Area Forecast Discussion
Issued by NWS Grand Junction, CO

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FXUS65 KGJT 202333

Area Forecast Discussion
National Weather Service Grand Junction CO
433 PM MST Mon Jan 20 2020

.SHORT TERM...(Tonight through Tuesday night)
Issued at 304 PM MST Mon Jan 20 2020

Satellite depicted a broad shelf of cirrus over the forecast area
while surface observations over southeast Utah and southwest
Colorado indicated some mid-level clouds began to push
northeastward over the area. A mid-level ridge of high pressure
was over the region early this afternoon while a trough of low
pressure was approaching the West Coast. Moisture streaming out
ahead of the trough was responsible for the clouds moving into the
western half of the ridge.

As the ridge axis is forced east of the Continental Divide by the
trough over the eastern Pacific moisture deepens this evening with
light showers developing late, mainly over the San Juan Mountains
and the eastern Uintas of northeast Utah. Later tonight, lift
provided by a mid-level shortwave trough in concert with the left
exit region of the 140+ KT subtropical jet will result in
widespread showers developing over southeast Utah and southwest
Colorado. Some of this energy will be lost to moistening the
subcloud layer limiting snowfall accumulations. In addition, mild
temperatures during the early phases of this storm suggest lower
snow ratios.

Shower coverage spreads north on Tuesday as the shortwave
mentioned in the previous paragraph transits eastward over the
forecast area. Model QPF output not all that impressive, though
snow, with mixed precipitation and rain in the lower valleys, will
be fairly widespread during the day. Finally, another low-
amplitude mid-level shortwave moves across the area resulting in a
shift to northwest flow. This will continue to bring precipitation
to the area throughout the day.

As per the previous shift, snow totals don`t yet warrant
highlights based on accumulations coming out of the models at this
point. Overnight lows tonight and Tuesday night will benefit from
cloud cover and, as a result, expect lows will be milder than
over the past couple of days. In contrast, highs on Tuesday will
be inhibited by cloud cover, but still won`t be much colder than
normal for this time of year.

.LONG TERM...(Tuesday night through Sunday)
Issued at 354 AM MST Mon Jan 20 2020

A secondary shortwave dipping across the northern Rockies Wednesday
morning will generate another round of showers sweeping mainly
across the northern half of the CWA. Once the trough axis passes to
our north, precipitation will favor the Elkhead, Park, Gore and Flat
Top ranges, where an additional 2-4 inches is possible by Thursday
morning. Light, orographically driven showers will continue across
higher terrain once the region falls under northwest flow. However,
most of the CWA can expect dry and quiet weather by Wednesday
evening as a ridge of high pressure builds over the Great Basin.

A general warming trend and dry weather pattern is expected as we
end the workweek. Meanwhile, a low pressure system stewing off the
PacNW will send another pulse of energy ashore Friday. This
shortwave will help transport the ridge axis overhead and leave the
area under zonal flow at mid levels. Models are not depicting much
moisture tied to Friday`s wave, so we`ll likely see more passing
cloud cover than precip reaching the ground. The next best chance
for widespread precipitation appears to reach eastern Utah by Sunday
night into Monday. So, anticipate benign weather and near normal
temps this weekend with an active pattern returning by Monday.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 432 PM MST Mon Jan 20 2020

A weather disturbance and upper level jet approaching the Four
Corners region will bring increasing chances of scattered snow
showers overnight, becoming more widespread by sunrise Tuesday.
Light snow and low stratus clouds may impact southern TAF sites
initially, including KDRO and KTEX, before spreading north-
northeast. Expect periods with conditions dropping below ILS
breakpoints during morning hours, with conditions improving
midday. However, chances of showers will persist into Tuesday
afternoon for mountain sites.




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