National Weather Service Forecast Discussion

000
FXUS65 KBOU 081556
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
856 AM MST Mon Mar 8 2021

.UPDATE...
Issued at 852 AM MST Mon Mar 8 2021

Water vapor imagery showing a weak upper level wave across Utah
and Arizona with a southwest flow aloft over Colorado this morning.
This wave has spread considerable mid and high level moisture
over the state leading to mostly cloudy skies. Based on timing
should be able to see decreasing cloudiness from mid afternoon
through evening from west to east. Given the thick cloudiness may
impact temperatures today so expect a few degrees cooling from
Sunday`s highs. Could see a few mountain showers but low level
moisture is lacking and with unfavored southwest mountain flow.
There is some concern for elevated fire danger across Lincoln
county this afternoon but with the cloud cover expect less mixing
with a result in less winds.

&&

.SHORT TERM...(Today and tonight)
Issued at 504 AM MST Mon Mar 8 2021

Southwest flow aloft continues to keep our area warm aloft (+5
degC over NE Colorado at 700 mb), and westerly downslope flow
will keep the warmth going today into Tuesday. There will however
be a fair amount of cloud cover today which may limit afternoon
max temperatures by 1-4 degrees compared to Sunday. Still, expect
mid to upper 60s most areas of the plains including the I-25 urban
corridor, and around 70 for the far eastern plains. It will
remain dry. The reason for the cloud cover this afternoon is a
weak short wave trough in the southern stream southwest flow.
Weak QG lift combined with upslope flow could lead to a brief
period of light snow above 9,000 ft this afternoon. Moisture is
very much lacking especially given much of the precipitation will
have already occurred across the southwest mountains of Colorado.
Thus, very little if any snowfall accumulation is expected today
in the higher mountains. The lift quickly departs such that any
light snow should be over by the evening hours.

On the backside of the weak trough, flow at 700 mb turns a little
more west and increases into the 30-40 kt range. Lapse rates are
not all that stable above ridgetops but weaken enough that some
wave amplification is possible down the east slopes. There is no
wind shear above ridgetop either so that may also help a little.
All that means that gusts to 35-50 mph are possible early Tuesday
from the Continental Divide down the east slopes, maybe as low as
the 7,500 ft elevation. Lows tonight will remain much above
average across the area for early March with 20s in the mountain
valleys and 30s to near 40 across the plains.

.LONG TERM...(Tuesday through Sunday)
Issued at 504 AM MST Mon Mar 8 2021

The first of a series of cold fronts will drop into northeastern
Colorado on Tuesday. It will still be a mild and dry day, but the
wind shift will take the edge off of it. We could still be near
Red Flag fire weather conditions south of I-70 before the wind
shift arrives. Probably just a couple degrees drop in the
afternoon, with the cooler air coming in overnight.

A shortwave passing north of us will drag a moisture band across
the northern mountains Tuesday night into early Wednesday. Models
differ on QPF amounts, but there`s a pretty good chance of light
snow in the mountains, and there could be a few showers over the
plains near the northern border, probably still rain on the plains
but cooling enough overnight for snow in the mountains. Another
shortwave will take a similar path later Wednesday, shoving a
strong temperature gradient aloft a bit further south over our
area. There will be a similar likelihood of light snow over the
mountains Wednesday night, with a little better chance of light
showers on the plains, either snow or a rain/snow mix. Shortwave
ridging ahead of the upstream system should provide a decrease or
break in precipitation Thursday, probably with a little more
cooling.

Now things get more interesting. There`s getting to be better
agreement now on a large upper low moving slowly from Southern
California Thursday across the southern Rockies Saturday and to
the central plains by Monday. There are still some differences in
the latitude and timing, but really given such a large, slow
moving system, they may not be that important. The main story is
that there`s a pretty good chance of a prolonged period of at
least light snow, and possibly a period of heavy snow, for most of
our area. The chance of significant snow looks greatest Friday
and Saturday from about Denver southward, though there are some
model solutions that have the significant precipitation further
north or have steady precipitation all the way from Thursday night
through Monday morning. Most model QPF for the Friday through
Saturday period ranges from 1 to 3 inches. There are heavier
solutions. It should be cold enough for this to be mostly snow, at
least at 5000 feet and probably across the area. It could be a
little warmer Thursday night and Friday for some rain mixed in,
but Saturday will be colder. If the system is as slow as most of
the models have it, Sunday won`t be much different although there
could be a transition to downslope winds near the Front Range to
reduce or end the snow. There could also be some wind as the low
moves east of the mountains, mainly Saturday into Saturday night
and maybe into Sunday on the plains that could exacerbate issues
with the snow.

We`re still having difficulty pinning down the location, timing,
and intensity details, but for now it`s appropriate to message
the increasing probability that there will be impactful winter
weather Friday through Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 852 AM MST Mon Mar 8 2021

VFR with considerable mid and high level moisture over the
terminals. Expect clearing from late afternoon/early evening with
this cloud deck and departing weak upper system. Surface winds
continue southwest this morning and expect a shifting to
southeast this afternoon. May see a bit of west to northwest push
later this afternoon, but not all that confident in that scenario
given cloud deck and less mixing expected.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
None.
&&

$$

UPDATE...Entrekin
SHORT TERM...Schlatter
LONG TERM...Gimmestad
AVIATION...Entrekin

NWS BOU Office Area Forecast Discussion