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Area forecast discussion 
National Weather Service Grand Junction Colorado
240 PM MDT Sat Sep 20 2014

Short term...(tonight through Sunday night)
issued at 240 PM MDT Sat Sep 20 2014

With a ridge axis overhead an upper low along the Southern
California coast is progressing inland. The ridge axis shifts
onto the eastern plains this evening allowing the flow aloft to
shift to moist S-SW. Models are in good agreement that precipitation
water values climb to 1.1 inches through eastern Utah and far
western Colorado overnight. This moisture advection will keep
some storm activity through the night...mainly south of I-70.

Sunday the upper low lifts through Nevada with its associated jet
streak pushing towards NE Utah. Showers are expected to be
widespread but the strongest storms may occur in NE Utah late
Sunday with a combination of deep moisture and jet forcing over
surface convergence. Storm motion to the NE at 20-25 kts will
limit runoff problems except where multiple cells train over the
same location. A Special Weather Statement has been issued to
highlight this change to a much more moist pattern.

Long term...(monday through saturday)
issued at 240 PM MDT Sat Sep 20 2014

The upper low will lift northeast-Ward across Wyoming Monday-
Monday night...with the trough axis passing over our forecast
area during the day. This will keep showers and thunderstorms
ongoing into Monday evening...especially over the northern half.
However drier air will begin to move in from the southwest by
late morning...with a downturn in activity over southeast Utah and
the valleys of southwest Colorado early in the day. As the flow
becomes westerly through the afternoon and evening...drier
conditions will spread across the remainder of the area from the
west-southwest. By late Monday night any lingering showers will
be confined to northwest Colorado and the central Divide

Once the low moves into the plains on Tuesday...high pressure will
begin to build over the Desert Southwest. The high will
strengthen through midweek and shift east...spreading over our
forecast area as the next significant low pressure system
develops along the northwest coast. Models then develop a
longwave trough-ridge pattern from coast to coast by late in the
week. There are some differences however between the GFS and
European model (ecmwf). While both of these models indicate a splitting tendency
for the western trough...the GFS is more progressive and keeps
the southern low phased with the northern branch wave. It then
moves the low into the Great Basin on Sat. The European model (ecmwf) develops a
very large and blocking high pressure system across the central
Continental U.S. By midweek...with the low strengthening over the Pacific
northwest by week's end. In either looks like moisture
could move into the area by later in the week carried by a
south/southwest flow ahead of the western system. Temperature
will run above normal through this period.


Aviation...(for the 00z tafs through 00z Sunday afternoon)
issued at 240 PM MDT Sat Sep 20 2014

Isolated showers and thunderstorms will persist mainly over the
southern mountains this evening...with a slight chance of a
thunderstorm in the vicinity of ktex. After 03z...showers and
thunderstorms will increase over southwest Colorado and southeast Utah.
There is a 30 percent chance of MVFR visibilities in heavier showers at
kdro and ktex through 06z. Then scattered showers and storms will
become widespread by 18z Sunday with showers producing visible down
to 4sm and ceiling at or below 040. Mountain tops will be obscured at times.


Gjt watches/warnings/advisories...


Short term...Joe

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