Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 240448

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1048 PM MDT Sun Jul 23 2017

.SHORT TERM...(Tonight through Monday night)
Issued at 358 PM MDT Sun Jul 23 2017

Lowered heights in the northern and central Plains has suppressed
the subtropical circulation back to out West. This has also
allowed much drier air to filter into the northern 2/3 of the CWA.
PWAT on this mornings`s sounding was actually just below the
normal July 23rd reading near 2/3 of an inch while the ground
based instrument showed Durango hovering just under an inch. This
trend is apparent on this afternoon`s radar mosaic as well with
activity hugging the southern mountains while limited storms form
to the north. The forecast challenge this afternoon focuses on the
next push of monsoonal based moisture northward impacting our
thunderstorm and cloud cover which impacts temperatures. Basically
the ridge axis shifts back to our east by tomorrow morning
allowing southerly flow to increase and our PWATs push back up to
1.25-1.5 inches. Moisture and instability will be a given in this is just finding a focus to force more widespread and
possibly heavy precipitation outside of the normal orographics.
Water vapor imagery and model PVU suggests two easterly waves near
the Gulf of California and back over W.Texas. Both are forcing
decent convection today and will be entrained in the flow around
the Plains high and sent our way. Convection will dwindle after
sunset tonight as usual. However strong moisture advection
begins in the early morning hours over the 4 Corners with the GFS
specifically showing decent upglide into our SW CWA. Though this
model is likely overdone it is hinting that at least isolated
showers will continue to linger or form during the early morning
hours. An uptick in thunderstorm coverage into our Central and
higher plateaus are likely with lesser coverage farther north.
Early cloud cover and this increase in convection should begin a
cooler trend for Monday. The main push of moisture arrives
tomorrow night and this will keep the threat of
clouds...thunderstorms...and efficient rain producing showers
around through the southwest 1/2 of our CWA and PoPs remain quite
high into Tuesday morning.

.LONG TERM...(Tuesday through Sunday)
Issued at 358 PM MDT Sun Jul 23 2017

Tuesday looks to be a rather cool and wet day as moisture some 2
to 4 std dev above normal is pushed across the Utah and Colorado
border region. The focus will be the above mentioned waves moving
through the SW flow aloft. Expect plenty of cloud cover and
rainfall on the radar to start the day and will will likely be
increasing pops the next few shifts if confidence stays this high.
Deep warm cloud depths suggest efficient raindrop production and
even moderate showers could be putting down some decent rainfall
rates. The challenge will be if and where stronger convection may
form to help produce rates high enough for substantial runoff
problems. The models area suggesting a punch of drier air moving
in across SE Utah into NW Colorado in the afternoon which could be
the trigger for stronger storms. Wednesday the ridge begins to
shift back westward with drier air undercutting the monsoon
moisture. Definitely enough moisture to keep storms in the
forecast for Wednesday but we should see a downward trend in
coverage and a decreased runoff threat late in the week. By next
weekend we will have 598dam high back to our west so mainly hot
and dry returns.


.AVIATION...(For the 06Z TAFS through 06Z Monday night)
Issued at 1042 PM MDT Sun Jul 23 2017

Subtropical moisture will be moving back northward into the area
today under a light southerly flow aloft that will lead to
increasing mid and high level clouds. Then expect scattered
showers and thunderstorms to begin developing from the south after
18Z and spreading northward, a few with heavy rain obscuring
mountain tops mainly above 12K feet. Otherwise, VFR conditions
will prevail across eastern UT and western CO through Monday




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