WW 238 SEVERE TSTM MT ND SD WY 312205Z - 010400Z
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 238
NWS Storm Prediction Center Norman OK
405 PM MDT Sun May 31 2020
The NWS Storm Prediction Center has issued a
* Severe Thunderstorm Watch for portions of
Parts of east central and southeast Montana
Southwest North Dakota
West central and northwest South Dakota
Northeast Wyoming
* Effective this Sunday afternoon and evening from 405 PM until
1000 PM MDT.
* Primary threats include...
Scattered large hail and isolated very large hail events to 2
inches in diameter possible
Scattered damaging wind gusts to 70 mph possible
SUMMARY...Scattered thunderstorm development is underway along and
east of a surface trough, and the storms will encounter somewhat
richer moisture to the east and should intensify some this evening.
The storm environment is supportive of a mix of organized clusters
and supercells, with the attendant threat for large hail and
damaging winds.
The severe thunderstorm watch area is approximately along and 60
statute miles east and west of a line from 15 miles east northeast
of Glendive MT to 15 miles southwest of Rapid City SD. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU8).
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
27025.
...Thompson
WW 0238 Status Updates
STATUS FOR WATCH 0238 HAS NOT BEEN ISSUED YET
MD 0776 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR FAR EASTERN WYOMING...SOUTHWEST SOUTH DAKOTA...NORTHWEST NEBRASKA
Mesoscale Discussion 0776
NWS Storm Prediction Center Norman OK
0443 PM CDT Sun May 31 2020
Areas affected...far eastern Wyoming...southwest South
Dakota...northwest Nebraska
Concerning...Severe potential...Watch unlikely
Valid 312143Z - 312345Z
Probability of Watch Issuance...20 percent
SUMMARY...A couple clusters of storms have developed across far
eastern Wyoming and will continue moving eastward into southwest
South Dakota and northwest Nebraska. Marginally severe hail/wind are
possible with these storms. A watch issuance is unlikely given the
isolated, marginal nature of the severe threat.
DISCUSSION...An upper-level shortwave trough is over the northern
Rockies and multiple low-amplitude shortwaves are rotating around an
upper high over Kansas/Oklahoma. A surface pressure trough extends
southward across the northern/central High Plains, which is helping
to focus surface convergence across eastern Wyoming as convective
temperatures are breached this afternoon across the region. Slightly
higher surface dewpoints (50+ F) are east of the surface trough, but
storms should remain high-based with LCLs around 3 km AGL. MLCAPE of
500-1000 J/kg and effective bulk shear of 20-30 knots should allow
for some updraft intensification with multi-cellular convective
modes are likely. Storm splitting and outflow dominant storms are
likely with damaging winds the likely main threat, although large
hail is also possible with the stronger storms. Storms may continue
to develop across eastern Wyoming into the evening before likely
weakening over western South Dakota/Nebraska under higher mid-level
heights/warmer mid-level temperatures.
..Nauslar/Thompson.. 05/31/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...LBF...UNR...BOU...CYS...
LAT...LON 40890352 41160471 43400504 44130513 44360419 44280309
44030223 43700208 43220200 42630199 42030205 41280227
40990277 40890352
MD 0775 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR NORTHEAST WYOMING...SOUTHEAST MONTANA...SOUTHWEST NORTH DAKOTA...AND NORTHWEST SOUTH DAKOTA.
Mesoscale Discussion 0775
NWS Storm Prediction Center Norman OK
0335 PM CDT Sun May 31 2020
Areas affected...northeast Wyoming...southeast Montana...southwest
North Dakota...and northwest South Dakota.
Concerning...Severe potential...Watch possible
Valid 312035Z - 312230Z
Probability of Watch Issuance...40 percent
SUMMARY...Thunderstorm development is probable in the next few
hours, and storms that do form will pose the threat for severe wind
and hail. A watch is possible if sustained, mature convection can
become established.
DISCUSSION...Recent visible satellite imagery shows a growing region
of agitated cumulus developing off of the Big Horn mountains in
northern WY. Thunderstorm development is likely within the next hour
in this region given sufficient MLCAPE values (500-1000 J/kg) and
favorable deep layer shear (30-40 knots of effective bulk shear).
Continued daytime heating and modest low-level moisture advection
across southeast Montana ahead of these storms should continue to
favorably modify the thermodynamic environment by reducing MLCIN and
somewhat augmenting MLCAPE. Given 7-9 C/km lapse rates and a dry,
well-mixed boundary within the lowest 1-2 km, strong to severe
downburst winds will be possible with the stronger storms. As
discrete to semi-discrete storms move into the MT/SD/ND tri-state
region, they should encounter higher instability that will continue
to support strong winds as well as the potential for severe hail.
The main uncertainty with this activity is storm coverage. Weak
forcing for ascent and lingering inhibition over southern/southwest
MT may limit the number of mature storms that will develop over
southwest MT/northern WY and casts some doubt into the overall
severe threat. Trends will be monitored and a watch is possible if
mature convection can become established as it moves towards the
tri-state area.
..Moore/Grams.. 05/31/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...BIS...UNR...BYZ...GGW...RIW...
LAT...LON 45040801 46030807 46720723 47270625 47530457 47320378
46760321 46010306 45060303 44840337 44470460 44360751
45040801
MD 0774 CONCERNING SEVERE POTENTIAL...WATCH UNLIKELY FOR NORTH-CENTRAL INTO NORTHEAST MT
Mesoscale Discussion 0774
NWS Storm Prediction Center Norman OK
0329 PM CDT Sun May 31 2020
Areas affected...north-central into northeast MT
Concerning...Severe potential...Watch unlikely
Valid 312029Z - 312230Z
Probability of Watch Issuance...20 percent
SUMMARY...An isolated strong storm or two could produce gusty winds
and hail across portions of north-central into northeast MT through
early evening.
DISCUSSION...A couple of showers over Blaine County, in the vicinity
of the surface trough/effective cold front, have shown some
intensification on radar recently. Additionally, some vertical
development has been noted in visible satellite imagery. This is
occurring as inhibition across portions of east-central MT continues
to weaken. Temperatures have warmed into the 80s with dewpoints
generally from the mid 50s to low 60s ahead of the surface boundary
and beneath steep midlevel lapse rates. This is supporting MLCAPE
around 500-1000 J/kg. Inhibition remains rather strong across
northeast MT where more persistent mid/high level cloudiness has
precluded stronger heating. Additionally, effective shear remains
marginal across the region, around 20-30 kt. Nevertheless, a strong
storm or two could develop as the surface boundary shifts eastward
toward axis of greater instability. If this occurs, strong gusts and
hail are possible. Given the conditional and isolated nature of the
threat, a watch is unlikely.
..Leitman/Grams.. 05/31/2020
...Please see www.spc.noaa.gov for graphic product...
ATTN...WFO...GGW...TFX...
LAT...LON 49010534 48300542 48010579 47880623 47770737 47800888
48230906 48600914 48990884 49010534
SPC 2000Z Day 1 Outlook
Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0254 PM CDT Sun May 31 2020
Valid 312000Z - 011200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
EASTERN MONTANA AND INTO SOUTHWESTERN NORTH DAKOTA...NORTHWESTERN
SOUTH DAKOTA...AND FAR NORTHEASTERN WYOMING...
...SUMMARY...
A few strong/locally severe thunderstorms may occur across southeast
Montana into southwest North Dakota and northwest South Dakota
between about 4 to 9 PM MDT.
...Discussion...
Latest guidance suggests that no appreciable changes are needed with
respect to current outlook areas/reasoning. Thunderstorm
development in the eastern Montana/northeastern Wyoming vicinity is
expected over the next 1-2 hours, with recent/deep cumulus
development indicated at this time near the Bighorns. A couple of
the strongest storms will be capable of producing hail and gusty
winds, with some upscale growth of storms possible as they spread
eastward with time.
..Goss.. 05/31/2020
.PREV DISCUSSION... /ISSUED 1123 AM CDT Sun May 31 2020/
...Northern High Plains...
Minor spatial changes to the cat 2 severe risk with the possibility
of wind/hail during the late afternoon and early evening.
With the shortwave trough over the northern Rockies advancing
northeast into the Canadian Prairies, mid-level height falls should
only glance the northern High Plains at peak heating. High-based
storm development is anticipated after 21Z across mainly southeast
MT into northeast WY along a lee trough, as a deeply mixed boundary
layer develops with surface temperatures warming into the upper 80s
to mid 90s. The presence of steep lapse rates and a dry/well-mixed
sub-cloud layer should promote efficient downdraft accelerations
with these storms as they spread east towards parts of the western
Dakotas. Here, convection will likely impinge on greater MLCAPE
where low-level moistening occurs beneath an EML capping inversion
that will be increasingly stout with eastern extent. Amid 30-40 kt
effective shear, this could support a few hour uptick in severe hail
potential. Convection will become increasingly elevated and weaken
in the central Dakotas where MLCIN will be immense.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook
NWS Storm Prediction Center Norman OK
1229 PM CDT Sun May 31 2020
Valid 011200Z - 021200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE NORTHERN HIGH PLAINS...AND ALSO THE UPPER MISSISSIPPI VALLEY
VICINITY...
...SUMMARY...
Isolated severe thunderstorms may occur Monday across parts of the
northern High Plains and Upper Mississippi River Valley.
...Synopsis...
Broad upper ridging will prevail across a large portion of the U.S.
Monday, flanked by troughing over the northeastern and northwestern
portions of the country.
At the surface, a very weak front will move across the north-central
U.S., while high pressure prevails over the southern/eastern
portions of the country through the period.
...Upper MS Valley area...
Scattered/elevated showers and thunderstorms will likely be moving
across Minnesota early in the period, as a weak upper disturbance
crosses the region in tandem with a 40 kt southwesterly low-level
jet. As the disturbance rides anticyclonically around the
large-scale ridge into the Upper Great Lakes region through the day,
and the low-level jet veers, storms may be maintained through the
day, spreading east-southeastward across Wisconsin with time. A few
stronger storms -- with some potential for marginal hail and/or a
stronger wind gust -- may occur, warranting maintenance of the MRGL
risk area.
...Northern High Plains...
Afternoon heating/mixing over the High Plains of eastern Wyoming and
into the Nebraska Panhandle may support development of an isolated
storm or two, in the vicinity of the weak cold front progged to be
draped across this area. While shear will remain weak, the deep
mixed layer may contribute to evaporative enhancement of any
downdraft locally.
Overnight, weak QG forcing into the southeast Montana/northeast
Wyoming/western South Dakota/southwestern North Dakota region could
support development of a few elevated storms, one or two of which
could produce hail to severe levels.
..Goss.. 05/31/2020
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0145 PM CDT Sun May 31 2020
Valid 011200Z - 021200Z
...CRITICAL FIRE WEATHER AREA FOR PARTS OF EASTERN NEVADA INTO
WESTERN UTAH...
Much of the forecast remains on track. Surface winds in the latest
model guidance still appear too weak overall to support an Elevated
area across parts of the Northeast into New England. However, should
models trend upward in surface wind speeds, portions of the Mid
Atlantic into New England may need an Elevated delineation in future
outlooks.
..Squitieri.. 05/31/2020
.PREV DISCUSSION... /ISSUED 0123 AM CDT Sun May 31 2020/
...Synopsis...
An upper-level ridge will remain over the central CONUS with an
upper low likely becoming cutoff west of Baja California tomorrow.
Additionally, an upper-level shortwave trough will slightly flatten
the ridge over the northern Rockies and northern Plains as it
traverses along the US-Canadian border. A surface pressure trough is
likely to extend out of the Lower Colorado River Valley into the
Great Basin under southerly mid-level flow of 45-55 mph.
...Great Basin and Four Corners...
Critical conditions are expected again across eastern Nevada and
western Utah tomorrow with south-southwest sustained winds of 20-25
mph and minimum RH of 8-15%. Surrounding areas will experience
locally critical conditions with winds likely being the limiting
factor. Elevated to possibly critical winds/RH are likely to develop
across southwest Wyoming into central Wyoming, and the area received
lightning in the last 24 hours. However, given the sparse fuels,
limited fire history, and recent/forecast precipitation, the
elevated area was not expanded into this area.
Isolated to scattered thunderstorms are likely to develop across
portions of the Four Corners region tomorrow. However, storm motions
will be slower than in past days and this will be multiple
consecutive days (3-5 days, depending on the area) of thunderstorm
activity, which will have likely increased fuel moisture.
...New England...
Locally elevated conditions are possible again tomorrow across
portions of New England. However, winds likely remaining below
elevated thresholds and recent precipitation currently preclude
introducing an elevated area.
...Please see www.spc.noaa.gov/fire for graphic product...
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