Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 07/11/19
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
700 PM CDT Wed Jul 10 2019
1237 PM CDT
Thunderstorm chances continue to be the main forecast question,
though heat indices around 100 degrees this afternoon may be
causing the bigger impacts. Regarding convective trends, most of
the latest CAMs have at best some spotty development for the rest
of the day into the evening, with the southeast portion of the
forecast area most favored. Cumulus development is very sparse
across our western half and just upstream of the area so far. This
is probably related to the nose of warm air just above 800mb being
seen in late morning AMDAR data and reflected in the latest RAP
soundings. The RAP shows this cap eroding somewhat but not
completely this afternoon, so have held onto a slight chance of
storms mainly across our southeast where the cumulus field is more
robust and the passing cold front will coincide with the best
diurnal support. Expect that anything that does manage to develop
this afternoon to wane during the evening and then dry conditions
to prevail into tomorrow morning.
With dewpoints in the 60s by morning rather than lower 70s like
this morning, low temperatures tonight behind the cold front
should also be a few degrees cooler than this morning.
218 PM CDT
Thursday through Wednesday...
A relatively quiet period is setting up for the long term forecast
period. The upper level pattern is transitioning to a broad low
amplitude long wave pattern with an upper high parked over the
Southern Rockies/Four Corners region and the western extent of the
Bermuda high staying east of the Florida Peninsula. Meanwhile, a
series of upper troughs will dig through the Eastern Great Lakes and
southeastern Canada. Broad wnwly flow aloft will persist from
Thursday into early next week. Weak shortwave energy dropping
through the wnwly flow aloft may bring a few chances for some
showers and thunderstorms, but with the main upper forcing shunted
north of the Wisconsin border, and pcpn chances will be low, and
likely be glancing the far nrn portions of the CWA.
For Thursday and through the weekend, sfc high pressure will also be
firmly established across the region, leading to warm, but less
humid conditions. By Friday night, a weak cold front from an
associated low over northern Ontario will sag southward across the
Upper Mississippi River Valley. This weak front may skirt the
northern extent of the sfc high pressure. Latest guidance still
suggests that the front will stall over or just north of the CWA
late Friday night into Saturday, supporting at least small chances
of convective activity during this time, mainly for the northern
portions of the CWA.
Through the weekend and into early next week, a weakness in the
upper level flow between the upper ridge over the swrn CONUS and the
Bermuda high east of FL may allow a potential tropical system to
sneak north into the Lower Mississippi Valley. While there is still
considerable uncertainty as to how this system will develop and
where it may track, it will need to be watched over the next few
days to see if any moisture associated with this system can get
into, at least, the southeastern portions of the CWA by the middle
of next week.
For the 00Z TAFs...
700 PM...Forecast concerns include...
Isolated thunderstorms this evening...southeast of the terminals.
Wind shift to northeast Thursday morning.
Mvfr cigs Thursday morning.
A weak cool front is moving across the area currently and isolated
thunderstorms will be possible southeast of the terminals for the
next few hours. Westerly winds will turn northwesterly this
evening with gusts into the lower 20kt range possible through
Winds will continue to turn northerly by daybreak and will become
northeast Thursday morning. Confidence on timing is only medium
and its possible that winds will shift northeast earlier than
currently advertised in this forecast. Gusts into the mid/upper
teen kt range will be possible Thursday afternoon diminishing
Much of the guidance is suggesting mvfr cigs will develop after
sunrise across the area with cigs near 1kft across much of
northwest IL. Followed these trends and introduced mvfr cigs with
this forecast but confidence on specific heights is low. Cigs
should begin to lift by late morning with scattering expected in
the afternoon. cms
IN...Beach Hazards Statement...INZ001-INZ002...2 PM Thursday to 4 AM
LM...Small Craft Advisory...LMZ743-LMZ744-LMZ745...2 PM Thursday to 4
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