Area Forecast Discussion
Issued by NWS Des Moines, IA

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FXUS63 KDMX 311142
AFDDMX

Area Forecast Discussion
National Weather Service Des Moines IA
642 AM CDT TUE MAY 31 2016

.SHORT TERM.../Today/
Issued at 337 AM CDT Tue May 31 2016

Current convection is entering western Iowa but outflow has moved
out well ahead of the updrafts.  This is causing a gradual decline
in intensity and coverage the past couple of hours and this should
continue through sunrise. The HRRR has had a decent handle the past
few hours on the evolution of the convection and have followed its
scenario through the morning as far as POPs are concerned.  This
would keep the main threat of precipitation in northern Iowa through
late morning.  However, a few storm may impinge on the far southeast
as well with a few showers/storms moving northward from Missouri.

The surface front will approach the I35 corridor by 18Z with
destabilization occurring ahead of the front quickly this morning.
Thunderstorms are expected to develop in vicinity of this boundary
near midday.  This convection will move gradually eastward through
the afternoon as the boundary progresses through the state with
subsidence increasing in the west by late in the period.  There will
likely be a few severe storms with marginally severe hail and strong
wind gusts, however shear is relatively weak with modest instability
and this should limit the overall extent of severe weather today.
Temperatures will warm nicely ahead of the boundary this morning
with readings near 80 in the eastern CWA.  Cooler readings will
occur in the west with more extensive clouds through the day along
with cooler air arriving behind the boundary by this afternoon.

.LONG TERM.../Tonight through Monday/
Issued at 337 AM CDT Tue May 31 2016

We will finally close the curtain on the warm and stormy
southwesterly-flow pattern we have been under the past week or so.

To start the long term fcst period, a boundary will be pushing from
WNW to ESE across Iowa. PWATs ahead of the boundary reach 1.5
inches. In short, the parameters are not there to carry svr wx into
the overnight hours...But there is enough moisture, instability,
and lift to warrant precip in the quarter to half an inch range by
the time the boundary exits the DMX CWA. For exit time, leaned
with a non-NAM solution, as the NAM was a slow outlier. Subsidence
and dry air behind the boundary will clear out pops fairly rapidly
Wednesday morning. Models are pushing the main SFC low with this
boundary across Minnesota on Wednesday afternoon, and are catching
some wrap- around moisture clipping our northern counties. Thus,
have increased cloud cover in the north and lowered temps a few
degrees relative to the rest of the CWA.

High pressure moves across Iowa on Thursday, which should keep the
state dry. Lower min temps a few degrees as center of high over Iowa
Thursday morning to add subsidence.

Friday into next weekend...
Confidence is becoming high in featuring a shortwave propagating
off the northern Rockies towards the upper Midwest. Ensemble
spread is starting to tighten, which is encouraging, given this
feature is 4or so days out. The 00z Tue GFS solution is a slight
southerly outlier with handling this system. Will be interesting
to see what the 12z runs look like. Models try to push an impulse
through NW/north-central Iowa ahead of the low. There is low, but
a sufficient amount of isentropic lift with an overrunning PV
anomaly along the theta-e axis to warrant mention of POPs.

The core this system does not reach central MN until Saturday
morning. At that time, it appears the DMX CWA will be in the warm,
moist sector. Again, the GFS is a southern outlier with this system,
but would suggest increased precip if its solution pans out. For it
being 5 days out, models are in good agreement with cutting off this
system over the great lakes. Subsequently, Iowa would be in
northerly/northwesterly flow until at least mid-week next week...A
pattern that should yield at least a few precipitation-free days.
There is not a lot of cold air being advected into Iowa as 850mb
temps stay in the +12C to +16C range...suggesting near-normal
temperatures in the extended.

&&

.AVIATION.../For the 12Z TAFS through 12Z Wednesday morning/
Issued at 639 AM CDT Tue May 31 2016

Conditions will generally be VFR for much of the forecast, however
there will be periods of MVFR conditions near thunderstorms today
into the evening. Also, some MVFR visibilities toward the end of
the period of light fog will also be possible. Otherwise, ceilings
will be at or above 5kft for the most part except in and around
thunderstorms. Surface winds will be southerly this morning but
become westerly behind a surface cold front. By tonight...winds
will generally become light and variable with conditions favorable
for some fog development toward the end of the period.

&&

.DMX Watches/Warnings/Advisories...None.

&&

$$

SHORT TERM...Cogil
LONG TERM...Kotenberg
AVIATION...Cogil


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