Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 221636
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1036 AM MDT SUN MAY 22 2016

.UPDATE...
Issued at 1036 AM MDT Sun May 22 2016

No changes to the forecast at this time, other than trimming back
the coverage of the isolated thunderstorms on the northeast plains
slightly. The HRRR and RAP both keep the plains dry this
afternoon and evening, so pops could probably be removed entirely,
except it would produce a discontinuity across political
boundaries. Also limited the coverage of any showers in the
mountains this afternoon to isolated. The southwesterly flow
aloft is dry, and the source of low level moisture on the eastern
plains is also being cut-off by the lee trough of low pressure in
place across the eastern half of the state. Everything else in the
forecast looks on track.

&&

.SHORT TERM...(Today and tonight)
Issued at 332 AM MDT Sun May 22 2016

Low level flow on the plains has become more southerly the last
few hours as expected. This is shifting the plume of low level
moisture to our eastern tier of counties with drier air working up
from the Monument Hill area toward Fort Morgan. There is still a
pool of low level moisture cut off from the main plume around Fort
Collins and Greeley. The wind shift on the plains is inducing
stronger north winds near the foothills, so there is still a small
threat of some fog/stratus forming in this pocket and advecting
toward Denver. It looks like it may be too well mixed or just a
little too warm for much of this though, so I will stick with the
previous forecast of just patchy fog and low clouds and keeping it
north of Denver.

With drying and slight cooling today, we should be more stable in
most areas and see a minimum of convection, perhaps not even much
cloud cover. There will be some lift and cooling aloft brushing
the northern mountains, so the main threat of showers and storms
looks to be in that area. Best lift and moisture should be further
north though so the isolated POPs look fine. Still a low threat of
storms in the northeast corner as well as the rich moisture is not
far away, but there will probably be nothing there due to
inadequate heating.

Tonight the piece of the trough brushing by us today moves north
of us, dragging a surface boundary/cold front by and shifting the
cooler air aloft a bit further east. This will bring in some
cooler and drier air. I lowered tonight`s lows a couple of
degrees, near the cooler edge of guidance. Lows will be 5-10
degrees cooler due to the cooling, lighter winds and not much
cloud cover.

.LONG TERM...(Monday through Saturday)
Issued at 332 AM MDT Sun May 22 2016

A dry southwesterly flow aloft will be over Colorado the first
part of the week. A cold front Late Sunday night into Monday
morning will slip into the northeast plains. As a result...it
will be cool Monday and relatively stable initially. The models
do show thunderstorms developing over the mountains and moving
into the adjacent plains by 21z Monday aftn. Best CAPE may be
along the Front Range...with more stable airmass to the north and
east. Best coverage will be over the higher terrain...some of this
will spill over into the adjacent plains. Southeasterly winds
will develop across the northeast plains by the aftn which should
help produce a Denver cyclone. Hard to say if the tstms can
overcome the stability behind the front...but the NAM12 soundings
show average CAPE around Denver of 700-800 j/kg. Best chc for
strong tstms may be south and southeast of Denver along the Palmer
Divide. Tuesday/Tuesday night...the upper level pattern does not
change much but temperatures will start to modify. Southeasterly
winds at the surface will again help produce a Denver cyclone.
Better heating, favorable shear and Less CIN around on Tuesday
may increase the chance for a few severe thunderstorms in the aftn
and evening...mainly east of Denver. The NAM12 soundings for
Denver after 18z dry out in the lower levels by the aftn...so the
best low level moisture would be north and east of Denver...with
mainly gusty winds with the storms around the metro area. Severe
potential greatest east of a Sterling to Akron line with sfc based
CAPE in the 1500-2000 j/kg range. Similar synoptic scale set up
for Wednesday...with the best thunderstorm coverage over the
higher terrain with the best svr potential over the northeast
corner of the cwa. The mdls still show the srn extension of the
trough to the west...eventually moving across Colorado Thursday
aftn to Friday aftn. Best mid level QG ascent over the cwa would
appear to be Thursday night. Potential for severe storms may be
better depending on when the trough crosses the cwa prior to fropa
Thursday afternoon. Cooler on Friday with more showers vs tstms.
Warmer with the more conventional aftn/evng thunderstorms next
weekend.

&&

.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 1036 AM MDT Sun May 22 2016

No aviation impacts expected through the next 24 hours as ceilings
and visibilities remain unrestricted. Wind directions will shift
around from time to time, depending on if any shower activity over
the Front Range foothills initiates outflow boundaries late in
the afternoon and early evening. After early evening boundaries
have passed over the area, a weak cold front moving through
overnight will keep winds out of the north to northwest most of
the night. The frontal system should consist of little more than
the wind shift to the north.

&&

.BOU Watches/Warnings/Advisories...
None.
&&

$$

UPDATE...Dankers
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Dankers



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