Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 09/04/19
Area Forecast Discussion
National Weather Service Grand Rapids MI
1022 PM EDT Tue Sep 3 2019
LATEST UPDATE...
Mesoscale Discussion
.MESOSCALE DISCUSSION...
Issued at 1024 PM EDT Tue Sep 3 2019
The thunderstorms are now becoming more active as a shortwave
rotates in on the upper level trough. The axis of MU cape is over
Southwest Michigan from near Grand Rapids to South Haven at 10
pm. There is around 3000 j/kg of MU cape south of I-94 and around
2500 j/kg of MU cape over the I-94 area. The axis of the low
level jet (LLJ) was from near South Bend to Detroit with the core
of the LLJ near Detriot. There is around 50 knots of effective
bulk shear near the front front where the storms currently are.
The early inversion seen on AMDAR sounding as gone now so
convection is now surface based ahead of the front. We expect the
storms to continue to develop and move east. It may take till
midnight now for the storms to clear our CWA. So, the area near
I-94 is still at risk for severe storms till midnight.
&&
.SYNOPSIS...
Issued at 308 PM EDT Tue Sep 3 2019
- Slight risk for severe thunderstorms this evening
- Cooler for Wednesday
- Some showers possible for Thursday Night into Friday
&&
.UPDATE...
Issued at 754 PM EDT Tue Sep 3 2019
We are watching for development on the cold front and it is
looking less and likely for severe storms. Actually it is becoming
questionable that there will be much in the way of thunderstorms.
I still think given the MU cape, and elevated mixed layer with a
shortwave moving through with the cold front it is still possible
a line of storms my form south or near I-94. No matter what this
should all be done by 10 pm.
&&
.DISCUSSION...(This evening through next Tuesday)
Issued at 308 PM EDT Tue Sep 3 2019
The atmosphere continues to gradually destabilize through mid
afternoon with a southwesterly flow advecting in considerable
moisture. The clouds have delayed/slowed the heating somewhat. At
the same time deep layer and low level shear were impressive. How
much if any severe weather we see will likely be determined by
the amount of destabilization from now until the cold front pushes
through this evening. Based on satellite imagery there will be a
window of an hour or two when decent destabilization could occur
just ahead of the cold frontal passage. HRRR does forecast surface
based CAPE values up over 2000 j/kg ahead of the frontal passage.
Even if we end up short of these values...given the strong shear
in place and lift with the wave moving in...a risk for severe
weather exists. Damaging winds...large hail and a risk for
tornadoes are possible.
By 10 pm the main area of instability should shift southeast of
the area. This is when I drop off the thunderstorm potential. A
much cooler airmass moves in overnight and into Wednesday. A few
showers could clip northern parts of the CWA late tonight.
A weakening wave of low pressure arrives for Thursday night into
Friday. We will only feature a low chance for a few showers given
the weakening trend noted in the models.
&&
.AVIATION...(For the 00Z TAFS through 00Z Wednesday evening)
Issued at 754 PM EDT Tue Sep 3 2019
The threat for severe storms has decreased but it is still
possible between now and say 02z that there could be a storm.
Whether or not that happens, there is an area of MVFR cigs near
the front. That will be cleared out by the front so by 04z or so
all TAF sites are VFR. There is a secondary surge of cold air that
will have an area of MVFR cigs with it and that moves through in
in the 12z to 16z time frame. After that enough cool dry air moves
in to once again clear the skies.
Winds will not be as strong behind the cold front as it was ahead
of the cold front, for the most part winds will in the 5 to 15
knot range Wednesday during the day.
&&
.MARINE...
Issued at 844 PM EDT Tue Sep 3 2019
I have downgraded our Gale Warning to a Small Craft Advisory since
we have not had gales since prior to noon. We have winds of 15 to
25 knots into mid morning Wednesday and with the cold air coming
in it makes sense to continue the Small Craft Advisory till late
afternoon. I through it good to keep the beach hazard and flood
advisory for the same time period.
&&
.GRR WATCHES/WARNINGS/ADVISORIES...
MI...Lakeshore Flood Warning until 4 PM EDT Wednesday for MIZ037-043-
050-056-064-071.
Beach Hazards Statement through Wednesday afternoon for MIZ037-
043-050-056-064-071.
LM...Small Craft Advisory until 4 PM EDT Wednesday for LMZ844>849.
&&
$$
MESOSCALE...WDM
UPDATE...WDM
SYNOPSIS...MJS
DISCUSSION...MJS
AVIATION...WDM
MARINE...WDM
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
620 PM CDT Tue Sep 3 2019
.MESOSCALE DISCUSSION...
500 PM CDT
Convective evolution continues to be monitored, with capping
from the morning convection and lingering clouds severely
impeding any mature development thus far. This will likely prevent
any rapid development and may very well keep any development that
can occur isolated, such as has been the case. A conditional
severe risk does exist though if any sustained mode can develop.
Convection in the southeast CWA over the past hour to hour and a
half will have moved mainly east of the area by 530 pm. This
activity is along an old outflow boundary and pseudo warm
front advancing higher theta-e air into the area. While this
convection has fair potential to be supercellular, it has
struggled to be mature and sustaining thus far, likely owing to
the cap.
Further northwest along the cold front -- our now best chance for
storms -- convection has been isolated in southern Wisconsin with
agitated cumulus struggling along the boundary. Aircraft
soundings from across northern Illinois and even into Wisconsin
show capping around 850 mb, that had weakened little since ILX`s
18Z sounding. In Wisconsin there are more noteworthy height falls
and associated cooling with the ascent that looks to only just
graze far northern Illinois. This is why we think development is
likely only to be isolated at least for the next few hours.
Observational trends indicate the front is slower than forecast
trends, and so did slow the forecast timing of chances slightly,
along with lower them some. The nature of development should
continue to be discrete given the orthogonal flow and shear with
respect to the front. Given the values of deep layer shear (50+
kt) and CAPE, including in the low-levels thanks to the high
moisture ahead of the front, supercellular mode is still favored
and a conditional severe threat if sustained enough. If convection
can grow more scattered into early evening as the front works
into eastern Illinois and northwest Indiana, it`s possible some
segments/clustering may develop and have a little more potential
for wind.
MTF
&&
.SHORT TERM...
300 PM CDT
Wednesday...
Primary concern for Wednesday will focus on winds.
As high pressure continues to slide into the Upper Missouri Valley
and the deep low and associated cold front continue to push to the
east, an area of moderate pressure rises and deep layer cold
advection will continue the strengthening north winds. the gradient
should be strongest over Lake Michigan and a little weaker over
land. So, while winds over land should remain in the 5-10 mph
range, winds over the lake should be in the 15 to 20 mph range, with
an occasional higher gust. Winds along the Lake County IL shore
should be mainly along shore while winds approaching the Cook County
and Lake/Porter Counties should be more directly on shore,
generating higher waves and a greater rip current threat. So, have
issued a Beach Hazard Statement for Cook County IL and Lake County
IN for the late morning through early evening hours and a bit longer
for Porter County IN, from early morning through early evening.
Otherwise, conditions Wednesday will be dry with below normal
temperatures. Lows in the morning should be in the middle to upper
50s, and low 60s for the Chicago area urban heat island. Highs
will, generally, be in the lower 70s, except along the lake where
temperatures should only reach the middle to upper 60s.
&&
.LONG TERM...
203 PM CDT
Wednesday Night through Tuesday...
Main weather concerns this period include a chance of showers and
storms with a cold front late Thursday and/or early Friday...
followed by a possible additional period of high swim risk at Lake
Michigan beaches Friday in the northeast flow behind the front.
Then possibly an unsettled pattern with periodic thunderstorm
chances Saturday night through Tuesday.
Sprawling high pressure moves overhead Wednesday night bringing
light winds and mainly clear skies along with very September like
temperatures with overnight lows in the upper 40s to lower 50s for
locations outside of the Chicago metro. Thursday sees a return to a
milder southerly flow but only marginally increased moisture ahead
of a cold front expected to move across the area late Thursday or
early Friday. Rain/storm chances are better north coincident with
stronger upper level forcing... with central and southern sections
of the CWFA quite possibly staying dry.
Northeast surface flow on the back side of this cold front may set
up yet another period of waves sufficient to produce a high swim
risk at Lake Michigan beaches before high pressure riding moves over
the area Friday night into Saturday.
Models then continue to diverge in solutions for Saturday night
through Tuesday with the GFS bringing a stronger area of surface
high pressure southeast out of the Canadian prairies and into the
northern Great Lakes Sunday into Monday. Meanwhile the Canadian
takes a more northward track of this high... and the ECMWF even more
so. Both hence shift the ribbon of shortwave energy in the
northwest flow aloft farther north... to include northern IL and
northwest IN. This would place the area under periodic chances of
thunderstorms Saturday night through Monday... until most of the
area comes under the warm sector with low pressure tracking along
the U.S.-Canadian border into the northern Great Lakes by late
Tuesday. Will continue to carry low pops in the forecast pending
further inter-model consistency.
Ed F
&&
.AVIATION...
For the 00Z TAFs...
The primary aviation weather concerns through the period revolve
mainly around a brief window of TS potential with a cold front
followed by breezy northwesterly winds. A cold front is about to
pass through RFD and will be through ORD and MDW around 0130 and
0200 respectively. Recent AMDAR soundings out of ORD and MDW
indicate capping remains in place with a plume of warm air in the
850-700 mb layer. Thus far, convection near the state line has
struggled to maintain itself in this very strongly sheared and
capped environment. However, the Cu field remains agitated
entering our CWA, and RAP forecast soundings reveal a rather quick
lifting/cooling of the aforementioned warm nose shortly after 00z
as the front makes its approaches to the Chicago-area terminals.
As a result, convective initiation remains possible, although
still conditional on erosion of the remaining warm layer just off
the surface. It may be that storms begin to initiate more
cohesively as the front begins to pass the Chicago area terminals
as better height falls overspread the region through the mid-
evening hours. As a result, will be maintaining a VCTS mention at
ORD, MDW, and DPA up through FROPA, and will continue a TEMPO for
TSRA at GYY. Any TS potential should be relatively short-lived,
however, as much drier air will invade the region quickly behind
the front. Northwesterly breezes will gradually abate through the
night, with winds trending to light northerly on Wednesday. A
modest push off the lake will turn the winds more northeasterly at
ORD and MDW through the afternoon.
Carlaw
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Beach Hazards Statement...ILZ014...11 AM Wednesday to 7 PM
Wednesday.
IN...Beach Hazards Statement...INZ001...11 AM Wednesday to 7 PM
Wednesday.
Beach Hazards Statement...INZ002...7 AM Wednesday to 7 PM
Wednesday.
LM...Small Craft Advisory...nearshore waters
until 10 PM Wednesday.
&&
$$
VISIT US AT HTTP://WEATHER.GOV/CHICAGO (ALL LOWERCASE)
FOLLOW US ON FACEBOOK...TWITTER...AND YOUTUBE AT:
WWW.FACEBOOK.COM/NWSCHICAGO
WWW.TWITTER.COM/NWSCHICAGO
WWW.YOUTUBE.COM/NWSCHICAGO
Area Forecast Discussion
National Weather Service Blacksburg VA
737 PM EDT Tue Sep 3 2019
.SYNOPSIS...
High pressure will remain over the area into tonight resulting
in continued fair weather across the region. A cold front
approaches from the northwest Wednesday before passing to the
southeast Wednesday night into Thursday. Hurricane Dorian will
move slowly up the southeast Atlantic coast into Thursday night
before exiting the Outer Banks on Friday.
&&
.NEAR TERM /THROUGH WEDNESDAY/...
As of 230 PM EDT Tuesday...
High pressure across the region should continue to maintain quiet
weather into the overnight under dry air aloft. This may again allow
temperatures to fall below guidance espcly given dry soil conditions
with some 50s in the valleys where likely to again see some patchy
dense fog late. Otherwise mostly clear and a bit more muggy east
where lows should mainly be in the 60s.
Surface high weakens on Wednesday in response to a passing weak
upper trough to the north. This feature should push a surface cold
front toward the area by late in the day preceded by westerly flow
and quite a warm airmass. This combined with subsidence well to the
north of Dorian and lack of much moisture ahead of the boundary
should limit convective coverage during the day. Appears best weak
convergence will develop over far northwest sections where isolated
coverage could occur espcly late, so only running with 20/30 pops as
supported by most short term guidance. Elsewhere expect downsloping
and lack of moisture to preclude chances with overall mostly sunny
skies outside of perhaps more mid/high clouds sneaking into eastern
sections by late afternoon. Should be quite hot for early September
given +21 deg/C at 85h which will be aided by westerly flow
compression and heating resulting in 80s to perhaps a few 90s out
east.
&&
.SHORT TERM /WEDNESDAY NIGHT THROUGH FRIDAY NIGHT/...
As of 300 PM EDT Tuesday...
Wednesday evening a cold front is expected to enter and cross into
our region. However, it and its associated showers will be
encountering significant subsidence on the north side of Hurricane
Dorian. This subsidence will have the impact of squelching any
substantial convection along it with any activity confined to
isolated coverage mainly over western and northern parts of the
forecast area.
The latest forecast cone from the National Hurricane Center still is
leaning towards a solution that greatly limits Dorian`s impact from
a precipitation and wind stand point across our region during the
Thursday and Thursday night time frame when Dorian makes its closest
approach to our area, just off-shore the NC/SC border. Any impact
still looks to be across the far southeastern portion of the
forecast area as Dorian`s precipitation shield skirts the area with
perhaps up to one or two tenths of an inch of rain in areas south
and east of Danville, VA. This same area also has the potential for
the strongest winds gusts which are in the neighborhood of 30 to 35
mph. Of course with any tropical system, a shift in the forecast
track would yield different results. A westward trend would yield
more rain and wind to a greater geographical portion of the area,
and likewise an eastward shift, lesser of an impact to the area.
Folks are encouraged to monitor the latest on Dorian as provided at
www.nhc.noaa.gov.
Another area Thursday where we will need to watch for precipitation
is far southwest Virginia, south into the Northern Mountains of
North Carolina. Here the presence of an increasing northeast flow
will yield enough of an upslope component such that moisture
advection in that area will be realized in the form of some isolated
to scattered showers and storms.
By late Thursday night into Friday, Dorian will be farther away,
near the Outer Banks of NC and the pressure gradient across the
area will already be weakening, yielding decreasing wind gusts.
Friday will start cloudy for most of the area, but trend to
mostly sunny to sunny by the afternoon. Skies will remain clear
into Friday night, and winds will trend to light and variable
conditions.
&&
.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 130 PM EDT Tuesday...
Synoptic flow will trend to a zonal orientation this weekend with
geopotential heights increasing slightly. A shortwave trough is
expected to cross the region late Sunday afternoon and evening
within this zonal flow. Temperatures are expected to be at or
slightly above normal. Precipitation chances are minimal, with only
isolated showers across central or eastern parts of the region late
Sunday afternoon and evening.
Monday into Tuesday, an upper level ridge is expected to start to
develop across the Ohio Valley in response to a notable trough
deepening across the Northern Plain States. The center of surface
high pressure will shift east of our region, thus helping to bring
low level winds around to a southerly orientation. This orientation
will help advect moisture back into the region, enough to help with
the development of isolated to scattered showers for the area on
Monday, and to a slightly greater extent for Tuesday. Temperatures
will average reading around normal for this time of year.
Confidence in this portion of the forecast is moderate to high.
&&
.AVIATION /00Z WEDNESDAY THROUGH SUNDAY/...
As of 735 PM EDT Tuesday...
Skies should clear with loss of heating this evening with some
late night fog possible espcly in the valleys and briefly out
east. Higher confidence again for LIFR or worse at KLWB and at
least MVFR at KBCB. May also see KDAN/KLYH drop down into MVFR
for an hour or two toward daybreak.
High pressure will weaken ahead of an approaching cold front
from the northwest Wednesday afternoon. However still expecting
VFR with any isolated convection confined mostly to the far
northwest and late in the TAF period. Thus wont include any
vicinity mention at this point with mainly scattered to broken
cumulus during the day once any early low clouds/fog burn off.
Winds turn west to southwest ahead of the boundary but overall
in the 5-15 kt range.
.Extended Aviation Discussion...
VFR conditions should generally remain intact for the remainder
of this week aside from any nighttime fog or clouds. While the
latest model guidance keeps Dorian well off to our east, there
still may be enough wind to affect aircraft operations by
Thursday. A few showers may also impact areas near and southeast
of KDAN later Thursday where brief sub-VFR could occur. Aviation
interests should monitor the progress of Dorian closely for the
next several days. VFR conditions will prevail Saturday.
&&
.RNK WATCHES/WARNINGS/ADVISORIES...
VA...None.
NC...None.
WV...None.
&&
$$
SYNOPSIS...JH/RCS
NEAR TERM...JH
SHORT TERM...DS
LONG TERM...DS
AVIATION...BMG/JH