Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1002 am CST Sat Mar 8 2014
328 am...forecast concern in the short term is potential for a
mix of wintry precipitation changing to snow over the next few hours.
Longer term concerns are temperatures through the next 7 days and
the potential for another period of rain changing to snow Tuesday
night into Wednesday morning.
A cold front will move south of the County Warning Area over the next few hours as
colder air slowly spreads across the area. Air temperatures remain at or
just above freezing except near the WI state line. Precipitation now
developing from western Illinois into the western County Warning Area will continue into
the middle/late morning as it slowly drifts southeast. Eventually the
column will cool sufficiently for precipitation to change to all snow.
However...prior to that occurring...a mix of wintry precipitation could
occur with some light freezing rain possible depending on surface
temperatures. Confidence is rather low for specific precipitation types
and trends will need to be monitored over the next few hours. With
the bulk of the precipitation expected to transition to snow...some areas
may receive up to an 1 inch...primarily over the central County Warning Area with
lesser amounts north and south. But again...if precipitation falls as a
mix or even as some rain...then snowfall could be much less.
Temperatures still in the lower 30s across southern WI and while temperatures
will drop a few degrees with precipitation...especially snow...temperature
trends today are also uncertain. Highs could be set at 12z with
current temperatures at that time...but also possible for some minor
recovery in temperatures later this afternoon with some sun. Regardless...
temperatures will be much cooler today. High pressure builds across the
region tonight with temperatures likely to tank in the evening and could
then become steady or even rise a few degrees overnight. Could be
quite a spread from single digits in the usual cold spots to middle
maybe upper teens in the immediate metropolitan area/downtown.
Warm air advection really increases Sunday on the backside of the
departing high. With ample sunshine...temperatures could easily reach
back into the Lower/Middle 40s and current temperatures maybe a bit cool.
Temperatures aloft continue to warm Sunday night into Monday. Thus temperatures
may remain quite mild Sunday night...in the Lower/Middle 30s...maybe
warmer in the city. These warmer temperatures overnight will further
assist highs reaching well into the 50s Monday over the southern
half of the County Warning Area and into the metropolitan area with temperatures near 50
possible even over the northwest County Warning Area. Again made no changes to
this time period with lower 60s advertised across the southern County Warning Area.
Another frontal boundary will move across the area Tuesday as low
pressure then develops over the plains and moves east across the
Ohio Valley Tuesday night. Similar situation to this morning as
temperatures ahead of the front will be quite mild allowing for precipitation to
initially fall as rain then transition to snow. Bulk of the precipitation
looks to remain south of the area. Colder air behind this front
will be short lived as the pattern quickly transitions back to
southwesterly flow. Have bumped temperatures up into the 40s for Thursday
and into the 50s for Friday...though another frontal boundary and
potential cloud cover will be possible Friday. Cms
//Ord and mdw concerns...updated 16z...
* MVFR ceilings gradually improving through this afternoon.
* Northeast winds with sporadic gusts to around 20 knots persisting
into this afternoon.
* Possible fog overnight.
While the surface cold front passed over the area last
evening...the elevated cold front is presently doing such. As it
does so it will continue to bring light precipitation. This has
mainly transitioned to snow at all taf sites already by 1130z...and
even likely ended for good at Rockford. The forcing for snow is
mainly light...but combined with already some fog present...IFR
visbys are temporarily possible and have been observed in snow
through 14z. The precipitation will end from north to south
through middle morning...however MVFR clouds are favored to linger
into the afternoon as drying happens aloft more so than in the
boundary layer. The low clouds should dissipate by evening and that
may offer the possibility of fog as winds fall off with nearby
The northeast winds are favored to last into the afternoon with
even some 25 knots gusts early this morning for chicagoland sites
near the lake. Late this afternoon into early this evening...the high
pressure center should move far enough south that it allows for
more of a northwest wind component to evolve...along with speeds
dropping off. Sunday looks to see gusty southwest winds as the
area becomes under the influence of quick-moving low pressure near
the Continental U.S. Border.
//Ord and mdw confidence...updated 16z...
* medium-low in timing of imrpovment in MVFR ceilings this afternoon.
* High in wind direction and speed through early afternoon. Medium on
23z shift back to northwest
* low on whether fog develops overnight.
//Outlook for Ord/mdw for 00z Monday-12z Saturday...updated 12z...
Sunday night-Monday...VFR likely.
Tuesday...slight chance of rain during the day and chance of snow during
the night. IFR possible.
Wednesday...slight chance of snow.
144 am CST
Northerly winds across the lake this morning will continue into this
afternoon. Such a synoptic pattern and wind speeds would normally
provide wave heights sufficient for a Small Craft Advisory along the
Indiana and possibly even Illinois shore...but due to the extent of
ice coverage waves will be a moot point. A few gusts around 25 knots
are possible in nearshore areas early today. Otherwise winds
should diminish late in the day and especially this evening with
nearby ridging to the southwest.
A progressive pattern along the northern Continental U.S. Border during
Sunday into Monday will steer a couple low pressure systems across
Lake Superior. The first of these will tighten the pressure
gradient quickly by Sunday afternoon and offer south southwest
winds likely to gale force across the north for a 6-9 hour period.
For that reason have issued a gale watch for Sunday afternoon and
early evening. The next system on Monday will be deeper but because
so closely on the heels to its predecessor will not have as strong
of isallobaric component. So less winds speeds are anticipated for
Monday. An accompanying cold front will ooze its way down the lake
Monday night into early Tuesday and shift winds northerly. High
pressure is favored to move over the lake during midweek.
The large amount of ice extent will continue to suppress waves in
many areas...however some ice movement/break-up is likely on Sunday
and Sunday night with warmer air and turbulent flow.
lmz868...noon Sunday to 9 PM Sunday.
Visit US at http://weather.Gov/Chicago (all lowercase)
Follow US on facebook...twitter...and youtube at: