FXUS65 KBOU 251620

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1020 AM MDT Tue Apr 25 2017

Issued at 1020 AM MDT Tue Apr 25 2017

Active weather day setting up for this afternoon and evening.
Many features are and will affect the area in the next 24 hours. A
cold front is sinking south across Wyoming at this time.
Northwest winds ahead of it along the Colorado/Wyoming border is
producing an anti-cyclone over the northern Front Range. Here,
winds are east to northeast with higher dew points and cooler
temperatures. This anti- cyclone is expected to slowly advance
south through the afternoon. East to northeast winds will produce
upslope flow along the Front Range and may produce showers this
afternoon. As the main cold front drops south across northern
Colorado this is expected to produce enough lift for scattered
showers and perhaps a few thunderstorms. The front is expected to
push through the Denver area 5-6PM. Upslope flow behind it is
expected to produce more widespread rain early this evening.

Rain is expected to continue to sink this evening and be south of
the Palmer Divide by midnight. It becomes cold enough for snow
mid to late evening. So any lingering precipitation will turn to
snow late this evening. Not expecting much for snowfall since
precipitation is expected to end. The main area of precipitation
will move over southern Colorado and intensify. This is due
upslope lift behind the advancing cold front and an upper level
trough moving into the Four Corners. This trough will also be
responsible for producing scattered snow showers over the
mountains this afternoon and early evening. Snowfall amounts for
the mountains are expected to be a trace to 4 inches.


.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


.AVIATION...(For the 18Z TAFS through 18Z Wednesday afternoon)
Issued at 1020 AM MDT Tue Apr 25 2017

Gusty northwest winds over southern Wyoming and far northern
Colorado is producing an anti-cyclone over the Northern Front
Range. Easterly winds and low clouds have formed over the KFNL and
KGXY area due to the anti-cyclone. West winds at KBJC and KDEN
are expected to turn north to northeasterly around 17Z as this
anti- cyclone sinks south. Tough to tell if the low clouds will
make it into KDEN and KBJC. Will have few 1000 feet for the chance
of these low clouds.

A strong cold front will drop south across the area late this
afternoon bringing northerly winds to 30 knots. This front is
expected to produce showers as well. Best chance for rain showers
will be 22z to 02z. After 02Z, precipitation is expected to sink
south of the KDEN. If it continues past 03Z, precipitation will
likely be snow. Doesn`t appear it will snow long enough for much
if any snow accumulation. Ceilings will lower to MVFR after 00z,
but should improve back to VFR after 09z. Winds will be decreasing
below 10 kts by 06z. If it clear out enough, there will be a
chance for radiation fog around 12z.




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

NWS BOU Office Area Forecast Discussion