Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 162145

Area Forecast Discussion
National Weather Service Denver/Boulder CO
345 PM MDT Wed May 16 2018

.SHORT TERM...(This evening through Thursday)
Issued at 344 PM MDT Wed May 16 2018

Upper level ridging with the dry conveyor belt pushing into the
region will bring high pressure and a capped atm. Some models
indicating enough low level moisture and heating that it could
break the cap over the far NE plains to pop off some light
convection but this will be late and have low confidence so kept
pops out of the forecast. Ceilings will gradually increase through
the overnight hours with lows only getting into the low to mid 50s
on the plains.

For Thursday, a shortwave embedded in the SW flow aloft will help
to destabilize the plains during the afternoon hours. Diffluence
aloft will combine with moderate RH values and good QG ascent to
increase chances of afternoon convection on the plains mainly
along and east of a Greeley to Limon line with the help of low
level convergence near the Cheyenne Ridge. Deep shear is decent
in the lower 30s with CAPE values from 1500 to 3000 j/kg. Severe
storms will be possible over the far NE plains with the main
threats being large hail, gusty winds and periods of brief heavy
rain. Highs will reach into the low 80s on Thursday with 50s and
60s in the high country.

.LONG TERM...(Thursday night through Wednesday)
Issued at 344 PM MDT Wed May 16 2018

Thunderstorms will be ongoing late Thursday afternoon in far
northeast Colorado and will continue into Thursday night as they
move eastward. Models indicate showers and storms may back build
into Logan, Phillips, and Sedgwick counties so POPs and QPF were
increased from 00-12Z Friday.

During Friday morning a low will develop over southeastern
Colorado which will increase the easterly component of the winds.
This upslope flow along with high amounts of low level moisture
could create patchy fog mainly north and east of a line from Fort
Collins to Limon so I have added this to the forecast. Stratus
will encompass much of the northeastern plains Friday morning due
to the same factors. This could end up limiting the instability
Friday afternoon for potential thunderstorms. If clouds do clear
by mid morning, moderate mixed layer CAPE values of 2000-2500 J/kg
along with sufficient 0-6km bulk shear values of 30-40 knots will
allow for strong to severe thunderstorms to form during the
afternoon and evening hours with large hail and strong wind gusts
possible. However, current thinking is that clouds will struggle
to clear out during the late morning meaning models are likely
overdoing instability forecasts. This may make the severe threat
more isolated across the CWA.

The focus then shifts to the precipitation on Friday night and
into Saturday. Rain and thunderstorms will be most likely across
the northern foothills and plains and will be moving rather
slowly. This may produce a heavy rain and localized flooding
threat. More information can be found in the hydrology section on
this. Otherwise, this system will draw in cooler air from the
north, dropping snow levels to around 10000 feet Friday night and
Saturday. By Saturday afternoon and evening, this system will
wrap-up and move off to the northeast allowing the precipitation
to exit Colorado.

Larger scale ridging will begin to develop over the central US
during the beginning of next week. This will allow temperatures to
warm above seasonal norms while conditions dry out a bit. A large
scale trough will move into the west coast region during this
time frame and will likely get cutoff from the flow. Over
Colorado, this will mean southwesterly mid to upper level flow
will develop as weak shortwaves will protrude from this trough
providing forcing for a daily chance of afternoon showers and
thunderstorms. This pattern generally favors wetter than normal
conditions but with the uncertainty in the timing of the mid to
upper level features, have kept POPs in the chance category.


.AVIATION...(For the 18Z TAFS through 18Z Thursday afternoon)
Issued at 344 PM MDT Wed May 16 2018

VFR conditions are expected through the period. Winds will
continue to be lighter with speeds ranging from 5 to 10 kts. Winds
will be out of the east than veer around to drainage between 04
and 05z. Winds will predominately stay out of the SSW fluctuating
between 160 and 200. Some outflows will be possible in the
afternoon with storms developing far to the North and East of the
area terminals that could possibly push out outflows that could
change the current wind patterns.


Issued at 344 PM MDT Wed May 16 2018

Heavy rainfall is possible on Friday night and into Saturday as a
mid level trough will move over northeast Colorado, strengthen,
and slow down. Diffluent flow aloft with the aid of a right
entrance region will create rising motion, strengthening a
surface low which will position itself in northwest Kansas on
Saturday morning. During Friday night and Saturday, precipitable
water values will be near 0.90 inches which is slightly above the
daily max precipitable water value for May 19 on the SPC
climatology page. Flow throughout the atmosphere will be rather
weak meaning storms will position themselves over the same areas
for an extended period of time. These factors will form heavy
rainfall especially along and near the Cheyenne Ridge and northern
foothills as roughly 2 to 4 inches could fall from Friday night
through Saturday night. In the heaviest thunderstorms, rainfall
rates could exceed 1 inch per hour and could create localized




LONG TERM...Danielson
HYDROLOGY...Danielson is the U.S. government's official web portal to all federal, state and local government web resources and services.