National Weather Service Raw Text Product

038 
FXUS65 KBOU 101736
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1036 AM MST Wed Feb 10 2021

.UPDATE...
Issued at 1020 AM MST Wed Feb 10 2021

The 12Z DNR sounding showed that the low level cold air was the
deepest of the previous three days and that is likely the reason
for low clouds continuing to cover all of the eastern plains and 
urban corridor. Considering mixing has done very little to erode 
the clouds this morning, the low clouds should last well into the 
afternoon and keep temperatures down. Highs were lowered a few 
degrees and light snow showers were added to the forecast. We are 
even seeing some refinery-effect snow most prevalent downstream of
Commerce City. The snow might be enough to the make the ground 
white but won't accumulate to anything more than a half an inch. 
There's not much snowfall occurring in the mountains so all signs 
point to allowing the advisory to end at 11am. 

&&

.SHORT TERM...(Today and tonight)
Issued at 440 AM MST Wed Feb 10 2021

A wash, rinse, and repeat forecast is on the menu for the plains 
today. The shallow arctic airmass continues to sit over the 
northeast Colorado plains, as an elongated high pressure system 
remains nearly stationary over the northern Rockies and central 
Great Plains. There's enough moisture near the surface for patchy 
fog this morning, and low clouds elsewhere. Should see fog slowly 
dissipate through the morning hours with low clouds retreating 
back towards the east during the day. Today's highs will be very 
similar to Tuesday, with highs in the 10s to 20s for most of the 
plains and the 20s to near 30 for the metro and the rest of the 
urban corridor. Above the shallow cold air, the foothills will 
once again be much warmer than the plains, with highs in the upper
30s to 40s. Could see a few spots in the southern Foothills or 
Palmer Divide make it to the low 50s too. With high pressure 
anchored to the east, winds will remain light and generally out of
the east through the day. 

Overnight lows tonight will unsurprisingly be largely similar to 
the past couple nights, with lows near 0 over the far northeast 
and the low 10s for the urban corridor. The main question for the 
overnight hours will be what happens with yet another round of low
stratus/fog. Cross-sections are a little drier, especially as you
get closer to the foothills, and I would suspect that there's 
slightly less low cloud cover around. There's still a shallow 
moisture layer that should support patchy fog again. There should 
also be a few flurries in our far east where the deepest moisture 
is. If cloud cover isn't as expansive, we could see lows in our 
far northeast drop below zero, but I'm hesitant to bet against low
clouds with this current pattern. Otherwise, the forecast is 
nearly a copy and paste from yesterday.

Meanwhile, over the mountains, light snow will continue through 
the day today and into the night. Webcams early this morning have 
shown the best accumulations falling over the Park Range, with 
lighter amounts as you head south towards Summit County. This will
be the theme through most of the day today. Generally light 
accumulations... on the order of just a few inches... are expected
by late tonight. Can't rule out snow showers continuing through 
the overnight hours as shallow moisture and upslope flow still 
remain overhead.

.LONG TERM...(Thursday through Tuesday)
Issued at 440 AM MST Wed Feb 10 2021

We'll make one more attempt to erode the west edge of the cold air
early Thursday, though there probably won't be much progress. By
Thursday afternoon there will be pressure rises on the plains
again and another westward surge of the cold air will be underway.
We trimmed highs a little for Thursday along with more
clouds/flurries/areas of fog in the morning.

We're getting more confidence for this weekend as models are
converging on the upper air pattern and the strength of the cold
air on the plains. There's still some uncertainty with the
position of the low over or west of Lake Superior Saturday and the
resulting focus of the cold high pressure dropping southward.
There's really good agreement now that the real arctic front will
come all the way into Denver by Saturday, with some runs now pushing
it westward late Friday. But there's also decent agreement that
the coldest of this air will slide east of Colorado as it usually
does due to the height of the terrain. It's still a shallow cold
air mass, with westerly flow continuing at 700 mb the whole time.
We're also seeing increasing confidence that there will be a fair
amount of moisture in this westerly flow to provide cloud cover,
and a weak low developing south of Colorado by about Sunday to
provide some warm/moist advection aloft. All this points to cold
temperatures, but probably too much cloud cover and moisture for a
clear and really cold night. There are still a few model runs that
have lows near -20 across the plains including Denver either
Sunday or Monday morning, but this looks unlikely. The
cloudier/moister solutions would likely have cloudy skies and
flurries with single digits above or below zero most of the time
from Friday night through Sunday night. There's an opportunity for
increased but still light snow with a shortwave Friday night, and
then with the warm advection lift over the cold air on Sunday.
Either of these could give a widespread inch or two of snow.

For the mountains, moderate westerly flow continues with varying
moisture depth and periods of weak QG lift as the shortwaves pass.
Thursday night and Friday night look like periods with a bit more
snow, and the snow/wind combo may need advisories. There should be
a bit less wind over the weekend with light snow still likely.

There's a bit more agreement for the early part of next week, with
the trough axis shifting east of us and northwest flow aloft
setting in. How much warming we get, the moisture content, and
embedded shortwaves still vary quite a bit. Most of the models
would suggest continued mostly light orographic snowfall with 
more wind again, and a chance of showers on the plains with the
shortwaves. Our model blend seems appropriate here, but we did
drop the temperatures a couple degrees Monday in case we're slower
to flush out the cold air or have enough snow cover to hold
temperatures back.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1020 AM MST Wed Feb 10 2021

Fog has eroded this morning and will not be an issue for the rest
of the daylight hours. A stratus deck will keep ceilings in the 
IFR or LIFR into the afternoon. There is low confidence in when 
this stratus deck will break up but indications are still the mid 
afternoon. Another stratus/fog deck appears likely to move back in
after midnight tonight. Similar conditions to this morning will 
occur with IFR/LIFR ceilings and visibility. Winds will be rather 
light during the entire TAF period. 

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST this morning for COZ031-
033.

&&

$$

UPDATE...Danielson
SHORT TERM...Hiris
LONG TERM...Gimmestad
AVIATION...Danielson