Winter Weather Advisory 6, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
311 PM MST Wed Feb 3 2021

.SHORT TERM...(This evening through Thursday)
Issued at 311 PM MST Wed Feb 3 2021

Banded convective snow showers have blossomed across the northwest
third of Colorado over the last few hours. The increase is largely
instability driven, as the original snow bands associated with the
deeper cold front are still 100-200 miles further northwest. There
have been pretty strong wind gusts in the 50-60 mph range with
some of the showers, in general the wind is about half that. The
main shower bands are also producing snowfall rates of around an
inch per hour.

Given that the best bands this afternoon look to be directed
toward the central mountains especially southern Grand and Summit
counties spilling a few miles over the Divide, we'll go ahead and
issue a Winter Storm Warning just for that zone. The same areas
will also do relatively well with the postfrontal orographic snow
later tonight. The advisory for the other high mountain zones
still looks appropriate, while the valleys and foothills will have
more transient snow showers with some accumulation. One other area
still to watch is west and southwest of Denver during rush hour.
Totals shouldn't wind up being that high, but several inches in a
few hours could still make those roads interesting for a while.
There's a lesser threat of the same thing happening south of
Denver later this evening, but the prefrontal showers will be over
air that should still be pretty warm for snow and ice, and then it
will be getting late and the interface of the trailing bands and
the decent upslope winds may just be a couple of hours.

Elsewhere, it's warm with weak showers trying to get through the
dry air, then cold enough for snow by late evening but fighting
downslope across most of northeastern Colorado. Again areas
further south have a better chance of getting a little snow.

We should clear out pretty well around sunrise, though some light
snow over the ridges may continue through the morning. Strong
winds aloft will mix down again by midday so it will be cool and
breezy. Previous forecast temperatures still look alright.

.LONG TERM...(Thursday night through Wednesday)
Issued at 311 PM MST Wed Feb 3 2021

Strong northwesterly flow aloft should be over Colorado later
Thursday night behind a weak upper trough. Later that night
through Friday into Saturday morning a 90-130 knot jet max will be
over the forecast area. Some weak lift is progged on Friday due
to that jet. The mountain top winds look pretty strong in the
cross sections, but the moisture in the mountains is just fair.
There will be some orographic snowfall, with the best amounts in
Zone 31. Perhaps amounts there could reach advisory levels on
Friday and Friday evening. Amounts over the rest of the mountains
are not very significant. There still should be enough snowfall
to cause winter driving conditions. There should be some decent
mid and upper level cloudiness for the plains on Friday but
precipitation is not expected with the dry lower levels and the
downsloping northwesterly winds. Cross section do indicate a
mountain wave set developing later Friday night on into Saturday.

On Saturday, the downsloping flow is pretty strong, with a mountain
wave set up in place. The downsloping could get strong enough to
warrant highlights by afternoon on Saturday, at least in the
foothills. We will continue to monitor this.  There is still a
little alpine moisture around Saturday, then the CWA looks pretty
dry through Saturday night. Temperatures look to be a bit colder
than normals on Friday, with only a slight warm-up for Saturday's
readings.

For the later days, Sunday through Wednesday, the current medium
range models show an upper trough over a good portion of North
America. There are some weak areas of lift around through the
period, with the models not agreeing to well right now on exactly
when. Some things the models agree on is that we should be under
under a fairly cold airmass. So below normal temperatures can be
expected. There will also be periods of upslope flow east of the
divide. The moisture is not very deep however. So some chance of
snow here and there as well as cold Monday through Wednesday.
Nothing significant at this time.

&&

.AVIATION...(For the 00Z TAFS through 00Z Thursday evening)
Issued at 311 PM MST Wed Feb 3 2021

Winds will become northerly this evening, with gusts to around 30
knots. Scattered rain and snow showers will develop early this
evening, with a few hours of snow showers likely 04z-08z and areas
of IFR visibilities in the showers. Most places will have an inch
or less, though locally heavier showers are expected south and
west of Denver. Quick clearing is expected between 08z and 12z
with lighter winds.

VFR for Thursday, with north to northwest winds gusting up to 30
knots developing around 18z.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Storm Warning until 9 AM MST Thursday for the central
mountains...COZ034.

Winter Weather Advisory until 9 AM MST Thursday for the northern
mountains...COZ031-033.

&&

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