SPC MD 1406

SPC MD 1406

MD 1406 Image

Mesoscale Discussion 1406
NWS Storm Prediction Center Norman OK
0127 PM CDT Wed Aug 05 2020

Areas affected...northern/northeastern Colorado...southeastern
Wyoming...and western Nebraska

Concerning...Severe potential...Watch possible 

Valid 051827Z - 052030Z

Probability of Watch Issuance...40 percent

SUMMARY...Convection over the higher terrain of Colorado/Wyoming
will migrate eastward/southeastward and deepen through the
afternoon, posing a hail/wind threat in areas downstream.  A WW will
be considered later this afternoon.

DISCUSSION...Deepening convection was noted across higher terrain in
north-central Colorado and south-central Wyoming in the past hour or
so.  These storms are in a steep-lapse-rate environment, with 8-9
deg C/km and boundary layer moisture contributing to weak to
moderate  instability (2000-3500 J/kg MUCAPE) in areas immediately
downstream of initiating convection.  The combination of weak
low-level upslope flow beneath 40 knot westerly mid/upper flow will
allow for developing convection to migrate eastward through the I-25
corridor and into lower elevations over the course of the afternoon,
with initial supercellular structures and clusters potentially
capable of large (perhaps significant) hail and damaging wind gusts.
 A tornado can also not be completely ruled out despite high cloud
bases.  Eventually, one or two linear segments will evolve from
initial convection while moving toward the CO/KS/NE border regions
toward evening.

Pending convective coverage, a Severe Thunderstorm Watch may need to
be coordinated with affected offices in the 19-21Z time frame. 
Trends are being monitored.

..Cook/Kerr.. 08/05/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   42570628 42650501 42260365 41970272 41630220 41310193
            40680184 39660207 38830235 38160331 38020426 38250517
            39020602 39890639 40880638 42570628 

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SPC MD 1405

SPC MD 1405

MD 1405 Image

Mesoscale Discussion 1405
NWS Storm Prediction Center Norman OK
1237 PM CDT Wed Aug 05 2020

Areas affected...Southern Appalachians

Concerning...Severe potential...Watch unlikely 

Valid 051737Z - 051930Z

Probability of Watch Issuance...5 percent

SUMMARY...Widespread multi-cell storm development with the
possibility of a damaging wind gust or two will be possible this
afternoon. A weather watch is unlikely.

DISCUSSION...Visible satellite data showed showers and weak
thunderstorms  developing along a broad frontal zonal located along
the spine of the southern Appalachians. Additional storm development
appears likely this afternoon, given warm and moist surface
conditions, lift along the front, and developing orographic
circulations. Upper-air support for convection is weak and is
forecast to continue decreasing as the closed low over southern
Canada continues to retreat northward. Effective shear is forecast
to remain relatively weak, despite the moderately unstable
conditions present with 1000-1500 J/kg of MLCAPE. As a result, a
multi-cellular storm mode is expected. A few of the stronger storms
may develop sufficiently strong downdrafts to generate near severe
criteria outflow winds. Due to the limited coverage and severe
potential, a weather watch is likely not needed.

..Lyons/Kerr.. 08/05/2020

...Please see www.spc.noaa.gov for graphic product...


LAT...LON   35838344 36678208 37058127 37138053 36817992 36087983
            35578044 34118247 33858311 33738382 34018407 34398426
            35038431 35838344 

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SPC Aug 5, 2020 1730 UTC Day 2 Convective Outlook

SPC Aug 5, 2020 1730 UTC Day 2 Convective Outlook

SPC 1730Z Day 2 Outlook
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1212 PM CDT Wed Aug 05 2020

Valid 061200Z - 071200Z


Isolated strong to severe storms are possible Thursday afternoon and
evening from Montana southward through the central High Plains and
into portions of the Texas Panhandle.  Severe gusts and hail will be
possible with the strongest storms.  Localized damaging gusts may
accompany several thunderstorms from the Delmarva into the western

...High Plains...
A mid- to upper-level ridge over the High Plains will slowly move
eastward across the northern High Plains as a mid-level shortwave
trough moves from the Pacific Northwest into the Northern Rockies
during the period.  The strongest southwest to westerly mid- to
high-level flow will remain across MT and WY with weaker flow
further south that is increasingly displaced from northwestern CONUS
disturbance.  Strong heating is forecast over the High Plains amidst
an adequately moist boundary layer.  Initial thunderstorm
development will favor higher terrain over southwest MT, the Front
Range, and Raton Mesa before storms gradually spread east.  Isolated
to scattered clusters of storms are forecast by early evening with
isolated severe gusts/hail the primary hazards.  The severe risk
will eventually spread east into eastern portions of the Marginal
Risk by mid evening before increasing convective inhibition and
lessening instability lead to a diminishing severe risk.

...Delmarva into the western Carolinas...
A weak mid- to upper trough over the western Great Lakes to the Mid
South will shift slowly east towards the Appalachians during the
day.  A ribbon of 20-35 kt flow will move through the base of the
trough and 20-35 kt effective shear will be sufficient for some
storm organization from the western Carolinas into parts of the
Mid-Atlantic states.  A very moist boundary layer sampled by
Wednesday morning upper-air soundings along the Carolina coastal
plain (12 UTC CHS and MHX showing 16-18 g/kg lowest 100mb mean
mixing ratios), will combine with strong heating to yield moderate
destabilization by early-mid afternoon.  Wet microbursts with
localized gusts primarily in the 50-60 mph range will be capable of
pockets of wind damage with the stronger storms.  The risk for
thunderstorm wind damage will probably focus during the early-mid
afternoon to early evening period before dissipating thereafter.

..Smith.. 08/05/2020

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SPC Aug 5, 2020 1630 UTC Day 1 Convective Outlook

SPC Aug 5, 2020 1630 UTC Day 1 Convective Outlook

SPC 1630Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1130 AM CDT Wed Aug 05 2020

Valid 051630Z - 061200Z


A few severe thunderstorms are possible this afternoon and evening
from the Front Range of the Rockies into adjacent portions of the
central Great Plains.

A fairly significant mid-level low to the northeast of the Great
Lakes region appears likely to accelerate east-northeastward across
Quebec through the remainder of today and tonight.  In its wake, a
broadly confluent mid-level flow regime will prevail east of the
Mississippi Valley, and broadly anticyclonic across much of the
Southeast, on the western periphery of prominent subtropical ridging
over the western Atlantic.  Weak troughing may persist west of the
southern Appalachians, west-southwestward into the north central
Gulf of Mexico, between the Atlantic ridging and another prominent
subtropical high shifting east of the southern Rockies.  A notable
short wave trough is forecast to continue digging from the eastern
Dakotas toward the lower Ohio Valley, downstream of a broad
mid-level ridge axis gradually shifting across and east of the
northern Rockies.  Farther upstream, models indicate that
significant mid-level troughing within the mid-latitude westerlies
will pivot into the British Columbia and Pacific Northwest coast,
gradually coming in phase with weak troughing slowly migrating
into/across California through late tonight.

Despite the transition toward a less amplified mid/upper flow
regime, in the wake of days of larger-scale troughing across the
east, seasonably high moisture content air generally remains focused
along and east of the middle and southern Atlantic Seaboard, and a
corridor across the southeastern Great Plains into the western Gulf
coast.  Steeper lower/mid tropospheric lapse rates associated with
warm elevated mixed-layer air are largely confined to the higher

...Front Range into adjacent Great Plains...
In conjunction with the steep lower/mid tropospheric lapse rates,
and modest low-level moisture, moderate mixed-layer CAPE may again
develop within a sheared regime beneath modest northwesterly
mid-level flow.  In conjunction with orgographic forcing, it appears
that a subtle short wave impulse may focus the most widespread
thunderstorm development near and south of the Cheyenne Ridge
vicinity.  This probably will initiate across the higher terrain by
20-22Z, before intensifying while propagating southeastward.  A
couple of supercells are possible initially, before perhaps growing
upscale into an organizing cluster of storms which may pose a risk
for severe wind, in addition to severe hail.

...Central Great PLains...
As the short wave trough generally digs to the east of the Missouri
Valley, forcing to support thunderstorm development along a
southwestward trailing wind shift across parts of southern South
Dakota and northern Nebraska is unclear.  Moderately large
mixed-layer CAPE may develop along this axis by late this afternoon,
but it may not be until later tonight when a developing zone of
low-level warm advection near/east of the Sioux Falls/Sioux City
area provides supports for appreciable attempts at sustained
thunderstorm activity.  If this occurs, a few strong surface gusts
might not be out of the question.

...Southern Appalachians and Piedmont...
South-southwesterly deep-layer mean flow is generally weak, and in
the process of weakening.  However, downstream of weak mid-level
troughing, moderate boundary-layer destabilization appears possible
across the Piedmont into the higher terrain, where orography may
provide the forcing and focus for thunderstorm development this
afternoon.  Northwestward advancing outflow from ongoing convection
across the coastal plain may provide another focus for thunderstorm
development.  Given the instability, the environment may become
conducive to locally strong, potentially damaging surface gusts
through early evening.

...Piney Woods into upper Texas/Louisiana Gulf coast...
A weak mid-level short wave impulse, and perhaps a convectively
generated impulse and associated outflow, may provide the support
for vigorous new thunderstorm activity while continuing to progress
southeast of the Red River Valley.  Given the seasonably moist
environment, which may also contribute to sizable CAPE in excess of
2000 J/kg, this convection may become accompanied by the potential
to produce strong surface gusts.

..Kerr/Lyons.. 08/05/2020

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
1107 AM CDT Wed Aug 05 2020

Valid 051700Z - 061200Z

The previous forecast remains on track with only minor modifications
needed based on morning observational trends and ensemble guidance
(see previous discussion below for details). It is worth noting the
uncertainty regarding the potential for dry thunderstorms across
southeast WA and southeastern ID. Morning HREF guidance suggests a
storm or two could develop within these regions, but forecast
soundings are not overly supportive of lightning production.
However, a storm or two will be possible, especially over southern
to southeast ID where morning visible imagery shows early signs of
weak lift.

..Moore.. 08/05/2020

.PREV DISCUSSION... /ISSUED 0105 AM CDT Wed Aug 05 2020/

A weak upper-level shortwave will phase with a more substantial
upper-level trough moving into the Pacific Northwest today. At the
surface, a trough will develop in the Great Basin. A cold front will
move into the Washington and Oregon by the end of the period.

...Great Basin...
Dry and windy conditions will develop during the afternoon across
much of the central and southern Great Basin. While mid-level winds
will increase with the approach of the western trough, overall
speeds will still remain modest. Widespread elevated conditions are
expected as 15-20 mph winds coincide with 10-20% RH. A few areas of
locally critical appear possible, but it appears most of these
conditions would occur over desert terrain.

...Northern California and Pacific Northwest...
Isolated to scattered thunderstorms are likely with the greatest
coverage expected to occur within central Oregon. Wetting rain will
be possible in some locations given the forecast PWAT and storm
coverage. Even so, lighting occurring over dry fuels will bring a
concern for fire starts. There is some possibility that this
lighting activity moves northward into eastern Washington during the
evening and overnight. Profiles from forecast soundings are
marginally supportive of lightning across that area, but lift from
the approaching trough may be enough to promote a handful strikes.
Confidence is too low for highlights, however.

...Permian Basin...
With a lee trough developing in the nearby High Plains, locally
elevated conditions are possible within parts of the Permian Basin.
RH will likely fall to 15-20% with winds near 15 mph. Conditions are
not expected to be widespread and may only occur for brief periods.

...Please see www.spc.noaa.gov/fire for graphic product...

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