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Area forecast discussion 
National Weather Service Denver/Boulder Colorado
453 am MDT Thursday Sep 3 2015

Short term...(today through tonight )
issued at 453 am MDT Thursday Sep 3 2015

Moisture levels over the state have been gradually increasing
overnight as southwesterly flow aloft continues. The increase in
moisture should lead to an increase in shower activity this
afternoon...initially over the mountains and then out across the
plains in the late afternoon and evening. Lightning detection has
already recorded some thunderstorms over the San Juan Mountains
this morning...and the kgjx radar is showing a band of showers
over southwestern Colorado as the leading edge of the subtropical
moisture advances northward. Have bumped the probability of precipitation in the central
mountains up to likely for this afternoon. Other parts of the
County Warning Area should see scattered showers and thunderstorms
through the early evening. Model soundings on the plains show a
bit of an inverted-vee pattern...indicative of more gusty winds
than heavy rain. Soundings over the mountain show deeper saturated
conditions. An upper level jet will be moving into the state from
the southwest with the diffluence ahead of the jet being in a
favorable position to enhance convection through the afternoon
hours. Temperatures will be a little cooler today since skies will
be getting cloudy by mid-afternoon.

Showers will move off to the northeast plains during the evening
hours with drying conditions returning to the forecast area
overnight.

Long term...(friday through wednesday)
issued at 453 am MDT Thursday Sep 3 2015

Subtropical moisture in south-southwest flow aloft will continue over the area
on Friday as another possible disturbance moves across in the
aftn/evening. Precipitable water values range from 0.5"-0.7" over the
higher terrain with around an inch over the plains. Will keep scattered
probability of precipitation in the mountains however not sure about overall coverage over the
plains. For now will mention a chance closer to the Front Range with a
slight chance further east over the plains. As for highs readings will
remain above normal across northestern Colorado with temperatures in the upper 80s to
lower 90s.

On Sat an upper level trough will move into the Great Basin with
invreasing southwesterly flow aloft. Once again there are some differences
between the European model (ecmwf) and GFS as the European model (ecmwf) shifts the main plume of
subtropical moisture east of the area while the GFS keeps it over
eastern Colorado. Still not sure how things will evolve so will only
mention a slight chance of storms over the area. As for highs once
again readings will be in the upper 80s to lower 90s across northestern Colorado.

By sun the upper level trough will move east-northeast across the northern rockies
with dry west-southwest flow aloft across the area. A weak cool fnt will move
across northestern Colorado during the day however 850-700 mb temperatures only drop a
degree or two so afternoon highs will still be in the middle to upper 80s.
Low level moisture behind this weak fnt is lacking so will not mention
any thunderstorms. With increasing low level flow and low humidity levels
fire danger will increase especially over the higher terrain.

On Monday dry west-southwest flow aloft will continue over the area with gusty
winds and low humidity levels over the higher terrain so fire danger
will remain elevated. Over northestern Colorado a surface Lee trough will be in
place which will lead to another dry day over most of the plains.
However the European model (ecmwf) does show an increase in low level moisture over the
far eastern plains which could lead to some isolated late afternoon/evening
storms along a weak convergence zn. As for highs will keep readings
in the lower to middle 80s over northestern Colorado.

By Tuesday the European model (ecmwf) shows dry westerly flow aloft across the area with a
cold fnt moving across northestern Colorado. Meanwhile the GFS moves another
upper level trough quickly across the northern rockies with dry west-southwest flow
aloft and holds off this fnt until Tuesday night. The previous run of
the GFS had this trough a bit further south with more moisture along
with a weak fnt moving into northestern Colorado by afternoon. Thus this setup would
have produced at least a slight chance of thunderstorms while the latest
solution has nothing. The previous run of the European model (ecmwf) did not show the
cold fnt moving into Tuesday night and had enough low level moisture over
portions of the plains for some widely scattered storms. At this point will
leave previous forecast alone and keep low probability of precipitation in the forecast with highs
in the lower to middle 80s across northestern Colorado.

For Wednesday dry westerly flow aloft is supposed to be over the area however
the European model (ecmwf) and GFS differ on their surface solutions. The GFS shows
cooler air moving into northestern Colorado behind a fnt with readings in the
upper 70s to lower 80s while the European model (ecmwf) shows a Lee trough over
eastern Colorado with above normal temperatures. Once again not sure which way to
lean so will just go with a blend of the ECMWF/GFS.

&&

Aviation...(for the tafs through 12z Friday morning)
issued at 453 am MDT Thursday Sep 3 2015

Aviation impacts should be minimal through this morning and into
early afternoon. Later this afternoon...showers and thunderstorms
are expected to move across the Denver area...moving from the
southwest to northeast. Gusty winds and brief heavy rain are going
to be the main threats as the storms move through. Ceilings should
remain above 6000-8000 feet above ground level. Showers will move off to the east
by about 9 PM tonight with no additional weather expected after
that.

&&

Bou watches/warnings/advisories...
none.
&&

$$

Short term...dankers
long term...rpk
aviation...dankers

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