- Day Three
acus01 kwns 232000
Storm Prediction Center ac 231959
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0259 PM CDT Thu Mar 23 2017
Valid 232000z - 241200z
..there is a slight risk of severe thunderstorms this afternoon and
evening over parts of the High Plains...
..there is a marginal risk of severe thunderstorms from parts of
Minnesota/Iowa southward into Texas...
..there is a marginal risk of severe thunderstorms over central and
Strong to severe thunderstorms are expected from parts of the
central and Southern Plains to the mid Missouri Valley late this
afternoon into tonight, offering hail and damaging gusts.
Thunderstorms with a marginal risk for severe wind and hail remain
possible this afternoon into the early evening across parts of
central and southern Florida.
..western Texas to western Kansas and NE...
The previous forecast issued for these areas remains valid into
tonight, with no changes needed.
..central and South Florida...
No changes are needed for the marginal severe risk area across
central and South Florida as storms continue to develop and spread to the
west/southwest within a moderately unstable environment. The
general thunderstorm area has been expanded a little north across
west-central Florida (to the north and northeast of tampa), where an area
of showers with sporadic thunderstorm development will persist
through the late afternoon, advancing to the west/southwest.
The general thunderstorm area has been expanded a little to the
north, given a recent lightning strike or two in this area, within a
regime of low-level warm advection near the northeast extent of a
Previous discussion... /issued 1125 am CDT Thu Mar 23 2017/
A large upper trough is moving eastward across the western states
today. Upper-level height falls and associated large-scale forcing
for ascent will spread into the High Plains this afternoon, helping
to initiate scattered thunderstorms. Activity will likely form along
the dryline over western Kansas and the western Texas Panhandle, but also
in a region of stronger low level warm advection and lift across
western and central NE. This scenario will result in a
several-hour-long period of risk of severe storms capable of large
hail and damaging winds in these areas.
The primary forecast problem today is the limited low-level moisture
and capping inversion in place. 12z models suggest that storms will
develop in the 4-6pm window as stronger forcing impinges on the
dryline. Forecast soundings suggest this activity will be mainly
high-based. This will promote strong downdraft winds and
occasionally intense updrafts capable of large hail. Present
indications are that storms will not progress very far eastward this
evening before beginning to weaken due to the onset of diurnal
Forcing for convection will be more subtle over NE this afternoon
and evening. However, this area will be in proximity to the surface
warm front and weak cyclogenesis, where stronger low level vertical
shear is forecast. Storm Mode will likely be more
discrete-supercell in this area, with the potential for an isolated
storm or two capable of very large hail or significant wind gusts.
Low-level moisture will be limited, which should preclude a more
substantial tornado threat.
Few changes have been made to the marginal risk for this region.
Strong daytime heating and sufficient cape will promote scattered
afternoon thunderstorms today. Relatively steep low and mid-level
lapse rates suggest that hail will be possible in the stronger
cells. The coverage of severe storms is expected to remain low, so
will maintain the marginal categorical risk.
acus11 kwns 232054
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 232053
Mesoscale discussion 0312
National Weather Service Storm Prediction Center Norman OK
0353 PM CDT Thu Mar 23 2017
Areas affected...extreme southeastern Wyoming...portions of the
Nebraska Panhandle...southwestern Nebraska...extreme northwestern
Concerning...severe potential...watch likely
Valid 232053z - 232300z
Probability of watch issuance...80 percent
Summary...widely scattered thunderstorms will develop in the next
few hours. Severe hail and wind gusts are the main threat, but a
brief tornado or two are possible in a narrow zone near and around
the warm front. A Severe Thunderstorm Watch will likely be needed.
Discussion...large-scale forcing for ascent associated with an upper
low is slowly approaching the area and contributing to a broad area
of lowering surface pressures across the Central High plains.
Separate low pressure centers...one near cys and the other over
southeastern Colorado should consolidate into a single low over
northeastern Colorado this evening. A dryline stretches from far
southwestern Kansas to near Oga, where it intersects an east-west warm front
that has been reinforced by persistent low-level clouds and showers
from lbf to points east.
Very steep mid-level lapse rates...from 8.5 to 9 c/km...and a tongue
of mid-to-upper 50s boundary layer dewpoints...are contributing to
MLCAPE of 1000-2000 j/kg in the warm, moist air mass. Deep layer
bulk shear of 50-70 kt oriented at a large angle to the dryline and
warm front will support discrete supercells. Any storms that
develop along the dryline south of the warm front will move into a
high-local environment supportive of severe wind gusts, and steep
lapse rates will support severe hail with any of the storms. As
storms move northeast and interact with the warm front...local
enhancement of low-level shear and lowered LCLs could support
low-level rotation. However, given the strong reinforcement of the
cool air north of the warm front and relative fast storm
motions...35-40 kt...oriented at a large angle to the front, only a
brief period will exist where a tornado or two will be possible
before the storms interact with the stable boundary layer. Severe
hail will still be possible with these storms, however, as they
become elevated above the front.
Although the boundary layer is drier over the Nebraska
Panhandle...with dewpoints in the upper 30s to mid 40s...very steep
low and mid-level lapse rates are supporting 250-1000 j/kg of
MUCAPE. Deep inverted-v profiles suggest severe wind gusts and hail
are the primary threats in this area, although severe hail will also
Given the above expectation of a severe threat emerging in the next
few hours, a Severe Thunderstorm Watch will likely be needed for
parts of the area.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 41799879 42199948 42680117 42830256 42710339 42520411
42210447 41720443 41530428 41140376 41060308 41130226
41010171 40490120 40330105 40100095 39800072 39670002
39879901 40569859 41319846 41799879