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Area forecast discussion 
National Weather Service quadrant cities Iowa Illinois
733 am CDT sun Apr 19 2015

issued at 730 am CDT sun Apr 19 2015

Scattered showers continue to develop and move generally in a northward
direction...and were mainly west of a Macomb Illinois to Manchester Iowa line.
These showers were occurring in the axis of the better 850 mb moisture
transport and precipitable waters over an inch.

Elsewhere...low pressure was organizing in the lower MS valley and
a broad area of pressure falls was noted to the north indicating large
scale ascent/warm air advection was increasing. Also pressure falls
were occurring in the upper MS valley in association with the digging
northern stream trough. Regional Doppler radars were showing the leading
edge of a rather large area of rain/isolated thunderstorms from the
MO Ozarks and southern Illinois...moving northward.

The hrrr mesoscale model has captured this rain area with the leading
edge reaching Macomb by noon...the quadrant cities by early afternoon
and Dubuque/Freeport by late afternoon. Therefore...widespread
rain appears likely this afternoon and continuing tonight...which
the current grids depict.


issued at 345 am CDT sun Apr 19 2015

Models continue to struggle with the easterly feed of dry air into
our northeast County Warning Area and at some locations dewpoints were 10 degrees
lower than any guidance. In our western County Warning Area guidance was close to
reality as winds were more southeast. Storm Prediction Center mesoscale analysis showed
decent 850 mb moisture transport along with precipitable waters
over an inch in our western County Warning Area. And sure enough Doppler radar has
shown pockets of showers and isolated thunderstorms all night.
Rainfall estimates indicate 1/4 to 3/4 of an inch has fallen in
some spots in our west since last evening.

3 am temperatures ranged from 50 at Freeport to 61 at Macomb.
Elsewhere...Canadian high pressure was centered northeast of Lake
Superior and some sites in northwest WI were reporting dewpoints in the teens.

Upper level trough was digging into the northern plains while
another trough was pushing into the central/Southern Plains.


Short term...(today and tonight)
issued at 345 am CDT sun Apr 19 2015

Forecast focus on increasing rain and temperatures.

Today...upper level trough approaches from the west and this will provide
large scale ascent along with better moisture transport as the day progresses.
The more widespread rain appears to develop this afternoon with the
arrival of stronger a short wave pushes across Iowa ahead
of the main trough. Meanwhile...phasing begins to occur and models lift
a deepening cyclone out of the lower MS valley into far western Indiana
by 00z. Interesting that the NAM/European model (ecmwf) keep northwest Illinois dry much of the day
and they may be on to something with such a dry easterly feed into that
area. I will mention isolated thunderstorms this afternoon as deep layer
shear is weak and MUCAPE is 500 j/kg or less. With more cloudiness today
maximum temperatures should be cooler than than the past couple of days.
I am expecting highs in the upper 60s to lower 70s at most locations.

Tonight...phasing is nearly complete and a long wave trough pushes
across the Midwest with decent forcing and good moisture in place.
In the meantime...the slowly deepening cyclone lifts into northern
lower Michigan by 12z. Models indicate widespread rain over the County Warning Area much
of the night. This looks to be more of a stratiform/deformation type
rain rather than all out convective/mesoscale convective system type so will not mention thunder
as instability is very limited...and the entire column is very saturated.
A cold front will push across the County Warning Area during the night ushering much
cooler temperatures into the area by morning. Minimum temperatures
will range from the lower 40s at Independence to the upper 40s at
Princeton and Macomb in Illinois.

Rainfall amounts today through tonight should be 0.3 to 0.7 inches over
much of the County Warning Area.

Long term...(monday through saturday)
issued at 345 am CDT sun Apr 19 2015

Cooler and mainly dry for much of upcoming week with frost/freeze
potential later in the week.

Much of the upcoming week ahead will feature a large and slow
moving upper low from the Great Lakes to eastern Canada due to
highly amplified ridging over the eastern Atlantic and Greenland.
Our County Warning Area will be governed by northwest flow on backside of the
large upper low which will usher in reinforcing bouts of Canadian
air resulting in cooler highs in the 50s and 60s... with lows
mainly in the 30s. The cooler air will also be accompanied by
windy conditions Monday and Tuesday with the potential to be
near Wind Advisory criteria given juxtaposition of tight pressure
gradient... cold advection and deep mixing. After some lingering
showers possible early Monday am... will have the potential
for afternoon popcorn showers across mainly the northern County Warning Area both
Monday and Tuesday with steep middle level lapse rates... cold
air aloft... and skinny cape noted on forecast soundings. Will
need to watch for enhanced wind gusts with any showers via
evaporative cooling of precipitation in large... dry sub-cloud layer with
classic inverted v soundings.

Canadian surface ridge axis building in Thursday into Friday will
bring potential for frost and possibly freezing temperatures one or both
mornings. Min temperatures may need lowering by 3-5 degrees some locations
especially Thursday am based on 850 mb temperatures -4c to -7c with more
widespread 20s possible with any duration of clear skies and light

Rain chances look to return by either late in the week and/or next


Aviation...(for the 12z tafs through 12z Monday morning)
issued at 730 am CDT sun Apr 19 2015

VFR conds becoming MVFR/local IFR conds. Scattered showers in eastern
Iowa this morning will expand in coverage and the rain will be widespread
this afternoon and tonight. Isolated thunderstorms are also possible...mainly
this afternoon. A cold front will also arrive tonight. East to southeast
winds less than 10 knots today then becoming northwest 15 to 25 knots
behind the cold front tonight.


Dvn watches/warnings/advisories...


short term...haase
long term...McClure

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