SPC Severe Thunderstorm Watch 301

WW 301 SEVERE TSTM MT ND SD WY 212210Z - 220500Z
      
WW 0301 Image
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 301
NWS Storm Prediction Center Norman OK
410 PM MDT Sat Jul 21 2018

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Far Eastern Montana
  Western North Dakota
  Western South Dakota
  Northeast Wyoming

* Effective this Saturday afternoon and evening from 410 PM until
  1100 PM MDT.

* Primary threats include...
  Scattered large hail likely with isolated very large hail events
    to 2.5 inches in diameter possible
  Isolated damaging wind gusts to 70 mph possible
  A tornado or two possible

SUMMARY...Storms will continue to develop and intensify in several
different areas across the region, including a well-organized
cluster of storms already ongoing across northeast Montana into
northwest North Dakota. Large hail and damaging winds will be the
primary concerns as storms, including a few supercells, spread
east/southeastward across a relatively narrow axis of moderately
unstable air through this evening.

The severe thunderstorm watch area is approximately along and 55
statute miles east and west of a line from 25 miles north northeast
of Sidney MT to 55 miles southwest of Rapid City SD. 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.

&&

OTHER WATCH INFORMATION...CONTINUE...WW 300...

AVIATION...A few severe thunderstorms with hail surface and aloft to
2.5 inches. Extreme turbulence and surface wind gusts to 60 knots. A
few cumulonimbi with maximum tops to 550. Mean storm motion vector
29025.

...Guyer

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SPC Severe Thunderstorm Watch 300

WW 300 SEVERE TSTM AL GA NC SC 212140Z - 220600Z
      
WW 0300 Image
URGENT - IMMEDIATE BROADCAST REQUESTED
Severe Thunderstorm Watch Number 300
NWS Storm Prediction Center Norman OK
540 PM EDT Sat Jul 21 2018

The NWS Storm Prediction Center has issued a

* Severe Thunderstorm Watch for portions of 
  Eastern Alabama
  Northern and central Georgia
  Western North Carolina
  Western South Carolina

* Effective this Saturday afternoon and Sunday morning from 540
  PM until 200 AM EDT.

* Primary threats include...
  Scattered damaging winds likely with isolated significant gusts
    to 75 mph possible
  Scattered large hail likely with isolated very large hail events
    to 3 inches in diameter possible
  A tornado or two possible

SUMMARY...Strong mid/high-level northwesterly winds by mid/late-July
standards will continue to overspread a moist and moderate to
strongly unstable air mass across the region, including some areas
that were impacted by early-day storms. This will include the
potential for some supercells capable of large hail and damaging
winds with storms expected to generally spread southeastward through
the evening.

The severe thunderstorm watch area is approximately along and 75
statute miles north and south of a line from 40 miles west northwest
of Auburn AL to 35 miles east southeast of Spartanburg SC. For a
complete depiction of the watch see the associated watch outline
update (WOUS64 KWNS WOU0).

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
3 inches. Extreme turbulence and surface wind gusts to 65 knots. A
few cumulonimbi with maximum tops to 600. Mean storm motion vector
31030.

...Guyer

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SPC Severe Thunderstorm Watch 301 Status Reports

WW 0301 Status Updates
      
WW 0301 Status Image
STATUS FOR WATCH 0301 HAS NOT BEEN ISSUED YET
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SPC Severe Thunderstorm Watch 300 Status Reports

WW 0300 Status Updates
      
WW 0300 Status Image
STATUS FOR WATCH 0300 HAS NOT BEEN ISSUED YET
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SPC Severe Thunderstorm Watch 299 Status Reports

WW 0299 Status Updates
      
WW 0299 Status Image
STATUS REPORT ON WW 299

SEVERE WEATHER THREAT CONTINUES RIGHT OF A LINE FROM 15 NNE CTY
TO 30 NE CTY TO 10 SW SGJ.

..DIAL..07/21/18

ATTN...WFO...TAE...JAX...


STATUS REPORT FOR WS 299 

SEVERE WEATHER THREAT CONTINUES FOR THE FOLLOWING AREAS 

FLC029-041-212040-

FL 
.    FLORIDA COUNTIES INCLUDED ARE

DIXIE                GILCHRIST           


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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No Mesoscale Discussions are in effect as of Sat Jul 21 22:36:02 UTC 2018.

SPC Jul 21, 2018 2000 UTC Day 1 Convective Outlook

SPC 2000Z Day 1 Outlook
      
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
0252 PM CDT Sat Jul 21 2018

Valid 212000Z - 221200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS OVER PARTS OF THE
SOUTHEAST STATES...AND OVER THE NORTHERN HIGH PLAINS...

...SUMMARY...
Strong to severe thunderstorms are expected across parts of the
southeastern U.S. and the northern High Plains.

...20Z Update...

...Discussion...
Overall scenario outlined in the previous outlook discussion
(appended below) remains valid. Scattered thunderstorm development
is still anticipated across the higher terrain of the southern
Appalachians with storm motion into the moist and unstable airmass
extending across the Piedmont and into central GA. Vertical shear is
supportive of storm organization and resulting threat for damaging
wind gusts and hail. More short-term forecast details about this
area can be found in MCD 1122. 

Scattered thunderstorms are also still anticipated across the
northern and central High Plains. Southeasterly low-level flow
beneath moderate westerly flow aloft is resulting 40 to 50 kt of 0-6
km shear. This vertical shear, in tandem with moderate to strong
instability, supports the potential for isolated severe
thunderstorms. Primary severe threats are large hail and damaging
wind gusts. Recent guidance and visible satellite trends suggest
slightly higher severe storms coverage is likely farther south into
more of the NE Panhandle. Consequently, the Slight Risk was extended
southward into more of this region. Eastern extent of the threat is
mitigated by relatively cooler temperatures across the central
Dakotas. Additional information about this area is available in MCDs
1120 and 1121.

..Mosier.. 07/21/2018

.PREV DISCUSSION... /ISSUED 1123 AM CDT Sat Jul 21 2018/

...South GA into North FL...
A long-lived band of thunderstorms is tracking southward across
southern GA.  The air mass ahead of the storms is very
moist/unstable with dewpoints in the upper 70s and temperatures
warming into the 90s.  Increasing northwesterly mid level winds and
remnant mesoscale organization of convective band suggest the risk
of damaging winds across the region through the afternoon.

...North GA/western Carolinas...
In the wake of morning convection, skies are mostly clear across
northern GA into western NC and upstate SC.  Rapid heating and
dewpoints remaining in the lower 70s will yield strong afternoon
CAPE values.  A shortwave trough evident in water vapor imagery over
western KY/TN will approach the region and lead to the development
of scattered thunderstorms.  Strong effective shear values and
relatively steep mid-level lapse rates suggest the potential for
rotating storms capable of large hail and damaging wind gusts.  This
activity may persist through the evening and track across eastern GA
and much of SC.

...Northern High Plains...
Scattered thunderstorms will develop this afternoon from the plains
of eastern MT southward into eastern WY/CO.  Forcing mechanisms are
hard to identify this morning, and the region is under the upper
ridge axis.  Nevertheless, a consensus of 12z model solutions
indicate a few of these storms will become intense with large hail
and damaging winds possible.  Storms should remain strong as they
spread into the western Dakotas and western NE this evening.

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SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0216 PM CDT Sat Jul 21 2018

Valid 221200Z - 231200Z

Relatively small northward and southward expansions have been made
to the isolated dry thunderstorm area across parts of northern CA,
southern OR, and far northwestern NV. Mid-level moisture is forecast
to increase by Sunday afternoon on the western periphery of an upper
ridge, and at least isolated convection should initiate across the
higher terrain of this region. Flow through the cloud-bearing layer
is not expected to be overly strong, and this may tend to limit
storm motions. Regardless, very dry/receptive fuels will likely
support new fire starts with any lightning strikes. Confidence is
not high enough in greater thunderstorm coverage to include a
scattered dry thunderstorm area at this time.

No changes have been made to the isolated dry thunderstorm area
across northeastern NV into northern UT and western WY. Precipitable
water values should be close to 1.00 inch over much of this region,
and wetting rainfall may occur with some thunderstorms. Latest
short-term guidance continues to suggest that there will be a
relative minimum in thunderstorm activity across north-central NV
Sunday afternoon/evening. Have therefore not combined the two
isolated dry thunderstorm areas.

The elevated area across parts of the Snake River Valley of ID
remains warranted, and only minor expansions have been made. The
lack of even stronger forecast low-level winds continues to preclude
a critical area.

..Gleason.. 07/21/2018

.PREV DISCUSSION... /ISSUED 0203 AM CDT Sat Jul 21 2018/

...Synopsis...
A shortwave trough will move through Montana on Sunday and will
de-amplify throughout the day. This will lead to weakening mid-level
flow across much of the Pacific Northwest. Enough flow may remain
for some near-critical wind speeds in eastern portions of the Snake
River Valley during peak afternoon mixing, but currently it appears
sustained winds will remain less than 20 mph. Some isolated dry
thunderstorms will be possible on the periphery of the monsoon along
the northern portion of the Great Basin and also across northern
California into southern Oregon and northwest Nevada. Rainfall in
these areas has been limited over the past week or two and PWAT
values around 0.8 inches indicate that any storms which form will
likely be on the drier side.

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

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