Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 162220
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
320 PM MST Fri Nov 16 2018

.SHORT TERM...(This evening through Saturday)
Issued at 320 PM MST Fri Nov 16 2018

Latest model iterations appear little changed from the previous
runs. Although the southward progression of cold air, low clouds
and precip associated with the mid-level open wave trough over
Wyoming appears a bit slower to move over the forecast area next
12-36 hours. Before arrival of the trough, a sfc cold front is
still forecast to slide south across northeast Colorado this
evening; its passage in the Denver area around 03z this evening.
Expect to see gusty north-northeast winds for a short time behind
the front, then a drop off in speeds as winds gradually transition
to an east-northeast component late tonight and tomorrow. Models
show wind speeds increasing again across the far eastern counties
during the late morning and afternoon. The 100kt jet max and
moderate QG ascent over southeast Wyoming tonight moves over
northeast Colorado on Saturday. Models show the strength of the
jet and QG ascent weakening along the way. Before the deeper
moisture and large scale ascent arrives during the day tomorrow, a
shallow, moist upslope flow on the plains and a favorable
temperature profile will set the stage for several hours of
freezing drizzle and areas of fog in the lower Front Range
foothills and adjacent plains. As temperatures cool aloft and mid-
levels saturate, should see the freezing drizzle change over a mix
of freezing drizzle and snow by mid to late morning, first up
around Fort Collins, Greeley and Sterling, then southward across
southern urban corridor and I-70 corridor by early afternoon.
Could see depth of ice accumulation up to a tenth of an inch on
the plains and lower foothills, heaviest southwest of Denver.
Bridges, overpasses and sidewalks will be especially susceptible
to icing up with pavement temperatures falling below freezing.
Heavy cloud cover will significantly limit the amount of melting
tomorrow, and with daytime temps only slightly warmer than low
temps tonight.

Anticipated snow totals by late tomorrow afternoon; 1-3 inches
with the i-25 urban corridor, inch or less east of there, 3-6
inches in the Front Range foothills, and 4-8 inches in the mtns
with the greater amounts in the northern mtns and east facing
slopes.

Ice glazed road surfaces will most likely be the greatest hazard
on the plains with air temperatures expected to remain below
freezing from late tonight after frontal passage through all day
Saturday. Winter driving conditions will also a concern in the
high country on Saturday. Hence the winter weather advisory for
these areas.

.LONG TERM...(Saturday night through Friday)
Issued at 320 PM MST Fri Nov 16 2018

The disturbance that will be affecting our CWA on Saturday will
continue through much of Saturday night. A mid to upper level jet
streak will be near the Colorado-Wyoming border around 00Z Sunday
resulting in ascent over our CWA due to the right entrance region
being overhead. Consequently, the 00Z to roughly 04-05Z period
may have the heaviest snowfall rates from the I-70 corridor
mountains to the Denver metro because the jet dynamics will align
with the best snow ratios during this period. I have increased QPF
and snowfall amounts for the aforementioned areas to reflect the
recent forecast trend for this period. Around 06Z, the upslope
flow over the urban corridor and eastern plains will become much
lighter as the subsident region of the jet streak moves over the
CWA. Snow should begin to quickly diminish and will move out of
the CWA by 12Z Sunday.

By midday Sunday, ridging will develop in the mid to upper levels
with high pressure at the surface. This pattern will last through
Wednesday with no POPs in the forecast and temperatures gradually
increasing each day.

Models then begin to differ on Thanksgiving day. The operational
GFS shows a positively tilted, weak shortwave trough that keeps
almost the entire state of Colorado dry Thursday and Friday. The
Canadian and European models both show a much stronger, negatively
tilted shortwave trough that brings decent moisture to the
Colorado mountains. With this disagreement, confidence in the
forecast is low for Thursday and Friday but there does appear to
be a chance of snow in the mountains. Lower elevations including
the urban corridor look to remain dry for the holiday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 320 PM MST Fri Nov 16 2018

VFR through 03z with passage of a cold front. Then IFR CIGs
and VSBYS after frontal passage. North-northwest winds 6-15kt til
03z, then northwest 12-25kts til 05z, then a gradual shift to the
east-northeast at 6-12 kts where they will remain through tomorrow
afternoon. Low clouds, patchy fog, freezing drizzle and light
after 09z tonight. Light accumulations expected.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory from 3 AM Saturday to midnight MST
Saturday night for COZ035-036-038>046-048-049.

Winter Weather Advisory from 8 AM Saturday to midnight MST
Saturday night for COZ031-033.

&&

$$

SHORT TERM...Baker
LONG TERM...Danielson
AVIATION...Baker


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