- Day Three
acus01 kwns 211936
Storm Prediction Center ac 211934
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0234 PM CDT sun Sep 21 2014
Valid 212000z - 221200z
..no severe thunderstorm areas forecast...
scattered showers and a few thunderstorms with gusts approaching
severe levels are expected from the eastern Great Lakes across the
central Appalachians to the middle south. Scattered thunderstorms with
isolated strong thunderstorm wind gusts are also expected across
parts of the southwest and Great Basin this afternoon and evening.
a cold front continues to spread southeastward across lower MS/OH/TN river
valleys and into the lower Great Lakes region. Heating ahead of this
front and strengthening wind fields may still allow for isolated
severe wind gusts this afternoon before sunset. For more information
see mesoscale discussion 1754.
..NV into Utah...
Heating is leading to an increase in storm coverage across Nevada into
southwestern Utah under the upper trough with cool temperatures aloft.
Relatively cool surface temperatures exist across northern areas thus
have shunted the 5% wind probs farther southwestward. Veering and increasing
winds with height should favor a few strong cells capable of small
hail and perhaps strong wind gusts. For more information see
mesoscale discussion 1755.
Previous discussion... /issued 1125 am CDT sun Sep 21 2014/
A strong shortwave trough over the Great Lakes will pivot
east-northeast with the greatest 500mb height falls expected across
the St. Lawrence Valley and adjacent areas of New York/Vermont through tonight.
A belt of 60-75kt cyclonic middle-level flow will translate through the
eastern flank of the trough...from Ohio...across the central
Appalachians...and then over northern New England...through early
Monday. A weaker and warmer disturbance east of the Outer Banks is
forecast to accelerate northward and skirt southeast New England
coastal waters before becoming absorbed by stronger westerlies over
the Canadian maritime provinces late tonight.
Latest indications provide no compelling evidence to increase severe
weather probabilities ahead of the Great Lakes/Ohio Valley upper
trough and its associated strong surface cold front. A leading band
of showers moving east from northeast New York to eastern WV Panhandle
appears to be decaying as it becomes removed from deep-layer forcing
for ascent to the west. Despite generally clear skies and surface
heating immediately ahead of this leading convective band...latest
guidance and radar trends across western PA/New York support the idea of
new development occurring along the surface cold front. This
activity will spread east into a relatively stable airmass in the
wake of the leading band of showers/clouds. Despite strengthening
dynamics and the presence of 40kt vertical shear...new convection
will likely struggle given lack of greater buoyancy. A few line
segments/persistent storms may move east at up to 40kt and produce
minor wind damage such as downed limbs/trees but greater organized
severe weather potential appears limited.
..Delmarva/central Appalachians southwest to Tennessee Valley...
The trailing portion of the middle/upper trough will spread south from
the Ohio River valley with a smaller secondary height fall center
forecast across the southern Appalachians/Tennessee Valley by Monday
morning. Widely scattered thunderstorms should develop along/ahead
of the cold front as diurnal heating contributes to modest
destabilization. Stronger instability /SBCAPE around 1500 j per kg/
is forecast with southwestward extent along the front but these
areas also become increasingly removed from stronger large-scale
forcing and vertical shear needed for more persistent/organized
convection. While stronger storms with some potential to produce
wind damage may be realized just about anywhere along the extensive
frontal zone...from the central Appalachians and middle-Atlantic
southwest across the Tennessee Valley...the sporadic/limited nature of this
threat does not appear to warrant higher severe thunderstorm wind
probabilities with this outlook.
Thunderstorms are expected to continue across much of Utah today
amidst relatively deep moisture and broad zone of persistent lift on
the eastern flank of slow-moving closed low over Nevada. Additional
diurnal storm development may occur within/near the cyclone center
over Nevada where latest visible satellite imagery depicts strong
surface heating now underway beneath relatively colder temperatures
aloft. Pockets of stronger unidirectional deep-layer shear may lend
support for a couple of more persistent fast-moving cells/lines over
Utah... while a deeper mixed boundary layer over Nevada results in areas
of higher dcape. Both regimes could support isolated damaging gusts
through early evening.
acus11 kwns 211915
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 211915
Mesoscale discussion 1755
National Weather Service Storm Prediction Center Norman OK
0215 PM CDT sun Sep 21 2014
Areas affected...portions of central/eastern Nevada into far southwest
Utah and northwest Arizona
Concerning...severe potential...watch unlikely
Valid 211915z - 212045z
Probability of watch issuance...20 percent
Summary...a few strong storms may produce gusty winds this afternoon
across parts of central and eastern Nevada into southwest Utah and far
northwest Arizona. The severe threat is expected to remain limited and a
watch is not expected.
Discussion...thunderstorm coverage is increasing across southern and
central Nevada early this afternoon as daytime heating results in weak
destabilization. While high temperatures will remain on the cool
side this afternoon /mainly 70s/...steepening low level lapse
rate...increasing dcape and modest deep-layer shear may allow for a
few strong thunderstorm wind gusts as cells quickly migrate toward
the N/NE. Midlevel lapse rates will remain modest at best except
near the upper low center where colder temperatures aloft reside.
This...coupled with weak instability /less than 1000 j per kg
MLCAPE/ should generally limit longevity/intensity of individual
cells and any severe threat should remain brief and isolated. A
Severe Thunderstorm Watch is not expected.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 36481403 36511342 36701302 37041297 37661271 38281289
39401336 39901398 40141461 40391540 40511622 40451685
40031737 39551762 39181779 38891782 38241752 37591696
37171656 36851571 36661482 36481403