National Weather Service Forecast Discussion

000
FXUS65 KBOU 061021
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
321 AM MST Fri Dec 6 2019

.UPDATE...
Issued at 320 AM MST Fri Dec 6 2019

Areas of fog have thickened quickly over the northern and
northeastern plains, and won`t likely improve until mid morning,
will issue a Dense Fog Advisory.

&&

.SHORT TERM...(Today and tonight)
Issued at 240 AM MST Fri Dec 6 2019

The state has been left under northwesterly flow aloft as
yesterday`s weather system has moved into the Great Plains, and an
upper ridge builds over the western US. Moisture in the northwest
flow has kept the high country stuck under cloud cover with a few
flurries possible. High surface pressure over the Great Plains
has pushed stratus and areas of fog into the state`s northeastern
corner, while clearing skies early this morning have allowed for
patchy fog to form further west in the South Platte River valley
and closer to the urban corridor. 500 mb heights will increase
through the day as the ridge axis is expected over the forecast
area late tonight. Therefore expecting a subsident airmass today
with little mixing. What fog continues to form early this morning
will likely last quite a while, especially in the stable South
Platte River Valley. Some models, notable the NAM Nest keeps dense
fog in all day, however, it wanted near zero visibility by last
evening, and that didn`t happen. Will keep fog in the forecast
through the morning hours, dissipating after noon. This may need
to be extended into the early afternoon. Max temperatures may be
quite varied, depending on where its more stable and possibly fog
covered all day, with highs in the mid 30s there, and mid 40s
elsewhere. I did lower max readings in the South Platte River
valley in anticipation of the later fog dissipation. In the high
country, clouds will likely stick around in the northwesterly
flow, so similar readings to yesterday will be expected.

Tonight, a surface trough begins to deepen along the lee of the
Rockies to induce some downsloping warmer winds in and near the
foothills. Elsewhere, out on the plains, areas of fog will likely
form again under light winds and recent precipitation.

.LONG TERM...(Saturday through Thursday)
Issued at 240 AM MST Fri Dec 6 2019

The weekend will start off on a warm note under an upper level
ridge and strong warm advection. With 700 mb temperatures warming
to around +5C, healthy lee troughing, and a dwindling snowpack on
the plains, we`ll respond nicely to sunshine on Saturday. There
may be some morning fog in the Platte River Valley northeast of
Denver, and the greater snowpack/shallow inversions there will
likely limit the warmup. Outside of that, however, we`ll see much
above normal temperatures with upper 50s to mid 60s across Denver
and the Palmer Divide. The warmest readings should be over the
southern sections of town into Douglas and Elbert Counties where
inversions will be very shallow and quick to burn off. Even
locations like Boulder could pop above 60F if we get some westerly
winds off the foothills late in the day. Breezy/windy conditions
will persist across the mountains and foothills with the lee
trough and 30-40 knot cross mountain flow.

On Sunday, the deeper upper level storm system driving into
northern and Central California will undergo some shearing as
another trough drops southeast across the northern Rockies. There
will be some upper level support as seen in the QG fields, and
fair orographics with westerly flow and increasing mid level
moisture ahead of the trough. Moisture does not appear as
impressive in the latest guidance, with 700-500 mb specific
humidity only peaking at 2 g/kg early in the event. We`ll still
see snow and areas of blowing snow in the mountains and travel
impacts, with overall moderate snow accumulations thanks to the
duration of this event. The mountain snow should continue into
Monday with another shot of cold advection in favorable northwest
flow. A cold front will push across the plains, bringing a chance
of light snow as well by Sunday night and Monday. After mild,
pre-frontal temperatures on Sunday, we`ll return to below normal
temperatures Monday and Tuesday.

For the latter half of next week, ensemble guidance is still
showing a return to normal or slightly above normal temperatures.
A weak wave may push through the ridge late Thursday or Friday
with a chance of snow at least for the high country.

&&

.AVIATION...(For the 06Z TAFS through 06Z Friday night)
Issued at 240 AM MST Fri Dec 6 2019

An increasingly stable airmass and low level moisture is allowing
for patchy fog to form and remain near the Denver terminals
early this morning. High resolution models continue pushing the
fog to the north of the Denver terminals, with more forming in the
South Platte River Valley. This fog is shown to remain for most of
the day, with a slight push from the north between 12-16Z - which
may push it closer to DEN and BJC. For now will keep it out of the
airports, as some solar heating and a surface trough beginning to
form along the urban corridor are expected to dissipate it. But if
it does push further south into the airports, it is expected to
reduce visibility to less than half a mile. Overall expect light
drainage winds, less than 10 kts, veering to the NW after 15z,
then around to the NE by the afternoon.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Dense Fog Advisory until 9 AM MST this morning for COZ038-
042>044-048>051.

&&

$$

UPDATE...Kriederman
SHORT TERM...Kriederman
LONG TERM...Barjenbruch
AVIATION...Kriederman

NWS BOU Office Area Forecast Discussion