Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 231703
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1103 AM MDT Fri Jun 23 2017

.UPDATE...
Issued at 1100 AM MDT Fri Jun 23 2017

Cooler moist air continues to be held into the area by upslope
flow with high surface pressure spread from Montana down into
Kansas. Slightly cooler temperatures over the Palmer Divide than
forecast, have lowered the max readings for that area by a couple
degrees.

Decreased the potential for showers and thunderstorms over the
higher terrain, foothills and Palmer Divide with more stable air
expected. Did not pull it all the way out, especially with sunny
skies west of the divide that may produce just enough diurnal
heating to for showers/isolated weak storm.

&&

.SHORT TERM...(Today and tonight)
Issued at 339 AM MDT Fri Jun 23 2017

Cold front will drop through Denver over the next few hours. A
band of showers and thunderstorms will continue to drop south
behind the front, with most of the lightning out on the plains.
Not expecting a lot of precipitation for Denver, but there will be
showers in the area for several hours. Temperatures will also drop
about 10 degrees as this band passes. There is a substantial cloud
deck upstream, and the dissipation of this is getting slower in
the models. However, the thickness of the cloud cover seems a bit
overdone, as north of the shower band ceilings are generally 6-8
thousand feet without much lower cloud cover. With the cold low
level air and much drier air aloft above the inversion, there
should be no showers after this morning. I did slow down the
clearing tonight, but not as much as the slower models. Still a
bit more cold advection than we were planning on today, and then
with some clearing tonight temperatures will fall some more.
Dropped today`s highs a few degrees, and tonight`s lows about 5
degrees, all still in line with guidance. This gives lows in the
mid to upper 40s across the plains tonight.

.LONG TERM...(Saturday through Thursday)
Issued at 339 AM MDT Fri Jun 23 2017

Saturday and Sunday...upper level high pressure will be centered
over southeastern Arizona and northern Mexico...with a broad upper
level trough of low pressure centered over the northern Great Lakes
States. Colorado will lie between these two systems under the
influence of a moderate northwest flow aloft. Model soundings show
generally a stable airmass across much of northeastern Colorado with
weak upslope flow from the surface up to 700 mb. Models soundings
show some higher cape values around 1000 J/KG across central and
southern Park County both Saturday and Sunday...and between 500 and
1000 J/KG across the Palmer Divide on Sunday.  This pattern should
result in continued below normal temperatures across north central
and northeastern Colorado through the weekend with isolated to
scattered afternoon and evening showers and storms across the
mountains...Foothills...Palmer Divide and Park County. The showers
should be most numerous over the southern foothills...Park County
and portions of the Palmer Divide. With this pattern...wouldn`t be
surprised if one or two storms across these areas produced brief
heavy rain and small hail. With a couple of embedded disturbances in
the northwest flow aloft...the far northeastern plains could see a
few showers. However...with the stable airmass in place...any shower
that develop should remain on the light side.

On Monday...temperatures are expected to warm to near normal values
as an upper level ridge of high pressure builds over the Rocky
Mountain Region. There may be just enough residual
moisture...combined with daytime heating to produce isolated
afternoon and evening showers and storms across the high country.
Models are also showing a southeast surface flow bringing higher
dewpoints into the far northeastern plains which could aid in the
development of a few evening showers and storms. The GFS sounding
shows capes over 1200 J/KG...and if this verifies...some brief heavy
rain and hail would be possible.

Tuesday through Thursday...the upper ridge flattens with a westerly
flow aloft over the region. Downslope flow associated with this
pattern may bring hot and dry weather across the Front Range Urban
Corridor Tuesday and Wednesday...with high temperatures ranging from
the low to mid 90s. The GFS suggests a dryline moving across the far
northeastern plains during the late morning or early afternoon on
Tuesday which could kick off a few thunderstorms. Models are hinting
at a dry cold front moving across the northeastern plains on
Thursday...which would drop high temperatures across the plains back
into the 80s...with continued mostly dry conditions across north
central and northeastern Colorado.

&&

.AVIATION...(For the 18Z TAFS through 18Z Saturday afternoon)
Issued at 1100 AM MDT Fri Jun 23 2017

IFR-MVFR ceilings continue in the upslope flow across the Front
Range area. Starting to see the deck thin out on satellite and
webcams, needed to extend the break out a couple hours over the
area airports. VFR conditions are expected to prevail by 20z, with
the higher cloud deck expected to break up this evening. Wind
forecast will be difficult as surface low is forecast to be
somewhere around DEN overnight and into Saturday morning.
Southeasterly winds due to the high surface pressure over the
eastern plains should dominate the area, however some weak signals
of the weak surface low moving east of DEN which would bring in
northwesterly winds. Potential of fog is low at this point, but
will keep monitoring weather and model data.


&&

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

$$

UPDATE...Kriederman
SHORT TERM...Gimmestad
LONG TERM...Kalina
AVIATION...Kriederman


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