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acus01 kwns 210559
swody1
Storm Prediction Center ac 210558
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
1258 am CDT Thu Sep 21 2017
Valid 211200z - 221200z
..there is a marginal risk of severe thunderstorms across portions
of the north-central u...
...
Hail-producing storms are possible from the eastern Dakotas into the
Upper Peninsula of Michigan Thursday night.
...
Amplification of the upper flow field over the U.S. Is expected
today, as positive-tilt troughing over the western states acquires a
more neutral tilt with time. This will manifest as short-wave
energy digs southeastward across California and the Great Basin. In
response, ridging will increase across the eastern states.
At the surface, Tropical Storm Jose is forecast to linger off the
southeast New England coast, while weakening with time. Meanwhile,
a cold front is forecast to progress across the intermountain west
in conjunction with amplification of upper troughing. Ahead of the
main frontal advance, weak cyclogenesis is expected over the
Nebraska/South Dakota area overnight as a weak lead short-wave
trough aloft moves northeastward across the plains.
..the north-central states...
Weak short-wave troughing shifting northeast across the plains
through the second half of the period will combine with development
of a southerly nocturnal low-level jet to yield some increase in
quasi-geostrophic ascent across the north-central U.S. Overnight
Thursday and into Friday morning. With relatively steep mid-level
lapse rates contributing to fairly substantial elevated cape, ascent
should prove sufficient for isolated/elevated storm development
during the late evening and overnight hours. With sufficient
veering of the wind field with height expected within the
cloud-bearing layer, a couple of organized -- possibly rotating --
storms could evolve, which would be accompanied by a risk for large
hail. With that said, questions persist regarding potential for --
and coverage of -- convective development, and thus at this time
will maintain only 5%/marginal risk area.
.Goss/Dean.. 09/21/2017
$$
Mesoscale Discussion
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acus11 kwns 202017
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 202017
wiz000-ilz000-iaz000-mnz000-202215-
Mesoscale discussion 1662
National Weather Service Storm Prediction Center Norman OK
0317 PM CDT Wed Sep 20 2017
Areas affected...northeast Iowa through central Wisconsin
Concerning...severe potential...watch possible
Valid 202017z - 202215z
Probability of watch issuance...40 percent
Summary...storms may become capable of producing a few strong to
locally damaging wind gusts and hail this afternoon into early
evening from northeast Iowa into southern and central Wisconsin.
Trends will continue to be monitored.
Discussion...cold front extends from western WI through northeast
and southwest Iowa. Upper 60s f dewpoints have advected through
pre-frontal warm sector which, in conjunction with diabatic warming,
have boosted surface temperatures to 85-90 resulting in 2000-3000
j/kg MLCAPE. Despite weak forcing aloft and a gradual weakening of
the low-level jet in wake of a shortwave trough lifting north
through Manitoba and western Quebec, convergence and a destabilizing
boundary layer are sufficient to initiate storms along the front
this afternoon. While the stronger winds aloft remain Post frontal,
moderate flow with 40-50 kt in the 700-400 mb layer resides in
frontal zone, but vertical shear remains modest and supportive of
mostly multicells and possibly some marginal supercell structures.
Primary limiting factor for a more robust threat is the weak
mid-level lapse rates with warm temperatures aloft (-6 to -7 c at
500 mb). Nevertheless, overall parameter space appears sufficient
for at least a modest risk for isolated strong to damaging wind
gusts and some hail.
.Dial.. 09/20/2017
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...grb...mkx...dvn...arx...dmx...
Latitude...Lon 43339151 44479055 44898969 44348877 43398889 42608981
42059139 42529221 43339151
