Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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295
FXUS65 KBOU 220304
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
904 PM MDT Fri Apr 21 2017

.UPDATE...
Issued at 853 PM MDT Fri Apr 21 2017

Current satellite imagery shows lingering showers over the
foothills and plains east of Denver. Some isolated showers have
made their way over the Denver metro but will clear out over the
next hour. Models indicate mid level energy moving SE that will
help to bring a slight chance of showers to portions of the
southern foothills and south of I-70 on the plains through the
late evening hours. Weak upslope conditions will be possible
as the surface low that is placed over the eastern plains moves
west keeping some weak snow showers over the higher terrain
through the overnight hours. Still can`t rule out the possibility
of light snow over the foothills and urban corridor overnight as
temperatures drop but confidence is low that anything will occur
east of the foothills. Made minor adjustments to pops and sky
grids, otherwise forecast is on track.

&&

.SHORT TERM...(This evening through Saturday)
Issued at 336 PM MDT Fri Apr 21 2017

Current satellite and radar analysis shows mid level circulation
spinning southeast across southern Washington county late this
afternoon. Subsidence is building in behind it, with
precipitation intensity and coverage generally diminishing. The
exception is the convective development occurring in/near the
Front Range but even here intensity has been limited by northwest
flow a couple thousand feet above the ground. This downslope
component however is expected to decrease through the evening with
a more of a northeasterly push. As a result, should see further
shower development through early evening along the Front Range.
Snow level is already lower than advertised by most model data,
with snow still occurring in the middle of the afternoon from
Cheyenne to Pine Bluffs and southward just across the Wyoming
border. Foothill locations should see amounts in the 1-4 inch
range through tonight, with perhaps up to 6 inches in a few spots
that see more persistent heavier convective showers. Right now
that favors the foothills north of I-70, and most likely toward
the Wyoming border as another convective area is sinking southeast
with another weak short wave. That wave is indicated to reach the
northern portions of the forecast area late this evening, so may
see showers linger overnight with a few more spreading onto the
plains. Overall these should be light, but that also means lower
elevations will see a chance of some snow including the Denver
metro area. At this time, we do not anticipate more than a dusting
possible on grassy surfaces, and a worst case scenario of an
inch.

On Saturday, expect any lingering morning rain and snow showers
to dissipate with stronger subsidence finally building in. Can`t
rule out a few convective showers in/near the Front Range
Foothills through the afternoon, but overall expect some
moderation and drying on Saturday. High temperatures will be about
5 degrees below normal.

.LONG TERM...(Saturday night through Friday)
Issued at 336 PM MDT Fri Apr 21 2017

The forecast period will start out dry and warm from Sunday into
Monday as an upper ridge builds over the Great Basin then moves
over Colorado. However, the ridge will be developing in the
larger context of a very progressive upper level flow pattern
that is going to dominate weather over the western U.S. through
the latter part of next week. As soon as the ridge develops it
will be moving out, with each of the mid-range models showing the
positively tilted ridge axis over eastern Kansas and Missouri by
Sunday evening. Colorado will be under southwesterly flow aloft
through Monday with increasing moisture through the day. Scattered
snow showers should be moving into the northern mountains by
Monday afternoon. The rest of the week is forecast to have brisk
westerly flow across the western half of the country, including
Colorado. Pacific moisture will be embedded in the westerly flow,
and next week will feature periods of light snow continuing in the
mountains. On the plains, short wave impulses embedded in the flow
pattern will likely kick off diurnal showers each day. It is
difficult to pinpoint whether any day is preferred over any other.
This will also keep temperatures around normal through the week.

By the end of the week, the ECMWF and GFS present two different
solutions as some sort of trough amplifies over the intermountain
west. The main feature of this is going to be cooler temperatures
and a better chance at a more organized storm system next Friday
or Saturday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Saturday evening)
Issued at 853 PM MDT Fri Apr 21 2017

Showers will linger around area airports through the overnight
hours with conditions going between IFR and MVFR through 07z. IFR
conditions expected through at least 04z with the possibility of
extending until 05 to 06z with increased low level moisture at BJC
and DIA. Winds will be light from the NE before moving more
easterly then SE by 07z. ILS conditions expected through 18z
tomorrow before conditions are able to scatter out in the lower
levels. Winds will return to NE during the afternoon tomorrow
before returning to the south.

&&

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

$$

UPDATE...Bowen
SHORT TERM...Barjenbruch
LONG TERM...Dankers
AVIATION...Bowen



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