Area Forecast Discussion
Issued by NWS Grand Junction, CO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
FXUS65 KGJT 251701

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1101 AM MDT Tue Jul 25 2017

.SHORT TERM...(Today through Wednesday)
Issued at 429 AM MDT Tue Jul 25 2017

A shortwave trough evident in 500 mb flow continues to track
northeastward through eastern Utah and western Colorado this
morning. While more intense rainfall rates have subsided
overnight, light to moderate stratiform rainfall will likely
continue for at least a few more hours over central and northern
zones before dynamic support finally exits to the north later this

The forecast for this afternoon remains active as a subtle maximum
in southwesterly 500 mb flow passes over the western slope. This
uptick in flow may aid in organizing afternoon thunderstorms to
some extent. Additionally, near-surface moisture content is notably
high after overnight rainfall. 30 kts of 0-6km Shear and ML CAPE
values peaking around 1500-1900 J/Kg, along with straight
hodographs apparent in NAM/NAMNest forecast soundings...may allow
for a few stronger single- cellular/splitting cellular convective
modes. PWAT values averaging in the 1.1-1.2 range area- wide will
certainly result in heavy rain being the primary threat from
today`s convection. However, a few isolated reports of hail and
stronger wind gusts may be possible in any longer-lived discrete
or clustered/bowing storm organization. The Flash Flood Watch
remains in effect for the entire CWA until midnight Wednesday
morning. For more details on the flooding threat, see FFAGJT.

Overnight, precipitation will diminish as instability wanes.
The plume of monsoonal moisture will shift slightly eastward, but
not far enough to significantly reduce the afternoon thunderstorm
threat over the western slope on Wednesday. Afternoon showers and
thunderstorms will once again affect much of the higher terrain
as southwesterly flow continues.

.LONG TERM...(Wednesday night through Monday)
Issued at 429 AM MDT Tue Jul 25 2017

The pattern begins to shift by midweek, but not soon enough to
erase the threat of heavy rain and thunderstorms early Wednesday
night and on Thursday. PWATS still near or in excess of one inch
Wednesday/Thursday but no major forcing mechanism passing through.
That being said, forecast CAPE looks sufficient in this time
period with bulk shear marginal for well organized storms in the
intermountain west. 500 mb pattern bringing high pressure back
westward over the Four Corners, but forecast models still keeping
PWATS near an inch through Friday across much of eastern UT and
western CO. The first good signal of potential drying looks to be
Friday evening across NE Utah and NW Colorado while the Four
Corners remains primed for monsoonal-like storms. This slight
drying Friday evening is correlated with the center of high
pressure shifting west to the southern NV region. Forecast
confidence is moderate with this pattern shift.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1101 AM MDT Tue Jul 25 2017

A pair of disturbances continued to generate showers and just a
few embedded thunderstorms in a broad swath stretching from Lake
Powell north-northeastward across east-central Utah and northwest
Colorado. As temperatures rise expect shower/thunderstorm activity
will spread across the remainder of eastern Utah and western
Colorado, initiating first over the higher terrain. The atmosphere
is just soupy with moisture according to morning sounding data so
chances are high that all TAF sites will experience showers from
time to time between 18Z through 04Z this evening. Showers and
thunderstorms will be capable of generating brief MVFR visibility
with CIGS falling below ILS breakpoints for some sites. Heavier
cells may produce brief IFR conditions as well. Showers and
thunderstorms will decrease, but not entirely diminish overnight.
Chances are reduced for additional activity during the
overnight/Wednesday morning period, but KRIL, KEGE, and KASE may
experience periods where CIGS are below ILS breakpoints.



CO...Flash Flood Watch through this evening for COZ001>014-017>023.

UT...Flash Flood Watch through this evening for UTZ022>025-027>029.



AVIATION...NL is the U.S. government's official web portal to all federal, state and local government web resources and services.