National Weather Service Forecast Discussion

000
FXUS65 KBOU 230134
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
734 PM MDT Sun Oct 22 2017

.UPDATE...
Issued at 733 PM MDT Sun Oct 22 2017

Cirrus cloudiness is still moving southeastward across the CWA at
present in the strong northwesterly flow aloft. Models are still
showing weak cold front to move into the plains and lower
foothills from 12Z to 15Z Monday morning. Sky grids look okay, so
do the wind fields.  Will make a few minor alterations.

&&

.SHORT TERM...(This evening through Monday)
Issued at 240 PM MDT Sun Oct 22 2017

Strong west/northwest flow aloft will keep gusty winds in the
forecast across the mountains and wind prone areas of the
foothills through early Monday. Cross sections show cross mountain
flow increasing to 45 knots this evening, and stable layer
lowering a bit toward mountain level. As a result, should see
mountain wave increase and could see some gusts upwards of 70 mph
on the higher mountain peaks and wind prone areas of the
foothills. Later tonight into early Monday the forward shear
increases, so mountain wave should begin to break down with wind
speeds gradually decreasing. On the plains some gusty winds to
around 30 mph have spread onto portions of the I-25 corridor and
Wyoming/Nebraska border area. Those winds may stay occasionally
gusty in proximity of mountain wave, and then a cold front
arriving late tonight near the northern border.

That front should push back through Denver and the rest of the
plains Monday morning. Gusty winds will occur behind the front
especially on the eastern plains where gusts around 40 mph
expected. There is a bit of mid level moisture associated with a
passing short wave to our north, so will continue mentioning a few
light snow showers in the northern mountains mainly north of the
I-70 Corridor. Temperatures will be a good 10 degrees cooler,
leaning toward the cooler side of guidance this time of year with
upslope component in place.

.LONG TERM...(Monday night through Sunday)
Issued at 240 PM MDT Sun Oct 22 2017

Northwest flow aloft will prevail Monday night into Tuesday, with
speeds decreasing as the upper high builds in to the Great Basin
and the jet pushes east over the Great Plains. Gusty northwest
winds are expected with downward QG motion and a surface high
pressure pushing down from the northern Rockies. Tuesday`s
temperatures will be similar to Monday`s readings.

Wednesday will see a warm up, of 8 to 15 degrees as prevailing
flow aloft becomes westerly ahead of the incoming weather system
out of Canada. Humidity readings will be the lowest Wednesday,
though the only concern fire weather wise will be over the
northern state border where the higher winds will be. Nothing up
to criteria at this time however.

An initial cold surge is expected in the early morning hours of
Thursday as the upper positively tilted trough moves into western
Colorado. the moisture isn`t expected to arrive until the
afternoon with an additional cold northeasterly push. This is when
precipitation will affect mainly the Front Range mountains,
foothills, urban corridor and Palmer Divide. At this time, wet
bulb zero height should change rain to snow over the urban
corridor during the late afternoon. This will be a quick hitting
storm, so amounts overall may not be impressive, but could be
impactful due to the short time it will fall in. The area will be
under the left front quadrant area of the jet as well, adding to
the dynamics of the system. Warm temperatures from the day before
will have ground temps likely warm enough to melt the initial
snowfall. Not sure how fast it will clear behind the initial
moisture push as another jet max moves down, so low temperatures
may not bottom out as cold as what is currently forecast, into the
20s over the plains.

The second jet max will delay the upper trough from kicking out
until later Friday, so expect continued cold temperatures on
Friday but mostly dry conditions. The weekend will then return to
warm and dry conditions as a strong upper ridge over the west
coast pushes inland.

&&

.AVIATION...(For the 00Z TAFS through 00Z Monday evening)
Issued at 733 PM MDT Sun Oct 22 2017

Models keep weak westerly surface winds at DIA overnight. They
appear weak enough that normal drainage flow will likely win out.
Maybe a bit more southwesterly in direction than normal drainage.
Speeds look to be no more than 12 knots overnight. There will be
no ceiling issues, just some higher altocumulus and cirrus clouds.
A cold front is expected to get into DIA around 13Z-14Z. Wind
directions should be 360 to 030 degrees initially. Speeds should
be no more than 15 knots initially, then decrease and become more
northeasterly during the morning. Even with the upslope a low
Stratus ceiling is unlikely.

&&

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

$$

UPDATE...RJK
SHORT TERM...Barjenbruch
LONG TERM...Kriederman
AVIATION...RJK

NWS BOU Office Area Forecast Discussion