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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
335 am MDT Sat Aug 1 2015

Short term...(today through tonight )
issued at 252 am MDT Sat Aug 1 2015

Elongated upper high extending from the Pacific northwest and
stretching southeast through Texas with resultant northwest flow
aloft over northern Colorado. Airmass in this flow is rather dry
and stable over far northern Colorado and qg fields still showing
substantial subsident airmass in the 500-700mb layer over the
northeast plains. Best moisture will again remain over southern
Colorado and extending to just south of the Interstate 70
corridor. Soundings indicate continued capping inversion in the
middle levels on the plains while low level warming continues with
readings a few degrees higher today. Will continue the trend of
lower probability of precipitation over southern portions of the County Warning Area.

Long term...(sunday through friday)
issued at 252 am MDT Sat Aug 1 2015

Shortwave trough pivoting around a deep upper low off the northern
California coast is forecast to swing over the 4-corners region Sunday
morning...then over central Colorado by late afternoon...and
eventually over the Colorado Front Range by Monday morning. Models
best resolve this feature in the 700-500 mb layer with the wave
showing up strongest on the NAM and weakest on the Canadian Gem.
European model (ecmwf) appears to be a suitable compromise among the operational
models. That said...European model (ecmwf) indicates some amplification in this short wave
trough as it slowly passes over Colorado during the day Sunday. Its
passage weakens and displaces eastward the resident upper ridge and
the shift to southwesterly flow aloft taps into a region of subtropical
moisture pooled over northern New Mexico/northestern Arizona. European model (ecmwf) qg Omega
fields indicate only weak lift with this feature and yet the ec
and other models show light/moderate quantitative precipitation forecast over much of southwestern/central
Colorado by Sunday evening. NAM and to a lesser degree the
GFS...show a few bands of light quantitative precipitation forecast extending eastward over the
plains of northestern Colorado by late afternoon with a moist and
marginally unstable east-southeasterly low-level flow. Not showing up in this
latest model run is the band of 1200-2200 j/kg of cape over the
Palmer Divide late Sunday afternoon. However the NAM indicates a
northwest-southeast band of 1000-1400 cape straddling the northestern corner of the
state at that time. Convective available potential energy on the other models under 250 j/kg.
Therefore have less confidence that T-storms capable of
hail...heavy rainfall and strong gusty winds will form over the Palmer
Divide. For now will stick with 30-50 percent probability of precipitation in the high country
and 10-30 percent probability of precipitation at lower elevations on Sunday. And with greater
cloud cover going with maximum temperatures a degree or two lower than those on
Saturday.

Sunday night/Monday...expect to see considerable middle/high-level
cloudiness with passage of the shortwave. Models indicate the best
forcing and middle-level instability over mountain areas overnight and
over the northestern plains during the day. During the day...models show
a 700-500 mb shear/deformation axis and a surface trough/dryline
moving out across the northestern plains. Models not indicating much 0-3 km
cape and lapse rates only marginally unstable presumably because
of all of the cloud cover. Still models indicate several pockets
of light quantitative precipitation forecast on the plains. Previous forecast had 10-20 percent probability of precipitation
at lower elevations. Now chance of measurable precipitation looks
slightly better. So will raise probability of precipitation by 10-20 percent. Monday should be
cooler with highs 2-3 degree f lower than the day before.

On Tuesday...eastern portions of the County Warning Area may still feel modest affects
of the shortwave in the form of cooler temperatures and upslope cloudiness
along the Front Range during the morning hours. Shortwave moves east
of the state by afternoon allowing the upper ridge to regain its
hold on the region. With cooling at low levels and warming
aloft...see only a slight chance of precipitation/T-storms over the
higher slopes of the Front Range in the afternoon...and across the
far northestern corner of the state as the back side of the short wave trough
brushes the area.

On Wednesday...models show the upper ridge over the central/southern Rocky
Mountain region continuing to gain strength. Local airmass also continues
to warm and dry with highs on Wednesday likely to be the warmest of
the week with middle-90s maximum temperatures common on the plains.

Rounding out the week...medium range models show the upper ridge
holding strong over the Rocky Mountain region...although its northern
fringe flattens as a shortwave trough races east across Montana and
Wyoming on Thursday. Not looking for any precipitation on Thursday except
perhaps a few late day showers over the high mountains Friday appears
to start out dry. Then models show a weak disturbance rounding the
top of the ridge and generating a smattering of showers/T-storms as
it passes over the forecast area during the afternoon. For now will
stick with low probability of precipitation. Temperatures Thursday and Friday near to slightly
below average with Friday being the cooler day.

&&

Aviation...(for the tafs through 12z Sunday morning)
issued at 252 am MDT Sat Aug 1 2015

VFR today with minimal impacts today as any convection will
remain well south of terminals. Could be some return outflow from
showers to our south. Otherwise south to southeast surface winds
will become some sort of easterly component this afternoon.

&&

Bou watches/warnings/advisories...
none.
&&

$$

Short term...entrekin
long term...Baker
aviation...entrekin

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