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fxus63 klot 162319 

Area forecast discussion
National Weather Service Chicago/Romeoville, Illinois
619 PM CDT sun Jun 16 2019

Short term...
223 PM CDT

Through Monday night...

Surface low/trough and front continue to slowly push through the
region this afternoon. Dry conditions currently in place, though
much of the area remains under solid stratus with even some fog
still lingering this afternoon. Some continued clearing possible
south of I-80 this afternoon/evening, but would expect any clearer
skies later today to be filled back in with cloud cover as
stratus slides south on the back side of this system. Think the
area will stay fairly dry for the remainder of the day into
tonight, as focus looks to stay just south of the County Warning Area. It is still
possible for a stray shower or storm to move across areas
along/south of the Kankakee River valley this afternoon, but
expect chances to remain low. Will need to monitor fog trends once
again tonight into Monday morning, as some patchy dense fog is
possible. Some cold air advection/dry advection is likely later this evening, but
I wonder if it will be enough to scour out lower level moisture
in some spots. If patchy dense fog were to develop tonight, the
highest chances would be for areas near Lake Michigan and then
along/south of I-80. Mainly dry conditions expected Monday, but
with cloud cover to likely remain. Did lower high temps slightly,
with low to mid 70s expected Monday.



Long term...
248 PM CDT

Tuesday through Sunday...

A quasi-zonal and not overly fast-paced upper flow will be present
during midweek, before both slightly more amplified and stronger
flow are indicated, which could make for an active end of week
and especially next weekend.

Tuesday will find the remnant surface front to the south of the
area with weakening high pressure over the County Warning Area. While some weak
instability is forecast, there looks to be little in the way of
forcing aloft or low-level focus. Late Tuesday night through
Wednesday, a gradually amplifying/strengthening short wave is
forecast to move across the middle of the country in the GFS and
ec solutions. The present track of this would keep the moderate
instability values just south of the County Warning Area for a severe
thunderstorm threat, and possibly keep thunder more isolated to
widely scattered.

However, precipitable waters in excess of 1.5 inches return
northward and the 925-700 mb moisture transport nose and
convergence along it could be centered over the County Warning Area potentially
bringing a heavy rain risk. Over half of the 00z GFS ensemble
members had provide in excess of an inch of rain in 24 hours
across the southern half of the County Warning Area...a decent warm season signal
for three-four days out. Did want to note that subsequent gefs
runs and the European ensemble shifted south with the heaviest
precip axis, which is something to watch. Further southward shift
would take the heavy precip/localized flooding risk potentially
south of the southern County Warning Area counties altogether.

At some point Thursday, possibly even beforehand, the area looks
to get on the backside of this system with diminished rain
chances. A surge of stronger northerly winds on the backside of
this system could bring dangerous swimming conditions to the Lake
Michigan beaches.

Temperatures should be able to bounce back to closer to normal
range on Tuesday (except lakeside), and if Wednesday has
prevalent clouds and showers then highs would probably dip back
into the 70-75 Arena. Thursday will also likely feature cooler
than normal temps area wide again, coolest and only in the mid 60s

For Friday into next weekend there remains a fair amount of
spread in the GFS and ec deterministic solutions and ensembles,
however both would provide a convectively active pattern in the
middle of the country, especially the ec with a longer wave trough
over the western conus, though today's GFS leaned a bit in that
direction. For now have trended a little warmer Saturday and
preserve thunderstorm chances within that time. Mass fields of
flow and moisture would support some severe weather threat,
possibly multi-day if the ec were to pan out. In addition to the
severe threat, there is a strong signal on the European ensemble
for precipitable water over 1.5", with even some 2"+ potential indicated. Thus,
any well organized mesoscale convective system would likely have a noteworthy flooding
risk associated with it as well. The increase in moisture will
also be felt in much higher humidity than we've had this season,
with 70+ degree surface dew points possible.



for the 00z tafs...

Should start the taf cycle with nearly steady conditions or
possibly some very minor improvement until sunset, followed by a
steady lowering of ceilings after dark and through the night. See no
reason to deviate from previous forecast of LIFR ceilings most
locations late tonight into Monday morning. Gradual improvement in
ceilings expected again Monday late morning into the afternoon. Lower
confidence in visibility trends tonight, though conceptually would
expect lowering visibility overnight so continued previous forecast
depicting that trend. Hard to say just how low the visibility will get,
but dense fog is certainly possible.

- Izzi


Lot watches/warnings/advisories...
Illinois...beach hazards statement...ilz006-ilz014 until 10 PM Sunday.

Lm...Small Craft Advisory...Illinois nearshore waters until 10 PM Sunday.

Dense fog nearshore waters until 10 PM Sunday.



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