Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/15/19

Area Forecast Discussion

National Weather Service Denver/Boulder CO

 853 PM MST Thu Feb 14 2019

.UPDATE...
Issued at 850 PM MST Thu Feb 14 2019

Confidence is lower in seeing freezing drizzle or rain this
evening over the urban corridor and eastern plains after reviewing
the newer guidance, as well as the current conditions. Lower
clouds are forming near the foothills in the upslope flow, and
beginning to spread east, while 0.5 degree radar echoes are
increasing from the south. This would point to more possible ice
crystals for a seeder-feeder process being able to form snow,
rather than freezing drizzle. Viewing recent ACARS soundings from
aircraft, there is a little warm layer around 700-750 mb which is
above 0 degrees C, with below freezing on top and below. All of
this together makes me think if precipitation does form, it should
arrive at the surface as snow or sleet. I can`t totally rule out
some localized spots of drizzle, but confidence is less in seeing
it this evening. The better chance to see this is farther east,
over the northeast plains.

Another confusing point, is the 00z NAM shows precipitation around
the Urban Corridor and nearby plains between 09-12Z, however the
westerly downslope winds will be increasing at this point as well
as QG ascent weakening and become downward motion. So confidence
in this model is low.

Snow continues to increase over the mountains with visibilities
lowering and roads becoming more snowcovered via webcams. Winter
weather advisory is now in effect until tomorrow morning. Snow
should be heaviest for about the next 6 to 8 hours before trending
down.


&&

.SHORT TERM...(This evening through Friday)
Issued at 242 PM MST Thu Feb 14 2019

Snow will increase again late this afternoon and early evening
over the north central mountains as the next Pacific wave hits the
state. Radar showing a large area of precipitation over the Four
Corners area. Moisture will continue to stream east-northeast into
the state through the night. Even with the unfavorable southwest
upper level winds, expect enough moisture and forcing to produce 4
to 8 inches of snow across the north central mountains. Will
continue the Winter Weather Advisory for this.

Challenging forecast for the Front Range Urban Corridor and
eastern plains for tonight. The models are doing a very poor job
resolving the cold front and the amount of cold air behind it.
Even the HRRR has been quite bad. The 18Z HRRR temperature 2HR
forecast (for 20Z) was 16 degrees off. Feel confident temperatures
will be below freezing across northeast by the time precipitation
forms. This will lead to snow or freezing drizzle/freezing rain.
There may be two mechanisms for precipitation. First, scattered
precipitation is expected to move off the mountains and across
eastern Colorado. This will fall as snow, unless there is a layer
of above freezing temperatures above the cold surface. A few
models show this, most don`t. A deeper layer of saturated air near
the surface may form due to the cold and moist air and produce
freezing drizzle. Models don`t show this happening, but with this
airmass being colder and deeper than the models forecast, can`t
rule out freezing drizzle. Will add this to the forecast.
Precipitation amounts over eastern Colorado will be light with
snowfall around an inch or lees.

It will quickly dry out behind this system Friday morning with
sunny skies for most of the area by late morning. Some moisture
will get trapped against the mountains and produce cloud and light
snow Friday. Windy conditions are expect late tonight and Friday
in the foothills where gusts to 50 mph will be possible. Models
indicate the cold air will scour and shift off to the east.
Somewhat skeptical about the amount of warming over the plains and
especially for the low lying area across the plains. Lower
temperatures some, but still expect a mild day.

.LONG TERM...(Friday night through Thursday)
Issued at 242 PM MST Thu Feb 14 2019

For Friday night into Saturday, a low center off the Pacific NW
coast will bring a 180+ kt jet around the base of the trough into
the Great Basin late Friday. With the region being under the better
lift of the LER of the jet, QG values are higher with good
instability into Saturday morning. This will bring another decent
shot of snow to the mountains early Saturday with gusty winds
through the day. Over the plains, a deep lee side sfc low will keep
precipitation at bay through the majority of the morning Saturday
with a slight chance of snow with the help of a cold front dropping
South by the afternoon. Surface winds will generally be from the NW
to W that will increase downsloping effects along the front range
and could keep most of the precip more over the eastern plains.
Highs for Saturday will be in the 40s with lower temperatures over
the eastern plains.

For Saturday into Sunday, the upper disturbance will continue to
push through the state with the GFS slightly slower than the EC.
Snow will continue in the mountains but will come to an end
gradually over the far eastern plains as the surface low slips SE
across the OK panhandle. A deep low will transition across the
northern portions of the CONUS pushing the jet across the South.
this will keep the state under NW flow with weak moisture. This will
allow for a slight chance of snow in the mountains through Sunday
with highs in the lower 30s and overnight lows in the teens on the
plains.

For next week conditions will become colder with an arctic push from
the NW. Sunday into Monday an upper level low over southern CA will
begin to move eastward  as a secondary system over the northern
rockies moves SE. Models show the best QG ascent and lift across the
southern rockies with decent moisture in the lower and mid levels
from SW flow aloft. This will bring snow to the central and Southern
mountains of the State starting overnight into Monday. For the
plains, cold, surface high pressure will be south with winds
transitioning to a NE direction and increase upslope flow along the
foothills Monday morning. This will increase chances of light snow
for the plains. With little jet support and the main QG south,
expect light snowfall amounts on the plains. Temperatures Monday and
through Thursday will start to reflect this cold push with highs in
the 20s and low 30s with overnight lows in the single digits. By
Monday night into Tuesday, the secondary trough will push SE from CA
and move across the state Tuesday morning. Models are showing decent
moisture from the SW but with surface winds from the SE, upslope
flow will be limited so only expect light accumulations. By
Wednesday, the trough will have pushed through drying out conditions
and leaving the colder air in place.

&&

.AVIATION...(For the 00Z TAFS through 00Z Friday evening)
Issued at 850 PM MST Thu Feb 14 2019

Low clouds are expected to form after 04Z, with ceilings falling
below 1000 feet. There will be a chance for snow, with a tiny
chance of seeing freezing drizzle as well. Precipitation is
expected to be light. Low clouds and possible fog will move in as
a Denver Cyclone wraps in the moisture and last through most of
the night into the early morning hours. Dry air quickly moves in
Friday morning helping to clear skies out. The low clouds should
scatter out by 15Z.


Gusty east winds will continue at the Denver airports through
04Z before winds turn northerly direction behind a Denver Cyclone
that will develop somewhere around southern suburbs, then shifts
east of the area. For Friday, light winds are expected during the
morning with gusty west winds possible after 16Z.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM MST Friday for COZ031-033-034.

&&

$$

UPDATE...Kriederman
SHORT TERM...Meier
LONG TERM...Bowen
AVIATION...Meier/Kriederman