Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211109
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
409 AM MST Fri Feb 21 2020

.SHORT TERM...(Today and tonight)
Issued at 409 AM MST Fri Feb 21 2020

Northeast Colorado will get an early glimpse of Spring today as
temperatures warm to slightly higher than normal under sunny skies
and gentle breezes. High pressure ridging at the surface and aloft
will be responsible for the dry and pleasant weather. Temperatures
will start the day quite cool in some spots, including the high
mountain valleys of North, Middle and South Parks. However, the
cold and dense air should yield to the warm airmass that is moving
into the state by early afternoon. Temperatures on the plains will
also undergo rapid warming through the late morning and early
afternoon hours.

Mostly clear skies and normal seasonal temperatures will prevail
tonight as the upper level ridge axis remains over the state. High
level moisture will begin moving over the state, but should do
nothing more than increase high level cloud cover, mainly after
midnight.

.LONG TERM...(Saturday through Thursday)
Issued at 409 AM MST Fri Feb 21 2020

A storm system will be over srn California, on Sat, with a flat
upper level ridge across nrn Colorado. Thus, should see dry
conditions, with warmer temps across nern CO, as a sfc lee trough
is in place. The only potential issue, is for a higher level deck
of clouds, to move northeast across the plains by midday, which
would cut off insolation. For now, have kept aftn highs in the 55
to 60 degree range across the plains.

By Sat night, the upper level low over srn California, will
begin to eject rapidly east northeast, and by 12z Sun, will be
near the four corners area. Ahead of this feature, there will be
considerable moisture advecting into the region, which will
affect portions of the mtns late Sat night. Across nern CO, expect
generally dry conditions Sat night, although could see a chc of
rain and snow along the front range after 09z.

On Sun, there is general agreement among the models, that the
upper level low will track mainly eastward along the srn CO/nrn NM
border, and will be located over swrn KS by early Sun evening.
Unfortunately, despite the the agreement in the track of this
system, there are substantial differences in QPF forecasts among
the models. The NAM, Canadian and Hires WRF have QPF amounts in
excess of an inch, from the srn foothills across the Palmer
Divide extending into Lincoln county, with areas further north
having substantially less precip. Meanwhile, the latest ECMWF has
QPF amounts generally less than a quarter inch across much of the
area for Sun. Furthermore, the normally wet GFS has QPF amounts
similar to the ECMWF, except up to a half inch in and near the
foothills.

Overall, there appears to be a few factors leading to the large
discrepancy in QPF forecasts.  The NAM, Canadian and Hires WRF
have a much more organized system moving across, with far deeper
upslope, moisture and stronger mid level ascent. Meanwhile, the
ECMWF is more disorganized and has much weaker upslope, less
moisture and only weak mid level ascent. The GFS has more of a
compromise solution between the wetter models and the much drier
ECMWF. At this time, overall confidence in the amount of precip
that may occur with this system is low. Naturally, if the wetter
solutions are to be believed, there would be the potential for
heavy wet snow especially along and south of I-70 from the
mountains across the plains.

Moving ahead to Sun night, the storm system will gradually shift
eastward into the central plains, with precip ending over the
area during the evening. On Mon, a strong upper level trough will
dig south southeast from the nrn Rockies, with a strong upper
level low developing over the central plains by Mon night. Cross-
sections show favorable orogrpahics, in the mtns, with steep
lapse rates and moisture depth up to 500 mb. In addition,
position of the upper level jet, would place the mtns in favored
left front quadrant, for increasing vertical motion. Thus, should
see decent snowfall across portions of the mtns, Mon aftn thru
Mon night.

At lower elevations, a bora type front is currently fcst to blast
across nern CO Mon aftn into Mon evening.  Current cross-sections
show strong downslope in place which would limit precip potential.
However, if winds turn more to the north over the Palmer Divide,
there could be a chc of light snow in those areas.

For late Mon night into Tue, an intense upper level low will remain
over the central plains, with north to northwest flow aloft over
nrn CO. A surge of colder air will move across nern CO, with
cross-sections showing a substantial increase in moisture as
well. Thus, may see a better chc of light snow along the front
range and plains. In the mtns, will continue to see periods of
snow, although orographics will be weaker. Temperatures will be
colder over nern CO, with readings likely staying in the 20`s for
highs.

Looking ahead to Wed and Thu, drier air in NW flow aloft will be
over the area. This will lead to dry conditions along with
moderating temperatures.

&&

.AVIATION...(For the 12Z TAFS through 12Z Saturday morning)
Issued at 409 AM MST Fri Feb 21 2020

No aviation impacts today. Mostly clear skies and unrestricted
visibilities through the next 24 hours. Winds will generally be
light and out of the south to southeast.

&&

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

$$

SHORT TERM...Dankers
LONG TERM...RPK
AVIATION...Dankers



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