Synopsis: There’s lots to talk about today as we prepare for a possible high impact weather event unfolding Monday through Wednesday. A Pacific disturbance will dig south into the lower CO River Valley by Monday before slowly meandering east across AZ. Southerly flow ahead of this system will pull ample moisture, shed from former tropical system Lorena, north into AZ overnight tonight. Multiple waves of storm activity will be possible across southcentral AZ beginning tomorrow morning before increasing in coverage Monday afternoon and lasting into Tuesday. All modes of severe weather will be possible during this time including damaging wind gusts and large hail along with the threat of heavy rainfall leading to flash/urban flooding.
Plan on dry and quiet weather conditions across the region today. Afternoon temperatures will warm into the 97°F-99°F range around the Valley. Variable winds will generally hover in the 3-8mph range with no gusts of any consequence. Moisture levels and cloud cover will be on the rise later tonight into the early morning hours Monday. We will likely see a leading round of showers/t-storms moving north into the County during this period with the focus across our eastern zones.
Deeper moisture and upper level forcing (lift) will overspread the area tomorrow creating a favorable environment for scattered to widespread strong/severe storms. There’s still some uncertainty in guidance as to exact storm coverage, but we’re expecting activity to ramp up as the day progresses and a well-defined cold front eventually sweeps across the County later Monday night. As highlighted above, our initial concerns will be the severe weather hazards with early activity. However, a greater flash/urban flooding threat may evolve through the day due to greater storm coverage and multiple waves of activity moving across the Valley (storm training). A Message 2 (Flash Flood Watch) may need to be issued later today/early Monday morning if conditions/guidance warrant. Also to all local agencies, it’s never too early to be considering response and staffing needs for Monday and Tuesday. The next Outlook will be issued no later than Monday morning with additional details on storm evolution and updated forecast rain amounts.