Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 110344
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
944 PM MDT Thu Aug 10 2017

.UPDATE...
Issued at 704 PM MDT Thu Aug 10 2017

Quick update to the grids to drive pops up a bit through this
evening as convection continues to expand in coverage across east-
central and northeast Utah. Additional showers driving east near
the I-70 corridor in western Colorado. HiRes models keep showers
going into the late-night hours, likely ending between 2 and 4 am
tonight.

&&

.SHORT TERM...(Tonight through Friday night)
Issued at 314 PM MDT Thu Aug 10 2017

Storms have fired this afternoon over the higher terrain, with the
northern and central areas seeing the best coverage. This is due
to a weak disturbance moving through the westerly flow on the
northern periphery of an area of high pressure sitting well to our
south. A weak 60-70 kt upper level jet is laid across the central
CWA from west to east, providing some upper level support for
storm development in the left exit region where the northern half
of the CWA is located. Storms are moving along at a pretty good
clip thanks to this upper level support, with some locally heavy
rain and small hail reported with the stronger cells. Expect most
activity to wind down this evening with some lingering showers
overnight.

This area of high pressure is expected to slide eastward over
Texas on Friday, thanks to an upper level trough moving inland
along the Pacific Northwest coast. This will help turn the flow
ever so slightly to southwesterly, allowing a bit better moisture
into the region with precipitable water (PW) values in the 0.75
to 1.0 inch plus range across much of the area. A weak shortwave
will also move into the Four Corners region Friday morning and
progress through the area Friday afternoon and evening, leading to
an increase in storm activity and coverage. Increased PoPs as a
result. Temperatures should still be near to slightly above
normal during the daytime through Friday as this better moisture
begins to infiltrate the atmosphere.

.LONG TERM...(Saturday through Thursday)
Issued at 314 PM MDT Thu Aug 10 2017

Saturday through Monday are looking to be more active days as
deeper moisture works across the region in southwesterly flow
with several embedded shortwave disturbances moving through the
flow. These shortwaves will come from two low pressure systems,
one over the Pacific Northwest and another over the northern Great
Lakes and eastern Canadian Prairies. The Pacific low will be the
primary driver for our sensible weather, while the eastern low
will mainly impact the Front Range, with some boundaries trailing
back into our area. Bottom line is that the weekend into early
next week looks more active with widespread coverage of showers
and thunderstorms each afternoon and evening. Due to the embedded
shortwaves and deeper moisture in place, storms have good
potential to continue through the overnight hours. PW values will
be approaching 1.25 inches in some areas during this period.
Therefore, increased PoPs enough for all areas to see some
coverage of storms Saturday through Monday evening/Tuesday
morning. The most active of these periods looks to be Monday
through Tuesday morning as a stronger shortwave moves through.

Drier air will slowly begin to infiltrate into the area from the
southwest beginning Tuesday, as this upper Pacific Northwest low
carves out a trough that will dive into the Desert Southwest.
Enough moisture will remain on Tuesday with PW values of 0.75 and
above, which is sufficient for decent storm coverage given more
surface heating taking place. Wednesday and beyond appears to be
the days where this drying will be most noticeable. Confidence on
this drying trend remains low, however, as models want to dry
things out too quick after each monsoonal moisture surge. Still
kept afternoon showers and storms favoring higher terrain in the
forecast for Wednesday and beyond.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 940 PM MDT Thu Aug 10 2017

Nocturnal convection will linger over the region through 09Z
before ending with dry conditions expected through midday. The
next round of storms will develop after 15Z with showers and
thunderstorms persisting through the evening hours. Strong
outflow winds and brief heavy rainfall will occur with any storms
passing through with gust potential to near 50 kts. Small hail
will also be possible. Most sites will see VFR conditions persist,
although brief ILS CIGS should be expected in the vicinity of
storms.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

UPDATE...JDC
SHORT TERM...MDA
LONG TERM...MDA
AVIATION...JDC



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