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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
847 PM MDT Tuesday Jun 2 2015

issued at 826 PM MDT Tuesday Jun 2 2015

Colorado remains under a much drier airmass today as southwest
flow continues over region. Storms have remained further north
across Wyoming and Nebraska this evening and still a slight chance
for a storm over the far NE corner as frontal boundary approaches
Colorado with still ample low level moisture. No other changes for
tonight. Still looks like an active day Wednesday afternoon and
evening with potential for strong and severe storms.


Short term...(this evening through wednesday)
issued at 349 PM MDT Tuesday Jun 2 2015

Will keep a slight chance of thunderstorms in place for the far
northeast plains through 09z tonight. There will still a nice low
level moisture pool over this area. An isolated severe
thunderstorm or two not out of the question. Further be
much drier. The dry flow aloft will be southwesterly with a Flat
Ridge of high pressure over the County Warning Area this evening. This ridge axis
will shift to the east by 12z Wednesday. On Wednesday...a much
better setup for thunderstorms...some possibly severe. A cold
front will push into the northeast plains in the morning...and
settle along the Front Range foothills and Palmer Divide. By the
afternoon...northeast to easterly upslope winds will develop below
700 mb with an increasing southwesterly flow aloft. Convective available potential energy across
the urban corridor and northeast plains are prognosticated to be in the
2000-3000 j/kg range. 0-3 km helicity values pretty healthy as
well...around 180 m2/s2. The low level Theta-E moisture will end
of centered along the Front Range foothills and Palmer Divide. In
addition...there will be weak middle and upper level qg ascent
associated with a weak upper trough axis brushing across northwest
Colorado in the afternoon. Best chance of severe thunderstorms would appear
to be along the surface Theta-E maximum gradient after 21z Wednesday.
Enough shear for the storms to produce damaging winds and
potential tornadoes. Highest thunderstorm coverage in the
afternoon will be in and near the Front Range foothills.

Long term...(wednesday night through tuesday)
issued at 349 PM MDT Tuesday Jun 2 2015

Slowly changing pattern expected after our transition to cooler
and moister low level air on the plains Wednesday. Upper air
pattern is locked up with a trough well to our west and a ridge
just east of US. For several days...probably into the
weekend...the air coming over US is still quite warm and dry while
the low levels on the plains are cool and quite moist. This sets
up an all-or-nothing convective environment that features high
convective available potential energy but marginal temperatures. Suspect there will be various
combinations of low level convergence...weak upslope...and little
upper level features to produce some thunderstorms each day...and
in such a moist environment they would likely develop into larger
clusters that could be efficient rain producers. However there
really are not any large features evident that will provide any
clear focus. Models have a variety of precipitation patterns...but the
theme is late day convection each day in different places but not
widespread. GFS is a bit less sharp with the ridge/trough pattern
and still tries to bring up some tropical moisture...though it
GOES into Nevada and Utah and keeps Colorado on the edge of it.
That is not necessarily unfavorable...sometimes the edge of a big
cloud shield winds up having the strongest convection. The European model (ecmwf)
on the other hand keeps US in the dry air through the
weekend...then actually bumps the ridge westward a bit and puts US
in a dry westerly flow. The end result of the GFS solutions is
probably a gradual moistening aloft as the moisture that does come
up gets diffused through the ridge axis over the weekend...while
the European model (ecmwf) does not have this change. Main threat for Thursday will
be severe storms as there will be enough wind to keep storms
moving and enough cape/shear for all kinds of severe weather. By
the weekend the winds aloft should be lighter...and a more uniform
southerly flow will be more conducive to slow moving and back-
building storms. So the threat over the weekend will trend to more
of a flooding threat. This would continue into next week in the
GFS solutions...while the ec pattern would bring US back to more
of a severe threat with the drier westerly flow aloft. The
resulting forecast is a fairly broadbrush of scattered mainly late
day storms...seasonal highs and above average lows through the


Aviation...(for the tafs through 06z Wednesday evening)
issued at 826 PM MDT Tuesday Jun 2 2015

Surface low over the Denver area as resulted in complicated wind
pattern with mainly light east to northeast winds over terminals
but should transition to southeast to south with boundary
approaching from the southeast. Frontal boundary will move across
terminals later tonight/early Wednesday morning with increasing northerly
flow and higher low level moisture. This will set the stage for
potential strong/severe storms by later Wednesday afternoon.


issued at 349 PM MDT Tuesday Jun 2 2015

Increased snowmelt will cause the Cache la poudre and the South
Platte in the Greeley area to remain just above flood stage...
for the Cache la poudre tonight and the the South Platte on Wednesday.
This will cause renewed flooding in the most vulnerable areas.
Other rivers will be high and could cause some minor impacts...but
are expected to stay below flood stage. The storms on Wednesday
afternoon/evening could produce heavy rainfall but on a localized

Scattered storms are expected each day through the weekend and
some could produce heavy rain and localized flooding. The flash
flooding threat is still fairly low on Thursday...but may increase
this weekend as storms are expected to be slow moving in a very
moist environment. Rain through Friday will likely have little
effect on the larger rivers...but a wetter weekend could cause a
renewed flood threat. Meanwhile the mountain temperatures will
drop slightly...but it will still be fairly warm in the high
mountains so snowmelt will only decrease a little through Friday
and then just a little more over the weekend.


Bou watches/warnings/advisories...


short term...Cooper
long term...gimmestad

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