Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 240137
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
737 PM MDT Sat Jun 23 2018

.UPDATE...
Issued at 724 PM MDT Sat Jun 23 2018

Severe weather threat has ended over Lincoln county for the
evening. However, attention returns further north as cold
front/outflow from storms north of Colorado border will effect
Northern Colorado for the rest of the night. Cold front is about
an hour ahead of earlier forecast as should be down into the
Denver area between 03-04z this evening. As the front interacts
with weak boundary from earlier convection and richer low level
moisture, could see some stronger/marginal severe storms over the
far northeast Corner where dewpoints have been rising into the
lower 50s.

Further west, showers have been developing in the
mountains with the main threat of gusty winds up to 50 mph
possible. Still a bit unclear on coverage of showers/storms
further west towards the urban corridor as low level moisture has
been more lacking. Expect some brief rain but gusty winds may be
the main threat as mountain showers interact with frontal
boundary this evening. Certainly looking at much cooler
temperatures on Sunday along with scattered showers and storms but
may be fighting the subsidence moving in during the afternoon.

&&

.SHORT TERM...(This evening through Sunday)
Issued at 223 PM MDT Sat Jun 23 2018

Little change to the forecast thinking. It is looking like a
little less favorable environment for significant rainfall on
Sunday. For the rest of the afternoon, current Palmer Divide
convection will continue to redevelop for a while, then eventually
shift eastward. Moisture transport will be increasing as southerly
winds increase this evening, so this convection may persist and
work north toward Akron and Fort Morgan this evening ahead of the
front. Further west little or no convection is expected in the
drier air ahead of the front.

The cold front is still on track for late evening, with a little
burst of wind for a couple hours behind it. Models are keeping
showers and storms along and north of the front past midnight, and
there still could be some strong storms generating on the front
across northeastern Colorado into the early morning hours. While
cell motions should be decent, there could be some short term
anchoring/training due to the front, so there is still a bit of a
heavy rain threat generally east and southeast of Fort Morgan in
the late evening.

For Sunday, there will be a dry slot aloft rotating across
northeastern Colorado as the low spins to our north and northeast.
There is a pocket of colder air/moisture/instability at low to mid
levels that swings over in the morning to early afternoon, then
there will be warming and drying in this layer that should shut
off any showers. Shower activity will be very sensitive to the
temperatures in the lowest two kilometers--at some point far
enough northeast there should be a few hours of rain, but this may
not extend too far back toward Denver which will have some
moisture and weak instability. For these reasons I lowered PoPs
across most of the area but not as much near the northern border.
It also looks like it should be pretty cloudy most of the day and
the forecast looked a little warm, so I lowered temps a couple of
degrees. With the cooling aloft, it may be cold enough for some
light snow above timberline but probably not much in the way of
accumulation.

.LONG TERM...(Sunday night through Saturday)
Issued at 223 PM MDT Sat Jun 23 2018

By 00z Monday, the closed low will be over sern SD/nwrn NE.
A drier west northwesterly flow aloft will be over the cwa
with moderate qg descent in place. Mainly isolated showers
or thunderstorms over the cwa will diminish Sunday evening,
as the system continues to track east overnight. Monday and
Monday night, a subsident northwesterly flow aloft wl be ovr
the region with a ridge axis stretching from the Great Basin
northward into ern MT. Very little QPF generated by the models
in the aftn and evening. If anything does develop it will be
confined to the higher terrain. Temperatures will climb back to
normal Monday afternoon. A broad upper ridge will stretch across
the southern U.S. Tuesday into Wednesday, with a weak wly flow
aloft over the state. The models show some weak QPF over the
higher terrain Wednesday, so will have a slight chc of
thunderstorms there. The fire danger will start to creep up late
in week as temperatures climb back above normal. Trouble spots
wl be the high mountain valleys, Front Range Foothills and Palmer
Divide. Saving grace initially may be a weaker flow alf and lack
of thunderstorms which should help to minimize the danger to some
degree. By the late in the the week, the ridge wl center itself
ovr the sern U.S. and another trough moves into the Pacific
Northwest. This will result in a stronger southwesterly and
continued dry flow alf. The extended models differ slightly by the
end of the week. The ECMWF keeps a weaker westerly flow alf ovr
the state while the GFS is stronger and more southwesterly.
Either way it will be hot and dry with highs generally the 90s.
As the upper trough shifts into srn ID next weekend, there could
be a chc of showers and thunderstorms and a little cooling by
Sunday.

&&

.AVIATION...(For the 00Z TAFS through 00Z Sunday evening)
Issued at 724 PM MDT Sat Jun 23 2018

Have moved up the timing of frontal boundary between 03-04z at
local terminals due to quick progress with front almost to
Greeley at this time. Still expect scattered showers/storms
developing behind the front but overall coverage still looks
spotty and continue with a VCTS. Low confidence on stratus
developing later tonight as some of the later model runs have
backed off on the amount of low level moisture available.

&&

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

$$

UPDATE...Entrekin
SHORT TERM...Gimmestad
LONG TERM...Cooper
AVIATION...Entrekin



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