Scientific Forecaster Discussion
Area forecast discussion
National Weather Service quadrant cities Iowa Illinois
955 am CDT Wednesday Jun 3 2015
issued at 953 am CDT Wednesday Jun 3 2015
Mesoscale convective system continues to roll across northeast Kansas and northwest MO on the nose of
the low level jet and where the deep moisture axis and MLCAPE is
being tapped. Farther northeast towards the dvn County Warning Area the northern
end of the mesoscale convective system continues to diminish and warming tops are seen on
infrared satellite movie loops. Hi-res mesoscale models continue to struggle
with this mesoscale convective system taking the remnants across the County Warning Area during the
afternoon. However...with this diminishing trend due to the system
outrunning the moisture axis and better forcing I have my doubts
we will see any rain this afternoon. Will monitor trends this
morning and update grids as needed. Amount of debris clouds will
also make for a challenging temperature forecast.
Update issued at 633 am CDT Wednesday Jun 3 2015
A narrow line of elevated convection was showing up on early
visible satellite images from far southeast WI through Kalo to kotm with
one discrete cell on kdvn 88d about to move into SW Benton
County. This line was well ahead of the convection triggered by a
fast moving outflow boundary moving through central Iowa.
Have updated the forecast to include isolated showers in the far
west early this morning...anticipating this leading area of
convection to dissipate with the diurnal processes. Will continue
to monitor the central Iowa convection trends closely. If it does
not break up as expected as it enters drier air to the east...current
timing would place it into the western forecast area border around
8 to 9 am.
issued at 343 am CDT Wednesday Jun 3 2015
The local area remains under the influence of high pressure over the
Great Lakes. This...combined with a broad upper level ridge reaching
from Texas to the western Great Lakes was providing continue quiet
weather with light winds...low humidity and seasonably cool
temperatures early this morning. Satellite imagery showed high
clouds from earlier plains convection streaming over the
area...while further upstream...a large mesoscale convective system was rapidly advancing east-
southeast across Nebraska. Radar mosaic also an area of scattered...slow moving
thunderstorms over northwest MO.
Short term...(today and tonight)
issued at 343 am CDT Wednesday Jun 3 2015
The main challenge is the onset of rain and thunderstorm chances
today and tonight. 00z models...and most recent high-res
convective models...were having a difficult time with the
large...bowing mesoscale convective system over eastern Nebraska early this morning. The 00z
European model (ecmwf) appeared to be better initialized on the location of this
complex...and depiction over the past 6 hours...and is thus the
The European model (ecmwf) continues this complex east-southeast into western Iowa and northwest MO this
morning...but it should gradually weaken as it moves away from the
elevated instability and thermal axis along the edge of a building
heat dome over the SW u... also away from the better surface
through 850 mb moisture axis over the Central Plains. An associated
middle level vorticity maximum will likely move through the upper ridge axis
overhead from midday through early afternoon. As it moves away from
the better moisture feed and steeper middle level lapse rates...into
a more stable environment remnant from the departing ridge...it
is not likely to trigger additional convection. Models reflect
this...generally keeping quantitative precipitation forecast and probability of precipitation confined to only as close as
central Iowa through the day.
Thus have kept only low chance probability of precipitation for showers and thunderstorms
over the far west and SW for late this morning through afternoon.
High cloud cover from the upstream complex should keep skies
partly to mostly cloudy providing only filtered sunshine today...
limiting high temperatures to the middle 70s to near 80. Light southeast
winds out of the departing surface high will keep dewpoints in the
50s through most of the day...with lower 60s possibly advecting
into the far west late as winds begin to veer more southerly.
Tonight...parameters for mesoscale convective system generation initially point toward the
MO River Valley and models generally focus rain and thunderstorms
over western Iowa in the evening. A weakening...veering 850 mb jet may
then support advancement of non-severe storms into the local area...
especially after midnight. Thus have low chance probability of precipitation in the
evening...then slightly higher chance probability of precipitation after midnight for mainly
the western half of the forecast area. Cloud cover and slowly
increasing surface moisture levels will limit lows to a range
from around the upper 50s northeast to the lower 60s SW.
Long term...(thursday through tuesday)
issued at 343 am CDT Wednesday Jun 3 2015
Thursday morning...an area of convection will form or become
reinvigorated over southeast Nebraska/north-central Kansas/western Iowa
Wednesday evening/night in a zone of enhanced moisture flux-
convergence on the nose of a strengthening nocturnal low-level jet.
Then...the majority of model solutions bring scattered showers and
storms into the western portion of the County Warning Area Thursday morning...although
the low level jet will be weakening with time as should the convection or
potential storm complex.
850-300mb mean winds and forward propagating corfidi wind
barbs are light but both have a general west-to-east orientation
helping guide some of the storms into the dvn County Warning Area. MUCAPE values are
forecast to exceed 1000-1500 j/kg through the morning to the south
of I-80...could have a few strong or marginally severe storms in
that area. Current forecast has 40-50 probability of precipitation along and west of the
Thursday afternoon...highs should reach to around 80 f. Winds will
be light as pressure gradient refocuses across the plains. Isolated
to scattered daytime thunderstorms are possible. GFS/European model (ecmwf) are
projecting decent conditional instability of 1000-2000 j/kg MUCAPE
by the afternoon. Widespread thunderstorm activity does not appear likely.
Thursday night...models are displaying many different scenarios in a
weakly forced synoptic regime. The favored zone for storms is again
west of the Mississippi River and a little more likely along and
south of I-80. 850mb nocturnal low-level jet is forecast to veer to
a more SW-NE orientation and extend further east compared to Wednesday
night. As such...have likely probability of precipitation for areas along/south of I-80 and
west of the river.
Precipitable water values around 1.50 inches are supportive of localized heavy
rainfall in any storms that form in the dvn County Warning Area.
Friday...daytime instability...a discernible middle-level low/vort.
Maximum...and possible lingering outflow boundaries warrant 50-60 probability of precipitation.
Surface winds will gradually develop out of the NE as high pressure
builds into the Great Lakes. Consequently...highs are forecast to
range from the lower 70s over the far north to the lower 80s in the
Saturday and Sunday...temperatures look seasonal in the 70s. Both the GFS
and European model (ecmwf) are forecasting a shortwave trough to dive southeastward
into the upper Midwest/Great Lakes Sat night into sun dragging a
cold front through the area. The European model (ecmwf) is much more robust than the
GFS and has a much better chance for showers/storms in association
with the front. All-in-all Saturday looks mainly dry then have 30-40
probability of precipitation Sat night/sun.
Monday and Tuesday...the European model (ecmwf) is mostly dry with large-scale
subsidence on the western side of the shortwave trough.
However...the GFS brings a shortwave and shower/storm chances into
the upper Midwest. Only have slight chances for showers/storms at
this time. Forecast currently favors the warmer/drier solution of
the European model (ecmwf) that has 850mb temperatures near +16c and 1000-500mb thicknesses
around 572 dam and highs in the lower 80s. The GFS is much lower
with its thickness values as it brings a cold front through east Iowa/west
Illinois Monday night.
Aviation...(for the 06z tafs through 06z Wednesday night)
issued at 633 am CDT Wednesday Jun 3 2015
An area of showers and thunderstorms moving through western and
central Iowa is expected to fall apart before reaching the eastern
Iowa terminals this morning. While not included in the latest
forecasts...there is a potential for at least vicinity showers or
thunderstorms at Cid through middle morning which will be monitored
closely for updates. Otherwise...light southeast winds will veer
to the south today with continued VFR conditions as high pressure
retreats to the east. The next round of showers and thunderstorms
is expected to develop well to the west this evening...than move
into eastern Iowa late tonight. For now...with low confidence in the
timing and this convection...thunderstorms have been included in