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- Day Three
000
acus01 kwns 171948
swody1
Storm Prediction Center ac 171947
Day 1 convective outlook
National Weather Service Storm Prediction Center Norman OK
0247 PM CDT Mon Jul 17 2017
Valid 172000z - 181200z
..there is a slight risk of severe thunderstorms over parts of Minnesota
and vicinity...
..there is a slight risk of severe thunderstorms from northeast PA
into Vermont...
..there is a marginal risk of severe thunderstorms over parts of
the central and northern plains and upper Midwest...
..there is a marginal risk of severe thunderstorms over parts of
the northeast states...
..there is a marginal risk of severe thunderstorms across portions
of the lower Colorado River valley and vicinity...
...
Isolated to widely scattered severe thunderstorms are expected into
this evening across portions of the upper Mississippi Valley, and
across portions of the northeast.
...
A marginal risk area has been added for portions of the lower
Colorado River valley and vicinity. Strong surface heating is
ongoing along the northern zone of rich monsoon-related moisture
across portions of the southwest states. Based on the Storm Prediction Center sounding
climatology, the 12z Las Vegas sounding sampled an anomalously
substantial magnitude of precipitable water this morning (around 1.4
inches). With temperatures climbing well into the 90s to around 105f
as dewpoints only slowly fall into the upper 50s to lower 60s,
buoyancy is becoming moderate to strong amid steep low- to mid-level
lapse rates. Convection will continue to deepen along the Mogollon
Rim and westward across the higher terrain of southern Nevada and
vicinity into the late afternoon hours. Intensifying cold pools
should tend to congeal at the meso-Beta scale owing to the
anticipated substantive convective coverage in the moist environment
and along the northern periphery of an mesoscale convective vortex spreading westward across
southern Arizona. Into the evening hours, there will be the potential for
small convective clusters to spread southward/southwestward across
the vicinity of the lower Colorado River valley. Given the
substantial buoyancy, anticipated convective clustering, and dcape
values in excess of 1500 j/kg, the risk for isolated severe wind
gusts may exist -- warranting the addition of the marginal area.
The western part of the slight risk area across portions of the
northeast has been trimmed owing to antecedent convective
overturning in association with loosely organized convective
clusters crossing parts of New York and western New England. This activity
will continue spreading across the updated slight risk area. Modest
air-mass recovery in the wake of this activity could sustain some
isolated severe potential into the early evening, as sufficient deep
shear persists peripheral to a mid-level cyclonic perturbation
crossing parts of southeast Canada.
No other appreciable changes have been made to the ongoing forecast.
.Cohen.. 07/17/2017
Previous discussion... /issued 1109 am CDT Mon Jul 17 2017/
..Minnesota vicinity...
Morning water vapor imagery shows a shortwave trough moving across
ND toward Minnesota. Models remain consistent in the development of
scattered afternoon thunderstorms over eastern ND/western Minnesota, with
storms moving rapidly eastward across the slight risk area. Strong
heating is occurring in this zone, while dewpoints climb into the
mid/upper 60s. This will yield afternoon MLCAPE values over 2500
j/kg with little cap. Forecast soundings also indicate favorable
wind fields, with effective shear values over 35 knots and
considerable low-level shear. These parameters should encourage the
development of rotating/bowing storm structures capable of damaging
winds and large hail. 12z cam solutions suggest the potential for a
fast-moving bowing complex moving into The Arrowhead region this
evening.
...
Current visible satellite imagery shows mostly clear skies with a
growing cu field from central PA across southeast New York into central
New England today. This corridor should become moderately unstable
with MLCAPE values over 1500 j/kg. Thunderstorms are expected to
form relatively early this afternoon over parts of PA/New York and move
eastward across the slight risk area. Mid-level lapse rates are
moderately steep, and winds in the upper-levels are favorable.
However, relatively weak winds through much of the lower-half of the
convective layer lend some uncertainty regarding the overall severe
risk today. Nevertheless, the stronger cells and bowing lines this
afternoon will pose a risk of gusty/damaging winds and hail.
$$
Mesoscale Discussion
000
acus11 kwns 171958
sels mesoscale discussion
Storm Prediction Center mesoscale discussion 171957
wiz000-mnz000-sdz000-ndz000-172100-
Mesoscale discussion 1331
National Weather Service Storm Prediction Center Norman OK
0257 PM CDT Mon Jul 17 2017
Areas affected...portions of the northern plains and upper
Mississippi Valley
Concerning...severe potential...watch likely
Valid 171957z - 172100z
Probability of watch issuance...80 percent
Summary...thunderstorms will continue to develop across the region
through this evening, with an attendant threat of damaging winds,
large hail, and perhaps a Tornado. Watch issuance is likely within
the next hour.
Discussion...a cumulus field continues to organize across portions
of NE South Dakota, southeast North Dakota, and western Minnesota this
afternoon, as a cold front and associated low pressure shift across
the region. Surface heating (i.E., Temperatures in the 90s) has
combined with sufficient boundary-layer moisture and instability
aloft to promote MLCAPE values upwards of 1500-2500 j/kg this
afternoon. While mid-level westerly flow remains modest, veering of
winds with height has provided around 30-40 kt of effective shear.
Combined with ample mid-level buoyancy, a mixture of supercells and
multicell clusters will likely organize over the next few hours,
with a resultant threat of damaging winds and large hail.
Additionally, while low-level flow remains relatively weak, ample
boundary-layer moisture and backed flow with eastward extent may
favor a tornado or two as well this evening. As such, watch issuance
is expected within the next hour.
.Picca/Hart.. 07/17/2017
..please see www.Spc.NOAA.Gov for graphic product...
Attention...WFO...dlh...mpx...fgf...abr...
Latitude...Lon 45199575 45189698 45509747 46309777 46659766 46819738
47209646 47569451 47529304 47479248 47059216 46309220
45619236 45269418 45199575
