Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 141700

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1000 AM MST Tue Nov 14 2017

Issued at 1000 AM MST Tue Nov 14 2017

Forecast on track. High clouds are mostly thin and allowing for
modest insolation, and 12Z Denver sounding shows another shallow
inversion. Expect a couple spots to push 70F near the foothills
where inversion is very shallow, but most of the plains should
hold in the mid to upper 60s.

One cold front arrives late this afternoon/early evening, but main
punch of cooler air arrives closer to midnight.


.SHORT TERM...(Today and tonight)
Issued at 330 AM MST Tue Nov 14 2017

Southwest flow aloft ahead of a short wave trough moving across
the Northern Rockies will bring high clouds to the area today.
Surface low pressure will deepen over southeast Colorado. This
brings north to northeast winds to eastern Colorado and ushers in
slightly cooler air. The pressure gradient tightens over the
higher terrain with gusty winds expected. The main cold front will
push south across the area early in the evening bringing even
cooler air into the area. Low levels will remain dry with no
chance for precipitation across the area. As high pressure builds
in from the north, skies will clear overnight. This combined with
a cooler airmass moving into the area will result in overnight
lows in the upper 20s to lower 30s across northeast Colorado.

.LONG TERM...(Wednesday through Monday)
Issued at 330 AM MST Tue Nov 14 2017

The large upper level ridge to our west will continue to amplify on
Wednesday with a 140+kt jet cresting the ridge. Colorado will still
be on the downhill side of this ridge and with a northerly low-level
flow to start the day, daytime temperatures are expected to be 8-12F
lower than those on Tuesday. Should see plenty of sunshine to start
the day with strong sinking aloft, but later in the day with passage
of the 500mb ridge axis and a shift to a west-southwesterly mid-
level flow, models show the leading edge of mid and high-level
moisture spreading over nwrn Colorado, but no precip yet.

Wednesday night into Thursday, a strengthening southwest flow aloft
will continue to transport moisture into the state, although the
bulk of this moisture should remain west of the Continental Divide.
East of the Divide, a deepening lee side sfc trough will stimulate a
west-southwesterly low-level flow moving down off the Front Range to
give the foothills, plains and Palmer Divide another unseasonably
day. Latest model temperature guidance indicates highs on the plains
in the upper 60s and lower 70s. That`s 15 to 20 F above average, but
see several degs F below the record highs for the date. The
unseasonably warm temperatures, low relative humidity and gusty sfc
winds during the afternoon will elevate the rangeland fire danger,
most notably on the Palmer Divide centered on Elbert County.
However, thresholds are not expected to exceed levels necessary to
hoist any fireweather highlights at this time. In the high country,
the gradual influx of moisture should lead to the formation of
isolated to scattered rain and snow showers over higher elevations
in the northern mtns by mid-afternoon. The snow level will start out
high, say around 10,400 ft msl, but then lower to around 9000 ft msl
by evening as temperatures cool aloft with the approaching longwave
trough. Any high country snow accumulation during this 24-hour
period should be light and spotty.

Thursday night and Friday, models are in general agreement as they
all show the West Coast digging trough gradually shifting over the
Great basin. The faster GFS and Canadian models continue to advance
cold air core of this trough over the Great Basin during the Friday,
while the European model shows the trough still hanging back over
California and Nevada all day. Nevertheless, all three models
indicate the presence of the powerful jet, in the 140-160kt range,
slipping south over northern Colorado Friday afternoon/evening.
While snow and rain will already falling across much of the high
country Thursday night and Friday morning, it`s late on Friday when
the best orographics, the lift and instability generated by the jet,
and the deepest moisture could produce several hours of significant
snowfall along and west of the Continental Divide. It`s too early to
issue any highlights as model timing and placement of the trough
remain in question. Furthermore, the GFS and Canadian models show a
fairly strong cold front dropping south across the plains of nern
Colorado Friday afternoon, possibly generating a few showers along
the way. Precip will likely be in the form of rain with temperatures
still in the upper 40s/lower 50s, although precip may turn over to a
mix of rain and snow along the higher Cheyenne ridge around sunset.

Friday night into Saturday, the European model shows the trough with
its low clouds and light precip still hanging around til Saturday
morning. Whereas the GFS and Canadian models shows the trough well
east of the fcst area by Saturday morning, and a much drier and
warmer northwesterly flow overhead. By late on Saturday, all models
show the area under the influence of a strong upper ridge, returning
dry conditions and above average temperatures to the region through
early next week.


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1000 AM MST Tue Nov 14 2017

VFR conditions will prevail through Wednesday morning. There`s
just a slight chance cold front later this evening could bring
enough moisture and upslope for a MVFR stratus deck after 12Z.
Winds should transition more easterly through 21Z this afternoon,
and then forecast become more uncertain later tonight with
possible anticyclonic flow developing behind front. This could
bring a more southeasterly wind flow rather than northeast. Wind
speeds should stay under 15 knots.




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