Monsoon moisture moving into the San Juans today….

National Weather Service ~ Grand Junction, Colo.

Deep monsoon moisture poised to the south over Arizona and New
Mexico is shown to creep northward beneath the ridge and over the
Four Corners region beginning today. Precipitable water values
will approach the 1 inch mark along the border of southeast Utah
and southwest Colorado late this afternoon. Elevated moisture will
feed increased shower and thunderstorm activity over the San Juan
La Sal, and Abajo mountains with more isolated activity over the
central and northern mountains. Initial storms will be high based
as the sub-cloud layer will be dry at the outset producing outflow
wind gusts to 35 to 40 MPH. However, storm characteristics will
change later in the day and into the evening as moisture works
downward causing some storms to generate localized heavy rain.
Though higher terrain will be favored, some storms will drift over
adjacent valleys from late afternoon into the evening.

Diurnal cooling will cause moist convection to decrease late in
the evening with just a few showers lingering later in the night.
However, it appears the forecast area will see a sharp uptick in
thunderstorm activity Wednesday as an inverted trough now over the
Las Vegas area swings north, then eastward around the periphery
of the high pressure center. Models indicated this sheared
disturbance will arrive over the area around peak heating which,
when combined with deepening moisture, should bring scattered to
numerous showers and thunderstorms to much of the area.

LONG TERM…(Wednesday night through Monday)

Wednesday night storm and shower coverage will remain high

as sheared dynamics has increased moisture to work with. In fact,
this may be the most active period with precip water values
approaching 1.25 inches in east-central Utah along with dynamical
support. Gusty storm-produced winds may become widespread over the
southern and central zones. Boundary interaction should keep
storms going into and through Thursday.

Friday, deep moisture remains in place but upper-level forcing is
lacking so scattered storms and showers will form mainly with and
beyond afternoon heating.

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