Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 280843
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
343 AM CDT Fri Apr 28 2017

.SHORT TERM.../Today through Tonight/
Issued at 343 AM CDT Fri Apr 28 2017

A large, cool area of high pressure dominates the upper Midwest
early this morning, even as low pressure develops over the southern
High Plains. Broad forcing for ascent associated with southwesterly
flow aloft is inducing the broad warm air/moisture advection zone
north of the low pressure area to produce widespread showers and
thunderstorms across parts of Missouri, Kansas, and far southern
Nebraska at this time. As flow aloft becomes even more southerly
this transition zone of precipitation will pivot around and move
northward across Iowa, however, it will also be eroded by dry air
entrainment from the high pressure ridge to the north. Nevertheless,
radar trends support a scenario whereby rain moves across at least
the southern half of our forecast area today, and possibly further
north, and have increased POPs in these areas accordingly.
Precipitation will diminish by late in the day and overnight as the
upper-level support departs, but then return again over the weekend
as detailed in the long term section below.

The other forecast challenge for today is temperatures, given the
anticipated clouds and rain and the effect the clouds had yesterday,
when Des Moines cleared out and reached 58 but Mason City stayed
socked in and only reached 38. Today the trend will be reversed,
with the thickest and most persistent cloud cover across our
southern counties where temperatures are currently warmer, and our
northern counties which are currently below freezing seeing at least
filtered sunshine and light winds, leading to better diurnal
heating. This has resulted in some adjustments to the temperature
forecast for today.

.LONG TERM.../Saturday through Thursday/
Issued at 343 AM CDT Fri Apr 28 2017

Concerns for the period centered around precipitation for the
weekend into Monday with the large storm system still on track to
impact the region. Main changes were to fine-tune pops and precip
types, with a rain/snow mix possible across portions of the northern
CWA late Sunday through Monday. Remainder of the extended beyond
Tuesday looks fairly quiet with temperatures gradually warming
through next week.

Precipitation still set to spread northward across the state
Saturday as the upper low digs through the southern Rockies and the
sfc low still situated across northern Texas. Inverted trough
feature stretches northeastward into MO and could precip could be
near southern Iowa by early Saturday. Sfc low will lift NE into NE
OK by late Saturday with overrunning/WAA/moisture advection across
Iowa. This should bring areas of showers across much of the state by
late Saturday into Saturday night. Cut-off upper low will move very
slowly lifting out of the southern Rockies and into the central
Plains toward mid-day Sunday with continue precip chances across the
CWA. Slightly westward shift in the track will keep warmer air
across the area for Sunday which should allow for mainly rain
through the day Sunday. However Sunday still expected to be kind of
a raw day with rain, windy conditions and temps across
northern/western IA only in the upper 30s to lower 40s. SFC low to
track northward slowly through IA Monday with the system becoming
stacked as the upper low moves across the state as well. This will
allow precip to continue into Monday with temps falling below zero
aloft. Expect little warming in the far north, with temps hovering
in the 30s to around 40 which may still be too warm. With the
temperature profile aloft cooling through the day expect a fairly
decent chance for a rain/snow mix if not all snow across the north
through the day Monday after some transition to rain/snow is
expected Sunday night. Right now not expecting much in the way of
accumulations given ground temps and the thermal progs mainly above
freezing. Still wouldn`t be surprised to see some light
accumulations especially on grassy surfaces, etc. before
precipitation moves out Monday night.

Overall a fairly soggy period setting up through Monday, with
widespread 1 to 2 inch rainfall amounts expected. Could potentially
see some sites across southern IA push toward 2.5 inches of rain
with the system through Monday, especially in areas across the
south/east where some thunderstorms could flare up Sunday afternoon.

Northwesterly to westerly upper level flow pattern in place for the
remainder of next week with a few weak impulses potentially moving
through the region. Hard to nail down and mostly went dry for now,
with the exception of Wednesday when a stronger shortwave trough
could drop southeastward through the state. This could bring some
light rain. Also expect moderating temperatures through the week as
mentioned previously.

&&

.AVIATION.../For the 06Z TAFS through 06Z Friday night/
Issued at 1152 PM CDT Thu Apr 27 2017

Stratus clouds that were producing MVFR ceilings over the
northern terminals sites earlier this evening have largely moved
out of the area. A thin band of showers is moving toward KOTM and
have VCSH, but drier air may win out. Otherwise, VFR conditions
will prevail tonight as high and mid-level clouds are streaming
into southern Iowa. Ceilings and visibilities will lower from
south to north through the day Friday as rain moves into the
state. The MVFR ceilings and showers may come near KMCW. As the
showers end Friday afternoon, IFR conditions may develop over the
southern sites.


&&

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

&&

$$

SHORT TERM...Lee
LONG TERM...Beerends
AVIATION...Ansorge



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