Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 220442
AFDGJT

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1042 PM MDT Wed Jun 21 2017

.UPDATE...
Issued at 943 PM MDT Wed Jun 21 2017

Latest numeric model guidance suggesting more wind on Thursday
than previously indicated. Given persistent heat, relative
humidity will continue to run in the single digits during the
afternoon. Low RH combined with frequent wind gusts to 25 MPH and
above for much of the area will bring critical fire weather
conditions to much of eastern Utah and southwest and west-central
Colorado. Therefore, have decided to issue a Red Flag Warning from
noon to 10 PM MDT Thursday for the areas defined in the
WATCHES/WARNINGS/ADVISORIES section which follows.

&&

.SHORT TERM...(Tonight through Thursday night)
Issued at 305 PM MDT Wed Jun 21 2017

A 596 DM ridge of high pressure remains centered over the
southwestern CONUS this Wednesday afternoon. Diurnally driven
afternoon convection has once again developed over the higher
terrain, aided by marginal mid-level moisture still lingering on
the northern fringes of the ridge of high pressure. Some lightning
has been noted throughout the day with this convection, as well
as briefly gusty winds. DCAPE values sit in the 1000-2000 range
per model sounding analysis, with the KGJT morning sounding
indicating around 1570J/kg. Temperatures remain on track this
afternoon, and convection should diminish after sunset this
evening.

One more day of near record warmth is expected on Thursday before
temps cool down a bit this weekend. A weak 300mb speed maximum
will pass north of the Four Corners on Thursday morning. This
increase in winds aloft will tend to aid/organize any
thunderstorms that do form during the afternoon hours, and some
dry lightning is again expected area-wide in the higher terrain.
There will be an uptick in afternoon winds and wind gusts as well,
however guidance is in fairly good agreement keeping values below
Red Flag Warning thresholds. Will continue to hold off on any
headlines in this forecast package. Once again with the loss of
daytime heating, any lingering convection will diminish
overnight.

.LONG TERM...(Friday through Wednesday)
Issued at 305 PM MDT Wed Jun 21 2017

A diffuse frontal boundary will drift south and east through
eastern Utah and western Colorado on Friday morning as a larger
upper-level trough moves east through the high plains. This front
will act to take the edge off the extreme heat over the western
slope on Friday and through the weekend. Temperatures are still
expected to be around 5 degrees above average each day, however
record heat will no longer be in the forecast. As the front passes
Friday, some mid-level cloud cover will pass through. Mostly
clear skies will return on Saturday and Sunday as the southwestern
ridge of high pressure reloads for early next week.

The next peak in afternoon high temperatures will come early next
week as the renewed ridge of high pressure in the southwest builds
eastward. The hottest day during this time period will likely come
on Tuesday as the ridge axis passes just east of the Four Corners
and southwesterly warm air advection inches mid-level temperatures
up slightly. Beyond Tuesday, models begin to diverge with the
evolution of a weak trough moving in along the Pacific coast. The
GFS shows a deeper system that brings a strong gradient and a
windy day on Wednesday, before a frontal passage and possible
thunderstorm activity next Thursday. The ECMWF keeps this trough
weaker and much farther north, with dry weather and mostly zonal
flow through the period. This forecast package reflects the drier
solution, in line with the operational ECMWF as well as EPS
ensemble guidance.

&&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 1042 PM MDT Wed Jun 21 2017

A few showers will linger overnight bringing a slight chance for
rain and strong outflow winds. High based showers and
thunderstorms are again expected Thursday afternoon with gusty
outflow winds being the primary threat with not much rain
expected. Otherwise, VFR conditions will prevail over the next 24
hours.

&&

.FIRE WEATHER...
Issued at 943 PM MDT Wed Jun 21 2017

Fire Weather conditions are now expected to exceed critical levels
for much of eastern Utah and southwest and west-central Colorado
Thursday afternoon/evening. Some stronger winds aloft will move
over the region overnight into Thursday morning. As mixing
commences during the afternoon hours, frequent gusts upward of 25
mph can be expected in the areas previously mentioned. Dry
lightning is again possible on Thursday, however chances are a bit
lower with best chances over the higher peaks along the
Continental Divide. Precipitation chances will drop to near 0
during the weekend.

&&

.HYDROLOGY...
Issued at 305 PM MDT Wed Jun 21 2017

A flood advisory has been issued for the Roaring Fork River in
Aspen as snowmelt and tunnel closures upstream have caused the
river to reach bankfull. This advisory will run through Friday
evening.

A number of streams and creeks also continue to run strong, cold,
and high and will continue to do so through the week. Where water
is running high, river banks may become saturated and unstable.
Lowlands along the rivers may also become inundated with water.
Remember if you are going to raft, kayak or tube on the rivers be
sure to always wear a life jacket.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Red Flag Warning from noon to 10 PM MDT Thursday for COZ203-207-
     290-292.

     Heat Advisory until 10 PM MDT Thursday for COZ006.

UT...Red Flag Warning from noon to 10 PM MDT Thursday for UTZ486-487-
     490-491.

     Heat Advisory until 10 PM MDT Thursday for UTZ022-027-029.

&&

$$

UPDATE...NL
SHORT TERM...MAC
LONG TERM...MAC
AVIATION...MMS
FIRE WEATHER...TGJT
HYDROLOGY...TGJT


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