Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 261738
AFDBOU

Area Forecast Discussion
National Weather Service Denver/Boulder CO
1138 AM MDT THU MAY 26 2016

.UPDATE...
Issued at 1138 AM MDT Thu May 26 2016

Due to the wet storm approaching the area with cold enough
temperatures and good upslope flow through tonight, decided to
issue a Winter Weather Advisory for zone 34 which will impact the
mountains of Park, Summit and Clear Creek counties the most.
Convection this afternoon may produce localized areas of heavy
snowfall rates with low visibility and producing slick to slushy
roads over high mountain passes.

UPDATE Issued at 948 AM MDT Thu May 26 2016

Storm activity has already begun over the northern Colorado plains
this morning. As more of the stratus deck over the area erodes and
sunlight reaches the ground, more convection will occur with
thunderstorms expected earlier across the area today. Hi-res
models have activity over the urban corridor beginning right
around noon or slightly after.

A very moist airmass with upslope winds turning northerly and
increasing to 35 to 40 knots tonight with the mid and upper lows
focusing precipitation from central Colorado northeast into
Nebraska brings the threat of heavier precipitation. Around 2
inches of water will be likely through tonight...however
convection may create localized areas of higher amounts. This will
likely occur over the Palmer Divide then northeast through
Washington County.

Still expecting the main threat to be large hail and strong
damaging winds from these storms...although a surface boundary
could help spin up a tornado or two.

&&

.SHORT TERM...(Today and tonight)
Issued at 316 AM MDT Thu May 26 2016

An upper level low over northern Arizona will move east-
northeast into southeast Colorado tonight. Easterly winds around a
surface low over southeast Colorado will transport moisture into
the area today. This moisture combined with lift ahead of the low
will trigger showers and thunderstorms today. HiRes models
indicate numerous showers and thunderstorms will form between noon
and 3PM along the Front Range and near by plains. This activity
will spread northeast through the rest of the afternoon and early
evening. Surface based CAPE is expected to be 1000 to 1500 J/kg
from the Front Range and eastward. Main threat will be hail today
due to cool temperatures aloft and steep lapse rates. Can`t rule
out wind damage or a tornado or two, but the threat for these
today is lower than Tuesday.

Thunderstorms will decrease west to east this evening. Widespread
rain is expected to develop tonight due to lift from the upper level
over southern Colorado. As the surface low moves off to the east
tonight, surface winds become more northerly. This will bring
heavier rainfall to the Palmer Divide due to upslope flow. The snow
level is expected to lower to 9000 to 10000 feet tonight. So
there may be minor snow accumulation on the higher mountain roads.
For areas above 12,000 feet, several inches of snow is expected
through tonight along the Front Range Mountains.

.LONG TERM...(Friday through Wednesday)
Issued at 316 AM MDT Thu May 26 2016

An upper level low will be over sern CO at 12z Fri and will then
move slowly ene into wrn KS by early Fri evening.  Cross-sections
show upslope flow in the morning along with abundant moisture and
some wk qg ascent.  This should see a good chc of showers along with
a few tstms across the plains especially in the morning.  Over the
higher terrain there will be a good chc of showers east of the
divide and across the srn foothills with the snow level around 9000
ft.  In the aftn will still see a chc of showers and a few tstms
especially over the far ern plains and across the higher terrain.
As for highs will keep readings in the 60s across nern CO.

For Fri night into Sat wly flow aloft will dvlp over the area with
some drying occurring.  However enough moisture will linger to allow
for a chc of showers/tstms over the higher terrain Sat aftn with a
slight chc across nern CO.  Highs will rise back into the lower to
mid 70s across the plains.  On Sun the flow aloft will become more
swly as weak sfc low pres resides over ern CO.  Once again aftn
heating combined with lingering moisture will lead to a chc of aftn
convection over the higher terrain.  Across nern CO should begin to
see some deeper low lvl moisture move back into the area with better
instability by aftn which may lead to a few strong storms. Highs on
Sun will be in the 70s across the plains.

On Mon the ecmwf is quicker with moving an upper level trough into
the nrn and cntrl Rockies while the gfs is slower.  Overall still
will see a chc of convection no matter which solution pans out with
some potential for strong storms over nern CO.  As for highs will
keep readings in the 70s over the plains.

By Tue the ecmwf moves the upper level trough into the nrn plains
while the gfs has an upper level low over WY.  In addition the ecmwf
moves a cdfnt across nern CO Tues morning while the gfs has this fnt
affecting nern CO Tue Night into Wed morning.  At this point not
sure which solution to believe so will just mention 20-30% pops
across the area.  As for highs readings would only be in the 60s
based on the ecmwf while the gfs has temps in the 70s.

For Wed the ecmwf keeps a rather stg upper level low over the nrn
plains with wnw flow aloft across nrn CO while the gfs keeps a
weaker low over nrn WY.  Despite their differences both models have
some moisture remaining over the area to keep in a slight chc of
tstms.

&&

.AVIATION...(For the 18Z TAFS through 18Z Friday afternoon)
Issued at 1138 AM MDT Thu May 26 2016

Thunderstorms are developing in the Denver area and will continue
to become more widespread through around 00z. Showers and
thunderstorms eventually decrease and a steady rain forms after
00z. Main threat with the thunderstorms today will be heavy rain,
hail and wind gusts to 40 knots. VFR conditions expected through
about 00z, then ceilings will lower to 1000 to 3000 feet with the
steady rain. Easterly winds will turn to the north tonight. Wind
speeds are expected to be less than 25 knots, except under and
near thunderstorms.

&&

.HYDROLOGY...
Issued at 316 AM MDT Thu May 26 2016

Precipitable water values will climb to 0.60 to 0.80 along the
Front Range today, which is around the 90th percentile. The
stronger storms may be able to drop an inch or two of rain due to
slower storm motion today and possible training of storms. The
thunderstorms combined with steady rainfall tonight may cause
elevated streams and creeks to rise more. Low lying areas
susceptible to flooding could see issues this afternoon and
tonight. Main area to watch is south of Denver where the heaviest
rain is expected.

&&

.BOU Watches/Warnings/Advisories...
Winter Weather Advisory from 3 PM this afternoon to 9 AM MDT
Friday for COZ034.

&&

$$

UPDATE...Kriederman
SHORT TERM...Meier
LONG TERM...RPK
AVIATION...Kriederman
HYDROLOGY...Meier



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