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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
345 am MDT Sat may 23 2015

Short term...(today through tonight )
issued at 342 am MDT Sat may 23 2015

An upper level low over eastern Utah will move very slowly eastward
through tonight. Qg fields show middle level ascent through the day into the
early evening hours. Meanwhile at the surface low pressure will extend from
the central mountains into southeastern Colorado with mainly southeasterly low level flow across the
plains. With southeasterly low level flow a Denver cyclone will probably develop
by early afternoon with a convergence zn over Denver or just to the east.

Should see a gradual increase in shower and thunderstorm development
across much of the area by midday which will linger into the early
evening hours. As far as severe potential it appears highs over northestern
Colorado may stay mainly in the upper 50s to lower 60s with convective available potential energy around
1000 j/kg except possibly over Lincoln County where they may reach
around 1500 j/kg. There will be decent shear so expect a few severe
storms over the plains with marginal large hail and a few
tornadoes due to low LCLs. Meanwhile there will be some potential
for heavy rain across the plains so will issue a Flash Flood Watch
due to saturated soils as a few locations could see a few inches
of rain in less than an hour.

For tonight the upper level trough will be centered over western
Colorado however the middle level ascent will gradually lift north of the
area this evening with precipitation chances decreasing by midnight from SW to
NE. May see some fog develop after midnight across the plains.

Long term...(sunday through friday)
issued at 342 am MDT Sat may 23 2015

M... of the same best describes the daily weather cycle
anticipated during the upcoming week. Let's start with the large
scale flow pattern. Models show upper troughs repeatedly forming
over the intermountain west...and a continuous feed of subtropical
air up into the Desert Southwest or onshore in Southern California
through the period. The first of these troughs is forecast to
track over the central Rocky Mountain region on Sunday bringing cooler
temperatures...scattered showers...isolated T-storms and lighter
winds to the forecast area. Prognosticated 6-hour precipitation amounts on the
order of 1/10th to 3/10th inch by evening. Shear and instability
not as great as the day before due to weaker flow and cooler
temperatures. So severe weather risk will be much lower. Models lift this
trough newrd over the northern Great Plains by Monday morning which
positions northestern Colorado in a somewhat drier and warmer northwesterly flow
to start the day. But by afternoon moisture and instability return
with a passing middle-level disturbance...resulting in another round
of scattered showers and isolated T-storms mainly over and near
the mountains through the early evening hours. On Tuesday models show
even drier and warmer conditions with a passing shortwave ridge.
Still strong daytime heating and residual moisture should be adequate
to produce scattered afternoon/evening showers/T-storm in the high
country and isolated T-storms on the nearby plains. Nothing severe
and rain amounts should be on the light side.

By Wednesday...the next upper trough settles in over the Great
Basin. As it does so...strengthening southwesterly flow out ahead of it pumps
moist and unstable air up from the Desert Southwest potentially
resulting in another round of soaking showers and thunderstorms
for portions of north-central and northeast Colorado during the
afternoon and evening hours. Shower coverage should be more than
the day before and with mean layer specific humidity on the
increase...odds increase for locally heavy rainfall over southwestern
portions of the County Warning Area.

Thursday and beyond...models differ some on when the western
trough shifts east and the degree of impact it'll have on the
forecast area. Most models show a cold front slipping into northestern
Colorado Erly on Thursday and a fairly moist upslope flow on the
plains throughout the day. For now will hold off on going hog wild
with precipitation Thursday but will still hold onto a chance of
showers/T-storms for most areas...together with slightly cooler
temperatures. Friday could possibly be wetter and cooler yet if the
medium range models are correct...the product of deep moisture
wrapping around a closed low spinning over east-central Colorado.


Aviation...(for the tafs through 12z Sunday morning)
issued at 342 am MDT Sat may 23 2015

A weak Denver cyclone was over Denver which has kept the brunt of low
clouds and fog to the north of dia. The hrrr and rap still show
that some brief dense fog may develop for a few hours in the 10z-14z
time period so will keep in a tempo group for LIFR. Otherwise
ceilings/visibility will be MVFR through 16z. Should begin to see
shower/thunderstorm development by 18z with activity gradually ending by
23z if hrrr/rap can be believed. May see some small hail and gusty
winds with visibility down to 3-5 miles in the stronger storms. Winds
will be light and variable early this morning and then more east-northeast by
early afternoon.

For tonight the shower/thunderstorm threat should end by 02z with winds
briefly northwesterly for a few hours before becoming light drainage before
midnight. There could be some fog and low clouds late tonight into
Sun morning.


issued at 342 am MDT Sat may 23 2015

May see from 1 to 2 inches of rain across portions of the plains
this afternoon into the early evening hours with some potential for flash
flooding due to saturated soils. In the mountains and foothills amounts
will average from one quarter to one half inch with isolated amounts
up to an inch in a few locations.

The Cache la poudre and South Platte rivers remain above flood stage
in Weld County and across western portions of Morgan County...and
will stay that way for another day or so.


Bou watches/warnings/advisories...
Flash Flood Watch from noon MDT today through this evening for



Short term...rpk
long term...Baker

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