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Area forecast discussion 
National Weather Service Grand Junction Colorado
1105 am MDT Sat Jul 4 2015

Short term...(today through sunday)
issued at 314 am MDT Sat Jul 4 2015

Another day of pop and drop type storms expected today and this
evening under the influence of light west-northwest flow aloft. Expect the
most active region to remain over the San Juans and adjacent
southern valleys today...although some increase in storms expected
for the northern mountains as moisture profiles improve a bit in
this area. Locally heavy rain expected from the stronger cells
with small hail possible.

Moisture ramps up overnight and early Sunday morning as the broad
northwest flow transitions to a more southerly component as the
persistent ridge to our west heads East. Ridge axis will be east
of our forecast area around midnight...with deeper moisture over
Arizona lifting northeast. This will drive available moisture
up...with precipitable water values approaching near record
levels once again for this time of year...or around 1.2 to 1.3
inches. Models look to be a tad aggressive based on soundings
last night across the levels should still be in excess
of an inch by Sunday morning. In addition...shortwave energy
rotating around the back side of the ridge will be arriving Sunday
morning. Steepening lapse rates...abundant moisture and lift
associated with this wave and our complex terrain will lead to
widespread showers and thunderstorms. Expect heavy rain to be the
primary concern early on. Shear profile improves during the
afternoon... so some decent storm structure expected...and with
cooling aloft and lowering wet bulb zero heights...should see some
hail potential develop. Biggest concern will be debris clouds and
lack of strong surface heating if heavier rain occurs early in the
event. Plan for now is to increase probability of precipitation even higher...especially
during the morning hours on Sunday...with activity becoming more
scattered and stronger as the day wears on.

Another hot day expected today...with readings dropping down below
seasonal norms on Sunday. Cooling advertised in the latest met
guidance actually appears reasonable with expected cloud cover and
deeper surface will be knocking temperatures back about 4 to 8
degrees for Sunday afternoon.

Long term...(sunday night through friday)
issued at 314 am MDT Sat Jul 4 2015

Forecast precipitable waters remain high at the start of the long term period with
the nam12 showing over an inch for almost the entire County Warning Area though
values will drop in the wake of the wave that passed earlier in
the day. NAM really drops precipitation off after sunset while...of
course...the GFS keeps precipitation going. Anticipate what will happen
will fall between these two solutions. Enough moisture will
remain in the atmosphere for Monday to make another wet day
though models have consistently shown the Front Range getting the
brunt of heavier precipitation.

Starting Tuesday...the stream of moisture from the south starts to
look much more monsoon-like as cyclonic flow around an area of
low pressure off the California coast brings southwesterly flow to the
desert SW advecting in subtropical moisture. This moisture will
continue to allow afternoon/evening convection to fire through the
remainder of the long-term period and with moisture content still
relatively high...heavy rainers will continue to be the concern.
Models have remained fairly consistent with this moisture plume so
confidence is increasing for this wet event. Flash flooding
certainly in the realm of possibility and will need to be watched
as we get closer to Sunday and beyond.


Aviation...(for the 18z tafs through 18z Sunday afternoon)
issued at 1105 am MDT Sat Jul 4 2015

After a downturn in convection this morning...the trend has begun
to reverse at 17z. Expect that the chance for showers and
thunderstorms will increase through the afternoon...then continue
during the evening. Flight conditions today will generally be
similar to friday's with vcsh and thunderstorms in the vicinity being common for taf
sites. The best chance for convection remains over the southern
mountains and adjacent valleys. However isolated valley storms and
scattered mountain storms will be possible for the remainder of
the forecast area. Ils breakpoints may be reached briefly for ktex
and kdro under the stronger cells and showers. While the strongest
convection dies after 03z...showers and thunderstorms will remain
possible overnight and through Sunday morning.


Gjt watches/warnings/advisories...


Short term...jdc
long term...tgr

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