Area forecast discussion
National Weather Service Des Moines Iowa
352 am CDT Sat may 18 2013
Short term.../today /...
issued at 352 am CDT Sat may 18 2013
Upper level ridging to build over the state today...with southerly
flow ahead of a developing area of surface low pressure across the
western High Plains of SD/NE/co. Dry conditions are expected across
the County Warning Area today...however push of moisture advection could allow for
some thunderstorm development just to the west of the County Warning Area by late
afternoon/early evening. For now looks like any activity will hold
off until after 00z across the area...so have kept the grids dry.
Temperatures are tricky today...with cloud shield initially over portions
of the County Warning Area from ongoing mesoscale convective system activity across central NE/SD/MN. Do
expect skies to clear some through the morning...with decent mixing
allowing temperatures to push into the 80s across the County Warning Area. Could also see
some breezy conditions as stronger winds aloft mix down through the
day.
Long term.../tonight through Friday/...
issued at 352 am CDT Sat may 18 2013
Shortwave will eject towards the state tonight with middle level qg
forcing increasing. Instability will already be in place with the
arrival of the forcing and anticipate convection developing/moving
into the west and spreading northeast with time. This convection
persist into Sunday morning across a broad swath of the forecast
area before the forcing passes to the northeast. Will likely see
some break in the activity late Sunday morning into the early
afternoon in subsidence behind this initial wave and have
decreased probability of precipitation early in the afternoon. However...next shortwave
will be quickly approaching by late afternoon/evening with very
good upper level divergence. Good middle level lapse rates move into
the state during this time as surface low moves into eastern
Nebraska. Still some question as to recovery behind departing
convection during the morning but the southwest should see the
best chance of this occurring by late afternoon. Storm Prediction Center has also
highlighted this area with best potential for severe convection
during the afternoon as bulk shear will be increasing with
approaching middle level speed maximum and low level helicity will also
be increasing as surface low moves into Nebraska. Some concern
with a warm layer in the low levels of forecast soundings that may
at least slow parcel acceleration in the 0-3km layer. Overall
still plenty uncertainty as to the eventual evolution...but severe
weather with at least large hail appears a good bet with the
possibility of a few tornadoes in the south late afternoon/evening
timeframe.
The threat of convection will persist into Sunday night...although
dry slot moving up into the state may begin to cut off more
significant precipitation with time. Upper low will then sit and
spin near Iowa through Wednesday with ongoing threats of precipitation
during this time. May see the potential for more severe weather in
the southeast on Monday with other convection across far northern
Iowa underneath the upper low. Chances of showers/isolated thunder
will linger into Tuesday/Wednesday as low slowly moves through the
state with quiet weather arriving late in the week.
&&
Aviation...18/06z
issued at 1240 PM CDT Friday may 17 2013
Low level moisture working its way northward will moisten up the
atmosphere overnight producing some MVFR conditions in patchy
fog...especially along a boundary that exists along and north of
Highway 20. Middle/hi level clouds from a huge thunderstorm complex to
the west will keep VFR ceilings over taf locations and could keep fog
limited to eastern locations where better radiational cooling will
occur due to less cloud cover. After 19/00z and especially after
19/06z thunderstorms will develop across the Missouri River valley
and drift east overnight.
&&
Dmx watches/warnings/advisories...none.
&&
$$
Short term...beerends
long term...cogil
aviation...fab
