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Area forecast discussion 
National Weather Service Grand Junction Colorado
1144 am MDT Friday Jul 3 2015

issued at 927 am MDT Friday Jul 3 2015

Forecast today generally on track. Made a morning update to
reflect current trends of showers and thunderstorms moving slowly
south over the San Juan Mountains...associated with weak shortwave
and narrow band of 700-500 mb Theta-E advection in the northwest
flow aloft. Elsewhere...plenty of sunshine will get surface
heating and attendant instability going...leading to isolated to
scattered showers/storms. Coverage expected to be better over the
San Juan mountain areas and adjacent areas to the south.


Short term...(today through saturday)
issued at 308 am MDT Friday Jul 3 2015

High pressure centered over southern Utah will keep eastern Utah
and western Colorado under west northwest flow. Moisture pooled
underneath the ridge combined with hot daytime temperatures will
result in a continuation of daily convection...focused over the
higher elevations in the afternoon...with storms then drifting
over the valleys by early evening. Best and deepest moisture will
remain over The Four Corners and across the southwest San
Juans...with precipitable water values are holding around 1.2
inches per model soundings. Would expect heavy rainfall...hail and
gusty winds to near 40 miles per hour with this activity this afternoon and
evening and again on Saturday. Across the north...storms will be
more isolated in coverage...but still capable of producing locally
heavy rain. MOS temperatures look good and no reason to stray far.

Long term...(saturday night through thursday)
issued at 308 am MDT Friday Jul 3 2015

Convection will continue Saturday evening with some showers and a
few isolated storms persisting after midnight. As this
occurs...moisture will keep streaming up from the south causing a
significant increase in available moisture. Forecast precipitable water values
vary from 1 inch to 1.3 inches for much of the area by Sunday
morning. This is about 200% of normal for this time of year. Add
this moisture to the trailing edge of an upper level trough and
you have ingredients in place for some decent convection. With
this much moisture...the biggest concern becomes storms producing
heavy rains and possible flash flooding beneath them. Available
moisture drops to about an inch by Monday though this might be a
bit too quick. Even so...still a lot of moisture available for
storms that form.

A low will approach the California coast Tuesday while the ridge
of high pressure remains over our area. While this is not a
classic monsoon per southeast...the stream of moisture from the
subtropics and location of this plume certainly looks monsoon-
like. Regardless...afternoon and evening showers and storms will be
the rule Tuesday through Thursday.

Plenty of clouds across the region will bring temperatures to more normal
values Sunday and beyond.


Aviation...(for the 18z tafs through 18z Saturday afternoon)
issued at 1144 am MDT Friday Jul 3 2015

SW Colorado...scattered -shra/-tsra is expected with isolated
+shra/+tsra ceilings below ils breakpoints for ktex and kdro.
Thunderstorms across this area will be slow to dissipate after
sunset with isolated -tsra/-shra persisting through 12z Saturday

Northwest Colorado and eastern Utah...mostly dry but isolated -tsra/-shra
will occur along the higher terrain. The chance that any of these
storms move over a taf site (such as kvel and kcny) is low.
Any thunderstorms across this region should end between 03z-06z this


Gjt watches/warnings/advisories...


short term...jdc
long term...tgr

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