Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 210832
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
332 AM CDT Sun May 21 2017

.SHORT TERM.../Today through Tonight/
Issued at 332 AM CDT Sun May 21 2017

Upper low has rotated up through IA and is now moving into WI, with
the associated surface low located near the IA/MN border in south
central MN. Low level cloud shield to spread across the state this
morning, with some light showers or drizzle possible for the next
few hours. Any precip with this system will then likely be relegated
to the far northern portion of the state through the morning hours,
before lifting north and east as the upper level system pulls away
from the state. As the system lifts into northern MN/WI, skies are
expected to clear from south to north.

Another lobe of energy rotating around the main upper level system
will approach the state late tonight into Monday. WAA is expected
ahead of this wave late tonight resulting in increasing cloud cover
late tonight. As for temperatures, cool conditions are expected
today especially in the northeast where low clouds to remain all day
and coldest air aloft expected. Could see some of the southwest rise
into the low/mid 60s as clouds clear and some sun expected by late
afternoon/early evening.

.LONG TERM.../Monday through Saturday/
Issued at 332 AM CDT Sun May 21 2017

A large gyre draped across the northwestern Great Lakes region on
Monday will elongate and separate into two cyclones by Monday
night, with one ejecting eastward across Quebec and the other
digging slowly southwest and closing off over or near Iowa on
Tuesday and Tuesday night. Initially on Monday low-level flow
across our forecast area will be southwesterly with quiet weather
prevailing. However, the aforementioned elongation will begin with
a robust shortwave rounding the southwestern periphery of the
Great Lakes gyre, swinging over northwest Iowa with an attendant
surface trough around Monday evening. The vertical forcing
associated with this feature will support convective development
across much of Iowa late Monday into Monday night and chance POPs
are maintained with some uncertainty as to coverage of resulting
precipitation. Moisture return ahead of this system will be quite
limited, however, the forcing and flow fields are strong enough
that if meager instability is realized it would support
thunderstorms and some risk of severe weather around Monday
evening or so. This threat is well-outlined by current SPC
products.

Once the initial surface trough and its associated/preceding
convection move across our area and exit to the southeast late
Monday night, the developing closed low over the Upper Midwest
will sink down across Iowa on Tuesday and Tuesday night bringing
cool, cloudy, and damp weather to the area with light rain likely
at times. Any amounts will be light, and instability for
thunderstorms appears to be lacking so have gone with straight
showers wording. The low pressure system will move away on
Wednesday and be replaced by modest deep-layer ridging through
Thursday, leading to a dry period and slowly warming temperatures
late in the week.

By Thursday another large gyre will be parked over southern
Saskatchewan, where it will remain into next weekend. A series of
shortwave impulses will eject out of the southern half of this
gyre, pushing the preceding ridge over the Midwest rapidly
eastward and bringing several period chances for showers and
thunderstorms to end the week. There is decent convergence in
solutions regarding the initial impulse moving across Iowa
roughly around Friday morning with good precipitation chances,
but after that the details become increasingly uncertain.

&&

.AVIATION.../For the 06Z TAFS through 06Z Sunday night/
Issued at 1152 PM CDT Sat May 20 2017

Area of VFR cigs moved into the region earlier in the evening
though IFR/MFR cigs area wrapping back into central Iowa from the
west. The lowest cigs will be across the north. Cigs will
gradually improve on Sunday. Winds will become more westerly
overnight and become breezy to gusty on Sunday before diminishing
again toward sunset.

&&

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

&&

$$

SHORT TERM...Beerends
LONG TERM...Lee
AVIATION...Donavon


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