Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1250 PM CDT Sat Mar 15 2014
348 am CDT
The main forecast concerns this morning continue to center around
temperatures through the weekend and snow chances and amounts
Temperatures across the area remain relatively mild across the area
early this morning. However...a second cold front will drop across
the region around daybreak. So in spite of the decent temperatures
at this hour...temperatures will likely not recover much across far
northern Illinois today...especially for areas near the lake...where
flow will become northeasterly off the lake resulting in cool
The main concern will be very late this afternoon and tonight...as
it still appears to be a good bet for a period of light to moderate
snow across the area. Yesterday evenings radiosonde observation analysis indicates the
presence of decent baroclinic zone along the far southwestern
periphery of the Hudson Bay vortex. For example...temperatures at
850 mb ranged from +9 at kunr...to -3 at kbis and kabr...to -15 at
kinl. Middle level deformation is expected to continue to increase in
the middle levels across the northern plains...from South Dakota
eastward across Iowa and northern Illinois through the day today as
a storm system takes shape across the central and Southern Plains.
This will ultimately set up a band of decent band of frontogenesis
across the region late this afternoon and into tonight. It also
appears that this will be setting up within the favorable right
entrance region of an upper level jet developing across the Great
Lakes. As such...I expect good chances for snow across the
area...and have went with likely probability of precipitation in most areas. It appears
things could get going as early as late this afternoon across far
northern Illinois...then gradually shifting southward across areas
primarily north of Interstate 80 this evening...and finally shifting
mainly south of Interstate 80 later tonight. Overall...although the
snow may fall at a decent clip at times...total snow accumulations
should remain light. It appears that an inch or less will be favored
in most locations...with a few amounts possibly just in excess of an
inch possible across my western areas.
All the snow should shift south of my area by Sunday morning...as
the aforementioned storm system begins to shift eastward across the
lower Mississippi Valley. Therefore...during the day Sunday the main
story will be the cold temperatures across the area. Sunday really
looks to be a cold raw day...with afternoon highs likely remaining
in the middle to upper 20s across the region. However...stiff
northeasterly winds of 15 to 25 miles per hour will making it feel more like
its in the low teens.
After a cold morning on Monday with surface high pressure
overhead...temperatures will rebound nicely by Tuesday. An active
storm track will lead to another storm system setting up across the
central and northern plains early next week. This will force
much warmer air to lift northward across the Mississippi Valley and
into the Great Lakes region. It appears temperatures on Tuesday
could top out well into the 50s...if not even near 60 across most of
the area. The main exceptions...would be areas near the lake across
far northeastern Illinois where the threat for onshore
east-southeasterly flow could result in colder air coming in off the
It appears that the storm system may be a slower system. As
such...it appears the best chances for rain will hold off until
Tuesday night into Wednesday. A brief cool down is expected in the
wake of this storm system for Thursday. However...it appears that
warm weather back into the 50s will return for most areas by late
week as the upper flow across the country becomes more zonal.
//Ord and mdw concerns...updated 18z...
* northeast winds generally less than 10 knots this afternoon becoming
gusty to around 25 knots at times overnight/Sunday.
* Low potential for brief MVFR ceiling around 2500 feet this afternoon.
* Period of light snow likely this evening...IFR conditions
Weak surface high pressure ridge axis has drifted off to the east
of the terminals this mid-day...allowing winds to shift to the
northeast. Winds will remain northeast through the remainder of
the taf period...with speeds generally less than 10 knots this
afternoon gradually increasing to near 15 knots tonight and Sunday
with gusts near 25 knots at times especially after midnight tonight
through early Sunday afternoon.
VFR middle/high level clouds were increasing across the region...in
response to an upper level disturbance over the plains. This
disturbance will move to the east-southeast through early Sunday
and is expected to produce a relatively narrow band of light snow
from Iowa east into northern Illinois/northwest ind by this evening...
associated with strengthening of the middle-level thermal/frontal
zone across the region. Models generally indicate Chicago area
will be on the eastern fringe of this snow band...and weaken it as
it drifts southeast across the region tonight. Thus the greatest
potential for light snow appears to be during the evening/midnight
hours...with the focus then shifting south of the terminals beyond
VFR middle/high clouds will continue to lower/thicken through early
evening. There appears to be a slight potential for a brief MVFR
2500 feet ceiling with some stratocu developing per visible satellite
with the current northeast wind shift...to satellite trends
indicate these ceilings not an immediate threat and appear to be
dissipating over lake Colorado Illinois and northwest in at 1745z. Light snow
tonight will likely produce IFR visible for a time...though confidence
low in extent/coverage/duration into the Chicago area. Snow and
IFR/MVFR threat looks to diminish quickly after 06z.
//Ord and mdw confidence...updated 18z...
* high confidence in wind trends.
* Medium-high confidence in prevailing VFR conditions through
* Low-medium confidence in snow chances/intensity...medium-high
confidence in snow timing
//outlook for Ord/mdw for 00z Monday-12z Saturday...updated 12z...
Sunday night through Monday night...VFR.
Tuesday...VFR. Gusty south winds.
Wednesday...slight chance -shra.
Thursday and Friday...generally VFR.
214 am CDT
Period of fairly strong northeast winds expected tonight into Sunday
morning over southern portions of the lake with ice coverage having
decreased enough to probably allow large waves into the Illinois/in
nearshore waters. Plan on hoisting a small craft advection for tonight
into Sunday evening to cover the strong winds and lingering high
waves. Winds quickly veer to east/southeasterly Monday into early
Tuesday as the high moves east of the region and new/strong low
pressure develops over the northern plains. Strong southerly winds
are expected Tuesday night veering to southwest/west Wednesday with
some potential for lower end gales in the wake of the low Wednesday.
Lm...Small Craft Advisory...lmz740-lmz741-lmz742-lmz743-lmz744-
lmz745...7 PM Saturday to 9 PM Sunday.
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