SPC Forecast Products

Storm Prediction Center

12/17/2017 02:52 AM
SPC - No watches are valid as of Sun Dec 17 08:53:01 UTC 2017
No watches are valid as of Sun Dec 17 08:53:01 UTC 2017.

12/17/2017 02:52 AM
SPC - No MDs are in effect as of Sun Dec 17 08:53:01 UTC 2017
No Mesoscale Discussions are in effect as of Sun Dec 17 08:53:01 UTC 2017.

12/17/2017 02:52 AM
SPC Dec 17, 2017 Day 4-8 Severe Weather Outlook
Day 4-8 Outlook
Day 4-8 Outlook Image
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0249 AM CST Sun Dec 17 2017

Valid 201200Z - 251200Z

...DISCUSSION...
...Wednesday/Day 4 and Thursday/Day 5...
The medium-range models including the ECMWF, GFS, UKMET and Canadian
move an upper-level trough across the Southeast on Wednesday.
Thunderstorms will be possible ahead of the system during the day
across Alabama and Georgia. The upper-level trough is forecast to
move eastward into the western Atlantic on Thursday. Further west,
an upper-level trough is forecast to move into the Four Corners
region as low-level moisture advection takes place in the southern
Plains.

...Friday/Day 6 to Sunday/Day 8...
The upper-level trough is forecast to move into the Great Plains on
Friday as a moist airmass moves into the lower Mississippi Valley. A
marginal severe threat will be possible along and ahead of a cold
front moving into the lower Mississippi Valley. The ECMWF and GFS
remain similar on Saturday with the cold front moving into the
eastern U.S. and an upper-level trough moving into the central
states. The upper-level trough is forecast to remain in place on
Sunday as a cold and dry airmass settles over much of the CONUS. For
this reason, thunderstorm activity should be limited on Saturday and
Sunday.

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12/17/2017 01:39 AM
SPC Dec 17, 2017 0830 UTC Day 3 Severe Thunderstorm Outlook
SPC 0830Z Day 3 Outlook
Day 3 Outlook Image
Day 3 Convective Outlook  
NWS Storm Prediction Center Norman OK
0137 AM CST Sun Dec 17 2017

Valid 191200Z - 201200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
THE MIDDLE TO UPPER TEXAS COAST INTO SOUTHEAST TEXAS...

...SUMMARY...
Scattered thunderstorms will be possible on Tuesday from the
southern Plains eastward into parts of the lower Mississippi Valley.
A marginal severe threat may develop across parts of the middle to
upper Texas Coast into southeast Texas.

...Middle to Upper Texas Coast/Southeast Texas...
An upper-level low will move from eastern New Mexico eastward into
the southern Plains on Tuesday as an associated upper-level trough
moves from northern Mexico into central Texas. Moisture advection is
forecast to increase ahead of the trough across the middle to upper
Texas Coast as a 30 to 40 kt low-level jet develops Monday morning.
A cold front is forecast to move into east Texas as scattered
thunderstorm development takes place along and ahead of the front
during the day. NAM and GFS forecast soundings for Houston gradually
increase MLCAPE to around 1000 J/kg by midday. This combined with 40
to 50 kt of deep-layer shear and strong low-level shear associated
with the low-level jet, will be sufficient for a marginal severe
threat. Given the strong shear environment, a marginal tornado
threat would be possible. A few strong wind gusts may also occur.
Any severe threat will probably remain concentrated in southeast
Texas Tuesday afternoon where the most instability is forecast. The
severe potential should diminish from west to east as the front
moves eastward.

..Broyles.. 12/17/2017

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12/17/2017 01:15 AM
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
0112 AM CST Sun Dec 17 2017

Valid 181200Z - 191200Z

...Synopsis...
...Portions of Southern CA...

Elevated fire weather conditions will persist across southern CA on
Monday. RH values will start out higher than in previous days during
the morning but will fall into the 15-25 percent range away from the
immediate coastal areas. The surface pressure gradient will be much
weaker, especially heading into the afternoon, but still favorable
for offshore winds. As such, gusty winds will likely be ongoing
Monday morning. Sustained winds around 15-25 mph with higher gusts
will be possible in wind-prone areas before weakening through the
day. Overall, conditions will be much improved over the last week or
so.

..Leitman.. 12/17/2017

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

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12/17/2017 01:14 AM
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
0111 AM CST Sun Dec 17 2017

Valid 171200Z - 181200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHERN AND CENTRAL
CA...
...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF SOUTHERN CA...

...Synopsis...
...Portions of Central into Northern CA this Morning...

Strong north to northeast winds were ongoing as of 07z, and a few
hours of critical fire weather conditions are possible through about
midday. RH values in the 15-25 percent range will be common with
sustained wind speeds around 15-25 mph and higher gusts. Deep-layer
northerly flow will weaken through the day and conditions should
improve by afternoon. Overnight recovery will be good, with RH
values rebounding to around 40 percent or greater.

...Portions of Southern CA...

Gusty winds were ongoing this morning and should continue into at
least this evening. Strong deep-layer northerly flow will persist
longer across the southern portion of the state as the upper trough
only slowly progresses eastward. The surface pressure gradient
across the region is forecast to remain favorable for moderate to
strong offshore winds through at least this evening but could
stretch into early Monday morning. Sustained winds of 15-30 mph with
higher gusts are expected. RH values of 15-25 percent early this
morning will fall to around 10-15 percent during the afternoon.
Overnight recovery should be better tonight compared to recent days,
with values climbing into the 25-45 percent range and even higher
values near the coast.

..Leitman.. 12/17/2017

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

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12/17/2017 12:03 AM
SPC Dec 17, 2017 0700 UTC Day 2 Convective Outlook
SPC 0700Z Day 2 Outlook
Day 2 Outlook Image
Day 2 Convective Outlook  
NWS Storm Prediction Center Norman OK
1151 PM CST Sat Dec 16 2017

Valid 181200Z - 191200Z

...NO SEVERE THUNDERSTORM AREAS FORECAST...

...SUMMARY...
Isolated to scattered thunderstorms are expected across the western
and central Gulf Coast region on Monday into Monday night.

...DISCUSSION...
An anticyclonic west to southwest mid-level flow pattern will remain
in place on Monday across the Gulf Coast region as a moist airmass
remains just offshore. Low-level flow is forecast to be maximized
along the Texas and Louisiana Coasts where isolated to scattered
thunderstorm development will be possible Monday into Monday night.
Instability is forecast to be weak along the western and central
Gulf Coast during the day 2 period. For this reason, a severe threat
is not expected to develop.

Elsewhere, thunderstorm activity is not expected cross the CONUS on
Monday or Monday night.

..Broyles.. 12/17/2017

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12/17/2017 12:02 AM
SPC Dec 17, 2017 0600 UTC Day 1 Convective Outlook
SPC 1200Z Day 1 Outlook
Day 1 Outlook Image
Day 1 Convective Outlook  
NWS Storm Prediction Center Norman OK
1158 PM CST Sat Dec 16 2017

Valid 171200Z - 181200Z

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PARTS OF
COASTAL SOUTHERN LOUISIANA...

...SUMMARY...
A strong wind gust or an isolated/brief tornado may occur near --
but more likely off -- the Louisiana coast this morning.  Otherwise,
severe weather is not expected.

...Synopsis...
A short-wave trough in the upper-level flow will move quickly
eastward from the Canadian Prairies and northern Plains across the
Great Lakes today, while farther south, a low closes off and moves
very slowly eastward along the southwestern U.S./Mexico border.  At
smaller scales, a trough moving quickly across the Ozarks/lower
Mississippi Valley region during the morning will weaken within a
confluent flow field, shifting east-northeast across the Ohio Valley
through the afternoon, and then off the Atlantic coast during the
evening.

At the surface, high pressure will largely prevail over the U.S.,
with a weak low/inverted trough to cross the lower Mississippi
Valley and central Gulf Coast region early in the period before
weakening thereafter.

...Coastal Louisiana...
Convection will be ongoing at the start of the period across the
lower Mississippi Valley area, with thunderstorms largely confined
to southern Louisiana and spreading across southern portions of the
central Gulf Coast states and possibly/eventually the Florida
Panhandle.

With richer Gulf air to remain confined to coastal areas, storms
will largely be elevated above a shallow/stable boundary layer. 
However, given very favorable low-level shear, a brief tornado
cannot be ruled out near the coast.  A locally stronger wind gust or
two may also occur within the organized convective band -- and thus
will maintain low severe probability/marginal risk across a small
portion of southern Louisiana during the morning hours.

..Goss/Leitman.. 12/17/2017

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