Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 170611
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1211 AM MDT Tue Apr 17 2018

.UPDATE...
Issued at 1208 AM MDT Tue Apr 17 2018

Relative humidity values have started to slowly climb back above
15 percent across Fire Zones 203 and 290 late this evening. Still
some pockets below 15 percent, but trend will be upward for the
remainder of the night. So while the winds will continue to below,
overall conditions related to fire weather concerns have been
eased a bit. Therefore, went ahead and allowed the Red Flag
Warning to expire. However, wind advisories remain in effect for
these same areas with gusts to 50 mph possible through Tuesday
morning.

UPDATE Issued at 954 PM MDT Mon Apr 16 2018

Extended the Red Flag Warning through midnight tonight for west-
central Colorado Fire Weather Zones 203 below 6000 feet and 290
(Paradox Valley) due to winds still gusting in the 40s and
relative humidity still below 15 percent in the low teens for the
majority of these zones. Cancelled the Red Flag Warning for
southwest Colorado zones including Cortez, Durango and Pagosa as
relative humidities have recovered well above 15 percent for the
majority of those zones. This is likely due to cloud cover still
present with some light virga showers reaching the ground with
spitting rain in Durango earlier and a brief wind gust to 40 kts
(as a direct result of the virga shower as winds are now light and
variable after that virga shower passed by). Thinking humidities
should recover after midnight tonight but this will have to be
monitored as winds still remain quite strong.

UPDATE Issued at 824 PM MDT Mon Apr 16 2018

Decided to extend the wind advisories out until noon Tuesday.
Satellite shows a sharp area of clearing occurring across eastern
Utah into northwest Colorado and now entering in portions of
extreme west-central Colorado with absolutely no cloud cover.
Plenty of clouds exist across extreme southeast Utah and western
Colorado south of I-70. This dry slot is all occurring ahead of a
strong cold front set to move through the area late Tuesday
morning. Underneath this dry slot and associated area of clearing,
stronger winds aloft were finally mixing to the surface with winds
reaching and exceeding wind advisory criteria. Expect this trend
to continue as this dry slot shifts eastward across the remaining
zones. Latest guidance indicates these winds remaining elevated
overnight through Tuesday morning with wind advisory criteria
being reached from time to time or sustaining throughout, which is
sustained winds of 30 mph or greater and gusts of 45 mph or
greater for any duration throughout that time period. This seems
reasonable as skies will be clearing and the gradient will be
tightening as this front approaches with H7 winds approaching 60
kts or greater. Being pre-frontal, winds are unlikely to decouple
overnight so thinking strong winds will remain elevated. Felt
confident enough to extend the wind advisory through frontal
passage which is between 12Z (6 am) and 18Z (noon), peaking around
15Z (9am) as strong wind potential will remain through that
timeframe. Precipitation will fill in behind the front after noon
but models indicate a very dry air mass ahead of this front,
lending to higher confidence that skies will also remain mostly
clear overnight helping keep winds stronger.

&&

.SHORT TERM...(Tonight through Tuesday night)
Issued at 343 PM MDT Mon Apr 16 2018

Though winds have been slow to develop today thanks to persistent
cloud cover, we have begun to see wind gusts hit advisory
criteria. Strong winds will continue through the overnight hours
tonight as another potent spring storm rolls in from the west. We
are anticipating that winds may decouple in the valleys somewhat
overnight keeping winds below advisory thresholds, but it is
possible they will gust all night. The front should roll through
the UT/CO border during the mid morning hours on Tuesday when
winds will quickly change from southwesterly to northwesterly. A
line of showers will roll through with the front on Tuesday
morning, bringing rain and snow to mainly northwestern CO favoring
those locations in northwest flow. Weather conditions over the
high passes in Colorado Conditions will stabilize Tuesday evening
with temperatures generally -6 to -8C at 700mb...a cold airmass
for this time of year. Cold, well below normal northwesterly flow
will shroud the region Tuesday night into Wednesday morning.

.LONG TERM...(Wednesday through Monday)
Issued at 343 PM MDT Mon Apr 16 2018

Have issued freeze watches for an expected deep freeze across the
Grand Valley Wednesday morning. Really, everywhere is going to see
a hard freeze, but the Grand Valley is the only zone truly in its
growing season with such a warm spring so far and only one day
below freezing so far this month. Temperatures begin to moderate
later in the day on Wednesday as transitory high pressure builds
over the Four Corners. The progressive roller coaster pattern
continues with the next longwave trough developing over the West
Coast on Wednesday and the development of a closed low over
California. This trough will move eastward on Thursday into the
western Great Basin and will greatly increase southerly winds and
push a warm front northward into eastern UT and western CO.
Forecast models have been consistent on bringing this closed low
in during the late week for awhile, so confidence is decent on
this system. The main cold front will roll through sometime early
Friday, with significant uplift expected to produce convection
Friday afternoon as the closed low moves through the Four Corners.
This system indicates the lowest temperatures at 700 mb at -4C,
so snow level should be right at mountain bases, impacting the
usual trouble spots - all mountain passes above 9000 ft. Right
now, models identify a strong TROWAL signal on the backside of
this closed low, with significant wrap around precipitation
possible late Friday into early Saturday. Conditions on the Front
Range will be much more exciting than here, however the West Slope
and even eastern Utah may see decent moisture Friday as the storm
dynamics hop on over to the Front Range.

Drier conditions should develop Sunday into Monday as ridging
builds back across the southwestern US.

&&

.AVIATION...(For the 06Z TAFS through 06Z Tuesday night)
Issued at 954 PM MDT Mon Apr 16 2018

Winds will continue to remain strong through the overnight hours
into Tuesday morning out of the southwest with frequent gusts in
the upper 30s and 40s at a majority of lower valley TAF sites,
with exception of KDRO, KGUC, and KHDN which remain further east
from the direct influence of the approaching cold front. Skies
will be clear for most areas with persistent broken to overcast
skies over KDRO, KGUC, KTEX and KASE with clearing slowly working
in from the west. The cold front will move through between 12Z and
18Z Tuesday with a shift to northwest winds. Winds will remain
breezy Tuesday afternoon with some showers possible across
northwest Colorado down to KASE through about 00Z Wednesday.


&&

.FIRE WEATHER...
Issued at 337 PM MDT Mon Apr 16 2018

Windy conditions have not been as high as we thought so far today
due to cloud cover inhibiting significant mixing aloft. However,
many spots are hitting red flag conditions with RH values
in the single digits and wind gusts over 25 mph. In areas where
fuels have been deemed critical, Red Flag Warnings will remain in
effect (Colorado zones 207, 290, 295 and 203 below 6k) until 10 pm
MDT this evening. The windy conditions will persist into the
overnight hours, but RH is anticipated to climb by 10 pm. A
strong cold front will pass through Tuesday morning. Another dry,
warm and windy day is likely on Thursday.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Wind Advisory until noon MDT today for COZ001>003-006>008-011-
     020-021.

     Freeze Watch from late tonight through Wednesday morning for
     COZ006.

UT...Wind Advisory until noon MDT today for UTZ022-024-025-027>029.

&&

$$

UPDATE...JDC
SHORT TERM...JAM
LONG TERM...JAM
AVIATION...MDA
FIRE WEATHER...TGJT



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