Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 232341
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
641 PM CDT Sun Apr 23 2017

.SHORT TERM.../Tonight through Monday/
Issued at 304 PM CDT Sun Apr 23 2017

Ridge of high pressure stretched from Texas though southeast Iowa
and towards the lower Great Lakes, will settle slowly southeast
overnight. A short wave trough will cross the Rockies overnight
with surface cyclogenesis commencing across Colorado and Wyoming
as a response. This will increase the pressure gradient over Iowa
as the developing low pressure moves east into western South
Dakota and Nebraska late tonight.

Windy conditions will develop on Monday due to the increasing
pressure gradient and good mixed layer winds. Gusts greater than 30
mph are likely though the mixing efficiency of the mixed layer winds
will be dampened due to the warm advection. A ribbon of good theta-e
advection will also develop by Monday afternoon across western Iowa.
Very dry air will be in place across the state preceding the
moisture return and the initial surge will be above 12 kft. There
may be enough instability to generate a few showers or isolated
thunderstorms across northwest Iowa though any developing
precipitation aloft will be subject to evaporation during descent.
Have kept chances for precipitation quite low. High temperatures
Monday will be in the low to mid 70s central and south and 60s north
where more cloud cover will reside.

.LONG TERM.../Monday night through Sunday/
Issued at 304 PM CDT Sun Apr 23 2017

A few light showers over northern Iowa will be ending as a shortwave
trough pushes through and surface low pressure heads toward the
western Great Lakes Monday night. A cold front extending southwest
from this low will slowly move across central Iowa on Tuesday and be
near the Mississippi River Wednesday morning. This slow moving front
will be the focus for showers, especially given the strong
frontogenetical forcing that traverses the northwestern half of Iowa
Tuesday afternoon and evening. Therefore, have raised PoPs over this
area for this timeframe. May also have some thunder out ahead of the
cold front over southeastern Iowa. Tuesday will also see a wide
range of temperatures over central Iowa. Highs will struggle to
reach 50 degrees in northwestern CWA where clouds and rain will
limit heating while highs in the 70s are expected in the
southeast part of the CWA where the front will not have passed.

As the longwave trough crosses the Rockies Tuesday night into
Wednesday, surface low pressure will form over the central Plains
and move northeastward into eastern Iowa by midday Wednesday
promoting more showers. With current track of the low, any thunder
would be confined to areas over southeastern Iowa out ahead of the
low. As cold air begins to funnel into the state on brisk winds
from the north and northwest, may have a rain/snow mix over
northern Iowa given soundings that show below 0C from the surface
to 5500 feet by 12z Thursday. However, the atmospheric column will
be drying out so it is a question of whether or not the cold air
will match up with the moisture in time. Regardless, for now, have
continued the rain/snow mix over the north similar to previous
forecast.

As the longwave trough pushes east of the area, high pressure passes
through the region and will provide a day of drier weather as
well as a brighter sky. However, temperatures will remain about 10
degrees below normal.

By late this week into this weekend, a longwave trough will dig into
the Southwest US with an upper level closed low. This closed low
will eventually make its way into the High Plains by later Sunday.
Overall for a week out, large scale features are fairly similar,
though timing and placement varies with the various global models.
For sensible weather in Iowa, this will likely mean rounds of
showers and thunderstorms next Saturday and Sunday.

&&

.AVIATION.../For the 00Z TAFS through 00Z Monday evening/
Issued at 640 PM CDT Sun Apr 23 2017

There is a high confidence in VFR conditions through the period,
but the main impact will be gusty south winds Monday which may
reach or exceed 30kts at times north and west (KFOD/KMCW). There
is a brief, low confidence window for LLWS in these locations
early in the morning, but not worthy of a mention as of yet.
Similar thinking for low chances for high based convection north
and west very late in the period.

&&

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

&&

$$

SHORT TERM...Donavon
LONG TERM...Ansorge
AVIATION...Small



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