Area Forecast Discussion
Issued by NWS Chicago, IL

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FXUS63 KLOT 201858

Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
158 PM CDT Fri Apr 20 2018

158 PM CDT

Tonight through Saturday...

Quiet weather takes us into the weekend, though increasing
mid/high clouds and modest easterly winds will keep temps near but
just below average.

Early afternoon surface analysis indicates surface high pressure
spread across the upper Mississippi Valley and western Great Lakes
region. Dry air, plenty of sun and light winds have produced a
pleasant spring day, though a lake breeze has pushed in off the
lake keeping lake shore areas in the 40`s this afternoon while
other areas approach 60 degrees. The surface high will continue to
drift eastward tonight and Saturday, becoming centered across the
central and eastern Lakes by Saturday evening. Further west, a
closed upper low near the four corners region will cross the
southern Rockies by tomorrow morning, with diffluent upper level
flow downstream into the Midwest resulting in an increase in mid
and high cloud cover across the region from late tonight through
the day Saturday. With low level winds from the east, and the
thickening high cloud cover, 925 mb temps are progged about 2C
lower than today, supporting max temps in the mid-upper 50`s for
the most part, while onshore winds again limiting locations along
the shore of Lake Michigan to the mid 40`s. Winds generally 10 mph
or less however, making it feel much better than last weekend.



225 AM CDT

Saturday through Friday...

Quiet weather will continue throughout much of the extended time
frame with only slightly below normal temperatures expected
through the end of next week.

Fair weather and mild conditions relative to the cold streak we`ve
experienced of late will persist over the weekend. Main change
from today will be increased cloud cover on the northern periphery
of an upper low that undercuts the region moving into the Deep
South over the weekend. GFS develops a few showers in portions of
the CWA Saturday afternoon as a weak shortwave moves across the
area, but forecast soundings show very dry conditions below 750mb.
With the other models dry, opted to maintain a dry forecast at
this point. Even if the GFS verifies and precip occurs, it`d
likely only be a few high based sprinkles. Temps look to top out
in the upper 50s/around 60 both Saturday and Sunday, but onshore
flow will suppress high temps in the 40s near Lake Michigan.
Should see a few more peeks of sunshine on Monday as the upper low
continues to move away from the local area, and widespread 60s
away from the lake seem a better likelihood.

Much of the same on Tuesday, but there is some chance for showers
Tuesday night into Wednesday as a cold front sags south towards
the region. Main areas of vorticity are progged to bifurcate the
local area and surface cold front only gradually sags into the
area at a diurnally unfavorable time, so precip chances aren`t
terribly high but something to keep an eye on in the coming days.
Another wave is expected late in the week and will provide
additional chances for some showers.



For the 18Z TAFs...

No significant aviation concerns next 24-30 hours.

Surface high pressure drifting east across the area early this
afternoon, with calm or light variable winds predominant. Lake
breeze has developed and begun to move inland off Lake Michigan
per ORD TDWR data, and extrapolation of the boundary would suggest
it will arrive at MDW by 19Z and ORD by 1930Z. Some airport
sensors already showing some light NE or E component per CWSU ZAU,
prior to lake breeze boundary passage.

With surface high off to the east of the terminals tonight and
Saturday, modest east flow is expected to persist. VFR conditions
will prevail, though with a thickening and gradual lowering of
high and mid cloud late tonight into the day Saturday.



159 AM CDT

Little in the way of concerns over the lake with strong high
pressure moving overhead into this weekend. There will be variable
light winds at times over the open water with this, along with
afternoon lake breezes in the nearshore. Low pressure is expected
to develop south of the lake in the Tuesday-Wednesday time frame,
but there is uncertainty as to how strong. Winds look to turn
northerly during midweek in response to this.






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