February 20 Severe Weather Threat

[Hoosier]

With the area already outlined by SPC and the general move toward a more impressive solution on the 00z runs, it's time for a thread.

 

As we've been talking about in the other thread, shear certainly not going to be an issue.  Main questions at this point are instability and how far north this threat may extend.  In particular, the 00z UKMET/ECMWF suggest a threat could get fairly far north. 

[Stebo]

With the area already outlined by SPC and the general move toward a more impressive solution on the 00z runs, it's time for a thread.

 

As we've been talking about in the other thread, shear certainly not going to be an issue.  Main questions at this point are instability and how far north this threat may extend.  In particular, the 00z UKMET/ECMWF suggest a threat could get fairly far north. 

I made mention of the instability up here, I forgot to mention that is with a surface temp/dew point around 50. Needless to say if we can get a bit higher here and especially South of here, the instability will go up quickly.

[andyhb]

You mentioned the mid level lapse rates in the other thread, that will be a key factor in developing more impressive instability further north. Generally anything 7˚C/km or greater at this time of year (maybe even 6.5+) is noteworthy, especially with strong wind fields in place and a rapidly deepening surface low that especially the Euro and UK suggest.

 

In addition, if we get those types of lapse rates further south as well towards the Mid MS Valley and OH Valley, could be sitting on a rather impressive thermodynamic environment down there.

[OHweather]

If a stronger solution like the Euro/UK pans out and areas farther north are in play, it will be interesting to see how the deep snow cover north of about I-70 that probably won't melt by Thursday affects temperatures. It really doesn't take much instability to maintain a forced line of low topped convection with at least a damaging wind threat with such strong wind fields, and with steep lapse rates it won't take particularly warm temperatures to get enough instability for a pencil thin line of convection, even north of I-70. Any bigger threat will probably be closer to the Ohio River/points south where the Euro is suggesting highs near 70 on Thursday to go along with impressive wind fields and dew points possibly pushing 60.

[Hoosier]

You mentioned the mid level lapse rates in the other thread, that will be a key factor in developing more impressive instability further north. Generally anything 7˚C/km or greater at this time of year (maybe even 6.5+) is noteworthy, especially with strong wind fields in place and a rapidly deepening surface low that especially the Euro and UK suggest.

 

In addition, if we get those types of lapse rates further south as well towards the Mid MS Valley and OH Valley, could be sitting on a rather impressive thermodynamic environment down there.

 

 

Yeah the GFS had widespread 700-500 mb lapse rates near 7-7.5 C/km.

 

The question I continue to have is what effect the melting snow will have on boundary layer temps/dewpoints, especially if the quicker bombing/westward solution pans out. 

[Stebo]

Huge Day 4 and 5. Hell the risk area is almost to here:

 

 

DAY 4-8 CONVECTIVE OUTLOOK    NWS STORM PREDICTION CENTER NORMAN OK  0358 AM CST MON FEB 17 2014    VALID 201200Z - 251200Z     ..DISCUSSION    MEDIUM-RANGE MODELS REMAIN IN GENERAL GOOD AGREEMENT WITH RESPECT TO  DEVELOPMENT OF A LARGE CENTRAL/ERN U.S. TROUGH THIS PERIOD...WITH  THE INITIAL PIECE OF SHORT-WAVE ENERGY TO MOVE ACROSS THE CENTRAL  U.S. DAY 4 /THU. 2-20/.  AS THIS INITIAL TROUGH SHIFTS INTO THE  PLAINS THROUGH THE AFTERNOON HOURS...A DEEPENING SURFACE LOW IS  FORECAST TO PROGRESS QUICKLY NWD TOWARD THE UPPER GREAT LAKES  REGION...WHILE ALLOWING A STRONG/TRAILING COLD FRONT TO MOVE  EWD/SEWD ACROSS THE CENTRAL U.S. WITH TIME.    WITHIN A MOISTENING/DESTABILIZING WARM SECTOR...EXPECT STORMS TO  DEVELOP ALONG THE FRONT DURING THE AFTERNOON -- FROM SRN IL/ERN MO  SSWWD ACROSS THE ARKLATEX REGION...IN A LINEAR CONFIGURATION  NEAR/AHEAD OF THE FRONT.  GIVEN VERY STRONG FLOW ALOFT WHICH WILL  ACCOMPANY THIS SYSTEM...IT APPEARS THE DAMAGING WINDS WILL BECOME  RELATIVELY WIDESPREAD BY LATE AFTERNOON AND CONTINUING THROUGH THE  EVENING AS THE CONVECTIVE LINE ROLLS EWD.  IN ADDITION...A COUPLE OF  TORNADOES WILL ALSO BE POSSIBLE -- MAINLY WITH EMBEDDED VORTICES  WITHIN THE LINEAR CONVECTIVE SYSTEM.    WITH THE FRONT NOW PROGGED TO ADVANCE MORE SLOWLY THAN IN PRIOR  RUNS...SEVERE RISK APPEARS LIKELY TO LINGER OVER THE ATLANTIC COAST  STATES THROUGH THE FIRST HALF OF DAY 5 /FRI. 2-21/.  WHILE THE  STRONGEST ASCENT ASSOCIATED WITH THE UPPER SYSTEM SHOULD SHIFT  ACROSS THE NORTHEAST U.S. -- WELL REMOVED FROM THE GREATER  MOISTURE/DESTABILIZATION POTENTIAL FARTHER S -- THE STRENGTH OF THE  FLOW FIELD ALOFT SUGGESTS THAT DAMAGING WIND RISK WILL SPREAD EWD TO  THE MIDDLE AND SRN ATLANTIC COASTAL REGION AS THE CONVECTIVE LINE  DIURNALLY RE-INTENSIFIES AHEAD OF THE FRONT.    WITH THE BOUNDARY APPEARING LIKELY TO MOVE OFF THE ATLANTIC COAST BY  EARLY EVENING AND THE UPPER TROUGH EXPECTED TO EXPAND/PERSIST ACROSS  THE ERN U.S. THROUGH MOST IF NOT ALL OF THE REMAINDER OF THE  PERIOD...APPRECIABLE SEVERE RISK IS NOT EXPECTED BEYOND DAY 5 OVER  THE CONUS.    

[hm8]

Jeebus... Largest day 4 risk evah?

[AppsRunner]

WWA for today and a D4 severe risk. Crazy.

Either way its probably going to be really hard to get a lot out of a 12" snowpack but its still cool to see

[Stebo]

GFS trended toward the Euro/Ukie with a very strong solution, the wind fields are stronger than the previous 2 runs as well. I do expect subsequent runs to bring up more instability as we get closer to the event, that being said the GFS brings 55 degree dew points to Indy and 60 degree dew points to Paducah. Needless to say this potential needs to really be monitored as it won't take much instability to bring the winds down to the surface when they are very strong just above the surface.

[Indystorm]

This really seems to be trending to a possible extensive svr wind event with QLCS spin ups possible.  Am quite amazed at that area coverage for Thursday.

[Stebo]

This really seems to be trending to a possible extensive svr wind event with QLCS spin ups possible.  Am quite amazed at that area coverage for Thursday.

Completely agree, just to visualize it a bit better, this is the wind field at 850mb at 21z on Thursday:

 

 

If you add even modest instability to that wind field with the associated ascent from the front you could be looking at a high end wind event. Even outside of thunderstorms you would be looking at very strong winds.

[Hoosier]

IND mentioned the snowpack in the morning afd.  Wonder if SPC will mention it in any of their discussions.

 

...

WHILE THE POTENTIAL FOR CONVECTION AHEAD OF AND ACCOMPANYING THE   FRONT CONTINUES TO GROW...THE POSSIBILITY OF A STRONG LOW TOPPED   CONVECTIVE LINE INTO CENTRAL INDIANA REMAINS CONTINGENT ON A FEW   FACTORS. IF THE ECMWF SOLUTION WERE TO COME TO FRUITION...QUITE   PLAUSIBLE THAT HIGHER DEWPOINTS AND INSTABILITY WOULD BE BROUGHT   NORTH INTO THE FORECAST AREA. A SLOWER DEEPENING TO THE LOW WOULD   KEEP BETTER INSTABILITY AND STRONGER CONVECTION SOUTH OF THE OHIO   RIVER. ADDITIONALLY...UNCERTAINTY EXISTS WITH HOW NEAR SURFACE LAYER   TEMPS MAY BE IMPACTED BY THE REMNANT SNOWPACK AND IF MODELS ARE   TAKING THAT INTO ACCOUNT AND OVERDOING WARMTH. FOR NOW...WILL   CONTINUE WITH CHANCE FOR THUNDERSTORMS UNTIL THE FRONTAL PASSAGE   THURSDAY NIGHT. 

[Hoosier]

FWIW, I don't think the new probability/categorical scheme has gone into effect yet. 

[Hoosier]

DAY 3 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0217 AM CST MON FEB 17 2014

VALID 191200Z - 201200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...

SUBSTANTIAL AMPLIFICATION OF THE UPPER PATTERN IS EXPECTED FOR DAY

3...AS SHORT-WAVE TROUGHING DIGS SEWD ACROSS THE GREAT BASIN DURING

THE DAY...AND THE CENTRAL ROCKIES OVERNIGHT. AS THE SYSTEM NEARS

THE HIGH PLAINS...A DEVELOPING LEE CYCLONE OVER ERN CO IS PROGGED TO

SHIFT EWD ACROSS THE OK/KS VICINITY OVERNIGHT...WITH THE ATTENDANT

WARM FRONT TO SHIFT NWD ACROSS AR/MO AND THE MID MS VALLEY WHILE A

TRAILING COLD FRONT EMERGES FROM THE SRN ROCKIES AND THEN CROSSES

THE SRN HIGH PLAINS THROUGH THE END OF THE PERIOD.

...PARTS OF KS/SERN NEB ENEWD TO SRN WI/IL...

NWD ADVECTION OF LOW-LEVEL MOISTURE WILL CONTINUE ACROSS THE WARM

SECTOR OF THIS DEVELOPING CENTRAL U.S. STORM SYSTEM...BUT BACKGROUND

SUBSIDENCE/CAPPING IS EXPECTED TO PRECLUDE ANY APPRECIABLE RISK FOR

SURFACE-BASED CONVECTION. INSTEAD... CONVECTIVE DEVELOPMENT WILL

LIKELY REMAIN CONFINED TO THE ZONE OF WARM ADVECTION/ISENTROPIC

ASCENT N OF THE WARM FRONT. HERE...ELEVATED SHOWER/THUNDERSTORM

DEVELOPMENT IS EXPECTED MAINLY AFTER DARK...INITIALLY ACROSS THE

CENTRAL AND ERN KS/SERN NEB VICINITY AND THEN SPREADING ENEWD ACROSS

PARTS OF IA/MO/IL/SRN WI THROUGH THE END OF THE PERIOD. ATTM...IT

APPEARS THAT ANY HAIL PRODUCTION WITH THE STRONGER CELLS SHOULD

REMAIN LARGELY SUB-SEVERE...AND THUS WILL NOT INTRODUCE ANY SEVERE

PROBABILITIES THIS FORECAST.

..GOSS.. 02/17/2014

[attachment=122251:day3otlk_0830.gif]

[chase_stormz]

From Louisville AFD...

 

 

 

By late Thursday afternoon into Thursday evening, attention will
turn toward the west as a strong cold front approaches the region.
Timing of this front remains a bit off between guidance, with the
ECMWF being the slowest and the 17/12Z GFS being the fastest. These
amplified systems tend to trend slower, thus will lean on the slower
ECMWF with this forecast. Severe weather with this system continues
to look possible, with the magnitude hinging solely on the amount of
instability that is realized. The NAM is the most aggressive with
its northward push of surface-based instability, while the GFS and
ECMWF only get the axis to the KY/TN border. In these very dynamic
cases, guidance typically underdoes the amount of available
instability due to their underestimation of surface
temperatures/dewpoints right ahead of the front. Therefore, think
the NAM is likely the most accurate. At this time, the highest
threat appears to be across KY, TN, and southern IN, where the best
kinematics will align with the northern edge of the instability
axis. CIPS analogs from the 12Z run also agree with this region,
painting the highest probabilities from KY into TN. With 850mb
winds progged at anywhere between 65 and 80 knots, damaging winds
will be the main threat with this convection. However, given
forecast effective SRH values of 200-300+ m2/s2 (if we can realize
surface-based instability), isolated tornadoes embedded within the
QLCS will be possible.

[Hoosier]

Spent some time looking at past February severe weather occurrences, specifically tornadoes and damaging wind.  Not surprisingly, it is more likely to occur the farther south you go into the Ohio Valley.  Here's a map of February tornadoes from 1950-2012...very little activity in the Lakes area.

 

 

 

 

Wind reports follow the same general pattern though not quite to that degree.  One of the more notable February severe weather outbreaks in the Lakes occurred on February 11, 1999.  FWIW, this date shows up as one of the CIPS analogs based on the 12z GFS.

 

 

 

 

Bottom line, February severe weather is pretty unusual north of the Ohio Valley but it can happen.  And of course we know about January outbreaks that have occurred pretty far north.

 

 

 

 

 

 

 

 

[IWXwx]

The northern cutoff of February tornadoes in Indiana looks to closely follow the Wabash River. Interesting maps.

[chase_stormz]

The 0z Nam really bombs out the low, I think we're looking at a pretty significant damaging wind threat IF dew points can climb into the lower 60s instead of the upper 50s as advertised by most major models. The 850mb winds are a little displaced from the main trough but they are screaming and it shouldn't take much to mix those down. I wouldn't be shocked to see quite a few 70-80 mph wind gusts with the main line of thunderstorms. 

 

[SirSonic]

With a low as strong as it depicts on the NAM, it will be easy to pump of good moisture and warm air, despite having lots of snow cover, maybe the snow cover could enhance instability 

[OHweather]

With a low as strong as it depicts on the NAM, it will be easy to pump of good moisture and warm air, despite having lots of snow cover, maybe the snow cover could enhance instability 

No. There's a reason you usually don't get big outbreaks with snow on the ground.

 

Near and south of the Ohio River where the snow should melt, given 850mb temps of 10-12C, strong southerly winds and any amount of sun on Thursday temps could push 70, so instability numbers may be more than progged there. But snow cover won't help things farther north where it's deep.

[Minnesota Meso]

I know that the vast majority of poster here live south and east of MSP, so therefore I understand the attention to the warm sector possibilities, but if I started a thread called something like the cold sector for Feb 20th, would anyone be interested in forecasting that as well?  After all it is one storm system and peeps like me, go saints and DDL live in the far NW portions of this subforum.

[Chicago Storm]

I know that the vast majority of poster here live south and east of MSP, so therefore I understand the attention to the warm sector possibilities, but if I started a thread called something like the cold sector for Feb 20th, would anyone be interested in forecasting that as well?  After all it is one storm system and peeps like me, go saints and DDL live in the far NW portions of this subforum.

There's already a thread...

 

http://www.americanwx.com/bb/index.php/topic/42902-february-20-24-winter-weather-threat/

[Minnesota Meso]

There's already a thread...

 

http://www.americanwx.com/bb/index.php/topic/42902-february-20-24-winter-weather-threat/

 

sorry my bad

[Hoosier]

Unclear whether the inversion will be able to mix out in the snow covered areas of the warm sector but I could envision a scenario where watches are out for damaging winds in areas with temps in the 40s.  It will be a battle between good storm organization/momentum transfer and potentially stable air near the surface. 

[chase_stormz]

Does anyone know if the 12/21/13 storm system popped up as an analog for this upcoming event? Seems like a similar synoptic setup.

[Hoosier]

Does anyone know if the 12/21/13 storm system popped up as an analog for this upcoming event? Seems like a similar synoptic setup.

 

 

I don't recall seeing it and I'm not sure how quickly the newer data gets put in.

[chase_stormz]

I don't recall seeing it and I'm not sure how quickly the newer data gets put in.

 

Another system that pops into my head after quickly looking over the data is 1/29-30/13.

 

EDIT: The number 1 analog from the 0z NAM is 3/2/2012. I'd say that's a little generous lol...

[SirSonic]

Does anyone know if the 12/21/13 storm system popped up as an analog for this upcoming event? Seems like a similar synoptic setup.

 

That was an interesting event. There was a lot wind damage for occurring in the winter and being so far north

[Hoosier]

Another system that pops into my head after quickly looking over the data is 1/29-30/13.

 

EDIT: The number 1 analog from the 0z NAM is 3/2/2012. I'd say that's a little generous lol...

 

 

I saw 3/12/12 on the GFS list but didn't even want to mention it. 

[andyhb]

Another system that pops into my head after quickly looking over the data is 1/29-30/13.

 

EDIT: The number 1 analog from the 0z NAM is 3/2/2012. I'd say that's a little generous lol...

 

Yeah this is generally looking like a damaging wind event especially if there is a threat north of the OH Valley. The better potential for isolated tornadoes and a more substantial damaging wind threat will likely be from the OV south, with increased instability.

 

I did notice the 00z GFS was getting -4 LIs north of Memphis into the bootheel of MO at 21z, which is rather impressive given the windfields in place with 50-70 kts of 0-6 km shear and >50 kts in the lowest km, not to mention the fact that there is -15 to -18˚C H5 temps being indicated over the region, which is quite substantial in terms of mid level lapse rates.