Forecast Discussions mentioning any of "ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/06/19

Area Forecast Discussion

National Weather Service Chicago/Romeoville, IL

 926 PM CDT Fri Apr 5 2019

.UPDATE...
925 PM CDT

Only concern overnight into Saturday morning is potential for
some patchy fog, with grid updates focusing on cloud cover and
forecast low temps. Based off trends on the nighttime microphysics
RGB on GOES-East, the stratus deck covers most of the area except
the far north and northwest (western Lee/Ogle, NW Winnebago,
parts of McHenry and Lake). AMDAR soundings out of MDW indicated
that the stratus is about 1000 feet or so thick. There has
recently been some erosion on the edge of the cloud deck in
aforementioned areas in far north/northwest. These are likely the
main areas to watch for any patchy dense fog development due to
better radiational cooling. On the other hand, there is also some
high cloud cover spreading toward the area, so it again appears
risk for anything more than localized poor visibility in fog is
fairly low. Otherwise, bumped up forecast low temps a bit except
near Lake Michigan and far north/northwest areas discussed above
to the mid to high 40s.

Looking ahead to Saturday, increasing south-southwest winds aloft
and some existing holes in the stratus should be conducive to
eroding the clouds and supporting the mid to upper 60s forecast
high temps inland. The Illinois shore may struggle to even get
out of the 40s with southeast winds to start backing more easterly
in the afternoon with lake influence.

Castro

&&

.SHORT TERM...
224 PM CDT

Through Saturday night...

Short term challenges center around cloud cover and fog potential
overnight. Stratus has remained rather pesky across the area with
moisture trapped below an inversion, though the inversion is
weakening a little per AMDAR soundings. Low level flow remains
rather weak given the presence of surface high pressure overhead.
The high will shift to the eastern Great Lakes tonight. Guidance
is still somewhat mixed as to how much clearing will take place.
With peak heating and some limited mixing on the back side of the
high across northwest/north central IL, expect we will at least
see some scattering to continue, though it is not clear to what
extent this will continue past sunset and would think that we
would still have at least some cloud cover linger much of the
night as southwest low level flow continues the low level moisture
advection. For areas that do scatter out, dewpoint depressions
will remain low as southwest flow maintains dewpoints in the 40s
such that fog is a concern. It could get briefly dense in spots
given the light winds, but confidence on how low/what locations/
or how long lasting it will be is not high.

Upper ridging on Saturday will allow southwest flow to advect
even warmer area into the lower Great Lakes region. Expect better
clearing on Saturday and temperatures should climb well into the
60s away from the lake, where 40s to maybe low 50s would be found.
A lake breeze will likely reinforce the chill toward the IL
lakeshore in the mid to later afternoon.

A progressive upper level trough will pass through the central
Plains and into the mid/upper Mississippi valley Saturday night.
We could see some showers and maybe a thunderstorm toward daybreak
Sunday, with mild lows Saturday night mostly in the 50s away from
the lakefront.

KMD

&&

.LONG TERM...
311 PM CDT

Sunday through Friday...

The long term pattern looks to be mild and somewhat stormy to
start the period, but quickly looks to transition to a an active
and colder pattern by mid to late week. The main weather concern
initially will focus on the threat of thunderstorms on Sunday,
some of which could be strong in far southern portions of the
area. However, later in the period attention turns to the
increasingly active and much cooler weather pattern likely to
impact the central CONUS by the middle to end of next week. Within
this pattern, there continues to be good signals for a
significant precipitation system, which could produce rain and
snow across portions of our area later in the week.

The period will start Sunday with an approaching mid-level impulse
and a surface trough. Increasing warm air advection setting up
ahead of this system could produce some widely scattered morning
showers, and perhaps a thunderstorm. After a mild day, with highs
in the mid to upper 60s, a surface frontal boundary is forecast
to shift over the area by early evening. This boundary could
result in some additional showers and thunderstorms over the area
late Sunday. It still appears that the threat for any strong
thunderstorms will be over far southern sections of the area, with
the better threat of severe storms south of the area.

Monday looks to be a quiet and mild day across the area.
Temperatures on Monday could reach the lower 70s, especially
inland from the lake. Light surface winds may result in a lake
breeze along the Lake Michigan shores Monday afternoon, thus
resulting in cooler temps here. Gradually cooler weather will
then work into the area through midweek as a baroclinic zone sags
southward over the area.

By midweek a significant eastern Pacific system is forecast to
shift eastward over the central Rockies. Model/ensemble guidance
continues to be in decent agreement with this system spawning a
significant storm system the shifts somewhere across the central
CONUS through Thursday. While it is way too early to talk about
weather specifics, there are signs that this could result in a
good precipitation event for portions of our area through
Thursday. Heavy snow is certainly possible for some with the
storm, but the areas most favorable for such will largely depend
on the actual track of the storm system. The main message at this
time is that inclement weather appears likely over the area
Wednesday through Thursday, with much cooler and windy weather. As
such, this system will need to be monitored closely in the coming
days.

KJB

&&

.AVIATION...
For the 00Z TAFs...

625 PM...Forecast concerns include...

Fog overnight/Saturday morning.
Mvfr cigs through Saturday morning.
Lake breeze Saturday afternoon.

Mvfr cigs remain prevailing across the area late this afternoon
with vfr across far northern IL/southern WI as well as across
east/central IL. Confidence is low for cigs tonight. For now...
have maintained 2kft cigs at ord/mdw/gyy a bit lower at rfd/dpa.
Its possible these may lift to vfr this evening and then fill back
into mvfr overnight/Saturday morning. Where cigs are able to
scatter or lift to vfr...fog will be possible overnight into
Saturday morning. The best chance of 1sm or lower appears to be
centered across northwest IL and areas west of the Chicago Metro.
Confidence is also low for fog at the terminals and maintained
just mvfr for rfd/dpa. Cigs should lift to vfr by early Saturday
afternoon and possibly scatter during the afternoon.

A lake breeze has moved inland this afternoon with light
southeasterly winds at ord/mdw. This boundary will dissipate with
sunset with light winds tonight...favoring a southeast direction.
Winds will become south/southeast Saturday morning and increase
toward 10kts in the afternoon...perhaps 10-15kts at rfd. Another
lake breeze is expected to move inland in the afternoon shifting
winds more easterly at ord/mdw. This boundary may stall near gyy
with low confidence for winds there. cms

&&

.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&

$$

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