Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231223 CCA
AFDBOU

Area Forecast Discussion...CORRECTED
National Weather Service Denver/Boulder CO
523 AM MST Thu Nov 23 2017

.SHORT TERM...(Today and tonight)
Issued at 144 AM MST Thu Nov 23 2017

Strong upper ridge seen on WV over the pacific with a moist
conveyor belt and jet moving over and into Colorado. This feature
will bring upper clouds through the day with possible wave
amplification in the morning hours. The jet placement will be on
the subsidence side as it moves slightly eastward through the day
into Friday morning. By Thursday afternoon the jet will have
displaced enough for the stable layer to weaken and downsloping to
take over helping to reduce some cloud cover over the Urban
corridor. This could offset the slight cooling from upper level
clouds to bring record breaking temperatures to the Denver Metro.
Current record for the day stands at 73 which will be possible as
models show 700 mb temps 8-9 degrees C combining with a warm and
dry downsloping flow by the afternoon. Winds will be generally
light through the day with increased winds near the Wyoming border
with some gusting to 25 mph possible. Winds over the higher
terrain will also pick up through the day with gusts up to 40
possible. Highs in the mountains will also be above normal for
this time of year with values in the 50s.

By Thursday night the ridge will flatten ahead of the next upper
level trough. Wind speeds at mountain top will increase with gusts
from 45 to 50 mph possible at times by early Friday. Lows
overnight will continue to be on the mild side with temperatures
in the low 40s on the plains and 30s in the mountains.

.LONG TERM...(Friday through Wednesday)
Issued at 144 AM MST Thu Nov 23 2017

A weak upper level trough will move across nrn CO on Fri.  The ECMWF
is roughly 6 hours slower with this feature versus the GFS.  As a
result the GFS has the best chc of pcpn over the Mtns from late
morning thru Fri aftn while the ECMWF has the best chc from late
aftn thru mid evening.  Overall not sure about timing, so will keep
the best chc from mid aftn into the early evening hours.  Overall
moisture depth with this feature is rather shallow so accumulations
will only be a few inches in the mtns.  Elsewhere it will remain dry
as a weak pacific fnt moves across the area.  Gusty Nwly winds will
develop behind this fnt, especially fn the nrn Foothills across the
Plains, however speeds will stay blo high wind criteria.  As for
highs, temps should drop back into the 60s across nern CO.

On Sat Nwly flow aloft will be over the area with some higher level
moisture embedded in the flow.  Thus may see some periods of higher
level cloud cover thru the day but no pcpn is expected.  Highs
across the plains will be in the upper 50s to mid 60s.

For Sun dry zonal flow aloft will be over the area as a sfc lee
trough develops over ern CO.  This will allow for wly downslope low
lvl flow to occur.  As a result, readings across nern CO will rise
into the lower to mid 70s with a few records possible.

Moving into Mon there are some differences between the ECMWF and
GFS.  The GFS has a progressive upper level trough moving across the
area Mon aftn into Mon night while the ECMWF is slower and further
west.  The first implication of these differences is that the GFS
has a pacific fnt moving across much of the area by midday Mon while
the ECMWF keeps this fnt further west.  As a result, the ECMWF has
decent downslope warming across the area in the aftn, with highs in
the 70s across the plains with record temps possible.  Meanwhile the
GFS has readings roughly 10 degrees cooler.  For now will split the
difference as not sure which way to lean.  Meanwhile the second
implication is the timing of pcpn in the Mtns.  The GFS would bring
some pcpn into the nrn Mtns by early aftn while the ECMWF solution
would hold things off until Mon night.

For Mon night into Tue the ECMWF and GFS continue to differ.  The
ECMWF has a decent upper level trough affecting the area while the
GFS shows the upper level trough well to the east.  A few of the GFS
ensemble members do show a slower and further west upper level
trough so the ECMWF can`t be completely discounted.  If the ECWMF
were to end up being correct then there would be a good pcpn across
much of the area late Mon night into Tue morning along with temps
dropping back to seasonal levels.  If the GFS is correct then it
would be cooler and mainly dry.
 &&

.AVIATION...(For the 06Z TAFS through 06Z Thursday night)
Issued at 144 AM MST Thu Nov 23 2017

VFR conditions are expected through the period with drainage winds
at APA and DEN through 19z before turning westerly with speeds
from 10 to 15 kts. A high ceiling will persist through the period
but should not impact area operations.

&&

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

$$

SHORT TERM...Bowen
LONG TERM...RPK
AVIATION...Bowen


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