Area Forecast Discussion
Issued by NWS Grand Junction, CO

Home | Current Version | Previous Version | Graphics & Text | 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

FXUS65 KGJT 141008

Area Forecast Discussion
National Weather Service GRAND JUNCTION CO
408 AM MDT Wed Mar 14 2018

.SHORT TERM...(Today through Thursday)
Issued at 408 AM MDT Wed Mar 14 2018

Some low and mid level clouds are seen on satellite and being
detected via observations across portions of the forecast area,
with high clouds seen to the west across much of Utah entering
into eastern Utah this morning. Expecting high clouds to encompass
much of the region by afternoon. There will be some periods of sun
but the cloud cover will have an impact on stronger winds aloft
mixing to the surface. Temperatures are expected to be warm again
despite the increasing cloud cover with 10 to 15 degrees above
normal, but a few degrees shy of record highs. Low 70s look to be
most likely across southeast Utah along with the strongest winds,
where winds could gust in the 30s. Elsewhere, latest guidance
indicates gusts reaching the 20s at times, probably a result of
the increased cloud cover. Therefore, decided not to issue any
wind advisories with this forecast package. Moisture increases
quite a bit today as specific humidity values rise above 4 g/kg
and precipitable water (PW) values rise upwards of 0.5 inches
across eastern Utah and extreme western Colorado near the Utah
border. Showers and thunderstorms are not expected to develop
until mid to late afternoon across the higher terrain of eastern
Utah before spreading across western Colorado by evening and into
some adjacent valleys. Due to presence of drier low levels, virga
under any showers could result in stronger wind gusts to 40 mph,
especially across northeast Utah where low CAPE and steep lapse
rates support the potential for stronger storms today. Coverage
this afternoon looks isolated to scattered, becoming more
widespread by Thursday.

The upper level trough and cold front will move through the region
from southwest to northeast Thursday, bringing with it cooler air
and better chance of widespread showers and thunderstorms as lapse
rates remain steep upwards of 8 to 9 degrees C/km with 200 to 400
J/kg of CAPE. This convective environment makes forecasting
snowfall tricky as banding is expected to set up in some areas.
There will be some areas that receive heavier precipitation, while
other areas see next to nothing. Large scale ascent increases over
southwest Colorado and progresses northeast through central
Colorado into northeast Colorado as this trough moves through. So
the San Juans look favored for the better snowfall amounts with
the central Colorado mountains coming in second place. The flow
remains southwesterly throughout most of this event which favors
these areas. Moisture does decrease on Thursday as the cooler air
arrives, with PW dropping to less than 0.3 inches by afternoon
and specific humidity in the 2 to 3 g/kg range. H7 temps will be
in the 4C to 6C range today, dropping to the -3C to -6C range by
Thursday afternoon and ending up in the -6C to -8C range by
Thursday evening. This is not sufficiently cold air as the polar
jet never sinks southward, and the flow never switches around to
northwest as another system develops out west. Overall, expecting
snowfall amounts to be sub-advisory overall with 3 to 6 inches on
average across some mountain areas. There may be some areas that
see locally higher amounts due to convection and where banding
sets up. As far as the valleys are concerned, looks like precip
type will remain rain for the majority of this storm with
potential for some good wetting rain in some areas. By the time
temps get cold enough to change any liquid over to snow Thursday
night, the system will be gaining momentum over the Front Range
with drier air moving into our CWA, resulting in a dusting at

.LONG TERM...(Thursday night through Tuesday)
Issued at 408 AM MDT Wed Mar 14 2018

The bulk of precipitation from the next Pacific trough should
move through eastern UT and western CO Thursday evening when the
surface cold front pushes through. Supporting the front will be a
developing shortwave trough and jet speed maxima which passes over
the Four Corners overnight. Friday will be an in-between day
under NW flow aloft and decreasing moisture. This quickly gives
way to the influence of the next trough. On Saturday, a broad
closed low moves from the western Great Basin to the northern
Rockies and pushes another cold front through the area sometime
between Saturday night and Sunday afternoon, depending on which
model you believe. Another shortwave trough moves through behind
this front on Sunday, keeping precipitation going mainly in the
mountains. Monday and Tuesday will be drier as high pressure
dominates. There are some timing and track discrepancies between
models with the GFS being most progressive and the ECMWF and
Canadian holding off until Sunday when most the precipitation is
expected. There are some hints next week of another stronger
system potentially impacting the area towards the latter half of
the week, but the models are in large disagreement on how far
south this will extend. Confidence for Sunday through next week is
lower due to model inconsistencies, so will like to see more
agreement before buying off on this moisture potential.


.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 408 AM MDT Wed Mar 14 2018

Clouds will increase from the west this morning, becoming broken
to overcast in most areas by afternoon. Winds will become breezy
with gusts in the 20s for most areas with gusts in the 30s across
eastern Utah. Isolated to scattered thunderstorms are expected to
develop over the higher terrain, especially over eastern Utah by
late afternoon, with showers spreading across western Colorado by
this evening. Some isolated showers and storms may linger past
midnight through Thursday morning, with more widespread
precipitation expected after 12Z Thursday.




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