Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/08/20
Area Forecast Discussion
National Weather Service Louisville KY
906 PM EDT Tue Apr 7 2020
.Forecast Update...
Issued at 905 PM EDT Tue Apr 7 2020
The trend is less with any precipitation tonight into tomorrow
morning. Most of the region remains capped, and moisture remains
only in the lowest levels. Lowered rain/thunderstorm chances in
southern Indiana and west of Interstate 65. Soundings look a little
better for precipitation in general east of Interstate 65 and south
of Interstate 64. Believe this area could see a little uptick in
precip, but still not expecting much in the way of severe.
Temperatures will need slight adjustments as well.
&&
.Short Term...(This evening through Wednesday)
Issued at 305 PM EDT Tue Apr 7 2020
...Strong Storms Possible Tonight In The Northern Areas...
Things continue to be quiet across the CWA at this hour, mainly due
to a notable capping inversion (~9C) around 750-800 mb. This feature
is evident on forecast soundings and on recent AMDAR soundings out
of SDF. Visible satellite imagery has indicated plenty of convective
potential, but vertical growth is likely being limited by the
aforementioned cap. Will keep an eye on things through the afternoon
and early evening, but overall expect it to hold and for us to stay
largely dry during this time. Temps will likely top out in the upper
70s and low 80s for this afternoon.
As we move past sunset, a surface low will move through the Great
Lakes area, with convective initiation expected ahead of a trailing
cold front across northern OH/central IN around Midnight or a little
after. The broken line of storms is then expected to make it down to
our northern CWA border by sometime around 8 or 9Z. It does appear
there will be some modest available instability (1000-1500 J/KG SB
CAPE) left over, although some capping may try to hold. Given that
deep layer shear appears to be sufficient, expect that main limiting
factor to be the capping, and many model solutions continue to show
a weakening batch of storms in our northern CWA between 08-14z time
frame. Some even take the bulk of the convective activity off to our
north and east where the better forcing is.
Like the placement of the SPC Slight/Marginal risks, with the best
chance across our far NE. Biggest threat would be gusty/locally
damaging winds along with brief heavy rainfall and lightning. There
could be a large hail threat if cells are able to stay more isolated
in nature. There will still be plenty of instability/steep mid level
lapse rates across our western CWA, but the overall cap is stronger
the farther west you go and at this time think convective potential
will be mitigated by this. Or, any updrafts that do get going will
likely struggle and die.
The rest of Wednesday should be mostly dry and capped once again.
There appears to be a good window for some afternoon heating, so
temps should once again rise into the 75 to 80 degree range. We`ll
be poised for another round of potential strong storms heading into
later Wednesday evening, which will be discussed in the long term
discussion below.
.Long Term...(Wednesday night through Tuesday)
Issued at 330 PM EDT Tue Apr 7 2020
A robust upper trough will continue dropping southeast over southern
Ontario, Upper Midwest, and Great Lakes Wednesday night. A mid level
vorticity maxima also pivots ESE across the Upper Midwest and Great
Lakes, with winds aloft increasing with time into Thu morning. Upper
diffluence is noted around 06z Thu in the exit region of a 120 kt
mid level jet streak. This is also when a strong sfc cold front will
be pushing southeast across southern IN and central KY.
00z Thu looks dry and even mostly clear underneath a cap at 850 mb.
That cap is expected to hold until just before the actual front
dives through overnight. While we lack deep Gulf moisture return,
high theta-e air will continue to be advected into the region ahead
of the boundary in the 00-06z Thu time frame. A plume of upper 50s
to near 60 sfc dewpoints is forecast immediately ahead of the cold
front. 700-500 mb lapse rates in the neighborhood of 7.5 C/km will
support close to 1000 J/kg MUCAPE above the cap most of the night.
However, as indicated in some hires forecast soundings, the rich BL
moisture and strong forcing right along the front could allow a very
brief (1-2 hr) window for strong to severe sfc based storms.
However, if storms grow upscale as expected with the linear forcing,
any squall line outrunning the robust low level forcing would have
very little severe threat. But given the environment, there is
certainly a Slight Risk for a brief threat for strong to severe
storms late Wednesday night. The front is still expected to push
through the area between about 05-11z.
Clouds are forecast to clear out fairly quickly behind the front,
resulting in a sunny, cool, and windy Thursday. Lingering stronger
winds aloft will likely be mixed down to the sfc with dry adiabatic
low level lapse rates. Gusts to 30-35 mph seem likely, but peak
gusts may push higher. Cold air advection continues in a NW flow
pattern through Thursday night until the upper trough axis finally
swings through early Friday. Lows in the mid 30s Thursday morning
could pose a risk for some frost, but elevated winds may mitigate
that risk.
The frost/freeze risk for sensitive plants is higher Friday
night/Saturday morning, when temperatures will likely drop into the
low to mid 30s. Sfc high pressure drifting across the region will
result in clear conditions with light winds. Will go ahead and
highlight frost potential in the HWO. Otherwise, fair weather is
expected through the first half of the weekend. The persistent
closed low over southern CA currently is finally expected to eject
eastward across the southern Plains, bringing us our next chance of
rain by early Sunday. This system lifting northeast across the Ohio
Valley could result in storms and heavy rainfall. Sunday and Sunday
night are currently the most likely time frame for heavier rainfall.
Drier weather looks to return following that system early next week.
&&
.Aviation...(00Z TAF Issuance)
Issued at 734 PM EDT Tue Apr 7 2020
Confidence not high with this forecast. The most straightforward
part of the package is the first several hours this evening with
VFR conditions and a southwest breeze with occasional low amplitude
gusts. Overnight things get more uncertain. Models are enthusiastic
about bringing low ceilings into the region from around midnight
through late Wednesday morning. Over the past few days the low cloud
forecast data have been much too pessimistic, so am reluctant to
accept these solutions. However, there is a pool of low level
moisture manifesting itself in low ceilings over the lower
Mississippi Valley at this hour, which could easily advect into the
Tennessee and Ohio Valleys on the aforementioned southwest winds.
So, will go ahead and bring in low-end prevailing MVFR ceilings late
tonight into Wednesday morning. Atmospheric moisture profiles are in
good agreement with VFR ceilings (if any ceiling at all) Wednesday
afternoon.
Thunderstorms have already developed near a cold front from Michigan
to Iowa this evening. Storms will continue ahead of this feature as
it progresses southward overnight and into Wednesday morning. While
convection will be robust to our north, it should exhibit a
weakening trend as it approaches our TAF sites. So, for now will
just continue the PROB30 from the previous TAF package, with the
most likely time for storms and IFR cigs in the 8Z-15Z time frame.
Additional storms are expected to move in from the west in the last
few hours of the extended forecast in the SDF TAF as a cold front
nears. Wednesday night should be stormier than tonight.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...KDW
Short Term...BJS
Long Term...EBW
Aviation...13
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
648 PM CDT Tue Apr 7 2020
.MESOSCALE DISCUSSION...
436 PM CDT
Severe convection has initiated along the cold front just north of
Milwaukee late this afternoon in an unstable and weakly capped
environment. Modified AMDAR soundings from MDW and a 19Z Valparaiso
University sounding suggest surface-based inhibition across
northeast Illinois and northwest Indiana has diminished over the
past few hours, with only a weak cap remaining. However, mixed-layer
parameters indicate a modest cap remains in place, which is
supported by dew points holding steady or even slightly falling in
some locations as well as a slight decrease in cumulus coverage in
the last two hours. However, the cumulus field is exhibiting more
pronounced horizontal convective rolls as of 4pm, implying stripes
of better surface convergence and potentially locally increased
moisture pooling. With all that said, chances are increasing that at
least an isolated cell or two may develop across far northeast
Illinois within or around the 6-7pm hour. Given effective deep layer
shear around 50 knots and MLCAPE around 2000 J/kg, organized severe
convection is likely if initiation occurs. For this reason, a Severe
Thunderstorm Watch has been issued for McHenry and Lake(IL)
counties. A southward expansion into Cook and DuPage counties is
possible if convection is able to initiate. Overall potential of
supercell convective mode supports a severe hail and wind risk with
any storm. LCL heights in excess of 1km and marginal 0-1km SRH
suggest a fairly low tornado risk across northeast Illinois.
Kluber
&&
.SHORT TERM...
311 PM CDT
Through Wednesday night...
The primary forecast challenges continue to focus on the threat
and coverage of severe thunderstorms early this evening.
Temperatures across the area have warmed nicely into the mid to
upper 70s across the area. This as dew points have mixed out a
bit into the upper 50s. The main challenge that continues is to
anticipate the extent of thunderstorm coverage early this evening
over northern IL. A capping inversion, associated with an EML,
remains present, with a base around 6500 FT AGL per some of the
latest aircraft soundings our of ORD and MDW. This capping
inversion will be the main negative for much thunderstorm activity
over northern IL. With that being said, thunderstorms are likely
to develop to our northeast as the cap begins to erode over the
next few hours as forcing for ascent begins to increase in
association with a mid/upper-level speed max currently shifting
east- southeastward across southern MN. With a majority of this
forcing for ascent likely to miss, or just glance my eastern areas
into early this evening, there remains questions as to how far
west the convection will be able to develop over northern IL.
If storms are able to develop over northern IL early this
evening, nothing has changed with the potential for them to be
severe. Steep mid-level lapse rates above the capping inversion,
as well as strong deep layer shear will be more than sufficient
for supporting large hail and damaging winds. The best potential
for the storms continues to be over my eastern CWA and points
east, namely northern IN and Lower Michigan. The best timing also
continues to be in the 6 to 10 pm timeframe.
Looking a quieter weather overnight, though we could see some more
fog develop overnight as the winds become light. Any fog should
burn off by mid-morning on Wednesday.
Wednesday will be our last mild day before conditions turn much
cooler in the wake a cold frontal passage late in the day. This
front also looks to produce our next good chance for some showers
and thunderstorms Wednesday afternoon. As the previous discussion
mentioned, some very gusty winds could accompany these showers and
storms before they end in the evening. Thereafter, expect breezy
and cooler conditions Wednesday night.
KJB
&&
.LONG TERM...
Thursday through Tuesday...
235 PM...Primary forecast concern is strong winds on Thursday.
Strong low pressure will move across the upper Great Lakes region
Thursday and be absorbed by even stronger low pressure developing
over New England Thursday night. Much cooler air spreading across
the region with a tight pressure gradient will allow for strong/
gusty northwest winds across the region on Thursday. Still some
uncertainty regarding how strong winds will become but gusts into
the 40-45mph range look possible and if these continue to look
likely...a wind advisory may be needed on Thursday. Winds should
slowly diminish Thursday evening but remain gusty Thursday night.
An unsettled pattern is taking shape for this weekend as low
pressure is expected to lift northeast through the Ohio Valley
Sunday/Sunday night. A little early for specifics but could be
some showers before this time period and then a rather wet period
Sunday...if trends continue. Models trend colder again early next
week with a breezy/windy conditions possible. cms
&&
.AVIATION...
For the 00Z TAFs...
Primary aviation forecast concerns:
* Potential for scattered strong/severe thunderstorms this
evening. Approximate timing 00-02Z for RFD, 01-03Z for
ORD/MDW/GYY. Very large hail with cell approaching metro
Rockford at this time.
* Possible IFR stratus/fog off the lake after midnight, as winds
turn light north/northeast behind front.
* Showers and some thunderstorm potential Wednesday afternoon.
* Gusty northwest winds Wednesday evening behind another cold
front.
Latest surface analysis indicates surface low pressure near
Milwaukee, with a cold front trailing west-southwest into central
Iowa. A broken line of scattered strong/severe thunderstorms was
just ahead of the front, along a MKE-RFD-CID line. Individual
storm motion was to the east at around 40 mph, while the line will
move more slowly southeast with the front this evening. Currently
the strongest storm is near KRFD, likely producing very large hail
to the north/northwest of the airfield. While some weakening is
possible into the evening as daytime heating abates, will likely
see storms fester along/ahead of the front until the front passes.
As indicated above, approximate timing of the highest threat
is 00-01Z for KRFD and 01-03Z for the Chicago terminals.
Winds will shift northwest and then north-northeast behind the
front late this evening, and model guidance suggests they may turn
light northeast during the pre-dawn hours (or light/variable).
This may increase the potential for IFR low stratus/fog to spread
into ORD/MDW/GYY, though winds should be fairly light at that
time. Confidence is rather low, but for now have maintained a
mention of a scattered low deck and will have to monitor further.
Winds turn southerly Wednesday morning as another cold front
approaches. Shower and isolated thunderstorm potential should
increase by mid-late afternoon as the front approaches. Southwest
winds will likely become modestly gusty during the midday and
afternoon hours. Winds shift northwest and become strong and gusty
behind the cold front toward evening. Gusts may approach 30 kts by
mid-late evening.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...Small Craft Advisory...nearshore waters
until 7 PM Tuesday.
&&
$$
Visit us at weather.gov/chicago
Follow us on Facebook, Twitter, and YouTube at:
www.facebook.com/NWSChicago
www.twitter.com/NWSChicago
www.youtube.com/NWSChicago