Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
248 PM CST Wednesday Feb 10 2016
Tonight and Thursday...
248 PM...only concern is light lake effect snow showers in far
northeast Porter County.
A ridge axis extends from Minnesota southeast to central Illinois this
afternoon and will slowly turn easterly as it builds across the
Ohio Valley Thursday. Current wave with light snow over parts of
Iowa into southwest Illinois will remain southwest of the County Warning Area. West/
northwest winds will maintain the chance of lake effect snow
showers over far northeast Porter County tonight with minor new
accumulations possible. These will begin to diminish Thursday as
winds turn more westerly. Low temperatures tonight will dip into the low
single digits with the usual cold spots possibly dipping below
zero. These temperatures will combine with northwest winds to allow wind
chill values 10 below zero. Cms
Thursday night through Wednesday...
248 PM...forecast concerns include light snow Friday morning...
wind chills possibly reaching advisory criteria Saturday morning
and another period of light snow Sunday afternoon/Sunday night.
Another surge of very cold air will arrive Friday afternoon into
Friday night and ahead of this surge...there will be a period of
light snow Friday morning. There is some differences regarding how
far north this light snow will occur...with the GFS furthest north
and across the entire area. Best chances for light snow along with
any minor accumulations appear to remain across the southern County Warning Area
and maintained low chance probability of precipitation for now. But as trends emerge...
higher probability of precipitation may be needed despite the low quantitative precipitation forecast expected. Temperatures also
appear to hold fairly steady Thursday night into Friday or perhaps
an evening low then steady or slowly rising into Friday morning.
As the colder air arrives Friday afternoon...temperatures will begin to
fall with lows likely below zero across much of northwest Illinois by
Saturday morning and only low single digits elsewhere. Northwest
winds will also become strong/gusty Friday afternoon/evening with
gusts perhaps into the 30 miles per hour range. Wind chills will likely fall
below zero by early Friday evening and into the 15 below to 25
below zero range Saturday morning.
While the coldest air will begin to push east of the area Saturday
highs will likely struggle to reach the middle teens and then a sharp
drop Saturday evening is possible but dependent on how fast cloud
cover arrives which may then keep temperatures steady or even begin to
slowly rise early Sunday morning. Regardless...temperatures during this
time period will likely be in the single digits along with wind
chills below zero.
A clipper like system will quickly move into the area Sunday
afternoon into Sunday night. This system has been fairly
consistent for several days...but now appears to be in a weakening
phase as it arrives. So while it will be cold enough that precipitation
should be all snow...fairly low confidence on quantitative precipitation forecast amounts
especially across the eastern County Warning Area. Current trends would suggest a
few inches of accumulation would be possible...but too early for
any specifics. Temperatures look to rise back into the low/middle 20s Sunday
and then may remain generally steady Sunday night into Monday
Monday and Tuesday appear generally dry with a period of rain or
snow possible late Tuesday night/Wednesday as warmer air spreads
back into the region though differences remain between the
for the 18z tafs...
Fairly quiet forecast on tap for the Chicago/Rockford area
terminals through tomorrow. Area of thin overcast stratus that
was in place this morning has become scattered-broken this hour and expect
primarily VFR conditions to prevail through remainder of the
forecast period. Ridge of high pressure currently stretches from
the lower to upper Mississippi Valley and will inch towards the
terminals allowing winds to diminish...and eventually back to the
west/southwest Thursday. An area of low pressure is prognosticated to
move from the plains into the lower Mississippi Valley tonight
resulting in an increase in mainly upper level cloud
cover...though any precipitation with this system will stay well to our
west and south.
202 PM CST
A moderately strong north to northwesterly gradient will persist
over Lake Michigan through tonight ahead of a ridge that stretches
from the northwest territories into the Mississippi Valley.
Winds of 30 knots and freezing spray will continue into some of the
overnight hours then should diminish early Thursday as the high
inches east allowing the gradient to relax. Winds also back to the
west on Thursday as the high builds south of Lake Michigan...then
freshen up as low pressure forms over Ontario. This low will bring
a reinforcing shot of cold air south on Friday behind a trailing
cold front and as a strong Arctic high builds across Canada into
the upper Midwest. At least a short window of northerly gales are
expected behind the cold front Friday evening or overnight...then
winds should gradually diminish over the weekend as the high
builds across the Great Lakes.
Lm...Small Craft Advisory...Indiana nearshore waters until 3 PM
Small Craft Advisory...Illinois nearshore waters until 9 am
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