LU9DCE > ALERT 09.07.18 00:03l 255 Lines 14539 Bytes #999 (0) @ WW
BID : 10192_LU9DCE
Subj: Storm Prediction Center 08 07 2018
Sent: 180708/2121Z 10192@LU9DCE.TOR.BA.ARG.SOAM BPQ6.0.16
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MD 1019 CONCERNING SEVERE POTENTIAL...WATCH POSSIBLE FOR PARTS OF
SOUTHEASTERN NORTH DAKOTA AND ADJACENT PORTIONS OF SOUTH DAKOTA
INTO NORTHWEST MINNESOTA
Mesoscale Discussion 1019 NWS Storm Prediction Center Norman OK
0116 PM CDT Sun Jul 08 2018
Areas affected...Parts of southeastern North Dakota and adjacent
portions of South Dakota into northwest Minnesota
Concerning...Severe potential...Watch possible
Valid 081816Z - 082045Z
Probability of Watch Issuance...60 percent
SUMMARY...Ongoing thunderstorm development across parts of central
North Dakota is expected to persist, with an eventual more rapid
intensification possible while spreading into Minnesota by the 3-5
PM CDT time frame. This may be followed by additional thunderstorm
development southwestward across southeastern North Dakota.
Timing remains a bit uncertain, but it seems probable that a severe
weather watch will be needed by late afternoon.
DISCUSSION...Some increase in convective development appears underway
across portions of central North Dakota (roughly to the north of a
Bismarck/Jamestown line). This is currently within a narrow band,
likely associated with a zone of enhanced lower/mid tropospheric
warm advection, near the nose of a plume of very warm elevated
mixed-layer air emanating from the Great Basin. Models suggest that
this forcing will gradually shift eastward through areas near/east
of Bemidji MN between now and 20-22Z, before the elevated mixed-layer
plume becomes suppressed southward in the wake of stronger mid-level
height falls spreading into northwestern Ontario.
The latest Rapid Refresh suggests that inhibition for moist
pre-frontal boundary layer air is beginning to diminish along
this corridor. As this weakens further with continuing insolation,
there appears potential for this initially elevated convection to
become rooted in the boundary layer. As this occurs, coincident
with boundary layer parcels becoming characterized by CAPE in excess
of 2500-3000 J/k, a more rapid intensification likely will ensue.
Beneath 40-50 kt westerly 500 mb flow, this may include the evolution
of supercell structures posing a risk for severe hail and perhaps an
isolated tornado, before the risk for strong surface gusts becomes
Thereafter, in the wake of this initial activity, additional
thunderstorm development may occur west/southwestward along the
pre-frontal surface trough across southeastern North Dakota into
adjacent portions of South Dakota by 22Z.
...Please see www.spc.noaa.gov for graphic product...
LAT...LON 48039678 48009442 47149400 46139711 45569843 45619955
46509999 47199915 48039678
SPC 1630Z Day 1 Outlook
Day 1 Convective Outlook NWS Storm Prediction Center Norman OK 1122
AM CDT Sun Jul 08 2018
Valid 081630Z - 091200Z
...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS THIS
AFTERNOON/EVENING FOR PARTS OF THE DAKOTAS/MN AND AZ...
...SUMMARY... Severe thunderstorms are possible this
afternoon/evening across portions of the Dakotas/Minnesota and
...Synopsis... Midlevel ridging will dominate from the Rockies to
the OH Valley, with the main belt of westerlies from the Pacific
Northwest to the northern Plains/upper Great Lakes. South of the
ridge, deep easterly flow and moist profiles (PW values at or above
2") will again support scattered (mainly diurnal) thunderstorms
across the Gulf Coast states. Low-midlevel moisture increases
with the early stages of the Southwest monsoon will also support
scattered thunderstorms over the high terrain of the central/southern
Rockies. The areas with the greatest potential for organized severe
storms will be from southeastern ND into northern/central MN this
afternoon/evening, and storms with strong/damaging outflow winds
will be possible this afternoon/evening across central AZ.
...Eastern Dakotas/MN through early tonight... Thunderstorm clusters
from overnight have been weakening gradually this morning over the
MN Arrowhead. Outflow with these storms, as well as differential
surface heating, will reinforce the synoptic cold front drifting
southeastward across ND and northwestern MN and provide a focus
for additional thunderstorm development this afternoon/evening.
Afternoon temperatures in the 80s and a narrow corridor of
boundary-layer dewpoints in the upper 60s to lower 70s, beneath
the northeastern extent of an elevated mixed layer, will support
strong buoyancy (MLCAPE values 2500-3000 J/kg) with weak convective
Surface-based thunderstorm development is expected in the 20-23z
time frame near the front/outflow, along the southern fringe
of the ongoing convection now approaching east central ND in
association with an embedded mid-upper speed max. Storms will
subsequently spread east-southeastward and develop southwestward
along the boundary. Wind profiles and buoyancy will support the
possibility of supercells initially, though storm interactions
should lead to upscale growth into clusters/lines this evening.
Thus, large hail and damaging winds will be the main threats this
evening into early tonight, though a tornado or two may occur with
the initial storms across northern MN.
...Central AZ this afternoon/evening... The large-scale pattern
is transitioning to a summer regime with the early stages of the
Southwest monsoon underway. Modified 12z soundings suggest buoyancy
will be rather modest (MLCAPE of 500-750 J/kg) near and southwest of
the Mogollon Rim. However, hot afternoon temperatures will drive
a deep mixed layer and inverted-v profiles supportive of strong
downdrafts, while a belt of 25-35 kt east-northeasterly midlevel
flow will help convection move from the higher terrain toward the
lower deserts. The coverage/intensity of the storms away from the
Rim is still somewhat in question, but there still appears to be
some threat for a few strong/damaging gusts this afternoon/evening.
SPC 1730Z Day 2 Outlook
Day 2 Convective Outlook NWS Storm Prediction Center Norman OK 1206
PM CDT Sun Jul 08 2018
Valid 091200Z - 101200Z
...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF ARIZONA AND THE LOWER COLORADO RIVER VALLEY...
...SUMMARY... Isolated strong to severe gusts are possible over
portions of Arizona and the Lower Colorado River Valley late Monday
afternoon through the evening.
...Synopsis... An expansive anticyclone centered over
Colorado/Wyoming will continue to dominate the synoptic pattern
Monday. Modest easterly mid-level flow will persist on the southern
extent of this anticyclone over Arizona and New Mexico. A ridge
axis will extend into Montana and the Dakotas through the day in
advance of a vigorous mid-level disturbance, which will approach
the Pacific Northwest late Monday night into Tuesday morning.
...Arizona into the Lower Colorado River Valley... A seasonally
moist low-level airmass (characterized by 50s to low 60s F
dewpoints and 1-1.75 inch PW values) will remain in place during
the forecast period across the region. Strong insolation will aid
in weak to moderate destabilization, with thunderstorm development
likely along higher terrain/ridgelines during peak heating hours.
Mid-level flow will aid in westward propagation of these storms
into lower-elevation areas as cold pools mature, with damaging
wind gusts becoming increasingly possible through the evening
hours as storms approach the Lower Colorado River and vicinity.
5%/marginal wind probabilities remain in place for this regime,
and portions of this area may need a Slight risk upgrade in later
outlooks depending on convective coverage.
...Southern Montana into northern Wyoming... Despite stout mid/upper
ridging across the region, models persist in developing scattered
convection across the region on the southern periphery of stronger
mid-level flow to the north. Weak to moderate buoyancy will foster
very isolated downburst potential with any storms, although this
threat should be very localized given weak shear profiles.
...MAXIMUM RISK BY HAZARD... Tornado: <2% - None Wind: 5%
- Marginal Hail: <5% - None
SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK
1128 AM CDT Sun Jul 08 2018
Valid 081700Z - 091200Z
...CRITICAL FIRE WEATHER AREA FOR NORTHWEST NEVADA AND FAR NORTHEAST
No changes were made to ongoing elevated and critical areas.
Extended the dry thunderstorm area westward to include any storms
that develop on the Sierras this afternoon. Limited instability
will support only an isolated threat of thunderstorms, but any
storms which form will likely be on the drier side considering
PWAT values are forecast to be around 0.7 or 0.8 inches with a dry
.PREV DISCUSSION... /ISSUED 0116 AM CDT Sun Jul 08 2018/
...Synopsis... A short-wave trough located over the Northern
Great Plains and southern Canada will move eastward throughout
the day, with a small ridge developing in its wake across the
Northern Rockies and another short-wave trough entering the Pacific
Northwest. Enhanced mid-level flow will accompany these features
throughout the day. Farther south, upper-level high pressure will
remain in place across portions of the Great Basin and Desert
...Central California... Afternoon heating will lead to RH values
falling into the single digits, coincident with the development
of sustained northerly winds of 10-15 mph. Fuels in this region
remain marginally receptive to large-fire spread. Nevertheless,
elevated fire-weather conditions are likely across this region.
...Western Great Basin... Daytime heating and vertical momentum
transfer will allow enhanced mid-level flow to extend toward the
surface, leading to sustained westerly winds of 10-20 mph for most
areas, with a zone of enhanced winds of 15-25 mph possible across
portions of far northwest Nevada and far northeast California. RH
values will also fall into the teens during the afternoon in the
presence of dry and receptive fuels. Thus elevated to critical
fire-weather conditions will develop across the region.
...Central Great Basin... As subtropical moisture continues to
advect westward along the southern periphery of the upper-level high
pressure, there will remain a chance for dry/isolated thunderstorms
during the afternoon. The best chance for dry lightning fire starts
will be confined to areas where precipitable water values remain
below 0.75-1 inch. The previous forecast appears on track and thus
no adjustments were made to the highlighted area.
...Please see www.spc.noaa.gov/fire for graphic product...
SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK
0223 PM CDT Sun Jul 08 2018
Valid 091200Z - 101200Z
Only slight modifications to ongoing elevated areas. Trimmed the
eastern edge of the isolated DryT area to take Utah out due to
deeper moisture moving into that area.
Winds will likely reach 20 to 25 mph for a few hours in the late
afternoon and early evening in the Columbia River Gorge and Columbia
Basin. RH values will drop to around 25 to 35 percent and will
start to rise as a higher dewpoint airmass west of the Cascades
accompanies the strengthening winds through the Gorge. Therefore,
an elevated area was added to cover the marginal/brief critical
fire weather conditions which may be possible.
Also added an isolated DryT area for northeast Washington and far
northern Idaho. Forcing along the cold front ahead of an approaching
shortwave trough will be sufficient for convective development after
06Z. Instability may limit the number of lightning strikes, but with
around 200 to 300 J/kg MUCAPE, at least a few strikes are possible.
These showers/storms will likely be quite dry given a storm speed of
35 to 40 mph and limited moisture with PWAT values around 0.8 inches.
.PREV DISCUSSION... /ISSUED 0119 AM CDT Sun Jul 08 2018/
...Synopsis... A ridge located over the Northern Rockies will
amplify throughout the forecast period, while a short-wave trough
enters the Pacific Northwest. Farther south, upper-level high
pressure over the Great Basin and Desert Southwest will move east
toward the Central Rockies.
...Central California... Sustained northerly winds of 10-15 mph
and single-digit RH values should redevelop during the afternoon
hours. Thus, an area delineating the potential for elevated
fire-weather conditions has been included, with perhaps locally
critical conditions possible in terrain-favored locations.
...Western Great Basin... Diurnal heating will again allow enhanced
mid-level flow over the region to extend toward the surface,
resulting in sustained westerly winds of 10-15 mph and RH values
into the teens. Currently winds do not appear as strong as indicated
on Day 1/Sunday, but any enhancement to flow aloft may warrant the
inclusion of a critical area in later outlooks.
...Central Great Basin... Despite an eastward progression of the
upper-level high pressure, there should be enough subtropical
moisture left in the region to result in a few isolated dry
thunderstorms during the afternoon. This area has been refined
considerably, as precipitable water values are forecast to be a bit
higher (exceeding 1 inch) than previously indicated across much of
Utah, negating the dry thunderstorm potential here.
...Please see www.spc.noaa.gov/fire for graphic product...
Weekends were made for programming.
-- Karl Lehenbauer
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