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LU9DCE > ALERT 18.09.22 22:56z 205 Lines 9474 Bytes #999 (0) @ WW
BID : 1539_LU9DCE
Read: GUEST
Subj: STORM PREDICTION CENTER 18-SEP22
Path: HB9ON<IW8PGT<IZ3LSV<IQ2LB<IR2UFV<SK0BO<SM0YOS<VE3CGR<LU9DCE
Sent: 220918/1900Z 1539@LU9DCE.TOR.BA.ARG.SOAM LinBPQ6.0.23
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ESTACION DE PACKET RADIO - BUENOS AIRES (GF05OM)
BOLETINES INFORMATIVOS PROGRAMADOS (BIP) PHP
Copyright 2022 - Eduardo A. Castillo
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SPC - No watches are valid as of Sun Sep 18 16:35:01 UTC 2022
No watches are valid as of Sun Sep 18 16:35:01 UTC 2022.
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SPC - No MDs are in effect as of Sun Sep 18 16:35:01 UTC 2022
No Mesoscale Discussions are in effect as of Sun Sep 18 16:35:01 UTC
2022.
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SPC Sep 18, 2022 1300 UTC Day 1 Convective Outlook
SPC 1300Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0750 AM CDT Sun Sep 18 2022
Valid 181300Z - 191200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS OVER PARTS OF
SOUTHEASTERN IOWA...EXTREME NORTHEASTERN MISSOURI...AND
WESTERN/CENTRAL ILLINOIS...
...SUMMARY...
Scattered severe thunderstorms should develop across Iowa to the
middle Mississippi Valley region late this afternoon into evening,
offering a few tornadoes, large to very large/destructive hail, and
occasional severe gusts.
...Synopsis...
The mid/upper-level pattern will be dominated by mean troughing near
the West Coast, and a building anticyclone centered over central/
north TX through the period. The western trough will be anchored by
a complex cyclone with several embedded vorticity lobes. The
cyclone -- cut off for now from the prevailing westerlies -- will
dig southward, with its center remaining just off the OR/northern CA
coastline. Downstream, a broad fetch of southwesterlies over the
Great Basin and Intermountain Region will veer to westerlies with
eastward extent, as ridging connected to the TX high amplifies
across the Great Plains. A shortwave trough -- evident in moisture-
channel imagery over parts of southeastern MT and eastern WY -- will
move through the building mean ridge over the north-central Plains
today, then reach parts of MN, western IA and eastern NE by 00Z.
The southern part of this trough should be reinforced by
convectively generated vorticity tonight, while the northern part
crosses the Upper Great Lakes.
At the surface, 11Z analysis showed a cold front extending from a
weak low over the MN Arrowhead, across northwestern WI, southeastern
MN, northern/western IA, southeastern NE, and north-central KS,
becoming quasistationary to a low over northwestern KS. The KS low
should move eastward through the day, along the front, to near FNB
by 00Z, when the front will extend from there northeastward across
southern/eastern IA to eastern Lake Superior. By 12Z, the front
should extend across southern Lower MI and parts of northern/western
IL to northern MO, though its baroclinicity over IL/MO may be
overwhelmed on the mesoscale by that from prior convection. An
outflow boundary was drawn from central/southwestern IL across MO
near a STL-JEF-MCI line, and over northeastern KS north of TOP.
This boundary will move northeastward over northern MO and into
parts of southern/eastern IA through this afternoon and early
evening, likely merging with the front on its western segment.
...IA/MO/IL/IN...
Scattered thunderstorms are expected to form near the front and
retreating outflow boundary late this afternoon into this evening
over IA. Initial mode should include supercells, one or two of
which may be persistent and cyclic enough for a threat of tornadoes
(some possibly strong) and/or significant, damaging hail.
An ongoing area of clouds/precip, and embedded precip/thunderstorms
was evident in radar composites from central IL to portions of
central/eastern MO. This activity is expected to continue weakening
through the remainder of this morning, while its trailing outflow
boundary begins to retreat/reposition northward across northern MO
in the face of low-level WAA and diurnal heating. Some uncertainty
remains as to how far north the favorable airmass near the boundary
will retreat and surface cold front. However, given the latest
convective trends compared to assorted CAM guidance since 00Z, and
likelihood of diurnal heating to its north, the general idea remains
on track for strong surface-based destabilization to occur this
afternoon well into southern and perhaps part of central/eastern IA.
That destabilization should continue into the evening ahead of
convection that develops over IA as well, supporting its maintenance
and potential for upscale growth this evening.
The environment south of the front and near the retreating boundary
(which will broaden and become more shallow/diffuse with time) is
reasonably progged to be favorable for both early-stage supercells,
followed by upscale clustering/MCS development tonight. Forecast
soundings suggest steep low/middle-level lapse rates atop upper 60s
to low 70s surface dewpoints, yielding MLCAPE commonly in the 2000-
3500 J/kg range south of the front. Mass response and large-scale
ascent ahead of the approaching shortwave trough will strengthen
vertical shear in tandem with the front and boundary, such that
effective-shear magnitudes of 45-60 kt may be realized, along with
effective SRH in the 200-400 J/kg range.
A small, unconditional significant-tornado area is being added
within the "enhanced" risk, and may need to be adjusted some as
mesoscale trends warrant. The already supercell-favorable ambient
environment will be augmented in the vorticity-maximized
remnant-boundary corridor, where the largest hodographs and very
rich boundary-layer moisture should be maintained. Any relatively
discrete storm remaining in this environment during maturity -- and
especially into the time window when the LLJ enlarges hodographs
still more -- could become an intense and cyclic (but perhaps also
heavy-precip) supercell. A damaging-wind and sporadic large-hail
threat may persist through much of the night over parts of
central/northern IL into IN, both with the MCS and any convection to
its northeast in the strongest WAA/moisture-transport regime.
..Edwards/Leitman.. 09/18/2022
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SPC Sep 18, 2022 1630 UTC Day 1 Convective Outlook
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
1130 AM CDT Sun Sep 18 2022
Valid 181630Z - 191200Z
...THERE IS AN ENHANCED RISK OF SEVERE THUNDERSTORMS SOUTHEAST
IOWA...NORTHEAST MISSOURI...AND WEST-CENTRAL ILLINOIS...
...SUMMARY...
A few intense supercells, capable of very large to giant hail, along
with tornadoes, one or two of which may be strong, may evolve into
an MCS producing scattered severe wind gusts. This appears most
likely across portions of south-central to southeast Iowa, northeast
Missouri, and west-central Illinois, beginning after 5 PM CDT and
continuing through tonight.
...IA/MO/IL...
A low-amplitude shortwave impulse over the western Dakotas will move
east across the Upper MS Valley to the south of a deeper shortwave
trough shifting from MB to far northwest ON. This evolution will
yield an amplifying mid-level jetlet (with 500-mb winds in excess of
50 kts) across southern MN and IA into WI by this evening. A
strengthening baroclinic zone across IA, aided by robust
differential boundary-layer with low 90s into northwest MO and low
70s behind the cold front in northern IA, will support initial
thunderstorm development in the 22-00Z time frame centered on
south-central IA as MLCIN wanes. The initial environment will be
characterized by weak 0-1 km SRH, but large 0-3 km SRH with further
increase in wind speeds through the mid to upper portion of large
buoyancy amid rather steep mid-level lapse rates. This setup appears
favorable for potentially a few long-lived discrete supercells with
the primary hazard being very large to giant hail given the expected
hodograph structure.
The degree of tornado threat is more uncertain. Low-level
southwesterlies will strengthen this evening, but primarily across
northern MO and displaced largely south of expected convective
development. The greatest tornado threat may evolve with the
southern-most supercell which would have uninterrupted inflow and
greater 0-1 km SRH near the IA/MO/IL border during the early
evening. As such, have shifted the inherited 10 sig tor area south,
but this threat appears more conditional than previously forecast.
Consensus of latest CAM guidance still suggests potential upscale
growth into a small MCS as supercells congeal near/east of the MS
River, with the relatively greatest severe wind threat across
southeast IA and far northeast MO into west-central IL. How far
downstream this threat lasts is more uncertain, as there's a
reasonable signal for low-level warm theta-e advection to support
potential regenerative supercells on the upshear (northwestward)
side of broader-scale convective outflow within the feed of steeper
mid-level lapse rates. This may yield a persistent threat for large
hail into the early morning before convection weakens further into
the overnight.
..Grams/Lyons.. 09/18/2022
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