Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 02/20/19
Area Forecast Discussion
National Weather Service Columbia SC
1020 PM EST Tue Feb 19 2019
.SYNOPSIS...
A wet pattern will occur through the week. A continued southwest
upper flow, with a series of embedded upper disturbances and
resultant surface waves, combined with abundant atmospheric
moisture will bring rain at times. A cold front will cross the
area Sunday with dry high pressure returning Monday.
&&
.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
High pressure will continue to ridge into the forecast area
from the north through tonight. Cold air damming wedge in place.
Model and ACARS soundings along with radar data suggest
deepening warm nose across the area. Temperatures in the mid 30s
to low 40s. Little change in temperatures expected overnight.
Light rain and drizzle across the region this evening. Latest
models suggest light rain in the low country lifts north as
moisture flux/isentropic lift increases during the overnight.
Will continue high pops mainly late tonight.
The NAM, GFS, ECMWF, plus SREF guidance indicate rain amounts
less than one-quarter of an inch. Models indicate some wind
overnight, mainly from 8 to 12 mph with a few higher gusts from
time to time. Models suggest a strong low level jet possible
above the inversion overnight.
&&
.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
Surface high pressure will continue to wedge in from the north
for the majority of the day on Wednesday. The southern/eastern
edge of the wedge front is expected to be close to the border of
the forecast area through the day. The exact position of this
boundary will be the overall determining factor across the south
and east in regards to whether temperatures there climb out of
the 50s. At this time it appears as if the boundary will remain
just outside the cwa, so have only brought temps into the
mid/upper 50s in those extreme southeastern locations. The
remainder of the cwa will remain strongly entrenched in the
wedge during the day, with temperatures mainly in the 40s. Rain
chances remain high during the daytime hours, but the rainfall
amounts will be on the light side. May be a mixture of light
rain/drizzle.
To start off Wednesday night, the area will still be in the
wedge. As the night goes on, guidance is indicating that the
surface wedge will be breaking down and lifting out as the
center of the surface high moves offshore and a cold front
approaches from the west. Light rain/drizzle will still be
common over the area as this wedge retreats and the main surface
cold front the moves into the area. Temperatures will start off
on the cold side, then as the wedge retreats, readings should
actually rise late Wednesday night into Thursday morning.
The cold front will then be pushing through the area Thursday
before stalling out south of the cwa Thursday night.
Temperatures during the day rebound nicely even though the cold
front will move through. Readings into the lower/middle 60s
north, to the lower to middle 70s south where the colder air
behind the front will lag. Rain chances continue both during the
day and overnight Thursday due to the vicinity of the cold
front.
&&
.LONG TERM /FRIDAY THROUGH TUESDAY/...
Not a whole lot of changes in the longer term. Rain will
continue off and on for much of the weekend. Yet another front
should move through the area during the afternoon/evening on
Sunday, continue rain chances ahead of the boundary. Behind this
weekend front, a drier airmass is expected to finally arrive to
start off next week.
Temperatures in the longer term remain tricky due to the potential
for additional weaker cold air damming to move back into the
area at Friday/Saturday. Went generally with a model blend for
temperatures through the period.
&&
.AVIATION /03Z WEDNESDAY THROUGH SUNDAY/...
VFR conditions initially...lowering to MVFR/IFR overnight.
Cool high pressure ridge nosing into central SC and the CSRA.
This will remain in place through the next 24 hours as a series
of upper level troughs pass overhead. Winds above the low-level
inversion will shift southeast overnight, bringing warmer air
and moisture over the cooler dome at the surface. Coupled with
at least 2 upper-level troughs...high confidence ceiling
heights will lower to MVFR after 03-04Z and become IFR after
09-12Z. Visibilities will gradually lower as moisture increases
due to rain falling through the cool layer aiding saturation and
fog formation. Moderate confidence for IFR conditions to remain
through 18Z and beyond as the surface ridge slowly breaks down
and warm frontal overrunning remains in place. LAMP and other
model guidance is in good agreement. Expect LLWS to develop
after 03-04Z as winds just above the inversion increase in
response to an upper level trough approaching. Low-level jet is
expected to be between 35-40 kts through 15Z.
EXTENDED AVIATION OUTLOOK...Precipitation and flight restrictions
are expected at times through Saturday as a series of weather
systems move through or near the area.
&&
.CAE WATCHES/WARNINGS/ADVISORIES...
GA...None.
SC...None.
&&
$$
SYNOPSIS...99
NEAR TERM...99
SHORT TERM...99
LONG TERM...99
AVIATION...99
Area Forecast Discussion...UPDATED
National Weather Service Fort Worth TX
947 PM CST Tue Feb 19 2019
.UPDATE...
Quick update to remove the mention of thunder from the rest of the
overnight grids and to trim PoPs back based on latest radar and
satellite trends.
Mid-evening water vapor loops show the mid-level dryslot has
blasted through our entire CWA which has shunted the reservoir of
deepest moisture off to our east. Recent ACARS soundings show that
we`re still saturated up to about 800 mb, and this is probably
just deep enough to support some episodic bouts of drizzle as the
last shortwave/vort max (seen on water vapor loops impinging on
the I-35 corridor) pivots through the region. With the loss of
deeper moisture, the steeper lapse rate plume above 700 mb should
be out of reach, so the risk for thunder is rapidly diminishing
across our eastern-most counties. Sub-freezing surface
temperatures will lag far enough behind this last shortwave to
preclude any issues with patchy freezing drizzle in our western
and southwestern counties overnight.
While we may see some 1-3 mile visibilities in any heavier
drizzle, don`t envision widespread dense fog issues overnight with
additional high-level moisture streaming overhead after midnight
and decent westerly flow in place just off the surface. We`ll keep
a close eye on observations, however. Updated products have been
transmitted.
Carlaw
&&
.AVIATION... /Issued 555 PM CST Tue Feb 19 2019/
/00z TAFs/
Poor flying conditions will persist this evening, but
improvements are anticipated late tonight and into Wednesday
morning as drier air filters into the region.
Early-evening water vapor loops reveal the mid-level dryslot
associated with this latest storm system pivoting into the I-35
corridor. Associated drying above 750 mb will result in saturated
depths steadily decreasing over the next few hours at our TAF
sites. Lingering lift from a couple straggling shortwaves will
allow for some light precipitation for a few more hours, but the
loss of moisture above 10 kft will result in a transition to
periodic bouts of light drizzle.
As westerly flow deepens overnight, cigs should improve first at
Waco as the initial dry air intrusion sweeps into parts of Central
Texas. The Metroplex TAF sites should take a bit longer to clear
out, but should return to VFR towards the 13-15z timeframe. With
plentiful near-surface moisture in place, the potential for fog
development is non-zero. However, the combination of modest
westerly flow just off the surface and increasing mid-high cloud
cover should temper this possibility. If low clouds clear out
earlier than expected and incoming cirrus is slower to arrive, the
fog potential would increase. We`ll continue to monitor
observations this evening, but the potential for additional
IFR/LIFR vsbys reductions after 09-10z is too low to mention
explicitly in the current TAFs.
VFR conditions will prevail from mid-morning Thursday and onwards.
Surface winds will eventually become southeasterly late Thursday
afternoon and evening.
Carlaw
&&
.SHORT TERM... /Issued 342 PM CST Tue Feb 19 2019/
/Tonight/
Showers and isolated thunderstorms will shift steadily eastward
through the evening as the upper trough axis swings through the
region. We will maintain the highest PoPs across the eastern
zones, mainly though mid evening. All precipitation will end
overnight with increasing large scale subsidence on the backside
of the departing system. Although drier air will work in from the
northwest, clouds will be slow to clear due to the depth of the
moisture. Therefore, dense fog formation is unlikely even though
the ground will remain near saturation and wind will be fairly
light. The clouds will also keep temperatures from falling rapidly
so overnight lows should remain in the 30s.
79
&&
.LONG TERM... /Issued 342 PM CST Tue Feb 19 2019/
/Wednesday through the Weekend/
The main concern in the extended forecast will be the potential
for thunderstorms, mainly across Central and East Texas.
Otherwise, expect generally temperate conditions across the
region.
Dry northwest flow will continue to overspread much of the region
on Wednesday morning which should erode the pesky deck of stratus
that has been in place. NAM forecast soundings do hint at the
potential for some patchy drizzle/fog in the morning hours, but at
this time, the potential looks low with west flow expected.
Wednesday should be rain-free and low clouds will be shunted
eastward. It won`t be nearly as cool with west winds helping to
promote some downsloping. A dense cirrus canopy will stream in
from the southwest which will result in partly sunny skies for
most of the area.
Return flow should establish itself as upper level troughing
induces lee-side cyclogenesis to the northwest late Wednesday and
into Thursday. At this time, most of the pre-dawn hours on
Thursday should remain rain-free, but that will likely change very
quickly after sunrise. Isentropic ascent should ramp up quickly
and with steepening lapse rates (nearly 7-8 C/km), there will be a
risk for some elevated thunderstorms. With the deep layer wind
shear magnitudes on the order of 30 knots, there could be a window
elevated storms capable of hail. We`ll monitor this potential
over the next 12-24 hours.
Warm air advection will increase even more on Friday, which
should yield additional chances for showers and a few
thunderstorms. I`ve undercut blended guidance rain chances a
little as most of the strong forcing for ascent should still
remain west of the area, but given the strong WAA and steep lapse
rates, a 50-60 PoP across at least the eastern 2/3rds of the area
seems appropriate. The severe weather potential isn`t great on
Friday as instability may still remain on the marginal side. If
instability values are a little higher than currently believed,
the risk will increase.
Saturday features the best chances for showers and thunderstorms
as a sharp Pacific frontal feature slides eastward. Model guidance
has converged some on the position of an upper level low and this
yields slightly greater confidence in the positioning of the
aformentioned frontal feature. At this time, it appears that the
upper trough will eject quicker to the east than previous model
iterations and this casts some doubt on the severe weather
potential. I`ll hold on to PoPs across the entire area, but if
these trends continue, we may be able to remove rain chances for
the Big Country all together on Saturday. Low level moisture will
stream northward after a couple of days of good southerly flow.
and this should boost instability values into the 1000-1200 J/kg
range. With a very dynamic upper trough, deep layer shear values
will easily exceed 30 knots and the combination of the
aformentioned instability will promote organized convective modes.
There are a couple of caveats that preclude "sounding the alarm"
right now. 1) A faster frontal timing would mean that convection
would possibly fire at a less than ideal time of day for North and
Central Texas (smaller amounts of surface based instability). 2)
The widespread cloud cover and possibly early day convection (due
to a strong cap) could hamper afternoon storm development and/or
diminish instability necessary for severe storms. While it is a
little too early to nail down the specifics surrounding the
thermodynamic environment currently, it is likely that these
details will be ironed out in later forecasts.
Behind the front, there should be decent west winds and with a
greater degree of vertical mixing, temperatures should easily
climb into the mid to upper 60s with low relative humidity.
Depending on the areal coverage of rainfall over the next several
days, a slightly elevated fire weather threat may materialize.
Sunday will be a little cooler as we lose some of the downsloping,
but conditions look to still remain seasonal. Low rain chances
re-enter the forecast next week as return flow establishes itself
across the region.
Bain
&&
.PRELIMINARY POINT TEMPS/POPS...
Dallas-Ft. Worth 34 56 40 56 45 / 10 0 5 10 20
Waco 33 59 37 56 46 / 60 0 5 20 30
Paris 34 51 36 54 42 / 100 0 5 20 20
Denton 31 55 36 56 43 / 10 0 5 10 10
McKinney 32 53 36 55 43 / 20 0 5 20 20
Dallas 36 56 40 56 45 / 40 0 5 10 20
Terrell 35 54 38 55 44 / 100 0 5 20 20
Corsicana 36 57 41 55 47 / 80 0 5 30 30
Temple 34 60 39 56 47 / 20 0 5 20 30
Mineral Wells 31 57 37 57 44 / 10 0 5 5 10
&&
.FWD WATCHES/WARNINGS/ADVISORIES...
None.
&&
$$
90/26
Area Forecast Discussion
National Weather Service Louisville KY
943 PM EST Tue Feb 19 2019
...Forecast Update...
.Forecast Update...
Issued at 940 PM EST Tue Feb 19 2019
After analyzing some of the incoming 00z model and observational
data, plan to keep the advisory in place for the overnight hours. KY
Mesonet and ASOS/AWOS obs show temperatures in the advisory area
ranging from 33-35 degrees, with T/Td spreads around 10 degrees.
Precipitation currently in central KY will overspread the advisory
area within the next hour or two, and will likely start out as sleet
and quickly transition to rain. Evaporative cooling in the low
levels of the atmosphere will help drop surface temperatures some,
and most 00z model guidance shows a 1-3hr window where temperatures
in the advisory area could fall to 32 degrees or colder. Any rain
falling during this time could freeze on elevated surfaces (i.e.,
freezing rain). Everything is then expected to turn over to a plain,
cold rain as surface temperatures warm above freezing in response to
strong WAA. The odds for snow continue to look slim... but some snow
may be possible in parts of northern KY and southern IN where
slightly cooler temperatures aloft remain, but think any snowfall
accumulations in those areas will be very limited due to its brief
duration.
Issued at 750 PM EST Tue Feb 19 2019
Some of the latest observations and high-res model guidance
indicates we may be in for a less wintry night than earlier thought.
AMDAR soundings from SDF show a pretty stout warm nose in place
(~3C), and several high-res models show this warm nose remaining
intact through the overnight hours across much of the region. Dual-
pol data from regional radars show melting of snowflakes aloft along
the leading edge of the precipitation band that is currently in
southern KY, marching northward. Precipitation being observed on the
ground has been all rain thus far.
The AMDAR soundings, dual-pol data, and recent high-res model
guidance would suggest that as this band of precipitation moves
northward, p-type will primarily be rain, with pockets of sleet
along the leading edge of the precipitation. A brief period of
freezing rain may be possible at sites where temperatures remain at
or below freezing. Snow chances, at this time, look pretty slim
everywhere due to warm temperatures aloft, except perhaps the far
northern tier of southern Indiana counties where a small window of
snow may be possible. Updates have been made to the forecast, and
snow totals have been dropped considerably across most of the area.
There was some consideration for dropping some counties from the
winter weather advisory along and near the I-64 corridor, given that
snow looks very unlikely now. The concern now, though, is that
surface temperatures in these areas could be close to freezing when
precipitation begins, and even brief periods of freezing rain could
result in slick elevated roadways. Will hold off on any advisory
cancellations for a little bit and keep a close eye on KY Mesonet
temperatures while analyzing 00z data as it comes in. Expect another
forecast update before 10pm.
&&
.Short Term...(This evening through Wednesday)
Issued at 309 PM EST Tue Feb 19 2019
Tonight...
Precipitation will spread throughout the region this evening and
continue through the night with strong isentropic lift and a very
moist column ahead of a deep upper trough over the Plains.
While southern and much of central Kentucky will be all rain, a
light wintry mix will be found on the leading edge of the
precipitation shield. Road temperatures are mostly in the 40s and
surface air temperatures are expected to hover just above freezing.
Soundings in north central Kentucky and southern Indiana support
mostly a rain/snow mix with perhaps a brief period of snow for a
couple of hours this evening when temperatures hit their minimum and
dew points are still in the 20s. Best chances for any wet snow
accumulation will be north of the Ohio River where an inch...maybe
2...will be possible. Accumulations elsewhere should be light. Slick
spots will be possible on elevated untreated surfaces with the
possibility of some very brief light icing as the precipitation
changes to rain and bridge/overpass temperatures lag and remain
cold. Will drop a few southern counties from the Winter Weather
Advisory where impact should be minimal, but hold on to it over most
of southern Indiana and the Kentucky Blue Grass where colder
conditions will linger the longest.
Temperatures will bottom out in the lower and middle 30s this
evening, then rise into the upper 30s - mid 40s by morning.
On the heavy rain side of things, 0.75-1.25" of precipitation looks
like a good bet tonight, especially after midnight with a 60kt low
level jet nosing in with increased theta-e ridging and precipitable
waters. Will add just a few counties on the Indiana side of the
Louisville metro into the Flood Watch where QPF and FFG numbers are
similar to areas where the watch is already out.
Wednesday...
Significant moisture will remain in the area...K Index in the mid
30s...though there is some weak mid-level drying in the afternoon.
The 5H trough over the Plains will lift northeastward, but its
surface low will travel from KC to the Twin Cities and pivot an
occluded front into the Ohio Valley by evening. Rain will continue,
though likely in a more showery fashion, as opposed to the large
area of steady rains we see tonight. A few rumbles of thunder will
be possible, especially in the Lake Cumberland region. An additional
.5-1" of rainfall will be possible.
Southeast winds in the morning will turn to the south in the
afternoon and push temperatures into the 50s.
.Long Term...(Wednesday night through Tuesday)
Issued at 345 PM EST Tue Feb 19 2019
...Additional Heavy Rainfall and Thunderstorms This Weekend...
Sfc cold front is forecast to push east to the Appalachians by 06z
Thu, so have showers exiting off to the east late Wednesday night. A
1022 mb sfc high quickly builds east from Missouri Thursday morning,
diminishing the westerly winds. Morning lows should range from the
lower 30s in southern Indiana to the upper 30s/low 40s along I-75.
Thu/Thu night still look mainly dry for a good chunk of the area as
a warm front lifts north through the Deep South. Partly sunny skies
for Thursday with highs ranging from the mid 40s north to mid 50s
south. Low chance PoPs for some light rain seems reasonable for
areas south of the Cumberland Parkway Thursday night.
=============================
Friday through Saturday Night
=============================
Friday into Friday night, a deep upper trough will swing east across
the Four Corners. SW moisture transport and isentropic ascent over a
sfc warm front will result in widespread light rain by Friday
morning into early afternoon. Lift and theta e advection continue to
increase late Friday through Friday night, resulting in heavier
showers. May see elevated convection develop by the early hours of
Saturday.
The heaviest rainfall in the long term will fall in the 24-hour
period from early Saturday morning through early Sunday morning. On
Saturday, a very dynamic system rotates northeast from the Plains to
the Midwest. Central KY/southern IN will be favorably located in the
exit region of the increasing 140-150 kt upper jet. Strong moisture
transport will aid in the development of widespread showers and
scattered elevated storms during the first half of the day. This may
play a role in limiting sfc based instability during a potential
window for severe weather later in the evening. Certainly not seeing
much opportunity for sunshine with this forecast.
Still, a strong, fast-moving cold front will approach from the west
late Saturday evening. BL moisture return should be healthy in the
warm sector, with sfc dewpoints in the neighborhood of 60 degrees.
Sfc LIs are forecast to be slightly negative, perhaps -1 to -2. 3-6
km lapse rates look pretty good actually, but a low level inversion
will linger most of the day (until perhaps right before fropa). So
the instability looks modest, but it really won`t take much to
produce significant convection.
SW winds of 75 kts will be seen as low as 700 mb. Deep layer shear
will be more than sufficient, and right-curving hodographs suggest
some potential for low-topped supercells. Based on the 12z run, CIPS
analog guidance shows 30 to 40 percent of the top 15 analogs exceed
5 severe weather reports.
We will of course monitor the severe weather potential closely for
this weekend. Confidence is highest, however, in flooding. PW values
will climb to around 1.5 inches ahead of the cold front Saturday
evening. Additional heavy rainfall through the weekend will
exacerbate ongoing flooding and prolong/extend rises on the rivers.
Minor to potentially moderate river flooding will be an issue well
into next week.
Sunday and Monday...
Even outside of convection, it will become quite breezy on Saturday
afternoon in the warm sector. It will become downright windy
Saturday night and Sunday with CAA developing. There`s potential for
advisory-level gusts on Sunday. The weather turns cooler and dry for
Sunday and Monday.
&&
.Aviation...(00Z TAF Issuance)
Updated at 614 PM EST Tue Feb 19 2019
Ceilings will continue to lower this evening and overnight as
moisture advects in from the south. Expect to see conditions quickly
go from VFR to MVFR/IFR as the stratus and precipitation move
northward. Widespread IFR with isolated LIFR ceilings will be
possible by early tomorrow morning. Precipitation will continue
through much of the day tomorrow.
As the precipitation moves northward, we could see a brief period of
wintry precipitation along and north of the I-64 corridor. This is
expected to quickly change over to rain as we head into the early
morning hours.
Low level jetting will rev up after midnight and continue into
Wednesday morning. At this time it appears that the strongest winds
will remain above 2000 feet, with a steady 10-15kt breeze sustained
at the surface, which should only result in borderline LLWS within
the restrictions of the TAFs. As a result, no LLWS will be mentioned
in the TAFs at this time.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...Winter Weather Advisory until 4 AM EST Wednesday for INZ077>079.
Flood Watch through Thursday morning for INZ090>092.
Winter Weather Advisory until 2 AM EST Wednesday for INZ076-083-
084-092.
KY...Winter Weather Advisory until 4 AM EST Wednesday for KYZ032-036-
037-042-043.
Flood Watch through Thursday morning for KYZ023>031-033>043-
045>049-053>057-061>067-070>078-081-082.
Winter Weather Advisory until 2 AM EST Wednesday for KYZ031-
033>035-040-041-048-049.
&&
$$
Update...DM
Short Term...13
Long Term...EBW
Aviation...DM
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
847 PM CST Tue Feb 19 2019
.UPDATE...
847 PM CST
Going forecast appears to generally be in good shape and no big
changes made.
Skies have clouded up and that should stop or greatly slow the
temperature fall, so did tweak hourly temps upward some over the
next few hours, which did result in slightly warmer min temps for
tonight. Generally look for nearly steady or perhaps very slowly
rising temps, though once precip begins evaporative cooling will
probably cool temps a couple degrees late tonight.
Regarding precip, the 00z soundings from DVN and ILX both show
only a very shallow, but quite dry, dry layer left just below
850mb. Radar has shown echoes aloft over these areas since I came
on shift at 21z, so the persistent virga has clearly been eating
away at the dry air. By comparison, an ACARs sounding from MDW
last hour showed a much deeper dry layer, extending from the very
dry layer just below 850mb up to around 700mb, so there is a bit
of work that still needs to be done to saturate the column farther
north.
Guidance remains in good agreement, including the high-res short
range models, in bringing a band of precip north through the area
driven by the strong WAA. Column should be cool enough to support
all snow, though models show very rapid drying of the mid levels
early Wednesday morning. The result will probably be a change over
to freezing drizzle/light freezing rain, possibly mixed with some
very fine snow as min cloud bearing layer temps rise to warmer
than -10C, indicating decreasing chances of ice nuclei needed for
snow being present.
As it looks now, should see a quick 2-4 hour period of snow, which
could deposit an inch or two, before precip mixes with or changes
to freezing drizzle or light freezing rain for a period before
ending or changing to drizzle (non-freezing variety) as temps inch
above freezing Wednesday.
- Izzi
&&
.SHORT TERM...
245 PM CST
Through Wednesday night...
The main forecast concerns continue to focus on the wintry
precipitation expected to develop across the area overnight and
continue on Wednesday. Timing of P-Type changes, as well as snow
and icing amounts remain the primary challenges with this system.
Overall not much has changed in terms of thinking with this
system, so no changes are planned to the going headlines. Overall,
expect snow to begin to develop southwestward to northeast across
the area tonight in response to the rapid intensification of
isentropic upglide (warm air advection) via a strengthening
southerly 40+ kt low-level jet. It appears that the snow could
fall at least briefly at a moderate to heavy rate overnight as the
mid-level warm front shifts northward over the area. A band of
enhanced frontogenesis along this elevated boundary will likely
help to drive this period of heavier precipitation into daybreak
Wednesday morning. Given this potential for at least a short
period of heavier rates, I would not be surprised to have some
snow amounts up around, or just above 2 inches with this initial
period of snow into early Wednesday morning. It does appear
though that the fairly progressive nature of this heavier snow
tonight should keep amounts from getting much higher.
Changes then look to occur early to mid morning Wednesday over
much of the area. The the combination of strong warm air
advection aloft and an influx of drier air aloft (mid-level dry
slot) will likely allow the precipitation to change over to a
period of light freezing rain/drizzle from south to north during
the morning. This will likely result in some minor icing
potential following the initial period of snow. Overall ice
accumulations look to remain at, or under a tenth of an inch.
Conditions should then improve for most areas during the
afternoon as surface temperatures begin to warm above freezing as
the surface winds turn south-southeasterly. The only area in which
some freezing precipitation could continue Wednesday afternoon,
is over far northern IL (north of I-90), where temperatures may
struggle to get much above freezing. Some light drizzle and low
clouds will likely continue into early Wednesday evening before
ending.
KJB
&&
.LONG TERM...
304 PM CST
Wednesday night through Tuesday...
After the departure of Wednesday`s low to our northeast, the next
system of interest approaches this weekend. Before then, Thursday
has us positioned on the east side of a surface high with ridging
also present aloft. With mostly clear skies and light westerly flow
along the leading edge of the high, and with no significant change
in airmass except to drier conditions, highs Thursday look similar
to Wednesday. Thursday night then looks a bit chilly as the ridge
moves overhead, especially northwest where lows could approach the
single digits again.
By Friday the ridge axis has moved east of the area allowing
slightly milder southeast flow to warm us a few degrees above
Thursdays highs, but the cold start to the day will make it tough to
push temperatures up too far.
Warm advection continues Friday night into Saturday, with the
overnight low likely occurring in the late evening and a non-diurnal
trend appearing favorable overnight. This trend will be significant
as precip chances increase after midnight ahead of a low pressure
system developing in the lee of the Rockies and beginning to lift
toward the area. Models overall are in pretty decent agreement
through this time period, but all suggest there will be ongoing
uncertainty regarding hourly temperature trends relative to POPs.
For now it appears there could be a period where surface
temperatures remain below freezing while warmer air moves in aloft,
at the same time precipitation chances are increasing. So have
mentioned the possibility of light freezing rain early Saturday
before the whole area switches over to rain by the afternoon. The
GFS actually shows temperatures climbing above freezing by the time
we have sufficient saturation to support precip. In any case, it
will bear watching.
Saturday itself looks relatively mild though unsettled. With models
in reasonable agreement showing a negatively tilted trough over the
southern Plains with the associated surface cyclogenesis, SPC does
have an outlook for severe weather across southern portions of the
Midwest. It does not look like that severe risk and outlook area
appear favorable to work their way this far north, at least not
with a surface based warm sector. Elevated thunderstorms could be
possible Saturday and Saturday night as the surface low and upper
trough lift overhead.
Sunday and the first part of next week look drier and cooler behind
the departing low, but only back toward more seasonable values. The
next chance of precip appears to be Monday night into Tuesday ahead
of the next upper wave. This could be snow initially Monday night,
possibly transitioning to rain sometime Tuesday.
Lenning
&&
.AVIATION...
For the 00Z TAFs...
No major changes to the forecast thinking early this evening.
Snow is expected to spread across the terminals from southwest to
northeast and may begin at RFD by about 06z and closer to 09z at
the Chicago area terminals. Snow may be moderate to heavy at
times over a 2-4 hour window after it begins and 1-2 inches may
accumulate prior to 12z. Did accelerate the lowering of ceilings
to lower end MVFR overnight. Snow will likely result in IFR vsby
around 1SM and may be fall to around 3/4SM at times. Warmer air
aloft will move into the area and combine with a layer of drier
air bringing a transition from snow to freezing drizzle after
about 12z in the Chicago area and a bit later at RFD. Ceilings and
vsby will likely remain IFR and possibly LIFR at times through
Wednesday morning. Surface air temperatures should warm above
freezing by midday allowing FZDZ to become DZ in the Chicago area
but RFD may hold on to FZDZ through much of the afternoon.
Winds will be east to southeast tonight and more southeasterly
during the day Wednesday. Winds will shift to the southwest late
Wednesday afternoon bringing in drier air and an end to the
drizzle. Vsby will increase with IFR ceilings scattering/improving
at a slower rate Wednesday evening.
MDB
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Winter Weather Advisory...ILZ019-ILZ023-ILZ032-ILZ033-
ILZ039...midnight Wednesday to noon Wednesday.
Winter Weather Advisory...ILZ003-ILZ004-ILZ008-ILZ010-
ILZ011...midnight Wednesday to 6 PM Wednesday.
Winter Weather Advisory...ILZ020-ILZ021-ILZ022...3 AM Wednesday
to noon Wednesday.
Winter Weather Advisory...ILZ005-ILZ006-ILZ012-ILZ013-ILZ014...3
AM Wednesday to 3 PM Wednesday.
IN...Winter Weather Advisory...INZ001-INZ002...3 AM Wednesday to noon
Wednesday.
Winter Weather Advisory...INZ010-INZ011-INZ019...midnight
Wednesday to noon Wednesday.
LM...None.
&&
$$
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