Area Forecast Discussion
Issued by NWS Grand Junction, CO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
FXUS65 KGJT 232119
AFDGJT

Area Forecast Discussion
National Weather Service Grand Junction CO
319 PM MDT Thu Mar 23 2017

.SHORT TERM...(Tonight through Friday night)
Issued at 300 PM MDT Thu Mar 23 2017

As of 2pm Thursday afternoon, the axis of a sharp trough at 500mb
was positioned over central Utah. This trough will continue to cut
off as it heads eastward through the central Rockies this evening
and overnight. At the surface, lee cyclogenesis has commenced
over the high plains of southern Colorado per latest surface
analysis. A subtle inverted trough axis extends north and westward
through the front range and into the central Rockies. Breaks in
cloud cover over Utah and western Colorado ahead of the 500mb
trough has allowed for slightly higher instability levels over the
region. Depending on your parcel of choice, anywhere from 250 to
500 j/kg of CAPE is apparent in latest SPC mesoanalysis in the
Canyonlands-Vernal corridor. Some convective cloud cover has begun
to develop on latest visible imagery over portions of Utah to the
east of the Wasatch range. Convective shower and thunderstorm
coverage should increase over all portions of eastern Utah and far
northwest Colorado. this evening as daytime heating is maximized
just ahead of the trough. Southern and western Colorado will also
see a few thunderstorms this afternoon, however morning and early
afternoon cloud cover has limited the instability in these
regions.

As the upper level trough cuts off and heads east through southern
Colorado, colder air will slowly filter in from the northwest this
evening and overnight. With the trough so far to the south of the
region, a `sharp` and distinct frontal passage seems less likely
area-wide. Rather...a gradual drop in temperatures, snow levels,
and instability will take place between 6pm and midnight across
the western slope. Precipitation will linger long enough in the
central and southern mountain ranges of Colorado for snow levels
to drop to around 7500`. Above 8500`, a general 2-5 additional
inches of snow are still forecast before precipitation ends on
Friday morning. Due to the convective nature of both the rain and
snowfall across the region, confidence is not particularly high
regarding precipitation totals. Areas that see one or more heavier
showers and thunderstorms could pick up as much as a half of an
inch of liquid from this event (including liquid equivalent
snowfall in the mountains, while some valleys that manage to
escape the heaviest showers may only see a tenth of an inch or
less. Not exactly the best of news for those looking for a soaking
spring rainfall event.

Friday will turn out mostly dry across the western slope of the
Rockies as the now vertically stacked storm system heads east
through the central plains. A few snow showers may linger in the
highest elevations of the central mountains before the last of the
moisture is scoured out. With lower 700mb temperatures and
northwest flow in place, high temperatures will be notably cooler
across the entire region, returning to near normal values for mid-
April.

.LONG TERM...(Saturday through Thursday)
Issued at 300 PM MDT Thu Mar 23 2017

The weather pattern will stay active through the weekend and into
early next week. Brief ridging will occur during the early morning
hours on Saturday before the next system spreads clouds and
eventually some showers into eastern Utah by afternoon. This
system has continued to trend slightly weaker and further north
over the past 36 hours of forecast model runs, leading to slightly
less confidence in the southern extent and depth of moisture.
Confidence is higher for some accumulating snow in the central and
especially northern mountains during the afternoon and overnight
Saturday. 700mb temperatures along and north of the I-70 corridor
will be in the -3 to -5 degree range. In the higher elevations
especially above 8000 feet, 3 to perhaps 6 inches of snowfall may
be possible with this event. Valley locations such as Grand
Junction, Montrose, and Durango will struggle with dry air at the
surface, and may only see a few showers - certainly less than
0.1" of rainfall is the mean for today`s guidance.

Forecast guidance begins to diverge after Saturday regarding
details for the remainder of the weekend and next week. The GFS
cuts off Saturday`s trough at 500mb over the central high plains,
slowing the system and allowing for some scattered snow showers to
linger in the Colorado Rockies through the day on Sunday. The
ECMWF is a bit more progressive and open with the wave, bringing
precipitation to an end around late morning. Guidance is in
agreement on a dry overnight on Sunday night into Monday morning,
but thereafter differences emerge again. The ECMWF is once again
more progressive, bringing cloud cover and showers back into the
region as early as Monday afternoon with the next storm system. By
Midnight Tuesday, the ECMWF depicts low pressure in southern
Nevada with precipitation over the entire west slope of Colorado,
while the GFS keeps the low pressure much further west in central
California and only a few showers into eastern Utah.

Both models eventually develop a strong closed upper level low
pressure system over the southwest, with an extended period of wet
weather along and to the south of Interstate 70 throughout the
day Wednesday and into early Thursday morning of next week. GEFS
and EPS ensemble guidance both indicate 500mb heights in the -1.5
to -2 sigma range with this third storm system. Temperatures
aloft will be cooler than lately, but not altogether cold through
the forecast period. Therefore, snow levels during precipitation
will likely remain no lower than 7500 feet. These marginal
temperatures will favor meaningful accumulations only above 8000
feet or so. Welcome rainfall for many valleys is certainly
possible next week - however details will need to be ironed out as
we go through the weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1153 AM MDT Thu Mar 23 2017

A storm system continues to approach the forecast area this
afternoon, bringing periods of showers and isolated thunderstorms
to the forecast area. Thunderstorms will remain a possibility
through this evening. Cigs should remain VFR through this through
this evening becoming MVFR overnight. Southwesterly winds will be
gusty as the cold front portion of this storm sweeps across the
area the area.


&&

.GJT WATCHES/WARNINGS/ADVISORIES...
CO...Winter Weather Advisory until 9 AM MDT Friday for COZ009-010-012-
     013-018-019.

UT...Winter Weather Advisory until 9 AM MDT Friday for UTZ023.

     Winter Weather Advisory until 6 AM MDT Friday for UTZ028.

&&

$$

SHORT TERM...MAC
LONG TERM...MAC
AVIATION...Larry


USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.