Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Grand Junction Colorado
449 PM MDT Friday Jul 31 2015
Short term...(this evening through Saturday night)
issued at 354 PM MDT Friday Jul 31 2015
The Tongue of deep subtropical moisture will remain positioned
over Arizona/nm to the eastern side of the Colorado rockies. Some of
this deeper moisture will extend across our southern border and
across the San Juan and Abajo Mountains...and along our eastern
edge northward to around the central mountains. Much drier air
covers the northern portion of the forecast area with a strong
moisture gradient between the two. Therefore expect showers and
thunderstorms to continue to increase late this afternoon over the
wetter areas of the forecast area...roughly south of a line from
the Aspen/Vail Pass areas southwest to Page Arizona. Also an area of
thunderstorms over northwest nm looks like it will move into
southwest Colorado late this afternoon. Good convection will continue
into the early evening with coverage over some valleys increasing
for a spell. After sunset...most activity will diminish and will
become more showery (less thundery) by midnight. A few nocturnal
storms will be possible over this wetter portion of the area.
Nighttime temperatures will remain below normal in the drier air
over the north...and around normal under the more moist air mass
to the south.
Saturday and Saturday night...
not much different thinking from previous package...still
expecting slow northward movement of middle level moisture a little
further into central portion of the County Warning Area on Saturday. Then
embedded disturbance in southerly flow expected to begin moving
northward and helping to draw the moisture into the northern
portion of our County Warning Area Saturday night. So expect lingering showers and
isolated thunderstorms Saturday night mainly southern portion of
our County Warning Area. With increasing clouds Saturday night...min temperatures
should be significantly milder than tonight. Raised min
temperatures in most zones for Saturday night...and in some zones
they may need to raised even a little higher.
Long term...(sunday through friday)
issued at 354 PM MDT Friday Jul 31 2015
Sunday and Sunday night...
Sunday through Sunday evening should be a rather active time for
convective development across our County Warning Area...with combination of
daytime heating and dynamic lift...along with more low level
moisture. Precipitable water values rise significantly during this
time period...generally ranging from near 0.75 to 1.25 of an inch.
Storms will likely be moving relatively slowly...likely in the 10
to 15 knot range...and thus we will likely be dealing with
some flash flooding concerns.
Monday through Thursday night...
drier air moves into our County Warning Area by early Monday...in the wake of the
shortwave disturbance. Significant downturn in showers and
thunderstorms that should continue during this period to the north
of an east-west elongated upper high that will leave our County Warning Area under a
drier westerly flow aloft. Consequently...maximum temperatures will
rebound. Raised maximum temperatures about 5 degrees f from previous grids
on Monday for much of our County Warning Area. And maximum temperatures Tuesday may
yet be a tad too cool.
now looks like next surge of moisture from the south will wait
until Friday to begin spreading into our County Warning Area...as upper high
center shifts a little further east and the flow around the upper
high becomes more consolidated.
Aviation...(for the 00z tafs through 00z Saturday evening)
issued at 449 PM MDT Friday Jul 31 2015
Scattered rain showers/thunderstorms and rain will continue this evening for areas south of
a line from kcny to kase with best storms impacting the San Juans
and southern valleys with VFR conditions for most areas especially
north of this line. Ils breakpoints being reached and mountain
obscurations at times where storms occur. Brief heavy rain and
gusty winds to 30 kts are possible. Most activity will end by
midnight with some isolated -shra/-tsra lingering through Saturday
morning. Showers and thunderstorms will redevelop over higher
terrain and increase in coverage by 18z Saturday.