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April 2nd - April 5th Severe Weather


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The GFS also looks quite interesting for overnight Sunday into Monday. The 12Z GFS has 2,500 J/Kg of SBCAPE over OK at 6 AM Monday with a weak cap by afternoon/evening. I've already made the arrangements in my work schedule so I can be available to chase that day. Should the cap break on Saturday, then that has the potential to be an interesting caprock day.

And by 12z Monday the area along I-70 in MO and I-64 from St. Louis area se to sw IN looks under the gun with areal coverage Monday contingent upon the retreating warm front based on Wednesday's 12z GFS. Instability is less than in OK, certainly, but cap issues might not be so prominent. I would definitely keep the warm front in mind with this one.

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Looking at my AccuWeather pay per view graphics and skew-T, (Texas discussion here) while Houston looks post-frontal or outflow dominant, Euro seems to suggest a warm front in Northern Louisiana, with surface based cape near MLU (~32.6ºN, 92ºW) almost 1750 J/Kg and in excess of 300 m^2/s^2 with precip near/just West of the area. Monday late afternoon (Tuesday 0Z).

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ZCZC SPCSWOD48 ALL

ACUS48 KWNS 310909

SPC AC 310909

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0409 AM CDT THU MAR 31 2011

VALID 031200Z - 081200Z

...DISCUSSION...

SOME TIMING AND AMPLITUDE DIFFERENCES PERSIST AMONG GFS...ECMWF AND

ENSEMBLE MEMBERS. HOWEVER...MODELS HAVE GENERALLY CONVERGED TOWARD A

SIMILAR SOLUTION REGARDING UPPER TROUGH FORECAST TO AMPLIFY AND MOVE

INTO THE PLAINS LATE DAY 4...THEN MS/OH VALLEYS AND SERN STATES DAY

5 AND FINALLY ATLANTIC COASTAL REGION DAY 6. IT APPEARS THIS FEATURE

WILL REMAIN A PROGRESSIVE UPPER WAVE AS IT ADVANCES THROUGH THE ERN

2/3 OF THE COUNTRY.

...DAY 4...

LLJ ASSOCIATED WITH CNTRL PLAINS LEE CYCLONE WILL CONTINUE ADVECTING

RICHER GULF MOISTURE THROUGH WARM SECTOR ACROSS THE SRN-CNTRL PLAINS

AND LOWER-MID MS VALLEY. EML WILL EXPAND EWD AND EFFECTIVELY CAP

WARM SECTOR EAST OF DRYLINE OVER THE PLAINS. HOWEVER...POTENTIAL

WILL EXIST FOR IMPULSE TO EJECT EWD AHEAD OF MAIN UPPER TROUGH.

DIABATIC WARMING OF THE BOUNDARY LAYER AND DRYLINE CONVERGENCE MIGHT

BECOME SUFFICIENT FOR ISOLATED SUPERCELLS FROM KS SWD INTO OK AND

NRN TX. ADDITIONAL STORMS WILL BE MORE LIKELY AS THE COLD FRONT

ADVANCES SEWD AND INTERCEPTS THE DRYLINE FROM THE CNTRL PLAINS INTO

THE MID MS VALLEY AREA.

...DAY 5...

WIDESPREAD SEVERE STORMS ARE BECOMING INCREASINGLY PROBABLE DAY 5.

GULF MOISTURE WILL ADVECT NWD THROUGH LOWER-MID MS VALLEY...SERN

STATES AND OH VALLEY IN ASSOCIATION WITH VERY STRONG EWD MIGRATING

LLJ. MORE WIDESPREAD THUNDERSTORM DEVELOPMENT WILL BECOME PROBABLE

AS FORCING FOR DEEP ASCENT ATTENDING THE UPPER TROUGH SHIFTS EAST OF

STRONGER EML. THREAT WILL EXIST FOR SUPERCELLS AND LINE SEGMENTS

WITH TORNADOES...LARGE HAIL AND DAMAGING WIND.

...DAY 6...

SEVERE THREAT SHOULD CONTINUE THROUGH THE REMAINDER OF THE SERN

STATES AND THE MID ATLANTIC SEABOARD.

..DIAL.. 03/31/2011

post-783-0-69885600-1301573468.gif

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The GFS depicts a major severe weather outbreak beginning late Sunday Night and continuing through Tuesday.

Yes, and the projected track of the low is moving northward with each model run leading to an expansive warm sector over the Ohio and mid Mississippi Valley southward. Will be interesting to see if this trend continues.

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The 12z NAM paints an ominious picture along the IA/MO border for sunday with dew points in the low-mid 60's and CAPE values between 1500-2500 j/kg. The problem is quite the strong cap to overcome, if only we could get a subtle wave to come along. It does look like the cap is weaker further south along the dryline.

Will be keeping a close eye on this one.

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Monday evening (Tuesday 0Z) Euro 60ºF dewpoint is almost to Buffalo.

Narrow stripe of what I assume are MU CAPE of 500J/Kg up to Central Ohio on the Euro for 0Z Tuesday, better CAPE confined to the Gulf Coast states.

Euro seems to suggest one or two isolated cells Sunday afternoon/evening may go near DFW, over -100 J/Kg CING, hence the isolated, but TT of 56, 1800 J/Kg SB Cape and 200 m^2s^2. Cloud bases look about 800 mb, which may limit tornado threat, and the slight warm nose puts the LFC about 630 mb (small picture), but Euro does show something trying to pop, and a pretty good clockwise curved hodo at 96 hours (0Z Monday).

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The degree and extent of instability depicted on the models for the Monday/Tuesday event are extremely impressive thus far. This has been shown for some time now, owing to the favorable synoptics leading up to the event that favor deep moisture return and advection of the elevated mixed layer into the warm sector. What is going to make or break this event is the actual trough evolution. Although it seems too high-amplitude and a bit strung out right now for a large-scale tornado outbreak, this could change considerably over the next few days as it gets better sampled by radiosonde data, and the thermodynamic potential of this event is impossible to ignore.

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Latest thinking from Indpls. AFD shows the level of model uncertainty.

.LONG TERM /SUNDAY NIGHT THROUGH THURSDAY/...

THE MAIN FOCUS OF THE LONG TERM IS THE BIG STORM SYSTEM PROGGED

FOR MONDAY AND TUESDAY. IT LOOKS LIKE 2 DECENT ROUNDS OF STORMS

WILL BE POSSIBLE...THE FIRST WITH THE SURFACE LOW...AND THE SECOND

WITH THE UPPER LEVEL TROUGH.

THE RESULT WILL BE COMPLETELY DIFFERENT DEPENDING ON WHICH MODEL

PREVAILS. CURRENTLY...IF THE GFS WINS...IT WILL BE A SIGNIFICANT

EVENT FOR CENTRAL INDIANA. HOWEVER...THE TIMING AND FORCING WITH

THE EURO ARE NOT AS FAVORABLE.

FIRST...THE EURO AND GFS ARE SOMEWHAT CLOSE WITH TIMING OF SURFACE

LOW MOVING THROUGH AROUND TUE 06Z. HOWEVER...THE MAIN SOURCE OF

LIFT WITH THE SURFACE LOW WILL BE A STRONG LOW LEVEL JET...AND THIS

IS WHERE THEY DIFFER. THE GFS IS SHOWING THE JET IN EXCESS OF 75

KTS...BUT THE EURO IS SHOWING IT AT 60 TO 65 KTS AND FARTHER SOUTH.

IF THE GFS PREVAILS...OVERNIGHT CONVECTION WILL BE POSSIBLE ON

MONDAY NIGHT/TUESDAY.

THE MAIN SHOW THOUGH LOOKS LIKE IT WILL BE WITH THE UPPER LEVEL

TROUGH...WHICH WILL BE ON TUESDAY EVENING IF THE GFS PREVAILS ONCE

AGAIN. THE GFS TAKES THE VORT MAX DIRECTLY OVER CENTRAL

INDIANA...COUPLED WITH A 125 KT UPPER LEVEL JET. MORE

IMPORTANTLY...THE TIMING OF THE GFS IS MORE CONDUCIVE TO SEVERE

DEVELOPMENT SINCE IT WILL MOVE THROUGH DURING THE PRIME HEATING OF

THE DAY. THE EURO...ON THE OTHER HAND...IS ABOUT 12 HOURS SOONER

THAN THE GFS...WHICH WOULD BE TOO EARLY FOR THE MOST UNSTABLE

ENVIRONMENT. IN ADDITION...THE EURO TAKES THE VORT MAX OVER THE

TENNESSEE VALLEY.

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The degree and extent of instability depicted on the models for the Monday/Tuesday event are extremely impressive thus far. This has been shown for some time now, owing to the favorable synoptics leading up to the event that favor deep moisture return and advection of the elevated mixed layer into the warm sector. What is going to make or break this event is the actual trough evolution. Although it seems too high-amplitude and a bit strung out right now for a large-scale tornado outbreak, this could change considerably over the next few days as it gets better sampled by radiosonde data, and the thermodynamic potential of this event is impossible to ignore.

Agree with this completely. The consistent signal of impressive thermodynamics with the system leads to very little doubt that there will be at a minimum some significant severe in the form of wind/hail and maybe some tornadoes. The big questions come in the evolution of the trough and whether or not it will support a more major tornado outbreak. Right now, the models are really struggling, with the GFS trending toward earlier ECMWF runs, and ECMWF trending toward earlier GFS runs. Until all this is sorted out, trying to figure out the details/magnitude/timing of this system is almost fruitless.

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ILX favors the slower, stronger GFS at this time.

STILL SOME DIFFERENCES IN THE EXTENDED CONCERNING THE TRACK/TIMING OF

THE ROCKIES LOW EARLY NEXT WEEK. THE 00Z ECMWF IS FASTER THAN

THE GFS AND TAKES THE LOW ACROSS CENTRAL ILLINOIS EARLY MONDAY

MORNING. MEANWHILE...THE 12Z GFS IS SLOWER AND STRONGER WITH THE

SYSTEM...KEEPING THE LOW WEST OF THE AREA UNTIL MONDAY

AFTERNOON/EVENING. WITH THE NORTH ATLANTIC OSCILLATION BECOMING

POSITIVE...A STRONG ICELANDIC LOW AND RESULTING HIGHLY AMPLIFIED

PATTERN IS FAVORED ACROSS NORTH AMERICA NEXT WEEK. THIS WOULD

SUGGEST A SLOWER/STRONGER STORM SYSTEM LIKE THE GFS IS SHOWING.

HAVE THEREFORE TRENDED TOWARD THE GFS FOR THE EXTENDED FORECAST.

END RESULT WOULD MEAN A BREEZY AND VERY WARM DAY ON MONDAY...WITH

HIGH TEMPS SOARING INTO THE 70S. IT WOULD ALSO MEAN A GOOD CHANCE

FOR SHOWERS AND THUNDERSTORMS...SOME OF WHICH COULD BECOME STRONG

TO SEVERE MONDAY AFTERNOON AND NIGHT. HAVE GONE WITH LIKELY POPS

ACROSS THE BOARD DURING THE DAY MONDAY...AS ENTIRE CWA PUNCHES

INTO THE WARM SECTOR AND INITIAL SURFACE WAVE TRACKS JUST N/NW OF

THE AREA. SECOND WAVE RIDING ALONG THE TRAILING COLD FRONT WILL

LIKELY BRING ANOTHER ROUND OF SHOWERS AND THUNDERSTORMS TO THE

E/SE MONDAY NIGHT...WHILE PRECIP BEGINS TO WIND DOWN BEHIND THE

DEPARTING SYSTEM ACROSS THE ILLINOIS RIVER VALLEY. ONCE THE LOW

AND ACCOMPANYING FRONT EXIT THE REGION

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