Area Forecast Discussion
Issued by NWS Denver/Boulder, CO

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FXUS65 KBOU 180229

Area Forecast Discussion
National Weather Service Denver/Boulder CO
829 PM MDT TUE MAY 17 2016

Issued at 828 PM MDT Tue May 17 2016

Overall forecast is right on track. A few showers continue to move
north across the Denver area and Palmer Divide, and those will
likely continue through the rest of the evening with weak
deformation aloft. Then look for a slow but steady decrease
overnight as both low/mid level flow turn more southerly. Adjusted
chances of rain for latest radar trends.


.SHORT TERM...(This afternoon through Wednesday)
Issued at 325 AM MDT Tue May 17 2016

CWA remains sandwiched between an upper level trough/closed low
to our southwest and a broad anticyclonic circulation/upper high
over the northern Great Plains. Deformation zone separating these
systems and a gently easterly/upslope flow are largely
responsible for the lingering low overcast...unseasonably cool
temperatures and spotty showers over northeast Colorado this
afternoon. Overnight...sfc winds along the Front Range are prog to
turn southerly but remain light in speed. East of the I-25
corridor, a light southeasterly flow is expected to persist which
will continue to produce a nearly saturated boundary layer through
early Wednesday morning. This should keep low clouds, patchy fog
and spotty showers in place over and east of the Front Range
foothills. Although should see precip chances continuing to
decrease overnight. Above 700 mbs...models indicate gradual drying
overnight with a shift to southerly mid-level flow with the upper
low now over Las Vegas migrating south over southern Arizona by
morning. Clearing skies west of the Continental Divide will allow
radiational cooling to produce patchy dense fog on the valley
floors before morning. Low temperatures tonight expected to be
similar to those last night and still several degrees below
average. Normal low for Denver is currently 43F.

On Wednesday...temporal and spatial cross sections indicate a
gradual downward mixing of drier air aloft but not soon enough to
disperse low clouds and fog on the plains until mid-morning at the
earliest. Models show the upper low spinning over southern
Arizona weakening and moving eastward over western New Mexico by
late in the day. South-southeasterly sfc-600mb flow around this
compact system drives another batch of moisture northward along
the spine of the Rockies as far north as the I-70 corridor. Break
in the cloud cover by late morning will allow the strong May sun
to initiate scattered convection over the high terrain by
midday...while the plains essentially remain capped until mid-
afternoon. Believe high scattered pops will suffice for the high
country during the afternoon hours. On the plains...any shower
development on the plains should be confined to the higher fringes
where the cap will be weakest. With much more sunshine tomorrow
and the warming aloft, high temperatures should be 10-15 deg f
warmer than those today. Still not quite back to the norms for the

.LONG TERM...(Wednesday night through Monday)
Issued at 325 AM MDT Tue May 17 2016

The large upper level trough will slowly traverse eastward through
the day Thursday keeping enough moisture over the high country for
prolonged precipitation. On the plains a large surface high will
make its way south to the east of the state keeping the plains
mostly dry on thursday as drier air is pushed in. Model CAPE
values in the mountains hover between 1500 and 2000 j/kg so
thunder will be possible by the afternoon in the mountains and
foothills. Temperatures will be back to seasonal normals on
Thursday with highs in the mid 70s.

A large upper level closed low will continue to spin over the
Pacific NW Friday and through the weekend. This will bring ridging
over the state and increasing temperatures into the weekend. There
is enough moisture in the mountains with some embedded in SW flow
aloft to keep a chance of thunder in the mountains and foothills
with a slight chance over the Palmer Divide during the afternoon
time period Friday through Sunday. Conditions elsewhere will be
drier with downsloping off the foothills and increasing
temperatures into the upper 70s to lower 80s Saturday and Sunday.

By Monday morning the large upper closed low that was over the
Pacific NW will weaken into an open wave and push increasing
moisture in NW CO. However with a surface low over NE Colorado
conditions will remain dry with temperatures forecasted to be
above seasonal normals.


.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 828 PM MDT Tue May 17 2016

ILS approaches will continue through the rest of the evening with
areas of MVFR ceilings and visibilities in/near scattered rain
showers. The ceilings are still expected to lift and break
06Z-12Z with a more southerly flow developing surface through
6000 feet. Daytime heating on Wednesday will bring a scattered to
broken deck of mid level clouds over the Front Range airports by
20Z, but likely too stable for any showers. South to southeast
winds expected to prevail around 7-11 knots.


.BOU Watches/Warnings/Advisories...


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