SPC Enhanced Risk, IL, IN, OH

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SPC Enhanced Risk, IL, IN, OH

#1 Postby WeatherGuesser » Sun Nov 05, 2017 12:48 pm

Enhanced area has expanded twice today.

Is it extremely soupy outside at my place; windy too. 73 degrees, 75% humidity. Winds are only showing as 9, but they feel stronger due to the gusting.

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Re: SPC Enhanced Risk, IL, IN, OH

#2 Postby tolakram » Sun Nov 05, 2017 2:32 pm

Very humid here as well and already some strong echos on radar. Late October and early November second tornado season as posted by our NWS office.
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Re: SPC Enhanced Risk, IL, IN, OH

#3 Postby WeatherGuesser » Sun Nov 05, 2017 2:59 pm

No nearby echoes here yet, but 5 TOR in NW OH.

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Re: SPC Enhanced Risk, IL, IN, OH

#4 Postby Tireman4 » Mon Nov 05, 2018 10:58 am

FXUS64 KMEG 051240

Area Forecast Discussion
National Weather Service Memphis TN
640 AM CST Mon Nov 5 2018

V DISCUSSION... /issued 259 AM CST Mon Nov 5 2018/


Skies were generally cloudy across the Midsouth with patchy fog
being reported from a few stations. Winds were either calm or
light from the south...and temperatures varied from the mid 40s
to upper 50s. Just to the south in central Mississippi
visibilities were down to a half mile from fog.

For today and tonight...models including the short term CAM` were
bringing the evolution of today`s severe weather in a sharper
perspective. The culprit is the current shortwave seen on water
vapor imagery sliding across western Kansas...with the leading
edge of an approaching jet streak coming across Arizona. These two
features will track a surface low of roughly 1003mb from the
Oklahoma Panhandle to near Chicago by midnight. The tail end of
the associated cold front will pass through the midsouth late this
afternoon and through the evening. Believe convection with the
boundary will mainly be weak and mostly elevated up until 3pm with
thick cloud cover also delaying the onset of severe weather out
ahead of the front. Deeper gulf moisture of 60F+ dewpoints will
begin intersecting the boundary neat sunset across eastern
Arkansas. From then on activity should become more surface-
based/severe as the nose of a 75kt midlevel jet streak moves over
the increasing surge of CAPE. For now models are averaging 400 to
800 j/kg...about what was seen this past Wednesday night across
central Mississippi. Shear values will also compare to last week`s
event if not a bit stronger...so a initial broken line of
convection with a few discrete cells should translate into a more
robust QLCS through the mid to late evening hours. This scenario
is supported by the latest HRRR. The main severe threats continue
to be damaging winds and quick spin-up/weak tornadoes...perhaps
forming below 5kft. So another challenge for radar operators as
storms move further from the radar. Height falls will be minimal
so large hail remains a secondary threat. More than likely storms
will produce have no or small hail. The best tornado threat
appears most favorable across the southern Midsouth counties where
winds will be more backed against the slower moving portion of
the front and a better balance of shear and instability exists.
All models show the front out of the CWA in near or just after
midnight with a few lingering post frontal showers. So have
reduced PoPs in the west after midnight.

Tuesday through Sunday...westerly winds aloft with surface high
pressure will provide for a dry mild day tomorrow. Clouds will be
on the increase Tuesday night as midlevel WAA slides up over the
stalled frontal boundary near the I-20 corridor. This light to
moderate rainfall will continue Wednesday and into Thursday.
Strengthening northeasterly winds over the Midsouth will make it
feel more like December with temperatures in the upper 40s and
50s on Thursday. A stronger release of cP air will slide along a
more northwesterly oriented jet streak on Friday. This feature
will dry out the Midsouth...clear skies and allow for freezing
temperatures Friday night. So an end to the growing season for
many is anticipated. The cool and dry airmass will remain next
weekend with lows staying in the 30s and highs in the 50s.



12Z TAFs

A warm front will move north across the area this morning
resulting in a deterioration of VFR conditions down to IFR/LIFR
conditions due to fog. Once the front passes through TAF sites,
conditions should improve to MVFR/VFR conditions. Showers and
thunderstorms are anticipated to develop this afternoon and
gradually organize into a line of strong to severe thunderstorms,
affecting MEM/MKL/TUP by this evening. S winds will develop today
between 8-12 kts with occasional gusts, then veering W/NW with
passage of a strong cold front later tonight.





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Re: SPC Enhanced Risk, IL, IN, OH

#5 Postby Tireman4 » Mon Nov 05, 2018 1:27 pm

Fog has stuck around in several areas into the morning, though
dense fog has become less common. With southerly wind increasing
through the day, we should see more of a transition to low stratus
(which is what we`re already seeing in areas currently not
afflicted by fog). Through the rest of the daytime, the best
chance for rain will likely remain closer to the front up across
the Delta. More isolated warm advection type shower activity will
be possible across the remainder of the area this afternoon.

General thinking has not changed significantly for the severe
weather threat tonight. Scattered supercells should begin to
develop closer to sunset across North LA/Southeast AR/Northwest
MS and could quickly become severe as they spread northeastward.
Through the evening, these storms could evolve into more of a
broken line/QLCS, but with the front beginning to stall and the
storms moving into an area with decreasing forcing support, they
will begin to lose steam in areas farther southeast. This will not
be the type of event that produces damage over a widespread area
as our previous one did, but in the areas where severe weather
occurs, it could be significant with the greatest potential for
that across the Delta and along and north of Highway 82. We`ll
have more information to come in later updates through the day.

Prior discussion below:

Today & tonight:

An active weather period is on tap for the region today. This
morning at the surface, a stationary front is lingering across the
western half of the area. A weak surface ridge of high pressure is
departing off to the northeast over northern Alabama. However, in
the wake of the rain showers yesterday, we have been very moist in
the boundary layer & will continue to remain that way in the low-
levels through the night. This morning there are scattered mid-high
clouds from the continued west-southwesterly flow aloft. Special 06Z
regional soundings & upper air analysis shows the departing
shortwave moving into the Appalachians while more powerful upper
jet is diving down through the Pacific Northwest & into the
Rockies. Due to the weak flow & high moisture, a scattering of low
stratus & dense fog are scattered through the area, with some
along & northwest of the Natchez Trace corridor. Due to some light
winds & stratus & warm air advection, we have had some increase
in visibilities in some location. However, will maintain the
current ongoing dense fog advisory as some CAM guidance continue
to keep some low fog around the edges of the county warning area,
especially along & west of the Mississippi river. Expect this fog
& lower stratus clouds to lift by mid-morning as low level WAA
increases & winds begin to increase.

Main story continues to be the expected late evening to overnight
severe weather across most of the northern half of the region, with
conditional severe weather threat over the southern half of the
area. By this afternoon, WAA & moisture advection will increase as
the strong synoptic jet (i.e. ~140-160kts) dives through the nation
& takes on a negative tilt. This will help very strong shear, upper
diffluence & favorable jet quadrants to overspread the area. Overall
as this occurs, a strong surface low will develop over the central-
northern Plains with some potential for secondary low-redevelopment
possible in southeastern Missouri to northern Arkansas. Regardless
of this scenario, expect a warm front currently situated offshore in
the northern Gulf of Mexico to lift north & bring with it nearly mid-
upper 60s to even low 70s dewpoints. As that moves in, the
juxtaposition of decent lapse rates & high boundary layer moisture
will lead to sufficient instability by this afternoon. Due to
increasing lift & divergence, showers will begin to develop off over
the ArkLaTex & Oklahoma & spread northeastward into the afternoon.
Overall expect enough low-level ridging & capping to hold back most
convection from developing but some of the guidance (i.e. HREF suite
& HRRR) indicate some isolated cells could develop over the
southeastern Pine Belt into the mid-afternoon (i.e. ~3-5pm). If
these developed, these could have some isolated severe storm & some
tornado potential as there will be copious amounts of shear (i.e.
effective shear ~50kts, 0-3km & 0-6km bulk shear ~30-50kts & ~200
effective SRH). However, the best severe weather potential will come
in the overnight hours.

By late afternoon to early evening, expect a round of storms to
begin developing just to the northwest over Arkansas & Louisiana as
the trough & cold front swing off to the east-southeast. In
addition, there is some potential for a pre-frontal surface trough
that could help back surface wind flow. Due to that, expect these
storms to begin developing across the ArkLaMiss Delta closer to the
5-7PM timeframe with the best potential moving in overnight. Local
HREF suite of guidance, including the ARW, NMM & NAMNest show a QLCS
& broken supercell structures developing after 6PM & moving east-
southeast across the Delta & Highway 82 corridor. Due to copious
shear upwards of 40-50kts @ 0-3km & 60-75+kts @ 0-6km, expect a
broken QLCS structure, which is what a lot of the CAM guidance
depicts. This will spread eastward through the I-55 corridor to
Golden Triangle around midnight. With nearly 300-500 effective SRH,
these broken QLCS structures, especially ones that move east-
northeast, will have potential for tornadoes, with some being
strong. As it gets near the I-20 corridor after midnight, due to the
trough & flow pulling off northeast & some outflow dominance, the
severe weather threat should somewhat lessen. Due to that, expect a
sharp southern cutoff in most severe potential, but we can not rule
out some isolated storms, with damaging winds & isolated tornadoes
along & south of the I-20 corridor. Due to this, only small tweaks
were made to the outlook, with the main change to portions of
central Mississippi due to the sharp cutoff in favorable
orientation. However, the southern extent of the "Marginal" may have
to be adjusted northward as we get closer due to more capping & less
potential the line may make it there. Main takeaway is these storms
will bring the risk of damaging winds up to 70mph, tornadoes (some
strong) & large hail up to quarter to golf ball size. Expect this
front to move through most of the area by early-mid morning Tuesday
but most if not all severe weather threat will be done before
daybreak. Continue to make sure to stay weather aware & have your
severe weather plans in place for tonight. /DC/

Tuesday through Sunday night:

The period will feature a chance of rain over most of the CWA
until Friday afternoon when dry weather is expected that will last
through the weekend. Temperatures will start out warmer than
normal areawide Tuesday and progressively trend cooler each day
from the north until the weekend when cooler than normal
temperatures are expected areawide through Monday morning. Come
sunrise Tuesday morning the threat for any severe weather will
quickly come to an end as the cold front continues pushing through
our southeast most zones. Our winds aloft will remain near zonal
to slightly backed, offering little support to the cold front
which looks to stall just south of our CWA. Most of our CWA will
be dry Tuesday afternoon and evening but wl maintain very low
chance of rain along and south of Highway 84 due to the stalled
front. The first of several shortwaves to traverse the region
through the week is slated to arrive over our CWA after midnight
Tuesday night. This shortwave will lead to rain chances increasing
through Wednesday morning and then decreasing again Wednesday
afternoon as it shifts east of our CWA. Also on Wednesday a
>1030mb high will drop over the northern plains and continue
spreading south into Thursday morning. This will bring cooler and
dryer air into our CWA and help hold temperatures below normal.
Afternoon highs will likely remain in the 50s over our northwest
zones Thursday. A more potent shortwave will move across our
region Friday and help bring another >1030mb high south over the
central Plains. This reinforcing shot of cooler and dryer air will
lead to the end of rain chances and clearing skies going into the
weekend. More of our CWA will top out in the 50s Friday. The
surface high will become centered over the mid Mississippi valley
by Saturday morning helping to send morning lows in the upper 30s
across our northern zones. The surface high will shift east
through the weekend as broad upper level troughing remain over our
region. Models differ on rain chances by Monday morning with yet
another shortwave moving across the region but cooler than normal
temperatures and dry weather should last into Sunday evening. /22/


Jackson 78 66 76 58 / 17 78 16 35
Meridian 78 68 77 56 / 17 80 27 32
Vicksburg 79 65 76 58 / 29 80 9 37
Hattiesburg 81 70 81 62 / 22 40 33 18
Natchez 79 68 77 62 / 22 63 18 22
Greenville 74 58 72 53 / 70 90 4 46
Greenwood 76 60 73 54 / 36 93 6 39





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Re: SPC Enhanced Risk, IL, IN, OH

#6 Postby Tireman4 » Mon Nov 05, 2018 2:26 pm

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1015 AM CST Mon Nov 05 2018

Valid 051630Z - 061200Z


Severe storms capable of damaging winds and tornadoes are likely
this evening and overnight across the ArkLaMiss region and Tennessee

...ArkLaMiss this evening to the TN Valley overnight...
A mid-upper jet streak over the Red River Valley of TX/OK will
progress east-northeastward to the OH Valley overnight, within a
broad cyclonic flow regime over much of the central/northern CONUS.
Cyclogenesis in association with the left-exit region of the jet is
expected from the central Plains to the Great Lakes, and the
influence of the cyclogenesis will extend far enough south to draw
low-level moisture northward today into tonight from the Gulf Coast.

The surface warm sector is confined to southeast TX and the LA coast
as of mid morning, with extensive low clouds to the north in the
developing warm advection regime across the lower MS Valley.
Strengthening low-level flow will result in fairly rapid moisture
transport to the northeast just above the surface today, and will
contribute to elevated thunderstorm development across MO/AR. The
northeastward progress of the surface warm sector will be slower,
with boundary-layer dewpoints into the upper 60s and at least weak
surface-based buoyancy expected into the ArkLaMiss by this evening.

The initial elevated storms could pose a marginal hail threat into
the afternoon, though the more substantial storms rooted near the
surface are not expected until closer to 00z across northern
LA/southeastern AR. Wind profiles will become favorable for
supercells (effective SRH 400-600 m2/s2), and assuming sufficient
destabilization with mid 60s dewpoints into middle TN and upper 60s
into northern MS by tonight, there will be a threat for tornadoes,
including a couple of strong tornadoes. Convection will
subsequently spread northeastward along a cold front and likely
evolve into a QLCS. Low-midlevel flow of 50-70 kt, large curved
hodographs, and weak buoyancy in a narrow corridor ahead of the
front will support a threat for damaging winds and tornadoes with
embedded circulations into the overnight hours.

..Thompson/Cook.. 11/05/2018



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Re: SPC Enhanced Risk, IL, IN, OH

#7 Postby AnnularCane » Mon Nov 05, 2018 4:39 pm

How come there isn't a new thread for this?

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