Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 231950
AFDDMX

AREA FORECAST DISCUSSION
National Weather Service Des Moines IA
220 PM CDT Fri Sep 23 2016

.SHORT TERM.../Today/
Issued at 359 AM CDT Fri Sep 23 2016

Main concern today will exist primarily during the morning hours
with the ongoing convection.  While moisture transport is not as
intense as last night, it is still focused into northern and
eastern Iowa and this will persist over the next few hours.
Therefore, anticipate the shower and thunderstorm activity to
continue through the mid morning hours before gradually
diminishing as low level inflow weakens. Rainfall rates will
remain problematic with PWATs continuing to range from 1.5-2.0" in
northern Iowa and given the very saturated conditions, will
maintain the flash flood watch into today although it may be able
to be lifted later this morning.

Otherwise, the surface boundary will lift northward gradually
through the day as heights rise.  This will also shift focus for
thunderstorms finally north of the state with little
additional redevelopment across the forecast area later
this afternoon. Temperatures will continue to be unseasonably warm
across much of the forecast area, especially the central and
south where temperatures will continue to be around 15 degrees
above normal.

.LONG TERM.../Tonight through Thursday/
Issued at 359 AM CDT Fri Sep 23 2016

The primary focus during the extended period was with rain
chances Saturday afternoon into Sunday morning. The rest of the
forecast dealt with temperatures. Models have finally come into
good agreement with the dry pattern throughout the week next week
as well as with the timing of the cold front Saturday night into
Sunday.

Tonight through Sunday...Brief upper level ridging moves across
the region tonight ahead of a deep 500mb trough ejecting out of
the central to northern Rockies by Saturday morning. The deep
moisture returns Saturday as good moisture transport and strong
Theta-E advection pushes through the state. The main concern with
the cold front is additional heavy rain over already
saturated/flooded locations over northern Iowa. By Saturday
evening, PWATs in the 1.5-2.0" range, soundings become deeply
saturated, and warm layer cloud depths range from 3500-4000
meters. The 200-300mb jet brings a steady flow of tropical
moisture into the region Saturday and places Iowa within the
right entrance region of the upper level jet. In addition, decent
frontogenetical forcing transitions across the forecast area
between 00-12z Sunday from west to east. Hence, high confidence
with another round of heavy rain and a Flash Flood Watch might be
needed in a future forecast package. The cold front moves east
Sunday morning with the 500mb vort max and trough to follow during
the afternoon. However, much of the moisture will be cleared east
ahead of the surface front, so not anticipating much additional
rain past 18z Sunday. It will likely to be breezy during the
afternoon with the vort max pushing throughout and increased winds
a few knots Sunday afternoon.

Monday through Thursday...Large surface high pressure builds into
the region and looks to dominate the weather pattern for much of the
week. The 23.00z GFS and even the ECMWF are still holding onto the
upper low stalling across the Great Lakes. The GFS is a bit slower
in moving it eastward and thus keeps Iowa in the cooler air much
longer. Regardless, not much moisture to work with any weak
shortwave that transitions southward within the 500mb flow and kept
the forecast dry attm.

&&

.AVIATION.../For the 18Z TAFS through 18Z Saturday afternoon/
Issued at 225 PM CDT Fri Sep 23 2016

MVFR/IFr cigs and and patchy fog will continue over Northern/
Northeast Iowa this afternoon with minor improvement before dropping
again tonight after 03Z.  Otherwise VFR conditions South until 06Z
when patchy fog will impact vsbys.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...
None.

&&

$$

SHORT TERM...Cogil
LONG TERM...Podrazik
AVIATION...FAB


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