Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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000
FXUS65 KBOU 191526
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
926 AM MDT Sat May 19 2018

.UPDATE...
Issued at 914 AM MDT Sat May 19 2018

Current visible satellite imagery and surface obs show circulation
just east of Washington county pulling cool and moist air in from
the NNE. Current rainfall amounts for areas within the Morgan,
Logan and Washington county areas have 1.5 to over 2 inches of
rain from last evening. Short term models are showing the eastward
progression of this closed circulation which will pull CAA and
rain south through the afternoon. Currently looking at an
additions tenth to close to an inch of rain through the afternoon
hours, with the most centered over the Morgan county areas. Will
continue with the Flood Watch given the rain forecast and radar
trends. Adjusted QPF amounts slightly as well as temperatures.

With some clearing over portions of the higher terrain to the
south, cannot rule out a slight chance of thunderstorms for the
afternoon hours so maintained the forecast for those areas.

&&

.SHORT TERM...(Today and tonight)
Issued at 338 AM MDT Sat May 19 2018

Radar trends and models indicate an upper level low will stall
over northeast Colorado this morning and then slowly weaken and
move off to the east by early evening. Based on radar and reports,
estimate that 1-2 inches of rain has fallen over north central
Weld, Morgan, western Logan, and northern Washington counties.
Rain is expected to persist much of the day north of a line from
Briggsdale to Fort Morgan to Akron. This area will need to be
monitored for flooding since up to 2 more inches of rain is
expected through this afternoon. Will continue with the Flash
Flood Watch for these areas.

It is uncertain how far west precipitation will make it today.
Many of the 00Z model runs show the rain making it to the base of
the foothills and into the Denver area. However, the few 06Z
models in so far now keep most of the rain where it is with little
west/southwest progression. Looking at radar trends, believe this
is a reasonable solution. Cold air advection will occur over
northeast Colorado due to northerly winds on the back side of the
low. This is helping low clouds form at this time. Expect clouds
to lower more through the morning. Best chance for precipitation
along the Front Range and in the Denver may come in the form of
drizzle. Temperatures are expected to remain steady in the upper
40s to lower 50s today due to cloud cover.

Rain associated with the upper level low is expected to stay east
of the higher foothills and mountains. Cold air aloft will help
destabilize the airmass this afternoon. Isolated to scattered
showers and thunderstorms will be possible. Will cancel the Winter
Weather Advisory for the mountains since widespread snow is no
longer expected.

For tonight, rain is expected to end this evening as the low
weakens and exits the area. Low clouds will linger through the
night and could see some drizzle and fog in places. Temperatures
will be chilly with readings in the lower 40s expected.

.LONG TERM...(Sunday through Friday)
Issued at 338 AM MDT Sat May 19 2018

On Sun the flow aloft will become more WSW as a weak disturbance
moves across late in the aftn into Sun evening. MLCAPE values
are around 500 j/kg over the higher terrain with very little CAPE
over nern CO. Thus best chc of showers and storms will be over
the higher terrain with some of the activity possibly affecting
the front range urban corridor. As for highs, readings will rise
into the 60s across the plains.

For Mon an upper level low will develop over srn California with
WSW flow aloft remaining over nrn CO. Meanwhile a weak sfc lee
trough will develop along the front range. This should allow for
deeper low level moisture to gradually increase over the plains.
So expect better instability by aftn with MLCAPEs in the 500-1000
j/kg range. Overall will keep in a chc of storms in the mtns with
a slight chc across nern CO. Temps will continue to rise as
readings reach the 75 to 80 degree range over the plains.

By Tue the upper level low will begin to move north into Nevada
with the flow aloft becoming more SSW across nrn CO. There will
still be favorable CAPE across portions of the plains so will keep
in a slight chc of storms. Over the higher terrain there will
still be enough moisture for a chc of storms as well. Highs across
nern CO will continue to warm as readings rise into the lower to
mid 80s.

On Wed the upper level low will continue to move basically northward
into the nrn Rockies as SSW flow aloft remains over the area.
Some drier air may spread across the area which could reduce the
chc of storms over the higher terrain. Over nern CO will keep pops
mainly in the slight chc category. Highs on Wed will be similar
to Tue.

By Thu the upper level low will move across the nrn Rockies with the
flow aloft becoming more SW.  Once again there is limited moisture
over the higher terrain so will keep pops on the low side.  Across
nern CO there should still be decent instability across portions of
the plains so will keep in a slight chc of storms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 914 AM MDT Sat May 19 2018

MVFR with periods of IFR conditions are possible through 18z
today with the continued moist and cool northerly push. As the
surface circulation continues to progress eastward expect the rain
to slowly diminish and ceilings to increase to MVFR roughly by
19z at KDEN and slightly later at BJC and APA. Winds will be be
light from the NNE with speeds from 5 to 10 kts. At this time VFR
ceilings are anticipated after 22z.

&&

.HYDROLOGY...
Issued at 914 AM MDT Sat May 19 2018

Current rainfall amounts are highest over the Logan, Morgan and
Washington county areas with 1.5 to over 2 inches as of 7 am this
morning. Short term models are showing the possibility of an
additional half to one inch through the day. Contacted the EM in
the Morgan county area and at this time there are not reports of
flooding in the region. Will hold off on any areal advisories for
now as rainfall amounts are expected to be light enough through
the day that flooding potential will remain low. Will maintain the
Flood Watch however as light to moderate rain is still on going.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Flash Flood Watch until 6 PM MDT this evening for COZ042-044-
048>051.

&&

$$

UPDATE...Bowen
SHORT TERM...Meier
LONG TERM...RPK
AVIATION...Bowen
HYDROLOGY...Bowen



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