Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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163
FXUS65 KBOU 200224
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
824 PM MDT Sat May 19 2018

.UPDATE...
Issued at 820 PM MDT Sat May 19 2018

500mb low spinning over swrn Nebraska this evening continues to
feed low clouds and bands of light rainfall back into nern
Colorado. Rainfall rates have been on the light side past several
hours. Even the showers in the high country have decreased in
number past couple of hours with the loss of daytime heating. The
forecast grids have been adjusted to account for this down turn
to shower activity. However, we`re probably not entirely out of
the woods yet when it comes to precip. There`s still a decent
amount of moisture and mid-level instability around associated
with the upper trough over the region to warrant at least
scattered PoPs for the mtns and nearby plains through midnight.
After which time, expect to see just scattered light rain-snow
showers in the high country with possibly some light snow
accumulation up around timberline. On the plains, partial
clearing late and narrow temperature/dewpoint spreads should
result in patchy to areas of fog. Models indicate the best chance
for fog just east of the Denver Metro Area and down across eastern
Douglas and Elbert Counties towards sunrise. Could see visibilities
as low as 1-3 miles for a few hours in this area. Otherwise,
min temperatures on the plains tonight may end up being the
coolest we`ve seen this month with mid to upper 30s as a general
rule.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 326 PM MDT Sat May 19 2018

Current satellite imagery has the surface low center over the CO
and KS border continuing to move eastward. Most of NE Colorado
plains is in the TROWAL portion of the low def zone pulling in
cooler air from Wyoming. This is helping to keep light rain on the
plains through the early evening hours. Precipitation will end
from the West to the East as subsidence increases. Clearing our
over portions of the southern foothills and Park county helped to
initiate some high based convection with small hail, gusty winds,
lightning and brief heavy rain being the main threats. As the rain
moves off there is a threat of patchy fog over a majority of the
plains and foothills. The main hindrance to widespread fog
coverage will be the lowered cloud deck that could stay in place
through the afternoon hours on Sunday. Kept a mention of it in the
grids to account for the uncertainty. Temperatures overnight will
be more mild with lows in the upper 30s to lower 40s on the
plains and 20s to 30s in the high country.

Sunday will see a gradual warming and clearing through the day
with a slight chance of thunderstorms over the mountains. A short
wave embedded in the SW flow aloft will help to initiate storms
in a decently unstable environment. Some of these storms could
make it onto the plains, however, it will have to fight against
the low level moisture and cap to survive. It is not looking
promising at this time so left any mention of thunder out of the
plains...but kept some for the higher foothills and Palmer Divide
areas. Highs on Sunday will be warmer with temperatures reaching
into the mid 60s for the plains and 40s to 50s in the mountains.

.LONG TERM...(Sunday night through Saturday)
Issued at 326 PM MDT Sat May 19 2018

Models are showing a warm week in the offing as we transition into
an early summer weather pattern. The first half of the week will
feature an upper level low over California with southwesterly flow
aloft across Colorado. At lower levels, weak low pressure will be
in place over eastern Colorado with southerly flow across the
plains transporting Gulf moisture northward. This should provide
adequate moisture into Colorado to feed afternoon thunderstorm
development each day. MOS guidance from the different models shows
high temperatures reaching into the lower 80s with dew point
temperatures in the lower and mid 40s. These temperature and
moisture levels are in the "sweet spot" for the development of
afternoon thunderstorms. Wind shear profiles should also be
favorable to support thunderstorm development. Convective activity
each day should begin over the mountains and then spread onto the
plains during the afternoons and evenings. At the end of the week,
the upper ridge over the state will shift slightly westward, but
the results will be the same as weak upper level ridging will not
be enough to cap any mid-level instability. Hence, the forecast
will be a very repetitive one.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 820 PM MDT Sat May 19 2018

IFR and MVFR ceilings are likely to persist overnight at Denver
area airport terminals. Precipitation chances will be low, and
mainly prior to midnight. After midnight, should there be any
clearing, could see patchy to areas of fog form. Scattered areas
of 1-3 mile VSBYs will be possible, and more likely across
northern and eastern portions of the metro area towards sunrise
(11z-13z). Most of this fog is expected to dissipate before 15z
with a gentle shift from light north-northeast winds this evening
to a light east-southeast wind towards morning.

&&

.HYDROLOGY...
Issued at 326 PM MDT Sat May 19 2018

Current rainfall amounts are highest over the Logan, Morgan and
Washington county areas with 1 to 3 inches reported. Short term
models are showing the possibility of an additional half to one
inch through the evening hours. Still no major flooding or
damage from the rains in the Morgan county area. Will not be
issuing an areal flood advisory and will continue the flood watch
until it expires at 6 pm this evening.

&&

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

$$

UPDATE...Baker
SHORT TERM...Bowen
LONG TERM...Dankers
AVIATION...Baker
HYDROLOGY...Bowen



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