Area Forecast Discussion
Issued by NWS Grand Junction, CO

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999
FXUS65 KGJT 182345
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
545 PM MDT MON JUL 18 2016

.SHORT TERM...(This evening through Tuesday night)
Issued at 245 PM MDT Mon Jul 18 2016

Showers and extensive cloud cover were seen across the north this
morning as the leading shortwave moved through from south to
north overnight. The 12Z GJT sounding showed 0.93 inches of
precipitable water (PW). The sub-cloud layer was still fairly dry
with very light rain and virga mainly observed with some breezy
conditions under showers. No lightning associated with the
activity across the north with breaks in the cloud cover and more
sun being seen on satellite across southeast Utah and southwest
Colorado. This has resulted in the development of thunderstorms
with frequent lightning strikes across areas of SE Utah and SW
Colorado with this activity and the clearing working its way
northward this afternoon. Expect thunderstorm activity to pick up
across the north as well later today. The latest HRRR model run
indicates storm activity picking up this evening and continuing
through the overnight from south to north, as another shortwave
disturbance moves through the region from Arizona.

Although moisture is increasing today, the low levels still
remain dry with fire weather concerns as lightning and gusty
outflow winds can lead to new fire starts or exacerbate already
present conditions. So the Red Flag Warning for today continues
until 10 pm MDT this evening. The chance of wetting rain will
increase tonight into Tuesday. PW values will increase to an inch
or greater in most areas by Tuesday with another round of showers
and thunderstorms as this monsoonal moisture continues to increase
from the south. High pressure will remain over the central Plains
with a low pressure trough positioned over the Pacific Northwest,
allowing sub-tropical moisture to be drawn into the Four Corners
region through much of the week.

.LONG TERM...(Wednesday through Monday)
Issued at 245 PM MDT Mon Jul 18 2016

Wednesday through Thursday: Elevated PW values of an inch or
greater with the NAM indicating up to 1.3 inches over some areas
will remain in place through Thursday. Embedded shortwaves and
perturbations in the flow will continue to move through the
region from time to time and are hard to time at this point.
Regardless, this will allow for widespread to numerous showers and
thunderstorms with some activity continuing through the overnight
hours as outflow boundaries and disturbances interact to provide
added lift with moisture and instability already in place.

Friday through Monday: By Friday, the low over the Pacific
Northwest will eject a stronger disturbance across the northern
Rockies, which turns the flow from southwest to westerly and
breaks down the ridge of high pressure over the Plains that is
allowing deeper moisture to be drawn up into the region. PW values
decrease to 0.5 inches across portions of NE Utah and NW Colorado.
The high center will reposition itself westward with drier air
moving into the Great Basin. This all leads to a downturn in storm
activity towards the coming weekend into next week. Enough
moisture will still linger south of I-70 and along the divide with
PW values of 0.75 inches or better for afternoon convection mainly
over higher terrain, although some storms could drift or form over
valleys late in the day.

Max temperatures will be cooler more towards normal values with
increased clouds and showers/storms and higher relative
humidities this week. A warmup towards above normal is expected by
the weekend into next week as a result of the drier airmass.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 545 PM MDT Mon Jul 18 2016

Thunderstorms have finally started to pick up in coverage south of
I-70. Ceilings will lower with thunderstorms as they pass and some
areas will see lowered cigs through the overnight hours due to low
level moisture post-rains. Gusty outflow winds are expected near
storms through about 04Z with moderate to heavy rainfall
developing as the evening progresses. This may bring temporary
MVFR conditions in rainfall to some forecast terminal sites. KASE
and KTEX should have the highest probability of this occurring but
all sites can not be ruled out. The period of highest confidence
in storm development will be through 19/03Z. Nocturnal showers and
storms are likely to continue.

&&

.GJT Watches/Warnings/Advisories...
CO...Red Flag Warning until 10 PM MDT this evening for COZ200>203-205-
     207-290>295.

UT...Red Flag Warning until 10 PM MDT this evening for UTZ486-487-490-
     491.

&&

$$

SHORT TERM...MDA
LONG TERM...MDA
AVIATION...TGJT



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