880 
FXUS65 KBOU 200617
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1217 AM MDT Sat Apr 20 2024

.KEY MESSAGES...

- Springtime snow in the Rockies, with accumulations expected in
  most locations tonight through Saturday morning. 

- Slick and hazardous travel in the foothills, and possibly onto
  the adjacent plains into Saturday morning

- Cold through Saturday, then drier and warmer for Sunday through
  much of next week.

&&

.UPDATE...
Issued at 811 PM MDT Fri Apr 19 2024

With temperatures dropping and snow bands persisting throughout
the Denver metro and parts of the Palmer Divide, decided to
include Boulder, Denver, and Castle Rock into a Winter Weather
Advisory. Totals will likely be just shy of 6 inch criteria but a
few localized spots could reach 5-7 given the potential for bands
to continue through Saturday morning. 

&&

.SHORT TERM /Through Saturday/...
Issued at 257 PM MDT Fri Apr 19 2024

Current radar shows banded precipitation has made its way off the 
higher terrain and is moving eastward across the plains. While there 
is not one 'main' forcing responsible for this banding, there are a 
multitude of weaker forcings at play providing enough lift for these 
bands to develop. While the westerly jet stream aloft is a tad north 
and east of CO to supply robust lift, modest lift is occurring in
northeastern CO due to its proximity to the jet's right entrance 
region. Within the upper level flow, a shortwave trough will pass 
over the forecast area tonight bringing weak PVA. Additionally, 
weak 600-500 mb frontogenesis is present, and light northeasterly 
surface winds will bring weak upslope flow to the Front Range 
Mountains and Palmer Divide. A Winter Weather Advisory remains in 
effect from 6 PM this evening through 9 AM tomorrow for these 
locations. 

Guidance are in good agreement with location and amounts, however, 
banded precipitation can be tricky to pinpoint exact location, 
therefore there may be some localized heavier amounts mixed in with 
forecast totals. Lower elevations across the plains can expect 1 to 
3 inches. The foothills can expect to see 3 to 6 inches, and up to 
10 inches are possible for the highest mountain elevations. 
Travel may be slick for tonight's evening commute underneath 
locations where snow bands develop. Snowfall should taper off in
the morning with some lingering showers possible through the
afternoon. 

&&

.LONG TERM /Saturday night through Friday/...
Issued at 257 PM MDT Fri Apr 19 2024

The second half of the weekend will feel much more like spring, 
as ridging builds across the Rockies. Guidance is in good 
agreement with westerly flow developing across the forecast area, 
with warm air advection also aiding in getting warmer temperatures
back into the area. This airmass also will be drier, with cloud 
cover quickly dissipating through the day. Temperatures should 
make it back into the 60s across the lower elevations, though this
may depend a bit on how quickly moisture moves out Sunday 
morning.

The warming trend should continue Monday, with highs likely 
returning to the 70s across the plains. There should be a bit more
moisture embedded in the westerly flow aloft, which combined with
some weak/broad ascent and instability... could lead to some 
widely scattered showers and perhaps an isolated thunderstorm. 

A cold front is expected to drop into the region sometime Monday 
afternoon or Monday night, ushering in briefly cooler 
temperatures. However, the day to day pattern will not change 
significantly, as a series of weak shortwaves/pockets of moisture 
traverse the region over the course of the week. 

By the end of next week, guidance does begin to diverge a bit. 
There is broad agreement on broad upper trough axis swinging 
across the Pacific Northwest into the central Plains by next 
weekend. The GFS is a bit quicker and stronger with a lead 
shortwave, leading to a bit wetter end of the week, while other 
guidance keeps us mostly dry until next weekend. The model blend 
in this time period appears to be a good enough middle ground for 
now, and we'll hope for more model certainty on another day.

&&

.AVIATION /06Z TAFS through 06Z Sunday/...
Issued at 1217 PM MDT Fri Apr 19 2024

A few snowbands are moving across the terminals early this
morning. Based on current radar trends, anticipating some form of
a lull for the next couple of hours. Even during this lull, could
still see light snowfall and reduced visibilities with perhaps
some subtle improvements in those fields for brief periods. Likely
not categorical improvements. There are increasing chances for
another wave of higher coverage snow showers to move through 
after 08z. Light snowfall should overall continue into the morning
hours of Saturday diminishing in the 14-16z timeframe. There is 
lower confidence on how much conditions improve through the day 
and how quickly they would do so. Low clouds will likely be here 
to stay for Saturday straddling MVFR and VFR. Low confidence on
how long the BR sticks around for which will impact those
categories. In the afternoon, a few nearby showers can't be ruled
out. Will re-evaluate that potential for the 12z TAF. 

Wind-wise, looks like another Denver cyclone day with the cyclonic
wind circulation setting up this morning. This will shift winds to
the NW across the terminals this morning with slight shifts to
more northerly in the afternoon. Tonight's main source of impacts 
will be fog potential. Already hinted at in the DEN TAF. If it
does develop, the 07-09z timeframe is more likely. It is also a
possibility that a really low stratus deck develops with BR as
opposed to standard FG. Worth mentioning the potential now and
adding more confidence/detail as we get closer. 


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 9 AM MDT Saturday for COZ033>036-
039>041.

&&

$$

UPDATE...AD
SHORT TERM...Bonner
LONG TERM...Hiris
AVIATION...Mensch