout all of the coming week.

SHORT TERM /Today through Monday/

The main forecast concern early this week (and even through the middle of the week) will continue to be the conditional probabilities of thunderstorms across the area, some of which could produce localized strong winds, blowing dust, and heavy rainfall. The subtropical ridge continues to give way to broad upper level troughing building in across the Northwestern U.S. By Monday, the ridge center is forecast to be positioned over the Southeastern U.S. with the broad troughing filtering more into our region and likely staying there for much of the week. At least the eastern half of Arizona will remain well positioned much of this week for periodic influxes of moisture out of northern Mexico and off the Gulf of California. Moisture levels are expected to remain very adequate for shower and thunderstorm potential over the next several days with the main limiting factors being the overall weak upper level support and weak to moderate convective inhibition.

Saturday's showers and storms overachieved compared to forecast guidance, just like Friday. Models have had a difficult time with depicting storm potential in this somewhat conditional environment and under a southwesterly steering flow. Unfortunately, this is likely to be the case for today and probably most days for the coming week. Our expectations is for today and Monday to at least have a 2 or 3 periods of showers and isolated thunderstorms with the CAMs favoring late this afternoon/early evening, Monday morning and again later Monday. We should have plenty of insolation today resulting in modestly high CAPE of 1000-1500 J/kg with little CIN later in the afternoon into the evening. Although CAMs really can't agree on convection for today, it is logical for storms (some potentially strong) to develop with a focus over higher terrain areas. Chances into the south-central Arizona lower deserts are expected to be more limited, but PoPs have been adjusted upward to at least include 10-15% chances for eastern and northern portions of the Phoenix metro.

After a brief reprieve in rain chances later this evening/early tonight, a couple HREF members are pointing at a round of elevated showers and embedded thunderstorms at some point between 3 AM-10 AM Monday. The more likely time frame for this type of convection should be a couple hours before sunrise before gradually diminishing shortly after sunrise. Given the expected elevated nature of these potential showers and storms, we should only expect localized heavy rainfall as the only threat. For the latter half of Monday, the best potential for showers and storms should be over southeast Arizona and potentially into the higher terrain east of Phoenix. Given the forecast CAPE values of up to around 1500 J/kg and very respectable low level mixing ratios of 13-14 g/kg, this should present a heavy rainfall and localized flood threat into southern Gila County later Monday.

LONG TERM /Tuesday through Saturday/

The weather pattern through at least the middle of the week will continue to support good moisture levels over at least the eastern half of Arizona and likely improved upper level ascent for Tuesday-Thursday. Tuesday may involve a brief period of drier air moving into south-central Arizona from the southwest and this shows up in the fairly limited PoPs Tuesday afternoon/evening. However, NBM guidance shows a resurgence of moisture and rain chances during the overnight hours Tuesday night/Wednesday morning. Chances Wednesday into Thursday are also looking better with a potential disturbance tracking northward into central/eastern Arizona at some point. Needless to say, the model differences call into question the best timing for rain chances and the exact areas, but as long as the upper level support and good moisture remain present chances will remain elevated.

WPC has added a slight risk on the Days 2-4 (Monday- Wednesday) Excessive Rainfall Outlooks over the eastern Arizona high terrain. It would not be surprising for subsequent issuances of the EROs to extend the risk through Thursday or even Friday depending on the forecast available moisture. Although the risk for heavy rainfall and flooding will be present through at least the middle of the week, the risk for strong downdraft/outflow winds is likely to decrease with guidance showing decreasing forecast DCAPEs. Models are still trending toward drier air finally moving eastward through most of Arizona by Friday or Saturday. This should mostly shut down rain chances over the lower deserts and decrease chances over higher terrain areas.

Temperatures throughout the entire week are expected to remain fairly close to seasonal normals with the lowest forecast highs occurring on Tuesday and Wednesday. As long as models are correct with the drying trend late in the week into next weekend, temperatures are favored to drift back to above normal with highs more in a 103-108 degree range by Friday or Saturday.

AVIATION

Updated at 0920Z.

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

Primary forecast uncertainty and potential impact will be the possibility for VCSH/VCTS this afternoon and evening and again Monday morning. This afternoon storms are favored outside just outside the metro, but there is still a low chance (5-10%) activity spreads into the metro between 23-03Z. An area of showers and storms may also develop in the metro Monday morning as early as 10Z, but this looks to be a conditional scenario and confidence is low. Winds will mostly follow typical diurnal tendencies with speeds below 10 kts and with periods of light and variable conditions. Any showers or storms will be capable of generating locally strong and erratic winds. FEW to SCT clouds will be common through the TAF period with lowest bases around 8K ft AGL.

Southeast California/Southwest Arizona including KIPL and KBLH:

No aviation weather concerns expected under mostly clear skies. At KIPL, winds will mostly favor the southeast, with a period of southwesterly this evening/tonight. Wind speeds at KIPL will mostly stay below 10 kt with periods of light variability. At KBLH, winds will continue to favor a southerly component with speeds generally between 8-14 kt with some afternoon gusts up around 20 kt.

FIRE WEATHER

Chances for scattered showers and isolated storms will continue today before increasing and becoming more widespread into the south-central Arizona lower deserts beginning Monday. Moisture levels will remain high enough to support localized heavy rainfall with any storms. Minimum humidity levels over the next several days will only fall into a 15-25% range in western districts and 25-40% in eastern districts. This will follow fair to good overnight recovery of 40-70%. Outside of thunderstorms, winds will generally remain light with a southwest heading through nearly calm conditions will be common in the morning hours.

PSR WATCHES/WARNINGS/ADVISORIES

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