Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
323 am CDT sun Mar 16 2014
322 am CDT
The main forecast concerns center mainly around temperatures through
the period...with a typical Spring see saw pattern of warmer periods
followed by cooler periods through the upcoming week.
A decent area of snow has developed across Iowa and northern
Illinois overnight. This band of snow is associated with a strong
band of frontogenesis that exists within the favorable right entrance
region of an upper level jet streak across the Great Lakes. Radar
returns suggest that this band of snow is fairly intense across
portions of the I-80 corridor as of this writing. Visibilities under
this band of snow range from around 1 to 2 miles. However...some of
the more intense snow could be resulting in some isolated brief
periods of sub mile visibilities. Overall...not much has changed with
the thinking of this snow. This band of snow should gradually sag
southward over the next few hours...likely ending across my southern
counties around or shortly after daybreak. So...although the snow is
falling at a decent rate...it appears that overall snow
accumulations should remain around an inch or less.
In addition to the main band of snow...there is actually also some
light lake effect light snow showers/flurries developing across
southeastern Wisconsin. The cold airmass spilling across the lake is
producing some modest lake induced el's up around 4,000 feet
above ground level...per model BUFKIT soundings. Although this will not be a big
deal...there may be a few additional light snow flurries across
northeastern Illinois through middle morning before things begin to
clear out. I added a few isolated flurries to the forecast to account
for this activity.
Otherwise...the main story today will be the return to unseasonably
cold weather. Winds will remain northeasterly between 15 to 25 miles per hour
today as a storm system moves across the lower Mississippi Valley
and a cold Canadian high settles southeastward across Wisconsin.
This will continue to drive a much colder airmass in across the
region...and as such...this will result in cold raw day across the
region. I have remained a bit higher than most guidance on high
temperatures today. This is mainly due to the fact that local
climatology for 925 mb temperatures suggests that temperatures
could be a touch warmer than what guidance suggests. However...this
will not change the fact that it will still be a cold day.
The surface ridge axis is expected to shift over the area
tonight...setting up lighter winds...and likely a very cold night
across the area. Some higher clouds may try to move across the area
late tonight...but overall...it appears that skies should remain
mostly clear to partly cloudy...and this should allow temperatures
to drop into the teens in most areas. Some single digit temperatures
are even possible in the climatologically favored areas.
A warmer airmass will begin to advect northward again later in
the day Monday. So temperatures will begin a rebound during the
day. However...the better warmth will not set up until Tuesday. An
active storm track will lead to another storm system setting up
across the central and northern plains on Monday. This will force
much warmer air to lift northward across the Mississippi Valley
and into the Great Lakes region into Tuesday. There continues to
be differences in the track and timing of this system into middle
week. However...overall...prefer the slower solutions given the
amplitude of the system. This should result in a fairly warm day
for most of the region Tuesday...with temperatures looking to be
well into the 50s...especially away from the lake. However...it
appears areas across northeastern Illinois will be much
cooler...likely in the lower 40s...due to an easterly wind
component off the lake.
The storm system looks to move somewhere across southern Wisconsin
early Wednesday morning. This timing and track would favor the best
chances of rain for the area later Tuesday night through Wednesday
morning. It appears that the region will remain in the warm sector
Tuesday night...resulting in a very mild night...potentially even
warmer than the current forecast suggests. Therefore...the threat
for any snow should remain well north of the area. Cooler air will
move across the region following the cold frontal passage Wednesday
The active storm track appears that it could produce and drive yet
another storm system across the area sometime late in the week
around Friday. However...there are even larger discrepancies with
amongst the forecast guidance with the evolution and timing of this
system. So overall confidence is fairly low. This could result in
our next chance of precipitation...as well as chances for warmer
weather into Friday...before another shot of colder air drops back
across the region into next weekend.
//Ord and mdw concerns...updated 06z...
* MVFR ceilings linger through pre-dawn hours Sunday
* moderately strong/gusty northeast winds through Sunday
Band of snow that is mainly west of Chicago...will continue to
translate south overnight. Still could be some flurries or brief
light snow at the Chicago area terminals for the first few hours
of the taf cycle...but should be of little significance and have
no operational impact. MVFR ceilings...possibly lake induced...should
linger through the overnight and possibly into Sunday morning
before conditions trend VFR. Strong/gusty northeast winds expected
to last through the day with a few gusts possibly nearing 30kt
through Sunday morning. Gustiness and then winds will diminish
early Sunday evening.
//Ord and mdw confidence...updated 06z...
* low confidence in timing transition from MVFR ceilings to VFR
* high confidence in other forecast elements
//outlook for Ord/mdw for 12z Monday-12z Saturday...updated 00z...
Tuesday...VFR. Gusty south winds.
Wednesday...slight chance -shra.
Thursday through Saturday...generally VFR. Slight chance for light
snow Thursday night through Saturday morning.
251 am CDT
Fairly strong northeast winds to just below gale force this
morning over the south third of the lake should begin to ease this
afternoon and especially tonight as high pressure inches closer to
region and low pressure to our south scoots off to the east.
Southeasterly winds should develop and gradually freshen up Monday
night through Tuesday night in advance of the next low. Fairly
strong low and formidable shot of cold air behind it could allow
for a period of westerly gales Wednesday before winds slacken a
bit late in the week.
Lm...Small Craft Advisory...nearshore waters
until 9 PM Sunday.
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