Forecast Discussions mentioning any of
"ACARS" "MDCRS" "AIRCRAFT" "TAMDAR" "AMDAR" "WVSS" received at GSD on 04/17/23
Area Forecast Discussion
National Weather Service Louisville KY
953 PM EDT Sun Apr 16 2023
.Forecast Update...
Issued at 950 PM EDT Sun Apr 16 2023
Current regional radar imagery shows widely scattered light echo
returns moving west to east along the prevailing cyclonic flow.
Surface observations have reported light rain/sprinkles associated
with this activity while the latest Louisville ACARs sounding
depicts shallow moist layer below the - 10degC isotherm. Upstream
radar observations along with CAM guidance support the expansion of
the low rain chances overnight from southern Indiana to an area
roughly south of the I-64 corridor. No lightning activity is
expected whatsoever. In addition, winds have been subsiding since
sunset and will turn light at least until after 17/09Z when the LLJ
starts to nose in from the west and cloud-layer mixing gets
increased gustiness transfered to the surface. Rest of the forecast
looks on track and the grids have been refreshed.
&&
.Short Term...(Tonight through Monday evening)
Issued at 250 PM EDT Sun Apr 16 2023
Cool and windy conditions expected to close out the weekend and
start into the upcoming week. Closed upper low over northern
Illinois will lift NNE tonight, and become vertically stacked with
its sfc reflection near Green Bay. Main sensible wx impact will be
wind as the tight pressure gradient around this system keeps speeds
at a solid 15 mph through the night, and kicks back up with renewed
mixing Monday morning, resulting in another round of 30-40 mph
gusts. Should stay short advisory criteria, but we`ll push another
Special Weather Statement to highlight the gusty conditions.
Cold pool showers pinwheeling around the low could get very close to
our southern Indiana counties, especially tonight. However,
probability of measurable precipitation is very low, and we`ll only
mention possible sprinkles over our northern tier of counties in
southern Indiana. Temps several degrees below normal in a mixy cold
advection pattern.
Relative humidity values across south central Kentucky will drop to
around 25 percent on Monday afternoon, but fuel moistures appear to
remain a mitigating factor in fire wx conditions. If it continues to
look dry and windy first thing Monday morning, we`ll check in with
forestry partners on any potential fire danger issues.
&&
.Long Term...(After midnight Monday night through Sunday)
Issued at 300 PM EDT Sun Apr 16 2023
Dry weather is expected at the onset of the long term period, with a
dome of sfc high pressure located to our south, and upper ridging
moving in from the Central Plains. Some areas of frost will be
possible Tuesday morning as morning temps drop into the 30s for some
of the area. Dry weather, and warming temps are expected for Tuesday-
Wednesday. Highs on Tuesday will be in the 60s to low 70s, and a bit
warmer on Wednesday with temps ranging between the 70s and low 80s.
Upper ridging will be sliding east of the Ohio Valley on Thursday,
making way for a large deepening upper trough to ride across the
High Plains, and pull a sfc low from Texas to the Great Lakes
towards the end of the week. This will result in a trailing cold
front to drag through much of the Central Plains. Ahead of the
front, we`ll see an increase in WAA flow as deep layer SSW flow
increases, resulting in quite possibly the warmest day of the long
term period, with forecast highs in the upper 70s and low 80s.
Clouds will be on the increase during the day as the upper low
tracks over the Great Lakes, though most of the day should be dry.
Precip chances increase Thursday evening, and especially Thursday
night, ahead of the cold front. Soundings suggest any instability
should be rather weak and elevated, so severe threat appears low at
this time.
Guidance diverges for Friday and beyond, with the ECMWF, GFS, and
Canadian all varying quite a bit on solutions. With lots of
uncertainty, it`s difficult to nail down timing of PoPs for the
Friday-Saturday timeframe. At least light precip chances are needed
for the first half of the weekend, though overall confidence remains
low. The highest precip chances of the entire period are Thursday
night-Friday morning. Regardless of the precip chances, we do have
more confidence on seeing cooler temps after the cold frontal
passage. Highs for the weekend are in the upper 50s and low 60s for
both days.
&&
.Aviation...(00Z TAF Issuance)
Issued at 740 PM EDT Sun Apr 16 2023
Impacts/Confidence:
- High confidence in fresh to strong westerly breeze returning
tonight
- Low confidence in brief periods of MVFR ceilings at HNB/SDF/LEX
Discussion...Deep low pressure system will slowly track northeast
across the upper Great Lakes leaving the Ohio Valley under cyclonic
flow and a persistent wrap-around cloud layer. Currently, VFR
conditions prevail as the cloud base is around 4-6 kft and the
overall trend in the model guidance is to continue having such
conditions before clouds start lifting/scattering Monday afternoon.
On the other hand, there is a non-zero chance of brief periods of
MVFR ceilings at HNB, SDF, and LEX overnight. However, MVFR ceilings
were not included in the official forecast given the low confidence.
Although winds will initially ease a bit after sunset, a
reinvigorated semi-stationary LLJ extending across the upper
Mississippi Valley will support westerly wind gusts between 20-30
mph around sunrise and 30-40 mph in the afternoon hours. This LLJ
jet will eventually weaken and move to the east Monday night.
Extended Outlook...There is a signal for LLWS after 18/0Z as the
weaker LLJ translates through the northern portion of the TAF area.
&&
.LMK WATCHES/WARNINGS/ADVISORIES...
IN...None.
KY...None.
&&
$$
Update...ALL
Short Term...RAS
Long Term...CJP
Aviation...ALL
Area Forecast Discussion
National Weather Service Chicago/Romeoville, IL
909 PM CDT Sun Apr 16 2023
.UPDATE...
Issued at 909 PM CDT Sun Apr 16 2023
The going forecast remains on track with no major changes to the
expectation for the rest of tonight into Monday morning.
Rain showers continue to be observed across much of the area this
evening, but recent observations are showing rain transitioning to
snow across portions of far northwestern Illinois. As temperatures
continue to cool through the night snow will become the dominant
precipitation type which is expected to lead to some slushy
accumulations primarily on grassy and elevated surfaces. While
most areas will only see a tenth or two at most, areas west of the
Fox Valley and north of I-88 will have the potential to pick up
higher amounts possibly up to an inch.
Additionally, blustery westerly winds will persist through the
night and much of the day on Monday with gusts in the 40 to 45
mph range. Couple these winds with the near freezing low temperatures
tonight will create wind chills in the upper teens and lower 20s.
While these are not extremely cold temperatures, they are a big
difference from those we have been experiencing so be sure to
bundle up before heading out in the morning.
Yack
&&
.SHORT TERM...
Issued at 323 PM CDT Sun Apr 16 2023
Through Monday night...
Key Messages:
* Late season snow tonight into Monday morning, with some minor
slushy wet snow accumulations likely especially north of I-80
and west of the Fox Valley.
* Cold and windy Monday. Gusts up to 45 mph likely, especially for
my west and southwest areas. In collaboration with neighboring
offices we have issued a wind advisory for tonight and Monday,
generally along and west of I-39.
* Widespread freezing temperatures likely Monday night outside of
Chicago. A freeze warning will likely be needed.
Surface low pressure near KGRB continues to deepen as in response
to increasing upper level diffluence just downstream of the
deepening mid-level low now shifting across northern IL. Periods
of showers continue to develop under this mid-level low, and we
have even had numerous reports of snow already trying to mix in
with the rain across far northern IL. This is a sign that the
deepening mid/upper low overhead is dynamically cooling the
column, and resulting in wet-bulb zero heights falling to near
1200 ft AGL (per early afternoon AMDAR sounding from MDW). In
spite of this, surface wetbulbs still remain rather warm, with
readings as of this writing generally in the upper 30s. This will
prevent any accumulations though the afternoon.
Rain will transition to all snow from northwest to southeast late
this afternoon through the evening as the column continues to
undergo dynamic cooling under the deepening mid-level low
shifting into southeastern WI. Some wet slushy snow accumulations
(mainly on grassy areas) are likely, especially across
northwestern sections of the area west of the Fox Valley and north
of I-80. Amounts should generally be light, however, with up to
an inch or two (possibly a few isolated amounts as high as 3" in
my far northwest near the WI state line). This will not be the
case to our northwest across western WI, however, as signs
continue to point at several hours of very heavy snow tonight into
Monday morning along the west-northwestern periphery of cyclone,
where low-to-mid level frontogenesis will be maximized within the
TROWAL (Trough of Warm Air ALoft) axis. Anyone planning travel
northwest of the area tonight into Monday should so keep this in
mind as there could be some significant travel impacts.
Snow is likely to continue through at least Monday morning before
ending during the afternoon. The coverage should become more
showery and scattered with time, however. Additional accumulations
are unlikely during the daytime hours. Expect temperatures to
only top out in the 30s in most areas Monday as gusty west-
northwesterly winds make it feel even colder. Wind gusts will
continue to increase tonight and on Monday as the storm system
continues to deepen to our north. While it will be windy areawide
on Monday, with gusts up to 40 mph, it appears wind gusts as high
as 45 mph will be probable across my western and southwestern
areas. For this reason, we have issued a wind advisory for late
tonight through the day Monday for areas generally along and west
of I-39.
A surface high pressure ridge will move overhead Tuesday morning,
which should lead to a very chilly morning with freezing
temperatures probable away from the inner metro. While we do look
to see some subfreezing temperatures tonight over far northern IL,
more widespread freezing temperatures are likely Sunday night. We
thus may end up needing freeze warning for this period.
KJB
&&
.LONG TERM...
Issued at 310 PM CDT Sun Apr 16 2023
Tuesday through Sunday...
* Multiple rounds of storms possible WED-THU, also monitoring
potential severe threat THU
* Warming up midweek though with a large temperature gradient
across area WED-THU
* Settle back into a colder pattern late week with additional
precip chances
Tuesday brings a much needed break in the wet weather as upper
ridging moves overhead. Expect dry conditions to prevail with
temperatures beginning to moderate some (albeit still cooler than
normal) with highs in the 50s and mostly clear skies. However, an
afternoon lake breeze likely limits highs to the mid-upper 40s
along and near the lakeshore.
Meanwhile an upper trough will be moving across the Rockies
toward the central and northern Plains by midweek. This will eject
multiple disturbances off the Rockies toward the region. The
first of which arrives on Wednesday when long-range guidance
develops isolated to scattered thunderstorms across our area
Wednesday afternoon along a stationary boundary/pseudo warm front
extending east/southeast of a developing surface low. Though the
timing and placement of these features continue to vary some
between models and from run to run. What is perhaps more
consistent is that an EML plume is expected to expand over the
area by Wednesday afternoon. As such, any storms that develop
would likely be elevated with noted capping around 750hPa. At this
range the severe threat appears to be on the lower side given
weaker shear, though can`t rule out some large hail given the
steep mid-level lapse rates.
A second and potentially deeper surface low develops in the wake
of this system as the upper trough translates east of the Rockies
which could bring additional rounds of showers and thunderstorms
to the region late Wednesday night through Thursday. Perhaps of
greatest interest is the timing of the associated cold frontal
passage across the area. Since this is still several days out the
timing of the front will likely change but if it does move through
during the afternoon per latest operational guidance, more than
sufficient deep layer shear will be in place and if the nose of
the MUCAPE axis can push far enough north, strong to severe storms
certainly cannot be ruled out. Something to keep an eye on over
the coming days.
Temperatures Wednesday and Thursday are low confidence thanks to
a large temperature gradient likely setting up across the area.
This could result in high temperatures in the upper 40s to 50s in
our north and upper 60s to 70s in our south. The location and
orientation of the tighter temperature gradient will be dependent
on the evolution of potential surface lows and associated fronts.
In the wake of Thursday`s storms and cold front we settle into a
cooler pattern heading into the weekend. There are additional
chances for precipitation though there remains some variability in
the timing and placement of additional weather disturbances so no
changes were made to the blended PoPs at this range. Lows near to
below freezing appear plausible by next weekend. Winter is not
ready to give up just yet!
Petr
&&
.AVIATION...
For the 00Z TAFs...
Aviation Forecast Concerns:
* Strengthening west winds with an extended period of gusts above
30 kts. Strongest gusts expected from after 06Z tonight through
the day Monday, with frequent gusts of 35+ kts for Chicago sites
and 40+ kts at KRFD.
* Scattered showery precipitation trending toward all snow from
later this evening through Monday morning. A few waves of more
persistent light snow likely during this time. Precip changes
back to rain and becomes more showery again Monday afternoon.
Slushy accumulations of an inch or two cannot be ruled out at
RFD by the end of the TAF period.
* Ceilings expected to be largely low-MVFR 1000-1500 feet, though
some IFR possible especially for KRFD tonight. Reductions in
visibility into IFR possible during periods of more widespread
snow tonight into early Monday.
Deep surface low pressure was over northern Lake Michigan early
this evening, in association with a strong upper level trough
across the region. The stacked low pressure disturbance will drift
only slowly eastward through the forecast period, eventually
drifting off into southwest Ontario Monday evening. This will
result in strong, gusty westerly winds (eventually turning more
northwest late Monday), persistent advection of cold low level air
and a broad area of showery precipitation with embedded areas of
more persistent precipitation affecting the terminals at times.
Rain showers are expected to mix/change to mainly snow/snow
showers this evening and continuing through Monday morning,
changing back to rain and gradually decreasing in coverage Monday
afternoon with somewhat "warmer" daytime temps. MVFR ceilings will
trend downward into the 1000-1500 foot range as precipitation
becomes more widespread later this evening, and IFR ceilings are
possible overnight especially for KRFD and areas north and
northwest. Lowest visibilities will likely dip into IFR range
tonight and early Monday in snow, with MVFR vis likely in lighter
precip. Some slushy snow accumulations are possible overnight,
especially at KRFD where an inch or two of wet snow can`t be ruled
out especially on grassy surfaces. Gradual advection of drier low
level air should allow an improving trend to cigs above 2000 feet
Monday afternoon and evening.
Winds will remain strong and blustery through Monday, initially
from the west-southwest this evening and west-northwest later in
the period. Frequent gusts above 30 kts are expected, with a
period of stronger 35-45 kt gusts from late tonight into Monday.
Winds will gradually ease late Monday/Monday night as the low
pulls away and the gradient weakens.
Ratzer
&&
.LOT WATCHES/WARNINGS/ADVISORIES...
IL...Wind Advisory...ILZ003-ILZ008-ILZ010-ILZ019-ILZ032-
ILZ039...midnight Monday to 7 PM Monday.
IN...None.
LM...Gale Warning...nearshore waters until 10 PM Monday.
&&
$$
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Area Forecast Discussion
National Weather Service Los Angeles/Oxnard CA
834 PM PDT Sun Apr 16 2023
.SYNOPSIS...16/833 PM.
A cooling trend with strengthening onshore flow and low clouds is
expected Monday and Tuesday. Gusty northerly winds at times are
expected this week with much warmer temperatures by Thursday.
&&
.SHORT TERM (SUN-WED)...16/830 PM.
Current satellite imagery showing areas of low clouds across
the coastal areas of LA county, otherwise mostly clear skies
this evening. Upper level trough of low pressure over northern
California will gradually deepen across the state into Monday,
bringing some lowering of heights as well as strengthening
onshore flow. As of 7 pm, LAX-Daggett pressure gradient is
at +6.1 mb and is expected to peak around +7 mb on Sunday.
This in combination with a developing eddy circulation is
expected to deepen the marine layer across LA/Ventura counties.
Current ACARS data showing the marine layer depth around 1500 feet
across the LA Basin, but is expected to rise to around 2500 feet
by Monday morning, likely resulting in low clouds and fog
overspreading most of the valleys and possibly to the coastal
slopes. With the deepening marine layer, there is the possibility
of patchy drizzle across LA county in the morning. HREF guidance
showing lower probability of low clouds and fog reforming tonight
across areas north of Point Conception. There will likely be some
upslope clouds that form across the interior slopes overnight into
Monday morning. The stronger onshore flow pattern and deeper
marine layer will likely lead to slower clearing across coastal
areas of LA/Ventura counties in the afternoon hours on Monday, as
well as a cooling trend for most areas.
Meanwhile, tightening northerly pressure gradients are generating
northwest winds gusting between 30 and 40 mph across Southwest
Santa Barbara county this evening (especially near Gaviota and
Refugio). The gusty northwest winds are expected to expand
across the I-5 corridor and Antelope Valley overnight into Monday.
By Monday evening, the Santa Barbara-Santa Maria pressure gradient
is expected to reach -4.5 mb while upper level support also
strengthens. As a result, looking for stronger and more widespread
northwest winds across the Santa Ynez range and Santa Barbara
south coast, with wind advisories likely being needed for western
portions with wind gusts of 40 to 50 mph.
*** From previous discussion ***
The latest satellite showed low clouds lingering across some
beaches, most notably the LA coast, especially near Malibu, and
portions of the Central Coast. Sharpening northerly gradients may
support isolated or brief gusts to advisory levels for southwest
Santa Barbara County or the I-5 cooridor in the mountains, but
probably shy of needing an advisory. Low clouds may dissipate
across much of the area by this evening, and may struggle to
reform in some areas, leading to a low confidence cloud and fog
forecast for tonight.
A cold front passing through the region will likely (60-80
percent chance) support advisory level winds for southwest Santa
Barbara County and the I-5 cooridor in the mountains, spreading
into portions of the Antelope Valley Monday evening into the
night. Continued sharp northerly gradients may support advisory
level winds at times for much of the same areas through at least
Wednesday evening. The strong northerly flow and weakening
inversion may wipe out the marine layer and associated clouds
Tuesday. Before then, the lifting marine layer may squeeze out
patchy drizzle focused across the eastern LA county foothills and
coastal slopes.
Modest 500 mb height falls and an earlier and stronger sea breeze
should support cooling just about everywhere into Monday and
Tuesday with highs in generally in the low 60s to low 70s. Coasts
and western Ventura County valleys may begin a warm up Tuesday or
Wednesday thanks to a combination of the retreating marine layer
and downslope compression heating off of the Transverse mountain
ranges.
.LONG TERM (THU-SUN)...16/159 PM.
Model guidance shows only average agreement in the extended
period, support moderate confidence in the forecast. Moderate to
strong offshore flow with periods of gusty northerly winds may
continue through Friday before waning. A weak to moderate ridge
may build over the region during this time frame, possibly
supporting a significant warm up for many areas heading into next
weekend. Current forecast calls for widespread highs in the mid
70s to mid 80s by next Saturday, but these temperatures could be
off by 5 degrees.
&&
.AVIATION...16/2358Z.
At 2340Z at KLAX, the marine layer was 1500 feet deep. The top of
the inversion was around 3800 feet with a temperature of 14 C.
Areas of low clouds lingering across portions of the LA county
coast late this afternoon, including KLAX and KSMO where sct-
bkn010 conditions are expected until sundown. Hi resolution models
showing an eddy circulation developing tonight, with marine layer
depth expected to increase for LA/Ventura counties where HREF
models are showing higher probability of low clouds developing
tonight into Monday morning. There is a 40 percent chance of
cigs not arriving during period at KSBA, KSMX, KSBP, and KPRB.
There is also a 50 percent chance of MVFR cigs lingering into
Monday afternoon at KLAX and KSMO. Gusty west winds are expected
to continue in the Antelope Valley.
KLAX...Moderate confidence in the 00Z TAF. SCT-BKN010 conditions
expected to continue until sundown. MVFR cigs expected tonight
through Monday morning, with a 50 percent chance of cigs lingering
into the afternoon. A weak eddy circulation will develop overnight
into Monday morning, but the east wind component is expected to
remain below 8 knots.
KBUR...Moderate confidence in the 00Z TAF. MVFR cigs likely to
develop later tonight into Monday morning, but arrival time could
be +/- 2 hours from TAF timing.
&&
.MARINE...16/215 PM.
For the afternoon issuance, lots of changes and lots of wind
forthcoming.
In the outer waters, a SCA has been extended for zone 670 through
late Wed night. SCA remains in effect for zones 673 and 676
through Monday afternoon. There is a 50 percent chance of Gale
Warnings for zones 673/676 Monday afternoon/evening thru Wed
evening, so a Gale Watch has been posted for that region.
In the inner waters north of Pt. Sal, SCA conds are likely this
afternoon thru late tonight and again Mon/Tue afternoon and night,
so the SCA has been extended through Tue night. There is a 40%
chance of SCA conds Wed/Thu. There is a 30% chance of gale force
winds Tue afternoon/evening.
In the Santa Barbara Channel, SCA conds are expected in western
sections late this afternoon thru late tonight, and again across
western section Mon afternoon thru late Mon night. SCA conds are
likely across most of the channel during the afternoon thru late
night hours Tue and Wed, and there is a 40% chance of gale force
winds late Tue afternoon thru late Tue night. The current SCA has
been extended through Tue afternoon.
Across the southern inner waters, SCA conditions are expected
Monday afternoon through Wed morning, mainly in the westertn
portions. There is a 20-30% chance of gale force winds across
western sections late Tue afternoon thru late Tue evening.
&&
.LOX WATCHES/WARNINGS/ADVISORIES...
CA...NONE.
PZ...Small Craft Advisory in effect until 3 AM PDT Wednesday for
zone 645. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 PM PDT Tuesday for
zone 650. (See LAXMWWLOX).
Small Craft Advisory in effect from 5 PM Monday to 5 AM PDT
Wednesday for zone 655. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 AM PDT Thursday for
zone 670. (See LAXMWWLOX).
Small Craft Advisory in effect until 3 PM PDT Monday for
zones 673-676. (See LAXMWWLOX).
Gale Watch in effect from Monday afternoon through late
Wednesday night for zones 673-676. (See LAXMWWLOX).
&&
$$
PUBLIC...Gomberg/Munroe
AVIATION...Gomberg
MARINE...Sweet/DB
SYNOPSIS...Gomberg
weather.gov/losangeles
Experimental Graphical Hazardous Weather Outlook at:
https://www.weather.gov/erh/ghwo?wfo=lox