Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 191628

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1028 AM MDT Fri May 19 2017

Issued at 1058 AM MDT Fri May 19 2017

The upper trough has elonged along a north-south axis over
central CO this morning. The upper low visible on GOES-16
satellite loops is now centered south of Steamboat Springs.
As a result the flow up to around 550 mb over the Front Range
and adjacent plains has gone northerly. Above that...flow was
southeasterly also evident on GOES-16 IR and water vapor imagery.
On radar...precip echoes over and along the Front Range has
dropped off considerably in the past few hours and the trend for
the remainder of the afternoon according to our suite of mesoscale
models including the NAM is for the northwest-to-southeast band of
light to moderate precip cutting across the CWA to continue to
shift east through early afternoon. Models then show this precip
axis assuming a more west/northwest-east/southeast tilt and a
westward push of showers back into central and southern portions
of the I-25 corridor. Temperatures by then will likely keep most
of this precip in the form of rain or a rain/snow mix. Any snow
accumulation will be minor and mainly in areas above 5000 feet.
But no impact on roads. However, across the northeast corner of
the state, slow moving showers could produce locally heavy
snowfall after 2 PM today. NAM and GFS indicate 1-3 inch snow
amounts out there by evening and locally up to a half inch of
QPF. All of this precip should gradually shift east of the CWA
this evening with the upper trough.

UPDATE Issued at 542 AM MDT Fri May 19 2017

GOES 16 imagery shows the upper low is currently trying to become
better organized over north central Colorado. This is having an
impact on shower redevelopment on the plains with an organized
band from roughly along/north of a line from Boulder to DIA and
then to just west of Limon. End result should be a little more
accumulation from the northern mountains into eastern Larimer
county as this feeds west/northwest. Current Warnings cover this
area well. Overall, minor adjustments made to PoPs, QPF, and


.SHORT TERM...(Today and tonight)
Issued at 324 AM MDT Fri May 19 2017

Storm system is winding down across the forecast area as energy
did split as advertised in the NAM and ECMWF 24 hours ago. As a
result, precipitation intensity had decreased significantly during
the evening, with only light precipitation for the most part
continuing early this morning. Exception was in the northern
foothills and northern mountains where enough easterly flow was
still producing locally heavier snowfall. However, this too will
be decreasing through the early morning hours with orographic
enhancement weakening. From Boulder and Denver southward to the
Palmer Divide, have opted to cancel the Winter Storm Warning with
additional accumulations expected to be an inch or less and
little additional impact.  Advisories for South Park and Middle
Park also let go. Will continue the Winter Storm Warnings for the
Front Range Mountains and Foothills with impacts including
continued power outages and hazardous travel, but overall only
expect light snow this morning (very little in the I-70 Corridor),
and then heavier convective snow showers this afternoon. Looks
like another 1 to 4 inches possible with most of that in the
northern Front Range this morning, and then over the I-70 corridor
of Summit County in the afternoon. Those Warnings may end up
getting cancelled early too depending on how this evolves.

There is a potential fly in the ointment with another wave of
energy now taking shape near the CO/NM border early this morning.
This feature will lift northeast across southeast Colorado, but
increasing Q-G lift ahead of it will likely bring more widespread
showers for the afternoon. At this point, we think the bulk of
precipitation with this wave should end up east of the I-25
Corridor, but at the same time a weak surge may end up pushing it
back into Denver. We will adjust PoPs accordingly to have higher
PoPs again by this afternoon. Precipitation type will again be
tricky, mainly snow along/west of a Greeley to Limon line this
morning, but then some daytime heating and higher wet bulbs this
afternoon may bring some rain all the way back to the I-25
Corridor. At the same time, heavier precipitation rates could lend
itself to some light snow accumulation out toward Limon.

For tonight, the upper level storm system will move eastward with
subsidence and drying eventually building in. Lingering showers
this evening will push east across the plains while ending along
the Front Range during the evening. Some clearing late would
likely allow temps to drop to or just below freezing, so will
issue a freeze warning for the plains from the I-25 corridor
eastward to Fort Morgan and Limon. May see some patchy fog develop
as well in places that clear.

.LONG TERM...(Saturday through Thursday)
Issued at 324 AM MDT Fri May 19 2017

The upper level storm system will move into cntrl Nebraska on Sat.
There still could be some light pcpn over far nern CO in the morning
on the back side of the upper level low.  Otherwise outside of a
slight chc of showers in the mtns it will be dry with moderating
temperatures.  Aftn highs will be in the 55 to 60 degree range
across the plains.

On Sun an upper level trough in nwly flow aloft will affect the area
Sun aftn thru Sun night.  There is some wk mid lvl ascent associated
with this feature along with quite a bit of moisture.  In addition
there will be a fnt moving into nern CO during the aftn with upslope
flow developing.  Overall should see a good chance of snow showers
in the mtns Sun aftn into Sun evening with a chc of showers and a
few tstms across the plains.  Highs will be in the lower to mid 60s
across nern CO.

For Mon drier air in nnw flow aloft will be over the area thru the
aftn with only a slight chc of showers in the mtns.  Aftn highs will
be in the 60s across the plains.  Mon night into early Tue another
disturbance embedded in the nnw flow will affect nrn CO with some
mid lvl ascent.  In addition another fnt will move across nern CO
Mon evening which will enhance upslope flow.  Thus will see a good
chc of snow showers in the mtns with another chc of showers and a
few tstms across the plains.

By Tue aftn drier air will spread across the area as the disturbance
moves se of the area.  However there still could be a slight chc of
showers across the higher terrain and plains. As for highs
readings will be in the upper 50s to lower 60s across nern CO.

On Wed dry nnw flow aloft will be over the area with no pcpn
expected.  Temperatures will be warmer as aftn highs rise into the
upper 60s to lower 70s across the plains.  By Thu the flow aloft
will become more wly.  There is some moisture embedded in the flow
and will decent lapse rates will keep in a slight chc of
showers/tstms over the higher terrain.  Temperatures will continue
to rise with highs in the 70s across nern CO.


.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1058 AM MDT Fri May 19 2017

Low cloud ceilings in the 500-1200 feet AGL range presently over
the Denver metro area will gradually lift to the 1200-2200 ft AGL
range by aroun midday. However, ceilings may again lower through
the afternoon as showers move back into the metro area from the
east. Showers this afternoon will mainly by rain, but the heavier
showers expected after 3 PM could turn to a mix of rain and snow.
However, little to no snow accumulation is anticipated on paved
surfaces. Conditions should then improve, slowly at first, this
evening, with VFR conditions on or before 06z tonight. As for
winds, north-northwest winds 10-20kts through 19z, then northeast
8-16kts for most of the afternoon. Then, wins will gradually turn
southerly overnight at speeds under 14kts under gradually clearing


Issued at 1028 AM MDT Fri May 19 2017

No changes to highlight at this time.

Mainly light QPF amounts under one half inch expected through
today. Rises are occurring on the South Platte downstream of
Denver, and on the Cache La Poudre near Greeley. Flood Warning for
the South Platte at Kersey remains in effect today with a forecast
crest less than 1 foot above flood stage, but considerable
lowland and meadow flooding expected along that stretch.


Freeze Warning from 2 AM to 9 AM MDT Saturday for COZ038>046.



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