Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 131715

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1115 AM MDT Thu Jul 13 2017

.SHORT TERM...(Today through Friday)
Issued at 415 AM MDT Thu Jul 13 2017

Models are indicating a return the pattern we experienced last
week with a carving trough over the Great Lakes and deeper
troughing off the Left Coast. This allows the ridge to build over
the Inter-Mountain West with the axis running across our CWA. The
caveat this round however is a subtle area of low pressure under
cutting the northern portion of the ridge to create a weak rex
block the next 48 hours or so. This area of lower heights is
showing up in the H500 RAOBs this morning and is very subtle in
the water vapor imagery. PWAT at 00Z, as mentioned in the previous
discussion, was running wetter than at least 90% of the soundings
for mid July. Though models suggest a slow decline in PWAT the
next few days we will have plenty around for afternoon
thunderstorm initiation. Just where storms fire and concentrate is
always problematic but with the current pattern in place the
better coverage will be in the south near the low pressure
circulation while storms will be more focused on the terrain in
the northern half. Soundings still suggest slow moving and back
building storms will be possible. Warm cloud depths of 2.5-3km
also favor storms with heavy rainfall rates as warm rain processes
kick in this afternoon and evening. Temperatures a bit
problematic with clouds and moisture in place. Basically lowered
temperatures from going forecast across the south from the above
mentioned precipitation factors and kept trend in place across the
north. Temperatures again may depend on left over convective
debris on Friday but for now have a warming trend across the
desert valleys.

.LONG TERM...(Friday night through Wednesday)
Issued at 415 AM MDT Thu Jul 13 2017

The high will continue to strengthen into the weekend with another
cell rotating into Great Basin and creating a 596 high off to our
west. Heights expand far enough east to push the weak low
pressure system off to the Plains with QG progs showing mainly
weak subsidence over our CWA. Expect storms to initiate and stay
mainly over the terrain until enough storm cycles push isolated
storms into the valleys. Temperatures continue to slowly warm
into Sunday with triple digits showing up a bit more in the lower
desert valleys. A shift in the high latitude energy during the
early week period will shift the subtropical high axis to our
east by Tuesday. This shift forces a better feed of moisture
across the 4 Corners and an uptick in convection should occur with
the valleys seeing better rain chances into the mid week period.
The stronger westerlies look to dip into our northern border
counties and this will suppress the moisture to the southern
border and bring a drying trend to many areas but especially the
northwest CWA going into the late week period.


.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1100 AM MDT Thu Jul 13 2017

VFR conditions will prevail early this afternoon. Convection will
fire first in the higher terrain with some showers and
thunderstorms affecting higher terminals such as TEX ASE and EGE.
VFR CIG heights may briefly drop to MVFR levels in any stronger
cells. Winds could gust as high as 30 mph in any cell. Convection
will diminish after sunset.




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