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Area forecast discussion...updated 
National Weather Service Grand Junction Colorado
807 am MDT Thursday Jul 24 2014

issued at 753 am MDT Thursday Jul 24 2014

Made a quick update to increase coverage of precipitation this
morning over eastern Utah. A disturbance at 500mb is moving to the
northeast over northeast Utah and northwest Colorado this
morning. Infrared satellite indicates a wide swath of cloud cover over
the region with radar returns maintaining as they drift to the
east northeast.


Short term...(today through friday)
issued at 422 am MDT Thursday Jul 24 2014

Monsoonal moisture stream has spread from the southwest to
northeast and covers the forecast area today. Precipitable water
easily exceed an inch /Max values around 1.40 inches/ for the
desert values...although they do trend downward this afternoon but
manage to stay well above the seasonal average. High pressure will
be supressed today as strong Pacific northwest wave moves east
across the Canadian/northern rockies. Steering winds become westerly
late in the day...which accounts for some drier air beginning to
seep into the region from the west.

This influx of moisture will boost cape values that exceed 1000+
j/kg by late morning across parts of eastern Utah. High resolution
models show highest quantitative precipitation forecast values anchored to the mountains with
much lower values in the surrounding valleys. While precipitable waters and 700
mb specific humidities support heavy rainers...surface dew points
range from the middle 40s to lower 50s. Would prefer to see higher
dew point values to get the soaking rains. Other factors that
limit quantitative precipitation forecast include a veering winds with time (training cells may
be limited in this environment) and that storms will not be slow
movers. Isolated heavy rains (mostly brief as cells quickly move
downwind) will occur with good portion of the forecast area
expected to observe some rainfall.

A Canadian low pressure system moving across Alberta and
Saskatchewan this evening will drag a shortwave through the high
pressure ridge centered over the Texas Panhandle. This will act on
the prevalent moisture in place and lead to an increase in storm
activity through the evening hours. Some storms may last into the
overnight as this wave...which is evident based on frontogenesis
fields and upper level divergence...moves through. This low will
also act to flatten the ridge of high pressure on Friday...allowing
moisture to lay over Colorado and southeast Utah. Precipitable water
values are still around an inch for areas south of I-70 where the
better storms are expected. Expect another round of convection
firing over the higher terrain in the afternoon with outflow
boundary interactions allowing storms to drift over or form over
valleys later in the day.

Long term...(friday night through wednesday)
issued at 422 am MDT Thursday Jul 24 2014

Expect most convection to die down by midnight Friday night with
a few lingering into the overnight as moisture remains with precipitable water
values in the 0.75 to 1.0 inch range through early Saturday
morning. The Canadian low dives southeast through the Great Lakes
region and gets absorbed by a large area of low pressure over the
eastern U.S. This low pressure trough deepens over the east which
causes the high pressure ridge over the Texas Panhandle to
negatively tilt and push westward towards The Four Corners region.
This also pushes the best moisture westward and allows drier air
to infiltrate from the north on Saturday. Precipitable water values of 0.5 to 0.6
inches show up north of I-70 with 0.75 inches south of I-70 and
slightly higher values near The Four Corners. The drier air on
Saturday combined with no distinct disturbances moving through
will result in a downturn in storm activity. Enough moisture will
be around for storms to form over the higher terrain in the
afternoon but will most likely remain anchored here as steering
flow remains fairly light.

Sunday through Wednesday...strong Four Corners ridge will amplify
over the western Continental U.S. Through this time period. Monsoonal moisture
takes a roundabout way to get into Utah and western Colorado rather
than a moisture plume from old Mexico. Diurnally driven storms
will occur each day with some storms linger through nighttime. But
difficult to say at this time if any day will be wetter than
another day. Forecast is fairly broadbrush with the highest pop
values over southwest Colorado.


Aviation...(for the 12z tafs through 12z Friday morning)
issued at 555 am MDT Thursday Jul 24 2014

All taf sites can expect showers and/or thunderstorms in the
vicinity through 04z tonight. Brief +tsra with wind g30kts may
accompany the strongest storms. MVFR ceilings and mountain
obscurations from passing +shra/+tsra. Decreasing -shra/-tsra is
expected after 04z tonight.


Gjt watches/warnings/advisories...


long term...mda/pf

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