Area Forecast Discussion
Issued by NWS Grand Junction, CO

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000
FXUS65 KGJT 222340
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
540 PM MDT Sun Apr 22 2018

.SHORT TERM...(Tonight through Monday night)
Issued at 254 PM MDT Sun Apr 22 2018

Some high clouds are streaming across the Four Corners region this
afternoon with cumulus building over the higher terrain over
eastern Utah and extreme western Colorado, particularly in areas
with little to no snow cover where greater surface heating is
taking place. Cumulus is starting to now form over the rest of the
higher terrain where surface heating was slower due to better snow
cover. This was very evident in the Day Cloud Phase Distinction
RGB satellite imagery. Expect isolated thunderstorms over the
higher terrain late this afternoon into the evening, dissipating
tonight as the sun sets and surface heating is lost. Partly to
mostly sunny skies expected elsewhere with warmer temperatures
than yesterday, pushing a few degrees above normal.

Temperatures warm significantly by Monday afternoon as H7 temps
climb to +5C north and +10C south with high temps pushing upper
70s to low 80s across some of the lower central and southern
valleys. Instability also increases as lapse rates climb to near 9
degrees C/km with CAPE values batting 800 to 1,000 J/kg over the
higher terrain of western Colorado. Thunderstorm chances will
increase Monday afternoon and evening with peak surface heating as
a disturbance also approaches from the north, resulting in breezy
conditions. Conditions will be drier across the central and south
with some breezes above 25 mph at times, but not widespread
enough for a long enough duration to warrant Fire Weather
highlites at this time. Something for later shifts to keep an eye
on, but overall looks very borderline. Precipitation will increase
across the north Monday night as a cold front drops southward
with showers favoring the northern and central mountains mainly
along the divide. Snow levels will remain high above 10,000 feet
until after midnight Monday night.

.LONG TERM...(Tuesday through Sunday)
Issued at 254 PM MDT Sun Apr 22 2018

The cold front is projected to drop southward across the region
Tuesday morning, getting as far south as the I-70 corridor and
central mountains before lifting back north Tuesday afternoon. The
NAMNest and NAM in general is most aggressive with precipitation
and snowfall showing decent precipitation along the cold front,
while the GFS and EC appear much drier showing some scattered
showers over the high terrain along the divide. H7 temps drop to
around 0C near Vail Pass with H7 temps down to -4C on average up
north over the Park Range by Tuesday morning. Colder air spills
down the Front Range but doesn`t quite make it over the divide
onto the western slope. There could be some impacts over Vail Pass
Tuesday morning, as this cold front drops southward if the
NAMNest is correct, however timing and placement differences exist
between all the models leading to lower confidence in any one
solution. Overall thinking 2 to 4 inches of snow looks reasonable
for the northern and central Colorado mountains mainly above
9,000 feet, staying sub-advisory at this time.

Much drier air moves in behind this associated trough Tuesday
afternoon, pushing the moisture out of the region to the east with
some lingering showers and isolated thunderstorms possible along
the divide. Temperatures on Tuesday will be much cooler than
Monday, with below normal readings. High pressure moves back into
the region Wednesday and Thursday, resulting in a return to above
normal temperatures with warm and dry conditions.

Beyond Thursday, inconsistencies exist in the deterministic
models. The GFS is wetter with some warm advective precipitation
moving in from the southwest Friday afternoon as a trough of low
pressure moves into the Great Basin and across our region,
clipping the north Saturday evening into Sunday, with dry and
breezy conditions. The EC on the other hand, is drier with a ridge
of high pressure holding strong from mid-week through the weekend.
The ensemble guidance seems to favor this ridge of high pressure
with a drier and warmer pattern, so stuck to the drier and warmer
forecast until better consensus is reached.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 537 PM MDT Sun Apr 22 2018

Isolated light showers along the higher peaks will gradually
dissipate this evening with clearing conditions expected after
03Z. No significant impact is expected at terminal sites from
these showers with VFR conditions persisting through Monday
afternoon. A slight better chance for showers will arrive over the
northern and central mountains in western Colorado by Monday
evening as an upper level disturbance moves south through the
area.

&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...None.
UT...None.
&&

$$

SHORT TERM...MDA
LONG TERM...MDA
AVIATION...JDC


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