Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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448
FXUS65 KBOU 251036
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
436 AM MDT Tue Apr 25 2017

.SHORT TERM...(Today and tonight)
Issued at 430 AM MDT Tue Apr 25 2017

The band of showers and thunderstorms that pushed over the area
overnight is diminishing over the mountains as moisture decreases,
and continuing east over the eastern plains, although weaker as
the main upper trough pushes into Nebraska and Kansas. Expect the
rest of the showers to exit the state by 8am this morning.

Another shortwave trough rounding the upper low over Wyoming will
move across the state this afternoon pushing a cold front across
the area. High temperatures will be about 10 degrees cooler than
yesterday. Snow levels will be around 7000 to 8000 feet today
with showers increasing this afternoon across most of the area.
The cold front should sink south in the late afternoon, increasing
moisture, upslope flow and lowering the snow level. Northerly
winds will be gusting to 40 mph. Look for snow to begin to mix in
over the plains by around 9pm, but at the same time, most of the
moisture will have pushed south of the area where the greater
upward QG motion will be located, and subsidence will be spreading
over northern Colorado. The southern suburbs and the Palmer
Divide will have the best chance of seeing accumulating snow over
the plains, with a trace to 2 inches possible. 2 to 6 inches of
snow can be expected over the high country, mainly along the
higher eastern slopes of the Front Range mountains. Skies will
clear late tonight to allow for temperatures to reach or drop
below freezing. Enough moisture in favored northwesterly flow
should allow for some clouds and light orographic snow showers
over the mountains.

.LONG TERM...(Wednesday through Monday)
Issued at 430 AM MDT Tue Apr 25 2017

...Active weather will remain in place this week...

For Wednesday, we should start off mostly on the dry side with
flat upper level ridging over Colorado. There is enough moisture
in the high country to mention a few snow showers in the morning.
In the afternoon, we will be destabilizing and enough moisture is
still present to keep a few showers over the mountains, and a low
chance of those spreading onto portions of the plains. Temperatures
will be a few degrees warmer with slight downsloping to work
with, but still below normal.

By Wednesday night and Thursday, Q-G lift will be increasing
as the nose of a strong 150+ knot jet drives across the Great
basin. This in combination with deep Pacific moisture should bring
another round of accumulating snow to the high country. There is
some drying as noted in the Specific Humidity progs by Thursday,
but orographics appear pretty strong with near neutral to slightly
unstable lapse rates. As a result, we should see a moderate
accumulation of snow over the mountains with generally a 4-8 inch
forecast for the elevations above 9000 feet. Should see a few of
the showers in the form of rain spill onto the plains, with the
highest chance near the Wyoming border where Q-G support is deep
from the surface through the upper levels. With the passing short
wave, there may also be a frontal surge and low level convergence
to help generate showers and a couple thunderstorms through the
afternoon and evening.

Attention will then turn to Friday and Saturday. While the models
are all pretty similar now, the difficulties in this forecast
period hinge on the details and exact evolution of this system.
For the most part, models have trended a bit northward with some
energy lost to the lead short wave on Thursday. Then, the next
piece of energy still drops toward the Four Corners area with a
good chance of upslope for the plains late Friday into Saturday.
Temperatures are colder and will be sufficient for most of the
resultant precipitation to fall in the form of snow. The main
question will be how much as all of the details have yet to be
worked out. Overall, precipitation forecasts have been decreasing
since some energy is lost to Thursday`s lead short wave. Will
continue to watch the medium range models for better consensus on
the details, but confidence remains limited at this time.

Drier and warmer weather is expected to develop by Sunday and
Monday, before another potential storm system moves in toward
Tuesday.

&&

.AVIATION...(For the 12Z TAFS through 12Z Wednesday morning)
Issued at 430 AM MDT Tue Apr 25 2017

Winds have become southeasterly behind last nights precipitation
band, with ceilings improving to above 10kft with drier subsident
air moving in. Winds will become northwesterly again later this
morning as winds mix down, before a cold front pushes in stronger
northerly winds late this afternoon, with speeds of 15-30 kts.
Look for showers to increase in coverage after 20z, with locations
against the foothills favored in upslope flow. Some snow will mix
in after 03z, though precipitation will be decreasing and pushing
south by then. Ceilings will lower to MVFR after 00z, but should
improve back to VFR after 09z. Winds will be decreasing below 10
kts by 06z.


&&

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

$$

SHORT TERM...Kriederman
LONG TERM...Barjenbruch
AVIATION...Kriederman



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