Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 162113

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

.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 306 PM MDT Tue May 16 2017

VFR conditions will prevail through the period. Winds will
continue from the ESE with gusts to 25 mph and storms in the
vicinity through 23z. Storms forming and moving NE closer to the
foothills could bring an outflow from the NW with another round of
storms between 01 and 03z. Largest hazard with storms will be
gusty outflow winds up to 30 kts...small hail and lightning. Winds
will switch around to the east after 03z then veer back to the
north by midnight. Drainage will occur by 11z then move westerly
with increased winds to 24kts by Wednesday morning. Winds will
calm and move northerly by 18z.




LONG TERM... rjk
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