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Area forecast discussion 
National Weather Service Des Moines Iowa
1159 PM CDT Tuesday Jun 2 2015

Short term /tonight/...
issued at 323 PM CDT Tuesday Jun 2 2015

Stubborn stratus/stratocu deck over south central/southeast Iowa
should continue to erode through the evening hours.

Southwest to northeast oriented upper level ridge will flatten
during the course of the evening and overnight as multiple transient
shortwaves eject northeastward from a northwest Pacific coast low.
Low-level southerly flow will veer to the southwest
overnight...transporting a 925-700mb thermal ridge/moisture plume
currently over Nebraska into Iowa by Wednesday morning. Evolution of
convection during the overnight hours is a bit uncertain. Most high-
res cams take an mesoscale convective system out of the western Dakotas and western Nebraska
this evening...though various solutions take the track anywhere from
northern South Dakota to northern Nebraska.

Additional solutions like the 18z hrrr develop new convection in
western Iowa around 09z. This solution is certainly plausible given
the MUCAPE values of around 1500-1800 j/kg rooted at the top of the
850mb warm nose/moisture plume along with a 30-40 knots low level jet.
Have maintained a broad pop grid gradient given these uncertainties
that increases from west to east after 06z. Severe threat appears
low given the lack of vertical wind shear. Heavy rain and isolated
hail appear to be the main threats. Forecast precipitable water values of around
1.5 inches rank in the 99th percentile based on oax sounding

Long term /Wednesday through Tuesday/...
issued at 323 PM CDT Tuesday Jun 2 2015

Complicated forecast the next few days. Trends increasing for
several periods of thunderstorms with considerations needed for both
mesoscale scale and synoptic scale evolution of systems. This will limit
confidence of details...but should still allow for main features to
be forecast with some confidence. Subjective h850 analysis shows
ridge exiting to the east while the moisture channel begins to
edge east with time. By 12z Wednesday models in general agreement
with decaying mesoscale convective system over eastern Nebraska/western Iowa moving east
during the morning hours. With the high continuing over the
eastern Great Lakes...likely that the eastern/southeast counties
will have a more limited thunder chance through early Wednesday afternoon.
Despite some cloud cover from overnight thunderstorms...breaks in
clouds with increasing instability should return by middle afternoon
Wednesday. The combination of a weak h700 wave and unstable
conditions will promote showers and thunderstorms over the area
during the afternoon with the focus shifting from central/northern
sections to the south by late afternoon closer to another surface
warm front. From Wednesday through Wednesday night...severe
chances remain low with the better chances for any severe late Wednesday
afternoon into the evening hours and perhaps again Thursday
afternoon. However...will need to monitor locally heavy rainfall
potential through this period.

Confidence beyond 36 hours begins to evolution of
mesoscale convective systems may alter the synoptic evolution of the
main trough and associated boundaries over the Central Plains. By
Wednesday night...h850 low level jet should refire convection over
northern Missouri or southern Iowa. Mesoscale nmm model shows southward
drift of the boundary as well as the Euro keeping most of the
convection south of the region. The GFS and NAM have a more
northerly trend for now. Through Friday the Euro continues the trend
for most of the heavier rainfall to remain just south of the Iowa
Missouri border...while the GFS/NAM and to a lesser extent the Gem
continue to focus the axis of best lift/thunder over central to
southern Iowa. This will determine the area of most rainfall and
potential for any Hydro issues. High moisture return flow at h850 is
heading toward the forecast area...GFS precipitable water values
increasing to 1.5 to 1.75 inches from 12z Wednesday to 12z Friday. GFS
warm cloud depths also are on the a range of 11kft to near
13kft south Thursday night. Though the GFS may not be the preferred
solution for its more northerly placement of storm features...will
need to monitor efficient rainfall processes in any storms that
develop over the next 72 hours. Currently the GFS with its more
northerly placement over Iowa is showing 4.25 to 4.75 inches of quantitative precipitation forecast
over the i80 corridor through Friday morning while the Euro has only
0.5 to 1.25 inches with the heavier values south of us34. The Euro
has its axis of heavy rain is from northern Kansas through northern
MO. Despite the lack of is likely that heavy
downpours and perhaps locally heavy rainfall will accompany some
of the storms. For now Hydro situation can take a round of heavy
rainfall as guidance remains at 2 to 3 inches for a 3 hour period
across the south. If rainfall rates approach 2 inches per hour at
any time...may have some concerns with local urban runoff effects
or with any subsequent episodes of heavy rainfall that might occur
may need to consider headlines. Given todays uncertainty of
evolution of mesoscale/synoptic feature interactions will not issue any
headlines for now. Temperatures through the period will remain
mild...75 to 85 range...with dew points and humidity rather high
the next few days in the middle to upper 60s. Some breaks in the
rainy pattern will occur mainly for later on Sunday into Monday.


issued at 1159 PM CDT Tuesday Jun 2 2015

Low VFR ceilings developing across western Iowa to spread across
entire County Warning Area overnight. Thunderstorm development expected toward
sunrise...still greater certainty of this activity impacting the
northern and western taf sites. Otherwise mainly VFR conditions
with southeasterly to southerly winds expected.


Dmx watches/warnings/advisories...none.



Short term...skow
long term...rev

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