Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/10/20
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
941 PM CDT Mon Mar 9 2020
.UPDATE...
930 PM CDT
The main update to the forecast was to issue a Lakeshore Flood
Advisory for the entire Cook County shoreline (central and
northern zones) from 4AM to 3PM Tuesday.
1010 mb surface low pressure was analyzed just east of Waukegan
Illinois this evening. Temperatures and dew points were in the 50s
for most locations, with a cold front starting to enter northwest
and far northern Illinois. The breezy, moist and mild warm sector
was typified by southerly surface winds gusting up to 35+ mph at
times given the very strong low level jet associated with this
system. In fact, Midway Airport earlier had a brief gust to 44
mph. Steady light to moderate rain continues associated with well
defined short-wave noted on water vapor imagery. Any thunder
threat will remain south of the area. Some impressive rain amounts
have occurred, especially in north central and northwest
Illinois. Rockford was up to 1.18" as of 9pm, the largest calendar
day rainfall there since September 13th and breaking record for
March 9th of 1".
As the surface low ejects east of the area tonight, there will be
a surge of northerly winds down the lake with stout pressure
rises due to expansive high pressure building in from the
northwest. There could be a brief period of gusts near 40 mph over
southern Lake Michigan and possibly immediate shoreline areas
from about 2-4am, with only a gradual decrease into Tuesday
morning. Given close to due northerly wind direction (averaging
about 350 degrees during peak winds) with over 6 hours of 20-25+
mph sustained winds, north to northeast wave direction, and record
high lake levels, opted to include the entire Cook County
shoreline in the Lakeshore Flood Advisory. Expecting typical flood
prone locations to flood, particularly along Chicago`s lakefront
path. Winds and waves will subside earlier along the Illinois
shore than the Indiana shore, so went with 3pm end time for the
advisory.
Castro
&&
.SHORT TERM...
248 PM CDT
Through Tuesday night...
Stout upper wave continues to progressive swiftly northeast early
this afternoon and has begun to toss a more cohesive area of
moderate rain into Illinois. PoPs will be trending quickly up
across all of the area here through the rest of the afternoon as a
result. Combo area of enhanced mid-level f-gen and DCVA is
approaching our I-39 corridor counties and should help to locally
maximize rainfall there through the evening. Overall rainfall
amounts of about a half to one inch appear reasonable, with some
pockets of 1"+ amounts across our west before things come to an
end later tonight/early Tuesday morning. Area VAPOR AMDAR
soundings show lapse rates have clearly trended moist adiabatic
through the mid-levels and am seeing little in the way of
electrification to our south. RAP/HRRR combo continue to be a
little too aggressive in the way of temperatures and dewpoints,
and as such, it looks like the main area of instability will
remain immediately to our south this evening as the mid-level
dryslot attempts to punch in overhead. As a result, have formally
left a thunder mention out of the forecast this evening, but
couldn`t rule out a rumble of thunder or two ahead of the cold
front, mainly south and east of I-57.
The presence of plentiful mid and upper level cloud cover seems to
have stunted our ability to more readily mix into some rather
robust flow immediately off the surface this afternoon. Area VWPs
continue to sample about 50 kts present around 3 kft, but 0-3 km
lapse rates have thus far not gotten steep enough to get a larger
proportion of this flow to the ground. With additional clouds and
rain moving in, it may be increasingly difficult to realize our
true gust potential, but have elected to continue the Wind
Advisory for a few more hours across our southeast given the
degree of flow immediately off the deck. Later this evening it`s
possible that any more deeply-developed showers/updrafts that
manage to develop this evening could help tap into some of this
lingering flow to produce some sporadic 40-50 mph wind gusts.
Once we get rid of the lingering low-level moisture Tuesday
morning, skies should begin to clear through the afternoon.
Temperatures will range from the upper 30s lakeside to the upper
40s to near 50 degrees inland on Tuesday. Our next wave, a
clipper-type system, will approach the region late Tuesday night
into Wednesday morning. Best dynamics associated with this look to
remain mainly to our north but have spread some likely PoPs down
to around the I-88 corridor through daybreak. While some snow may
mix in, little to no accumulations are expected mainly north and
east of I-90.
Lakeshore Flooding: North winds will quickly increase behind a
cold front late tonight and look to continue into Tuesday morning,
then gradually diminish through the afternoon and evening. A
period of waves of 8 to 11 feet along the Indiana shoreline
support a Lakeshore Flood Advisory late tonight into early Tuesday
evening given the already susceptible shoreline, especially after
high waves late last week.
Carlaw
&&
.LONG TERM...
231 PM CDT
Wednesday through Monday...
Mid-level clouds and a weak low-level pressure gradient will follow
the weak clipper system discussed in the section above leading to
light, variable winds and highs in the lower 50s on Wednesday. Even
with mid-level clouds, lake breeze development is probable with
locally cooler temperatures along the lakefront.
As a cut-off low pressure system drifts onshore the Baja California
Peninsula (deja vu?) Wednesday night into early Thursday, a broad
region of warm air advection will commence across the central
United States leading to the development of a large mid-level
ridge. At the same time, a short wave-length trough embedded in
the polar jet will be driving south across the northern US and
toward the developing ridge. As the two features interact, a jet
streak is expected to develop over the central united States
enabling the rapid development and movement of a surface low
pressure system from the Plains to upper Great Lakes Thursday into
Friday. As the low first develops Thursday, southwesterly low-
level flow will allow temperatures to jump back into the 60s as
supported by both the ECMWF EPS and our in-house climatology-driven
high temperature tool.
The low is then poised to speed through the Great Lakes Thursday
evening, ushering in showers areawide. Given the features will be
coming together in quick fashion overhead, the ensemble solution
space is somewhat vast with low tracks ranging from central
Illinois to central Wisconsin; however confidence is reasonably
high we`ll have liquid precipitation with even a rumble of thunder
possible (further northward track would favor higher thunder
chances). Regardless, overall precipitation amounts do not look
high--half inch or less.
By Friday morning, the low will be entering Ontario or Quebec with
cold air wrapping around its backside into the Great Lakes.
Confidence is high that highs Friday through Sunday will be some 10-
15 degree cooler than Thursday (and indeed closer to average in the
40s) given the ECMWF ensemble median 850 mb temperatures fall toward
-4 C with an IQR of only 1-2 degrees (e.g. very small range of
outcomes in the ensemble solution space).
Borchardt
&&
.AVIATION...
For the 00Z TAFs...
The primary concerns for the Chicago airports are:
- South winds gusting into the mid 20 kt range this evening, with
a few gusts of 30 kt possible
- Steady rain, often moderate in intensity, through mid-evening
becoming more showery late evening before ending overnight
- 800-1200 ft ceilings this evening, with any 700 ft or less
likely temporary and most favored 03Z-07Z
- Winds becoming near due north Tuesday morning while gusting into
the lower 20 kt range, with a few higher gusts possible, before
winds bend northeast into early afternoon
Quick-moving low pressure across northwest Illinois early this
evening will scoot to the northeast and swing a cold front
through the Chicago area around 06Z. Prior to that, southerly
winds will be gusty especially prior to 03Z. Some gusts to 30 kt
are possible at ORD and MDW. Winds aloft are currently measured on
radar and aircraft sensors at around 50 kt at 2000 ft, which is
close to low-level wind shear not far above cloud base level.
Also ahead of the front is widespread rain through 03Z or so
becoming more showery for a few hours after. Within this rain
temporary IFR visibility is expected with high confidence. Before
and near the frontal passage some more steady IFR visibility in
BR may settle in especially at RFD but possible at Chicago for a
few hours (approximately 03Z-07Z). This is also the time window
where 700 ft or less cigs could occur at ORD and MDW. Any LIFR
conditions are more favored at RFD than the Chicago airports.
Behind the front winds will turn northwest and north-northwest by
daybreak Tuesday. Confidence on winds being 340-350 for much of
the morning rush at ORD and MDW is with high confidence. The later
morning is the favored time for a nudge to north-northeast, with
likely a lake component taking over during the mid-afternoon.
MVFR ceilings should scatter and lift in the mid-late morning.
MTF
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Lakeshore Flood Advisory...ILZ014-ILZ103-ILZ104...4 AM Tuesday
to 3 PM Tuesday.
IN...Lakeshore Flood Advisory...INZ001-INZ002...4 AM Tuesday to 7 PM
Tuesday.
LM...Small Craft Advisory...IL nearshore waters until 7 PM Tuesday.
Small Craft Advisory...IN nearshore waters until 10 PM Tuesday.
&&
$$
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