Special Weather Statement, NWS Denver/Boulder, CO

Area Forecast Discussion
National Weather Service Denver/Boulder CO
244 PM MDT Thu Aug 3 2017

.SHORT TERM...(This evening through Friday)
Issued at 244 PM MDT Thu Aug 3 2017

Upper level ridge has shifted west over CA bringing increasing NW
flow over the state. This circulation allows for embedded
perturbations to continue to bring unsettled weather over the
forecast area. Currently the passage of a cold front earlier today
as left strong NNE flow on the plains and cloud cover keeping
conditions more stable. Elsewhere, solar insolation will
destabilize the atm enough to produce convection. Upper level SE
flow will allow for some storms to move off the higher terrain and
onto the wester portions of the plains and south to the Palmer
Divide through the late afternoon. Increased instability over the
Palmer Divide...Elbert and Lincoln counties could produce storms
capable of strong winds, brief rain and small hail. Precipitation
will gradually come to an end this evening with mostly cloudy
skies and lows in the mid 50s.

For Friday, models indicate a surface low pressure building over
the central mountains with a strong high pressure over KS helping
to increase SSE flow on the plains and west flow over the higher
terrain. Downsloping off the foothills will help to break up lower
ceilings from the Front Range with gradual clearing out through
the day. Models show increasing moisture on the plains by Friday
afternoon with lift seen in the flow. QG ascent is seen in the mid
levels that would help with afternoon convection formation.
Instability numbers increase east of an Akron/Sterling/North
Elbert line. Main threats based on shear values would be large
hail. Further west storm coverage will be less with isolated
strong storms possible. With increasing sunny skies and
downsloping temperatures will rebound back into the lower 80s.

.LONG TERM...(Friday night through Thursday)
Issued at 244 PM MDT Thu Aug 3 2017

Ingredients are in place for severe thunderstorms on the plains
Friday evening. However, large scale subsidence is expected to
limit the amount of convection. Will go with 20-30 pops for Friday
evening and keep a mention of possible severe thunderstorms in
the Hazardous Weather Outlook.

A surface low will sink south across eastern Colorado Saturday. A
weak cold front associated with the low will also drop south across
the area Saturday. Northeast upslope flow is expected to increase
low level moisture and help produce lift. Expect scattered to
isolated showers and storms to form behind the front and then spread
eastward during late afternoon and evening hours. Appears there will
be enough shear and instability for isolated severe storms over the
eastern plains.

Sunday through Thursday...autumn like temperatures will prevail as
northwest flow aloft persists. Temperatures will be well below
normal with highs in the 70s. Could end up with a day or two in the
60s if cloud cover lingers through the day. Normal high temperatures
are in the upper 80s. Short wave troughs embedded in the northwest
flow will bring a good chance for showers and thunderstorms. Timing
the arrival of these waves is still somewhat uncertain. The models
are in decent agreement with one affecting the area Sunday
afternoon/evening. The next one may be Tuesday, depending if the
timing is accurate on the GFS and ECMWF. For Pops, plan on going
with mainly scattered pops for most periods with higher pops on
Sunday to try and match up with the timing of the first wave.
Thursday appears to be warmer due to short wave ridging forming over
Colorado. However, with this being a week away, would not be
surprised if this ridging stays farther west and the area stays
cooler.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 244 PM MDT Thu Aug 3 2017

Ceiling conditions will gradually improve through the period.
Winds will be out of the NE through 01z where they veer to the SE
with speeds staying around 5 to 10 kts. Light rain from storms
moving off the foothills could impact area airports from 21 to
02z. By 12z ceilings will increase with a small reduction in mist
for the early morning hours, 12 to 15z. VFR conditions will
prevail after 15z with winds becoming more westerly by the
afternoon.

&&

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

SHORT TERM...Bowen
LONG TERM...RJK
AVIATION...Bowen

Hazardous Weather Outlook
National Weather Service Denver/Boulder CO
1019 AM MDT Thu Aug 3 2017

COZ030>051-041630-
Jackson County Below 9000 Feet-
West Jackson and West Grand Counties Above 9000 Feet-
Grand and Summit Counties Below 9000 Feet-
South and East Jackson/Larimer/North and Northeast Grand/
Northwest Boulder Counties Above 9000 Feet-
South and Southeast Grand/West Central and Southwest Boulder/
Gilpin/Clear Creek/Summit/North and West Park Counties Above
9000 Feet-Larimer and Boulder Counties Between 6000 and 9000 Feet-
Jefferson and West Douglas Counties Above 6000 Feet/Gilpin/Clear
Creek/Northeast Park Counties Below 9000 Feet-
Central and Southeast Park County-
Larimer County Below 6000 Feet/Northwest Weld County-
Boulder And Jefferson Counties Below 6000 Feet/West Broomfield
County-
North Douglas County Below 6000 Feet/Denver/West Adams and
Arapahoe Counties/East Broomfield County-
Elbert/Central and East Douglas Counties Above 6000 Feet-
Northeast Weld County-Central and South Weld County-Morgan County-
Central and East Adams and Arapahoe Counties-
North and Northeast Elbert County Below 6000 Feet/North Lincoln
County-
Southeast Elbert County Below 6000 Feet/South Lincoln County-
Logan County-Washington County-Sedgwick County-Phillips County-
1019 AM MDT Thu Aug 3 2017

This hazardous weather outlook is for northeast and north central
Colorado.

.DAY ONE...Today and Tonight

Cooler today with a chance of showers and thunderstorms this
afternoon. Stronger storms that are able to produce brief
moderate to heavy rain, gusty winds and small hail will be
possible over the higher terrain and Palmer Divide areas. On the
plains showers will be isolated with rain and gusty winds being
the main hazards. Showers should end this evening with lows in the
50s overnight.

.DAYS TWO THROUGH SEVEN...Friday through Wednesday

There will be a scattered to isolated thunderstorms Friday. The
best chance for storms will be over the eastern plains where
isolated severe storms will be possible. For Saturday through
Monday there will be a chance of afternoon and evening
thunderstorms each day. Isolated severe storms will be possible
over the plains each day.

.SPOTTER INFORMATION STATEMENT...

Spotter activation will not be needed today or tonight.

Special Weather Statement
National Weather Service Denver CO
345 PM MDT THU AUG 3 2017

COZ033-032215-
South and East Jackson/Larimer/North and Northeast Grand/Northwest
Boulder Counties Above 9000 Feet CO-
345 PM MDT THU AUG 3 2017

...SIGNIFICANT WEATHER ADVISORY FOR SOUTHEASTERN JACKSON...
SOUTHWESTERN LARIMER AND NORTHEASTERN GRAND COUNTIES UNTIL 415 PM
MDT...

At 345 PM MDT, Doppler radar was tracking a strong thunderstorm 4
miles south of Cameron Pass, or 43 miles west of Fort Collins, moving
southeast at 25 mph.

Nickel size hail, heavy rain and winds in excess of 30 mph will be
possible with this storm.

Locations impacted include...
Cameron Pass, Trail Ridge and Gould.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

Torrential rainfall is also occurring with this storm, and may lead
to localized flooding. Do not drive your vehicle through flooded
roadways.

&&

LAT...LON 4042 10556 4040 10558 4041 10566 4039 10561
      4036 10564 4035 10567 4034 10563 4028 10568
      4035 10586 4042 10608 4045 10610 4045 10613
      4048 10612 4055 10608 4052 10605 4052 10603
      4054 10603 4055 10601 4056 10603 4058 10603
TIME...MOT...LOC 2145Z 305DEG 22KT 4046 10588

KRIEDERMAN