Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 232225
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
325 PM MST Mon Jan 23 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 234 PM MST Mon Jan 23 2017

Today is the warmest day of the week with good southwest downslope
flow across the I-25 urban corridor where temperatures in the low
to mid 50s have occurred. The 150kt jet streak has slid south
over the southern half of Colorado. Combined with the steep lapse
rates at and above 700 mb a few convective showers have popped up
east of the Rockies. Virga is the main result though rain
sprinkles have reached the ground in a few spots given surface wet
bulb temperatures are near 40 degrees this afternoon. Do not
expect any accumulation from these showers through this evening.
In the mountains, light snow is ongoing and should continue
through Tuesday. Isolated moderate snow showers given the
instability and jet streak dynamics are possible late tonight
across the northern mountains.  Amounts should reach advisory
levels across the Park and northern Gore ranges through tomorrow
evening and the Winter Weather Advisory for those zones will
continue. Further south and east across Summit County and the
Front Range mountains amounts should be lighter given the less
favorable orographic flow, and amounts should remain below
advisory criteria through Tuesday. There will still be enough
snow to impact travel along the I-70 corridor from Vail to
Georgetown, and along US 40/Berthoud Pass, especially Tuesday
morning.

Tonight a surface low pressure center develops in the lee of the
Rockies and moves east into northwest Kansas and deepens to ~994mb
just prior to sunrise. This will generate a strong northerly push
of cold air that enters Colorado from Wyoming and Nebraska between
2-3 AM local time. The cold front should reach Denver metro area
by 5 AM. North winds will develop behind the front and throughout
the day Tuesday will turn NNE and be 10-20 mph with stronger
gusts along I-25, and be NNW 20-30 mph across our far northeast
counties Tuesday afternoon. Though the atmospheric column slowly
saturates several hours after frontal passage and there is an
upslope component to the low-level flow, there does not appear to
be much support for accumulating snow across the Plains. The
exception is the far northeast along the Nebraska border where
synoptic lift is maximized associated with the departing mid-level
trough. Those areas could see 1-2 inches by late Tuesday. Have
kept PoPs low across the Denver metro and I-25 corridor, and any
snow that falls Tuesday would occur late morning to midday and be
less than an inch. The mountains again should see accumulating
snow during the day Tuesday but without the mid- and upper-level
dynamic support, snowrates and amounts should be lighter than
during the Monday into Tuesday overnight period. Max temperatures
on Tuesday will be 15-20 degrees cooler across the I-25 urban
corridor, and will remain in the upper 10s to low 20s across the
mountains as the trough moves across the state.

.LONG TERM...(Tuesday night through Monday)
Issued at 234 PM MST Mon Jan 23 2017

An upper trough is over the CWA Tuesday night through Thursday
night with fairly weak southwesterly and westerly jet level flow.
The QG Omega fields have weak upward motion for the CWA Tuesday
night into Wednesday. After that through Thursday night, weak
downward motion is progged. The boundary layer flow is northerly
much of Tuesday night, then northwesterly on Wednesday. Normal
drainage patterns look good for Wednesday night, then more
northwesterlies Thursday into Thursday night. There is pretty
decent and deep moisture over the CW Tuesday night. Moisture
decreases slowly on Wednesday. There is little moisture over the
plains down low on Wednesday. By Wednesday night, the plains are
pretty dry and the alpine moisture is still around but pretty
shallow. The QPF fields have small amounts of measurable snow for
the mountains and some of the plains Tuesday evening. After that
the models keep a tad of measurable snow in the high mountains
only into Thursday evening. For pops, will keep go with 40-70%s
Tuesday night through Wednesday. Will drop them to "chance"s
Wednesday night into Thursday morning. After that, just "slight
chance"s for Zone 31 only. Over the plains will go with a "slight
chance" over the northeast corner Tuesday evening, then nothing.
For temperatures, Wednesday`s highs are 1-3 C cooler than
Tuesday`s. Thursday`s highs are similar to Wednesday`s. For the
later days, Friday through Monday, models still have an upper
trough over the forecast area into early Saturday, then northerly
flow aloft is progged. Upper ridging moves in by Sunday continuing
into Monday. There is very little moisture all four days.

&&

.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 234 PM MST Mon Jan 23 2017

A weak boundary from the east has crept across the DEN terminal
with easterly winds this afternoon. Expect this boundary to wash
out or weaken and the winds to turn back to the west this evening.
Current thinking is frontal passage at the terminals pre-dawn in
the 09-11Z time frame. Winds will shift to the north at about
10kts. As the cold air pours in and the surface low moves a bit
further east, winds at APA, BJC, and DEN should go more NNE by
mid- morning and remain that way through the afternoon. Winds are
expected to be 10-12 kt with gusts to 20 kts.  There is only a
slight chance of snow at all three terminals from late morning
through the afternoon. If snow falls accumulations should be an
inch or less tomorrow. Not expecting MVFR conditions but cannot
rule them out if a snow shower impacts the airports. In those
cases ceilings could briefly dip to MVFR conditions, mostly likely
during the late morning into early afternoon.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 5 PM MST Tuesday for COZ031.

&&

$$

SHORT TERM...Schlatter
LONG TERM...RJK
AVIATION...Schlatter



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