Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 180905
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
305 AM MDT Wed Apr 18 2018

.SHORT TERM...(Today through Thursday)
Issued at 301 AM MDT Wed Apr 18 2018

High pressure builds overhead today with lighter winds, plenty of
sun and warmer conditions. The ridge axis passes this evening with
very dry southwest flow setting back up as another strong Pacific
storm digs ESE into the Great Basin. This will tighten pressure
gradients back up late tonight and Thursday. Winds will increase
over the ridges tonight and gradually mix down into the valleys by
midday Thursday. With very dry low levels, expect another critical
fire weather day with winds gusting over 25 mph and humidity
values dropping below 15 percent. Some concern we could see a
blanket of high clouds that may inhibit some mixing and nudge
moisture values up a bit. However, conditions are so dry that even
a slight bump upward does not appear to be enough to alleviate
our fire weather concerns. As such, another Red Flag Warning will
be issued. Be sure to check for local burn bans and refrain from
any open burning as any fire starts will be difficult, if not
impossible, to contain.

The main core of this incoming system will be slow to push
eastward, so expect dry weather to persist through Thursday
afternoon.

Temperatures will be running on the cooler side of normal today,
before jumping 10 degrees or more on Thursday under strengthening
southwest and warm advective flow. Southwest component along will
be good for 2 to 3 degrees of warming for many of our valleys.

.LONG TERM...(Thursday night through Tuesday)
Issued at 301 AM MDT Wed Apr 18 2018

Moisture and precipitation surges northward across the southern
divide and Front Range ahead of a closed low moving into the Great
Basin as the upper level jet rounds the base through the Four
Corners region Thursday night. Very dry air will be evident in
between this moisture to the east and the closed low to the west,
which paints the dry air over much of eastern Utah and western
Colorado. The track of this low is key to how far east or west the
moisture surges and also how much snowfall if any the San Juans get
Thursday night. As the low moves further east across Utah into
western Colorado by Friday morning, the deepest moisture gets pushed
further east over the Front Range with moisture wrapping around this
closed low. This shifts the flow to easterly as the moisture wraps
around in TROWAL like fashion with the eastern foothills being
favored initially Friday morning into the early afternoon. A
northeast component is evident across northeast Utah though, which
favors the eastern Uintas with snowfall. By late Friday afternoon,
this deeper moisture is making its way into northwest Colorado with
the flow shifting to a northerly component through Friday evening.
Friday afternoon through Friday evening looks to be the best time
period where deeper moisture combined with colder air work over the
region in favorable orographics to give our mountains the best
chance for decent snowfall accumulations. H7 temps look to range
from -2C to -6C, which means the higher elevations above 7000 to
8000 feet have the best chance to see better snowfall accumulations.

There is still timing differences and differences in the track of
this low. The EC and Canadian have slowed the storm down somewhat
with a more southern track through the Four Corners than the GFS
which is more progressive and a bit north of the Four Corners. These
details are key to which areas would be favored for snowfall as the
EC and Canadian solution would bring the better moisture over our
side of the San Juans Thursday night whereas the GFS would keep our
side drier and the eastern San Juans wetter. Time will tell but
looks like Friday afternoon and evening would be the better snowfall
chances due to the effects of the TROWAL and favorable flow with at
this time solid advisory amounts.  The eastern Uintas and northern
San Juans may need to be watched closely though due to more
favorable orographics that if the moisture and temperatures are
right, could lead to better snow numbers.

This system pulls out of the region by late Saturday morning with
snow lingering and conditions slowly improving through the day.
Ridge of high pressure slides back over the region by Sunday into
Monday leading to a return to warm, above normal temperatures.
Differences lie beyond Monday as what appeared like a shortwave
coming up from the southwest on Tuesday with much warmer temps
pushing 80 in some lower valleys has now turned into a shortwave
dropping in from the northwest, bringing much cooler air with valley
temps dropping into the 60s. Suffice it to say, low confidence
exists beyond Monday in the going forecast so will lean towards a
dry and warmer solution until better consensus is reached.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 301 AM MDT Wed Apr 18 2018

High pressure will pass over the Central Rockies today brining VFR
conditions and lighter winds. Winds will be on the increase after
06z tonight along the higher mountain ridges as another Pacific
storm pushes into the Great Basin.

&&

.FIRE WEATHER...
Issued at 301 AM MDT Wed Apr 18 2018

Red Flag conditions will be moving back into the area on Thursday
as another strong Pacific storm tracks into the Great Basin. This
will bring gusty southwest winds to the area, along with humidity
values tumbling back below 15 percent. Land management partners
report critically fuels over many of the valleys of western
Colorado. With all the ingredients in place, will be upgrading the
Fire Weather Watch to a Red Flag Warning for Thursday afternoon
and evening for portions of fire zones 200, 202, 203, 207, 290 and
295. The cold front associated with this system is expected to
move over the area Thursday night with widespread precipitation
expected by Friday. Until that precipitation arrives, open
burning is highly discouraged as any fire starts will be
difficult, if not impossible, to contain.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Freeze Warning until 9 AM MDT this morning for COZ006-011-020-
     021.

     Red Flag Warning from noon to 9 PM MDT Thursday for COZ200-202-
     203-207-290-295.

UT...Freeze Warning until 9 AM MDT this morning for UTZ022-027-029.

&&

$$

SHORT TERM...JDC
LONG TERM...MDA
AVIATION...JDC
FIRE WEATHER...JDC


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