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fxus63 kdmx 171046 

Area forecast discussion
National Weather Service Des Moines Iowa
546 am CDT Thu Oct 17 2019

Discussion.../today through Wednesday/
issued at 256 am CDT Thu Oct 17 2019

There has been little change in overall forecast thinking
overnight, however confidence in details regarding the forecast
period from late Sunday into Tuesday has decreased.

A large 500 mb ridge will approach Iowa from the west today, move
overhead tonight, and then push off to the east on Friday. At the
surface this will be reflected by light southeast winds gradually
increasing today and tonight, then on Friday turning to south and
becoming breezy and gusty. Combined with warm air advection and
mostly clear skies this will induce a pronounced warming trend,
with temperatures reaching the lower 70s in some areas by Friday
afternoon. The warm and breezy conditions may support a marginal
fire weather risk on Friday and we are monitoring this possible
hazard. Otherwise today and Friday look to be gorgeous fall days
for most outdoor interests.

During the day on Friday a mid-level trough will approach our
region from the west, moving over central Iowa on Friday night
into early Saturday. The surface front associated with this
feature will move through on Saturday morning, and while it will
carry little punch in terms of strong winds or cold air advection,
it will provide a focus mechanism for some convective development
supported by broad and increasing lift associated with the mid-
level system. This will lead to the development of showers and a
few thunderstorms on Friday night, mainly across about the
southeastern half or two thirds of Iowa, lingering into Saturday
morning before pushing off to the east. Severe weather and heavy
rain are not expected, and any impacts should be minimal. From
Saturday into early Sunday a brief period of weak ridging will
provide dry and quiet weather for the middle of the weekend, with
temperatures a bit cooler than Saturday but still fairly pleasant
as forecast highs for Saturday remain roughly around the mid 60s.

By Sunday a larger, more robust deep-layer trough will emerge from
The Rockies over the Great Plains, undergoing cyclogenesis with a
surface low pressure center quickly spinning up and moving
near/along the Nebraska/South Dakota border during the day. A cold
front will trail the low to the southwest, with a rather
pronounced pre-frontal trough approaching the Nebraska/Iowa border
sometime around Sunday afternoon or evening. Unfortunately, model
solutions regarding the track and timing of this system have
diverged somewhat tonight, with the GFS speeding things up a bit
and the European model (ecmwf) alternating between much slower solutions and then
backing off again. Meanwhile the Gem is the slowest of them all
and also the furthest south with the low track, which seems a less
feasible solution. These differences have significant effects on
the timing of precipitation in our forecast area, thunderstorm
chances, timing of a clear slot, extent/duration of wrap-around
precipitation on the back side of the low, etc., Etc. With
confidence in these details decreasing at this time, there is
little to hang ones hat on regarding the forecast from around
Sunday afternoon into Tuesday. However, a few things can be said
with relative confidence:

1. A swath of scattered showers, and probably a few thunderstorms,
will likely move across Iowa in association with the
aforementioned pre- frontal trough sometime around Sunday

2. Severe weather remains possible, but unlikely given the slower
evolution of the system and associated effects on instability.

3. The trailing cold front will likely move through our area late
Sunday night or Monday morning, ushering in notably cooler and
breezy conditions from Monday into Tuesday.

Model trends will likely converge again in the next 24-48 hours,
giving US a clearer picture of some of the finer details of
sensible weather during this active period early next week.


Aviation.../for the 12z tafs through 12z Friday morning/
issued at 546 am CDT Thu Oct 17 2019

Patchy br may produce brief MVFR vsbys in the next hour or two,
otherwise no aviation concerns today with light winds and clear
skies. Late tonight, in the last six hours of the new taf period,
low level wind shear will increase as winds strengthen aloft. Otherwise, no
reduced flight conditions or restrictions anticipated.


Dmx watches/warnings/advisories...none.


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