Area Forecast Discussion
Issued by NWS Des Moines, IA
FXUS63 KDMX 142339
AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
639 PM CDT Fri Oct 14 2016
.SHORT TERM.../This evening through Saturday/
Issued at 240 PM CDT Fri Oct 14 2016
A large stratus deck has plagued most of the area today. It is
showing signs of rapid erosion this afternoon, however, the densest
area across southwest Iowa and neighboring states persists.
Southerly low-level flow will persist and even increase a bit
overnight as our pressure gradient tightens, resulting in an
additional influx of unseasonably high moisture content with
dewpoints approaching 60 degrees. Forecast soundings illustrate a
strong surface inversion and with the increasing moisture trapped
beneath it it is likely that stratus and fog will redevelop
overnight, possibly more so than last night/this morning. Given the
strength of the flow it is unlikely that the fog will become dense,
however, it is a possibility given the magnitude of the dewpoints
and resulting widespread saturation. We will also see drizzle late
tonight/Saturday morning and have maintained this in the forecast.
All in all it will be grey and damp well into Saturday.
.LONG TERM.../Saturday night through Friday/
Issued at 240 PM CDT Fri Oct 14 2016
Saturday and Sunday...Confidence Low to Medium
Main challenges are early in the period on Saturday but also may
crop up again on Sunday. Subjective analysis this morning shows
significant moisture stream at H850 moving into the region ahead
of eventual trough passage Saturday afternoon/evening. Meanwhile...
surface dew points are also on the increase. Low level stratus
anticipated to hold on through much of Saturday morning with the
deck rising in height as daytime heating takes over. However...
Bufkit and MOS output guidance suggest that layer for the most
part will remain through the afternoon. With that in mind...it is
difficult to see highs reaching magnitudes that are forecast. More
likely that highs tomorrow fall 5 or so degrees below current
projected forecast unless mixing can break the deck. Given time of
year the latter processes would not be favored. As heating increases...
will stick with chance iso thunder in the late afternoon and early
evening...but will keep better chances confined to the southeast/east
nearer KOTM where Bufkit soundings show better elevated instability.
As the boundary shifts south early Sunday...it will begin to later
retreat northward during the afternoon hours as the next western
Plains shortwave amplifies a trough and pulls the boundary into
northern Iowa by late day. It is very likely that similar processes/results
will occur with regard to stratus on Sunday either gradually lifting
or slowly mixing out by afternoon. This may result in a downward adjustment
to Sunday high forecast in the next 24 hours. By Sunday night the front
will lift far enough north that any linger showers will be focused across
the north during the overnight and end toward morning as the warm front
lifts into southern Minnesota.
There has been a consistent signal for very warm and breezy conditions
on Monday and this signal continues. Monday looks to be the warmest
day of the extended period as H850 temperatures warm to near 15C north
and around 20C in the southwest. As the front exits the area Monday
night...temperatures will cool on Tuesday with a ridge of high pressure
moving across the area.
Tuesday through Friday...Confidence Medium
With a fast moving and somewhat energetic pattern continuing...
confidence in some of the details of the forecast will once again
lessen. The area will continue to experience west northwest through
the end of the period. This will result in temperatures nearer normal
readings for this time of the year. There are some differences between
the 12z GFS and 12z Euro after Wednesday. The GFS is advertising a
more pronounced northern stream shortwave with precipitation while
the Euro remains dry and has a lesser developed system driving southeast
with time. The net result will be lower confidence regarding rain
chances/clouds/ and temperatures. Especially next Friday...the Euro
solution would support warmer highs while the GFS would support cooler
temperatures and light rain.
.AVIATION.../For the 00Z TAFS through 00Z Saturday evening/
Issued at 639 PM CDT Fri Oct 14 2016
Low stratus expected through the period with CIGS dropping to
likely IFR overnight. Could see some light fog and drizzle develop
late tonight as well dropping VSBYs. Drizzle potential continues
into Saturday, but kept VSBYS up during the day for now. Gusty
southerly winds picking up again into Saturday.