Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 190021

Area Forecast Discussion
National Weather Service Denver/Boulder CO
621 PM MDT Sun Mar 18 2018

Issued at 620 PM MDT Sun Mar 18 2018

Strong spring storm will race across the region tonight.
Precipitation west of I-25 has changed to snow or will shortly in
the few locations it hasn`t. Nudged snowfall amounts up a little to
reflect the earlier change over the snow. This puts snowfall amounts
in the 2-4 inch range for the Denver area. HRRR and RAP models show
the precipitation ending in the metro area around or a little before
midnight. If the heavy precipitation rates linger for a few hours or
if it appears snow will last a little longer may need to expand the
winter weather advisories.


.SHORT TERM...(This evening through Monday)
Issued at 258 PM MDT Sun Mar 18 2018

Satellite pictures are showing an oblong circulation right over
the four corners at the bottom of the upper trough to our west.
Convection is breaking out over the high mountains and foothills
and Palmer Ridge at this time. There is a bit of lightning
detected over southwestern Larimer County. The cloud shield of the
system is slow to get across the CWA. Have been backing
off/delaying the cloudiness on the GFE grids all day. The wind
field over the plains shows mainly northeasterlies in place at
this time. The 12Z models all show an upper closed low over the
northeastern corner of the Texas Panhandle at 06Z and over
southeastern Kansas at 12Z. I suppose it better get moving.
Weakening zonal flow aloft is progged all day Monday. The
strongest QG ascent is progged at 00Z late this afternoon. The
system is moving quickly and by 06Z-09Z tonight downward energy
is in place over the CWA; pretty strong too. The low level winds
are progged to be north-northeasterly into mid evening, then more
north-northwesterly for the rest of tonight. They are due
northerly all day Monday. Moisture-wise, there should be plenty
over the CWA tonight, and fairly deep as well. Models have quite
a bit still around on Monday too. The QPF fields have measurable
precipitation across all of the the CWA tonight. There is some in
the high mountains all day Monday. Overall, the 12Z model runs
showed a bit less precipitation than the previous runs. Will keep
the current highlights going as is. Strong wind gusts will cause
havoc to travelers later tonight with blowing snow. Areas under
decent convection could see more precipitation and snow then is
expected otherwise. Monday`s highs will be about 10-15 F below
normals for the plains and foothills.

.LONG TERM...(Monday night through Sunday)
Issued at 238 PM MDT Sun Mar 18 2018

By Monday night, the upper level trough will push eastward bringing
NW flow over the state. Conditions on the plains will be dry, but
some light snow will continue in the mountains with model cross
sections showing decent mid level moisture through the morning
hours. Less than an inch in accumulations will be possible.

Tuesday and Wednesday will see upper level ridging increasing
bringing a period of dry conditions and warming temperatures.
Temperatures should rebound back to above normal conditions with
highs in the 60s.

The next weather system will be moving onshore over the western
coast by Thursday with continued ridging over the state. WAA will
increase 700mb temps in the +6-7C range. This will give surface
temperatures on the plains of lower 70s, the warmest day of the
week. In the mountains, increased subtropical moisture from the SW
ahead of the trough will bring increased chances of light rain and
snow to the western slopes through the day Thursday. Thursday night
into Friday and upper level shortwave combined with some CAA from
the WNW will help to bring cooler temperatures and accumulating snow
to the mountains Thursday night into Friday. A deep surface low over
the CO/KS border will help to maintain dry conditions on the plains
through Friday morning according to the GFS. The EC is slightly
slower with the progression of the upper level energy that could
bring a slight chance of rain to the plains by Friday afternoon.


.AVIATION...(For the 18Z TAFS through 18Z Monday afternoon)
Issued at 258 PM MDT Sun Mar 18 2018

Models have been doing okay with the wind direction so far. They
keep north-northeasterlies in at DIA well into the evening, then
they become more north-northwesterly around 04-06Z. The cloud
cover has been slow to move in and or develop with this system.
Ceilings could get below BKN060 after 23Z. The lower ceiling and
precipitation is still expected this evening. Ceilings should get
above BKN060 around 15Z Monday morning.


Winter Weather Advisory until noon MDT Monday for COZ031-033>035.

Winter Weather Advisory until 6 AM MDT Monday for COZ041-046.



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