Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

FXUS65 KBOU 170224

Area Forecast Discussion
National Weather Service Denver/Boulder CO
824 PM MDT Tue May 16 2017

Issued at 824 PM MDT Tue May 16 2017

Showers and thunderstorms have shifted over eastern Colorado.
Expect showers to linger after midnight as an upper level trough
moves across the Southern Rockies tonight and into Kansas
Wednesday. Over the mountains and along the Front Range, expect a
dry night as short wave ridging moves in. Lowered pops where it
has dried out and increased them over the northeast part of the
state. Made minor adjustments to cloud cover and temperatures to
reflect current trends.

UPDATE Issued at 442 PM MDT Tue May 16 2017

The 18Z models continue to show significant precipitation over the
area associated with the upper level low. Snow level is expected
to fall to 7000 feet MSL by Thursday morning. Decided to issue a
Winter Storm Watch for the Foothills and Mountains where the
chances for heavy snow is likely. For the lower elevations along
the Front Range, including the Denver metro area. Snowfall amounts
are highly uncertain at this time due to the uncertainty when/if
the rain changes to snow.


.SHORT TERM...(This evening through Wednesday)
Issued at 306 PM MDT Tue May 16 2017

Current satellite imagery showing low center over the southern CA
and AZ border with strong SW flow over the state. Moderate
instability along a border over southern portions of the CWA
combined with strong deep layer shear values will bring
thunderstorms to the mountains and plains through the evening
hours. Higher moisture values combined with better shear could
bring a chance of some isolated severe storms along and east of a
line from Sterling south to Akron. Showers, wind gusts to 55 mph
and hail will be possible. Elsewhere wind gusts to 40 mph with
slushy hail under 1 inch is possible. Storms will dissipate to
the east through the evening hours with increasing subsidence as
ridging increases between two upper lows. The exiting low will
move into Kansas through Wednesday morning with another and deeper
low right on its heels spinning over southern ID by 12z
Wednesday. This system will increase moisture across the mountains
on Wednesday that will bring a chance of showers through the day
Wednesday. Current model trends show freezing levels dropping
between 8000 and 9000 ft by Wednesday afternoon so some snow mixed
in at higher levels. Little to no accumulation is expected. On
the plains conditions will remain mostly dry with increasing
clouds in the afternoon. Temperatures will be similar to today
with highs in the upper 60s and lows in the mid 40s.

.LONG TERM...(Wednesday night through Tuesday)
Issued at 306 PM MDT Tue May 16 2017

Models have short lived upper ridging over the CWA early Thursday
evening between two upper closed lows. The second upper low moves
south-southeastward into the four corners area late Thursday
afternoon/early evening. The upper circulation weakens somewhat on
Friday with the upper trough axis still over the eastern border
of Colorado at 12Z Saturday morning. The QG Omega fields have
decent upward vertical velocity over the CWA Wednesday night well
into Friday. Downward synoptic scale energy is in place Friday
night. The low level pressure and wind fields show a cold front
move in late Wednesday afternoon. There is prolonged period of
upslope from Wednesday evening through Friday. For moisture,
models have pretty deep moisture over the CWA into Friday night,
then there is some decrease. There is some CAPE around Wednesday
evening, with the highest values along a theta-e axis over the
plains. The only decent CAPE around Thursday is over the mountains
west of the divide. It looks similar for Friday. The QPF fields
are loaded with decent amounts of measurable precipitation from
later Wednesday night into Friday afternoon. The snow level will
be tricky, it will likely snow, or at least snow mixed in, over
the the western third to half of the plains for sure by late
Thursday afternoon/early evening on into Friday. Not much may
accumulate on the pavement unless you get up into the foothills a
bit. Models have significant snowfall amounts over the western
half of the plains so it all bears watching. As far as the
mountains are concerned, decent snowfall is likely, especially
along the divide and above 10,000 feet. The best snow looks to
fall after 06Z Thursday on into into Friday. No highlights yet.
For temperatures, Thursday`s highs are some 6-14 C colder than
Wednesday`s highs. Friday`s highs are 0-1.5 C colder than
Thursday`s. For the later days, Saturday through Tuesday, models
show the weakening, slowly moving upper trough getting east of
Colorado by late Saturday. The flow aloft is pretty zonal Sunday
and Monday, then another upper trough comes in later Monday and
Tuesday. Temperatures pretty much stay below seasonal normals
through the period.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 824 PM MDT Tue May 16 2017

VFR conditions are expected to prevail through 00Z Thursday with
mid and high clouds. There is a slight chance for fog around 12Z
if skies clear out after 06Z. Winds will be on the light side
tonight and Wednesday. After 22Z, there will be a slight chance
for a short lived thunderstorm.


Winter Storm Watch from late Wednesday night through Friday
afternoon for COZ035-036.

Winter Storm Watch from Wednesday evening through Friday
afternoon for COZ033-034.



LONG TERM... rjk
AVIATION...Meier is the U.S. government's official web portal to all federal, state and local government web resources and services.