acus01 kwns 251932
Storm Prediction Center ac 251930
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0230 PM CDT Sat may 25 2013
Valid 252000z - 261200z
..there is a slight risk of severe thunderstorms across parts of the northern
and Central High plains...
Severe probabilities have been adjusted upward across the southern High
Plains into portions of western Kansas for this afternoon/evening. Despite
relatively weak deep layer shear...very steep lapse rates will
contribute to somewhat greater risk of hail/wind with any storms
that manage to organize from southeastern nm across the western Texas Panhandle
into western Kansas. Latest visible/radar imagery suggest deepening convection
across Lincoln County nm and considerable cumulus is now observed northward
along the Lee slopes of the nm rockies. For this reason have
increased severe probs to 15 percent for hail/wind.
Elsewhere...1630z outlook has been changed little. Strong heating
across the High Plains will prove instrumental in severe
thunderstorm development from eastern Montana into the Nebraska Panhandle. Latest
visible imagery suggests this process is in its infancy and thunderstorms should
evolve along western fringe of moisture/instability over the next few
Previous discussion... /issued 1127 am CDT Sat may 25 2013/
Little change to the synoptic pattern is forecast during the d1
period with upper lows centered over the Pacific northwest into southwestern Canada
and New England...and ridging from mb/on southward into the middle/lower-MS
valley. Within the prevailing southwesterly midlevel flow regime from the
Great Basin into northern/Central High plains...morning water vapor imagery
shows a weak impulse over Wyoming which should continue northeastward into the
Dakotas today. Elsewhere...a sheared vorticity maximum over Texas will
slowly progress eastward.
In the low levels...an elongated Lee cyclone will be maintained from
eastern Wyoming into southwestern Nebraska/northestern Colorado. A trough/dryline will extend southward from
the low pressure to along the Texas-nm border with an inverted trough
situated over central or eastern Montana. A warm front will stretch southeastward from
an intersection with the Lee trough across southeastern Montana into the middle-MO
valley while an outflow boundary gradually modifies across northern Kansas.
..nrn/Central High plains this afternoon into tonight...
A gradual deepening of the Lee cyclone will result in the backing
and strengthening of the low-level wind field which...in turn...will
enhance the nwwd flux of an increasingly moist planetary boundary layer from the Central
Plains into South Dakota. This process will occur beneath an eml...
characterized by 700-500-mb lapse rates of 7.5-8.5 c/km...per 12z
radiosonde observations. When coupled with daytime heating...the air mass from southeastern
Montana into the Central Plains is expected to become moderately to
strongly unstable with MLCAPE values approaching 1500-3000 j/kg.
Elevated thunderstorms have already developed this morning over eastern Montana into
western ND and northestern Wyoming where DCVA associated with above-mentioned
vorticity maximum and low-level warm air advection are interacting with a steep
lapse rate environment /see 12z rap sounding/. The more recent
storm development near and north of the Black Hills will likely persist
today with storms eventually becoming rooted within the
destabilizing planetary boundary layer...along and S of surface warm front. Other
surface-based storms should develop this afternoon along the Lee
trough and/or favored terrain as daytime heating and the influence
of the migratory short-wave trough overcome remaining convective
Supercells appear likely as the initial storm Mode given a
vertically veering wind profile with 40-50 knots of westerly deep-layer
shear. Large hail will be the predominant hazard...though a few
tornadoes will be possible this afternoon into evening from southeastern Montana
into western parts of South Dakota/Nebraska where a corridor of enhanced low-level
shear is forecast. Upscale growth of storms into clusters or an mesoscale convective system
is anticipated later this evening into tonight with a continued
threat for hail and damaging winds.
..srn High Plains this afternoon and evening...
The juxtaposition of a moist planetary boundary layer and eml will promote moderate
instability this afternoon along the length of the Lee
trough/dryline with afternoon MLCAPE values of 1000-2500 j/kg
forecast. Though large-scale forcing for ascent will remain
negligible through the peak of the diurnal heating cycle...low-level
convergence along with orographic influences will promote isolated
storm development amidst a kinematic environment featuring veering
winds with height. Marginal vertical shear /bulk shear values at or below
30-35 knots/ may limit the degree of storm organization...though
isolated occurrences of hail and damaging winds will be possible
through this evening.
..cntrl/southern Texas this afternoon into tonight...
The influx of a very moist air mass /I.E. Precipitable water values approaching two
inches/ should maintain scattered thunderstorms in vicinity of midlevel vorticity
maximum slowly moving across central Texas. Deep-layer vertical shear is
weak...though the moist/low local environment coupled with modest
low-level shear may be sufficient to support storm rotation with a
risk for a brief tornado. Otherwise...excessive rainfall will
remain the primary hazard.
acus11 kwns 252312
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 252311
Mesoscale discussion 0798
National Weather Service Storm Prediction Center Norman OK
0611 PM CDT Sat may 25 2013
Areas affected...eastern nm...West Texas...western Texas/OK panhandles
Concerning...severe potential...watch possible
Valid 252311z - 260015z
Probability of watch issuance...40 percent
Summary...ongoing strong/severe storms may increase somewhat in
coverage this evening. A Severe Thunderstorm Watch is being considered.
Discussion...several strong/potentially severe thunderstorms are ongoing
across eastern nm as of 23z. While upper flow is marginal...modest southwesterly
midlevel flow of atop southeasterly surface winds is resulting in effective shear
of 25-30 kts...which is sufficient for some storm organization when
combined with moderate MUCAPE of 1500-2500 j/kg. Large hail will be
possible with any organized multicell/marginal supercell
structure...while severe winds will also be possible given large
temperature/dewpoint spreads. Some upscale growth is possible as outflows
merge this evening...though a general lack of upper level support
and diminishing of available buoyancy with diurnal cooling will
begin to limit the threat near/after sunset.
While this scenario is marginal for organized severe wind/hail...ww
issuance will be considered if coverage trends continue to
increase...especially across southeastern nm and adjacent areas of West Texas.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 32820486 33860451 35350412 36950358 37000258 36960186
36980155 36050157 35550161 35020176 34800177 33800193
33060209 32080254 31460359 31700506 32820486