167 
FXUS65 KBOU 060338
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
838 PM MST Tue Feb 5 2019

.UPDATE...
Issued at 822 PM MST Tue Feb 5 2019

Not major adjustments in regards to the timing of the front and
the onset of snowfall late Wednesday morning through Wednesday
evening. Latest NAM12 update still appears to support this 
solution. Bands of light to moderate snowfall over western CO this
evening will continue to shift eastward into the north central 
mountains overnight. Current highlight looks on track at this 
time. Otherwise, only minor adjustments planned for tonight's 
forecast.

&&

.SHORT TERM...(This evening through Wednesday)
Issued at 325 PM MST Tue Feb 5 2019

A trough is visible on water vapor imagery digging into the 
California coast today. Mid to upper level southwesterly flow will
continue over Colorado as this system approaches the area. This 
flow will create snow showers throughout the night in the 
mountains with the Park Range seeing the heaviest totals of around
6-12 inches. 

Tomorrow, the shortwave associated with this trough will rotate
northeastward toward Colorado. Meanwhile, at the surface, a strong cold
front will move southward through the urban corridor and eastern 
plains during the late morning on Wednesday. The combination of 
PVA associated with the trough, the left exit region, surface 
frontogenesis and upslope flow will provide QG ascent for this 
storm and create snow showers around midday across the 
aforementioned area. I have kept storm total snowfall amounts 
consistent with previous forecasts as 2-5 inches are expected 
across the Denver metro. The message is also consistent that the 
evening rush hour will see hazardous travel conditions and evening
commuters looking to travel during this time should use caution 
or reconsider their travel. This event has the makings of a flash 
freeze because road temperatures will be above freezing before the
cold front moves through the urban corridor. Snow will initially 
melt on contact and then, due to the much colder temperatures 
moving in behind the front, the wet pavement will freeze making 
roads slick and icy. The greatest impacts will be over bridges 
and overpasses. During the onset of the front, there may be a 
brief period of freezing drizzle as relatively warm air will be
overrunning the colder air at the surface. Light to moderate snow
showers will begin accumulating by the early afternoon which will
only make the road conditions worse. A Winter Weather Advisory 
was issued for the urban corridor, eastern plains and foothills 
from noon through early Thursday morning to account for the impact
on the commute and others who may be traveling.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 325 PM MST Tue Feb 5 2019

Snow will continue into the evening hours across much of the 
area. Expect snow to end from west to east overnight as the system
shifts east across the Colorado. The arctic airmass moving into 
the state will drop temperatures below zero over most of northeast
Colorado late Wednesday night. By 12Z Thursday, the trough axis 
will be east of the area taking most of the snow with it. However,
there will be enough moisture embedded in the northwest flow 
aloft to keep light snow going over the mountains Thursday. 
Additional snowfall of up to 4 inches will be possible. In the 
meantime, an arctic airmass over eastern Colorado combined with 
fresh snow will result in cold temperatures Thursday and Thursday 
night. Highs are expected to be in the teens Thursday. Clear 
skies, light winds, and fresh snow will lead to good radiational 
cooling Thursday night. Low lying areas over northeast Colorado 
are expected to fall below zero again. Mountain valleys will get 
very cold with temperatures around 20 below zero in places. 

On Friday, flow aloft turns west-southwest as a trough digs south
along the Pacific west coast. Weak ridging over the Central 
Rockies will bring dry conditions and mostly sunny skies. A 
stagnant airmass over northeast Colorado will modify some, but 
remain cool due to the snow cover.

Flow aloft will remain west-southwest through the weekend as a 
upper level low spins over the Pacific northwest. A weak wave 
embedded in the flow aloft is expected to bring light snow to the 
mountains Saturday night. Otherwise, dry conditions are expected. 
Surface high pressure will be parked over the Northern Rockies and
Northern Plains this weekend. An easterly flow around this will 
keep cooler air over northeast Colorado. A cold front may drop 
south across northeast Colorado Saturday night with the passing 
wave. If this occurs, highs will be colder on Sunday. 

A Pacific system is expected to sweep across the area sometime 
Monday or Tuesday. Models are still in disagreement on the timing.
This system should mainly impact the mountains with downslope 
flow keeping areas east of the mountains dry. 

&&

.AVIATION...(For the 06Z TAFS through 06Z Wednesday night)
Issued at 822 PM MST Tue Feb 5 2019

VFR conditions will continue through mid morning Wednesday. 
Light north/northwest winds this evening at KDEN should gradually
transition to west/southwesterly later this evening. A cold front
will move through the airports midday Wednesday with northeast 
winds behind it. Snow showers will increase in coverage and
intensity following the passage of the front. 

MVFR after 17z Wednesday with IFR ceiling and visibility 
restrictions in the heavier snow showers developing in the 
afternoon. There is low to medium confidence in the timing of this
front at the moment. The main concern is that is might move in a 
little sooner than forecast. No adjustments however to the timing
in this update.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from noon Wednesday to 5 AM MST Thursday 
for COZ035-036-038>045-048.

Winter Weather Advisory from 6 AM Wednesday to 5 AM MST Thursday 
for COZ034.

Winter Weather Advisory until 5 AM MST Thursday for COZ031-033.

&&

$$

UPDATE...Cooper
SHORT TERM...Danielson
LONG TERM...Meier
AVIATION...Cooper