Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 301950

Area Forecast Discussion
National Weather Service Grand Junction CO
150 PM MDT Mon Mar 30 2020

.SHORT TERM...(Tonight through Tuesday night)
Issued at 129 PM MDT Mon Mar 30 2020

Cold air has been quite stubborn throughout much of eastern Utah
and western Colorado today. The temperature forecast is shallowing
by 4-7 degrees across the western slope as of 1pm, and with
cumulus development over many places, we are not expecting highs
to gain more than a few more degrees today. Have opted to back
high temps off area-wide to cover for these changes. A few
isolated rumbles of thunder have been observed here and there,
especially over the higher terrain. Instances of pea-sized hail
will be likely with any shower or weak thunderstorm that develops
today, given low-end CAPE values and plenty of cold air aloft.

Showers and lingering storms will quickly diminish after sunset
with the loss of daytime heating. Scattered clouds will remain
however, and will help keep temperatures from dropping back too
much. Overnight lows will run right near seasonal averages for

A dry day is expected on Tuesday with westerly flow aloft. A
Pacific Jet will slowly sag southward through the northern
Rockies, resulting in some thicker high cirrus cloud cover over
northern Utah and Colorado by evening. Throughout central and
southern Utah and Colorado, expect a notable rebound in high
temperatures as warm air is transported eastward and northward
from the southern Great Basin. Highs on Tuesday will be 10 or more
degrees higher than what was seen on Monday - quite a refreshing
spring warm-up.

.LONG TERM...(Wednesday through Monday)
Issued at 129 PM MDT Mon Mar 30 2020

Forecast guidance remains in excellent agreement from Wednesday
through Friday. The prior forecast discussion addresses the next
storm well...

Upper level winds will shift to the southwest
Wednesday as the next Pacific trough digs into the northwestern
CONUS. The gradient will gradually tighten as the jet rounding the
base of the trough shifts east with the 90-100 knot jetstreak
projected to arrive across the northern tier of the region by late
Wednesday/early Thursday. This should help kick off more
widespread shower activity across northeast Utah and northwest
Colorado with showers spreading south throughout the day as the
trough elongates over the Great Basin. The trough`s base will lift
northeast across the area by daybreak Friday with showers
dissipating from west to east as a result. The northwest Colorado
mountains look to be favored with the passage of the trough`s cold
front, though projected snowfall totals will need to be tinkered
with over the coming shifts. Isolated orographic showers are
likely to continue throughout the day on Friday along the
Continental Divide while the remainder of the forecast area can
expect clearing skies. As the trough passes overhead on Thursday
700mb temperatures will cool to -3 to 3 degrees C south of I-70
with values of -4 to -10 degrees C north of the interstate. In the
trough`s wake on Friday values will range from -8 to -4 degrees C
across the south and from -9 to -12 degrees further north. At the
surface these readings will translate to daytime highs that are
upwards of 6 to 12 degrees below normal across the north and near
to a few degrees below normal across the south. Additionally,
overnight lows Thursday night are likely to drop below freezing
for the majority of the lower valleys.


Differences in forecast guidance continue to plague the end of
the long-term forecast. After a dry day Friday, the GFS continues
to insist on another wave of moisture moving through the mountains
on Saturday as a weak trough passes to the north. The ECMWF keeps
things mostly dry at this time, with the same system remaining
much weaker. Both models support the idea of warm southwesterly
flow on Sunday, ahead of a new system coming into the west coast.
The GFS brings a shortwave around this larger trough into the Four
Corners region by Sunday night into Monday, whereas the ECMWF
keeps all the moisture from this system west of the Green/Colorado
rivers. With so much run-to-run variation regarding the
spatiotemporal complexity of this event, forecast confidence is
extremely low from Saturday onward.


.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 1136 AM MDT Mon Mar 30 2020

Showers moving across the area are beginning to diminish from west
to east this afternoon producing mainly ILS/MVFR conditions, but
brief periods of IFR will continue especially in higher elevation
sites like TEX, GUC, and ASE. Skies will become more scattered
this afternoon with clearing this evening as showers move out of
the forecast area. Gusty winds can be expected along the southern
San Juans this afternoon.




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