Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 171134
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
534 AM MDT Tue May 17 2022

.SHORT TERM...(Today through Wednesday)
Issued at 402 AM MDT Tue May 17 2022

High clouds were sweeping eastward over the northern portion of
the forecast area ahead of a mid-level shortwave moving over the
Great Basin early this morning. Meanwhile, another weak shortwave
trough, split off from the main flow was over central Arizona
early this morning. However, this disturbance was having little
impact on the dry airmass over the Southwest and skies were clear
over the southern portion of the forecast area.

The shortwave trough over the Great Basin will push across the
region today with frontogenetic forcing provided by the jet above
causing a stationary boundary over southern Wyoming to sharpen and
drift southward across northeast Utah and northwest Colorado
during the day. Moisture entrained in the flow combined with steep
lapse rates and surface convergence along the front will result in
scattered showers developing first over the eastern Uinta
Mountains before spreading southward with the front as it tracks
southward toward the Tavaputs and Roan Plateaus and the Flat Tops.
Isolated thunderstorms are possible and latest CAMS indicated the
potential for strong outflow winds later this afternoon over the
aforementioned plateaus and potentially spilling across the Grand
Flat in eastern Utah and the Grand Valley of western Colorado.
Areas to the south, however, will remain dry and unseasonably warm
again today. In contrast, locations across the north behind the
front can expect around 5 degrees of cooling while temperatures
south of the I-70 corridor should be similar to those recorded
Monday; which is to say, unseasonably warm.

Expect showers and thunderstorms to diminish later this evening as
the shortwave passes east of the Divide while diurnal cooling
allows the airmass to stabilize. Clouds will slowly decrease
during the night limiting radiational cooling resulting in above
normal lows by Wednesday morning. Flow veers to the northwest
behind the trough on Wednesday, though temperatures will remain
quite mild. Residual moisture over the central and southern
Colorado mountains is expected to fuel afternoon showers and
thunderstorms, though mainly along the Continental Divide. This
activity will remain relatively high based so gusty winds are more
likely than any significant measurable precipitation.

.LONG TERM...(Wednesday night through Monday)
Issued at 402 AM MDT Tue May 17 2022

After a quiet night Wednesday night, attention turns to an
anomalously strong trough that will drop into the Pacific Northwest,
northern Rockies and northern Plains on Thursday. This system will
have all of the defining characteristics of a notable springtime
storm, including a ridiculous 170+ kt upper jet and a potent cold
front separating winterlike temperatures to the north and summerlike
temperatures to the south. In between, everything from roaring
winds, fire weather, severe weather and mountain snow will be on the
table across a large portion of the western two thirds of the CONUS.

Here locally, another very warm day is on tap for Thursday out ahead
of the cold front that will be surging southward towards northeast
Utah and northwest Colorado. Southwest prefrontal winds will be
quite gusty come the afternoon hours, particularly to the north of
Interstate 70. Frequent wind gusts of 45 to 55+ mph are likely and
those locations will probably need wind highlights at some point.
Near and south of I-70, 35 to 45 mph gusts are expected. Combined
with the very dry desert air, critical fire weather will be a
concern across the lower elevations of southwest Colorado.
Highlights will likely be needed to cover that threat as well.
Debated issuing a Fire Weather Watch, but decided to hold off
for now. Still some time left to iron out the details.

As far as frontal timing, the latest 00Z/Tuesday model guidance has
slowed down the arrival of the front and doesn`t begin to encroach
the northwest CWA until between 00Z and 03Z Thursday evening. The
front will make decent progress Thursday night and is progged to be
either on the doorstep or even through the I-70 corridor by 12Z
Friday. By the early afternoon hours, the front will have passed
through the entire forecast area. In its wake, much colder and well
below normal air will surge into all of eastern Utah and western
Colorado. In fact, high temperatures on Friday will be a good 20 to
30 degrees colder than on Thursday. So for those thinking it`s way
too early for this summerlike heat...relief is on the way.

Temperatures aren`t the only story on Friday, though. Precipitation
would like to have a word. Increasing moisture (to the tune of 100
to 150% of normal) along/behind the front combined with jet dynamics
and frontogenetical forcing will set the stage for fairly widespread
precipitation. Most of this precip will be confined to the northern
half of the CWA (including the I-70 corridor) and especially the
northern and central Divide mountains. Unfortunately, the front is
likely to pass through dry across southeast Utah and southwest
Colorado (outside of the San Juans). P-type will be rain in the
lowest valleys, but you won`t have to go too far up until profiles
are plenty cold enough to support snow. In the high valleys of
northwest Colorado, a dusting up to maybe an inch or two is
possible. GFS forecast soundings do show a period where the DGZ is
saturated, fairly deep and within a region of modestly strong
omega... but it`s brief and during the daylight hours with a strong
mid to late May sun angle. Impacts will likely be nil. The mountains
will do better of course and it`s very possible for some of the
highest peaks to accumulate 3 to 6 inches or more of new snow. Still
though, the same reasoning applies. Impacts (especially to roads)
will be minimal. That said, with a rapidly declining mountain snow
pack, we`ll take whatever we can get at this time of the year.

Precipitation will mostly taper off Friday night, though a few
showers may linger across the Divide into Saturday. Temperatures
Friday night will get quite chilly and may even near freezing in
some of the higher valleys. This shouldn`t be a concern to the
peaches here in the Grand Valley, but it`s worth keeping an eye on
as we get closer. Looking ahead to the weekend, Saturday will be
another cooler than normal day before temperatures start to rebound
Sunday into Monday as heights rise and ridging builds into the Great
Basin. Dry and partly to mostly sunny will generally be the rule.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 534 AM MDT Tue May 17 2022

A cold front which moved through KVEL earlier this morning will
continue to track southward during the remainder of the day,
stalling along the Tavaputs and Roan Plateaus and the Flat Tops
during the afternoon. This will result in a wind shift and
modestly breezy winds. TAF sites along the I-70 corridor aren`t
likely to experience this wind shift, but it may spill into the
Grand Flat of eastern Utah and the Grand Valley of west-central
Colorado. Showers/thunderstorms from this activity will mainly be
confined to areas surrounding the northern TAF sites so only made
mention of VCTS for KVEL and KHDN. CAMS models suggest outflow
winds to 45 mph could impact KCNY and KGJT during the late
afternoon or early evening. Otherwise, expect VFR conditions with
ceilings for all TAF sites remaining above ILS breakpoints.

&&

.FIRE WEATHER...
Issued at 402 AM MDT Tue May 17 2022

A weak disturbance and cool front will bring scattered showers and
isolated thunderstorms to the northern portion of the forecast
area from late morning through the afternoon and into the evening.
This activity will generate strong gusty outflows, but little
measurable precipitation. Areas south of the I-70 corridor can
expect modestly gusty west winds during the afternoon. Though,
there will be pockets of critical fire weather conditions, it
remains unlikely that this will be a sustained widespread event
for the susceptible southern zones. Similar conditions are
expected Wednesday so at this time fire weather highlights appear
to be unwarranted either today or Wednesday. However, this
changes on Thursday as a system moving out of the Pacific
Northwest causes the pressure gradient to tighten ahead of it
bringing the potential for widespread strong and gusty winds. The
airmass over the region will remain dry ahead of the storm so
there does appear to be a good chance for critical fire weather
conditions from late Thursday morning into the evening. Have held
off issuing a Fire Weather Watch with this package allowing the
next model runs to better resolve the details.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...None.
UT...None.

&&

$$

SHORT TERM...NL
LONG TERM...MDM
AVIATION...NL
FIRE WEATHER...NL


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