Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1108 am CDT Monday Jul 28 2014
251 am CDT
Synopsis...today will be a beautiful dry day with well below normal
temperatures. The below normal temperatures continue through the forecast period.
We stay in a pattern that has multiple waves of upper level energy
rotating through the region. As such diurnal showers and
thunderstorms are expected from Tuesday through Saturday.
Today and tonight...
the pattern aloft will not change much over the next week with a
large low/trough to our east and a ridge to our west. The surface
low is over New England while a high is building down the plains.
We are looking at a dry and cooler than normal day with highs in the
low 70s. Temperatures will be coolest along the Lakeshore due to
strong north winds. Waves along the Northwest Indiana shore are very
high at 11 feet at this time and still expecting dangerous swimming
conditions at all of the beaches. Rip currents are expected.
We will see gusts up to 35 miles per hour again early today with winds
diminishing in the afternoon as the pressure gradient weakens
overhead. Clouds clear tonight and expecting temperatures to fall
into the 50s...with lows around 60 downtown.
Tuesday through Thursday...
the surface low shifts north into Quebec while the plains high
slowly spreads over the Midwest Wednesday night. The main theme for
the rest of the week will be weak vorticity streamers rotating
around the upper level low. These streamers may provide enough
forcing for isolated to scattered afternoon thunderstorm
development. Confidence is medium-low in coverage and timing so have
low end chances of thunderstorms each afternoon. Given the weak
forcing and instability...not expecting severe weather and there
should be plenty of dry hours.
Lake breezes are expected each day...with highs along the Lakeshore
in the middle 70s. Highs away from the lake will be in the upper 70s to
around 80. Overnight lows will be in the upper 50s to around
60...and in the low 60s downtown.
Friday through Sunday...
a lobe of upper level energy swings through the region Friday which
will bring US our best chance for showers and storms. At this point
instability looks weak with 1000 j/kg of cape or less and shear does
not look favorable for severe weather. Have another less impressive
chance of afternoon storms Saturday. Temperatures remain below
normal with highs in the upper 70s and lows around 60.
//Ord and mdw concerns...updated 16z...
* gusty north to north-northeast winds today.
Winds continue to fluctuate between north and north-northwest at Ord/mdw but am
still anticipating a steadier north-northeast direction to take over into
midday. Latest radar imagery does show a boundary moving inland
from the lake and this may bring the shift to north-northeast over the next
hour. Still not highly confident in direction very late this
afternoon into the early evening but speeds will begin to diminish
during that time. Will continue with the north-northeast direction for now.
Low pressure will continue to depart eastward from the eastern
Great Lakes region. The pressure gradient in its wake will linger
through early afternoon supporting wind gusts of 18-22kt. The wind
direction at Ord and mdw are likely to turn from north-northwest
to more north-northeast sometime this middle to late morning due to
local effects of the lake. There is uncertainty on the wind
direction late this afternoon into early evening as it could turn more
northeast with almost an influence of a lake breeze enhancement to
the synoptic wind. If that does not occur...the wind direction
could back more to the north-northwest.
Scattered cumulus are expected this afternoon with possibly some
scattered VFR clouds tonight into early Tuesday morning.
//Ord and mdw confidence...updated 16z...
* high in wind speed and medium in north-northeast wind direction through middle-
afternoon. Low in north-northeast wind direction from 22z-02z.
//outlook for Ord/mdw for 00z Wednesday-12z Monday...updated 12z...
Tuesday night...slight chance of an evening storm.
Wednesday-Saturday...mainly VFR. Slight chance of afternoon thunderstorms and rain.
215 am CDT
Impressive winds and waves for July are occurring early this
morning across the southern part of the lake with 2 am
observations indicating the south buoy at 8.6 feet and Michigan City
at 11.1 feet. Northerly winds of 30 knots with occasional gales will
ever so slowly ease this morning across the south. The gradient
between a departing low in the northeast U.S. And a high over the
northern plains will ease this afternoon and more so tonight.
Waves will be slow to subside along the Indiana shore but are
expected to drop below Small Craft Advisory criteria by daybreak
A strong upper trough across eastern Canada will move little through
midweek. As is often the case...weaker secondary surface cold fronts
will move across the Great Lakes...with one such front expected on
Tuesday afternoon and night across Northern Lake Michigan. This will
have overall little influence however. The pressure gradient will
remain light across the lake for much of the Wednesday through
Saturday time period with an afternoon lake breeze on the
Illinois and Indiana shores Wednesday and Thursday...and overall
synoptic onshore flow on Friday and Saturday.
Illinois...beach hazards statement...ilz014 until 4 am Tuesday.
Beach hazards statement...ilz006 until 10 PM Monday.
In...beach hazards statement...inz001-inz002 until 4 am Tuesday.
Lm...Small Craft Advisory...nearshore Winthrop Harbor to northerly is until 10 PM Monday.
Small Craft Advisory...nearshore northerly is to Michigan City in until 4 am
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