Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 212048
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
248 PM MDT Thu Sep 21 2017

.SHORT TERM...(This evening through Friday)
Issued at 248 PM MDT Thu Sep 21 2017

Southwest flow aloft will increase over Colorado tonight and
Friday as an upper level trough over the western states slowly
progresses eastward. A very warm airmass has brought temperatures
in the upper 80s to lower 90s over northeast Colorado today. A dry
airmass with light winds will allow for good radiational cooling
tonight. Low lying areas over northeast Colorado where light winds
prevail should fall into the 40s. Higher areas will remain in the
50s.

A surface trough will be draped across northeast Colorado Friday.
Cooler air will prevail to the north of the surface trough while
it will be very warm again to the south of it. Models disagree
where the surface trough sets up. Some models show it staying
north of Colorado until early evening, while others show it
stalling along I- 76. So low confidence in the temperature
forecast for northern parts of the area. Moisture begins to
increase over the mountains and there will be a chance for showers
and thunderstorms late in the afternoon. The best chance will be
over the north central mountains. There will also be a slight
chance for storms over the far eastern plains. Though it doesn`t
appear enough moisture will be available.

.LONG TERM...(Friday night through Thursday)
Issued at 248 PM MDT Thu Sep 21 2017

Major changes in upcoming weather pattern for this weekend and
beyond across much of Colorado. Much cooler temperatures and a
better chance for showers will return starting on Saturday with a
return to typical fall weather. The culprit is a broad upper trof
which will settle across the Great Basin on Saturday and then
inch into far western Colorado on Sunday. Expect increasing QG
ascent spreading over the area on Saturday with the best chance of
showers by later Saturday evening and night. Expect some light
snowfall in the mountains, but snow levels will generally be above
10000 feet for the weekend.

In addition surface cold front will sweep over northeast Colorado
Saturday morning and will increase shallow upslope flow and
moisture. The low and upper trof will lift out and weaken as it
moves into Wyoming on Monday. Much of the moisture and lift will
shift further east of Colorado. There will still be enough
moisture for continued chance of showers right through the middle
of the week as more energy keeps dropping into the mean trof.
Temperatures throughout the period will be well below normal.

Drying and warming trend Thursday through next weekend as high
pressure ridge builds into the western U.S.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 248 PM MDT Thu Sep 21 2017

VFR conditions will prevail through Friday. Clear skies will
continue into Friday morning. High clouds will start to increase
Friday afternoon. Southerly winds will generally prevail through
Friday afternoon at KDEN and KAPA. A Denver Cyclone may bring
variable winds occasionally at KDEN. At KBJC, winds will be
variable and light most of the time.

&&

.FIRE WEATHER...
Issued at 248 PM MDT Thu Sep 21 2017

Gusty south to southwest winds to 35 mph combined with relative
humidities in the lower teens will keep critical fire weather
conditions in place through early evening along the Palmer Divide
and across the plains south of I-76. Gusty southerly winds are
expected Friday afternoon again over the eastern plains.
Humidities are expected to be in the upper teens, so no fire
weather highlights at this time. There is also a chance a cold
front north of Colorado moves in sooner and brings cooler and more
humid conditions Friday.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 7 PM MDT this evening for COZ241-245>247-
249.

&&

$$

SHORT TERM...Meier
LONG TERM...Entrekin
AVIATION...Meier
FIRE WEATHER...Meier


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