Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 082159
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
359 PM MDT Sat May 8 2021

.SHORT TERM...(This evening through Sunday)
Issued at 233 PM MDT Sat May 8 2021

Scattered showers and thunderstorms are developing in the pocket
of warmer air east of the Front Range that got sunshine early
this afternoon. Over northeastern Colorado the air is potentially
cooler, but there is probably enough warmth out around Limon to
maintain this activity for a while. The main threat from these
storms, other than lightning, is some amplification of the
background wind gusts. An isolated 60 mph gust isn`t out of the
question, but we mostly expect gusts to be in the 30-50 mph range.

As the storms move east, we`ll be left with drier air aloft at the
same time that low levels see increasing moisture with the cooler
air coming down from the north. This shold produce a stratus deck,
but that should be under an inversion so it`s not clear if we`ll
be able to produce any more showers. It may just become cloudy,
and if there is any precipitation overnight it would likely be out
of this shallow cloud deck and be pretty light. All of this is
still true for Sunday morning, though the clouds may be starting
to deepen a bit. By afternoon there will be a less stability, a
bit more moisture, and a little QG lift. Models look to be
overdoing the QPF from the showers they produce (the 12z NAM had a
foot of snow around Evergreen during the day). But increasing
light showers could produce some light accumulations in the
mountains. For now we cooled temperatures a few degrees to match
the middle of guidance, but with a solid cloud deck it could be
closer to the cooler NAM MOS which keeps the plains in the 40s.

.LONG TERM...(Sunday night through Saturday)
Issued at 233 PM MDT Sat May 8 2021

Sunday night...The airmass over northern CO will continue to
become increasingly moist with showers with some embedded
thunderstorms increasing in coverage across the forecast area.  The
snow level by 12z Monday will range from 6700-7200 feet MSL.  The
models weak to moderate qg ascent developing in the mid and upper
levels Sunday night and continuing across north central and northeast
CO Monday into Monday night.  One piece of energy appears to move
across the region late Sunday into Sunday night, with colder and
deeper main trough moving across northern CO Monday into Tuesday
morning. The most consistent feature associated with this system
will be steady mid and upper level QG ascent and deep moisture.
The upslope overall is deep but fairly weak through the period,
with moist adiabatic lapse rates in place. The best period of
upslope appears (E/SELY) to be Monday night through Tuesday
morning. Moderate to heavy snowfall most likely in the Front
Range mountains and higher foothills, heaviest Monday afternoon
through Tuesday morning. At this time, will hold off on a Winter
Storm Watch, but this will likely need to be issued at some point
with storm totals in the neighborhood of 8-16 inches possible.
The snow level will lower Monday night, 5000-5500 feet, which
could mean some light snow possible for portions of the urban
corridor by Tuesday morning. GFS has has been the coldest and much
more bullish regarding snowfall across the northeast plains, but
it also remains the biggest outlier. For this reason, will
continue with more of a blend with the other models as they seem
more reasonable regarding the precipitation. Mainly rain or
rain/snow mix for the urban corridor and northeast plains, with
the potential of a brief switch to snow around 12z Tuesday. By
Wednesday a drier and more subsident northwesterly flow aloft will
be in place ahead of a building ridge of high pressure. By the
end of the week, a broad ridge will be over the west with a
persistent northwest/westerly flow aloft over northern CO.
Temperatures will climb back above normal, in the mid/upper 70s by
Friday.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 233 PM MDT Sat May 8 2021

Thunderstorms will move east away from the Denver area in the late
afternoon. Scattered weaker showers are likely to develop by early
evening. The wind direction will continue to vary between west and
north, then become north behind a cold front by 00z. Instrument
approaches to KDEN will likely be needed after 00z. Areas of MVFR
conditions will develop by 12z as ceilings continue to lower,
with scattered showers continuing mainly south and west of Denver.
The showers will gradually increase with MVFR conditions becoming
more widespread on Sunday afternoon.

&&

.HYDROLOGY...
Issued at 233 PM MDT Sat May 8 2021

Only isolated weak showers are expected over the burn areas
through tonight. On Sunday the showers will become more numerous,
but precipitation is still expected to be light and the snow level
is expected to be between 7 and 8 thousand feet, so no flood
threat is expected.

For Sunday night thru Tuesday morning, there will be periods of
snow. Tuesday will see some snow in the morning with decreasing
chances by late afternoon. Since much of the precipitation is
expected to fall as snow, the flood potential is expected to be
low.

&&

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

$$

SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Gimmestad
HYDROLOGY...Cooper/Gimmestad


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