***February Severe Weather***

Thread starter #1

Day 4-8 Convective Outlook
NWS Storm Prediction Center Norman OK
0338 AM CST Sat Feb 04 2017

Valid 071200Z - 121200Z

Model differences/uncertainty persist at this time, with respect to
evolution of the large surface storm system to move across the
eastern third of the U.S. Day 4/Tuesday. However a somewhat more
consistent depiction of major features within the ECMWF and GFS
permits what appears to be a reasonable ability to highlight a 15%
severe risk area from roughly the mid Ohio Valley southward into the
central Gulf coastal region. Within this area, somewhat modest but
sufficient CAPE development should occur ahead of a
strengthening/advancing cold front -- particularly from the Ohio
Valley southward -- to permit development of fairly robust updrafts
by afternoon. Though what appears likely to be a westerly component
to the low-level warm-sector flow field should limit tornado
potential, large hail and locally damaging winds will be possible --
with potential for both rotating storms and lines/line segments.
Convection should eventually weaken overnight, especially over
northern parts of the risk area as storms move into a less-unstable
environment. Risk may linger farther south, as storms move into the
southern Appalachians overnight.

By Day 5/Wednesday, greater uncertainty exists, with the GFS
depicting the front to have moved off the Atlantic and Gulf coasts
by midday, while the ECMWF lingers a trailing, west-to-east portion
of the front over the Gulf Coast States/Carolinas through the
afternoon. Given these differences, will not highlight a risk area
at this time for Day 5.

Risk appears minimal for Day 6, but potential for convection could
increase into the central U.S. Day 7 and into the East Day 8 as the
next storm system shifts out of the Rockies. Model differences are
substantial enough with respect to the details, however, that no
risk areas will be considered at this time.

..Goss.. 02/04/2017
Thread starter #3
SPC AC 060752

Day 2 Convective Outlook CORR 1
NWS Storm Prediction Center Norman OK
0152 AM CST Mon Feb 06 2017

Valid 071200Z - 081200Z




Showers and scattered thunderstorms are forecast to affect the mid
Mississippi, Ohio, and Tennessee Valley areas and central Gulf Coast
States, and later spreading eastward across the Appalachians.
Isolated strong/locally severe storms will be possible mainly west
of the mountains.

Fast/low-amplitude cyclonic flow aloft will prevail Day 2/Tuesday
across much of the country. Several smaller scale vorticity maxima
embedded within the flow (comprising the broader troughing moving
across the eastern half of the country) will be associated with the
main area of convective risk this period.

At the surface, a low initially over the northern IL vicinity,
should deepen steadily while shifting northeast across the Great
Lakes region through the afternoon and evening, and then into
western Quebec late. A trailing northeast-to-southwest cold front
is progged to shift southeast across the OH/mid MS/TN Valleys, and
as far east as the Northeast/New England overnight.

...Ohio/mid and lower Mississippi/Tennessee Valleys and vicinity...
A complex scenario remains evident across the Day 2 risk area, with
successive model runs continuing to trend farther north with the
surface low and associated cold frontal progression with time.
Further complicating the scenario will be a lead short-wave trough
progged to shift into/across the risk area during the late morning
and afternoon hours.

At this time, it would appear that to main rounds of convection may
occur -- one ongoing early in the period which should shift
gradually eastward across the risk area through the afternoon and
evening, followed by some convective redevelopment across the OH and
TN Valley area overnight as the cold front advances southeastward
across this region.

While overall strength of the flow aloft across the region will
support shear sufficient for organized storms, degree of instability
remains questionable due to persistent/widespread convection and
cloud cover. Coverage of stronger cells, as well as mode, also
remains a question -- particularly during the first round of
convection crossing the area given the lack of a larger-scale
surface focus for storm development. Thus, while the scenario
remains nebulous with respect to the details, locally gusty/damaging
winds will likely be the main risk with stronger storms, though
marginal hail and even a tornado or two may also occur.

..Goss.. 02/06/2017
Thread starter #4
Looking at soundings and it looks like it could get a little bumpy late Wednesday into the after Midnight hours of Thursday for Georgia. It isn't the SPC area shown for Alabama and extreme NW Ga at present. Not sure why they aren't including Mid North Ga (I-20 corridor south to Central Georgia / Macon parallel) Maybe they see something I don't, but the 500mb winds out of the NW will be significant with a moist SW flow at the surface.

I first looked at the convective severe maps for that period that showed what looked like an elevated risk, so I pulled a sounding for Atlanta. We'll have to keep an eye and ear out the next couple of days and keep those weather radios ON !!!

severe 00z 0308.png

severe 03z 0308.png

blkshr 00z 0308.png

Thread starter #5
Looking at the NAM data on Pivotal WX everything is consistent with the COD Met maps I posted in the last post. This isn't appearing to be overtly threatening at present, but the ingredients are potentially there if it wants to ramp it up a notch.

Thread starter #6
To accompany my posts from earlier in this week associated with this afternoon's potential severe threat.

If this gets rough it is going to come through fast so very little warning will be available other than SPC NWS "polygons" and your weather radio, so be ready.

Simple math tells us with this time frame that this stuff will be clipping along at 40-50mph to cover this terrain in this time frame so straightline winds could be a big factor as squall lines develop. We're looking at near 70°f today so lifting mechanisms will be in place. Near 1.5" of PWAT is available so it will be soupy. Updraft helicity is minimal, which is in our favor. Most significant tornado parameters will be from S. Cent. AL to Lagrange, down to Columbus and over to Macon. Same for composite severe TS potential, but don't rule out some strong gusts for SOWEGA later tonight either.

So once again, keep your eyes and ears tuned. The time periods are from 14z to 18z on these slides. That is entering extreme NW GA around 6pm and passing SOWEGA up to Augusta around 5-6am.

Here is an hour by hour, slide by slide simulated radar shot.

Last edited:
Thread starter #7
Here is today's SPC. They missed the most severe potential areas I outlined, but that doesn't surprise me anymore.

SPC AC 081300

Day 1 Convective Outlook
NWS Storm Prediction Center Norman OK
0700 AM CST Wed Feb 08 2017

Valid 081300Z - 091200Z



Isolated severe thunderstorms may develop this afternoon and early
evening across parts of the Tennessee Valley and southern
Appalachians, continuing eastward into the Carolinas and southern
Virginia tonight.

...TN Valley/Appalachians to Carolinas and southern VA...
An upper trough (and related speed max) currently over the
north-central Plains/middle MO Valley will continue to amplify and
steadily progress east-southeastward toward the TN Valley and
Appalachians tonight. A cold front will advance generally
east-southeastward across the TN Valley and central/southern
Appalachians through tonight, with a frontal wave expected to
gradually deepen and steadily progress east/northeastward late this
afternoon into tonight.

While the boundary layer will not be particularly moist (50s F
surface dewpoints in many areas) or unstable ahead of the cold
front, relatively cool mid-level thermal profiles, related steep
lapse rates aloft should support some stronger/sustained updrafts
this afternoon. This would most likely initially occur across parts
of eastern TN and nearby southeast KY and far northern portions of
AL/GA. Relatively long/generally straight hodographs could support
some initial lower-topped splitting storms/supercells with a severe
hail risk, with storms subsequently spreading eastward toward/across
the Appalachians this evening with at least some hail/localized
damaging wind risk.

..Guyer.. 02/08/2017
Thread starter #14
February 16th

I mentioned it earlier. Here is the GFS showing a LPS coming out of the gulf with a pretty good weather maker for that period. Will be keeping an eye on this one. The potential for wrap around intrusion of cold air could bring us violent storms as well as white stuff on the backside. It's just too early to tell, but it is looking to be a doozy if it holds.

Thread starter #15
Between 9am Wednesday morning and 3 pm Wednesday afternoon folks in SOWEGA should keep their ears and eyes open. Not a big threat but the soundings I just did for the GFS panels from S. AL to SE GA were showing increasing intensity with the heating of the day as this next system moves across. Soundings gave me ranges from Severe potential to Tornado.

Y'all be on the lookout as this stuff rolls through. It should be moving at a pretty good clip.

SPC AC 130819

Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0219 AM CST Mon Feb 13 2017

Valid 151200Z - 161200Z


Showers and scattered thunderstorms are forecast across parts of the southeast U.S. Wednesday, with a few severe storms possible from southern parts of Alabama, Georgia, and South Carolina southward across Florida.

Large-scale ridging aloft is forecast to persist across western North America Day 3/Wednesday, while an eastern U.S. trough continues moving slowly eastward.
A smaller/southern-stream wave will cross the central Gulf coastal region early in the period, and continue to become absorbed within the larger-scale northern-stream troughing over the East.

At the surface, high pressure is progged to affect much of the country, though lee troughing in the vicinity of the High Plains is forecast to persist/drift east through the period. Otherwise, a low associated with the weakening southern-stream perturbation will cross the southeast U.S. during the day, while a trailing cold front shifts across the western and central Gulf of Mexico, and eventually southeastward across much of Florida through the end of the period.

...The Southeast...
Largely elevated showers and a few thunderstorms are progged to be ongoing at the start of the period, with any surface-based storms likely confined to the southern AL/FL Panhandle vicinity. As the surface low moves eastward across the area through the day (the timing of which differs fairly substantially amongst the different models), limited surface-based severe potential should spread across southern GA and possibly southern SC. All severe hazards appear possible, though risk appears limited overall at this time.

Farther south into the Florida Peninsula, severe risk should increase into the evening/overnight, as the cold front shifts southward. While somewhat veered boundary-layer flow ahead of the front is expected, limiting low-level veering/shear to some degree, low-end threat for all-hazard severe weather is expected to linger
until frontal passage (the timing of which being uncertain due to fairly substantial aforementioned model differences).

..Goss.. 02/13/2017