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Area forecast discussion 
National Weather Service Des Moines Iowa
627 am CDT Thursday may 28 2015

Short term /today/...
issued at 310 am CDT Thursday may 28 2015

A surface high pressure area dominating the region early this
morning will slide off to the east today...allowing for a return of
modest southeast to south flow across our forecast area. This should
promote fairly mild temperatures once again. However...at 500 mb the
ridge axis currently overhead will also shift eastward as a broad
shortwave trough approaches slowly from the southwest. This feature
is responsible for the clouds and thunderstorms currently affecting
eastern Kansas...and will spread showers and storms up into our area
later today tempering the potential for warming especially in our
southwest and west. The tricky forecast question is the timing of
rain beginning as it slowly spreads from southwest to northeast.
However...given the subsidence associated with the high pressure
currently over Iowa which will be slow to depart...as reflected in
the very limited instability forecast by high res models for
today...have continued the trend of slowing the leading edge of probability of precipitation
which will primarily be confined to our southwestern counties until
late in the day. At any rate...given the aforementioned relative
lack of instability along with weak deep layer shear...severe
weather probability will be quite low and no significant impacts are
expected.

Long term /tonight through Wednesday/...
issued at 310 am CDT Thursday may 28 2015

Primary concern will be precipitation window from tonight into early
Saturday. Broad weak forcing ahead of current Nevada/Idaho short waves has
produced scattered low end convection from NE into the Dakotas
overnight. Much of the forcing is in the 850 mb/700 mb layer with an
extended period of Theta-E advection...and this should enter Iowa
later today and continuing through Friday...especially southeast. The
baroclinic zone is not impressive so it may be driven more by
persistent moisture transport than anything. Surface based
potential will also come into play Friday afternoon and evening with
frontal passage. MLCAPES typically vary from 500-1500 j/kg and
appear to be uncapped. Wind profiles are not too impressive so deep
shear should be marginal. Thus agree with Storm Prediction Center low end outlook and
do not expect much severe weather. Although do not expect amounts
to be extreme...locally heavy rains may be more of a concern with
naefs specific humidities...precipitable water and integrated water vapor
transport in the 90th plus percentile. With warm cloud depths 11kft
and higher...a prolonged period of SW-NE mean wind may result in
some repetitive bursts Thursday night into Friday. The front should exit
the forecast area southeast Friday night...but higher based weak forcing may
linger behind the front ahead of the 700 mb/500 mb trough into Sat morning.

A cooler and especially drier airmass will then follow for the
weekend. The period of dry weather is expected to continue into
early next week with the passage of short wave ridging. Upper level
flow amplitude will then increase slightly heading into middle week
with another iteration of a western Continental U.S. Trough. Although any surface
feature affects will be beyond the valid period...weak middle level
forcing may bring some scattered weak convection around Wednesday.
Strengthening return flow well ahead of this system should finally
return temperatures to normal and just above by this time as well.

&&

Aviation...28/12z
issued at 627 am CDT Thursday may 28 2015

VFR conditions will prevail for most of today until showers and
storms move in from the southwest. Have taken best guess at timing
arrival of this activity at the terminals...but this timing will
need to be refined for the 18z issuance. Within showers and storms
MVFR or possibly lower conditions can be expected...but outside
convection generally VFR conditions should prevail even overnight.

&&

Dmx watches/warnings/advisories...none.

&&

$$

Short term...Lee
long term...small
aviation...Lee

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