Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 192058

Area Forecast Discussion
National Weather Service Des Moines IA
358 PM CDT Fri May 19 2017

.SHORT TERM.../Tonight through Saturday/
Issued at 357 PM CDT Fri May 19 2017

In the near term, patchy drizzle looks to persist through the
afternoon into the early evening and mention until 00z Saturday
when the deeper moisture begins to return to southern Iowa.

More rain to develop tonight and spread across the forecast area
through tomorrow.  Models remain in disagreement the surface low
track where the GFS/SREF are slightly further south than the NAM and
ECMWF and the NAM being the furthest north track. The HIRES models
such as the HRRR, ESRL HRRR, ARW, and NMM have precip moving into
southwest Iowa by around 00z-02z Saturday. Then much of the forecast
area will likely have rain by 06z at the latest. There is better QG
forcing, stronger Theta-E advection and moisture convergence located
over central to southeast portions of the forecast area and have the
highest QPF going in this location. Plus, precipitable water values
range around 1.00" in the aforementioned area and surprisingly warm
layer cloud depths as high as 12kft in the southeast, but lack
significant deep moisture for a long period tonight. Some chance for
brief heavy rain producers and thus reasoning why the southeast has
the higher QPF.  By late Saturday morning, dry air begins to entrain
into southern Iowa as the low tracks across southern Iowa. Very low
threat for severe weather with much of the forecast area remaining
in the cold sector. The only exception would be in the far southeast
if the low tracks slightly further northwest like the ECMWF
suggests.  Then a brief window for some weak instability to build
into this location. However, confident cloud cover will remain
fairly thick throughout the day tomorrow and thus limiting any
significant CAPE.

.LONG TERM.../Saturday night through Friday/
Issued at 351 PM CDT Fri May 19 2017

The weather will be relatively uneventful through the period with
two windows of precipitation and neither significant. At onset
our current system will be exiting with the dry slot well through
the state and forcing on the way out to the north. Some low end
wrap around PoPs will linger north but this will be driven more by
deep moisture than much forcing. Fair weather can then be
expected Sunday into Sunday Night with moderating temperatures in
weak warm advection ahead of the next system dropping southward
through Canada into the northern Plains.

Weak warm advection and DPVA will slowly increase into Monday and
strengthen as it reaches Iowa. This will eventually lead to a
fairly well defined H85/H7 rise/fall couplet as it exits the area
Monday Night with a decent back edge of frontogenetical forcing.
Mid level kinematic forcing looks to linger a bit longer however
as a deformation zone evolves and matures. This will keep cool
temperatures and low end PoPs going into Tuesday Night, especially
southeast, with 1-3km moisture in neutral lift sufficient for
light rain.

Models continue to show differences with how the pattern evolves
to end the period, but neither the ECMWF or GFS solution results
in much of the way of precip chances for Iowa. The GFS is
essentially dry and while the ECMWF shows a strong upper low
moving from ND to WI and some precip chances northeast its
ensembles are weaker and slower with its suggestions thus the end
of the extended forecast will remain dry for now. Temperatures
should be quite typical for late May to end the next work week after
warm advection returns by Thursday.


.AVIATION.../For the 12Z TAFS through 12Z Saturday morning/
Issued at 357 PM CDT Fri May 19 2017

IFR/LIFR ceilings likely to persist through much of the
forecast period. Some periods of MVFR to IFR visibility can be
expected with the rain tonight into Saturday. Some relief is likely
towards midday Saturday across southern Iowa with drier air pushing
into southern Iowa but MVFR ceilings to continue through the


Issued at 357 PM CDT Fri May 19 2017

A very saturated ground along with many streams and rivers
beginning to swell from recent rainfall this week, the river flood
threat continues to increase. With a widespread 1 to 2 inches of
new rainfall anticipated by tomorrow and even an isolated up to 3
inches possible in the southeast, some rivers may rise to Action
Stage or even Minor Flood Stage towards the end of the weekend
into early next week. Thus, additional River Flood Watches might
be needed on area rivers such as portions of the South Skunk, Des
Moine and Raccoon River basins as well as the smaller basins in
southern Iowa.





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