Weekend Severe Possibilities (2/9-10)

[Quixotic1]

Models, especially the Euro continue to show significant overnight destabilization across TX, even into OK, Saturday night, through Sunday morning (Euro builds over 2000 J/kg in spots).

 

Could see some nocturnal action as the LLJ kicks into gear.

 

FWD is playing a bit of a dangerous game here playing the climo card here, IMO, with their latest AFD, with the type of instability that is being shown by the more reliable thermo forecaster out of the dynamical guidance compared to the GFS...

 

Newest AFD is even more tepid. 

 

.MOISTURE AND SHEAR PROFILES APPEAR SUPPORTIVE OF SOMESTRONG STORMS...BUT WITH THE BEST FORCING FAR TO THE NORTH...ITDOES NOT APPEAR FAVORABLE FOR WIDESPREAD ORGANIZED CONVECTION.

 

SPC seems to agree:

 

RETURN FLOW ALONG THE WRN GULF WILL COMMENCE FRI NIGHT WHICH   COMBINED WITH STRENGTHENING LOW-LEVEL WAA SHOULD YIELD SHOWERS/TSTMS   ACROSS PARTS OF THE SRN PLAINS BY SAT NIGHT. THIS ACTIVITY WOULD   SEEMINGLY INCREASE IN COVERAGE/INTENSITY DURING D5 AS A COLD FRONT   MOVES EWD ACROSS THE SRN PLAINS TOWARDS THE LOWER MS VALLEY/WRN GULF   COAST. SUCH ABUNDANT RAINFALL POTENTIAL WILL LIKELY LIMIT THE NEWD   EXTENT OF MORE ROBUST DESTABILIZATION. IN ADDITION...THE CONSENSUS   TRACK OF THE SURFACE CYCLONE FROM THE CNTRL PLAINS TO THE UPPER MS   VALLEY WOULD REMAIN WELL-DIVORCED FROM THE RICHER GULF MOISTURE. AS   SUCH...ORGANIZED SEVERE TSTMS REMAIN POSSIBLE ON D5...BUT   PROBABILITIES DO NOT APPEAR A0A 30 PERCENT ATTM.

[andyhb]

@gooba: Yeah, the position of the sfc low may dictate this more than the thermos. That said, the Euro last night didn't have these kinds of thermos Saturday evening/Sunday morning IIRC (which I took to be the problem that FWD highlighted in the earlier AFD), and I'm also seeing some nice height falls extending from the sfc low.

@Brett: Not to beat a dead horse, but I could make the same meme saying "One does not simply take the 72+ hr NAM seriously for these kinds of things".

[Stebo]

This. Seen it too many times to count, including one (non-)event last November. The 18z NAM paints an eerily similar picture to that one for Saturday evening, with wasted hodos to make grown men weep throughout the southern Plains.

 

 

^ my first time using memegenerator... I think I made it count.

 

Using the NAM at 72hr range is a very dangerous assumption, especially when it can't get a 12 hour forecast right.

[brettjrob]

Guys, I'm not trusting a 72-hour NAM forecast. I'm just saying that I agree with Jim on this point: the monster nor'easter and a significant severe threat this weekend are almost mutually exclusive. If the downstream trough digs its heels in and drives a bomb straight up the coast meridionally, the surface ridge over the Midwest/Northeast won't budge, which just means more resistance to the expansion of our warm sector (which we certainly don't need, being that it's early February).

Maybe the NAM is completely out to lunch, and maybe it isn't. But basically every model has trended toward the nor'easter happening, and we're inside 72 hrs. I think the only real shot we have is if they're all wrong, and everyone in the SNE subforum is jumping off bridges Friday night as a fish storm slides 400 miles to their SE.

[bubba hotep]

Using the NAM at 72hr range is a very dangerous assumption, especially when it can't get a 12 hour forecast right.

 

[Stebo]

Guys, I'm not trusting a 72-hour NAM forecast. I'm just saying that I agree with Jim on this point: the monster nor'easter and a significant severe threat this weekend are almost mutually exclusive. If the downstream trough digs its heels in and drives a bomb straight up the coast meridionally, the surface ridge over the Midwest/Northeast won't budge, which just means more resistance to the expansion of our warm sector (which we certainly don't need, being that it's early February).

Maybe the NAM is completely out to lunch, and maybe it isn't. But basically every model has trended toward the nor'easter happening, and we're inside 72 hrs. I think the only real shot we have is if they're all wrong, and everyone in the SNE subforum is jumping off bridges Friday night as a fish storm slides 400 miles to their SE.

What model is showing the trough bombing meridionally along the EC, no offense but you and Jim are reaching for ways to downplay this.

[andyhb]

I'd like to make it clear that I'm not calling for a widespread severe/tornado outbreak here, I'm merely advocating for using model guidance for what it's worth.

[thewxmann]

What model is showing the trough bombing meridionally along the EC, no offense but you and Jim are reaching for ways to downplay this.

 

This is probably one of the more beautiful troughs I've seen in the Plains in awhile. The problem is, there is no warm sector... the front cannot retreat back north because of surface ridging behind the bombing noreaster. 

 

The models do indicate an expansion of the warm sector overnight and on into Sunday, but the strongest dynamics lift northeast and so remain displaced from the greatest moisture/instability. 

 

I'm not saying there won't be an event, just that it would be much more impressive-looking if that noreaster wasn't there and we had better moisture trajectories from the get-go. I have never recalled a major severe weather outbreak coming near the time of a major noreaster, and there's a reason for that.

[Stebo]

This is probably one of the more beautiful troughs I've seen in the Plains in awhile. The problem is, there is no warm sector... the front cannot retreat back north because of surface ridging behind the bombing noreaster. 

 

The models do indicate an expansion of the warm sector overnight and on into Sunday, but the strongest dynamics lift northeast and so remain displaced from the greatest moisture/instability. 

 

I'm not saying there won't be an event, just that it would be much more impressive-looking if that noreaster wasn't there and we had better moisture trajectories from the get-go. I have never recalled a major severe weather outbreak coming near the time of a major noreaster, and there's a reason for that.

 

Models almost always underdo WWA/moisture advection. I would be very skeptical of cooler/drier solutions.

[andyhb]

This is probably one of the more beautiful troughs I've seen in the Plains in awhile. The problem is, there is no warm sector... the front cannot retreat back north because of surface ridging behind the bombing noreaster. 

 

The models do indicate an expansion of the warm sector overnight and on into Sunday, but the strongest dynamics lift northeast and so remain displaced from the greatest moisture/instability. 

 

I'm not saying there won't be an event, just that it would be much more impressive-looking if that noreaster wasn't there and we had better moisture trajectories from the get-go. I have never recalled a major severe weather outbreak coming near the time of a major noreaster, and there's a reason for that.

 

Copied this from my post in another forum. (12z Euro instability/300 mb winds at 09z Sunday morning):

 

 

[andyhb]

Anyway, regardless of the outcome here, all of these intense Pacific Jet systems (Dec. 18th-20th, Christmas, Jan 29th-30th, this upcoming one, often with some nice phasing with the ST Jet) suggest to me that the Pac Jet may very well be significantly more active than last year (since there were essentially none of these really dynamic western systems last winter, aside from perhaps the one that lead to the Jan. 22/23 severe outbreak in the South). This raises my interests (although obviously things can change) for the severe season this year, as do the tendencies over the past couple of months for large sections of the Gulf with above normal SSTs.

[brettjrob]

What model is showing the trough bombing meridionally along the EC, no offense but you and Jim are reaching for ways to downplay this.

 

I was talking about the surface low driving up the coast. With that in mind, pick whichever model you like. The low goes from HAT to just off Cape Cod over a 24-hour period, then stalls for a bit. Meridional enough? A few days ago when moisture return looked more promising, the northern stream s/w for the nor'easter was supposed to be an unphased, low-amplitude open wave well on its way out into the Atlantic by Saturday morning, and the surface low was a fish storm. If you compare surface progs from early runs against current runs that show a New England bomb, you'll see two main differences farther west: a) the surface high/ridge is slower to progress, and associated with that is drier and cooler air lingering over the Plains and Midwest.

 

I'm not intentionally trying to downplay this. It's close enough for me to chase, so why would I? I think I've overhyped as many events as I've underplayed over the past year.

[brettjrob]

This is probably one of the more beautiful troughs I've seen in the Plains in awhile. The problem is, there is no warm sector... the front cannot retreat back north because of surface ridging behind the bombing noreaster. 

 

Strongly agree on this trough. If it were May or June and the nor'easter weren't there (at least in this bombed-out form), I'd probably be confident of a high-end MDT or HIGH risk from three days out with this trough.

[Stebo]

I was talking about the surface low driving up the coast. With that in mind, pick whichever model you like. The low goes from HAT to just off Cape Cod over a 24-hour period, then stalls for a bit. Meridional enough? A few days ago when moisture return looked more promising, the northern stream s/w for the nor'easter was supposed to be an unphased, low-amplitude open wave well on its way out into the Atlantic by Saturday morning, and the surface low was a fish storm. If you compare surface progs from early runs against current runs that show a New England bomb, you'll see two main differences farther west: a) the surface high/ridge is slower to progress, and associated with that is drier and cooler air lingering over the Plains and Midwest.

 

I'm not intentionally trying to downplay this. It's close enough for me to chase, so why would I? I think I've overhyped as many events as I've underplayed over the past year.

 

I don't think it ends up stalling there, I think it continues up into the Canadian Maritimes. Plus just because there is a Nor'Easter doesn't mean that there can't be moisture return back by Saturday night. The Euro which has been the most consistent model thus far has no problem bringing instability back Northward.

[patrick7032]

Looks like models are continuing to come into better (realitive) agreement. As such SPC did put a risk out for day 3...and earlier this evening I issued a graphiccast at work...with strong thunderstorm icons. Didn't wanna go severe yet since we didn't have it in our AFD...plus to await further guidence. Below are some segments from SPC and LBB. I think Lubbock nailed the scanerio pretty decently. The instability in the San Angelo CWA (see graphicast for outline area) did generally show -5 to -8 LIs...good shear and hodos...and CAPEs of 1200-1800. The NAM was a little overboard along the I-10 corridor near Junction...with -9 Showalter indicies.

 

Text that went with my graphiccast:

 

A strong upper level piece of energy will move east from southern California Friday afternoon...to north central Kansas by Sunday morning. As this system approaches...a surface low will form in the Texas panhandle...with a dryline and cold front extending south and southwest from this low. Moist air will stream into the region from the Gulf of Mexico...and winds aloft will gradually strengthen. The upper level energy will help act as a focus for shower and thunderstorm development. A few strong thunderstorms are possible Saturday evening through Sunday morning.

 

http://www.srh.noaa.gov/graphicast.php?site=sjt&gc=5

 

SPC Day 3 discussion:

 

...SRN PLAINS...   ROBUST LOW-LEVEL WAA WILL OCCUR THROUGH THE PERIOD BENEATH A STOUT   EML. GUIDANCE DOES DIFFER WITH THE DEGREE OF LOW-LEVEL MOISTURE   RETURN FROM THE WRN GULF WITH THE ECMWF/GFS UNUSUALLY MORE   AGGRESSIVE THAN THE NAM AND ESPECIALLY THE SREF MEAN. THIS DOES   BREED UNCERTAINTY OVER THE NRN EXTENT OF SEVERE POTENTIAL SAT NIGHT.   WITH SUCH A PRONOUNCED CAPPING INVERSION AND APPRECIABLE MID-LEVEL   HEIGHT FALLS /ALBEIT WEAK IN TX/ NOT OCCURRING UNTIL EARLY   SUN...PRIMARY DRIVER OF SURFACE-BASED TSTM DEVELOPMENT WILL BE THE   PACIFIC COLD FRONT INTERSECTING THE WARM SECTOR ACROSS CNTRL TX SAT   NIGHT. STEEP MID-LEVEL LAPSE RATES AMIDST STRENGTHENING DEEP-LAYER   SWLYS WOULD SUPPORT A THREAT FOR SEVERE HAIL WITH INITIAL UPDRAFTS.   ACTIVITY WOULD LIKELY FORM INTO ONE OR MORE LINE SEGMENTS WITH A   THREAT FOR DAMAGING WINDS AS WELL. SETUP APPEARS SUFFICIENT TO   WARRANT A LOW-END SLIGHT RISK DELINEATION.

SPC DAY 4 discussion:

 

   ON THE LARGE SCALE...GUIDANCE IS FAIRLY CONSISTENT WITH THE EJECTION   OF A VIGOROUS LEAD SHORT WAVE TROUGH FROM THE CNTRL PLAINS TO THE   WRN GREAT LAKES ON D4. THIS IS FOLLOWED BY A SECOND SHORT WAVE   IMPULSE EMANATING EWD FROM THE SOUTHWEST MID-WEEK. A PACIFIC   COLD/OCCLUDED FRONT WILL ACCOMPANY THE INITIAL WAVE...LIKELY   INTERSECTING A RETURNING WARM SECTOR ACROSS THE LOWER MS   VALLEY...WITH TRAILING PORTION STALLING ALONG THE WRN GULF COAST.   CONVECTION SHOULD BE ONGOING ALONG PORTIONS OF THE FRONT IN TX AT   12Z/SUN. ADDITIONAL SURFACE-BASED TSTMS MAY FORM DURING THE DAY FROM   THE GULF COAST TO THE LOWER MS VALLEY IN THE WARM CONVEYOR BELT.   WHAT PRECLUDES HIGHER-END SEVERE PROBABILITIES AOA 30 PERCENT ATTM   ARE 1) A RELATIVELY CONFINED RICH GULF AIR MASS WITH ABUNDANT   WAA-DRIVEN CONVECTION LIMITING NEWD DESTABILIZATION...2) WEAK TO NO   MID-LEVEL HEIGHT FALLS WHERE AT LEAST MODEST SURFACE-BASED BUOYANCY   IS ANTICIPATED...AND 3) WEAKENING PUSH TO THE SURFACE COLD FRONT   ALONG THE GULF COAST. STILL...DEEP-LAYER SHEAR PROFILES WILL BE   FAVORABLE AND SUGGEST THAT A SLIGHT RISK EQUIVALENT THREAT FOR   DAMAGING WINDS AND TORNADOES IS PROBABLE IN THE NEXT D3 OUTLOOK.

 

AREA FORECAST DISCUSSIONNATIONAL WEATHER SERVICE LUBBOCK TX400 PM CST WED FEB 6 2013

 

.LONG TERM...THE PRIMARY FOCUS IN THE LONG TERM REMAINS AN APPROACHINGTROUGH...WHICH WILL BRING WITH IT THE OPPORTUNITY FOR SOME MUCHNEEDED PRECIPITATION ACROSS THE AREA SATURDAY.  AS THIS SYSTEM DIGSALONG THE PACIFIC COAST AND EJECTS EASTWARD JUST NORTH OF THE FOURCORNERS... LEE TROUGHING WILL RESPOND IN EARNEST ALONG THE FRONTRANGE FRIDAY AND SATURDAY... WHICH WILL FORCE BREEZY SOUTHERLY RETURN FLOWACROSS THE REGION.  THIS WILL DRAW UPPER 40S TO LOW DEWPOINTS ACROSSTHE EASTERN PORTION OF THE CWA...AND ESTABLISH A DRYLINE ROUGHLYALONG THE I-27 CORRIDOR BY MID-DAY SATURDAY.  IN ADDITION TO THEPRIMARY TROUGH...BOTH THE GFS AND ECMWF ARE HINTING THAT A SUBTLELEADING IMPULSE WILL TRAVERSE THE AREA DURING THE LATE MORNING/EARLYAFTERNOON HOURS.  EAST OF THE DRYLINE...LOW-LEVEL MOISTURE WILL BESUFFICIENT FOR CONVECTION... HOWEVER LOW SURFACE TEMPERATURES ANDPOOR LAPSE RATES SEEM TO BE SEVERELY LIMITING AVAILABLE INSTABILITYUNTIL AFTER 00Z... WHEN TEMPERATURES ALOFT COOL SLIGHTLY WITH THEAPPROACH OF THE UPPER TROUGH.  REGARDLESS... VERY LITTLE IF ANYSURFACE BASED CAPE DEVELOPS DURING ANY TIME FRAME... AS THE BESTMODELS CAN GENERATE IS ABOUT 500 J/KG OF 0-4KM MUCAPE BETWEEN 00AND 06Z ACROSS THE ROLLING PLAINS. THUS... IT SEEMS LIKELY THATANY THUNDERSTORMS THAT DEVELOP WILL BE OF THE ELEVATED VARIETY.WIND FIELDS ARE VERY STRONG AND SHEARED...WITH 0-6KM BULK SHEARVALUES IN EXCESS OF 60KTS OVER A WIDE AREA. THIS IS MORE THANSUFFICIENT FOR SEVERE UPDRAFT ORGANIZATION GIVEN THAT ENOUGHINSTABILITY CAN DEVELOP.AS OF NOW... THE MOST LIKELY SCENARIO APPEARS TO FAVOR TWOSEPARATE ROUNDS OF PRECIPITATION DEVELOPMENT.  FIRST...SCATTEREDRAIN SHOWERS ARE EXPECTED TO DEVELOP DURING THE LATE MORNING/EARLYAFTERNOON HOURS DUE TO A COMBINATION OF SUBTLE FORCING FROM THE LEADIMPULSE AND MOIST... UPSLOPE WARM AIR ADVECTION ACROSS THE ROLLINGPLAINS.  WHILE A FEW STRIKES OF LIGHTNING AREN`T OUT OF THEQUESTION... A PAUCITY OF INSTABILITY WILL LIKELY LIMIT THUNDERSTORMACTIVITY UNTIL LATER IN THE EVENING.  SOMETIME BETWEEN 18-00Z... APACIFIC COLD FRONT WILL OVERTAKE THE DRYLINE FROM THE WEST AND BEGINTO SURGE EASTWARD... PROVIDING AN ADDED FORCING MECHANISM FORTHUNDERSTORM DEVELOPMENT LATER IN THE EVENING.  THIS FEATURECONTINUES TO SPEED UP IN LATEST MODEL GUIDANCE...AND THUS THE BESTWINDOW FOR STRONG STORMS APPEARS TO BE ON THE ROLLING PLAINS BETWEEN00Z AND 06Z... WHEN THE BEST FORCING AND INSTABILITY OVERLAP.  MOSTCONVECTION SHOULD EXIT THE REGION TO THE EAST BY 06-08Z AS THEPACIFIC FRONT COMPLETELY SWEEPS THROUGH THE AREA.  

[patrick7032]

Here are soundings for Del Rio...San Angelo...and Dallas-Fort Worth. San Angelo didn't have as much instability...but enough for elevated severe given the shear (I didn't zoom in on the top image so the win barbs could be seen...but zoomed in on the rest to see the instability parameters better). Bufkit doesnt currently show any instability at Childress or Oklahoma City. I still feel models are under-doing instability...with a further west and north push of moisture and instability likely to e further than model depictions.

[andyhb]

12z Euro shifted the sfc low south with a more easterly track compared to 00z, with stronger low level dynamics impinging on the unstable warm sector.

[Minnesota Meso]

12z Euro shifted the sfc low south with a more easterly track compared to 00z, with stronger low level dynamics impinging on the unstable warm sector.

 

 

Andy...Interesting that the severe threat for this storm is pinned, yet the northern portion and the winter precip is not, I know that most poster's in this sub forum are only interested in severe weather events, so I understand why that is pined, however the northern part of this storm is just as impressive and the southern part.  How about pinning the northern part as well?

[patrick7032]

The 00Z NAM is setting the dryline location further west this run...generally on a Dalhart-Midland line. The pacific cold front over takes the dryline by 03Z along the I-27 corridor. Best guess is a line of (semi) discrete storms will develop 6 PM-midnight near an Amarillo-Lubbock line...and evolve towards a QLCS...with it being on a Lawton-Sweetwater-Ozona (maybe not that far south) line around midnight...on a Oklahoma City-Throckmorton-Junction line around midnight-3 AM...and a Tulsa-Dallasline by 6 AM-9 AM. Point Soundings showed the following parameters which showed max instability and shear (00z nam):

 

SITE                    TIME                    CAPE                    CIN                LI               TT               SWEAT

Tulia                    6 PM                     589                       -57               -3.2             52               327

Sweetwater         Midnight                1177                     NONE           -4.8             54               480                                                 

Abilene               Midnight                1695                      -34               -7.5             57               545

San Angelo         Midnight                2316                    NONE            -10.0           56               420

Wichita Falls       3 AM                      983                      NONE            -3.5             51               283

Brownwood         3 AM                     1197                     NONE            -5.4             55               489

Oklahoma City    Midnight                NONE                   NONE            +1.1            56               522

Dallas                 6 AM                       454                     NONE            -2.1             52               353            

 

Sorry everyone...the website "skewed" the columns once posted. Looks fine when trying to edit.

[bubba hotep]

The 00Z NAM is setting the dryline location further west this run...generally on a Dalhart-Midland line. The pacific cold front over takes the dryline by 03Z along the I-27 corridor. Best guess is a line of (semi) discrete storms will develop 6 PM-midnight near an Amarillo-Lubbock line...and evolve towards a QLCS...with it being on a Lawton-Sweetwater-Ozona (maybe not that far south) line around midnight...on a Oklahoma City-Throckmorton-Junction line around midnight-3 AM...and a Tulsa-Dallasline by 6 AM-9 AM. Point Soundings showed the following parameters which showed max instability and shear (00z nam):

 

SITE                    TIME                    CAPE                    CIN                LI               TT               SWEAT

Tulia                    6 PM                     589                       -57               -3.2             52               327

Sweetwater         Midnight                1177                     NONE           -4.8             54               480                                                 

Abilene               Midnight                1695                      -34               -7.5             57               545

San Angelo         Midnight                2316                    NONE            -10.0           56               420

Wichita Falls       3 AM                      983                      NONE            -3.5             51               283

Brownwood         3 AM                     1197                     NONE            -5.4             55               489

Oklahoma City    Midnight                NONE                   NONE            +1.1            56               522

Dallas                 6 AM                       454                     NONE            -2.1             52               353            

 

Sorry everyone...the website "skewed" the columns once posted. Looks fine when trying to edit.

No worries, still easy to read, thanks for posting these.

[patrick7032]

No worries, still easy to read, thanks for posting these.

Anytime Bubba.

[patrick7032]

Well as usual Bufkit wasn't as untable as the point soundings at work...but usually the point soundings at work are the correct values closer to the truth when verifying. That said...Bufkit still shows decent instability...and check out the helicity...EHI values...and hodographs.

[patrick7032]

DAY 2 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1135 PM CST THU FEB 07 2013

VALID 091200Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PARTS OF THE SRN

PLAINS...

...SOUTHERN PLAINS...

GREAT BASIN UPPER TROUGH WILL EJECT ACROSS THE CNTRL/SRN ROCKIES

DURING THE DAY2 PERIOD IN RESPONSE TO UPSTREAM NRN ROCKIES SPEED

MAX/HEIGHT FALLS. LATEST GUIDANCE SUGGEST STRONG MID LEVEL SPEED

MAX SHOULD ROTATE THROUGH THE BASE OF THE TROUGH ACROSS NM INTO THE

SRN HIGH PLAINS BY 10/00Z. WITH BROAD DIFFLUENT UPPER FLOW

ANTICIPATED ACROSS THE HIGH PLAINS FROM THE NEB PANHANDLE TOWARD THE

MIDDLE RIO GRANDE VALLEY OF TX LARGE SCALE ASCENT SHOULD INCREASE

ALONG ADVANCING PACIFIC FRONT/DRYLINE AROUND PEAK HEATING. BOTH THE

GFS/NAM ARE CONSISTENT IN FRONTAL POSITION DURING THE LATE AFTERNOON

FROM ERN CO...SWD ALONG THE NM/TX BORDER. DESPITE CONSIDERABLE WARM

SECTOR BOUNDARY LAYER MOISTENING ACROSS TX STRONG INHIBITION...ON

THE ORDER OF 200 J/KG...DUE IN PART TO SUBSTANTIAL CLOUD

COVER...WILL PREVENT PRE-FRONTAL SFC-BASED WARM SECTOR TSTM

DEVELOPMENT MUCH OF THE PERIOD.

LATEST THINKING IS STRONG HEATING ACROSS THE HIGH PLAINS NEAR THE

TX/NM BORDER WILL CONTRIBUTE TO VERY STEEP LOW LEVEL LAPSE RATES

SUCH THAT NEGLIGIBLE CAPPING WILL BE PRESENT AS SFC BOUNDARY SURGES

INTO WRN FRINGE OF MODIFIED GULF RETURN. IF TEMPERATURES WARM INTO

THE MID 60S ACROSS THE TX SOUTH PLAINS AS NAM FORECAST SOUNDINGS

SUGGEST...SBCAPE ON THE ORDER OF 700-800 J/KG COULD BE IN PLACE FOR

STRONG CONVECTION. DEEP LAYER SHEAR WILL CERTAINLY SUPPORT

ORGANIZED DEEP ROTATING UPDRAFTS AND THERE IS SOME CONCERN THAT

ISOLATED SUPERCELLS MAY EMERGE ALONG THE FRONT BY LATE AFTERNOON

BETWEEN LBB-AMA. FOR THIS REASON HAVE OPTED TO EXTEND 5 PERCENT

SEVERE PROBS ACROSS THE HIGHER PLAINS OF NWRN TX. HAIL AND GUSTY

WINDS WILL BE THE PRIMARY SEVERE THREATS WITH THIS

ACTIVITY...PRIMARILY BETWEEN 22-02Z.

DOWNSTREAM...WILL MAINTAIN CATEGORICAL SLIGHT RISK ACROSS MUCH OF

WCNTRL INTO NCNTRL TX ACCOUNTING FOR THE POSSIBILITY OF STRONG

CONVECTION DURING THE OVERNIGHT PERIOD. PER EARLIER REASONING IT

APPEARS THE MAJORITY OF STRONG CONVECTION WILL BE CONFINED TO THE

COLD FRONT WHERE STRONGER FORCING WILL BE REQUIRED TO BREAK A STRONG

CAP. TSTMS THAT DEVELOP ALONG THE BOUNDARY WILL BE STRONGLY SHEARED

BUT FLOW WILL VEER SUBSTANTIALLY NEAR THE FRONT AND THIS SHOULD

FAVOR LINEAR DEVELOPMENT. AS A RESULT...HAIL/WIND WILL BE THE

PRIMARY SEVERE THREATS WITH FRONTAL CONVECTION.

..DARROW.. 02/08/2013

[LocoAko]

Nice disco out of LBB. I like the Childress - Floydada corridor after a cursory glance. 

 

 

AS FOR CHANCES FOR STORMS... LATEST MODEL GUIDANCE IS TRENDINGTOWARDS HIGHER AMOUNTS OF INSTABILITY THAN IN PREVIOUS RUNS... WITHSBCAPE VALUES SOLIDLY IN THE 500-1000 J/KG RANGE...LIKELY DUE TOWARMER FORECAST SURFACE TEMPS.  THE UPPER RANGE OF THIS SEEMS ABIT UNLIKELY GIVEN THE AFOREMENTIONED LOW CLOUD COVER DURING THEEARLY AFTERNOON...HOWEVER IT IS NOW LOOKING LIKE THERE WILL BESUFFICIENT...IF NOT SOMEWHAT MARGINAL...INSTABILITY FOR STRONGCONVECTION BY LATE AFTERNOON EAST OF THE DRYLINE.  A WARM EML ABOVETHE BOUNDARY LAYER WILL BE IN PLACE DURING THE AFTERNOON...AND WILLLIKELY SUPPRESS DEEP CONVECTION UNTIL LATER WHEN THE DRYLINE ISOVERTAKEN BY A SURGING PACIFIC FRONT.  WHILE A FEW STORMS WILL BEPOSSIBLE IN THE EARLY AFTERNOON BEFORE THIS OCCURS...THE CURRENTTHINKING IS THAT THE EXTRA FORCING FROM BOTH THE FRONT AND THEAPPROACHING UPPER TROUGH WILL BE REQUIRED FOR INITIATION.  AS SUCH...AREAS IN THE NORTHEAST PORTION OF THE CWA HAVE BEEN HIGHLIGHTED WITHTHE MOST LIKELY POPS... AS FORCING IN THIS AREA SEEMS TO BE THE MOSTFAVORABLE.  AS MENTIONED PREVIOUSLY...WIND FIELDS WILL BE IMPRESSIVEWITH THIS SYSTEM...WITH 0-6KM BULK SHEAR EXCESS OF 60KT ACROSS AWIDE AREA.  IN ADDITION... BACKED LOW-LEVEL WINDS AND VERY HIGH WINDSPEEDS ARE YIELDING LONG...CLOCKWISE LOOPING HODOGRAPHS...FAVORABLEFOR SUPERCELL DEVELOPMENT.  GIVEN THE UPWARD TREND OFINSTABILITY...IT APPEARS THAT SEVERE STORMS WILL BE POSSIBLE... WITHDAMAGING WINDS AND SMALL HAIL THE MOST LIKELY THREATS.  INADDITION... 0-1KM SHEAR OF UP TO 30 KTS AND 0-1KM HELICITY IN EXCESSOF 200 M2/S2 INDICATE THAT AN ISOLATED TORNADO OR TWO CANNOT BERULED OUT IF ANY SUPERCELLS CAN DEVELOP AND BECOME ROOTED IN THEBOUNDARY LAYER.  AS THE PACIFIC FRONT PUSHES EAST... STRONG FORCING WILLLIKELY TRANSITION THE STORM MODE FROM ISOLATED TO LINEAR... THEREBYREDUCING THE TORNADO THREAT BEFORE STORMS EXIT THE AREA BY 06Z.FURTHER WEST BEHIND THE DRYLINE... MODEL SOUNDINGS ARE EXHIBITINGDEEP MIXING PROFILES WITH WINDS IN EXCESS OF 40 KTS THROUGHOUT THEMIXED LAYER...ESPECIALLY NEAR THE TX/NM BORDER.  HOWEVER... HIGHCLOUDS AND A SOMEWHAT MARGINAL PRESSURE GRADIENT WILL LIKELY KEEPWINDS BELOW WIND ADVISORY CRITERIA.  ELEVATED TO CRITICAL FIREWEATHER WILL BE A CONCERN...HOWEVER...AND FOR MORE DETAILS PLEASESEE THE FIRE WEATHER DISCUSSION BELOW.

[brettjrob]

I agree with everything in that AFD. Despite the underperforming and late moisture, there should be a window of opportunity between 5-10pm or so across the eastern South Plains, eastern TX Panhandle and perhaps western OK. Deep-layer shear vectors are almost normal to the front, so all we need is for initiation to begin prior to overwhelming linear forcing, which models indicate should arrive around midnight. The 4 km WRF-NMM and 4 km NAM nest have so far been consistent in firing convection by 00z in the aforementioned region.

 

This setup has a few similarities to (and plenty of differences with) last Feb 2, which surprisingly produced a long-track tornado near Pampa just before midnight. This feels like one of those cases where the moisture tongue/gradient will be key to any surprises the atmosphere might have up its sleeve. From a chaser's perspective, though, the best chance for a decent supercell before dark is probably more south between LBB and CDS.

[patrick7032]

Think you got your dates mixed up. I checked the SPC event archieve...and there was no severe weather last year on Feb 2nd. On Feb 1st the severe weather was from eastern Texas and points north and east...with no tornadoes in Texas.

I agree with everything in that AFD. Despite the underperforming and late moisture, there should be a window of opportunity between 5-10pm or so across the eastern South Plains, eastern TX Panhandle and perhaps western OK. Deep-layer shear vectors are almost normal to the front, so all we need is for initiation to begin prior to overwhelming linear forcing, which models indicate should arrive around midnight. The 4 km WRF-NMM and 4 km NAM nest have so far been consistent in firing convection by 00z in the aforementioned region.

 

This setup has a few similarities to (and plenty of differences with) last Feb 2, which surprisingly produced a long-track tornado near Pampa just before midnight. This feels like one of those cases where the moisture tongue/gradient will be key to any surprises the atmosphere might have up its sleeve. From a chaser's perspective, though, the best chance for a decent supercell before dark is probably more south between LBB and CDS.

[patrick7032]

DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1148 PM CST FRI FEB 08 2013

VALID 091200Z - 101200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTN AND TONIGHT

ACROSS PARTS OF THE SOUTHERN PLAINS...

...SYNOPSIS...

AS AMPLIFIED UPPER RIDGING WEST OF THE PACIFIC COAST BUILDS

NORTHEASTWARD INTO WESTERN CANADA...A SIGNIFICANT SHORT WAVE

TROUGH...NOW DIGGING INTO NORTHERN BRITISH COLUMBIA/ALBERTA...

APPEARS LIKELY TO TURN MORE SHARPLY SOUTHWARD TOWARD THE NORTHERN

ROCKIES TODAY. AS THIS OCCURS...ANOTHER VIGOROUS SHORT WAVE IMPULSE

IS FORECAST TO LIFT OUT OF BROADER SCALE SOUTHWESTERN U.S. UPPER

TROUGHING. PHASING OF THIS LATTER FEATURE WITH A BELT OF WESTERLIES

EMERGING FROM THE SUBTROPICAL EASTERN PACIFIC IS ALREADY

UNDERWAY...AND VERY STRONG WEST SOUTHWESTERLY MID/HIGH LEVEL FLOW IS

EXPECTED TO GRADUALLY OVERSPREAD MUCH OF THE CENTRAL AND SOUTHERN

PLAINS.

LATE THIS AFTERNOON INTO TONIGHT...MODELS SUGGEST THAT A CYCLONIC

500 MB JET STREAK ON THE ORDER OF 100 KT WILL NOSE ACROSS THE

TEXAS/OKLAHOMA PANHANDLE REGION INTO THE CENTRAL PLAINS. THIS

APPEARS LIKELY TO BE ACCOMPANIED BY SIGNIFICANT SURFACE CYCLOGENESIS

ACROSS EASTERN COLORADO INTO SOUTH CENTRAL NEBRASKA...WITH A

TRAILING COLD FRONT ADVANCING EAST OF THE CENTRAL/SOUTHERN ROCKIES

INTO THE CENTRAL/SOUTHERN PLAINS.

AT THE SAME TIME...GUIDANCE IS SUGGESTIVE THAT A SERIES OF LESS

PROMINENT SPEED MAXIMA ASSOCIATED WITH THE SUBTROPICAL JET WILL

PROPAGATE EAST NORTHEASTWARD ALONG AN AXIS NEAR/SOUTH OF THE TEXAS

BIG BEND...TOWARD THE LOWER MISSISSIPPI VALLEY.

...CENTRAL/SOUTHERN PLAINS...

THE EVOLVING LARGE-SCALE PATTERN...IN MANY RESPECTS...IS TYPICAL OF

ONE THAT MIGHT BE ACCOMPANIED BY A SIGNIFICANT INCREASE IN SEVERE

WEATHER POTENTIAL TO THE LEE OF THE ROCKIES. HOWEVER...THE BOUNDARY

LAYER OVER THE NORTHWESTERN GULF OF MEXICO IS NOT PARTICULARLY MOIST

OR DEEP...AND A SUBSTANTIVE INLAND MOISTURE RETURN IS EXPECTED TO BE

SLOW TO DEVELOP...PARTICULARLY NEAR THE SURFACE...IN THE WAKE RECENT

LOW-LEVEL COOLING. THE NAM/SREF SUGGEST THAT EVEN RATHER MODEST

MID/UPPER 50S SURFACE DEW POINTS MAY NOT REACH PORTIONS OF THE TEXAS

SOUTH PLAINS UNTIL AT LEAST LATE AFTERNOON/EARLY EVENING. AND

BETTER BOUNDARY LAYER MOISTENING/DESTABILIZATION PROBABLY WILL

REMAIN WELL SOUTH OF THE STRONGER MID-LEVEL HEIGHT FALLS

OVERSPREADING THE CENTRAL PLAINS.

EVEN WITH LIMITED MOISTURE...STEEPENING LAPSE RATES/STRONG FORCING

FOR UPWARD VERTICAL MOTION MAY BE SUFFICIENT TO SUPPORT VIGOROUS

LOW-TOPPED CONVECTIVE DEVELOPMENT...PROBABLY IN A BROKEN

LINE...ROUGHLY NEAR/EAST OF THE COLORADO/KANSAS BORDER...SOUTHWARD

INTO THE TEXAS PANHANDLE...DURING THE 21-00Z TIME FRAME. IT DOES

APPEAR THAT THERE MAY BE A WINDOW OF OPPORTUNITY FOR BETTER COUPLING

OF LOW-LEVEL MOISTENING/DESTABILIZATION AND STRONGER LIFT...ON THE

DEVELOPING DRY LINE ACROSS PARTS OF THE EASTERN TEXAS

PANHANDLE/NORTHWEST TEXAS...FOR SOMEWHAT MORE VIGOROUS STORM

DEVELOPMENT. THIS MAY INCLUDE POTENTIAL FOR SUPERCELLS WITH A RISK

FOR TORNADOES...IN THE PRESENCE OF SIZABLE CLOCKWISE CURVED

LOW-LEVEL HODOGRAPHS.

THEREAFTER...EVOLUTION OF CONVECTIVE DEVELOPMENT AND CONVECTIVE

POTENTIAL REMAIN A BIT UNCLEAR. IT IS POSSIBLE THAT THE SOUTHERN

FLANK OF THE INITIAL CONVECTIVE ACTIVITY MAY PERSIST AND GROW

UPSCALE...OR NEW DEVELOPMENT MAY OCCUR OFF TO THE EAST

SOUTHEAST...WITHIN STRENGTHENING LOW-LEVEL WARM ADVECTION ACROSS

NORTHWEST INTO NORTH CENTRAL TEXAS LATER DURING THE

EVENING/OVERNIGHT HOURS. THIS ACTIVITY COULD BE ENHANCED BY FURTHER

DESTABILIZATION ASSOCIATED WITH CONTINUING SLOW MOISTURE

RETURN...AND DIVERGENT UPPER FLOW BETWEEN THE POLAR AND SUBTROPICAL

JET AXES. GIVEN THE STRENGTH OF THE DEEP LAYER MEAN FLOW...DAMAGING

WIND GUSTS MAY BE THE PRIMARY SEVERE THREAT...THOUGH THERMODYNAMIC

PROFILES MAY BE SUPPORTIVE OF LARGE HAIL.

..KERR/SMITH.. 02/09/2013

[brettjrob]

Think you got your dates mixed up. I checked the SPC event archieve...and there was no severe weather last year on Feb 2nd. On Feb 1st the severe weather was from eastern Texas and points north and east...with no tornadoes in Texas.

 

It was one of those events SPC didn't deem significant enough to include in their database, as there was only one TOR report: http://www.spc.noaa.gov/climo/reports/120202_rpts.html

 

Some decent forecast soundings showing up on the RAP for 23z around CDS. Laughable LCLs, but certainly supercell material nonetheless. That instability axis could hardly be narrower and still exist, though. The explicit convection modeled by the SPC and NSSL 4 km WRF variants reflects this, with cells developing 22-00z just E of I-27 and rapidly weakening a couple hours later as they hit the TX/OK border.

[patrick7032]

It was one of those events SPC didn't deem significant enough to include in their database, as there was only one TOR report: http://www.spc.noaa.gov/climo/reports/120202_rpts.html

 

Some decent forecast soundings showing up on the RAP for 23z around CDS. Laughable LCLs, but certainly supercell material nonetheless. That instability axis could hardly be narrower and still exist, though. The explicit convection modeled by the SPC and NSSL 4 km WRF variants reflects this, with cells developing 22-00z just E of I-27 and rapidly weakening a couple hours later as they hit the TX/OK border.

Ahhh ok thanks...will check out the link.

[patrick7032]

Here's the 00Z NAM soundings. Instability shows up at Childress (KCDS) by 5pm...and Oklahoma City (KOKC) now has instability...with a hodo off the scale. I also included Wichita Falls (KSPS)...San Angelo (KSJT)...and the Dallas-Fort Worth area (FDW).