Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 221755
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1055 AM MST Wed Feb 22 2017

.UPDATE...
Issued at 1048 AM MST Wed Feb 22 2017

Current satellite imagery showing most of the moisture staying
north into Wyoming with some light snow in the mountains.
Increasing westerly winds are still expected but the continued
strong push from the east due to subsequent shower activity to the
north will fight against the western flow through the afternoon.
Winds will increase over the mountains and Palmer Divide through
the afternoon. Made some minor adjustments to sky grids and onset
of precipitation on the plains Thursday afternoon. Models are not
in total agreement with timing of front and moisture behind it.
Expect snow to start over the Denver area between 11 am and noon
and continuing into the evening hours per the GFS and EC
solutions.

&&

.SHORT TERM...(Today and tonight)
Issued at 506 AM MST Wed Feb 22 2017

A weak shortwave in WSW flow aloft pushed mid level moisture as
far south as Rocky Mountain National Park early this morning. The
southward progress of this seems to have stalled, and flow should
become a bit more SW during the day and push it back north again.
For the most part northern Colorado will be in the dry slot
between the frontal band across Wyoming and the moisture across
Arizona and New Mexico. There is still some shallow moisture
upstream though and it may be increasing this afternoon coupled
with a little cooling aloft. This will likely lead to some shallow
convective showers. Overnight as the main trough approaches flow
will remain southwest with increasing lift, but still working on
limited moisture. We should get steadier snow eventually, but it
should still be fairly light. We never really got the mountain
wave setup this morning. Flow at ridgetop will decrease a bit this
morning then pick up again later tonight, but conditions will be
unfavorable for much amplification or downward momentum transfer.
Still breezy/windy in the mountains but little threat of high
winds.

For the plains it will be another warm day, but cooler than
yesterday for a couple of reasons. The lead shortwave kicked the
plains winds around to northwest is bringing in slightly cooler
moister air across the northeast plains. We will have a battle
today between the northwest plains winds trying to curl into
Denver and the westerlies coming off the foothills. With deep
mixing expect that the westerlies will hold their own much of the
day, but we could see cooler air come into the north and east
parts of the metro area at times. The dry air aloft could also
fill in with weak convection late in the day, most likely over the
north and probably too late to influence high temperatures much.
For tonight, expect the cooler air to eventually push across much
of Denver but the winds should swing around again ahead of the
main shortwave. Lift and shower potential should gradually slide
southward overnight, but will probably stay north of Denver until
late tonight or Thursday morning. Enough cooling by then for snow
showers at lower elevations.

Still dry, warm, and breezy in areas south of Denver today. See
the fire weather section below.

.LONG TERM...(Thursday through Tuesday)
Issued at 506 AM MST Wed Feb 22 2017

Moderately strong west-southwesterly flow aloft is over the CWA
Thursday morning. By midday Thursday, an upper trough is over the
CWA with all the models showing a weak closed circulation with it
located to our immediate north. The upper trough sticks around
the CWA with weaker westerly flow aloft Thursday night. There is
some weak upper ridging for the CWA Friday and Friday night. The
flow aloft is west-northwesterly Friday and Friday night. The QG
Omega fields show a decent batch of upward synoptic scale energy
for the CWA Thursday morning. After that it is mostly downward
motion or benign energy at best from later Thursday through
Friday night. Everything seemed to move north. This is quite a bit
different than yesterday`s 00Z model runs indicated for that time
frame. Looking at the low level pressure and wind fields, now the
boundary layer winds are convoluted on Thursday and a cold front
with north-northeasterly upslope doesn`t get into the plains
until early Thursday evening. Due northerly low level flow is
progged overnight Thursday, through Friday, on into Friday
evening. Looks like normal drainage patterns are in place before
Saturday morning at 12Z. For moisture, it gets pretty deep over
the mountains Thursday into Friday evening, then it decreases
Saturday morning. For the plains, now the moisture doesn`t get
deep on any of the models until late afternoon Thursday, and that
is over the eastern half mostly. The western plains only have
some mid and upper level moisture at best. This is quite a change
from yesterday`s 00Z model runs. Moisture deepens up over all the
plains overnight Thursday into Friday morning. All the models dry
the plains out Friday afternoon, even with the upslope still
ongoing. The QPF fields show little amounts of measurable
precipitation for the mountains Thursday through Friday night.
Certainly less than yesterday`s progs. For the plains, there is
limited precipitation Thursday into late Friday, but mostly over
the northern half of the plains. For pops, will keep them pretty
high in the mountains, with okay orographic enhancement not
kicking in until Thursday evening. I`m not impressed with what the
current models show for snowfall. I`m even less impressed with
the model consistency. Concerning the highlights, will let the
watch ride with everything considered. For plains pops, more of
the same reasoning will apply and right now, less seems better.
For temperatures, Thursday`s highs are still progged to be 9-14 C
colder than today`s highs. Friday`s highs are down another 1-3 C
colder than Thursday`s highs. For the later days, Saturday through
Tuesday, Models have a west-northwesterly flow aloft, with a jet
maximum over us Saturday late into Sunday evening. Winds aloft
stay strong and are west-southwesterly overnight Sunday through
Monday night. There is an upper trough to move into the CWA
Tuesday afternoon and evening.

&&

.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 1048 AM MST Wed Feb 22 2017

VFR conditions expected through the TAF period with winds and
timing of light snow being the main forecast challenges. Expect
light easterly winds to continue then switch westerly with some
gusting form 20 to 22 kts. This will continue until 00z then
switch to SE before veering around to the west then north with
frontal passage. A mid level cloud deck will increase but is not
expected to go IFR at this time. Light snow is forecasted to begin
by 21z with a light reduction in visibility. Confidence on the
timing is only medium due to some conflictions in the models.

&&

.FIRE WEATHER...
Issued at 506 AM MST Wed Feb 22 2017

It will remain warm and breezy over the plains south of
Interstate 70 today. Humidities will drop into the 12-20 percent
range along with gusty west to southwest winds. There may be some
cooler air out around Limon keeping humidities higher with some
variability in the wind and generally lighter speeds. The forecast
is more certain in Douglas and western Elbert, and southern
Lincoln counties.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 6 PM MST this evening for COZ241-246-247.

Winter Storm Watch from this evening through Friday morning for
COZ031-033.

&&

$$

UPDATE...Bowen
SHORT TERM...Gimmestad
LONG TERM...RJK
AVIATION...Bowen
FIRE WEATHER...Gimmestad


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