Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
215 am CDT Sat Mar 15 2014
issued by National Weather Service Milwaukee/Sullivan WI
at 337pm CDT Friday Mar 14 2014
Forecast confidence medium.
Water vapor imagery shows a fairly compact middle-level short wave
moving across Northern Lake Michigan...with surface low pressure
over Lake Huron and a trailing surface cold front moving southeast
through southern WI into northwest Illinois. The surface cold front will sweep across
the rest of the area late this afternoon/evening.
A quiet night expected with some lower clouds in the cold advection
behind front. 850mb temperatures dip to around -2c to -4c by 12z
Saturday leading to lows in the middle 20s inland north...with upper
20s in the southern forecast area and from the city and south along
the lake. Gusty west winds will ease somewhat this evening as the
surface low over Lake Huron moves away to the east...but will remain
strong enough along with some lower cold advection clouds to prevent
temperatures from getting even colder.
Next short wave approaches from the northwest Saturday. 12z runs of the GFS
and Canadian Gem bring precipitation to the northern counties by 00z
Sunday...while 12z NAM and European model (ecmwf) keep the forecast area dry...in
spite of strengthening 850-700 mb frontogenesis. Lack of precipitation looks
to be tied to dry layer below 5k feet on cross sections and forecast
soundings that is reflected as well in high condensation pressure
deficits on isentropic surfaces. A blended solution brings slight
chance/low chance probability of precipitation in the late afternoon to northern County Warning Area...with the
better chance coming Saturday night. Top down method indicates it
will be all snow...though warm air advection ahead of the wave and
associated surface low brings a tight temperature gradient across
the County Warning Area with highs in the upper 30s north to around 50 south.
Long term...(saturday night through friday)
issued at 337 PM CDT Friday Mar 14 2014
Saturday night...forecast confidence medium.
High pressure sinking into the Great Lakes region will push
Arctic air into northern Illinois beginning Saturday afternoon through
Sunday. There is increasing confidence for snow to spread into
northern Illinois early Saturday evening as a narrow zone of
strong...sloped 925-700mb frontogenesis slips southward. This will
be a wet snow over a fairly short period of time and amount to
around one inch total. Northeast winds will increase and become
gusty overnight with the cold air advection.
Sunday through Monday...forecast confidence high.
Sunday will be a bitter day with brisk northwest winds...scattered
low stratocumulus clouds and high temperatures in the 20s. With
skies clearing and winds tapering off Sunday night under high
pressure...low temperatures will drop into the teens.
A middle level ridge over the northern plains will move into the Great
Lakes on Monday as a middle level trough deepens over the Pacific
northwest. Warmer air will gradually return to the Midwest on Monday
with highs rising into the 30s.
Tuesday and Wednesday...forecast confidence low.
The middle level trough will dig into the northern plains Tuesday to
bring our next chance for precipitation. The GFS and European model (ecmwf) are in
agreement that northern Illinois will be in the warm sector as the surface
low tracks across northern Iowa/southern Minnesota Tuesday and into central
Michigan Tuesday night...so any precipitation will likely be rain.
Timing is uncertain for when the cold front will move through the
lot forecast area. The European model (ecmwf) is about 12 hours slower with this
front than the GFS. Either way...it looks like rain will transition
to snow with this front...with precipitation ending shortly after the
frontal passage so not much accumulation is expected.
Thursday and Friday...forecast confidence medium.
High pressure will take control of the center of the country for the
latter half of the work week. Maximum temperatures will be in the lower
to middle 40s...a little below normal for middle March. Models are showing
another push of warm air approaching Illinois on Friday with a weak
//Ord and mdw concerns...updated 06z...
* winds becoming NE Saturday...but generally less than 10kt
* period of snow likely Saturday evening...IFR conditions possible
* strong NE winds develop Saturday evening into the overnight
Winds will gradually veer around from westerly overnight to
northeasterly by late morning or early afternoon on Saturday.
Northeast winds expected to remain fairly light through the day
with increasing and lowering high and middle level deck overspreading
the area. Band of snow is expected to move south through northern
Illinois/Northwest Indiana Saturday evening...with heavier snow farther
west toward rfd. Doesn't look to be a big snow...but a several
hour period of snow with at least occasional IFR seems reasonable
Saturday evening across the terminals with only minor accums (less
than an inch). Strengthening low pressure passing to our south
will result in increasingly strong/gusty northeast winds Sat night
with gusts at or above 25kt expected by late evening into the
overnight in the Chicago area.
//Ord and mdw confidence...updated 06z...
* low-medium confidence in snow chances/intensity...medium-high
confidence in snow timing
* high confidence in remaining forecast elements
//outlook for Ord/mdw for 12z Sunday-12z Friday...updated 00z...
Sunday...VFR. Gusty northeast winds.
Tuesday...chance of rain Tuesday afternoon & night with VFR becoming MVFR.
Wednesday...slight chance of ra/sn. MVFR possible.
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 veerings to southwest/west Wednesday with
some potential for lower end gales in the wake of the low Wednesday.
Visit US at http://weather.Gov/Chicago (all lowercase)
Follow US on facebook...twitter...and youtube at: