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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
126 PM CDT Monday Jul 6 2015

issued at 108 PM CDT Monday Jul 6 2015

Updated forecast to lower high temperatures another notch with widespread
cloud cover. Also refined probability of precipitation/quantitative precipitation forecast grids to reflect a faster
progression of the cold front through the forecast area...per
recent hrrr/rap runs. The slight risk area has been trimmed to
roughly the southeast half of the forecast area...areas that have
been mostly dry to this point. Not excited above the overall
severe threat with the weak shear and meager middle level lapse
rates. Will likely be monitoring a few storms for strong wind
gusts. Of more concern is the deep moisture and potential for
additional heavy rain. Some locations along and north of I-80
picked up 1 to 2 inches through early afternoon and will need to
be watched closely. The highest quantitative precipitation forecast through tonight may be focused
south of these areas. If that ends up being the case...then the
main threat would be high rainfall rates and repeated rounds in
urban areas.

Update issued at 701 am CDT Monday Jul 6 2015

Complex of thunderstorms with heavy rain has become stalled and
was back-building just west of the forecast area...mainly west of
a line from Waterloo to Ottumwa. These were occurring in an area
of elevated moisture advection along the edge of steep middle level
lapse rates. Further east...isolated...more elevated storms were
mainly northwest of a line from Iowa City to Dubuque. Have updated to
increase probability of precipitation to cover scattered storms in this area.

All indications suggest the central Iowa complex to dissipate
within a couple hours and not advance much further eastward away
from the better upstream thetae advection and higher instability.
With heavy rainfall rates of 1 to 2 inches estimated by radar and
continued upstream cloud top cooling on infrared satellite...will
continue to monitor closely...but at this time it appears the
greatest heavy rainfall threat will be just west of the forecast
area this morning.


issued at 349 am CDT Monday Jul 6 2015

At 3 am...a large thunderstorm complex was situated from far western
WI west-SW across southern WI...northwest Iowa and eastern Nebraska. This was
occurring in an area of deep moisture convergence and wave of low
pressure along a cold front that reached from Western Lake Superior
SW across Minnesota...Nebraska into far western Kansas. Area radars showed
thunderstorms well out ahead of this boundary over central Iowa from
about Mason City south to Des Moines in an area of steep middle level
lapse rates and apparent elevated moisture advection. Over the local
area...backing light S-southeast winds were leading to slowly climbing
dewpoints in upper 60s to near 70s west of the MS river with mainly
lower 60s to the east.


Short term...(today and tonight)
issued at 349 am CDT Monday Jul 6 2015

Thunderstorm trends and the potential for severe weather and
heavy rainfall are the primary focus. Early this morning...the
central Iowa convection will be moving into a less favorable
environment as all models depict middle level lapse rates becoming
less unstable after sunrise...especially over eastern Iowa. the current rate...these thunderstorms will likely
reach into the far western counties around sunrise before
weakening. Beyond...forecast confidence wanes as models appear to
be overdone with precipitable water values compared to 00z soundings over the
plains and the anomalously high forecast precipitable water values well over 2
inches prognosticated over the forecast area today are questionable...
along with dewpoints shown reaching into the upper 70s by the WRF.
Recent high res convective models and operational models from 00z
are all being challenged by this system...both with respect to
convective coverage this morning and short term trends...thus forecast
confidence in details is below average.

The overall trends suggest a weakening of the leading convection
with the large mesoscale convective system trending mainly northwest of the forecast area through
the day as middle level lapse rates become less favorable and extensive
cloud cover seen on satellite covering most of the central and
northern plains from this complex will likely limit insolation as
it overspread the forecast area. Outside the now slower WRF...the
front is generally shown moving into far east central Iowa around
00z. This will have cape of at least 1500 to 2000 to work with as
low level moisture convergence pushes dewpoints into the lower to
possibly middle 70s and temperatures reach at least the upper 70s to
lower 80s ahead of the front due to warm advection. Models
disagree in the amount of deep shear...but generally suggest 30
kts plus in a zero to 3 km layer over at least the north for the
boundary to work with. This could support some bowing complexes
and possible damaging winds where the front moves through during
the most unstable late afternoon and early evening period. Storm Prediction Center has
the entire forecast area under a slight risk. Of a greater
potential will be heavy rainfall rates as precipitable water values are likely to
reach at least a 1.5 to 2 inch range. Considering that it has been
nearly a week since the last widespread rain event...flash flood
guidance values are high and rivers are have returned to well
below flood stage. The most likely Hydro threat will be Urban and
Small Stream type flooding if storms become slow movers or back
build...which will need to be monitored.

Thunderstorms and the threat of at least localized severe storms and
heavy rainfall will continue into the early evening hours...shifting
to east of the MS river after 7 PM. Current timing suggests storms
will end over most of eastern Iowa by midnight...with the back edge
of showers exiting the Illinois counties by 3 am. However...our
forecast will remain a more generous with hourly probability of precipitation overnight
that account for possible further slowing of the frontal system.
Forecast quantitative precipitation forecast amounts were placed in a widespread half to 1 inch
range for this system...but with the high amounts of
moisture...localized 2 to 3 inch amounts will be possible.

Long term...(tuesday through sunday)
issued at 349 am CDT Monday Jul 6 2015

Tuesday and Wednesday...a few Post-frontal showers possible in the
far south and eastern County Warning Area Tuesday morning...but would think more
progressive solution pans out with everything out of the County Warning Area by 15z
Tuesday. Then clouds clear in the afternoon especially along and north
of i80 as surface ridge pushes eastward across the upper MS River Valley.
Clouds and Post-frontal low level cool conveyor to make for well below
normal temperatures this period. First half of Tuesday night mainly clear with
temperatures cooling into the 50s...before high clouds start to sprawl in
from the Southern Plains ahead of the next incoming wave. Latest 00z
run model solutions advertise a type of large split flow pattern
taking over much of the Continental U.S. By middle week...with a vigorous wave
rolling out along the southern edge of the split and along the
northwest flank of southeastern Atlantic broad upper ridge complex.

Some model discrepancy still on how robust this wave will be as
well as how far north or south the trajectory path will occur as
this feature ripples out of the Southern Plains and toward the
southern Great Lakes by Thursday morning. Depending on it/S path...this
system may be of some impact on the local forecast area if it can ingest
an increasing Gulf moisture feed and induce a type of heavy rain def
zone across portions of the County Warning Area. The 00z run GFS just clips the
southeastern third of the County Warning Area with such a feature...while the 00z NAM
takes more of a direct hit across much of the local area. The 00z Euro
targets the southeast half of the County Warning Area with a pan handle Hooker type
low and 1 to 2+ inches of rain by 12z Thursday from this system. Deepening
on how much rain occurs today/tonight to prime soils...another heavy
rain system on Wednesday/Wednesday evening could lead to some Hydro issues. cover and induced east-northeast low level flow to the Lee
of this incoming system may make for some areas having trouble
getting out of the 60s for Wednesday highs. Any strong to severe weather concerns
would be on the southern flank of the compressed low pressure system
on Wednesday.

Thursday and Friday...latest 00z run medium range model trends/mref
solution paint this period as potentially more active and under a
type of mesoscale convective system window as upper ridging establishes across much of the
southeastern Continental U.S. And into the Southern Plains. Warm moist conveyor
rotating around this feature up into a low level boundary getting stalled
out somewhere across the Central Plains and into the southern Great Lakes
to occasionally focus rounds of convective development on from late
Thursday through Friday night. This could make for another temporary wet
regime and compounded heavy rain events into the start of the
weekend for renewed river flooding as well as urban/small stream
flooding issues if the boundary happens to lay out along or just
south of the dvn County Warning Area. Large temperature discrepancies possible this period
as well from north to south. Will have to blanket these days with
probability of precipitation and general temperature trends.

Next Saturday and Sunday...some longer range signs of enough upper
ridge amplification to shunt the main storm track to the northern
plains across to the Great Lakes this period and the dvn County Warning Area into the warm
side of building thermal ridge. But many times when the models
advertise this flux...the transition can be stormy as well and could
easily see the frontal retreat to the north of the area get hindered
by convection itself and outflow. Thus late Sat and Sat night we
could see another round of storms either in or very close to the County Warning Area
and will have to maintain probability of precipitation. Longer range trends suggest ridge
riding wave energy will look to try and dig down across the Great Lakes
and re-carve out troffiness and northwest flow down the upper Midwest
again by early next week. ..12..


Aviation...(for the 18z tafs through 18z Tuesday afternoon)
issued at 108 PM CDT Monday Jul 6 2015

18z tafs updated to reflect recent trends and high resolution
models. Expecting more widespread storms developing in the 20z to
22z time frame...then continuing into the evening hours and last
to end at kbrl. Mainly MVFR ceilings and visibilities then
expected overnight in the wake of the cold front. Have kept the
tafs pessimistic in terms of scouring out the low clouds.


Dvn watches/warnings/advisories...


Update...rp Kinney
short term...sheets
long term...12
aviation...rp Kinney

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