Scientific Forecaster Discussion
fxus65 kbou 131103
Area forecast discussion
National Weather Service Denver/Boulder Colorado
403 am MST Wed Nov 13 2019
Short term...(today and tonight)
issued at 226 am MST Wed Nov 13 2019
Currently 88-d radar imagery showing well defined mountain wave
signature over higher east slopes across Boulder and Larimer
counties. Observations showing wind gusts in the 30-50 mph range
with a few higher gusts up to 60 mph over the High Mountain
passes. Quite a bit of wave cloudiness as well and coupled with
the wind, has kept overnight temperatures in the 40s/50s across
foothills and adjacent plains. Based on cross sections and current
radar trends, the higher wind gusts will slowly decrease through
the morning hours.
An upper level disturbance and cold front will brush northern
Colorado today with mainly cooler temperatures and windy
conditions developing on the plains. The winds will be decreasing
in the mountains and foothills by later this morning as the
mountain wave breaks down due to increasing shear profile from the
upper jet to the north and weakening surface pressure gradient.
700mb temperatures expected to drop to around -3c with low level
cooling the atmosphere. The system is rather dry as any showers
will mainly remain further north across Wyoming and Nebraska.
Possibly a few morning flurries over the higher mountains would be
the extent of any precipitation. The winds will increase across
the plains later this morning and afternoon with modest subsidence
sweeping in behind the system and enough low level mixing. Gusts
in the 25-35 mph will be possible through late afternoon.
For tonight, appears another weak ripple will brush northern
Colorado with some cloudiness across the plains but no showers
expected. Temperatures will be cooler along with less windy
conditions across the mountains and foothills.
Long term...(thursday through tuesday)
issued at 330 am MST Wed Nov 13 2019
Outside of a quick shot of precipitation and cooler temperatures
on Saturday, the long term period will feature mild and dry
A shortwave trough will be exiting eastern Colorado Thursday
morning with ridging developing behind it. Subsident flow
associated with this ridge will stay over our County Warning Area through Friday
night which will keep conditions dry. Highs will be slightly above
normal on Thursday and then well above normal on Friday as
stronger downslope flow develops. A 70 degree high in Denver on
Friday is well within reason.
A shortwave trough will dive southeastward through Colorado on
Saturday. Models show rather large disagreement on the strength
of this trough. The GFS is the strongest with the trough showing 500
mb heights as low as 562 dm over Farmington, nm while the
Canadian is weakest with 500 mb heights of 578 dm over the same
location. The European model (ecmwf) is a nice middle ground between those two
solutions so I trended my forecast towards it. A quick shot of
precipitation will move over our County Warning Area likely starting as rain east
of the foothills but quickly changing over to snow around sunset.
Expect light snowfall amounts over the mountains, foothills, and
Palmer Divide while very little, if any, accumulating snowfall is
Colorado comes under the influence of a seasonally strong ridge
that moves across the Desert Southwest Sunday through Tuesday. Dry
northwestly flow will persist throughout this period with
temperatures warming well above normal.
The Wednesday through Friday period next week may be one to keep
an eye on. Models generally show a deep trough over the western
half of the U.S. Which taps into Pacific moisture. It's still way
too far out for any further details on this system, though. The
climate prediction center has eastern Colorado in a 60 percent
chance of above normal precipitation for the 6-10 day forecast so
a wet period seems to be a good bet.
Aviation...(for the 12z tafs through 12z Thursday morning)
issued at 226 am MST Wed Nov 13 2019
VFR with mainly mid/upper level cloudiness, mainly this morning.
Surface winds will be south to southwest, but shifting west and
then northerly by mid morning with weak cold front at den/apa.
The strong winds at bjc will decrease after 12z with receding
mountain wave and decreasing west to east pressure gradient.
Surface winds will gradually shift east and southeast by later
this afternoon as wind speeds decrease.