Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
901 am CDT Wednesday Jul 23 2014
248 am CDT
Today through tonight...
early this morning infrared imagery depicts a channel of cooler clouds
stretching from Ford County northeast through Northwest Indiana.
Radar continues to show a ragged line of convection under these
clouds...which should continue to sag southeast as the frontal
boundary pushes south across the forecast area this morning.
Instability along and south of the boundary remains...with most of
the convection being rooted in the middle-levels as lapse rates continue
to remain rather steep. Fortunately though the intensity of the
storms should continue to remain sub-severe and perhaps another Special Weather Statement
will be needed before activity pushes south of the forecast area.
Otherwise high pressure will build into the region today...with
winds shifting northerly to slightly northeasterly. This will
provide an inverse airmass from the past 48 hours...to a much drier
and sub-seasonal temperatures. The pressure gradient will remain tight on
the Lee-side of the surface ridge...resulting in a stronger marine
influence on temperatures along the immediate shoreline today. Thus it is
likely that afternoon highs may struggle to touch 70...meanwhile inland
areas will be generally in the low/middle 70s.
Tonight high pressure will be overhead with just a light northerly
flow and perhaps winds will become calm for the northern County warning forecast area. Temperatures
should easily radiate into the lower 50s. A few locations could dip
into the upper 40s just before sunrise Thursday...mainly across the Fox
anti-cyclonic flow will continue to dominate the region through
Thursday...with minimal cloud cover and temperatures generally in the middle 70s.
The exception will be locations adjacent to Lake Michigan where a
lake breeze/onshore flow will keep temperatures around 70.
Middle-level trough axis begins to pivot east Thursday night...with the surface
ridge drifting east and allowing winds to slowly turn southerly
ahead of the next wave set to arrive Friday.
Friday through Tuesday...
middle-level ridge centered over the Southern Plains will begin to
flatten along the northern fringes...allowing for an ease of systems
to traverse the northern tier states east across the Great Lakes
region. Guidance has continued to point towards a weak surface wave
sliding east from the Central Plains Friday...arriving over the
forecast area with some enhancement to the precipitation output due to warm
air advection and ascent to parcels. Thus have nudged probability of precipitation up
slightly during the day Friday...with the focus likely midday through
A middle-level vorticity prognosticated to be over the Canadian prairies Friday...will
slowly move east Friday night before sliding southeast across the Great
Lakes region later in the weekend. Ensembles continue to point
towards another pattern adjustment over the second half of the
weekend into early next week...as the North Atlantic ridge returns
and prevents the aforementioned upper Midwest shortwave from
departing. In addition a high amplitude ridge continues to be
prognosticated across the western Continental U.S....keeping the middle-level trough over
Hudson Bay/Great Lakes through Mon/Tue.
The overall theme continues to be a brief return to seasonal temperatures
for the weekend in the low 80s...however once the trough returns to
the Great Lakes region so will the unseasonably cooler air. Temperatures by
early next week will mainly be in the middle/upper 70s.
//Ord and mdw concerns...updated 14z...
* gusty north-northeast/NE winds through this evening.
A cold front has pushed across the region with thunderstorms now
primarily in central Indiana and downstate Illinois with high
pressure building in from the northwest today. A moderate pressure
gradient remains in place with efficient mixing today resulting
in gusty winds out of the NNE/NE. Winds likely will remain fairly
steady through the day then begin to taper this evening and
tonight. VFR conditions will prevail through the period.
//Ord and mdw confidence...updated 14z...
* high in wind direction...medium in wind gusts speeds.
* High confidence in all other forecast elements.
//outlook for Ord/mdw for 00z Friday-12z Wednesday...updated 12z...
Friday through Sunday...periodic chances for thunderstorms.
Monday through Tuesday...slight chances for showers.
316 am CDT
Winds and waves have already increased across Lake Michigan...now
blowing out of the north at around 30 knots especially over the south
half of the lake where a few gale force gusts are possible behind
a departing cold front. A Small Craft Advisory is in effect today
for the Indiana and Illinois nearshore waters due to the elevated
winds and waves. High pressure currently over the Canadian
prairies will begin to build across Lake Michigan tonight allowing
winds to subside overnight into Thursday.
Illinois...beach hazards statement...ilz006-ilz014 until 10 am Thursday.
In...beach hazards statement...inz001-inz002 until 10 am Thursday.
Lm...Small Craft Advisory...nearshore waters
until 10 am Thursday.
Visit US at http://weather.Gov/Chicago (all lowercase)
Follow US on facebook...twitter...and youtube at: