Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 271648
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1048 AM MDT Sat May 27 2017

.UPDATE...
Issued at 1048 AM MDT Sat May 27 2017

A band of showers associated with the passing upper level trough
has been moving south and eastward through the morning hours with
light rain on the plains and a mix of snow and rain in the
mountains. Web cameras in the mountains show that roads have been
staying bare and wet, even as snow showers continue. Radar data
shows weak showers re-developing over the mountains after the
passage of the main band of showers. Temperatures have remained
cool due to northerly winds and the presence of the rain showers.

No changes to the forecast necessary at this time. Sunbreaks
should be short-lived through the afternoon as any surface warming
that occurs will cause instability showers to pop up. The upper
trough axis is expected to remain over northeast Colorado through
tonight with cool temperatures aloft. Model soundings show only
weak instability, so only a few thunderstorms will be possible.
embedded in the other afternoon showers that develop.

Drying is expected through the evening and overnight with the
loss of daytime heating and a drier airmass moving in from Wyoming.

&&

.SHORT TERM...(Today and tonight)
Issued at 139 AM MDT Sat May 27 2017

An upper level trough will move across the area today and then move
southeast of the area by this evening.  Meanwhile sfc high pres will
move into nern CO with upslope low lvl flow.  As a result will see a
good chc of showers with a few tstms across the rgn today. Activity
will decrease fm nw to se by late aftn into the early evening hours.
Snow will occur in the mtns abv 10000 feet with 2 to 4 inches
possible in some areas.  As for highs readings will only be in the
upper 50s to lower 60s across most of nern CO.  By tonight pcpn will
gradually end by early evening as the upper level moves out of the
area.

.LONG TERM...(Sunday through Friday)
Issued at 139 AM MDT Sat May 27 2017

Sunday and Sunday night, a moderate northwesterly flow aloft will
be over CO with an upper level ridge centered over NV. The
airmass will be drier, but still enough moisture around in the
afternoon to trigger scattered showers and tstms. Surface high
pressure over the northeast plains will keep isold to scattered
showers and tstms in the afternoon, especially over the mountains.
Not much instability over the plains with fcst CAPES of 100-200
j/kg in the aftn. In addition, a weak disturbance embedded in the
flow aloft is progged to clip northeast CO late Sunday night,
which may help to produce some late night/erly showers around 12z
Monday. The overall pattern will not change much through the
middle part of the week, with temperatures gradually modifying. A
surface high will help to cap most the thunderstorm activity over
the northeast plains, with the best chc of showers and storms
over the mountains. Discrepancies pops up at the end of the week
between the GFS and ECMWF. The GFS shifts eastward with the flow
aloft transitioning from northwesterly to southwesterly. The ECMWF
maintains an upper level ridge over the region. For now will
continue with typical showers/tstm coverage each aftn/evng over
the area.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1048 AM MDT Sat May 27 2017

Off and on shower activity is expected through the afternoon with
mostly VFR conditions. Visbilities may drop to the 3 to 5 mile
range with some of the showers. Ceilings will mostly be in the
4000-6000 feet AGL range. Showers are expected to taper off after
4 PM with ceilings improving after that. Winds will be northerly
through the afternoon and then turn to drainage southerlies
overnight.

&&

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

$$

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



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