Area forecast discussion
National Weather Service Des Moines Iowa
637 am CDT Friday may 24 2013
Short term.../today /...
issued at 317 am CDT Friday may 24 2013
High pressure moves off to the east today with pressure gradient
beginning to tighten this afternoon. Decent Theta-E advection moved
into western Iowa by this afternoon...but other parameters are not
present. With some convergence aloft indicated through the day
today...combined by very limited low level moisture...do not
expect to see precipitation spread too far into the state today. Nothing
east of I-35...with chance probability of precipitation in the west. There will be a decent
gradient and would expect to see thunderstorms and rain advance east tonight. Should
see a good rise in temperatures today. Even with the cool start this
morning expect to see them close to a little above MOS guidance
with decent sun.
Long term.../tonight through Wednesday/...
issued at 317 am CDT Friday may 24 2013
The long term forecast remains very active and wet with slowly
warming temperatures overall. This weekend a 500 mb blocking
pattern will be characterized by low pressure over the
northwestern and northeastern U.S. And a broad ridge over the
central states including Iowa. The broad trough extending down the
West Coast from the northwestern low will eject multiple shortwave
ripples over the top of the ridge and Iowa...providing frequent
opportunities for convective development. At the surface a broad
low pressure area will develop over the High Plains to our west on
the forward flank of the broad 500 mb trough...resulting in
southeast to south low level winds and setting up one or more
nearly stationary boundaries stretching across Iowa and
neighboring states. This combination of factors supports multiple
rounds of shower and thunderstorm development beginning tonight
and justifies prolonged high ends probability of precipitation...generally 50 to 80
percent in any given period through the weekend. While the severe
weather probability is fairly low there is still some chance due
to the season and boundaries lurking nearby...and flooding
concerns may also increase with several days of rainfall expected.
On Monday the 500 mb low over the northeastern U.S. Will move off
into the North Atlantic...breaking the blocking pattern and
allowing the broad central U.S. Ridge to move eastward and the
western U.S. Trough to deepen substantially. As a result the ridge
axis will move east of Iowa and a more southwesterly flow will
become established overhead...leading to more pronounced warming
and less frequent thunderstorm events. Thus from Tuesday into
Thursday forecast probability of precipitation are lower...generally in the 20 to 40
percent range...and more concentrated to the northwest in closer
proximity to shortwaves riding up the southwesterly flow aloft. It
stands to reason that severe weather may be somewhat more likely
at times during this period...but attempting to predict the
details of such a threat at this range is not likely to be
fruitful. By Thursday or Friday it appears that the western U.S.
Trough will probably consolidate and move eastward...possibly
passing overhead toward the end of next week. Depending on how
things evolve that could finally bring an end to the wet and
active period...at least for a little while.
&&
Aviation...24/12z
issued at 634 am CDT Friday may 24 2013
High pressure extending from Lake Superior into northeast Texas will
move east with an increasing southeasterly gradient over the area.
Conditions will deteriorate from west to least later this
afternoon into tonight with ceilings lowering to 030-050 by morning
with numerous showers and scattered thunderstorms and rain overspreading the taf sites.
&&
Dmx watches/warnings/advisories...
none.
&&
$$
Short term...MS may 13
long term...Lee
aviation...MS may 13
