textproduct: NWS Flagstaff

SYNOPSIS

Deep monsoonal moisture will remain over the area through this weekend and well into next week. With this moisture comes the daily threat of thunderstorms, along with the risk for locally heavy rainfall and flooding. With the added moisture and cloud cover, daytime temperatures will remain below normal.

DISCUSSION

Another night of widespread nocturnal activity is slowly tapering off this morning, but not before large areas of moderate to heavy rain were recorded. The pattern of rain-cooled air, rain-cooled ground and extensive debris cloud cover will be an issue again today, with many areas staying suppressed into the afternoon.

Aside from that, we expect yet another day that features PW values and dew points about as high as the Monsoon Season can furnish. It will rain, just a question of when and where. Our current steering flow (this governs where storms go after they form) remains easterly or northeasterly for the next several days. This steering flow may transition to more of a southeasterly direction later next week, but that remains to be seen.

The current steering flow heavily favors locations just to the southwest, south and west of the central Mogollon Rim. A secondary area usually forms later each day across Apache and Navajo counties or over western New Mexico. These secondary areas are what supports nocturnal convection, which is expected at least for the next few nights. The nocturnal signal is fairly strong, largely due to the delayed convective development each day.

Compounding the issue is the arrival of an easterly wave, likely arriving Monday and Tuesday, possibly residing over central Arizona even into Wednesday. This easterly wave will increase storm motion and shear, which could strengthen storms and lead to a hail threat. While increased storm motion may lessen the flooding threat, it also leads to the possibility of training storms (additional thunderstorms forming over the same location). The bottom line, a very active and possibly historically wet period will continue until further notice.

Pertaining to the daily possibility of a Flash Flood Watch, we will again hold off, due the the complications of convective development that were outlined above.

AVIATION...Sunday 19/00Z through Monday 20/00Z

Rounds of SHRA/TSRA will continue through the evening hours becoming isolated after 06Z. Stronger storm cells will produce brief MVFR and IFR conditions. Outside of thunderstorms, expect light winds 5-10 kts. Another active day of monsoon storms is in store on Sunday. Expect scattered to numerous SHRA/TSRA with isolated +TSRA from late Sunday morning through the afternoon. The primary threat will be MVFR to IFR conditions in heavy rain. Gusty outflow winds up to 40 kts and hail are also possibilities.

OUTLOOK...Monday 20/00Z through Wednesday 22/00Z...Expect scattered to numerous SHRA/TSRA and isolated +TSRA each day, storms most numerous in the afternoon hours. Any stronger storms will produce brief MVFR to IFR conditions. Some IFR low clouds and fog possible, mainly for overnight hours. Outside of storms, expect light winds around 5-10 kts.

FIRE WEATHER...Sunday and Monday

Expect a medium to high grade monsoon environment, with generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce Flash Flooding. The presence of a weak low pressure system, moving from east to west, may introduce an enhanced hail threat for Monday.

Tuesday through Thursday...Chances for showers and thunderstorms continue, generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce localized Flash Flooding. The continued presence of a weak low pressure system will prolong the potential for an enhanced hail threat through Wednesday.

FGZ WATCHES/WARNINGS/ADVISORIES

None.