Scientific Forecaster Discussion
Area forecast discussion
National Weather Service Chicago/Romeoville Illinois
1229 am CDT Tuesday Oct 21 2014
249 PM CDT
upper level wave continues to rotate over northeast Ontario...with a
a couple weak lobes of vorticity rotating around the back edge of
this system...pushing south into the northern Great Lakes. Visible
imagery shows considerable cloud cover across Michigan...stretching
west across the lake and beginning to slide into far northeast Illinois.
Guidance suggests a few light showers will accompany this wave as it
pushes southeast across Wisconsin and perhaps into far northeast Illinois
late this evening...before shifting east into far northwest in by
daybreak Tuesday. Otherwise expect clouds to thicken this evening across the
County warning forecast area...perhaps less cloud cover across the far west/southwest
portions of the forecast area. With the cloud cover tonight...this
should keep temperatures generally around 40 to the low 40s tonight.
Tuesday through Thursday...
500mb trough axis will begin to push east...with a high amplitude
ridge beginning to build into the region from the Central Plains.
This will bring a broad surface ridge to the area stretching from
central Canada south to the western Gulf. Guidance then continues to
maintain this feature through Thursday morning...however there is a weak
wave sliding east across the central Continental U.S. Wednesday night that is prognosticated
to lift northeast of the County warning forecast area Thursday aftn/eve. This system could bring
some light precipitation to the area...but at this time have only gone with
slight chance of probability of precipitation given the moisture availability appears to be
minimal. Temperatures will generally be in the upper 50s to low 60s...with
overnight lows in the middle 30s to middle 40s.
Friday through Monday...
ensembles continue to feature a trough persisting along the far
southwest Continental U.S....allowing ridging to dominate the central Continental U.S.
Late in the week into the weekend. This will likely continue the dry
pattern for the region. In addition it appears temperatures will be able to
steadily moderate...perhaps reaching the upper 60s to around 70.
Ensembles do suggest that towards the second half of the weekend the
ridge will begin to drift east...with a trough digging into the
central Continental U.S. And perhaps bringing unsettled weather back into the
region early next week.
//Ord and mdw concerns...updated 06z...
* north/northeast winds 10-14 kts and gusty middle morning through late
* Slight chance for rain showers middle morning through middle afternoon.
* Possible MVFR ceilings middle morning through middle afternoon. Cms
A ridge of high pressure will build across the western lakes and
northern Illinois late this afternoon into tonight. Northerly winds
around/just under 10kts before sunrise will turn more to the
northeast middle/late morning and increase in speed to 10-14kts with
higher gusts in the upper teen range likely. Speeds/gusts should
quickly diminish by early evening as the high continues building
Colder air spreading south will aid lake effect rain shower
development early this morning which will affect Northwest Indiana
and gyy...but as winds turn northeast...may move west toward Ord
and mdw. Confidence regarding how widespread the showers become is
fairly low...and thus just not confident enough on coverage to
include at Ord or mdw. Trends will need to be monitored through the
VFR ceilings 4-5kft extend well north into WI with MVFR over the Upper
Peninsula and far northeast WI. As the colder air arrives...it
will likely push ceilings into high MVFR...but confidence also remains
low for duration of MVFR ceilings. Cms
//Ord and mdw confidence...updated 06z...
* high for wind speeds/gusts/directions through the period.
* Low for rain showers middle morning through middle afternoon.
* Medium for MVFR ceilings...low for timing/duration. Cms
//outlook for Ord/mdw for 12z Wednesday-12z Monday...updated 00z...
* Wednesday...dry/VFR. East/northeast winds.
* Thursday...dry/VFR. South winds.
* Friday...dry/VFR. Southwest winds.
* Saturday...dry/VFR. West winds.
* Sunday...dry/VFR. South winds.
250 PM...low pressure continues to influence the region centered
over Northern Lake Huron late this afternoon and is expected to
slowly drift east overnight. This low will then reach Lake Ontario
around daybreak Tuesday. The back edge of this low continues to
feature a tightening pressure gradient...which has produced gusty
winds just beginning to slide over the northern portions of the
lake. These gusty winds will eventually slide south this
evening...and expect north gusts up to 30 kts. High pressure over
Ontario will begin to build south overnight...then stretch from
Ontario south to the western Gulf of Mexico by Tuesday night. This will
bring much lighter winds to the lake by Wednesday.
Lm...Small Craft Advisory...nearshore waters until 7 am Wednesday.
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