Area Forecast Discussion
Issued by NWS Central Illinois
FXUS63 KILX 092337
Area Forecast Discussion
National Weather Service Lincoln IL
637 PM CDT Wed Jul 9 2014
ISSUED 250 PM CDT Wed Jul 9 2014
Weak trough was seen in surface observations roughly along the
I-70 corridor early this afternoon. The greatest concentration of
diurnal cumulus has been near this boundary northward to around
I-72, with lesser concentrations north of there. Drier air
continues to advect in from the northwest, with dew points in the
50s north of I-72. Larger view of the satellite imagery shows an
expansive shield of smoke aloft originating from northern Alberta
and the Northwest Territory of Canada, spreading as far southeast
as Missouri and western Illinois. This is being carried into our
area due to high pressure ridging aloft west of the Rockies, which
puts us in a northwest wind flow.
Main forecast concern for this package involves rain chances over
the weekend, due to potential MCS activity to our northwest.
SHORT TERM...Tonight through Thursday night:
Quiet weather on tap in the short term, as an area of high
pressure currently in western Missouri slowly drifts northeast
through the Midwest. Temperatures to remain rather comfortable for
this time of year, falling into the 50s tonight and reaching
around 80 on Thursday. Thursday night lows should be a bit milder,
as southeast flow starts to set up behind the high.
LONG TERM...Friday through Wednesday:
Expansive west-east axis of high pressure aloft will mark the
start of the weekend, then the ridging builds again west of the
Rockies Saturday night. As this occurs, a rather large upper low
will develop over Ontario, with spokes of energy around it
swinging through the Great Lakes. This will bring a period of
cooler conditions beginning on Tuesday, as 850 mb temperatures
fall to around 7C yielding surface highs in the 70s.
MCS activity expected to develop west of the Mississippi River
Thursday night as an upper wave approaches us from the northwest.
As is typical around here, main question is how much of this
survives the trip southeast. Model soundings showing respectable
temperature/dew point spreads lingering on Friday, which would
erode some of the activity as it approaches. The ECMWF remains the
most robust in widespread activity over most of the forecast area
through the day, whereas the remaining models have sharply reduced
rain chances, especially east of I-55. Have reduced the PoP`s
somewhat across the area due to the drier air on Friday, and
concentrated most of them Friday night after midnight, when
another thunderstorm complex forms across Iowa in response to a
surface low riding northeast along a boundary. Some model spread
exists in how fast this boundary moves through the forecast area,
ranging between midnight and late evening Sunday, so have elected
not to get too fancy in narrowing down the more likely time frames
at this point.
Rain chances Monday into Tuesday will hinge on weak troughs
rotating southeast around the upper low. Have leaned more toward
the ECMWF in its drying trends.
ISSUED 637 PM CDT Wed Jul 9 2014
VFR conditions will prevail over the next 24 hours. Scattered
cumulus cloud cover at around 5 kft AGL will dissipate after
sunset and re-develop after 13-15Z Thursday. Northwest winds
around 6-12 kts will diminish and gradually turn more northeast
overnight as an area of high pressure drifts across Lake
Michigan. After 13-15Z Thursday...winds will become E-SE 4-8 kts.