Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231530
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
930 AM MDT Tue May 23 2017

.UPDATE...
Issued at 930 AM MDT Tue May 23 2017

Current forecast for today looks on track. With strong northerly
flow instability is limited this afternoon. Dry air remains in
place east of the mountains with mid 30s dewpoints at the surface.
GOES-16 and and high res model output show quite well a 100 kt
jet streak diving south across Colorado midday through the
afternoon, and from Noon to about 3 PM northeast Colorado will be
in the left exit region of this jet. Isolated rain showers are
possible mainly along and east of a Ft. Morgan to Limon line, but
the chances of rain reaching the ground at any one point across
the Eastern Plains is still very low (15-20%). Thunder is not
likely today.  The core of the jet swings east by late afternoon
which should end rain chances and both mesoscale (from the jet)
and synoptic scale (from the approach of the upper ridge)
subsidence will lead to mostly clear skies tonight and zero chance
of precipitation.

&&

.SHORT TERM...(Today and tonight)
Issued at 419 AM MDT Tue May 23 2017

Current satellite imagery shows partly cloudy skies with scattered
to broken mid level cloud decks. Showers have ended for the most
part, with only a couple left in the mountains and a few up north
in eastern Wyoming.

Today will feature cool temps and breezy conditions in the post
trough environment. Low level lapse rates will steepen with
daytime heating, and should be enough to produce at least isolated
shower coverage over the plains. Most of these should stay east
of a Greeley to DIA line, as a sharp subsidence inversion will be
developing from west to east across the forecast area as upper
level ridge axis builds in.

Mostly clear skies and cool temperatures can be expected by this
evening as the upper ridge continues to build over the Central
Rockies.

.LONG TERM...(Wednesday through Monday)
Issued at 419 AM MDT Tue May 23 2017

Wednesday will be the warmest day of the week as medium range
models all show upper ridging over the southwestern U.S. with the
ridge axis centered over Colorado Wednesday afternoon. By that
time, warm air out of the desert southwest will have moved over
the state, delivering mostly sunny skies and afternoon
temperatures in the lower 80s. The warm spell will be short lived
though, as the ridge progresses eastward in advance of an upper
trough digging over the Pacific Northwest. An initial surge of
cooler air is expected to move in Thursday morning, holding
afternoon temperatures in the lower 70s. Dynamic forcing
associated with the approaching trough will generate afternoon
showers, mainly over the mountains. The effects of the upper
trough and then northwesterly flow aloft across Colorado are then
expected to persist into the holiday weekend. Cooler temperatures,
in the 60s, will last through Friday and Saturday along with
periods of afternoon and evening shower/storm activity. Friday
evening may have the highest chances of shower activity as the
ECMWF jet level charts show a sub-tropical jet over southern
Colorado and the northern jet over southern Wyoming. That will
make for lots of dynamic lift over the region.

The latter half of the holiday weekend will see moderation in
temperatures, but a continuation of the chance of afternoon and
evening showers. Northwesterly flow aloft will bring some warmer
air over the state, but any short wave impulses embedded in the
flow pattern will be able to support showers that initiate off the
higher terrain during the afternoon hours. The availability of
Gulf moisture is going to be limited by the progressive nature of
the weather pattern, so strong thunderstorms are not expected.

Mountain areas could see a mix of rain or snow showers at times,
but no significant snow accumulations are expected at any time.

&&

.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 930 AM MDT Tue May 23 2017

No CIG/VIS issues expected at DEN, BJC, or APA through Wednesday
afternoon, and VFR conditions will prevail.  A strong pressure
gradient is setting up presently that will continue through 00Z,
with current NNW flow at all three TAF sites turning almost due
north and increasing to 15 kt with gusts over 20-25 kts expected
late morning through the afternoon. Windspeeds will be a bit lower
at BJC however. After 00Z the gradient relaxes and winds should
stay 10 kts or lower thereafter, and draingage winds kick in.
Expect south and south-southwest drainage winds 8-10 kt at DEN and
APA by 06Z. BJC drainage winds will be out of the west and light
most of the night. After about 15Z tomorrow we anticipate the flow
pattern for midday through the afternoon to be west to west-
northwest at the three TAF sites, and in the 10 kt range.

&&

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

$$

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



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