- 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 231748
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 231747
Mesoscale discussion 0310
National Weather Service Storm Prediction Center Norman OK
1247 PM CDT Thu Mar 23 2017
Areas affected...central and southern Florida Peninsula
Concerning...severe potential...watch unlikely
Valid 231747z - 232015z
Probability of watch issuance...20 percent
Summary...thunderstorms will continue to increase in intensity and
coverage the next few hours but will pose a low threat for
marginally severe hail and brief wind gusts through the afternoon.
Discussion...widely scattered thunderstorms have percolated along
the East Coast of the central and southern Florida Peninsula through
the late morning hours ahead of a weak upper-level
perturbation...with one cell now showing some organization and weak
mid-level rotation moving southward into St. Lucie County.
Mixed-layer cape of 500-1250 j/kg aided by mid-level lapse rates of
7.5-8 c/km...somewhat larger than typical for late March in southern
Florida...should continue to allow for updrafts strong enough to
support small hail production. Marginally severe hail and brief
severe wind gusts are possible in the strongest updrafts that show
some mid-level rotation.
As low-level lapse rates steepen in afternoon heating, the larger
evaporative cooling should strengthen/amalgamate cold pools that
spread south and southwest to the Gulf of Mexico coast. Weak wind
shear in the lowest 1 km directed toward the cold pool motion should
augment the tendency for cold pools to spread rapidly south and
west. Although mean wind speeds are relatively weak, vertical bulk
wind shear magnitudes of 25-35 kt in the 1-8 km layer should
continue to support some thunderstorm organization for the expected
continuation of south-southwesterly storm motions. Otherwise...the
primary Mode will be multicellular/pulse in nature with storms
propagating somewhat discretely along the spreading cold pools. The
intensity and coverage of the threat is expected to remain low
enough to prevent a watch.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 28038068 27508032 26548003 25708017 25258037 25148081
25218109 25868156 26348204 26938234 27268249 27728256
28138234 28308161 28278112 28038068