Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 260952
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
352 AM MDT Thu Apr 26 2018

.SHORT TERM...(Today and tonight)
Issued at 340 AM MDT Thu Apr 26 2018

A cold front, associated with an upper level trough passing
through the region, pushed south across northeast Colorado early
this morning. Satellite and radar are showing mid level cloud and
scattered showers over Wyoming at this time. Cross sections
indicate moisture will increase, but remain somewhat limit over
northeast Colorado today. Will have mostly cloudy skies and low
pops for this morning. Best chance at seeing showers will be the
foothills and along the north side of the Palmer Divide where
upslope flow will help with lift. If showers form, they are
expected to be light with only a few hundredths expected. The
showers are expected to end by early afternoon as drier air moves
in. This will lead to breaks in the clouds. Highs will climb into
the upper 50s with a few lower 60s possible late this afternoon as
the clouds clear.

A surface high moving across the region will bring clear skies and
light winds tonight. Low lying will cool into the upper 20s with
other locations bottoming out in the low to mid 30s.

.LONG TERM...(Friday through Wednesday)
Issued at 340 AM MDT Thu Apr 26 2018

Warmer and drier conditions should dominate the entire forecast
area to start the long term period with the passage of a sharp
shortwave upper ridge on Friday. Ample sunshine and s-swly low-
level flow downsloping off the Front Range and Palmer Divide
should return daytime temperatures to the upper 60s/lower 70s on
the plains. Minimum relative humidities, though low, are still
expected to remain above values necessary to create serious
wildfire concerns. The recent precip and ongoing green-up should
also reduce the potential for wildfire on Friday.

Models all agree in shifting the 700-500mb ridge axis eastward over
the Front Range by Saturday morning, causing a shift to swly flow
aloft. The shift in flow appears to advect a north-south oriented
band of mid-level moisture and instability eastward across the
state during the day Saturday. Models also show strengthening sely
bndry layer flow on the plains driving a tongue of increasing theta-e
air up into ern Colorado during the afternoon. This influx of
low-level moisture and warm temps generate sfc based CAPES in the
300-400 j/kg range according to the GFS, and 700-850 j/kg range
as per the NAM. This instability and a favorable shear profile
would support the formation of showers/t-storms, first in the
high country and nearby plains (i.e., the I- 25 corridor) by late
morning or early afternoon, then along the Palmer Divide to srn
Washington and Lincoln counties by late afternoon/early evening.
Can see precip chances anywhere from 30-60 pct in the high
country, to 20-30 pct along the foothills and Palmer Divide, with
near zero chances acrs the far northeast corner of the CWA where
CIN will be difficult to erode. Precip amounts should generally be
on the low side, esply on the plains with a relatively dry sub-
cloud environment. High plains storms may produce more in the way
of gusty outflow winds than wetting rainfall. This plume of
mid-level moisture is progged to slowly lift out of the area by
morning opening the way to dry and slightly warmer conditions for
Sunday. Latest temperature guidance continues to indicate well
above average max temps in the upper70/lower 80s on the plains,
and balmy 50s/60s acrs the high country. Strengthening swly flow
aloft and pressure falls on the plains will also produce gusty
swly sfc winds which will lower Rh values and therefore elevate
the fire danger, esply in areas not receiving much precip in
recent days, such as along the Palmer Divide.

Looking ahead to next week, medium range models all indicate a
trend towards wetter and cooler weather beginning Monday with a
deep upper trough carving out over the Great Basin/nrn Rockies.
Models show this trough gaining strength as a pocket of jet level
energy dives down its back side, causing the parent trough to
close off in the vicinity of the Four Corners on Tuesday. Where
this closed low tracks will largely determine the type and amount
of precip we`ll see across the forecast area Tuesday and
Wednesday. GFS and ECMWF are now both indicating decent QPF both
days, esply along and east of the mtns. It`s really still too
early to know for certain what direction this low will track. For
now, will trend cooler, wetter and unsettled for the first half of
next week.

&&

.AVIATION...(For the 12Z TAFS through 12Z Friday morning)
Issued at 340 AM MDT Thu Apr 26 2018

Northerly winds with gusts to 30 knots will prevail today behind
a cold front. Low/mid clouds will form around or just after 12z
with ceilings of 4000-6000 feet. Clouds will lift and scattered
after 18Z. After 00Z, skies will clear and winds will shift to a
southerly direction and remain southerly through tonight.

&&

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

$$

SHORT TERM...Meier
LONG TERM...Baker
AVIATION...Meier


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