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000
FXUS65 KGJT 252152
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
352 PM MDT Thu Apr 25 2024

.KEY MESSAGES...

- Scattered showers and thunderstorms continue this afternoon
  and evening, with gusty winds and small hail the main threats.

- Cool and unsettled weather continues Friday through the
  weekend as another system moves through. Accumulating
  mountain snowfall is likely, mainly above 9000 feet.

- Warmer weather returns again next week.

&&

.SHORT TERM /THROUGH FRIDAY NIGHT/...
Issued at 352 PM MDT Thu Apr 25 2024

Scattered showers and thunderstorms have developed as expected
this afternoon, in response to a strong mid-level disturbance
rotating through overhead. The environment in place has been
quite favorable for convection, characterized by strong diabatic
heating, around 500 j/kg of SBCAPE... and steep mid-level lapse
rates between 8.5 and 9.5C/km. Combined with forcing for ascent
along a weak cold front, terrain enhancement, and modest height
falls aloft, it`s no surprise why current radar and satellite
imagery appear the way they do. Overall, the main threat from
showers and storms this afternoon and evening is gusty outflow
winds with gusts upwards of 45 to 55 mph. Forecast soundings,
along with this morning`s 12Z GJT observed sounding, show a lot
of dry air in the boundary layer... and while some of the
stronger storms will be capable of producing small hail and
brief heavier rain, the stout inverted V signatures suggest a
lot of precip evaporating before reaching the ground. The added
momentum of cooling/evaporating air aloft rushing to the surface
will thus lead to an isolated wind threat through the evening
hours. In fact, we`ve already observed this earlier today when
strong outflow produced a 54 mph wind gust at Cortez-Montezuma
County Airport. Otherwise, this afternoon`s weather is a far cry
from what we`ve had here as of late, with plenty of clouds and
much cooler temperatures taking the edge off our early summer
preview.

Most storms should diminish within a couple hours after sunset
with the loss of daytime heating and a stabilizing boundary
layer. That being said, do expect some shower activity to linger
into the overnight hours. By Friday morning, the disturbance
that is currently passing overhead will be well to our east with
a shortwave ridge building in from the west. This should result
in a very brief period of mainly dry weather before the next
storm system arrives later Friday afternoon. This next system is
looking stronger than the first and will be accompanied by a
much more potent cold front. Similar to today, we`ll have
another round of scattered to widespread showers and
thunderstorms develop mainly after 21Z with gusty winds and
small hail again the primary risks.

In the wake of the passing cold front Friday night, attention
then turns to winter as accumulating mountain snow is looking
likely to round out the work week and start the weekend. While
snow showers are probable in the mountains prior, the real
action gets going Friday night into Saturday as strong forcing
for ascent increases and becomes maximized within difluent flow
and the left exit region of a strong upper level jet. The air
aloft really isn`t all that cold with 700mb temps generally 0C
to -5C... but it will still be cold enough to support snow in
the eastern Uintas and the Continental Divide mountains near and
above 9000 feet. Given the late season nature of this storm and
possible impacts at pass levels, decided to go ahead and issue
a Winter Weather Advisory with this package for amounts of 6 to
12 inches from Friday night through early Sunday morning. For
more details on how the storm plays out through then, see the
long term discussion below.

&&

.LONG TERM /SATURDAY THROUGH WEDNESDAY/...
Issued at 352 PM MDT Thu Apr 25 2024

On Saturday the low pressure tracks right over the forecast
area, so plenty of lift and moisture in place for precipitation.
Widespread showers are expected through out the day. This is
supported by the high res models, which are now starting to
cover that timeframe. Despite being a cold core system
temperatures will be rather seasonal therefore snow levels are
expected to be in that 7-9 kft range. Impacts from snow above
these elevations will be limited by strong solar insolation. A
few thunderstorms are possible, but the amount of instability
will rely heavily on clouds clearing out. With the low center
overhead wind direction will be very location and time
dependent. Generally flow will go from southwesterly to
westerly, but there may be a period of north/northeast winds so
shower movement may be a bit chaotic compared to normal. On
Saturday night the low exits out over the Plains. We should see
a down tick with precipitation across our area. Although snow
showers may linger in the mountains and produce messy travel
around the passes. The QPF forecast has come down quite a bit in
the last few model runs so confidence in the amounts is low.
Just know that slick spots are possible Sunday morning generally
at pass level. Moisture is slow to work out of here so with the
steep lapse rates in place additional shower development is
possible. Monday is looking mostly dry, but a system moving over
the Northern Rockies could bring chances back to the northern
CWA. Regardless zonal flow becomes established and temperatures
begin to warm and by mid week southwest flow returns. This means
daytime highs will be 10-15 degrees above normal. For the most
part the entire week looks dry, but things could change.

&&

.AVIATION /18Z TAFS THROUGH 18Z FRIDAY/...
Issued at 1110 AM MDT Thu Apr 25 2024

An approaching cold front will bring some showers and a few
thunderstorms to the region this afternoon with high elevation
mountain snows possible overnight. Flight conditions should
remain VFR though ILS breakpoints may be met for KASE, KEGE and
KTEX in the evening hours after 00Z. Decided to include -SHRA
for some of the TAF sites this afternoon. Brief MVFR can not be
ruled out under the stronger cells.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...

CO...Winter Weather Advisory from 6 PM Friday to 6 AM MDT Sunday
     for COZ004-009-010-012-013-018-019.
UT...Winter Weather Advisory from 6 AM Friday to 6 AM MDT Sunday
     for UTZ023.

&&

$$

SHORT TERM...MDM
LONG TERM...KJS
AVIATION...TGJT