Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
956 PM CDT Monday Sep 22 2014
323 PM CDT
High pressure will be in control through the week and at least the
start of the weekend...keeping dry weather in place. Water vapor
imagery shows the upper trough that brought the unsettled weather
over the weekend digging across the southeast U.S. While broad upper
ridging is spread across much of North America. A cutoff upper low
continues to slowly spin northeastward across the central/northern
rockies. A large upper trough is pushing eastward toward the West
Coast. At the surface...expansive high pressure is centered just
west of the forecast area with a weak trough from eastern Alberta
into the northern High Plains.
Tonight and Tuesday...the surface high will steadily spread eastward
tonight keeping the forecast area under weak flow. Little if any
cloud cover will combine with the light winds to allow for good
radiational cooling for most areas. Southeast areas may see the
coldest readings being closer to the center of the high but expect
that most areas outside of the immediate Chicago metropolitan will fall
into the lower 40s...with a few spots possibly cooling into the
upper 30s...but the airmass may be a little too moist to radiate out
that much. The cutoff upper trough will open up as it moves across
the northern plains and will force a ridge axis over the local area
Tuesday. Quiet weather will persist with a light southerly flow
setting up. The airmass will modify and temperatures will warm aloft so
expect that most areas will see the lower 70s. The flow will likely
turn more southeasterly along the Illinois shoreline and possibly
even northeasterly along the Indiana shore. This will keep highs a
few degrees cooler than inland areas.
Wednesday through Monday...the cutoff upper trough lifts northeast
into Canada Wednesday and Thursday with associated ascent for any
precipitation expected to remain to the west of the area. The trough falls
apart allowing the massive upper ridge to become better established
for late week. South to southeast winds will continue through
Thursday before turning more easterly Friday and Saturday. Highs in
the middle to upper 70s are expected through the weekend with dry
weather continuing. Areas adjacent to the lake will continue to see
some modest cooling thanks to the flow off the lake with a more
concerted inland push of lake air possible just about every day
which may lead to some late day cooling several miles inland of the
lake. Medium range guidance continues to suggest that the ridge will
start to break down late in the weekend and early next week...with a
trough potentially working northeast from the Gulf Coast. There has
not been great consistency in the evolution at this point so will
continue with a dry forecast through Monday with mild temperatures
//Ord and mdw concerns...updated 03z...
* winds turning easterly on Tuesday afternoon associated with a lake
Sprawling Canadian high pressure is over the area with a fitting
air mass for the autumnal equinox. Basically no change in weather
is expected through the taf period. The air mass warmed and mixed
well today so not anticipating any ground fog development tonight.
With a similar air mass a lake breeze should develop again on
Tuesday afternoon. This will likely have less resistance than
today...so a quicker arrival at mdw and Ord is expected.
//Ord and mdw confidence...updated 03z...
* medium in lake breeze timing and associated wind speed on
//Outlook for Ord/mdw for 12z Wednesday-12z Monday...updated 00z...
Wednesday-Sunday...VFR with afternoon lake breezes.
224 PM CDT
High pressure is centered over the middle/upper Mississippi Valley this
afternoon with ridging extending over Southern Lake Michigan which
has resulted in diminishing winds today. Waves have been steadily
subsiding today with waves at the Michigan City buoy below 4 feet...
so will cancel the remainder of the Small Craft Advisory for the
nearshore waters this afternoon. Through midweek...the high will
translate east across the Ohio Valley into New England with winds
gradually backing to the south by Tuesday evening where they
should generally stay through the end of the week.
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