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fxus63 kdmx 202331 

Area forecast discussion
National Weather Service Des Moines Iowa
631 PM CDT Fri Sep 20 2019

Discussion.../tonight through Friday/
issued at 403 PM CDT Fri Sep 20 2019

Main concerns for this forecast period surround precipitation
chances, severe storm chances and flash flood chances through
Sunday. Little changes in the overall setup for the expected
upcoming storm system, so have mainly fine-tuned details and
opted to match up to surrounding offices with a Flash Flood
Watch across the far south/southeast for Saturday night into

Large upper trough still moving through the northern rockies with
the surface trough extending from south central Canada southward
through the central Dakotas back into northeastern Colorado.
Strong southerly flow off the Gulf has been in place all day more
oriented toward the plains today, and will veer into Iowa late
tonight and remain through Saturday into early Sunday. This will
allow abundant moisture to surge northward with moisture from
Imelda beginning to push toward Missouri and portions of Iowa
through early Sunday. This will allow for much above normal
moisture values across the southern portion of the state with
precipitable waters approaching 2 inches or higher at times across southern and
eastern Iowa.

With warm air advection and Theta-E advection push tonight, expect a few rounds
of showers and storms to move northward across the state mainly
after midnight then continued chances for more elevated activity
through early/mid afternoon with additional pushes of warm air advection/moisture
advection. Could see a strong to potentially severe storm with
this activity which would mainly be a hail or wind gust potential.
More widespread storms are expected to develop by early Saturday
evening into Saturday night as the main upper level trough ejects
from The Rockies in two different pieces. This will result in the
cold front dropping southward through Iowa Saturday night and
lingering across the far south into Sunday. Strong deep layer
shear in place late Saturday through late evening Saturday night
will present a severe threat, especially across south central into
southwest Iowa. Instability will be decent, however with cloud
cover and a very saturated profile, cape expected to top out
around 2k j/kg which could limit the overall severe potential
somewhat given the strong shear in place. With the abundant
moisture throughout the entire column and some training of storms
near and head of the boundary and continued redevelopment across
northern MO into southern Iowa late Saturday night into Sunday, the
potential for heavy rain continues. Additionally warm cloud depths
are close to 4km and should see efficient rainfall with close 2
inch per hour rates possible at times. Ffg is higher across the
south with 1 hr values over 2 inches and some 3-6 hr values close
to 3-4 inches. However with some storm potential through the 24
hours prior to the onset of the heavy rainfall and the potential
rainfall rates and expected duration of the rainfall still have
the potential for flash flooding across the far south/southeast.
Thus the issuance of the Flash Flood Watch.

As the front moves south of the area late Sunday into Sunday night
rain should diminish across the state with much drier air moving
in and temperatures falling back to near the seasonal values for
highs Sunday into Monday. Dry conditions expected into Monday with
some storm chances returning mid-week next week.


Aviation.../for the 00z tafs through 00z Saturday evening/
issued at 631 PM CDT Fri Sep 20 2019

Main challenge will be the development and expansion of
convection from 09-12z into southern Iowa which should lift
northeast into the morning hours and generally exit the taf
coverage area by 17-18z...with the exception of the south where
more development is expected to increase during the period 18-00z.
The most likely area of possible continuous thunder will be near
kotm with two periods likely moving through the region for the
remainder of the sites. Low cigs will also be a problem with MVFR
and IFR conditions expected beginning aft 05z over the southwest
and lasting most of the period with improvement at best to
MVFR/VFR conditions from 19-00z. /Rev


issued at 403 PM CDT Fri Sep 20 2019

See more detailed discussion in the forecast discussion above,
but overall expect higher rain rates with the thunderstorm
potential Saturday night through Sunday across far southern Iowa.
Could see rates pushing 2 inches per hour at times with some
storms moving over areas repeatedly and a prolonged duration of
heavy rainfall. Therefore even with higher flash flood guidance
currently, expect a decent chance of flash flood potential across
the far south/southeast and therefore have issued a Flash Flood
Watch for that area.


Dmx watches/warnings/advisories...
Flash Flood Watch from Saturday evening through Sunday evening
for iaz074-075-083>086-092>097.



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