Area Forecast Discussion
Issued by NWS Des Moines, IA

Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41

FXUS63 KDMX 290438

Area Forecast Discussion
National Weather Service Des Moines IA
1138 PM CDT Sun Aug 28 2016

.SHORT TERM.../Tonight/
Issued at 319 PM CDT Sun Aug 28 2016

Southerly flow in the lower levels with push of theta-e advection
into the southern CWA today. Energy lifting out of the southern high
plains northeastward toward the region, and push of theta-e
advection helping with the development of spotty storms across the
southern CWA today. Activity has increased in the past few hours
with latest SPC Mesoanalysis suggesting decent CAPE in the area, but
shear limited with effective values around 30kts. Therefore not
anticipating much in the way of organized cells, but may see a
strong storm or two with the potential for small hail or gusty
winds. Given the amount of CAPE, an isolated severe storm will be
possible especially in the next few hours before surface heating
starts waning with sunset.

Otherwise as sunset comes expect activity to diminish, but could see
it pick up again late tonight as the LLJ kicks in and another push
of theta-e advection sets up across the southern CWA. Therefore have
kept pops across the southern third of the CWA through the night.
Have mentioned fog again tonight with winds expected to be light and
the increased low level moisture around. Hi-Res models suggesting
pretty decent chance of development as well especially across the
north where vsbys were limited Sunday morning as well. Kept temps a
few degrees warmer though with the high dewpoints, therefore only
expect temps to fall into the mid to upper 60s across the CWA.

.LONG TERM.../Monday through Sunday/
Issued at 319 PM CDT Sun Aug 28 2016

From Monday through Tuesday the CONUS 500 mb pattern will be
characterized by zonal flow along the U.S./Canadian border, a weak
low pressure center over the four corners region, and nebulous
flow elsewhere. An old decayed 500 mb trough will extend
northeastward from the four corners low up across Nebraska and
Iowa, providing broad but weak forcing for vertical ascent.
Meanwhile in the lower levels a col region will develop over Iowa,
resulting in very light flow. With a fairly moist airmass in place
this will result in a couple of days of humid conditions, layered
clouds, and showers and thunderstorms at times. No strong
convection is anticipated and rain will likely be scattered and of
the "popcorn" variety. Thus will maintain 20-40 POPs through this
period, highest toward the south where the weak 500 mb trough will

By late Tuesday a 500 mb trough will be moving across Minnesota
and into the Great Lakes region, with a large and strong surface
high pressure system following in its wake. These two features
will combine to push the cloudy and humid early week airmass
southward on Tuesday night and Wednesday morning, ushering in dry
and clear weather from Wednesday night into the weekend. On Friday
a 500 mb ridge will build across the region but a low-level
inversion and lack of mixing will prevent significant warming.
Even so, winds turning to the southeast as the surface high
finally departs combined with another day of airmass modification
given clear skies and associated insolation should result in a
slight warming trend to end the week, potentially reaching 80
degrees in some areas by Saturday.

Toward the end of the long term forecast period, from Saturday
night through Sunday, the weather pattern looks to become more
active again as a large trough sets up over the western U.S. and
we find ourselves beneath southwesterly 500 mb flow. In response
an elongated surface trough will likely develop from eastern
Colorado up into South Dakota by Saturday and eventually
strengthen and kick out to the northeast as impulses round the
base of the 500 mb trough. This should lead to several rounds of
shower and thunderstorm chances over the latter part of Labor Day


.AVIATION.../For the 06Z TAFS through 06Z Monday night/
Issued at 1138 PM CDT Sun Aug 28 2016

Upper level boundary and old outflows from earlier convection
beginning to develop isolated convection at 0430z. Looking for
continued increase in coverage through 12z over south. Confidence
remains low regarding location both through 12z and day part 15z-
00z...though convection likely to be present across the area.
Overnight possible MVFR/IFR fog/br still likely at KMCW/KALO
elsewhere mitigated by clouds and shower potential through 15z.
Winds remain generally light through period. /rev




SHORT TERM...Beerends
AVIATION...REV is the U.S. government's official web portal to all federal, state and local government web resources and services.