RSS Mesoscale Discussions from Storm Prediction Center
WW 341 SEVERE TSTM CO NM 181845Z - 190200Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 341
NWS Storm Prediction Center Norman OK
1245 PM MDT Sat Aug 18 2018
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Southeast Colorado
Northeast New Mexico
* Effective this Saturday afternoon and evening from 1245 PM
until 800 PM MDT.
* Primary threats include...
Scattered large hail likely with isolated very large hail events
to 2 inches in diameter possible
Scattered damaging wind gusts to 70 mph possible
SUMMARY...Thunderstorms will develop off the mountains of
south-central Colorado and northeast New Mexico, and track eastward
across the watch area this afternoon. Large hail and damaging winds
will be possible in the strongest cells.
The severe thunderstorm watch area is approximately along and 60
statute miles east and west of a line from 40 miles east northeast
of Limon CO to 40 miles southeast of Las Vegas NM. For a complete
depiction of the watch see the associated watch outline update
(WOUS64 KWNS WOU1).
PRECAUTIONARY/PREPAREDNESS ACTIONS...
REMEMBER...A Severe Thunderstorm Watch means conditions are
favorable for severe thunderstorms in and close to the watch area.
Persons in these areas should be on the lookout for threatening
weather conditions and listen for later statements and possible
warnings. Severe thunderstorms can and occasionally do produce
tornadoes.
&&
AVIATION...A few severe thunderstorms with hail surface and aloft to
2 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 500. Mean storm motion vector
28025.
...Hart
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WW 0341 Status Updates
STATUS REPORT ON WW 341
THE SEVERE WEATHER THREAT CONTINUES ACROSS THE ENTIRE WATCH AREA.
..GLEASON..08/18/18
ATTN...WFO...PUB...GLD...BOU...ABQ...
STATUS REPORT FOR WS 341
SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS
COC009-011-017-025-039-041-055-061-063-071-073-089-099-101-
182140-
CO
. COLORADO COUNTIES INCLUDED ARE
BACA BENT CHEYENNE
CROWLEY ELBERT EL PASO
HUERFANO KIOWA KIT CARSON
LAS ANIMAS LINCOLN OTERO
PROWERS PUEBLO
NMC007-021-033-047-059-182140-
NM
. NEW MEXICO COUNTIES INCLUDED ARE
COLFAX HARDING MORA
SAN MIGUEL UNION
THE WATCH STATUS MESSAGE IS FOR GUIDANCE PURPOSES ONLY. PLEASE
REFER TO WATCH COUNTY NOTIFICATION STATEMENTS FOR OFFICIAL
INFORMATION ON COUNTIES...INDEPENDENT CITIES AND MARINE ZONES
CLEARED FROM SEVERE THUNDERSTORM AND TORNADO WATCHES.
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MD 1319 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF WESTERN/CENTRAL NE AND FAR NORTHEASTERN CO
Mesoscale Discussion 1319
NWS Storm Prediction Center Norman OK
0326 PM CDT Sat Aug 18 2018
Areas affected...Portions of western/central NE and far northeastern
CO
Concerning...Severe potential...Watch unlikely
Valid 182026Z - 182300Z
Probability of Watch Issuance...20 percent
SUMMARY...Isolated strong to locally damaging winds may occur with
thunderstorms moving eastward through this evening. Watch issuance
is unlikely.
DISCUSSION...20Z surface observations show a lee trough located
across western NE and northeastern CO. Low-level convergence along
this boundary and large-scale ascent attendant to an eastward-moving
shortwave trough have acted to generate thunderstorms across this
region over the past hour or so. Temperatures in the mid to upper
80s, dewpoints in the upper 50s to lower 60s, and modestly steep
mid-level lapse rates around 7.0 C/km are contributing to about
1500-2000 J/kg of MLCAPE along and east of the surface trough.
Similar to farther north in western SD, stronger mid-level
south-southwesterly winds are expected to generally lag to the west
of the surface boundary through the evening. This should limit
effective bulk shear values to no more than 20-25 kt across the warm
sector, and thunderstorms will likely struggle to become organized.
Even so, there may be some potential for isolated strong to locally
damaging winds given steep low-level lapse rates as convection
increases in coverage along the surface trough this afternoon into
the early evening. A couple instances of marginally severe hail
cannot be ruled out either. The overall severe threat will likely
remain too isolated/marginal to warrant watch issuance.
..Gleason/Hart.. 08/18/2018
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...BOU...CYS...
LAT...LON 40460292 40970300 42000276 42490282 42940293 42950057
42220060 41060097 40530138 40450212 40460292
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MD 1318 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR PORTIONS OF WESTERN/CENTRAL SD AND FAR NORTHEASTERN WY
Mesoscale Discussion 1318
NWS Storm Prediction Center Norman OK
0245 PM CDT Sat Aug 18 2018
Areas affected...Portions of western/central SD and far northeastern
WY
Concerning...Severe potential...Watch unlikely
Valid 181945Z - 182215Z
Probability of Watch Issuance...5 percent
SUMMARY...Thunderstorms should continue developing along a surface
trough/front this afternoon, with very isolated large hail and
strong/gusty winds possible. Due to the marginal nature of the
severe threat, watch issuance is not expected.
DISCUSSION...Initial convective development has occurred this
afternoon across the Black Hills region of western SD as an upper
trough/low centered over western WY continued eastward. Additional
thunderstorms may develop over the next couple of hours along a
surface trough/front evident in 19Z surface observations across this
region. Even with increasing mid/upper-level cloudiness spreading in
from the west, surface temperatures have generally warmed into the
mid 80s to lower 90s, and MLCAPE increases from around 500 J/kg west
to 2000 J/kg east across western/central SD. The 12Z sounding from
UNR showed lapse rates around 8.0 C/km in the 700-500 mb layer, and
several cores of potentially large hail have been recently noted
over the Black Hills per MRMS MESH estimates. The main limiting
factor that will likely preclude a greater severe risk is
displacement of stronger mid-level winds and related shear to the
west of the greater instability. Even so, very isolated large hail
will be possible with any thunderstorms given the steep mid-level
lapse rates present, and strong/gusty downdraft winds could also
occur along and east of the surface trough/front where low-level
lapse rates are steeper and instability is greater.
..Gleason/Hart.. 08/18/2018
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...ABR...UNR...
LAT...LON 43050308 43860361 44450432 44980399 45710349 45880304
45920189 45710107 44900037 43860038 43030059 43050308
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SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0300 PM CDT Sat Aug 18 2018
Valid 182000Z - 191200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER THE HIGH
PLAINS OF SOUTHEAST COLORADO/NORTHEAST NEW MEXICO AND INTO SOUTHWEST
KANSAS AND THE TEXAS/OKLAHOMA PANHANDLES...
...SUMMARY...
Isolated to scattered severe storms are most likely over the
southern High Plains late this afternoon and this evening.
...Discussion...
No appreciable changes appear necessary to the ongoing outlook areas
at this time, as prior forecast reasoning as laid out in prior
outlooks remains valid. Isolated thunderstorms are ongoing over
southern New England, where an isolated stronger gust remains
possible. Storms are also developing from southeast Virginia
southwestward across the Carolinas (please refer to SWOMCD #1317)
and over western South Dakota (please refer to SWOMCD #1318), where
severe risk may exist with a few stronger/developing updrafts.
Finally, storms are developing at this time over the southern and
eastern Colorado vicinity, in/near the existing SLGT risk area, and
should continue to increase gradually in coverage and intensity this
afternoon and evening, where hail and damaging winds will be
possible with stronger storms (please refer to SWOMCD #1316).
..Goss.. 08/18/2018
.PREV DISCUSSION... /ISSUED 1116 AM CDT Sat Aug 18 2018/
...High Plains...
Morning water vapor loop shows a shortwave trough moving eastward
across the northern Rockies. This system will eject into the
northern and central High Plains this afternoon, providing lift and
favorable shear for a few strong/severe storms. Scattered storms
are expected over eastern WY/CO/NM by mid afternoon, spreading
eastward into western SD/NE/KS and the TX Panhandle during the
evening.
While locally damaging wind gusts and hail are possible throughout
this region, low-level theta-e and resultant CAPE is forecast to be
higher from southeast CO into the TX Panhandle. Most 12z CAM
solutions show an organized cluster of storms traversing this
corridor later today.
...Carolinas/Southeast VA...
A shortwave trough and subtle mid-level speed max are noted over
east TN. As this impulse moves into western NC later today,
scattered thunderstorms are expected to form over the MRGL risk
area. Weak vertical shear will limit convective organization. But
robust CAPE and high PWAT values may lead to locally damaging wind
gusts in the stronger cells.
...Southern New England...
Visible satellite imagery and radar shows scattered convection
beginning to form along a cold front sagging into southern New
England. Relatively strong westerly flow aloft, coupled with
dewpoints in the lower 70s and modest daytime heating, will yield an
environment marginally favorable for gusty/damaging winds in the
stronger cells this afternoon. Please refer to MCD #1315 for
further details.
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SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1227 PM CDT Sat Aug 18 2018
Valid 191200Z - 201200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS FROM OKLAHOMA
AND PARTS OF NORTH TEXAS EASTWARD THROUGH ARKANSAS AND THE OZARKS...
...SUMMARY...
A few severe storms will be possible mainly Sunday afternoon and
evening over parts of the southern Great Plains, Ozarks, and
Ark-La-Tex region.
...Synopsis...
With stronger flow aloft confined to Canada Sunday, a relatively
weaker flow regime will prevail across the CONUS. Within this flow
field however, three areas of troughing are evident. Two -- one
departing the East and a second moving into/across the Pacific
Northwest -- will contribute to areas of convection, but very little
severe risk.
However, limited/low-end severe risk may accompany the third feature
-- a trough crossing the Great Plains region. This trough will
contribute to weak surface cyclogenesis -- with a weak low center
initially in the vicinity of Oklahoma shifting slowly northeast
across southeast Kansas and eventually into western Missouri. As
this low develops, a cool front will progress southward across
Oklahoma and the High Plains of Texas, while a warm front shifts
north across the Mid-Mississippi/Tennessee/lower Ohio Valleys later
in the period.
Elsewhere, a trailing cold front -- associated with an upper trough
crossing central Canada -- is expected to move across the northern
Plains/upper Mississippi Valley region through the period, with
showers and a few thunderstorms likely accompanying.
...Oklahoma/north Texas east through Arkansas and the Ozarks...
An ongoing -- though largely disorganized -- cluster of
thunderstorms is forecast to be crossing the Great Plains region at
the start of the period, ahead of the advancing upper trough. While
small hail and gusty winds may be possible with a few of the
stronger early-day updrafts -- particularly across the Oklahoma
vicinity -- storms should remain largely sub-severe.
Though weak cyclogenesis will likely occur through the day,
lingering clouds/convection will result largely in weak lapse rates
as well as some hindrance with respect to daytime heating.
Therefore, although a belt of enhanced (40 kt) westerly mid-level
flow will spread across this region, convective intensity -- and
thus severe risk -- should remain limited. Some redevelopment of
storms near the leading edge of the remnant convection/possible MCV
may occur over eastern Oklahoma and into the Ozarks vicinity, while
some heating in the wake of the convection may allow a few cells to
develop over southern Kansas and northern/western Oklahoma. While
gusty winds and marginal hail may occur with a few stronger
updrafts, overall risk appears likely to remain quite limited
through the period.
...MAXIMUM RISK BY HAZARD...
Tornado: 2% - Marginal
Wind: 5% - Marginal
Hail: 5% - Marginal
..Goss.. 08/18/2018
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SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0210 PM CDT Sat Aug 18 2018
Valid 191200Z - 201200Z
The ongoing forecast is on track. A few thunderstorms will develop
late in the evening across central/eastern Oregon and vicinity, with
dry lightning strikes possible outside of any wetting cores.
Additionally, locally elevated fire weather conditions will develop
in the lee of the Sierras (far western Nevada and far northeastern
California) during peak heating hours as surface winds increase to
around 15 mph amidst critically low (<15%) RH.
See the previous discussion for more details.
..Cook.. 08/18/2018
.PREV DISCUSSION... /ISSUED 0139 AM CDT Sat Aug 18 2018/
...Synopsis...
Another mid/upper-level trough is expected to progress eastward into
the Pacific Northwest on Sunday, as the downstream system moves
slowly eastward into the central Plains. The primary fire weather
concern will be the potential for thunderstorm development ahead of
the trough across parts of the Northwest into the northern Rockies.
...Northern/Central OR...Central ID...Far Southeast WA...Western
MT...
After a relatively warm and dry day across portions of the interior
Northwest, increasing large-scale ascent and midlevel moisture will
support the potential for elevated, high-based thunderstorm
development across portions of central/northern OR and adjacent
parts of southeast WA and central ID by early evening. Relatively
fast storm motions and dry subcloud layers will limit rainfall
potential with these storms, resulting in an isolated dry
thunderstorm threat.
Isolated thunderstorm development is also possible across parts of
eastern ID into western MT by late afternoon, largely driven by
sufficient instability and terrain-related circulations. This area
is forecast to be somewhat cooler and more moist compared to further
west, and storm motions will likely be somewhat slower, so this
region has not been included within an isolated dry-thunderstorm
delineation at this time.
...Please see www.spc.noaa.gov/fire for graphic product...
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