Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 222140

Area Forecast Discussion
National Weather Service Denver/Boulder CO
240 PM MST Sun Jan 22 2017

.SHORT TERM...(This evening through Monday)
Issued at 215 PM MST Sun Jan 22 2017

The upper ridge is currently over Western Colorado and continues
to slide east. The area will remain dry through this evening under
the influence of the ridge and associated subsidence. Tonight the
ridge axis moves east into Kansas and a moist southwest flow
enters Colorado. Light snow should begin before midnight across
the Park Range and higher elevations of Summit County with mostly
light amounts through Monday morning.

Monday morning a strong jet streak out of the southwest at
140-160 knots noses into Colorado. Initially the mountains are in
the right exit region of this jet, not favorable for enhanced lift
and associated moderate to heavy snow bands. The jet will advect
Pacific moisture into the state and the primary mechanism for snow
will be orographics into Monday morning. However, by Monday
afternoon the long wave trough across the Western U.S. digs
southeast, pushing the jet streak to the south over time. The
strong jet streak moves far enough south that the northern half of
Colorado will be in the left exit region of the jet, and lapse
rates just above the ridge tops look to be 7.0 - 8.5 degC/km
throughout Monday afternoon and into Tuesday morning. These
factors mean banding across the mountains is likely Monday
afternoon/evening and into early Tuesday. Under any band that
develops moderate to heavy snow is possible for an hour or two.
Total amounts through Tuesday afternoon could reach advisory
criteria across the Park Range and the Continental Divide along
the Front Range. Have decided not to hoist an Winter Weather
Advisory yet for parts of the mountains but one may be needed
once high res model data come in tonight/tomorrow.

East of the Rockies should remain dry tonight and much of the day
on Monday. There is no easterly upslope component to speak of, and
the snow bands that form over the mountains Monday afternoon
should not impact the Plains through Monday evening. 700 mb temps
are quite warm, and with strong southwest flow at the surface
Monday`s high temperatures should be 7-10 degrees above
average...reaching the mid 50s across the I-25 urban corridor and
near 50 furthest East Plains. Monday night the high res models
generate light precipitation near the foothills across Boulder and
Larimer Counties and along the WY border. Given that surface wet
bulb temperatures are near 40 Monday evening in those areas, any
light precipitation that forms is likely to be liquid. Otherwise
the Plains should remain dry until at least Tuesday.

.LONG TERM...(Monday night through Sunday)
Issued at 240 PM MST Sun Jan 22 2017

Models have the very strong southwesterly upper level flow
decreasing significantly Monday night as an upper trough moves
into Colorado and the CWA. The upper trough is over the CWA
Tuesday well into the extended period. Again, there a some closed
circulations within the upper trough but they are all over the
place and mostly north of the CWA. The jet level winds are
southwesterly and westerly under 45 knots from Tuesday midday
through Wednesday night. The QG Omega fields mostly show upward
synoptic scale energy for the CWA Monday night through mid day
Wednesday, then downward motion moves in. The boundary layer flow
looks to be a drainage/downsloping mix Monday night. Models now
show the cold front to move in around 12Z Tuesday morning. All the
models now show north-northwesterly boundary layer flow Tuesday
well into Wednesday. No upslope. Winds could go to normal
drainage patterns Wednesday night. Moisture-wise, the models agree
a bit better today compared to yesterday. Moisture is pretty deep
in the mountains Monday night well into Tuesday night. Moisture
decreases by Wednesday morning on the Nam and ECMWF, but not on
the GFS until mid day Wednesday. Some moisture remains in the high
country later Wednesday and Wednesday night, but it is pretty
shallow. Over the plains, the models do not agree very well. The
GFS has some Monday night, but nothing down low. The NAM and
ECMWF do have some in the lower levels at that time. There is some
moisture on Tuesday, but not great. The deepest moisture is
progged Tuesday night into early Wednesday, but it is still not
great and the ECMWF has less then the other models. Moisture is
insignificant later Wednesday and Wednesday night. The QPF fields
have minor amounts of measurable snow for the mountains and
northern border Monday night and Tuesday. The NAM has come more in
line for the other models concerning QPF over the plains on
Tuesday; not much. For pops in the mountains, will need "likely"s
Monday night and Tuesday, then "chance"s into Wednesday evening.
Snow model did not yield great amounts, the best over zone 31. No
highlights now. For the plains, will go with mostly, "slight
chance"s late Monday night into Tuesday evening. For
temperatures, Tuesday`s highs will be 3-6 C cooler than Monday`s.
Wednesday`s highs will be 0-1 C cooler than Tuesday`s. For the
later days, Thursday through Sunday, models still have upper
troughiness around with weak flow aloft and little moisture
through Saturday. By Sunday, upper ridging moves in.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 215 PM MST Sun Jan 22 2017

VFR conditions through 00Z Tuesday. SCT/BKN mid-level decks
expected Monday morning and afternoon. Winds have been tricky
today as neither the HRRR, ESRL HRRR, RAP, or NAM have been able
to model the low-level wind patterns for any of the terminals
this afternoon. The good news is that winds have remained in the
8-12 kt range for DEN and APA. Expect the winds to go from light
northerly currently to ESE at DEN and APA by 00Z. By 06Z winds
should go to SSW at APA and DEN as a surface low develops just
east of the Denver metro area. BJC should be mainly westerly
during this time. As this low builds to the east, southwest flow
at all three terminals in the 10-15 kt range (with stronger gusts
possible) is likely starting late morning Monday and continuing
through Monday evening.




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