National Weather Service Forecast Discussion

000
FXUS65 KBOU 102224
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
324 PM MST Mon Dec 10 2018

.SHORT TERM...(This evening through Tuesday)
Issued at 320 PM MST Mon Dec 10 2018

Deepening of an upper trough over the coast of CA has amplified the
ridge over CO bringing mild temperatures and party cloudy skies.
Increasing moisture ahead of the trough with mountain top
stabilization will continue to increase mountain waves over the
eastern foothills and adjacent plains. Mid and high level moisture
will increase through the evening as the trough continues to track
east. Clouds overnight as well as a deepening lee side low will help
to keep temperatures warmer with lows in the lower 30s on the plains
and teens in the mountains.

For Tuesday, the upper trough is projected to impact western CO by
the morning hours with pretty weak moisture and mild lift. This will
bring a slight chance of light snow showers to the higher terrain by
the early afternoon hours. Accumulation is expected to stay under a
few inches. Behind the trough moderate subsidence will help to
increase winds over the mountains and eventually the plains by the
afternoon hours. Model cross sections show cross barrier flow of 60+
kts by 15z with some amplification that could bring increased winds
to lower elevations of the NE plains for the afternoon and early
evening hours. Sustained winds of 20 to 25 mph with gusting in the
30 to 35 mph range will be possible East of a line from Wyoming to
Akron through 5 to 6 pm. Temperatures tomorrow will be mild once
again with highs in the mid 50s on the plains and 30s in the high
country.

.LONG TERM...(Tuesday night through Monday)
Issued at 320 PM MST Mon Dec 10 2018

Weak mid-level shortwave trough will be by the forecast area by
Tuesday evening. Subsidence and drying will exit behind the
trough which equate into gusty west winds mountain tops and higher
Front Range foothills, particularly up along the Wyoming border.
On Wednesday, should see zonal flow aloft strengthening through
the day together with warming aloft in advance of the next
shortwave pertabation driving southeastward out of the Pacific
Northwest. Leeslope troughing and slight amplification of the
mountain wave will equate to gusty west-southwest winds 40-45 mph
on mountain tops and upper east slope of the Front Range. Will see
warmest daytime temperatures at the base of the foothills with
highs in the low-mid 50s, with a steady drop out moving out away
from the I-25 corridor. Cross sections do not indicate much in the
way of cloud cover until the afternoon with mid and high-level
moisture streaming in within the warm sector of the upper trough
digging over Utah. Model QPF fields indicate light precip amounts
popping up over the northern mountains around 21z/Wednesday.
During the next few hours the passage of a tight baroclinic zone,
i.e., cold frontal boundary, could initiate a round of moderate
snowfall in areas generally along and west of the Continental
Divide. Travel over the higher passes could become a bit dicey for
a few hours with cold air advection. GFS appears most bullish
with snow totals by midnight MST Wednesday night running anywhere
from 5-6 inches in the Park and Rabbit Ears Ranges, to 1-3 inches
on ranges farther south. East of the mountains, GFS, ECMWF and
Canadian still indicate areas of light QPF mid to late evening
with the main batch of QG ascent associated with the upper trough
passing over head. Snow amounts on the look scanty at best.
Snowfall rates in the high country are expected to fall off after
midnight, although CAA and orographic forcing may keep light snow
showers going on northwest facing slopes until morning light.

Thursday and beyond, upper trough moves off and drier air slides
in on pretty strong northwest flow. Do not see much warming if any
on Thursday, so daytime temperatures will likely be coldest of
the week, the highs on the plains in the low-mid 40s. High country
will also be chilly with highs in the teens and lower 20s.
Beyond that, strong upper ridge building to our west promises to
warm and dry the region Friday, aided by periods of gusty
downslope winds in the lee of the Front Range. Yet another
weaker shortwave racing down from the Pacific Northwest will
bring another batch of cloudiness and perhaps scattered snow
showers to the high country Friday night. Nothing for the plains,
other than some gusty gusty. Models show this low amplitude wave
exiting the area by morning, setting off another round of warming
and drying Saturday and Sunday beneath an upper ridge.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 320 PM MST Mon Dec 10 2018

VFR conditions will persist through Tuesday. Light and variable
winds will turn to normal south/southwest winds at 6-14 knots 01Z-
03Z and then hold through about 15Z Tuesday. Then winds are
expected to turn more west/northwest and increase to 10-17 knots
with gusts around 25 knots possible through 22Z. However, a
developing anticyclone would support a 30-40% chance of
east/northwest winds during this time. After 22Z, the development
of east/northeast winds is more certain as conditions become more
favorable for an anticyclonic east/northeast push during this
time.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...Baker
AVIATION...Barjenbruch

NWS BOU Office Area Forecast Discussion