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Area forecast discussion 
National Weather Service Grand Junction Colorado
356 PM MDT Wednesday Jul 29 2015

Short term...(this evening through Thursday night)
issued at 238 PM MDT Wednesday Jul 29 2015

High pressure will continue to build and will shift westward...
with strong ridging from nm to the Pacific northwest by Thursday
night. As the ridge builds...subtropical moisture will increase
over AZ/nm...and will flow over our southern border during the
next 24 to 48 hours. The 12z models are much wetter than previous
runs...but still show a sharp gradient from south to north. By
late Thursday night the 12z NAM showed precipitable water at 1.5 inches
over The Four Corners...with some moisture extending as far north
as the I-70 corridor. It appears that a west-east deformation
zone sets up across northern nm/Arizona and north to around the
Abajo/San Juan Mountains with the best moisture concentrating
along and just south of the County Warning Area border.

For the details: for this evening expect isolated-scattered
showers and thunderstorms to continue from around Durango to
Silverton eastward. Storms will diminish overnight. However a few
nocturnal showers will be possible mainly over the southern slopes
of the San Juans as moisture streams across the border.

Look for an uptick in showers and thunderstorms on Thursday...with most
activity over the southern mountains and southward. I do expect
the active area will expand both west- and northward as compared
to this afternoon as the better moisture spreads. Nocturnal
activity is expected to continue Thursday night in this juicy
environment. The far north will remain dry.

Long term...(friday through wednesday)
issued at 238 PM MDT Wednesday Jul 29 2015

High pressure continues to rule through the end of the period. The
latest model runs do not allow the high pressure center to shift
as far west as previous runs as a Pacific trough blocks it from
the west. As a result the high center stays over the
central/southern rockies which is a more favorable placement for
the subtropical moisture plume to stream into our forecast area.
However subtle differences in the flow...and in available
moisture can make a big difference in the sensible
weather. Therefore forecast confidence is not high concerning
timing and day-to-day variations in thunderstorm coverage. It does
appear that there will be a good chance of showers and
thunderstorms over the southern half into the weekend as deep
moisture stays in place. Then drier conditions temporarily spread
from the north early next week. Moisture increases again from the
south by midweek.

&&

Aviation...(for the 00z tafs through 00z Friday evening)
issued at 1147 am MDT Wednesday Jul 29 2015

Moisture streaming across the Colorado/nm border will produce some
showers and thunderstorms this evening over the San Juan Mountains
and south...with an isolated storm possible overnight. Isolated-
scattered showers and thunderstorms will develop over the southern
half of the area by midday...with numerous storms over the San
Juan southward by late afternoon. These storms may impact ceilings and
visible at ktex and kdro taf sites at times in showers and low clouds
after 21z Thursday. Middle to high level clouds will increase from over
southwestern Colorado. Otherwise VFR will prevail...with the
northern half of the area remaining dry.

&&

Gjt watches/warnings/advisories...
Colorado...none.
Utah...none.
&&

$$

Short term...eh
long term...eh
aviation...as

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