Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 240921

Area Forecast Discussion
National Weather Service Denver/Boulder CO
321 AM MDT SUN JUL 24 2016

.SHORT TERM...(Today and tonight)
Issued at 230 AM MDT Sun Jul 24 2016

A moderate westerly flow aloft will remain over the state a jet max stretches across northern colorado...with 250
mb winds of 50-60kts. This has allowed for tstms to persist
overnight in the mountains while it is just now exiting the
northeast plains. At the surface low level moisture will increase
this morning as a cool front settles along the Front Range
Foothills and Palmer Divide. As a result...temperatures today
should be around 10 degrees cooler the yesterday. CAPES are
progged to increase however as east/southeasterly winds advect
high dewpoints into the northeast plains and urban corridor. NAM12
forecast soundings generate anywhere from 1500-2500 j/kg of CAPE
over east central and northeast Colorado...with the boundary layer
theta-e axis stretching from Limon to Fort Collins. precipitable
water values by this afternoon will be 1.2-1.3 inches with storm
motions northwest around 15kts. Southeasterly winds will also
increase the likelihood of a Denver Cyclone which will act as a
focus for tstms south and east of Denver. Enough shear today for a
severe thunderstorm or two which is why SPC has placed most of
eastern CO in the marginal category this aftn and evening. Main
threat will be thunderstorm strong wind gusts and a greater
potential for heavy rainfall. enough shear for hail up to one inch
as well. The 00Z experimental HRRR...the most complete run at this
time...appears to bring to areas of showers and tstms across the
cwa. The first one which is responsible for the tstms in mountains
west of Summit County early this progged to start
pushing into the Urban Corridor around 15z and into the northeast
plains by 20z...then another round develops from west to east
after 22Z. Not sure if this will pan out exactly as it has been
advertised..but will go with chc pops over the mountains and
Palmer divide...with lesser pops towards sern WY/western Nebraska
where the boundary layer will be a bit more stable by this aftn.
Best window for tstms this evening will be in the 00z-04z
windows...with decreasing pops thereafter.

.LONG TERM...(Monday through Saturday)
Issued at 230 AM MDT Sun Jul 24 2016

The upper level high over the srn Rockies will rebuild further north
into srn CO on Mon with wnw flow aloft over nrn CO. There are some
differences between the ECMWF and other models with regard
subtropical moisture. The ECMWF shows an increase in mid lvl
moisture across the area by aftn while the other models do not.
For now will continue with 20% to 30% pops over the higher terrain
with the best focus along and south of I-70. Over nern CO the low
lvl flow will become more sse with the hi res models showing a
Denver cyclone developing. Overall low lvl moisture should
continue over the plains with decent cape. Should see wdly sct
aftn tstms along the front range with some of the storms spreading
across the plains fm late aftn thru the evening hours. As for
highs readings will be in the lower to mid 90s across nern CO.

On Tue the upper level high will still be over CO however the ECMWF
and GFS still show a wk mid lvl trough moving across late in the
aftn into Tue night. If this feature is real then there would be a
better chc of storms across the area. As for highs will keep
readings once again in the lower to mid 90s across the plains.

By Wed the upper level high retrogrades back into the Great Basin
with the flow aloft becoming more wnw.  This would keep the flow of
subtropical moisture to the south of the area and decrease the chc
of storms.  Meanwhile there are some differences between the ECMWF
and GFS with respect to the sfc ptrn across nern CO.  The ECMWF has
a cool fnt moving across the plains while the GFS does not.  As a
result this leads to significant differences in high temps across
nern CO as the GFS has readings roughly 5 to 8 degrees warmer than
the ECMWF.  In addition the ECMWF has some convection developing
over the plains as low lvl moisture increases behind the fnt while
the GFS has nothing.  At this point will mention some low pops and
keep highs in the lower to mid 90s over nern CO.

For Thu and Fri the upper level high will remain over the Great
Basin with wnw flow aloft.  Thus the flow of subtropical moisture
will stay south of the area with limited tstm development in the
mtns and higher valleys.  Meanwhile over nern CO a fnt will move
across the area on Thu with significant temp differences between the
ECMWF and GFS once again.  The ECMWF has highs only in the upper 70s
to lower 80s across the plains while the GFS has readings in the 85
to 90 degree range.  As for tstms both models show a disturbance
embedded in the wnw flow which combined with decent instability
across the plains may lead to a better chc of storms.

On Fri the ECMWF and GFS are in better agreement with highs over
nern CO as both models have readings fm 85 to 90 degrees.  Meanwhile
with decent instability remaining over the plains will likely see
another round of sct storms.  In the mtns and higher valleys tstm
coverage will likely remain rather isold.  For Sat the GFS begins to
shift the upper level high eastward into CO while the ECMWF keeps it
over the Great Basin.  Meanwhile neither model shows much influx of
subtropical moisture so tstm coverage in the mtns will remain rather
isold.  Over nern CO there still will be favorable instability in
place so will mention widely sct storms.  Highs on Sat will be in
the upper 80s to lower 90s across the plains.


.AVIATION...(For the 06Z TAFS through 06Z Sunday night)
Issued at 230 AM MDT Sun Jul 24 2016

southeasterly winds this morning as frontal boundary backdoors into
the Urban Corridor from the east. Prevailing VFR through the
period...but will see bkn mid level cigs develop as showers/tstms
over the mtns possibly push into the Denver area by 15z. Will
mention at least vcsh in the Denver terminal forecast in the
15-19z period. A second wave is progged to move off the foothills
and into denver in the 22-23z time frame. Denver Cyclone should
persist through the afternoon...with strong thunderstorms winds
and moderate to heavy rainfall the main threats. Enough shear to
support some hail as well. could see brief ILS restrictions if
one of theses storms move across the airports. Should see the
tstms threat shift east of Denver after 04z this evening.

.BOU Watches/Warnings/Advisories...


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