Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 131443 CCA
AFDGJT

Area Forecast Discussion...CORRECTED
National Weather Service GRAND JUNCTION CO
843 AM MDT Sun Aug 13 2017

Added another line to the update section

.UPDATE...
Issued at 842 AM MDT Sun Aug 13 2017

Updated PoPs this morning to include mention across northeast Utah
and southwest Colorado where some isolated to scattered showers
with a few lightning strikes were approaching from the west. The
activity over Utah seemed to be associated with some form of
embedded shortwave in the flow and was being picked up fairly well
in the latest HRRR model run. Expect this activity to enter our
CWA within the next couple hours and progress eastward, weakening
as it does. Also, thinking the models are underplaying the
coverage of storms today with similar conditions to yesterday, in
which the models were underdone. Given the forcing, instability
and remnant moisture in place, thinking there will be more
coverage of storms this afternoon and evening. Therefore, also
increased storm chances and coverage this afternoon into early
evening hours. Will be something to watch.

&&

.SHORT TERM...(Today through Monday)
Issued at 310 AM MDT Sun Aug 13 2017

Model output for this morning was way overdone as both the NAM and
GFS show widespread precipitation for our CWA while current radar
shows a few showers. Upstream, things are a bit more interesting
in Salt Lake`s CWA as a few more storms and showers continue.
This convection will continue move eastward and if it stays
together, may bring some precip to our neck of the woods after
sunrise.

As far as the rest of the day is concerned, models are
really downplaying convection this afternoon and evening. There
will be some but coverage and intensity looks to be less than seen
lately. Forecast Skew-Ts continue to show instability across the
CWA and with no real cap in place to hinder development. PWATs
remain in the .75 to 1 inch range as we`ve seen over the last few
days while a weak wave is progged to move overhead this afternoon.
The only difference is the upper level jet, that`s been overhead
for the last several days, will shift southward and be over the
southern half of Utah and Colorado. Even with all of the above,
every model, including the NAMNEST, HRRR, RAP13, NAM, EC, and GFS,
all show a downturn in activity so with such a consensus in
place, dropped PoPs some for this afternoon and evening. As usual,
storms and showers will fire over higher terrain first before a
few drift into valleys. As has been the case lately, gusty winds
up to 40 mph, small hail, and occasional heavy rain can be
expected. A few showers will persist overnight but coverage will
be minimal at best.

Monday, moisture remains in place but just to our west PWATs will
start to drop and reach .5 inches or so. Also, an approaching
trough will start digging into northern Nevada and Utah keeping
most precipitation to our west. A few showers and storms are
possible, especially over the eastern Uintahs and northern half of
our CWA, but the widespread convection we`ve been seeing lately
looks to be slowly ending. Temperatures remain fairly steady and
remain near normal.

.LONG TERM...(Monday night through Saturday)
Issued at 334 PM MDT Sat Aug 12 2017

The broad upper level trough will continue to dig into the western
CONUS late Monday and into Tuesday. As a result, southwesterly flow
aloft will persist with precipitable water values remaining above an
inch across much of the region. A jetstreak at the 250mb level will
be overhead through early Tuesday morning which, when paired with
the passage of a leading shortwave, will support the presence of a
few nocturnal showers and storms Monday night. The arrival of the
upper level trough and associated cold front on Tuesday will
result in another day with some showers and thunderstorms across
the region. However, the front will be slow to progress out of our
forecast area, not exiting until early Wednesday, so another
round of late evening convection is possible for Tuesday night.
Temperatures on both Tuesday and Tuesday night will be several
degrees cooler than previous days in response to the slightly
cooler airmass.

Upper level winds finally begin to shift to the northwest on
Wednesday behind the passage of the trough. This will initiate a
drying trend from midweek onwards with a noticeable downturn in
storm activity. Even so, it is still the summer season so the
presence of any residual moisture over the higher terrain will keep
the threat for at least isolated showers and thunderstorms each
afternoon through the weekend.&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 310 AM MDT Sun Aug 13 2017

A few early morning showers persist this morning and will likely
continue through daybreak but should not pose any threats to TAF
sites. Convection will start firing between 16 and 17Z and
continue through the day. Coverage should be a bit less than seen
over the last few days but even so, chances certainly remain for a
few TAF sites to see VCTS or VCSH. Gusty winds, small hail, and
heavy rain briefly dropping vis and cigs are possible this aftn.
Any sites that drop below ILS should rebound quickly.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 310 AM MDT Sun Aug 13 2017

A few early morning showers persist this morning and will likely
continue through daybreak but should not pose any threats to TAF
sites. Convection will start firing between 16 and 17Z and
continue through the day. Coverage should be a bit less than seen
over the last few days but even so, chances certainly remain for a
few TAF sites to see VCTS or VCSH. Gusty winds, small hail, and
heavy rain briefly dropping vis and cigs are possible this aftn.
Any sites that drop below ILS should rebound quickly.


&&

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

$$

UPDATE...MDA
SHORT TERM...TGR
LONG TERM...MMS
AVIATION...TGR


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