Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 132147
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
247 PM MST Mon Nov 13 2017

.SHORT TERM...(This evening through Tuesday)
Issued at 247 PM MST Mon Nov 13 2017

Dry and mild weather will persist through Tuesday. A flat upper
level ridge will shift east as a trough moves through the northern
Rockies Tuesday. The gradient increases a bit with stronger winds
aloft Tuesday, so gusty winds across the mountains should spread
into the high mountain valleys during peak heating. On the plains,
generally lighter winds can be expected with a weak backdoor cold
front arriving in the afternoon. With regard to clouds, we look
for some mountain wave enhancement later tonight through Tuesday.
However, there should be enough thin spots and sufficiently
shallow inversions to allow temps to warm into the mid to upper
60s over the plains.

.LONG TERM...(Tuesday night through Monday)
Issued at 247 PM MST Mon Nov 13 2017

On Wednesday a flat ridge is centered over Colorado with dry
west-southwest flow aloft. The flow aloft should induce surface
lee troughing across the I-25 urban corridor, with a Denver
Cyclone setting up somewhere near metro Denver. This will act to
keep temps down along the urban corridor with a pretty good
inversion around 700/650 mb. It will be dry area-wide but cooler
with highs low 50s I-25 urban corridor, mid 50s eastern Plains and
upper 40s to mid 50s in the mountains with continued warm 700 mb
temps of 4-5 degC. Not expecting significant winds anywhere.

On Thursday a short wave trough approaches Colorado in the west-
southwest flow, with origins from the Central Pacific. As a
result, there appears to be a fair amount of available moisture to
work with. Before the storm arrives a significant amount of warm
advection occurs at 700 mb, warming temps 5-6 degC compared to
Wednesday, and the Plains will once again experience "shorts
weather" with high temps in the upper 60s. Mountains will also be
quite warm with upper 40s to mid 50s again on Thursday. The models
are still having a difficult time pinning down the timing of the
arrival of precipitation across northern Colorado. GFS and now
the NAM are faster than ECMWF and Canadian models. The U.S. models
have precip via west upslope flow beginning around midday
Thursday, while the ECMWF and Canadian models bring precip into
our area around midnight. In terms of ingredients for snow, west-
southwest upslope will be strong for 24-36 hours, likely resulting
in some impressive snow totals for favored locations like the
Park Range, northern Gore Range, and west slopes of the northern
Front Range. Best synoptic lift is across the northern half of
Colorado, with strong lift late Thursday night into Friday
midday. There will be added lift on the mesoscale via a 150 kt
westerly Jet Streak moving across colorado. The left exit region
of the jet looks to be across the northern half of Colorado around
midday Friday, through the GFS indicated much stronger lift from
the jet based on position and orientation, while the EC jet is
further north along the Wyoming border. Given the juxtaposition
of favorable lift and moisture, highlights may be needed for the
northern mountains late Thursday through Friday. Snow levels will
start off high for this time of year around 8500 during the day
Thursday. Cold air aloft is slow to arrive, looking like the snow
levels should come crashing down to the valley floors between 12
and 18Z Friday on the back side of the 700 mb trough. The
atmosphere dries out by late Friday, likely shutting off the
mountain snow with dry northwest flow. Across the East Slopes and
Plains, arrival of the strong WSW winds aloft late on Thursday
will increase the winds across Plains via mixing, and overnight
lapse rates do not look favorable to force the strongest winds
into the lower foothills and adjacent Plains. Will still be very
windy across the higher elevations of the Front Range. Friday will
be windy pretty much everywhere. In terms of precipitation
chances, downslope flow will limit precipitation chances the
further east of the Continental Divide you go, with just 15-20%
PoPs in place Friday across the Plains north of I-70. One thing to
watch is if the jet ends up being where the GFS places it further
south across C. CO, then PoPs would need to be higher than they
are now, particularly NE Plains with banded precipitation possible
with the jet. Any precip that falls across the Plains is likely
to be rain given warm temperatures and light precipitation rates.

Saturday and Sunday should be dry area-wide with northwest flow
aloft throughout the period. Temperatures should gradually warm on
Saturday and even more on Sunday...both days should be above
normal (Average high in Denver on 11/19 is 50). We do not
anticipate any wind issues during the day Saturday or Sunday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Tuesday afternoon)
Issued at 247 PM MST Mon Nov 13 2017

VFR conditions will persist through Tuesday with only sct-bkn high
level cloudiness. Light east/southeast winds should transition to
normal south/southwest winds 01Z-04Z and hold through about 18Z.
Then winds should turn more northeasterly 18Z-21Z Tuesday.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Schlatter
AVIATION...Barjenbruch



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