Area forecast discussion...updated
National Weather Service Chicago/Romeoville Illinois
847 PM CDT Wednesday Jun 19 2013
Discussion...
845 PM CDT
The only real change made to going forecast the rest of tonight
was to boost up cloud cover. High and even a few middle clouds
associated with a sheared out shortwave and very elevated /500mb+/
axis of moist return continue to stream east-northeast into the area. The
remnant short wave circulation is seen across southeast Iowa on visible and
infrared. The overall coverage of clouds looks like it has faded in the
past hour and rap forecast relative humidity continues this gradual diminishing
trend as the area comes across. Satellite along with visual
observation out the window would indicate however we would still
be dealing with a partly cloudy sky for a while. So have boosted
cloud cover up some. While the surface ridge axis remains across
Michigan into NE Illinois...these clouds may begin to stunt the temperature
drop some. Going mins still look alright though and in line with
18z guidance. If clouds linger through the entire overnight its
likely mins will be 3-5 degrees warmer. It is always a challenge
to predict 15000 feet and higher cloud behavior...but will not
complain that is the only real forecast challenge tonight.
Mtf
&&
Previous discussion...
322 PM CDT
Main forecast concerns/challenges are with precipitation trends over the
next several days with thunderstorm chances into the weekend...as
well as a warmer and more moist environment settling into the area
beginning as early as tomorrow.
Quiet and pleasant conditions in place across the area this
afternoon as high pressure spans much of the region. Partly
cloudy/sunny skies and temperatures generally in the 70s...except for 60s
near the lake...as well as lower dewpoint air in place have
provided these pleasant conditions. Although a sign to come of a
warmer airmass definitely moving up across the region are with the
low/middle 80s temperatures drawing close to the southern County Warning Area this
afternoon...as low level wind field already trying to flop over to
more of a southerly direction. A trend towards above normal temperatures
will occur over the next several days initially for areas away
from the lake tomorrow but with this trend extending towards areas
near the lake by Friday as southerly winds look to be in
place...and also remain in place.
Despite current high pressure beginning to slowly drift east of
the area tonight...quiet weather with mostly clear skies will be
observed once again with night time lows dipping down to the
middle/upper 50s for most areas and even staying in the lower 60s
across the southern County Warning Area. With this high continuing to slowly shift
east on Thursday...it does appear as if most of the day will
remain dry across the County Warning Area. Although...guidance is hinting at the
possibility for some convective activity in the afternoon
primarily over northern/northwest Illinois and cant completely
rule it out at this time. Current upstream middle level trough over
the Central Plains will work its way east towards the County Warning Area on
Thursday with forecast soundings indicating some moistening of the
column...as southerly flow aids in the return of this more moist
environment. As weak forcing moves over northern Illinois with the
approach of this wave while weak instability also settles back in
across the County Warning Area with minimal cin by the afternoon...could see at
least isolated showers/thunderstorms Thursday afternoon worthy of
slight chance probability of precipitation at this time.
Although the current NAM is indicating convection remaining
overhead through Thursday evening...do feel as if it is a bit
bullish. The majority of any convection on Thursday should be
diurnally driven with a diminishing trend then expected into the
evening...as the focus of more widespread development to remain
well to the north of the County Warning Area more towards the stronger westerlies
and low level jet focus. Still...persistent warm air advection along and just west of the
County Warning Area could help steer some lingering showers/thunderstorms across
northwest Illinois and have maintained the current slight chance
probability of precipitation for the far northwest tier of counties late Thursday night.
As a stronger wave/warm air advection move across the region on Friday...should
observe better chances for showers/thunderstorms especially into
the afternoon. Overall weak flow aloft is expected across the County Warning Area
on Friday with the stronger westerlies once again remaining just
to the north. Although...with instability/moisture really
increasing during the period...will need to monitor the potential
for strong thunderstorms to develop Friday afternoon. Confidence
begins to lower Friday night into the weekend with overall
convective trends. Although it does appear that there will remain
chances for showers/thunderstorms into the County Warning Area especially as a
moist and unstable environment settles in but with a more favored
location to be across the northern half of the County Warning Area...as the area
will be closer to stronger westerlies/passing middle level features.
Rodriguez
&&
Aviation...
//Ord and mdw concerns...updated 00z...
* none
Zebic
//discussion...updated 00z...
Large high pressure surface and aloft to dominate through Thursday.
Surface wind to keep easterly component
Land/Lake breeze wind pattern to last through Thursday as surface
high pressure shifts further east. Wind to drop off tonight and
become southerly then easterly component off lake to kick in during
the afternoon.
Limited available moisture to keep precipitation chances minimal
into Thursday night. Zebic
//Ord and mdw confidence...updated 00z...
* high confidence all elements
Zebic
//outlook for Ord/mdw for 12z Friday-12z Wednesday...updated 00z...
Friday through Tuesday...periodic chances for thunderstorms and rain...else VFR.
Zebic
&&
Marine...
210 PM CDT
A large area of high pressure centered over the eastern Great
Lakes extends from southern Quebec to the lower Ohio Valley and
from the upper Mississippi Valley to New England and the middle
Atlantic region. The high pressure will gradually slide to the
east as a trough of low pressure develops over the Central Plains.
While the high pressure will dominates Lake Michigan through
Friday...relatively light winds will prevail over the open waters
and lake breeze or onshore flow will prevail for the Illinois/in
nearshore waters through Friday. A surface low will drop out of the
northern rockies and track eastward to Lake Superior by Friday
evening. Another low will develop over eastern Kansas on Thursday as
the high slides off the middle Atlantic coast. Through this
period...southerly flow will reestablish over Lake Michigan and be
the prevailing condition over the lake through early next week.
Krein
&&
Lot watches/warnings/advisories...
Illinois...none.
In...none.
Lm...none.
&&
$$
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