Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 171040
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
340 AM MST Sun Dec 17 2017

.SHORT TERM...(Today and tonight)
Issued at 340 AM MST Sun Dec 17 2017

Areas of light freezing drizzle had developed pretty much as
expected. Enough drizzle to produce wet roads in a few spots.
Fortunately surface temps haven`t dropped much below 30F so roads
temps are holding just above freezing so far. We could still
see icy bridges and overpasses develop where freezing drizzle is
more pronounced. Foothills roads are also colder. We`ll continue
to monitor for any local impacts early this morning.

The drizzle will likely linger through mid morning with a light
upslope component in place - we like the HRRR and ESRL HRRR here.
Thicker fog is mainly confined to the higher terrain where cloud
deck is intersecting with the ground, but some light fog on the
lower elevations of the plains as well.

The low clouds, fog, and drizzle should all be lifting later this
morning into early afternoon as upslope component ceases. There
will likely be some mixing and thus more sunshine later in the
afternoon. High temperatures this afternoon should be able to
rebound to near normal highs for this time of year...in the lower
40s on the plains.

Dry conditions will prevail tonight. Can`t rule out patchy fog
development in low lying colder spots.

.LONG TERM...(Monday through Saturday)
Issued at 340 AM MST Sun Dec 17 2017

A tale of two weather patterns is on tap for the upcoming week.
First off, the first half of the week will be mild and dry, much
like the last month and a half. Flow aloft over the northern
Colorado will be generally weak and westerly as a cut-off low
meanders over the desert southwest. Dry and mild air will move
over the northern half of the state, and the northeast Colorado
plains will see afternoon temperatures climbing back into the mid
50 to lower 60s each afternoon from Monday through Wednesday. MOS
guidance says that Wednesday will be the warmest and last of the
warm days we have been seeing.

Big changes are then in store for the latter half of the week and
the holiday weekend. From Wednesday night through Thursday the GFS
and ECMWF show a sharp upper trough developing over Utah and the
Four Corners region. At the surface, a strong cold front will move
in overnight which will drop temperatures into the 20s through
Thursday. Upslope flow behind the front will combine with dynamic
forcing from the upper trough to produce a period snow over the
mountains and then the plains through much of Thursday. QPF
forecasts from the GFS and ECMWF models indicate that the snowfall
will be light to moderate. Temperatures will get cold Thursday
night as the weather system moves out and skies clear out. Friday
will see a continuation of chily temperatures with highs probably
remaining below freezing. On Saturday, another blast of cold air
is expected to arrive with another round of light snow.
Temperatures Saturday night and Sunday morning could be around
zero in normally cold locations and in the single digits
elsewhere. With the cold temperatures expected to hang around
through the weekend, it looks like any snow that falls on Thursday
and Saturday will still be on the ground come Monday morning.

The change in temperatures and weather conditions after Wednesday
is going to be significant, and residents should take the
opportunity early in the week to get prepared for the winter
conditions we will see over the holiday weekend.

&&

.AVIATION...(For the 12Z TAFS through 12Z Monday morning)
Issued at 340 AM MST Sun Dec 17 2017

IFR conditions have spread across most of the Front Range
Airports, including KDEN. Visibilities down to around 1/2-1 mile
at times, but there should be a slow improvement through 15Z as
surface winds trend slightly southeasterly off the Palmer Divide.
With regard to freezing drizzle, the bulk of it has been just
north and east of KDEN, but latest radar data shows very light
drizzle now in the proximity of KDEN. This may also hang around
through 15Z or so before low clouds start to lift. Expect a
gradual improvement in ceilings 15Z-18Z with a breakout roughly
18Z-20Z. Will have to watch low level wind fields and adjust these
times accordingly. Then VFR conditions later today through
tonight and Monday.

&&

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

$$

SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Barjenbruch



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