Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171159

Area Forecast Discussion
National Weather Service Denver/Boulder CO
459 AM MST Sun Feb 17 2019

.SHORT TERM...(Today and tonight)
Issued at 459 AM MST Sun Feb 17 2019

Colorado is in a break between two shortwaves this morning, though
we remain under the broader longwave trough with pretty cold air
aloft. There is a little batch of moisture producing some showers
mainly over the higher ridges right now. Some of this could
persist, though it shouldn`t add up to too much.

Lift ahead of the next wave will spread into western Colorado
today, sucking the cold moist air over Nebraska back into
Colorado. Steady east winds will develop by afternoon, both
advecting cooler moist low level air and producing upslope into
the Front Range. Meanwhile the lift and associated moisture should
be reaching Denver by around sunset. All of this coming together
should result in the development of widespread snow over the east
slopes and adjacent plains in a few hours, probably during the
early evening. We can`t say that rush hour is completely safe, but
it doesn`t look like the snow will be going in earnest over Denver
until the evening. Better odds of some snow in the foothills
during rush hour for those headed that way.

Cool moist air will be lifted over the low level cold air all
night long, which should produce steady light snow across most of
the area, with some upslope enhancement from Park county north
along the east slopes of the Front Range. The direction looks
fairly easterly, but our southern areas should be favored by a bit
stronger lift. The wind direction may help keep snow going up
around Larimer and Weld counties which may be on the fringe of the
better lift. Less of everything toward the northeast corner, but
it will still probably snow lightly for a while. The area that
might miss out is west of the Front Range where there will be some
downsloping undercutting the synoptic scale lift. Probably still
some light snow there as well, but amounts could be pretty light.

Consensus precipitation amounts plus a bit of upslope enhancement
and fluffy 20:1 snow ratios given good temperatures and the good
lapse rates aloft suggest 3-7 inches in the foothills by midday
Monday, with 2-4 for the Front Range cities, and less as you go
northeast. Forecast temps look pretty good, with mostly 20s during
the day and then falling to single digits by Monday morning.

.LONG TERM...(Monday through Saturday)
Issued at 459 AM MST Sun Feb 17 2019

Models have an upper trough axis to the west of Colorado on
Monday and Monday night. It gets into western Colorado on Tuesday.
The upper trough axis is right over the CWA on Tuesday night.
Moderately strong southwesterly jet level flow will be in place
for CWA Monday into Tuesday evening, then it will decrease. The QG
Omega fields show upward vertical velocity for the CWA Monday
into Tuesday evening. Downward energy is place after that all
Tuesday night. The low level winds are easterly early on Monday,
then they are southeasterly Monday afternoon well into Tuesday. By
Tuesday afternoon a Denver cyclone is progged. Later Tuesday
night, some sort of weak drainage pattern tries to kick in.
Moisture is a bit tricky, certainly from one model to the next.
Monday has pretty decent moisture early, then the lowest levels
dry out a bit during the afternoon. Moisture deepens up again
Monday night into Tuesday. The NAM dries out a bit Tuesday
afternoon, the GFS does not. The QPF fields have limited amounts
of measurable snowfall for much of the CWA Monday through at least
Tuesday evening. Will increase pops a bit Monday into Tuesday
night. At this time, there doesn`t appear to be enough snow
accumulations anywhere across the CWA to warrant highlights. For
temperatures, Monday`s highs will be 4-8 C colder than today`s
highs. Tuesday`s highs will only be a tad warmer than Monday`s For
the later days, Wednesday through Saturday, the medium range
models keep a mean upper trough over the western U.S. into Friday
night. There is weak upper ridging on Saturday for Colorado. The
airmass will remain colder than normal all four days. For
moisture, it increases later Thursday and continues fairly deep
over the CWA through Friday night. Saturday dries out somewhat. It
will also be the warmest day, but still below normals.


.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 459 AM MST Sun Feb 17 2019

VFR conditions most of today, but lower ceilings are expected with
snow developing between 22z and 02z for areas of MVFR. Conditions
will continue to lower during the evening, with widespread IFR and
localized LIFR by 06z. Those conditions will continue into Monday
morning, though some improvement is expected before 18z.




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