Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 180916

National Weather Service Des Moines IA
416 AM CDT Sun Sep 18 2016

.SHORT TERM.../Today/
Issued at 415 AM CDT Sun Sep 18 2016

Mid level clouds had been expanding across Northern Iowa overnight
in an area of theta-e advection and some weak forcing.  Some
isolated showers did develop with this.  These showers will shift
East and dissipate this morning as the forcing wanes.  Otherwise for
today we should see plenty of sunshine again and warmer
temperatures. Highs today will be in the 80s with some upper 70s far
North.  A South to Southwest wind will increase this morning to the
10 to 15 mph range and 15 to 25 mph this afternoon as high pressure
at the surface exits to the East.  A trough entering the state from
the Northwest will tighten the pressure gradient across the
Northwestern third to half of the state resulting in the stronger
winds in that area.

.LONG TERM.../Tonight through Saturday/
Issued at 415 AM CDT Sun Sep 18 2016

Strong push of theta-e advection through the region this evening
and this will bring a ribbon of increasing instability across the
state. There will be a moisture discontinuity as this instability
moves across as the initial airmass will be quite dry to begin.
The low level moisture will be streaming north from the Gulf
however the mid level moisture will be of Pacific origin and will
be arriving behind the primary forcing. Sounding profiles over
portions of northeast Iowa including the Mason City and Waterloo
areas would suggest that enough saturation will occur around 850
mb that convective initiation may occur. Therefore have added
mention for thunder over that part of the forecast area.

Overall Monday and Tuesday look mostly quiet with surface high
pressure moving into southern Minnesota and upper level zonal flow
focused north of the state as an upper level high becomes
established to the south. That said strong instability will remain
over southeast Iowa Monday afternoon and evening however an elevated
mixed layer should limit thunderstorm chances. A few solutions do
initiate convective activity over northern Illinois into eastern
Iowa where the capping is the weakest.

An upper level closed low moving southeast into the Pacific
Northwest late Tuesday then driving south towards the Four Corner
region the remainder of the week will bring increasing southwest
flow to the Midwest. This will bring increasing thunderstorm
potential during this period. Elevated thunderstorms are possible
mainly over northern Iowa Tuesday night into Wednesday morning. A
few of these storms may be strong and also have the potential for
heavy rainfall. Reference SWODY3 for additional details regarding
the severe weather potential. Additional storms will be possible
the remainder of the week as a boundary settles southeast as the
upper flow becomes more southwestern then remain in the vicinity
through the rest of the extended. Severe storms and heavy rainfall
will remain a concern with any of this activity. High temperatures
through this period will remain warm for mid September.


.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1126 PM CDT Sat Sep 17 2016

Weak Theta-E advection across northern Iowa will produce some
mid-level clouds overnight along with a few isolated
sprinkles/showers. Otherwise, surface winds will be light
overnight but increase from the south southwest on Sunday with
gusts, especially across the western half of the state. Any
ceilings will remain VFR.




LONG TERM...Donavon
AVIATION...Cogil is the U.S. government's official web portal to all federal, state and local government web resources and services.