Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
906 am CDT Tuesday Jun 30 2015
325 am CDT
Primary concern in the near term revolves around precipitation chances
today. Northwest flow aloft continues with series of disturbances
pivoting around eastern noam upper trough. One such vorticity evident on
water vapor imagery over northern Wisconsin will drop south into the
area later today and could spark some isolated shower and perhaps T-
storm development this afternoon. At the surface...broad low
pressure over western lakes will begin slowly begin moving eastward
allowing weak northwesterly winds at the surface to begin process of
advecting in drier air mass today...which should result in best
instability over southeastern County Warning Area. Water vapor also shows dry middle-
upper level air advecting southeast into the area which should also tend to
limit the coverage and intensity of showers this afternoon.
Generally focused chance probability of precipitation today in southeast County Warning Area where best combo of
instability and moisture will exist...though do hold onto a tongue
of slight chance probability of precipitation north into northeast Illinois in case more
focused low level convergence along the lake breeze ends up being
enough to pop some weak afternoon convection.
Stronger shortwave will ride the northwest flow into the Missouri
and lower Ohio Valley region tonight...but looks to pass far enough
southwest of our region to provide little threat of precipitation.
Dry and seasonably cool weather will be the dominant weather story
tomorrow with winds off the lake keeping temperatures at the beaches pretty
chilly by July standards.
325 am CDT
Wednesday night through Monday...
Extended period of dry and seasonably cool weather expected to
continue into the weekend as upper trough slowly deamplifies but
weak Canadian high pressure remains in control of the weather. Winds
off the lake will keep it consistently cooler by the lake with highs
generally in the 70s inland and 60s right along the lake. Moderating
trend in temperatures expected heading into the weekend as developing low
pressure over the plains flips winds to southerly direction and
brings a return to more seasonable temperatures over the weekend
along with a threat of some showers and thunderstorms by Sunday
night into Monday.
//Ord and mdw concerns...updated 14z...
* lake breeze and this afternoon.
* Vicinity showers this afternoon.
* MVFR ceilings possible again overnight.
Patchy fog this morning will continue to improve over the next
couple hours with sunrise with VFR conditions and modest northwest
winds expected through the remainder of the morning and much of
the afternoon. A lake breeze is expected to push inland this
afternoon turning winds to the northeast for the Chicago
terminals. Cannot rule out a few isolated showers or thunderstorms
developing along the boundary however confidence is too low at
this time to include in the taf. Winds will settle to the east
tonight. NAM/met guidance indicates that MVFR ceilings may develop
overnight...however other models indicate VFR conditions will
prevail and given the moist bias of the NAM...thought it was only
Worth a sct020 and mention in the concern section.
//Ord and mdw confidence...updated 14z...
* medium in lake breeze this afternoon.
* Low to medium on showers this afternoon.
* Low on MVFR ceilings overnight.
//outlook for Ord/mdw for 00z Thursday-12z Tuesday...updated 12z...
Wednesday night through Sunday...primarily dry and VFR. NE/east winds.
Monday...chance thunderstorms and rain. SW winds.
259 am CDT
A weak trough will push across Lake Michigan today with northwest
to north winds overspreading the lake through the day. Winds
freshen up to 15 to 20 knots across the lake this afternoon and
evening as the low deepens over the eastern lakes region and high
pressure builds south from Manitoba. Modest north to northeast
winds will remain in place through Wednesday night...then will
begin to diminish from the north. A gradient will hold on across
the far south end of Lake Michigan Thursday as low pressure moves
across the middle Mississippi Valley...but expect winds to diminish
across the south end by Thursday night as the ridge continues to
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