January 28-30 Severe Threat

[Tim from Springfield (IL)]

SPC already has a Day 6 outlook area outlined for the mid-Mississippi Valley, including as far north as the I-64 corridor in southern Illinois.

http://www.spc.noaa.gov/products/exper/day4-8/

DAY 4-8 CONVECTIVE OUTLOOK  
   NWS STORM PREDICTION CENTER NORMAN OK
   0342 AM CST THU JAN 24 2013
   
   VALID 271200Z - 011200Z
   
   ...DISCUSSION...
   MODEL TRENDS CONTINUE TO BE CLOSELY MONITORED FOR THE POSSIBILITY OF
   SIGNIFICANT SEVERE WEATHER AROUND TUE/D6 AND POSSIBLY INTO WED/D7.
   
   INSPECTION OF THE ECMWF...GFS...CMC...UKMET AND VARIOUS MREF MEMBERS
   REVEALS VERY GOOD AGREEMENT WITH THE PATTERN EVOLUTION THROUGH ABOUT
   108 HOURS OR VALID MON/D5 AT 12Z. ALTHOUGH DIFFERENCES EXIST FURTHER
   OUT...THEY ARE MOSTLY IN RELATION TO TIMING AND LOCATION OF THE
   LIKELY SEVERE THREAT.
   
   A WEAK LEAD SHORTWAVE TROUGH IS EXPECTED TO DE-AMPLIFY ACROSS THE
   MID MS VALLEY ON SUN/D4...WITH A SUBTLE UPPER RIDGE ACROSS THE OH/TN
   VALLEYS. THIS PATTERN WILL MAINTAIN SELY FLOW ACROSS THE GULF OF
   MEXICO AROUND THE SURFACE HIGH WHICH SHOULD BE CENTERED JUST OFF THE
   MID ATLANTIC COAST ON MON/D5. AS SUCH...LOW LEVEL MOISTURE WILL
   CONTINUE TO INCREASE WITH MID 60S F BOUNDARY LAYER DEWPOINTS AS FAR
   N AS DALLAS.
   
   SINCE THE QUALITY OF THE LOW LEVEL MOISTURE RETURN DOES NOT APPEAR
   TO BE IN QUESTION...ATTENTION TURNS TO THE TIMING OF THE WRN TROUGH.
   VIRTUALLY ALL MODELS SHOW A LARGE TROUGH THAT WILL MOVE EWD INTO THE
   PLAINS AROUND TUE/D6 AND WILL CONTINUE EWD THROUGH D8.
   
   MODELS ARE IN GOOD AGREEMENT WITH DEPICTING A LEADING SHORTWAVE
   MOVING ACROSS THE CNTRL AND SRN PLAINS AND INTO THE MS VALLEY BY TUE
   AFTERNOON. THE ECMWF AMPLIFIES THIS FEATURE MORE THAN THE
   OPERATIONAL GFS...BUT IS IN AGREEMENT WITH THE CMC AND A FEW MREF
   MEMBERS. IN THIS SCENARIO...A STRONGER SURFACE LOW FORMS FROM IA
   INTO WI...WHICH WOULD EXPAND THE SEVERE THREAT FARTHER NWD ACROSS
   IL. EVEN IF THE LESS AMPLIFIED GFS SITUATION DEVELOPS...SEVERE WOULD
   STILL BE LIKELY ACROSS MUCH OF AR AND NERN TX WHERE LARGER MOISTURE
   AND INSTABILITY WOULD BE PRESENT ALONG WITH STRONG SHEAR. HAVE
   MAINTAINED PREVIOUS AREA AND EXPANDED NWD AND EWD SLIGHTLY FOR
   TUE/D6.
   
   FOR WED/D7...WHILE THE GFS APPEARS TO BE AN OUTLIER LAGGING THE MAIN
   TROUGH OVER THE FOUR CORNERS...IT DOES INDICATE THE POTENTIAL FOR A
   SECONDARY SHORTWAVE TO EJECT EWD ACROSS THE SRN PLAINS AND LOW MS
   VALLEY ON WED/D7...THEN CONTINUING TOWARD THE E COAST ON D8. THE
   MOST LIKELY SOLUTION AT THIS TIME LOOKS TO BE FOR A MORE MARGINAL
   SEVERE THREAT PERSISTING INTO WED/D7 WITH THUNDERSTORMS ALONG A COLD
   FRONT ACROSS MUCH OF THE ERN STATES. HOWEVER...PREDICTABILITY FOR D7
   AND D8 IS QUITE LOW AT THIS TIME.
   
   ..JEWELL.. 01/24/2013

[Tim from Springfield (IL)]

SPC no longer seems impressed in their latest 4-8 day:

 

http://www.spc.noaa.gov/products/exper/day4-8/

 

DAY 4-8 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0320 AM CST FRI JAN 25 2013      VALID 281200Z - 021200Z      ...DISCUSSION...   GENERAL AGREEMENT EXISTS AMONGST THE GFS/EC/UK/CMC GLOBAL MODELS IN   THE EVOLUTION OF A LARGE SCALE POSITIVE TILT TROUGH ACROSS THE WRN   U.S. THROUGH D4/MON. HOWEVER...IT IS IMMEDIATELY THEREAFTER AND   BEYOND WHEN SUBSTANTIAL DIFFERENCES APPEAR AND PERSIST AMONGST THE   MEDIUM RANGE GUIDANCE...THUS INTRODUCING CONSIDERABLE UNCERTAINTY IN   THE FORECAST FOR NEXT WEEK.      THE ECMWF EXHIBITS THE GREATEST DEPARTURE FROM PRIOR RUNS AND IS AN   OUTLIER IN DEVELOPING A CUTOFF LOW WITHIN THE BASE OF THE POSITIVE   TILT TROUGH ACROSS THE SOUTHWEST AND BAJA THROUGH D5/TUE. THE   GFS...AND TO SOME EXTENT THE OTHER GLOBAL MODELS AND GFS   ENSEMBLE...MAINTAIN A MORE PROGRESSIVE AND PHASED DEEP UPPER TROUGH   AND STRONGER COLD FRONT THAT SPREAD EAST AND SOUTH ACROSS MID/LOWER   MS VALLEY THROUGH D6/WED. BUT...EVEN AMONGST THE GFS ENSEMBLE   MEMBERS...UNCERTAINTY IN THE AMPLITUDE OF THIS TROUGH IS HIGH WITH   THE STANDARD DEVIATION IN 500MB HEIGHTS ACROSS THE CNTRL U.S.   EXCEEDING 90M AT THE 120H FORECAST VALID D5/TUE EVENING.      DESPITE THE SPREAD IN GFS ENSEMBLE MEMBERS...THERE REMAINS A LOW   PROBABILITY SEVERE WEATHER THREAT FROM ARKLATEX TO MS DELTA REGIONS   AS THE COLD FRONT ASSOCIATED WITH THE UPPER TROUGH DEVELOPS INTO AN   AXIS OF POTENTIAL INSTABILITY THROUGH D5/TUE EVENING. WITH LATEST   MODEL SOLUTIONS AND ENSEMBLE MEMBERS EXHIBITING SUCH DIVERGENT   OUTCOMES HOWEVER...FORECAST CONFIDENCE IN A MORE WIDESPREAD SEVERE   WEATHER THREAT HAS DECREASED SINCE YESTERDAY. THUS...PREDICTABILITY   APPEARS TOO LOW TO MAINTAIN A SEVERE WEATHER AREA AT THIS TIME.      ..CARBIN.. 01/25/2013

[BeauDodson]

They had this outlined two days in a row then pulled the plug.  I think we see a risk zone return before all is said and done.  Question remain on the the intensity and track of the area of low pressure.  Plenty of moisture and warmth along the Gulf of Mexico to pull into a system.  GFS shows 850 mb wind fields in the 50-60+ range on Tuesday night.  Dew points in the 50s/60s into Illinois. 

 

This one is worth at least monitoring. 

[Hoosier]

They had this outlined two days in a row then pulled the plug. I think we see a risk zone return before all is said and done. Question remain on the the intensity and track of the area of low pressure. Plenty of moisture and warmth along the Gulf of Mexico to pull into a system. GFS shows 850 mb wind fields in the 50-60+ range on Tuesday night. Dew points in the 50s/60s into Illinois.

This one is worth at least monitoring.

Yeah, there is quite a bit of uncertainty on the handling of the trough.

[Chicago Storm]

Not really sure what to think yet.

 

Obviously some runs (Such as the 18z GFS) have shown nice severe potential for a large area, with chase potential...While you have some runs (Like the 12z ECMWF) that have a weak wave with far less potential. Given the poor performance of guidance pre-sampling this season we'll likely have to wait until Sunday for a better idea.

[Stebo]

Not really sure what to think yet.

 

Obviously some runs (Such as the 18z GFS) have shown nice severe potential for a large area, with chase potential...While you have some runs (Like the 12z ECMWF) that have a weak wave with far less potential. Given the poor performance of guidance pre-sampling this season we'll likely have to wait until Sunday for a better idea.

 

Yeah all of this hitches upon whether or not the vorticity gets pulled under the PNA ridge or not, if it doesn't things could be favorable especially with the explosive dynamics the 18z GFS showed.

[csnavywx]

00Z EC backed away from that idea and towards the remainder of the guidance. It looks like "game on" for an initial supercell threat followed by a strong QLCS with embedded supercells. 60+ dews in my neck of the woods this time of year are pretty exceptional.

[Stebo]

00Z EC backed away from that idea and towards the remainder of the guidance. It looks like "game on" for an initial supercell threat followed by a strong QLCS with embedded supercells. 60+ dews in my neck of the woods this time of year are pretty exceptional.

This could really be a high end event especially for the Mid MS Valley, the wind fields are really off the charts and then throw in 60+ dew points into the region. I am really impressed at the potential to be honest.

[csnavywx]

Models are going ape with QPFs after 18z Tue, an apparent response of the convective schemes to the very favorable conditions. Progged CAPEs are relatively modest, but when using virtual temperature to calculate it instead, they are easily double or triple the progged values in some instances.

[Stebo]

Models are going ape with QPFs after 18z Tue, an apparent response of the convective schemes to the very favorable conditions. Progged CAPEs are relatively modest, but when using virtual temperature to calculate it instead, they are easily double or triple the progged values in some instances.

 

Yeah, just checking around to local NWS across AR/TN/LA/MS, they are going with low to mid 70s for Tuesday, where as the GFS is closer to 65 for most of those locations. Hell with the wind fields progged 500-750 J/kg would be enough to get things done, jack it up closer to 1500 and things could be significant.

[Hoosier]

Not really excited about severe prospects this far north at this point. Moisture is very good...maybe too good as profiles become deeply saturated. Setup screams embedded thunder with heavy rain threat with isolated/low end severe threat at best. Greater severe threat probably near/south of the Ohio River.

[andyhb]

0-1 km shear from the 12z GFS...quite impressive over a substantial piece of real estate.

 

[IWXwx]

The warm sector looks like it will be where the action is at. Spring already lol?

• Wednesday Night Mostly cloudy, with a low around 19.
• Thursday Partly sunny, with a high near 25.
• Thursday Night Mostly cloudy, with a low around 10.
• Friday Partly sunny and cold, with a high near 19.
• Friday Night Mostly cloudy, with a low around 12.
• Saturday A chance of snow showers. Mostly cloudy, with a high near 29.

[Stebo]

Not really excited about severe prospects this far north at this point. Moisture is very good...maybe too good as profiles become deeply saturated. Setup screams embedded thunder with heavy rain threat with isolated/low end severe threat at best. Greater severe threat probably near/south of the Ohio River.

 

I wouldn't immediately toss this potential up North, it shouldn't take too much instability to make things interesting considering the magnitude of the wind fields.

[Hoosier]

I wouldn't immediately toss this potential up North, it shouldn't take too much instability to make things interesting considering the magnitude of the wind fields.

Not tossing, just being reserved at this range. These winter events are in some ways more difficult than others to forecast since instability is usually a big question mark.

00z NAM does bring some CAPE in here on Tuesday.

[Stebo]

Not tossing, just being reserved at this range. These winter events are in some ways more difficult than others to forecast since instability is usually a big question mark.

00z NAM does bring some CAPE in here on Tuesday.

Oh yeah I am not bold in this range either, I do think there could be potential though.

[Chicago Storm]

If  the GFS is right and there is enough CAPE to go along with the 50-60F DP's and dynamics in place, the threat will extend north. Could be looking at a sig QLCS wind threat across S. IL/IN/OH/KY.

 

50-60kts just off the deck at 925mb and 100kts at 850mb.

 

[Hoosier]

Holy moly...100 kts at 850 mb is luda.

[Chicago Storm]

Holy moly...100 kts at 850 mb is luda.

Indeed. Even showing 70mph+ wind gust potential at the surface...

 

[Stebo]

Indeed. Even showing 70mph+ wind gust potential at the surface...

 

 

Da hell? Man that is quite the graphic there. I mean I knew there was substantial dynamics in place but to see this kind of projection and probable convection in place, it won't take much for this to be realized.

[andyhb]

Holy moly...100 kts at 850 mb is luda.

 

When was the last time we saw that progged for a non-tropical origin system?

[Hoosier]

The thing about that 100 kts is that the layer from 850 mb to the surface is weakly stable on the forecast soundings. Not really a strong inversion.

[Hoosier]

When was the last time we saw that progged for a non-tropical origin system?

And not like a week out? I don't know.

[Stebo]

The thing about that 100 kts is that the layer from 850 mb to the surface is weakly stable on the forecast soundings. Not really a strong inversion.

 

 

Yeah on most soundings it is isothermal at best and that is using the GFS surface temperatures which might very well be underdone even at that time of day. The amount of WAA and strong gradient winds will keep the temperatures up overnight until the front crashes through.

[cyclone77]

Gotta love this from far northwest Ohio late Tue evening from the GFS lol...

 

[Stebo]

Gotta love this from far northwest Ohio late Tue evening from the GFS lol...

 

 

 

Unrealistically moist through the column up to 200mb lol. That being said very nice shear.

[Stebo]

 

 

DAY 3 CONVECTIVE OUTLOOK     NWS STORM PREDICTION CENTER NORMAN OK   0224 AM CST SUN JAN 27 2013      VALID 291200Z - 301200Z      ...THERE IS A SLGT RISK OF SVR TSTMS FROM TX NORTHEAST TO IL AND   EAST ACROSS THE LOWER MS VALLEY...      ...SYNOPSIS...   A POTENT HIGH AMPLITUDE UPPER TROUGH AND ASSOCIATED COLD FRONT WILL   SWEEP EAST AND SOUTH ACROSS THE PLAINS/MIDWEST AND LOWER MS VALLEY   FROM TUESDAY INTO EARLY WEDNESDAY. THIS SYSTEM COULD PRODUCE A   FAIRLY WIDESPREAD SWATH OF SEVERE WEATHER FROM CNTRL AND NERN   TX...NRN LA...ACROSS MUCH OF AR AND SERN MO...AND EAST AND SOUTH   ACROSS THE MS RIVER FROM IL TO MS. WHILE IT IS TOO EARLY TO BE   OVERLY DETAILED REGARDING THE CHARACTER OF THIS EVENT...THE   SIZE...STRENGTH...AND RAPID EVOLUTION OF THE LARGE SCALE TROUGH   SYSTEM...AS CURRENTLY FORECAST...SUGGESTS THE DEVELOPMENT OF AN   EXTENSIVE AND FAST-MOVING SQUALL LINE CAPABLE OF PRODUCING DAMAGING   WINDS ACROSS SOME OR ALL OF THE ABOVE MENTIONED AREAS FROM AROUND   MID-DAY TUESDAY INTO EARLY WEDNESDAY.      ...TX TO IL SOUTHEAST ACROSS THE LOWER MS VALLEY...   PREFER THE SOMEWHAT SLOWER AND NOT SO PHASED DEPICTION OF THE UPPER   TROUGH AS SHOWN BY LATEST ECMWF AND NAM THROUGH EARLY TUESDAY. THESE   SCENARIOS INDICATE A MOIST BUT GENERALLY WEAK TO MODERATELY UNSTABLE   AIRMASS WILL BE SITUATED FROM TX NEWD ACROSS MO AND INTO IL BY   TUESDAY AFTERNOON. LACK OF STRONGER INSTABILITY WILL LIKELY BE   COMPENSATED FOR BY RELATIVELY RAPID ONSET OF INTENSE ASCENT   ASSOCIATED WITH THE APPROACH OF MID/UPPER TROUGH AND 100KT MID LEVEL   SPEED MAX SPREADING OUT ACROSS THE WARM SECTOR TO NEAR ARLATEX BY   AROUND 00Z. DEEP CONVECTION WILL ERUPT ALONG THE ENTIRE LENGTH OF   THE SHARPENING COLD FRONT THROUGH THE LATE AFTERNOON WITH STORMS   COMING UNDER THE INFLUENCE OF EVER INCREASING DEEP-LAYER SHEAR/FLOW.   EXTENSIVE QLCS APPEARS LIKELY TO SPREAD EAST ACROSS THE MID/LOWER MS   VALLEY INTO TUESDAY NIGHT WITH CELL MOTIONS FORECAST IN EXCESS OF   50KT LEADING DAMAGING WINDS. LACK OF STRONGER CYCLONIC DEVELOPMENT   ALONG THE COLD FRONT SUGGESTS LINEAR MODE SHOULD DOMINATE BUT   SUPERCELLS AND LEWPS EMBEDDED IN THE LINE AND NEAR TRANSIENT FRONTAL   WAVE STRUCTURES WOULD POSE SOME TORNADO THREAT WITH TIME.   UNCERTAINTIES REGARDING OVERALL TIMING AND DEGREE OF SURFACE-BASED   DESTABILIZATION PRECLUDE HIGHER OR SIGNIFICANT PROBABILITIES AT THIS   FORECAST RANGE. HOWEVER...FUTURE UPGRADE TO MDT RISK SEEMS POSSIBLE   IF THESE DETAILS BECOME CLEARER.

 

The last line is more so for the Southern part of the region, but a pretty strongly worded discussion, although I don't quite agree with relying on the NAM/Euro combo as they are both trending toward the GFS solution.

[Central Illinois]

Holy moly...100 kts at 850 mb is luda.

Indeed. Even showing 70mph+ wind gust potential at the surface...

wow pretty impressive

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[hoosierwx]

 

From LMK:

 

By Tuesday night, the front will be pushing into the western

sections of the region.  Quite a bit of the model guidance is

showing a very impressive wind field developing with this system.

Tonight`s data is a bit more aggressive with the wind field showing

850 hPa winds increasing into the 65-85kt range.  Precipitable water

values increase to near 1.5 inches and dewpoints are likely to top

out into the lower 60s.  Surface instability parameters continue to

look rather poor, but there continues to be strong evidence of

elevated instability across the region.  Overall CAPE values are

still in the 100-200 J/Kg with higher amounts to our

south/southwest.  However, in the cold season, only a few hundred

Joules of CAPE is needed for severe weather.

Despite the rather low instability expected, combination of

increasing synoptic scale ascent due to large mid-level height

falls, strong convergence and slab-forced ascent along the

pre-frontal trough axis is likely to result in widespread shower

activity with a strong likelihood of some sort of squall line

developing and plowing through the region.  Given the overall

kinematic and thermodynamic setup, strong to severe thunderstorms

are increasingly likely with damaging thunderstorms winds being the

most favored hazardous weather threat.  Though, given the strong

shear, mesoscale vorticies along the squall line could potentially

lead to some isolated tornadoes.

 

 

 

Could be a wild night.

 

[csnavywx]

It's important to use virtual temperature to calculate instability this time of year. I get the feeling that most folks aren't.

 

http://journals.ametsoc.org/doi/pdf/10.1175/1520-0434%281994%29009%3C0625%3ATEONTV%3E2.0.CO%3B2

 

 

It tends to have a fairly large effect in these low CAPE situations.