textproduct: NWS Flagstaff

SYNOPSIS

Deep monsoonal moisture will remain over the area through at least mid week, with a slight decrease later in the week. With this moisture comes the daily threat of thunderstorms, along with the risk for locally heavy rainfall and flooding. Daytime temperatures will remain at or below normal much of the week, with hotter temperatures possible toward the weekend.

DISCUSSION

It has been a relatively quiet overnight period as of 2 AM with just a few isolated light showers and mostly clear skies for many areas. High pressure is centered over Colorado this morning and is forecast to start sliding southeast toward TX/OK by Tuesday and Wednesday. Much above normal precipitable water values will remain over our area over the next several days. A weak upper level disturbance near El Paso will move toward southeast AZ later today and then up into central/northern AZ Tuesday. This feature should enhance storm coverage, as well as introduce some higher wind shear values and increase the threat of hail with storms in addition to the continued flash flood risk. A few storms this afternoon into Tuesday may produce hail up to 1" diameter. As the disturbance moves into the area Tuesday, the flash flood threat may increase enough to warrant a Flash Flood Watch - we will continue to monitor. Active monsoon conditions look to continue Wednesday and Thursday, then much of the guidance moves the high pressure center westward toward Arizona and strengthens it. While this would not end storm chances, the warmer air aloft may reduce coverage of the activity and this is reflected in our latest forecasts. PoP values lower to 30-50% over the higher terrain and under 30% for lower elevations Friday through Sunday. With the ridge moving closer, daytime temperatures will slowly rise to above normal toward the end of the week/weekend.

AVIATION...Monday 20/12Z through Tuesday 21/12Z

Isolated SHRA/TSRA through 18Z. After 18Z, scattered to numerous SHRA/TSRA developing. Stronger storms will be capable of producing wind gusts 30-45 kts, hail, and brief MVFR and IFR conditions. Storms may continue well into the overnight period. Outside of storms, winds light and variable.

OUTLOOK...Tuesday 21/12Z through Thursday 23/12Z...Look for SHRA/TSRA activity through the period, most numerous during the afternoon/evening hours. Stronger storms will produce brief MVFR and IFR conditions and gusty winds to 30-40 kts. localized IFR conditions due to low clouds and fog possible during the overnight hours. Outside of storms, surface winds light and variable.

FIRE WEATHER...Today and Tuesday

A medium to high grade monsoon environment continues, with generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce flash flooding and hail.

Wednesday through Friday...Chances for showers and thunderstorms continue, though coverage is expected to decrease somewhat by Thursday and Friday. Generally light winds outside of outflow and thunderstorm activity. Most storms will produce wetting rain and any stronger storms may produce localized flash flooding.

FGZ WATCHES/WARNINGS/ADVISORIES

None.