Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 151808
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1108 AM MST Sun Jan 15 2017

.UPDATE...
Issued at 1102 AM MST Sun Jan 15 2017

With the first wave of precipitation pushing north over the
eastern plains, areas have experienced a mix of light freezing
rain and light to moderate snow. This band will continue moving
north with a brief break behind it before another round pushes up
this afternoon. Comparing current conditions to models, NAM had
its area of moisture/precip way too far west, where as the GFS has
a better idea of position but is too dry. The high res models do
pretty well initially, but the concern is that there may be a
slight influence from the NAM and bringing moisture too far west
too early. Have adjusted PoPs to reflect current conditions and
blended them into a blend of high res models and previous
forecast.

Expect areas of freezing rain and snow to continue east of a line
from Limon to Sedgwick this afternoon, with the threat of freezing
rain moving north and out of Lincoln County by this evening,
remaining over Washington, Sedgwick and Phillips counties.

Models are trending toward an extra push of snow against the
northern Foothills and nearby plains tonight then slightly more
snow tomorrow morning as surface to 700 mb winds going just east
of northerly. Have increased PoPs and snowfall amounts across the
Front Range mountains, foothills and adjacent plains to account
for this. Overall, snow amounts remain low, with 1-3 inches across
the urban corridor, and 2-5 inches over the eastern plains.
Mountains should see anywhere from a trace to 6 inches, with the
lesser amounts north and west of the Divide.

&&

.SHORT TERM...(Today and tonight)
Issued at 338 AM MST Sun Jan 15 2017

Upper level low will be near El Paso at 18z Sunday and then lift
northeast across Texas and Oklahoma tonight. By 12z Monday, the
center of the low will be over north central Oklahoma. Models are
in fairly good agreement with this. There are still large
differences in regards to the details for northeast Colorado. The
06z NAM12 shows a third to half inch of QPF along the Front Range
through 12z Monday where the 00z GFS has a trace to a tenth inch.
Think the drier solution is the way to go. This system will be a
long ways from the area. Plus upslope flow is weak through 12z
Monday. This is a moist system, so expect some snow to make it to
the Front Range tonight with a light accumulation likely.

Current satellite showing clouds streaming north ahead of the storm
system. Scattered showers are lifting north across southeast
Colorado. Some of these are expected to move over the eastern plains
today. Models generally showing snow or freezing rain today over the
plains. Though can`t rule out ice pellets or even rain if surface
temperatures get warm enough. Plan on going with light ice and snow
accumulation for the eastern plains today. The chance for freezing
rain will linger into the evening hours over the far eastern plains
with a change over to all snow by midnight. Will keep precipitation
amounts light through 06z Monday and then have higher snow amounts
late tonight as the storm system gets closer to the state. Will
leave the current Winter Weather Advisory as is with it beginning
this morning. Not expecting much precipitation today, but with
threat of freezing rain and icy roads, will leave the start time as
is.

.LONG TERM...(Monday through Saturday)
Issued at 338 AM MST Sun Jan 15 2017

By Monday morning...models show the positive tilt longwave trough
over the central Rockies and Great Plains and the upper low
spinning over swrn KS/wrn OK. 00z/06Z model runs slower to end
precip and clear skies east of the mtns on Monday with moisture
continuing to wrap back into northeast Colorado around the back
side of the departing low. Latest guidance indicates a west-east
band of light QPF along the Palmer Divide eastward to the KS
border. They also indicate a bit more QPF over and along the
Front Range esply during the morning hours. For that reason will
hang onto likely POPS acrs the sern corner of the CWA and
introduce likely pops over and near the Front Range foothills
roughly from Estes Park southward until the noon hour. That
includes the Denver metro area. Still believe new snow amounts
will be light...generally under an inch...except acrs ern Elbert
and nrn Lincoln Counties, as well as in the foothills where
we could see another 1-2 inches of snow fall. Temps certainly
cold enough for it to accumulate and with sub-freezing temp
profile, no longer see any chance for freezing rain/drizzle.
By afternoon with the upper low over nern KS, should see the
moist nely flow over nern CO ending and a shift to a drier nwly
flow. However, believe cloud cover east of the mtns will be slow
to clear--probably not until night fall. In the high country-
west of the Divide...clearing already well underway as this area
was little impacted by this storm system. Clear/mostly clear skies
overnight and small temp/dewpt spreads expected to result in
pockets of dense valley fog. Same goes for low lying areas on the
plains such as along the South Platte River where shallow dense
fog may form during the pre-dawn hours.

Looking ahead to the rest of the week...drier/warmer air spreads
over the state on Tuesday with an upper ridge bowing eastward
over Colorado. Counting on a 10-15 deg jump in temps on Wednesday
with plenty of sunshine and warming aloft. Tuesday night into
Wednesday...would expect to see warm advection mid and high-level
cloudiness spreading south over the CWA. Do not expect clouds to
have much of an impact on warm-up Wednesday. Wednesday likely
to be warmest day of the week with mild mid/upper 50s on the
plains and 30s in the high country. By Thursday...upper ridge over
Colorado flattens out as the first of several upper level waves
passes over the Pacific Northwest carried along by a powerful
Pacific jet stream. Over the next several days...medium range
models show this and other troughs cycling over the western CONUS.
Still far too early to know what impact they`ll have on the CWA
but one would assume a trend trends cooler temps, more cloud cover
and a greater chance for snow esply for the high country.

&&

.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 1102 AM MST Sun Jan 15 2017

Low and mid level clouds are increasing ahead of an upper level
low over northern Mexico. The airmass over the Denver area will
remain stagnant leading to haze and reduced visibility through
early this afternoon. Expect visibility to range from 2 to 6
miles. There will be a slight chance for a rain/snow showers
through 22z, then the chance for snow will improve overnight. Snow
is expected to move into the Denver area Sunday night and
continue into Monday morning. Uncertainty still high with most
models in the 1 to 3 inch range for snowfall. A few models show
over 4 inches of snow through 18z Monday. Since the center of this
storm remains far south of the area, will trend the forecast
towards the lower amounts.


&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Winter Weather Advisory until 11 AM MST Monday for COZ041-046-
047-049>051.

&&

$$

UPDATE...Kriederman
SHORT TERM...Meier
LONG TERM...Baker
AVIATION...Meier


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