Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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911
FXUS65 KBOU 231219
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
519 AM MST Wed Jan 23 2019

.SHORT TERM...(Today and tonight)
Issued at 519 AM MST Wed Jan 23 2019

A quick moving trough in moderate NW flow aloft will move over
Colorado tonight. Models are fairly similar but the differences
will matter. The GFS is a bit stronger with the wave and manages
to turn the low level flow slightly upslope into Denver early
Thursday, producing a few hours of light snow. Other models
struggle to get the low level winds around to northerly and have
the Front Range cities sheltered in low level downslope, with some
showers on the plains. Hard to say which one is correct, other
than to note that there will be general downsloping northwest flow and
any upslope that develops should be shallow, and that the QG
forcing is fairly weak. Our previous forecast splits the
difference on this and that still seems a reasonable place to be.
There will probably be some places that get an inch of snow, or
maybe two, but it`s not clear if the focus will be on the plains
or the Denver area. Whatever happens will be quick and probably
come with 30 mph wind gusts for a few hours.

For the mountains, the moisture looks to be slow coming today, as
the low levels are still dry across southwest Wyoming. The initial
moisture will also be under an inversion, which should limit the
snowfall most of the day. There should still be a period of decent
orographic snow this evening as the cooler air moves in. Again,
the QG lift is not great and the deep moisture is probably not
there for long, but there should be at least a few hours of
moderate snow. The advisory looks solid for the Park Range, it may
be more marginal for the rest of the northern mountains. For now,
we`ll just push back the start time to 2 PM this afternoon and
tweak the snow amounts to favor the Park Range.

First things last--downslope west winds are already becoming
widespread across the plains which will warm temps this morning.
Cloud cover should eventually limit the heating though. Current
temp forecast looks good, we delayed the clouds a few hours.
Strong winds with a bit of wave amplification in the higher
foothills should diminish with the wave breaking down this
morning.

.LONG TERM...(Thursday through Tuesday)
Issued at 519 AM MST Wed Jan 23 2019

Models keep the CWA on the back side of a mean upper trough
Thursday through Friday night. There is strong northwesterly flow
aloft through the period. The QG Omega fields have mostly downward
synoptic scale energy over the CWA through Friday night. The low
level winds start out northeasterly Thursday morning. By afternoon
they are weak and southeasterly. Normal diurnal patterns kick in
Thursday night and continue Friday. Friday night`s winds are
downsloping northwesterly for most areas. For moisture, models
show fairly deep cloudiness over the CWA much of Thursday. From
Thursday night through Friday night, there is still some moisture
in the mountains, and some in the mid and upper levels over the
plains. Overall the northwesterly flow aloft keeps cloudiness over
the CWA much of the time. The QPF fields have some minor
measurable snowfall amounts over much of the CWA into Thursday
afternoon. After that, snow is relegated to the high mountains on
the QPF fields Thursday night through Friday night. For pops, will
keep the 30-70%s going in the mountains all four periods due
mainly to the orographic enhancement. Will leave the Snow
Advisory going over the mountains into mid day Thursday. Will
leave, "chance"s for snow going over the plains, mainly Thursday
morning. For temperatures, Thursday`s highs are 3-7 C colder than
today`s highs. Friday`s readings come up 2-6 C from Thursday`s
highs. For the later days, Saturday through Tuesday, the huge
upper trough is still in place over much of the U.S. all for days.
On Monday a significant piece of energy moves down the back side
of the upper trough. There is strong northerly flow aloft on
Saturday, then strong northwesterly flow aloft on Sunday. It is
still quite strong on Monday but more due westerly. There will be
some moisture to move in late Sunday and Monday. Temperatures will
warm up above seasonal normals on Sunday, but cool off again
Monday and Tuesday. Will go with a chance of snow Sunday night and
Monday, but nothing significant at this time.

&&

.AVIATION...(For the 12Z TAFS through 12Z Thursday morning)
Issued at 519 AM MST Wed Jan 23 2019

VFR through this evening. West winds may gust as high as 20 knots
at KDEN/KAPA, while KBJC will have gusts to 30 knots. The west
winds should diminish this evening. A cold front will bring north
winds gusting to 20 knots and a chance of snow showers and MVFR
conditions after 09z Thursday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 2 PM this afternoon to 11 AM MST
Thursday for COZ031-033-034.

&&

$$

SHORT TERM...Gimmestad
LONG TERM...RJK
AVIATION...Gimmestad



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