Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1107 am CDT Wednesday Jul 1 2015
1101 am CDT
This afternoon and evening...
Surface ridge continuing to build south with elongated high pressure
area located across central and Western Lake Superior. A
northerly low level flow is helping to scour out residual low
level moisture as evident by thinning low clouds over northern Illinois.
Expect this trend to continue this afternoon with rap/sref/hrr
trending drier in the low levels. Still cant rule out a shower
far South County warning forecast area but feel chances of that will hold off till evening
given current radar trends and rap/hrr/serf and have dropped
mention of such in the grids/zfp. Going temperatures on target with
onshore flow holding temperatures significantly down near the
Lakefront... quite chilly by July 1 standards. Average high temperature
for the day is 84 at Ord and rfd. Shaved a degree or two off
maxes west and South County warning forecast area as temperatures struggling compared to average
dirunal trend for the time of year and middle-high cloudiness.
Rap picking up on low level moisture associated with low clouds
upstream over Lake Michigan and largely shunts this moisture off
to the east this evening. Hence expect mainly scattered-broken middle-high
clouds to continue this afternoon and evening as modest drying in
the low levels continues.
330 am CDT
Thursday through Tuesday...
Little change to the pattern is expected through the remainder of
the week. Upper trough responsible for our cool and dry weather
will gradually weaken and surface ridge will slowly migrate
eastward allowing for very slowly moderating temperatures and
gradual weakening of the lake breezes and associated lake cooling.
By the weekend...temperatures should moderate back closer to seasonal
norms as gradient flow turns more southerly and warm air advection
kicks in. Flow looks weak enough Saturday to allow weak Illinois
Lake breeze to form...and can't even rule it out Sunday
either...though the magnitude of any possible lake cooling looks
to be far less over the weekend.
Medium range models have slowed the arrival of cold front and
associated shower/storm chances until Monday/Monday night time
frame now...so outside of a slight chance of a shower or two
sneaking into our far southern County Warning Area at times through Friday...it
looks like dry weather will be the rule through the Holiday
//Ord and mdw concerns...updated 16z...
* periodic MVFR ceilings.
* NE winds increasing to 10-12 knots this afternoon.
High pressure lies north of the terminals and will provide modest
northeast winds and dry weather through the forecast period.
Patchy MVFR will float across the terminals through middle
morning...then should lift and scatter with VFR conditions the
remainder of the taf period. Winds are expected to increase at or above 10
knots for a few hours this afternoon into early evening.
//Ord and mdw confidence...updated 16z...
* high in MVFR through 17-18z.
* Medium high in timing of winds above 10kt.
//outlook for Ord/mdw for 00z Friday-12z Wednesday...updated 12z...
Thursday night through Saturday...dry and VFR. NE winds.
Sunday...dry and VFR. Southeast winds.
Monday through Tuesday...chance thunderstorms and rain. SW winds.
314 am CDT
North winds have picked up into the 15 to 25 knots range at times in
between an area of low pressure over the eastern Great Lakes and a
ridge over Ontario and the upper Midwest. The high will build south
over Lake Michigan with winds gradually abating from the north
today through Thursday. The high should provide quiet weather and
relatively light winds Friday through the weekend. Southwest winds
look to freshen up again Monday ahead of an approaching cold
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