- Day Three
acus01 kwns 211254
Storm Prediction Center ac 211252
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0752 am CDT Tuesday Apr 21 2015
Valid 211300z - 221200z
..there is a marginal risk of severe thunderstorms West Texas to southern portions KS/MO...
a few thunderstorms may produce hail and/or gusts near severe limits
this afternoon and evening over some of southern Kansas and
Missouri. Isolated strong to severe hail and thunderstorm gusts are
also possible this afternoon through tonight over the southern High
Plains and into western Oklahoma.
Upper-air pattern is characterized by split flow over western North
America and large area of cyclonic flow east of rockies. Latter flow
field is related to middle/upper-level low initially located over western
ls. Cyclone is forecast to move slowly east-northeastward across ls and parts of ont
to its NE through remainder period...orbited by several shortwave
perturbations and accompanying vorticity maxima. High-amplitude
ridging now over inland Pacific northwest and western Canada is forecast to shift eastward
as trough now over northestern Pacific moves ashore British Columbia and amplifies southeastward over
Pacific northwest coast. As this occurs...weak southern-stream low -- now near California
Channel Islands -- will move slowly inland/northeastward and reach southern Sierra
by 12z. Foregoing shortwave ridge -- currently located from northern Arizona
southeastward across Chihuahua -- will move northeastward to southern High Plains by end of
period. Vorticity maximum associated with weak shortwave trough --
evident in moisture-channel imagery over Pacific near 28n125w -- will
pivot cyclonically around southern semicircle of California perturbation then
move over northwestern mex after 00z...reaching nm/mex border around 12z.
At surface...leading cold front has moved offshore middle Atlantic and extends
southwestward over NC Outer Banks region to northern Florida and N-central/W-central
Gulf S bro. Cold front should move southeastward on Florida Peninsula while
weakening/decelerating. Gulf portion of cold front likewise will
weaken...with western segment soon returning northward across S Texas as diffuse
warm front. Secondary cold front -- now developing over northern plains
-- is expected to strengthen and move southeastward to northern MO...southern Nebraska and
central Wyoming by 00z...reaching Kentucky...southern MO/northern Arkansas Ozarks...and western OK
by 12z. Overnight...weak surface low is expected to develop over Texas
Panhandle...in zone of warm frontogenesis extending east-southeastward across southern
OK. This low may link with western segment of secondary cold front by
12z. As moisture returns northward through Texas...dryline should develop
from S-north across West Texas.
..KS/MO area...Aftn/early evening...
diabatic surface heating...steep midlevel lapse rates...and precipitable water
increasing into marginal .5-inch to .75-inch range will support
development of weakly inhibited MLCAPE in 250-500 j/kg range this
afternoon ahead of secondary cold front...near prefrontal
trough/confluence line. Though buoyancy will be limited by lack of
greater moisture...favorable deep shear and elongated/nearly
straight-line hodographs may support brief severe potential with any
sustained thunderstorms. Onset of nocturnal low level jet and impingement of combined
cold-frontal zone and warm-frontogenetic regime may help to continue
some thunderstorms on western limb of this process into evening over southern
Kansas...perhaps merging into initially separate nocturnal convective
regime described below.
..srn High Plains...Late afternoon through overnight hours...
isolated thunderstorms may form over higher terrain of eastern nm and move eastward
into increasing moisture...and/or in vicinity of sharpening dryline. Any
activity that does develop will occur atop well-mixed subcloud
layers that will support maintenance to surface of any hail/gusts
generated aloft..including some downdraft acceleration. Despite
increase in precipitable water...support for convection will be marginal with only 40s
to lower 50s surface dew points realized before dusk. Lack of more
robust moisture and of substantial upper-level support will limit
organized severe potential.
Late in period...probably after 06z...thunderstorms rooted above surface should
develop around eastern Texas Panhandle or northwestern OK. This area will reside
near juxtaposition of several important sources of lift at various
scales--cold front...elevated warm front...and northern rim of 30-40 knots
low level jet associated with substantial low-level warm air advection and increasing
moisture. This activity may continue southeastward over OK into day-2 period
and influence development/evolution of more widespread/sfc-based/svr
mesoscale convective system discussed in that outlook.
acus11 kwns 210633
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 210633
Mesoscale discussion 0411
National Weather Service Storm Prediction Center Norman OK
0133 am CDT Tuesday Apr 21 2015
Areas affected...northeast NC/far southeast Virginia
Concerning...Tornado Watch 93...
Valid 210633z - 210800z
The severe weather threat for Tornado Watch 93 continues.
Summary...an isolated severe risk continues overnight mainly across
far northeast NC/extreme southeast Virginia. Tornado Watch 93 continues
Discussion...ahead of a cold front...a quasi-linear band of
convection has evolved early in the overnight across across
northeast/east-central NC...with the strongest part of this
convective line near/immediately east of I-95 in areas just
northeast of Rocky Mount as of 0615z. The preceding air mass remains
modestly unstable/weakly inhibited amid modest boundary layer
moisture with surface dewpoints in the lower 60s f.
Low-level winds are generally weak/southerly...while strong /40+ knots/
winds just above the surface have tended to veer and are now more
uniform southwesterly per regional WSR-88D vwp data. With aid of
modest low-level storm-relative inflow...a quasi-linear Mode should
remain prevalent as storms spread east-northeastward overnight.
Particularly given a trend of weakening convergence near the
southwest portion of the line...the strongest/most-organized storms
including small bowing segments are likely to continue to across far
northeast NC and possibly extreme southeast Virginia...particularly as
storms interact with immediately preceding outflow. Locally damaging
winds and a brief tornado risk remain possible.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 35817865 36497722 36897682 36737609 36147619 35707772