Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 211645

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1045 AM MDT Sun May 21 2017

Issued at 1044 AM MDT Sun May 21 2017

Adjusted PoPs and wind forecast after following observational
trends. Nice focus line of cu building over Washington County
southwest into Elbert County. Likely a starting point for
convection shortly. Showers over the northern plains and foothills
will begin to spread south late this morning into the afternoon.
Models are having differing solutions of winds and precipitation
due to one or two northerly pushes. Seems precipitation may last
longer into this evening and past midnight. Adjusted the forecast
slightly to show this trend.


.SHORT TERM...(Today and tonight)
Issued at 310 AM MDT Sun May 21 2017

Satellite shows a very weak shortwave over the the forecast area
this morning with mid and high clouds, and even a few light
showers over southeastern Colorado. The next wave now located in
northern Utah and southeast Idaho will have more of an impact on
our weather today, with more numerous showers and thunderstorms.
This feature should reach the forecast area during or just after
peak heating, resulting in scattered showers and thunderstorms.
Highest coverage should initially occur over the mountains, and
then across the southern portions of the Denver Metro area/Palmer
Divide late this afternoon and evening, as those locations are
most likely to be in the right entrance region of a weak upper
level speed max. Overall, Q-G is rather weak so main forcing would
likely be driven by daytime heating and the speed max. There is
some shallow upslope to help coverage of showers a bit, so the
forecast will be adjusted slightly to account for those features.

Otherwise it will be a couple degrees warmer in most locations
today. Still some snow above 9000-10000 feet with a couple inches
in the heavier snow showers. Showers may linger a bit longer than
normal with some weak forcing this evening, but then gradually end
overnight with partial clearing as subsidence begins to build in.

.LONG TERM...(Monday through Saturday)
Issued at 310 AM MDT Sun May 21 2017

One disturbance will exit the rgn early Mon morning which will be
followed by another feature late in the aftn into Mon night.  The
2nd feature will have some weak qg support. In addition nrn CO will
be in the favored left fnt quadrant of an upper lvl speed max.
Thus with increasing moisture will see a good chc of showers and
a few tstms over the higher terrain by late aftn and across the
plains. Furthermore a cool fnt will move across the plains as well
by mid to late aftn with some upslope component into the evening
hours. As a result this may enhance pcpn potential in and nr the
foothills in the evening hours. As for highs readings will be in
the lower to mid 60s across nern CO before fnt moves across.

On Tue brisk nly flow aloft will be over the area with nern CO
remaining in the favorable portion of the upper level jet.  There
will still be some mid lvl moisture so can`t rule out at least a
slight chc of showers through the aftn hours.  As for highs will
keep readings in the lower to mid 60s over nern CO.

For Tue night into Wed drier air will spread across the area in nwly
flow aloft so no pcpn is expected.  Meanwhile as a sfc lee trough
dvlps downslope warming will occur which will allow for highs to
rise into the 70s across the plains.

On Thu the flow aloft will become more wsw as an upper level trough
moves across the nrn Rockies.  Meanwhile a wk bndry is now fcst to
move into nern CO which may allow for some increase in low lvl
moisture and increasing instability.  Thus will mention a slight chc
of showers/tstms across the area.  As for highs readings will stay
in the 70s across the plains.

By Fri the flow aloft will remain wsw as an elongated upper level
trough extends fm the nrn plains back to the pacific NW.  Both the
ECMWF and GFS show a bndry across the plains with deeper low lvl
moisture with better instability.  Thus this may lead to an
increasing chc of storms.  Over the higher terrain activity will be
more widely sct.  As for highs readings will remain in the lower to
mid 70s across nern CO.

On Sat a piece of energy moves across the area as a fntl bndry
affects the plains.  As a result both the ECWMF and GFS have a good
chc of showers and tstms over nrn CO.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1044 AM MDT Sun May 21 2017

VFR conditions will prevail, but there will be an increasing
chance of showers and thunderstorms after 21Z today with an upper
level disturbance and daytime destabilization. At this time,
expect 30-40% coverage of showers and storms, unless upper level
support ends up a bit farther north which would result in higher
coverage over the Denver Metro area airports. Brief visibility
restriction to 5SM, gusty winds to 30 knots, and ceilings down to
4000 feet or so possible with storms. Otherwise ceilings 18Z-06Z
should stay above 8000 feet. Wind forecast is difficult as models
are showing different northerly pushes later today. Terminals
currently light northerly, should increase to around 10-12 knots
after 18Z, though it may take until 20z, with perhaps another
push around 00z.


Issued at 310 AM MDT Sun May 21 2017

Latest river data shows the South Platte River is cresting early
this morning around Fort Morgan, while slowly receding upstream at
the Weldona and Kersey gauges. Kersey has fallen below action
stage so will cancel the advisory for the Weld county section.
Only minor flooding of fields and meadows can be expected farther
downstream from Morgan county into Logan county into Monday
morning where a flood advisory remains in effect.




SHORT TERM...Barjenbruch
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