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310
FXUS65 KGJT 201802
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
1202 PM MDT Mon May 20 2024

.KEY MESSAGES...

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- Warm and windy conditions today ahead of a cold front will
  drive temperatures back above climatology and winds will gust
  30-40 mph around the region.

- Showers and thunderstorms will develop along the front today.
  Storms will be capable of strong outflows and small hail. A
  few snow showers are also expected in the mountains behind the
  front Monday evening and into Tuesday morning.

- Cooler temperatures behind the front Tuesday will keep
  afternoon highs 10 degrees below climatology. Temperatures
  return to near normal Wednesday and beyond.
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&&

.SHORT TERM /THROUGH TUESDAY/...
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Issued at 401 AM MDT Mon May 20 2024

A frontal boundary stretching northeast from the Great Basin to
the Panhandle of Nebraska marks a rather abrupt moisture
gradient here in the CWA this morning. Dewpoints are in the mid
40`s across northwest Colorado, where light rainshowers have
been observed much of the night. The moisture/front are situated
along a strong jet streak turning the bend on the West Coast
trough digging into the Great Basin this morning. Those strong
winds aloft will gradually work their way over the Four Corners
this morning and drive up wind speeds across the CWA this
afternoon ahead of the approaching frontal boundary. The
strongest winds will concentrate around the Four Corners today
where southwesterly winds around 20-25 mph with gusts to around
35-40 mph can be expected. Held off on a wind advisory for now,
due to the lack of widespread zone coverage down there. Forcing
along the front holds across northeast UT and northwest CO into
the afternoon hours. A few showers and thunderstorms are
expected to develop this afternoon as the jet begins to pull the
front through the region. Early activity will remain north of
the Colorado River Valley, then begin to fill in during the
early evening hours as the actual front swings in northwest to
southeast. The front clears northwest Colorado by midnight and
cooler, drier air quickly puts the brakes on showers up there.
However, down south, showers and convection along the front will
keep going into the overnight hours, likely not calming down
until the early morning hours. Showers will likely hang up on
the mountains through the night Monday into Tuesday, where
accumulating snow above 10000 feet is expected thanks to the
generous shot of cold air behind this front. Tuesday, we remain
under the upper level trough as it lags the front. Gradient
winds will remain blustery behind the front. Afternoon highs on
Tuesday are expected to be nearly 20 degrees cooler. Showers and
additional thunderstorms are expected across the region Tuesday
as we see a series of shortwaves work through the upper trough
during the day. Steep lapse rates will help out with some gusty
outflows and small hail.
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&&

.LONG TERM /TUESDAY NIGHT THROUGH SUNDAY/...
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Issued at 401 AM MDT Mon May 20 2024

Tuesday night will finally see the axis of the prolonged trough
slide east of the Divide with subsident, dry air quickly
settling in behind it. Any lingering showers will diminish and
denser cloud cover will begin to clear under the now northwest
flow aloft. This will mean a sharp drop in temperatures compared
to the last several nights with Tuesday night`s lows trending
some 10 degrees cooler. In the wake of the cold front
subfreezing temperatures will be possible in portions of
southwest and northwest Colorado, while the central Colorado and
eastern Utah valleys will stay in the upper 30s to low 40s. No
freeze highlights are needed at this time since the current
forecast subfreezing temperatures correlates with our zones that
do not have vegetation susceptible to damage. A quiet day is on
tap for the Western Slope on Wednesday, though upper level flow
will shift to the west as the next trough digs into the Pacific
Northwest. Can`t rule a few afternoon storms over the higher
terrain once daytime heating kicks in but, overall, it`ll be dry
area-wide with temperatures beginning to rebound back to near
normal.

Models are beginning to come into better agreement regarding
the evolution of the Pacific storm as it pushes across the
Intermountain West Wednesday night before eventually tracking
through Montana and Wyoming on Thursday as it splits off from
the parent system. Flow will once again return to the southwest
across eastern Utah and western Colorado by Wednesday evening so
those overnight lows will quickly jump back to a few degrees
above normal. The base of the northern wave looks to straddle
the Wyoming / Colorado border on Thursday so expect isolated to
scattered showers and storms to develop across northeast Utah
and northwest Colorado that afternoon. Elsewhere will remain dry
but breezy as the gradient tightens with the trough.

The secondary wave looks to cross the forecast area sometime on
Friday but there are some discrepancies regarding how far south
it will drop. Depending on when this system pushes through we
could be looking at unsettled conditions going through the
weekend. But, not locking anything in at this moment as changes
can be expected under this persistent longwave troughing
pattern.
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&&

.AVIATION /18Z TAFS THROUGH 18Z TUESDAY/...
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Issued at 1202 AM MDT Mon May 20 2024

Winds will become gusty this afternoon and evening out ahead of
an approaching strong cold front. Gusts of 30 to 40 mph will be
common at most terminals. Showers and thunderstorms will also
continue to develop along the front in northeast Utah and
northwest Colorado before working south and east by this
evening. The strongest storms will be capable of producing very
strong winds and hail. Terminals will see periods of ILS
breakpoint conditions this afternoon and into the overnight
hours, especially mountain terminals, where rain and snow
showers will likely hang up along the Divide overnight into
Tuesday morning. More widespread showers are expected across
mountain and adjacent valley TAF sites through much of the day
Tuesday with MVFR ceilings and visibility possible.
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&&

.GJT WATCHES/WARNINGS/ADVISORIES...

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

&&

$$

SHORT TERM...LTB
LONG TERM...MMS
AVIATION...TGJT