Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 180542

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
1142 PM MDT Mon Apr 17 2017

.SHORT TERM...(Tonight through Tuesday night)
Issued at 258 PM MDT Mon Apr 17 2017

A weak shortwave trough will pass through Idaho and Montana, well
north of the forecast area, resulting in some breezy conditions
this afternoon and evening with scattered to broken cloud cover.
Drier air will advect into the region with clearing skies on
Tuesday as a stronger shortwave trough and cold front approach
from the west. This system has good upper level jet support with a
100 kt jet laying over Utah ahead of the cold front. The gradient
will tighten and allow for sufficient mixing of warmer air down
to the surface. This will also result in breezy conditions as
winds gust 25 to 35 mph in the lower elevations. The gusty winds
along with the low relative humidities has led to a Red Flag
Warning being issued for the west-central and southwest Colorado
Fire Weather Zones where fuels are deemed critical. More details
are included in the Fire Weather Discussion section below.

In addition to Fire Weather concerns on Tuesday, showers and
thunderstorms also look to develop initially over northeast Utah
Tuesday afternoon and then spread eastward into northwest Colorado
late Tuesday afternoon into the evening with the approaching cold
front. This front is currently projected to move through the
region Tuesday night sometime after midnight into Wednesday
morning with decent RH recoveries as specific humidity values
increase to around 5 g/kg. Showers will initially be high based
with virga leading to some enhanced wind gusts Tuesday afternoon
and evening, before the atmosphere moistens up enough to generate
some light rain in the valleys and light snow in the higher
terrain. Not expecting much snow accumulation with this system as
it is quick moving and doesn`t support much snowfall through
Wednesday morning, however the winds will continue to be breezy to
windy overnight Tuesday night into Wednesday morning with the cold
front passage.

.LONG TERM...(Wednesday through Monday)
Issued at 258 PM MDT Mon Apr 17 2017

The forecast models remain in fairly good agreement through Monday
so this is leading to more confidence in the going forecast. The
main story is that a fast and progressive flow will develop off
the Pacific leading to a series of open troughs skirting the area
with ridging in between when looking ahead at the extended. These
systems appear to be trending further north with each run and as
the system gets to be about 24 to 48 hours out, so keep in mind
that the exact storm track could change.

Wednesday will be cooler in the wake of the passing cold front
with a light westerly flow as the gradient relaxes. Thursday will
see an increase in southwest winds as a negatively tilted trough
makes its way onto the Northern California and Pacific NW coast,
tightening the gradient once again. Dry and breezy conditions
ahead of this system and associated cold front may lead to fire
weather concerns on Thursday afternoon and evening. This
negatively tilted trough will allow for increasing instability
with showers and thunderstorms developing Thursday afternoon and
evening, mainly across northeast Utah and northwest Colorado. The
trough will move through the area Thursday evening into Friday
afternoon with the northern and central mountains being favored
for snowfall as H7 temps drop to around -4C to -8C north of I-70.
This system will quickly take its energy out across the Front
Range and Plains as the main upper low slides southeast through
Wyoming into eastern Colorado and Kansas by Friday morning.
Meanwhile, an amplified ridge of high pressure will build across
the west helping force this system quickly eastward on Friday with
showers coming to an end by Friday evening. Temperatures will be
noticeably cooler on Friday and Saturday in the wake of this
system, but should quickly warm back up to above normal levels by
Sunday as the ridge of high pressure moves overhead.


.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 1136 PM MDT Mon Apr 17 2017

A weak disturbance and associated cold front will begin to work
through the region late Tuesday afternoon and Tuesday night.
Southwesterly winds will continue to increase ahead of the front
resulting in wind gusts up to 40 kts after 18Z. VFR conditions
will generally prevail though some ILS cigs will develop after
00z/WED. Isolated to scattered orographic showers will develop
after 18Z with isolated thunderstorms after 00Z.


Issued at 258 PM MDT Mon Apr 17 2017

Dry conditions remain in place across much of the CWA today as an
area of weak low pressure well to our north will allow a weak
front to pass over the region. Southerly winds will increase this
afternoon in response to this weak front. Gusts of 25 mph or
greater are anticipated for much of CO fire weather zones 200 and
202, where fuels are not critical at this time.

A stronger surface front with upper level jet support will
approach the area on Tuesday. Forecast soundings indicate deep
mixing will allow winds and wind gusts to reach 25 to 35 mph for
CO fire zones 207, 290, 292 and 203 where fuels are critical.
Therefore, a Red Flag Warning is in effect for Tuesday afternoon
and evening to account for these conditions. Important to mention
that much of southeast Utah will also see these same conditions
but fuels, at this time, are not critical so will hold off issuing
anything for that area.


CO...Red Flag Warning from 1 PM to 8 PM MDT Tuesday for COZ203-207-



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