Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 250704

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

Issued at 732 PM MDT Mon Apr 24 2017

Sfc low was just south of Denver with a fntl boundary extending
ese towards Limon. North of this bndry higher based showers
continued to dvlp as this rgn was in left fnt quadrant of upper
level jet. Meanwhile main upper level low was developing over
scntrl WY and associated mid lvl ascent was allowing for showers
to increase in the nrn mtns. Expect these showers will move across
nrn areas of the plains especially after midnight with a few
tstms possible.


.SHORT TERM...(This evening through Tuesday)
Issued at 221 PM MDT Mon Apr 24 2017

For late afternoon and early evening, an easterly upslope flow
and convergence along a boundary is expected to produce isolated
showers and thunderstorms along the Front Range and across the
eastern plains. Moisture and instability is limited, so the
showers and storms are expected to be weak and short lived.

GOES-16 water vapor satellite imagery showing a short wave trough
over northern Nevada and southern Idaho. It is producing
widespread precipitation ahead of it over southeast Idaho and
northern Utah at this time. As it progresses eastward, it will
close off over Wyoming tonight. The precipitation is expected to
shift eastward with the system tonight. This should result in rain
and snow over the high county. Snow level will be around 10000
feet MSL to start off with and lower through the night. Expect the
heaviest precipitation to be over northern Colorado where the
best lift will be. Moist westerly flow around the base of the
trough will result in orographic lift over the mountains which
will also help produce precipitation. In addition, the left exit
region of the jet will be over Wyoming and northern Colorado and
provide lift. The jet sinks south late tonight and will help
provide lift over central Colorado. Snow amounts for the mountains
are expected to be 2 to 6 inches overnight. The highest amounts
are expected to be over the northern mountains.

Expect a brief break in precipitation over the area Tuesday
morning. By afternoon, the next short wave trough digs southeast
and will be centered over the Four Corners. Lift from this,
combined with increasing north to northeast winds along the Front
Range, is expected to produce scattered showers. Best lift will be
south of I- 70, so will have the highest pops here. Cloud cover
and a cooler airmass will result in cooler high temperatures with
readings in the mid to upper 50s.

.LONG TERM...(Tuesday night through Monday)
Issued at 221 PM MDT Mon Apr 24 2017

A split-energy low will be over the state with the upper level jet
to the south over NM. QG energy will increase over the southern
portions of the state Tuesday night into Wednesday helping to focus
much of the precipitation south of I-25. With the aid of a northerly
push earlier in the day and cooler temperatures expect rain to
change over to snow with snow levels starting around 7000ft dropping
down to 5000ft overnight...however this will occur as precipitation
starts to diminish on the plains. At this time snowfall amounts
look to be 2 to 6 inches for the mountains and a trace to 3 inches
on the plains with the higher amounts over the Palmer Divide and
portions of Douglas and Lincoln counties by Wednesday morning.

The next system in line to impact the area will be embedded in NW
flow aloft by late Wednesday into early Thursday. Moisture will
increase ahead of the disturbance bringing snow to the mountains
late Wednesday into Thursday morning. For this system snowfall
amounts in the mountains will range from 4 to 8 inches by late
Thursday. Models indicate some showers making it onto the plains by
thursday afternoon with little QPF forecasted. Another cold push
will move south by late Thursday into early Friday.

By Friday the upper low will dig further south into CO with the
models showing the system cutting off by late Friday over the four
corners region. The changemaker for this system will be the much
cooler 700 mb temperatures along with the introduction of increased
Pacific moisture. This will help to increase chances of snow over
the Plains for Friday into Saturday. Models are still ironing out
the details but moderate rain and snow along with cooler
temperatures is expected for the region Friday and Saturday. The
cooler trend will start earlier in the week with highs on Thursday in
the mid to upper 50s cooling into the 30s on Saturday. With
increasing subsidence behind the main branch of energy Saturday
conditions could clear out dropping overnight lows below freezing.


.AVIATION...(For the 00Z TAFS through 00Z Tuesday evening)
Issued at 103 AM MDT Tue Apr 25 2017

A line of showers and embedded thunderstorms is pushing east
across the northern Front Range urban corridor, pushing low
stratus and gusty northwest winds ahead of the line. Ceilings of
2000 feet will be common. Thunderstorm activity should stay north
of DEN. Once this line passes in the next hour and out over the
eastern plains, some low ceilings may linger for another hour
before ceilings go back toward 8000 feet or higher. The
northwesterly winds look to transition to easterly behind the line
of showers/storms due to outflow, then will be difficult to
predict the direction through the rest of the night. Winds will
likely becom northwesterly again Tuesday morning before a cold
frontal push Tuesday afternoon. Look for showers to increase in
coverage after 20z, with locations against the foothills to be
favored. Ceilings will lower to MVFR after 00z.




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