Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 242153
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
353 PM MDT Sat Oct 24 2020

.SHORT TERM...(This evening through Sunday)
Issued at 343 PM MDT Sat Oct 24 2020

A major change is in store for tonight and Sunday.  An upper level
trough will move south from the nrn Rockies into the Great Basin by
Sun aftn.  Meanwhile a strong cold front will move across the area
tonight with gusty north to northeast winds developing behind it.

Overall, QG fields keep best QG to the west and north of the area
overnight thru Sun aftn. However, the position of the upper level
jet will likely enhance precip overnight near the CO-WY border.
This jet will then slowly move south on Sun with banded type snow
spreading southward during the day. Cross-sections vary with NAM
having a more northeast component in the lower levels while the
GFS is more from the north. The ECMWF is a compromise solution
with NNE winds. Moisture depth is favorable in all models. Main
driving force for heavier snow will be banded precip. This can be
difficult to forecast so confidence in snow amounts is still on
the lower side. Have issued warnings for the mtns, foothills and
higher valley for late tonight thru Sun night. At lower
elevations, have opted for a warning along the I-25 Corridor with
the heaviest amounts near the foothills. Across the plains will
have advisories.

Furthermore there also could be some freezing drizzle after midnight
through early Sun morning over the plains before precip becomes all
snow. As for highs on Sun, temperatures will stay mainly in the
teens to lower 20`s.

.LONG TERM...(Sunday night through Saturday)
Issued at 300 PM MDT Sat Oct 24 2020

A positively tilted trough will be positioned across far
northwestern Colorado Sunday evening with a surface low pressure
center located over northwestern New Mexico. Widespread snow will
be falling across our forecast area due to QG ascent out ahead of
this trough along with upslope flow in the low levels. A jet
streak over the upper Midwest along with a jet streak over
northern New Mexico will position our forecast area under
additional rising motion which could create heavy bands of snow
for much of the evening. Snowfall rates will be 1 to 2 inches per
hour in the heavier bands with hazardous travel conditions. As the
mid to upper level trough begins to cut off over eastern Arizona
and the best QG ascent moves to the south of our forecast area,
snow will begin to taper off Monday morning. Snowfall during the
day on Monday should be less than 2 inches south of Denver and
less than an inch north of Denver. Mid level height rises and
warming aloft will put an end to the snow late Monday
afternoon/evening.

Frigid temperatures will be of note during the latter part of this
storm system. The ECMWF MOS has been the coldest guidance with a
mean low temperature of -3 degrees at KDEN Sunday night. However,
with snow showers still ongoing and relatively thick, low level
cloud cover persisting, low temperatures should not end up being
that cold. Lows in the Denver metro should end up being in the low
single digits nearing the record low of 3. Highs Monday will be
in the upper teens in Denver setting a record cold max temperature
breaking the record of 31. Monday night will again see record
cold temperatures with lows in the single digits breaking the
record of 11.

Our forecast area will see subsident flow on Wednesday as a mid to
upper level ridge builds over the Intermountain West. Some models
are showing the cut off low over the Southern Plains coming far
enough northwestward to produce a little light snow over the very
far southeast portion of our CWA. The track of the cut off low
will need to be monitored but it doesn`t appear like much of a
threat to produce snow for our area.

Colorado will generally be under mid to upper level ridging Thursday
through next weekend with any trough being extremely minor. This
period will see a general warming trend with dry conditions. If snow
cover melts near the fires, fire danger will need to be monitored.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 243 PM MDT Sat Oct 24 2020

Winds were northeast late this as a sfc low was south of DIA.  Later
this evening a stg cold front will move across with gusty northeast
winds for a few hours with an increase in low clouds.  Overnight may
see light freezing develop and affect DIA in the 09z to 14z period.
After 14z precip should be all snow.  Snow will increase Sun aftn
and continue thru Sunday evening.  Total accumulations of 4 to 6
inches will be possible.

&&

.FIRE WEATHER...
Issued at 317 PM MDT Sat Oct 24 2020

Major pattern change will end fire danger threat later this
evening through Sun. Much colder temperatures will occur with
several inches of snow expected on the fires.

&&


.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 6 AM Sunday to 6 AM MDT Monday for
COZ042>051.

Red Flag Warning until 7 PM MDT this evening for COZ211>218-241.

Winter Storm Warning from midnight tonight to 6 AM MDT Monday
for COZ030-031-033-035.

Winter Storm Warning from 6 AM Sunday to 6 AM MDT Monday for
COZ032-034-036>041.

&&

$$

SHORT TERM...RPK
LONG TERM...Danielson
AVIATION...RPK
FIRE WESTHER...RPK



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