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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
944 am MDT Friday Aug 29 2014

issued at 940 am MDT Friday Aug 29 2014

There was quite a bit of dryness and stabilization over the area
overnight and early this morning...however this will be short
lived. Water vapor imagery showing another weak wave moving
southeast across Wyoming this morning. This will brush northern
Colorado this afternoon and evening with increasing moisture
values. Precipitable water values are only around a half inch at
this time but trends are starting to increase again over past few
hours. Upstream soundings also have cooling aloft at 500mb and
this cooling will help to destabilize the airmass this afternoon.
Marginal instability with surface based convective available potential energy up to around
800j/kg. Expect brief rain and gusty winds with the showers. Maybe
some small hail with the stronger storms. Only minor changes to
current forecasts with a slight upward trend in probability of precipitation and areal
coverage of showers later this afternoon and evening.


Short term...(today through tonight )
issued at 425 am MDT Friday Aug 29 2014

Decent quasigeostrophic subsidence presently over the area will
gradually weaken as the period progresses...changing sign in all
but the far northeast plains. This subsidence and modest
downslope flow have taken their toll on precipitable water east of
the mountains as GPS sensors are measuring roughly a third of an
inch less water than was the case yesterday at this hour. Despite
this current drying trend satellite imagery shows some middle level
cloud upstream from US in the northwest flow which supports the
model forecasts of increasing precipitable water and instability
numbers and generation of widely scattered convection over most
areas during the afternoon and evening hours. With forecast cape
values remaining rather tame expect most convective activity to
remain relatively benign although some hail and gusty winds are
not completely out of the question. Maximum temperatures in all
areas should be warmer today. Expecting skies to clear for the
most part overnight although CIRA-generated synthetic satellite
imagery shows cloudiness with the next system approaching the
western reaches of the County Warning Area towards 12z.

Long term...(saturday through thursday)
issued at 230 am MDT Friday Aug 29 2014

Operational models and ensembles show a long wave trough
extending from the Pacific northwest coast to the northern/
central Great Plains...with its axis passing over Idaho and Nevada
late on Saturday. This places Colorado under a warm...relatively
dry southwesterly flow during the day. Temperatures on Saturday
will have little difficulty climbing well into the 80s at lower
elevations...and into the very mild 60s and 70s across the high
country. Even with precipitable water values continuing to fall...
strong daytime heating and wet soils should still manage to
generate isolated to widely scattered T-storms in the high country
during the afternoon. May see some of this disorganized convection
drifting out over the plains by evening...with most of it only
producing gusty outflow winds and light rainfall based on the
inverted-v soundings from the NAM and GFS. Storms should let up by
middle-evening except perhaps along the far eastern edge of the County Warning Area
where models show a ribbon of high dewpoints being moved along by
gusty southerly winds along a stalled out surface trough. Therefore may see
a stray storm or two linger beyond midnight out that way. On
Sunday...the upper trough axis is prognosticated to swing eastward across
Colorado during the day with qg vertical velocities increasing
through the morning hours. Qg vertical velocity values appear somewhat stronger
on the slower NAM compared to the GFS. As the cold pool aloft and
trough axis pass...models show convective precipitation breaking out...
first in the high country as early as mid-morning. Convection
appears more developed and widespread on the NAM...esply along and
west of the Continental Divide. During the afternoon with the
trough axis passing overhead and with pressure falls on the
plains...models show gusty west-northwesterly winds developing over and along the
Front Range. This downslope flow is likely to sap much of the
energy and moisture from this system as it moves east of the mountains
as indicated by the GFS...European and Canadian models. Whereas
the NAM shows a more organized line of convection/storms tied to
the upper trough axis and a surface frontal boundary moving out across
the plains during the afternoon. Right now...based on the fact all
four models show a gusty downslope flow developing east of the leaning towards the drier model solutions. And with cold
air advection could see temperatures topping out not long after
midday. Storms should move out and/or dissipate by evening.

The period Monday through Thursday...starts out with a broad upper
trough over the western 2/3rds of the Continental U.S. And a dry zonal flow
over Colorado. Temperatures start out near seasonal norms on
Monday with ridge building along the West Coast. As the ridge
migrates inland across The Four Corners region...temperatures will
continue to rise and the chance of storms should remain low and
largely confined to the high terrain. By the end of the period...
medium range models show the start of another cycle of monsoon
precipitation for the southern and central Rocky Mountain region as models
show a tropical storm system exiting the Gulf of Mexico and
tracking across the northern Highlands of Mexico. However the effects
of this new surge of subtropical moisture may not be felt around
here until Friday or Saturday of next week at the earliest.


Aviation...(for the tafs through 18z Saturday morning)
issued at 940 am MDT Friday Aug 29 2014

No changes planned to upcoming 18z tafs with still best chance of
storms in the 21-00z time frame. Could still be some showers
beyond 00z but coverage not enough to continue probability of precipitation. Surface
winds expected to shift northwest later this am and then more
northeast this afternoon.


Bou watches/warnings/advisories...


long term...Baker

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