- Day Three
acus01 kwns 232000
Storm Prediction Center ac 231958
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0258 PM CDT Wednesday Jul 23 2014
Valid 232000z - 241200z
..there is a slight risk of severe thunderstorms from eastern Washington into the northern
..there is a slight risk of severe thunderstorms over parts of OK/AR/TX...
..There is a slight risk of severe thunderstorms from PA/New York into New England...
Severe storms with mainly large hail are likely from parts of
Washington eastward into the northern Great Plains this afternoon
into tonight. Storms with locally severe winds will occur through
the evening from eastern New York into New England. Additional
severe storms producing strong and potentially damaging winds are
expected across parts of Arkansas and southeast Oklahoma into North
The previous forecast is generally on track. Only minor changes were
made to the western edge of the sig hail area. Latest rap forecast
soundings and hi-res hrrr suggests better sig hail threat will exist
to the east from near hvr eastward into NE Montana.
..se OK...Nrn/cntrl Arkansas into North Texas...
The slight risk area has been expanded to encompass ongoing severe
storm clusters from NE Arkansas into eastern OK...and to include the dfw
metroplex. Several 60+ miles per hour gusts have already been reported with
ongoing convection...and threat should increase and become better
organized as line/bowing segment propagates generally S/SW into
greater instability. A 30 percent wind area has been included where
midlevel lapse rates are approaching 8 degree c/km and effective bulk
shear values have increased to near 30 knots across parts of southeast OK/SW
Arkansas. Here...strong downdrafts will have a better chance of producing
potentially widespread strong/damaging winds. Hi-res guidance shows
a strong line/bowing segment persisting into North Texas this
evening before weakening after about 01-02z near/just south of the
metroplex. For more details reference mesoscale discussion 1444.
The western extent of the severe threat is a little more uncertain
as some guidance suggests additional storms may develop into SW OK
late this afternoon/early evening. Effective shear and surface dewpoints
/while adequate/ diminish with westward extent however. As
such...the 5 percent area has been expanded slightly westward to
account for at least a small potential for isolated strong/severe
storms into this evening.
No changes needed.
Previous discussion... /issued 1128 am CDT Wednesday Jul 23 2014/
..northern rockies into High Plains...
A rather strong upper trough is digging into the Pacific northwest
region. Increasing large scale forcing and destabilization will
help to initiate scattered thunderstorms over the mountains of
eastern Washington/Oregon into Idaho and western Montana late this afternoon and
evening. Strengthening winds aloft and steep lapse rates will
promote the risk of strong/severe storms capable of hail and
damaging winds. During the evening...storms are expected to develop
eastward into the plains of central/eastern Montana where stronger low
level winds and moderate cape values will result in a greater risk
of supercell storm structures. These may be capable of very large
hail or isolated tornadoes...mainly after dark.
12z model solutions are less bullish on evolution of storms into the
Dakotas late tonight...so have reduced severe probabilities in this
region. Consensus of models also suggests that initiation of storms
over eastern Wyoming into western South Dakota will be very isolated this afternoon
and evening...so have reduced severe probs in this area as well.
A remnant cluster of thunderstorms is tracking southeastward over
southeast Kansas. Meanwhile scattered altocumulus castellanus/high-based storms are
forming over central Arkansas. It seems likely that some combination of
these two clusters of convection will spread south-southwestward
into eastern OK and western Arkansas this afternoon. Dewpoints in the middle
70s and strong heating will lead to extreme instability...along with
30+ knots of effective shear. More recent model solutions show
remarkable agreement that a bowing structure may form in this region
and pose a risk of damaging winds this afternoon and evening.
Storms may move into northeast Texas before weakening after dark.
A band of thunderstorms is slowing increasing along/ahead of a cold
front extending from Lake Erie into eastern Quebec. Strong heating
ahead of the front and ample low level moisture will yield afternoon
MLCAPE values of 1500-2000 j/kg. 12z observed and model forecast
soundings suggest that winds aloft will not be particularly
strong...and that middle level lapse rates will be only marginally
steep today. This suggests that while convective coverage may be
rather high...its unclear how many storms will become severe.
Nevertheless...have maintained the slight risk area across the
acus11 kwns 232307
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 232306
Mesoscale discussion 1449
National Weather Service Storm Prediction Center Norman OK
0606 PM CDT Wednesday Jul 23 2014
Areas affected...northestern Texas...southern Arkansas and northern la
Concerning...Severe Thunderstorm Watch 431...434...
Valid 232306z - 240030z
The severe weather threat for Severe Thunderstorm Watch
Summary...storms will continue to pose a threat for strong to
damaging wind gusts until middle evening from northestern Texas through southern Arkansas
and northern la. A new ww will likely be required south of ww 434 to
include northestern Texas and northwestern la.
Discussion...a large mesoscale convective system with expansive trailing cold pool and
stratiform region extends from east-central Arkansas southwestward through extreme northestern
Texas into extreme southeastern OK moving south at 30-35 knots. The latest
objective analysis indicates the storms are currently moving through
axis of maximum cape. However...downstream warm sector remains
moderately unstable with temperatures around 90f and 70f dewpoints.
Given the moist surface layer...weak cap and strong convergence along
the gust front...storms should continue developing southward next 3-4
hours before the stabilizing boundary layer contributes to the
ultimate demise of the mesoscale convective system later this evening.
..please see www.Spc.NOAA.Gov for graphic product...
Latitude...Lon 33839600 33189427 33799253 34309161 33409152 32299316
31939489 32699621 33719654 33839600