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 Thu Feb 22 2018

.UPDATE...
Issued at 1042 AM MST Thu Feb 22 2018

Radars are showing some snow showers over the CWA, mainly over the
northern boarder areas. The wind fields over the forecast area
remains light. There are limited radar returns in the upstream so
will will stay the course concerning pops, 10-30%s should do it.
Maybe a bit higher in the mountains. Temperatures should warm
little form current readings. Will make typical cosmetic fixes to
the GFE grids. &&

.SHORT TERM...(Today and tonight)
Issued at 256 AM MST Thu Feb 22 2018

The synoptic pattern is dominated be the deep trough over the
western states bookended by two 580+ DM highs south of Alaska and
into the Atlantic. The cyclonic side of the upper jet will be over
the state through the period helping to bring increased mid and
upper level instability over the region into Friday. QG model fields
show decent ascent in the mid levels with upper air soundings being
nearly moist adiabatic above 700 mb. The surface however stays more
stable with the exception of the far NE plains counties of Sedgwick
and Phillips that show some slight ascent per the latest GFS data.
The atmosphere is unstable enough with decent moisture upstream
provided by the incoming trough to increase pops for the high
country as well as on the plains for this afternoon and into early
Friday. Amounts in the high country will vary with 3 to 6 inches
possible into Friday. For the plains, amounts will be light near the
foothills with less than an inch expected and slightly higher
further east as instability will be better with 1-3 inches possible
through Friday morning. With the instability some areas could see a
quick half inch with amounts varying slightly. Adjusted daytime
temps for today below model guidance with the increasing cloud cover
and cold push.

The snow will continue for the mountains Friday morning while the
plains will start to dry out by 6 am. models show subsidence
increasing at all levels Friday morning helping to clear out
lingering clouds on the plains. This combined with low level
moisture will bring fog to the plains mainly east of I-25 to the
Kansas line. Please use caution if traveling. Temperatures overnight
into Friday will stay on the cool side with most areas in the single
digits and low teens.

.LONG TERM...(Friday through Wednesday)
Issued at 256 AM MST Thu Feb 22 2018

The weather pattern will remain active this weekend with a couple
more weather disturbances moving across the forecast area.

The strongest of these disturbances is the current system
dropping through the Pacific NW this morning. This trough will
settle into the Great Basin on Friday. Q-G lift will be increasing
across the forecast area through friday afternoon and evening, and
turning upward through a deep layer through the course of the
evening. Meanwhile, the airmass will be rather unstable over the
mountains and western Colorado with lapse rates of 7-8 C/km.
As a result, convective snow showers should become more numerous
ahead of this system through the afternoon, and then push across
the plains through the course of the evening. Snowfall may be
banded and heavier with the proximity of the upper level jet,
although it looks more like pure upright convection will dominate
versus any release of Conditional Symmetric Instability (CSI) as
potential instability/weak CAPE will be present. Nonetheless,
despite moisture being somewhat limited, we could still see a
couple bands/showers produce a quick inch or two of snow from the
mountains across the northeast plains during the evening,
eventually spreading to the northeast corner overnight. That`s
where there`s potential for a 2-4 inch snowfall as downslope
component is more limited there. Will increase PoPs and QPF for
this period. Temperatures will probably have a hard time warming
much on Friday with light easterly flow and most likely a stratus
deck over most of the plains. In fact, with the moist low levels
and weak upslope component, we`ll probably start this
precipitation event with some light freezing drizzle over the
northeast plains late tomorrow afternoon or evening. Will have to
watch areas northeast of Denver for a potential Winter Weather
Advisory for a combination of light freezing drizzle and snow.
Road temps would definitely be cold enough to allow for travel
impacts.

That system should exit all but the far northeast corner by early
Saturday, with drier but breezy conditions developing behind it.
Temperatures will only moderate a few degrees Saturday, and still
stay well below normal with snow cover and cold advection behind
the trough axis.

The next weaker disturbance is expected to reach the mountains by
Sunday, bringing another round of light snow to the high country.
Plains locations should remain dry with a sufficient downslope
component in place.

Then, we look for some moderation in temperatures for the first
half of next week with temperatures returning closer to normal.
Dry conditions are expected to persist until the middle of next
week as the next trough approaches. At this time, however, it
appears most of that system`s energy would be staying off to our
south and west.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1042 AM MST Thu Feb 22 2018

The weak winds will continue all of today through tonight and
into Friday at DIA. They may stay northwesterly or northerly
through early evening, then maybe some real weak drainage
overnight. Models keep showing lower ceilings then reality out at
DIA, so will not go as low as they as models advertise.

&&

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

$$

UPDATE...RJK
SHORT TERM...Bowen
LONG TERM...Barjenbruch
AVIATION...RJK



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