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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
251 PM MDT Sat Apr 25 2015

Short term...(this evening through sunday)
issued at 251 PM MDT Sat Apr 25 2015

Upper trough currently digging into the Great Basin with southwest
flow increasing over Colorado. Weak shortwave trough ahead of it
has sparked convection off over Colorado. A surface low over
south central Colorado will push further south as high pressure
from the Great Plains pushes in...advecting in higher dewpoints.
Increasing qg lift and convective available potential energy of 500-750 j/kg out on the northeast
plains will allow stronger storms mainly east of an eastern Weld
County to northern Lincoln County line. Not expecting too much in
the way of severe strength storms as winds aloft are not that
strong and given a more saturated airmass. Could still see gusts
to 40 miles per hour and small hail. Convective activity further west toward
the urban corridor will begin drier this afternoon with gusty
winds and virga...then as higher dewpoints filter in...there will
be a better chance for rain. Cape should stick around over the
northeastern plains most of the night with increasing
moisture...will likely see showers/storms continue through the
night. Mountains have snow levels around 10kft this afternoon and
it will likely only lower to about 9kft tonight. Showers and
thunderstorms will continue through the evening with some areas
able to pick up a few inches but it will be spotty in nature.

As flow turns more easterly and more moisture is advected in
overnight...will likely see low stratus and fog develop over the
plains especially as it hits up against the higher terrain. Flow
will turn more southeasterly which will likely pile moisture
against the northern foothills and Cheyenne Ridge. Have 1/2 mile
visible expected overnight...may need to think about a dense fog
advisory over this area.

Upslope flow will increase in speed and depth tomorrow as upward
qg motion remains overhead as the trough deepens into a cut off
low over northern New Mexico. Latest GFS and ec model runs have
trended slightly cooler. Therefore have issued a Winter Storm
Watch for the Front Range mountains starting noon tomorrow
with the east slopes the main focus. There will be plenty of will depend on temperatures on how much snow
accumulates. Also...some cape being forecasted over the high
terrain which could increase amounts in localized areas. For
now...expect 2 to 8 inches to fall over elevations above 9000 feet
tomorrow. Over the plains...upslope flow will keep
clouds....showers and fog around with a slight chance of
thunderstorms. This will limit heating during the
temperatures are expected to stay in the upper 40s to middle 50s.
Easterly surface winds will increase through the day.

Long term...(sunday night through saturday)
issued at 251 PM MDT Sat Apr 25 2015

Upper level low will track slowly east across northern/central New
Mexico Sunday night. Very moist upslope flow with around 0.6 inch
precipitable water will remain over the forecast area through the
night. The heaviest precipitation will likely continue from the
Sunday afternoon hours into Sunday evening in/near the Front Range
when upslope component is deep and strongest near 20 knots. It
should be noted the latest 12z model trends have turned a bit
colder...allowing for the snow level to drop quicker in the
evening during the heaviest precipitation. Snow level could now lower to
around 6500 feet by early Monday morning per latest data.

We ran the local orographic precipitation model and some rather
large numbers were kicked out for the Front Range mountains in
both quantitative precipitation forecast and snow...especially Sunday evening. There will likely
be a large variation over the higher foothills and Front Range
mountains with total snowfall amounts literally ranging from just
an inch or two to upwards of 20 inches. Overall forecast reflects
a blending of the orographic model with synoptic/mesoscale model
consensus. The Winter Storm Watch for the Front Range mountains
above 9000 feet will remain in effect for Sunday night until noon
Monday...although snow intensity is expected to gradually decrease
as the upslope component and q-g support both weaken through early
Monday morning. There is some potential a watch or jump to a
warning could be needed in the higher foothills...but given only
the latest model run has trended colder will allow further
diagnosis before adding any appropriate highlights there. Most
likely...the heaviest snow in the foothills would be confined to
elevations above 8000 feet since the heaviest precipitation occurs early
in the period when it is warmer...but will continue to monitor. We
will likely see the snow level eventually drop down to the Palmer
Divide late Sunday night into Monday morning with at least a
couple of inches there. Still expect nothing but rain from the
Denver metropolitan area north and east across the plains. The bulk of
the heavier precipitation will be shifting quickly tomorrow evening to
the Front Range...but a few showers should also continue on the
eastern plains into Monday morning.

By Monday afternoon...system support continues to drop away from
the region so we will see a gradual decrease in precipitation
into Monday evening. If skies clear Monday night then could see
below freezing temperatures even on the plains...but another short wave
could keep temperatures a bit warmer with some clouds. That weak wave may
attempt to produce isolated showers Tuesday...but models are
trending away from this scenario for now.

Then warmer and drier conditions expected for Wednesday. Above
normal temperatures will likely hold until next weekend when
a glancing short wave is possible. We do anticipate moisture to
gradually build under the ridge with isolated to scattered
afternoon and evening convection in the mountains by
Thursday...and over all of the forecast area Friday and Saturday.


Aviation...(for the tafs through 00z Sunday late afternoon)
issued at 251 PM MDT Sat Apr 25 2015

Expect showers and thunderstorms moving off the higher terrain
and across the Denver area through about 00z...then high res
models continue showing a break in activity through 03z...then
another wave of activity through 06z. Main threat will be gusty
outflow winds up to 40 knots. Ceilings will briefly fall below
6000 feet under the stronger showers and storms. Easterly winds
will transport low level moisture into the area late
tonight...after 06z Sunday. This will bring low clouds and areas
of fog. By 12z Sunday...expect ceilings will be below 1000 feet
with a good chance of fog with visibility a half mile or lower.
Hard to forecast right now if it will be drizzle or rain showers
overnight. Rain is expected to increase Sunday with continued IFR/LIFR

Wind direction continues to be very tricky as a Denver cyclone
is beginning to be affected by convection. Overall expect winds
to generally trend toward a northerly direction this afternoon as
the main surface low heads south...then easterly later this
evening...veering to southeasterly late tonight into Sunday. These
southeast/east winds will increase in speed through the day


Bou watches/warnings/advisories...
Winter Storm Watch from Sunday afternoon through Monday morning
for coz033-034.



Short term...kriederman
long term...barjenbruch

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