Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 191820
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1120 AM MST Thu Jan 19 2017

.UPDATE...
Issued at 1052 AM MST Thu Jan 19 2017

Very little cloudiness over the CWA currently. The wind field
across the CWA is pretty weak. The 18Z temperature at DIA was 7
degrees warmer than yesterday`s 18Z reading. May raise
temperatures a tad on the GFE grids.  not much else to change.
&&

.SHORT TERM...(Today and tonight)
Issued at 340 AM MST Thu Jan 19 2017

Next Pacific storm system now seen moving inland across California
with middle and high level moisture stream ahead over the Great
Basin. Main forecast challenge will be impact across North central
mountains tonight with snow and potential snow across the
adjacent plains towards daybreak on Friday.

Model consensus showing this as a light snowfall event for the
mountains tonight, generally in the 1-3 inch range. Orographic
wind flow from the West but only around 10-15kt while lapse rates
improve close to 7c/km by early Friday morning. Moisture depth is
rather shallow, generally from the surface to 550 mb. There is
weak QG ascent over the mountains by later tonight but latest 06z
runs of the NAM/GFS are stronger with the forcing as it moves over
the area after midnight. This potentially stronger development
even includes some qpf developing over the adjacent plains
especially from Denver southward to the Palmer Divide. Latest
forecast soundings have airmass moistening up fairly well but
there is really no front or upslope flow with this system. For now
will keep pops on the lower side across the adjacent plains later
tonight but bears watching as this weather feature evolves.

Temperatures will be similar to yesterdays readings across lower
elevations as still should see a good amount of sunshine through
at least mid afternoon. Readings will be in the mid 40s/lower 50s
on the plains today. Any significant precip in the mountains will
likely hold off until the evening hours.

.LONG TERM...(Friday through Wednesday)
Issued at 340 AM MST Thu Jan 19 2017

An upper low will push over the forecast area Friday morning with
weak QG lift. Light to moderate snow will continue through the
morning and early afternoon then decrease as subsidence pushes in
behind the trough. Overall amounts look to stay in the 1-3 inches
range. Over the plains, most models had light precip favoring
areas near the Palmer Divide, yet the 00z NAM kept the plains dry.
Discounted this solution and kept a chance in the forecast, then
the 06z run came in with over a tenth of liquid forecast. With no
real front or upslope flow, and just the dynamic lift, kept PoPs
capped at 40 percent chance, occurring in the morning before the
system pushes east during the afternoon and evening. Temperatures
will be cooler Friday with highs near normal for this time of
year.

The next system will push into the north central mountains
Saturday late morning and dive southeast quickly. This system will
impact western and southern Colorado more, with up to another few
inches of snow expected for the mountains while the plains stay
dry. Temperatures will be similar to Fridays readings across the
forecast area. A deepening surface low moving into the TX/OK
panhandles, a strengthening high pressure over the lee of the
Northern Rockies and a northwest to southeast oriented 140kt jet
aloft will increase northerly winds across the plains Saturday
night into Sunday.

Sunday evening, the next wave in the active pattern of moisture
will enter the mountains with westerly flow turning southwesterly
from an upper low digging into the western US. As this upper low
slowly pushes east across the Rocky Mountain region, the bottom of
the trough will hang up near the southwestern US keeping the state
under an upper trough regime and keep pumping moisture in. This
will bring an extended period of snowfall for the mountains, from
Sunday evening through Tuesday night or Wednesday morning. A
surface low is being progged to move into the eastern plains of
Colorado Monday then pushing southeast. Depending on where this
sets up, the plains could see more wind or more snow. Will need to
see how model trends are handling the surface and midlevel details
in upcoming runs. Expect the plains to see some snow at some point
during Monday, then winds will likely pick up out of the north as
high pressure aloft and at the surface build over the northwestern
US. The CMC, GFS and EC all have northerly winds of 15 to 25 mph
sustained over the plains Tuesday. There could be some blowing
snow as well.

Past this, the longer range models handle the small details
different in northerly flow as ridging builds along the west coast
and troughing is established over the Great Lakes and eastern
states. Will keep temperatures lower than average and not much in
the chance of precipitation.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1052 AM MST Thu Jan 19 2017

Models keep weak boundary layer flow over DIA today and tonight. I
left southeasterlies in this afternoon and went with normal
drainage patterns overnight. Models alos show some limited QPF
for DIA so will leave the PROB30 group in. &&

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

$$

UPDATE...RJK
SHORT TERM...Entrekin
LONG TERM...Kriederman
AVIATION...RJK


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