Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 122356
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
556 PM CST Sun Feb 12 2017

.SHORT TERM.../Tonight through Monday/
Issued at 328 PM CST Sun Feb 12 2017

High pressure has settled into southern Nebraska and north central
Kansas this afternoon. Temperatures remained mild this afternoon
across Iowa despite a cold front moving through the state overnight.
Good mixing today has kept northwest winds gusty with gusts near 35
mph. The mixing along with drier air behind the boundary has led to
good warming today under mostly sunny skies with temperatures in the
upper 30s in the snow cover at Mason City to the upper 40s and
approaching 50 at Des Moines and south. The area of high pressure
will move east tonight and be centered over Missouri by late
tonight. The main challenge tonight is fog potential. The breezy
wind and dry air have dried surfaces from last nights light rain and
areas that did have the most rain will have better pressure gradient
so westerly winds should not completely go calm despite rapid
decoupling this evening. Therefore, have left fog out of the
forecast at this time.

Temperatures are the main challenge on Monday. Increasing southwest
winds and warm advection should lead to another mild day with
readings a few degrees warmer that today. Cloud cover likely will
increase over southern Iowa in response to mid-level warm advection
and an approaching weak short wave. The clouds may become opaque
enough to have some impact on temperatures by the afternoon.

.LONG TERM.../Monday night through Sunday/
Issued at 328 PM CST Sun Feb 12 2017

Very little has changed since yesterday in overall expectations
for weather this week. The forecast remains dry with persistent
above normal temperatures. A cool front will traverse the area
around Monday night, followed by modest reinforcement around
Tuesday night, but even after this the forecast temperatures for
Wednesday are still a few degrees above normal as a weak high
pressure ridge slides by.

On Thursday low-level winds will begin to come around to roughly
southwest but remain fairly light. Meanwhile a large thermal ridge
will be building over the High Plains to our west and dry air
will work into Iowa. The combination of these factors will support
notable warming, even in the absence of better mixing, and have
boosted Thursday highs upward from guidance and the previous
forecast. The real warm-up will come after that however, as the
deep-layer ridge and associated dry air move across on Friday with
a bit more organized wind field. Have continued to raise highs on
Friday, which are now in the lower 60s across much of southern
and western Iowa and may still be underforecast. It will be a
glorious day that will feel more like late March than mid-
February.

On Friday night a northern stream shortwave will mover over the
Dakotas and Minnesota and push a weak cool front toward Iowa from
the northwest. There is some uncertainty as to whether this
boundary will make it across the state, as depicted by the GFS, or
whether it will stall out and retreat as indicated by the ECMWF
and GEM. Obviously this will affect temperatures next weekend, but
even if the boundary does get through the cold air behind it does
not appear remarkable and temperatures would likely remain well
above normal. There are some signs that the pattern may finally
change with a mid-level longwave trough/low pressure center and
associated precipitation chances just beyond the 7-day forecast
period, from Sunday night into the following week, but this will
be examined further in the coming days.

&&

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 556 PM CST Sun Feb 12 2017

VFR conditions and clear skies are in place across Iowa at 00z and
this should continue into the evening. There is fairly high
confidence VFR will persist through the entire period with nothing
more than patchy mid/high cloudiness into Monday. Winds will
diminish and gradually back to west, then SW and increase slightly
after 17z.

&&

.DMX WATCHES/WARNINGS/ADVISORIES...NONE.

&&

$$

SHORT TERM...Donavon
LONG TERM...Lee
AVIATION...Small



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