Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 261628
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1028 AM MDT Sat May 26 2018

.UPDATE...
Issued at 1025 AM MDT Sat May 26 2018

The current DIA temperature from the 16Z observation is 78 F
which is 3 degrees warmer than yeserday`s observation at the same
time. Satellite pictures are showing the leading edge of a batch
of upper level cloudiness moving northeastward into southern
Colorado at this time. It is associated with increasing
southwesterly flow aloft. The edge of this gets into the Denver
Metro area within the next two hours, with the thicker cloudiness
in about 3.5 hours. A new May record high for Denver could be set
or tied. Will leave the GFE temperatures grids as is for now. Dew
points out on the plains are in the 50s F right now, at least over
the eastern two-thirds of them. Latest models push all this low
level moisture out to east by mid afternoon. Will monitor this
situation. Will make a few minor alteration in the sky cover. Will
leave pops out for now.

&&

.SHORT TERM...(Today and tonight)
Issued at 354 AM MDT Sat May 26 2018

Record or near record heat can be expected as the upper level
ridge and thermal ridge shift right across the forecast area
today. There will be plenty of sunshine with a very dry airmass
aloft, and temps aloft warm another 2-3C from yesterday. As a
result, don`t see any reason we won`t at least tie or break
Denver`s record high for the date (and the entire month of May)
which is 95F set in 1942. We should see very high based flat
cumulus this afternoon, and it`s not entirely out of the question
we get a dry microburst considering the well mixed environment
from the surface through 500 mb. Fire danger increases across
Park County...see Fire Weather section below.

Tonight will be unseasonably warm as well with some mid/high
clouds and increasing low level gradient resulting in breezy
conditions over the Palmer Divide and eastern plains. Will bump up
temps a couple degrees from the previous forecast. Otherwise dry
conditions will persist.

.LONG TERM...(Sunday through Friday)
Issued at 354 AM MDT Sat May 26 2018

On Sunday, models show Colorado squeezed between a strong upper
ridge over the Great Plains and an unusually deep upper trough over
the Intermountain West. The strong pressure/height gradient
between these systems is forecast to produce 45-55kt swly mid-
level flow over the forecast area during the day. Most models
show strongest winds aloft over the area during the afternoon and
evening hours. 850-700mb winds east of the mtns also at their
strongest during this period. Gusty south-southwest sfc winds
in the high country and on the plains adjacent to the Front Range
will remain quite warm and dry, while farther out on the plains
winds will be southeasterly and possibly stronger in speed.
Expect to see a dry line set up where these two winds converge
just east of the I-25 corridor around midday. From there, models
show this dry line moving eastward into increasingly moist and
unstable which is taking aim on the state`s far northeast corner.
Within the moisture rich environment, models indicate impressive
sfc based CAPE values in the 2500-4000 j/kg range during the early
to mid-afternoon time period. Veering winds with height will help
to enhance storm organization, and modest bulk shear will favor a
mix of multi-cell and isolated supercell storms capable of large
hail and perhaps a tornado or two out that way. SPC has this area
in a slight risk for severe storms tomorrow. Can`t argue with
that. During the evening most of this heavy storm activity should
shift east of the state, while at the same time moist outflow from
these same storms appears to surge back towards the Front Range,
possibly producing a few non-severe t-storms along the Front
Range. Models show this low-level moisture lingering over much of
the plains overnight, possibly resulting in areas of low cloud
cover after midnight. Lastly, the green up of fuels thanks to
recent rainfall has reduced the risk of large fire growth and
spread, however fuels remain dry in South Park and with the very
warm, dry and gusty swly winds expected Sunday, a Red Flag Warning
has been issued for this alpine park from 12 Noon MDT to 9 pm
MDT.

On Memorial Day, the plains airmass looks cooler and more humid with
in the presence of a north-northeast low-level flow. Could see areas
along the Front Range under a broken stratus cloud deck to start the
day. Could see these low clouds lingering up against the foothills
through mid-morning. Above 700 mbs, swly flow remains warm and
dry as the large upper trough continues its slow progress towards
Colorado. By afternoon, a couple of weak mid-level disturbances
rotating around the bottom of this trough appear to interact with
a moist and marginally unstable east-southeast flow on the plains
to generate scattered t-storms over the Front Range by early
afternoon. NAM and GFS show this broken line of storms moving
northeast across the plains, gaining some strength along the way
as they move into greater instability. However, the risk for
severe storms appear lower than the day before. Increased cloud
cover and cooling aloft will make for cooler temperatures Monday,
though temperatures will still be near average for the date.

Looking ahead to the remainder of the week, the upper trough to our
west today is forecast to track northeastward over Wyoming and
northern Colorado producing seasonably mild temperatures and
another round of showers and t-storms for the forecast region.
Showers and t-storms will shift from the high country to the
plains through the day as the 700-500 mb mb trough axis passes
by. NAM is most optimist with QPF, while the Canadian and
European models barely indicate any precip on the plains. Will use
a blend of the models to populate sky cover, weather and PoPs for
Tuesday. By Wednesday and Thursday, models gradually trend drier
and warmer as an upper ridge attempts to build over the central
Rocky Mountain region. Thursday will likely be the driest and
warmest of the two days. Temperatures by Friday look about the
same, while humidities will be lower with a relatively strong
southwest flow setting up ahead of an large upper trough dropping
down over the Great Basin. By Saturday, models show this trough
lifting out over Wyoming causing temperatures to cool around here
and bring a chance of t-storms to the high country.

&&

.AVIATION...(For the 18Z TAFS through 18Z Sunday afternoon)
Issued at 1025 AM MDT Sat May 26 2018

Models still have an east or northeasterly component to the winds
by 18Z this afternoon, then normal drainage tonight. There will
be no ceiling issues and it will be hot.

&&

.FIRE WEATHER...
Issued at 354 AM MDT Sat May 26 2018

Fire danger will increase today with record/near record heat,
breezy conditions, and a very dry airmass. Critical Red Flag
conditions will develop over South Park by this afternoon where
the spring green-up has been paltry. Portions of the southern
foothills may also be in increased danger but winds appear to be
marginal there. Minimum humidities will drop into the single
digits from Denver south/west into Park County and the Palmer
Divide.

For Sunday, gusty southwest winds, low relative humidity and
unseasonably warm temperatures will produce another day of high to
extreme fire danger for South Park (zone 214) where fuels remain
dry. This has prompted the issuance of a Red Flag Warning for Zone
214 from 1200 to 2100 hours on Sunday. Conditions should improve
during the evening with wind speeds diminishing and temperatures
falling.

&&

.BOU WATCHES/WARNINGS/ADVISORIES...
Red Flag Warning until 9 PM MDT this evening for COZ214.

Red Flag Warning from noon to 9 PM MDT Sunday for COZ214.

&&

$$

UPDATE...RJK
SHORT TERM...Barjenbruch
LONG TERM...Baker
AVIATION...RJK
FIRE WEATHER...Barjenbruch/Baker



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