Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 03/12/23
Area Forecast Discussion
National Weather Service Indianapolis IN
1047 PM EST Sat Mar 11 2023
...Updated Aviation Discussion...
.Forecast Update...
Issued at 924 PM EST Sat Mar 11 2023
This evening, radar continued to show echoes across much of the
western half of the area. ACARS sounding from Indy shows a very dry
layer below the mid levels, so not much is reaching the ground.
Upstream observations show rain as the precipitation type across
much of Illinois, with some snow in western Illinois and northern
Missouri.
Believe the system tonight will play out as expected, so not
making much change to the forecast. Isentropic lift will ramp up
overnight as the system moves in. Rain will be the primary type at
first, but as evaporative and dynamic cooling occur, precipitation
will change to snow across the northeast half of the area with a mix
then rain farther southwest.
Potential loss of ice in the cloud later tonight could lead to snow
mixing with or changing to drizzle across the area, but surface
temperatures are expected to remain above freezing.
Still expect snowfall amounts of 0.5-1.5 inches across the northeast
half of the area. Exactly where the heaviest amounts will fall will
depend on where some frontogenetical forcing sets up some banding.
&&
.Short Term...(This evening through Sunday)
Issued at 240 PM EST Sat Mar 11 2023
Stratocu that was prevalent throughout the morning across parts of
the area has largely mixed out over the last few hours...allowing a
filtered sun to return with mid and high clouds quickly
overspreading the forecast area. 18Z temperatures were mostly in the
40s with a cool E/SE wind.
The focus for the short term will be on the two pronged system
poised to move across the region tonight into Sunday. Two surface
waves within the polar and subtropical jet streams respectively will
track east into the day Sunday. The northern low will move from the
northern Plains into the western Great Lakes while the southern low
tracks from the southern Plains into the Tennessee Valley. These two
lows will eventually phase as a strong upper low dives into the
Great Lakes early Monday and prompts an amplification of an upper
trough across the eastern US. A broad area of moisture advection
between both surface lows will expand northeast into the Ohio Valley
tonight into Sunday morning bringing a late season touch of winter
as snow becomes the primary precip type across the northeast half of
the forecast area.
For the rest of this afternoon...cloud coverage will steadily
increase as rain over Missouri lifts northeast. There is a chance
the leading edge of the rain could make it into the lower Wabash
Valley prior to 00Z but the dry air present over the region
currently will stunt top down saturation at least initially.
Gradually...the boundary layer will moisten through the evening with
rain becoming widespread across much of the forecast area prior to
midnight. May see a few wet snowflakes mix in by late evening over
the northeast half of central Indiana.
After midnight...precipitation type will become a bigger factor with
continued dynamical cooling processes ongoing and temps slipping to
below freezing through the lower levels. This will change the
predominant precip type over to snow for most of the forecast area
along and NE of I-74 but recent trends have suggested snow is likely
to mix in or become the main precip type at times as far south as a
Sullivan-Bedford line during the predawn hours and through daybreak.
The heaviest precipitation will fall between 06-12Z as the deepest
moisture aligns with strong isentropic lift noted on the 285 and
290K levels. Snow will be the main precip type for the northeast
half of the forecast area during this timeframe...but there are
multiple factors in play that would suggest accumulation potential
will largely underwhelm. The first issue is the dendritic growth
zone...which is narrow aloft and at times...above the level of
deepest moisture. This is likely to result in a chaotic nature to
snowfall rates that may be briefly heavier but not able to sustain
intensity for any length of time.
And that leads into the second and bigger issue which is surface and
road temperatures. Road surface temp forecasts courtesy of the METRo
model suggest road temps may briefly get to near freezing across the
area and likely get no colder than the mid 30s in spots late tonight
and early Sunday. Further analysis of the road subsurface temps
paint an even bleaker picture from an accumulation efficiency
standpoint...dropping no lower than the upper 30s. These numbers are
not conducive to much if any snow accumulation on roadways late
tonight with accums being confined to elevated and grassy surfaces.
Even there...the marginal air/surface temps combined with snowfall
rates that will be steady to light through much of the event will
lead to melting of the snow as it accumulates.
Considering all of the above...pulled back on model guidance snow
ratios which are too high. This lowered expected snowfall totals as
a result...with the expectation of up to 1-1.5 inches for much of
the northeast half of the forecast area with lighter amounts to the
southwest of a few tenths. Could see a few spots with higher amounts
up to 2 inches or so. With little impact expected for travelers
overnight and Sunday morning...have no plans to issue a Winter
Weather Advisory. An SPS for light snow accumulations will suffice.
Precipitation will become more scattered into Sunday afternoon
before diminishing to a few flurries/sprinkles later in the day as
surface ridging attempts to build in from the south. A sharp
boundary layer inversion will keep skies cloudy and gray all day
with a cold wind backing from easterly to northerly.
Temps...lows will fall into the low and mid 30s from north to south
tonight. Undercut guidance again for Sunday which appears too warm
considering the lingering thick clouds. Low level thermals support
upper 30s to lower 40s for much of the forecast area.
&&
.Long Term...(Sunday night through Saturday)
Issued at 240 PM EST Sat Mar 11 2023
Sunday Night Through Tuesday.
By Sunday night the bulk of the forcing associated with the Saturday
night/Sunday system will have exited, but moving in quickly behind
it will be a much deeper closed low. The low will track through
Minnesota into Michigan late Sunday night into Monday with little
local impacts other than a renewed shot of cold air, continued
cloudy skies, and brief light snow showers.
Temperatures Monday will struggle to get out of the mid 30s with
continued below normal temperatures into Tuesday. Strong
northwesterly flow will continue into Tuesday both at the surface
and aloft with non-zero instability due to the magnitude of the cold
in the mid levels. This will allow for additional isolated snow
showers during the daytime hours with some locally heavier showers
in lake enhanced bands.
Wednesday Through Saturday.
The pattern will then shift going into Wednesday with a brief period
of stronger ridging across the Central United States along with a
return to southerly surface flow which will help push temperatures
back into the low 60s by Thursday. This warmer period will be brief
though as a large and strengthening low pressure system builds and
pushes into the area Friday into Saturday.
Precipitation will begin during the daytime hours on Friday along a
frontal boundary that will stretch from Southern Canada into the
Deep South. Central Indiana will be within the warmer sector of the
system with precipitation type being all rain Friday, but colder air
and backend forcing may allow for some snow late Friday night into
Saturday.
&&
.Aviation...(06Z TAF Issuance)
Issued at 1047 PM EST Sat Mar 11 2023
Impacts:
- IFR conditions 07z-17z with improvement to MVFR after
- Rain will change to snow at KIND/KLAF after 07z, otherwise
rain at KBMG and KHUF. Precipitation will only be sprinkles
or flurries after 18z
- Winds 070-100 degrees 10 knots or less switching to 280-330
degrees after 18z. Gusts to 20 knots developing after 03z
Monday
Discussion:
Poor flying conditions overnight into Sunday morning in light
rain showers with snow or a Wintry mix at KIND and KLAF. Flying
conditions will improve to MVFR this afternoon as the precip ends
or becomes only sprinkles or flurries.
Winds will be east to 10 knots but then shift to the northwest this
afternoon. Meanwhile, gusts to 20 knots are expected late Sunday
night.
&&
.IND WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
Update...50
Short Term...Ryan
Long Term...White
Aviation...MK
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
855 PM CST Sat Mar 11 2023
.UPDATE...
Issued at 849 PM CST Sat Mar 11 2023
Light to moderate snow has just about filled in across the
northern part of the CWA, namely areas north of I-80. Webcams
across the Rockford metro and vicinity show snow accumulating on
cooler surfaces and even a few roads are beginning to gather a
dusting. Further south, we`re seeing light rain and rain/snow mix
filling in where there`s just enough positive energy above the
surface to melt the snow on its way down. As we continue to cool
both diurnally and dynamically with still a little bit of room
between temps and wet bulbs, we should see the rain/snow line drop
south through the remainder of the evening and into the
overnight. Additionally, many areas across the metro have been
struggling with some dry air through roughly the 800-900mb layer
inhibiting precip aloft from reaching the ground over the past
couple of hours. However, ACARS soundings out of MDW show that
we`ve recently managed to overcome that thanks to modest, albeit
ample, low level warm advection, a tad earlier than RAP and HRRR
soundings were suggesting we would. RAP mesoanalysis places a
notable swath of 700mb f-gen over the central and western CWA on
the leeward side of the encroaching trough which lines up well
with where we`ve been seeing the more moderate snowfall which has
been pulling visibilities down as low as one mile here and there.
This f-gen is expected to continue pushing to the northeast with
the trough through the rest of this evening. The better synoptic
forcing will also eject to the northeast as the trough axis
approaches meaning we`ll likely see the heaviest of the snow over
the next few hours. Snow is still expected to continue through
the night but will lighten up as forcing lets up and we maybe see
little bit of dry advection near 925mb, or so the RAP and HRRR say
though it`s tough to nail down where that`s coming from. All in
all, the forecast through the night looks to be on track.
Doom
&&
.SHORT TERM...
Issued at 308 PM CST Sat Mar 11 2023
Through Sunday night...
A pair of upper level disturbances are noted in the water vapor
imagery across the Plains early this afternoon. The first of
these is currently shifting eastward into the Lower to Mid-
Missouri Valley, while a more pronounced northern stream upper
low is moving eastward into western North Dakota. These features
will play a large role in our sensible weather tonight through
early Monday.
While cloud cover has been, and will continue to be persistent
through the day, warm air advection in advance of the approaching
Mid-Missouri Valley disturbance is helping drive temperatures
well into the 30s (with some low 40s south) as of this writing.
Expect these readings to hold steady in the 30s to around 40 into
early this evening. Precipitation is expected to hold off across
the area through late this afternoon. Thereafter, we should see
the warm air advection driven precipitation shield across IA
steadily translate eastward across the area through the evening
in concert with the parent mid-level disturbance.
While the entire area looks to see precipitation from this event
tonight, overall amounts will be much lower than they were with
Thursdays weather system. However, precipitation types do look to
be a bit tricky again with this event, especially for areas south
of I-80, where warmer boundary layer conditions will reside into
early this evening. These slightly warmer conditions will likely
result in areas south of I-80 onsetting as a period of rain for a
few hours this evening before potentially mixing with a bit of wet
snow later in the evening. Farther to the north, a brief rain
snow mix is possible at onset, but slight cooler conditions should
support primarily wet snow shortly after onset. While some wet
snow accumulations still appear likely tonight, especially for
northern areas, light precipitation rates and marginal surface
temperatures should keep total amounts mainly under 2". In fact,
many areas are likely to see less than an inch, and mainly on
grassy and elevated surfaces!
The main mid-level disturbance (the primary forcing mechanism) is
expected to shift east of the area a bit after midnight tonight.
As it does so, a much drier mid-level airmass is expected to shift
overhead atop a lingering low-level moist layer. In spite of this,
light precipitation is likely to continue across the area overnight
as low-level isentropic upglide continues in this moist layer in
response to the northern stream system shifting into the Upper
Midwest. While precipitation type may continue to support some
light snow overnight, there is concern that the snow quality will
become rather poor overnight, possibly even mixing with (or
changing to) drizzle at times as the much drier mid-level airmass
shifts overhead. This suggests that any additional snow
accumulations late tonight into early Sunday morning may become
minimal.
The lower level moist layer should become deep enough across far
northern IL to support a continued period of snow showers mid to
late Sunday morning as low-level warm air advection
continues. While this is the case, marginal surface temperatures
during the daylight hours will once again limit any minor slushy
accumulations to grassy areas and elevated surfaces. Temperatures
should warm close to 40 early Sunday afternoon, so any lingering
precipitation there will likely fall as light rain. Late in the
day and into the early evening hours, the northern stream system
is expected to drive a cold front eastward across the area. This
may result in a quick moving area of rain and snow showers as the
front interacts with a corridor of steep low-level lapse rates.
Certainly cannot rule out some minor accumulations with this
across parts of northeastern IL, especially if a brief period of
heavy rates materialize, but the main limiting factor for much in
the way of accumulation will be the warm surface temperatures
preceding the front.
Another period of possibly more robust snow showers looks
possible either very late Sunday night, or early Monday morning as
a secondary cold front and an attendant mid level disturbance
drops southward across the area. This potential will have to be
monitored as it could occur during the early Monday morning rush.
KJB
&&
.LONG TERM...
Issued at 221 PM CST Sat Mar 11 2023
Monday through Saturday...
Highlights for the long term forecast period:
* Lingering isolated/scattered snow showers and flurries on Monday
* Unseasonably chilly for the first half of the upcoming workweek;
milder heading into the latter half of the week
* Precipitation likely to return to the area Thursday and/or Friday
The vort max responsible for our late Sunday afternoon and Sunday
night precipitation chances will likely be centered over or near the
southern half of Lake Michigan come Monday morning. This feature
will continue to wander off to the southeast throughout the day on
Monday, and our forecast area will spend the day entrenched within a
cold cyclonic flow regime as the associated low pressure centers at
the surface and aloft remain east of our longitude. The ensuing cold
air advection should ensure that skies remain overcast or mostly
cloudy throughout the day and that high temperatures won`t make it
out of the 30s. Low-level lapse rates will also steepen in response
and should bring about some blusterier conditions for the morning
and afternoon hours on Monday with regular north-northwesterly
gusts into the 20-30 mph range appearing to be likely.
The main question forecast question for Monday is whether there will
be any additional snow showers lingering around and what the nature
of those showers would be like, in terms of both coverage and
intensity. The present thinking is that the residual forcing
associated with the mid/upper-level trough and the steepening low-
level lapse rates should be just enough to support isolated to
scattered snow shower activity in our forecast area on Monday, but
that the relative absence of quality moisture and the overall
magnitude of the forcing at play should limit impacts to just
occasional brief visibility reductions beneath the more coherent
snow showers and perhaps some streaky dustings or coatings of snow
occurring on colder surfaces. The exception to this could be in
portions of northwest Indiana, where marginally favorable lake
effect parameters may be able to support a longer duration snow band
or two that could leave behind a narrow corridor of 1+" of snow on
the ground when all is said and done. However, this is a low
confidence scenario at this vantage point. Considering everything
altogether, maintaining slight chance and chance PoPs across most of
our CWA in lieu of the lower NBM PoPs seemed warranted at this time.
Even if true snow showers didn`t materialize, think that some
flurries may still be wrung out of the overhead stratocumulus deck
over at least a portion of our forecast area on Monday.
The magnitude of cold air advection should wane Monday night, but
there appears to be a decent chance that the low cloud cover
overhead will scatter out to some extent. Low temperatures appear
likely to at least dip into the 20s either way, and if skies do
clear out, then lows in the teens appear very attainable, at least
across interior northern Illinois. High pressure will build into the
region on Tuesday, and while clear skies should allow temperatures
to bounce back a bit, the relatively cold starting point and
marginally cold to neutral thermal advection should still keep
Tuesday`s highs below normal for this time of year. Return flow on
Wednesday will then kickstart the return of warm air advection,
which will be further prolonged into Thursday as a developing
surface low over the Great Plains maintains poleward low-level
thermal and moisture trajectories to its east. A return of 50+
degree temperatures thus appears likely for most or all of our
forecast area on Wednesday and/or Thursday, and it would not be
surprising for some 60+ degree readings to be seen on Thursday as
well if the aforementioned low pressure system is not as progressive
as the fastest ensemble solutions currently suggest (most 12Z
guidance was not that progressive with this system).
The aforementioned developing low pressure system will be spawned as
northern stream and southern stream waves embedded within western
CONUS longwave troughing interact with one another Wednesday into
Thursday. Some forecast guidance is suggesting that these two waves
will phase nicely, culminating in a closed-off upper-level low that
will spiral over the Great Lakes as we head into next weekend. Other
guidance suggests that there won`t be much of any phasing between
these two waves, and whatever low pressure system develops won`t
hang around very long after passing through our area. Either way,
the odds of rain occurring here sometime in the Thursday through
Friday time frame look fairly good for a system that`s still 5-6
days away. Snow can`t be ruled out on the backside of this system,
especially if a closed low does come to fruition over the Great
Lakes, but this is still a lower confidence forecast item that,
along with the finer details of the earlier rainfall, will become
clearer in the coming days as additional forecast guidance continues
to come in.
Ogorek
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Snow develops this evening, with a period of IFR vis and minor
accumulations overnight. IFR ceilings linger at least into
Sunday morning before improvement to MVFR.
* Snow tapers off by morning and likely becomes a mix of snow and
drizzle. Period of heavier convective rain/snow showers possible
in the afternoon.
* East winds tonight become southeast Sunday morning, then south
briefly Sunday afternoon ahead of a cold front. Winds shift west
behind that front Sunday evening, with some gusts around 20 kt.
Light snow will spread across the area this evening as a mid-
level disturbance currently over IA approaches. There could be a
very brief rain/snow mix as precipitation begins, but should
change to all snow fairly quickly as intensity picks up. The
strongest forcing looks to be from late evening to past midnight,
when IFR visibility and minor accumulations are likely. Weakening
ascent and decreasing saturation in favored snow-growth
temperature levels suggests snow will weaken in intensity by the
pre-dawn hours, with visibilities improving to MVFR. Moist low
levels will likely maintain IFR ceilings into Sunday morning
however.
A second upper trough over the upper Midwest will maintain weaker
forcing across the region through the day Sunday, with lighter
intermittent light snow/flurries. Several models indicate loss of
saturation in the ice-bearing thermals range and thus may see a
mix of light snow and drizzle especially during the midday and
afternoon hours. A period of heavier snow/rain showers is possible
during the mid-late afternoon hours, as low-level lapse rates
steepen ahead of an approaching cold front. Scattered snow showers
may persist behind the front Sunday evening, though with low
confidence in coverage, as somewhat drier air spreads in.
Easterly winds tonight will turn southeast Sunday morning, then
light southerly ahead of the cold front during the afternoon.
Behind the front, winds will shift to the west-northwest, and
will become somewhat blustery with gusts around 20 kts.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...None.
IN...None.
LM...None.
&&
$$
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