Mar. 27-31 Severe Threats

[Hoosier]

12z NAM still on the slower side for Thursday and has a nice corridor of instability in IL/IN during the day.  00z ECMWF did slow down a little compared to yesterday's 12z run.

[weathergy]

Besides that, there was only 2 storm reports in DTX's CWA, only 1 of which were from a trained spotter.

And the 1 storm report from the trained spotter was only for hail that was 3/4" in diameter (not 1").

Someone on the DTX Facebook page posted a picture showing 1" hail with a quarter next to it in Newport

[Hoosier]

12z GFS not playing ball with the NAM for Thursday as far as timing. 

 

Given what I mentioned yesterday about recent systems trending slower, still have some optimism that the faster models could slow down enough to provide a threat assuming sufficient destabilization.

[ClicheVortex2014]

12z NAM - wowowowow.

 

Looks like Forbes is favoring the quicker solution

THURSDAY

Computer models differ somewhat, so confidence is reduced in forecast details. Severe thunderstorms in south OH, central and east KY, middle and east TN, northeast, central and south MS, southeast and south-central LA, AL, west FL panhandle, north half GA, northwest half SC, west and central NC, southwest VA, southwest WV. TORCON - 3 TN, NC, SC, GA, and AL areas, southeast MS; 2 to 3 rest of area

 

[Stebo]

The 12z NAM is really good but something also to note, it is putting out very impressive CAPE values with dewpoints near 60 only, the lapse rates are really doing work with this potential. If we realize dewpoints in the 60-65 range we would be looking real good.

[ClicheVortex2014]

The 12z NAM is really good but something also to note, it is putting out very impressive CAPE values with dewpoints near 60 only, the lapse rates are really doing work with this potential. If we realize dewpoints in the 60-65 range we would be looking real good.

That seems to be a common theme so far this year. It's nice to have lapse rates working for us for once.

[Chicago Storm]

GFS continues to be a bit faster than the ECMWF for Thursday.

Would be a non-event chase wise on either model, but the ECMWF would at least give a better chance for some sort of severe for MI/IN/OH/KY.

The NAM is on its own in being much slower, with the threat being more significant and further west on Thursday. But it's an outlier at this point.

[andyhb]

SREF STI showed quite a strong signal 84 hrs out for 21z Thursday, but it's also working off of the NAM so I have my doubts about that.

[RyanDe680]

NAM goes all out on the CAPE

 

Meanwhile, GFS says what CAPE

[tornadohunter]

18z NAM seems to have sped up a tad bit. 

Given the models' performance this year, I dont think we will have a good grasp on this until wednesday night. 

[Chinook]

For those of you who haven't found this yet- Pivotalweather just got a lot better. There is a cursor read-out of every type of map except model-reflectivity. There are global-model map choices for 6 continents, and regional map areas of Mexico and the Middle East. The same regional areas of the US exist. This should be somewhat more helpful in looking at severe weather indices.

[Hoosier]

00z NAM still looks like it will have a decent threat farther west on Thursday, though veered low level flow could be a bit of an issue.

[IllinoisWedges]

00z NAM still looks like it will have a decent threat farther west on Thursday, though veered low level flow could be a bit of an issue.

If the NAM comes to fruition, I'm thinking a larger hail threat than wind/tornadoes (at least in Illinois), opinion? 

[HillsdaleMIWeather]

I'm hoping some model consistency develops during the 0Z runs tonight or by 12Z tomorrow, this is getting ridiculous. 

 

 

If the NAM comes to fruition, I'm thinking a larger hail threat than wind/tornadoes (at least in Illinois), opinion? 

From looking at the soundings, I would think so.

[nwburbschaser]

I'm hoping some model consistency develops during the 0Z runs tonight or by 12Z tomorrow, this is getting ridiculous.

That's just how it goes man. Expect some sort of compromise to develop as we get closer. The NAM already seems to have corrected and sped up a bit so I think we're already heading towards a solution. I think people tend to forget that until you get within 48 hours the NAM can't be taken too seriously, if then even.

[OHweather]

I'm limited in how far I can chase until school is over in a month, but if we can get NAM-like instability or something close I may try to scramble west. GFS and Euro not as enticing.

[Hoosier]

Sort of odd to see the big timing differences between the NAM and GFS at this point. Unless I'm missing something, system should pretty much be sampled.

[ClicheVortex2014]

Even if all the models converge on NAM's slower solution, there's still going to be nearly unpredictable uncertainty about how Wednesday's event is going to impact Thursday until the day of the event; debris clouds/remnant showers/decaying MCS will determine the northward extent of the severe threat

[Chicago Storm]

The NAM came back a bit slower for Thursday again. Decent threat from IL/IN on south. There 0z GFS is still on the quick side. Not gonna really put much stock into the NAM until other guidance comes onboard.

0z NAM for 0z Thursday evening south of IND...

[HillsdaleMIWeather]

For what it is worth, the WPC is using a NAM/Euro blend

MID-LEVEL SHORTWAVE DROPPING SWD INTO THE N-CNTRL U.S. BY THU

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

PREFERENCE: NAM/12Z ECMWF

CONFIDENCE: SLIGHTLY BELOW AVERAGE

SIMILAR TO THE UPSTREAM SYSTEM...THE GFS IS GENERALLY MORE

PROGRESSIVE THAN THE DETERMINISTIC AND ENSEMBLE MEAN CONSENSUS.

THE NAM HAS TRENDED SOME TOWARD THE 12Z ECMWF...PLACING THE TWO

INTO BETTER AGREEMENT.

The GFS did up the instability a bit more this run, so it may be starting to cave in

[ClicheVortex2014]

They wrote an essay for the day 2 outlook. Literally 5 pages of double-spaced text... almost 1,000 words.

 

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT TUE MAR 29 2016

VALID 301200Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS SERN NEB AND CENTRAL IA TO
PORTIONS WRN GULF COAST...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING SLGT RISK FROM NRN
IA TO WRN/CENTRAL GULF COAST AND S TX...

...SUMMARY...
STRONG TO SEVERE STORMS WILL BE POSSIBLE FROM PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS INTO THE LOWER TO MIDDLE MISSISSIPPI
VALLEY REGION ON WEDNESDAY. THREAT MAY PERSIST INTO THE OVERNIGHT
OVER THE LOWER MISSISSIPPI VALLEY AREA. DAMAGING WIND...LARGE HAIL
AND TORNADOES WILL BE POSSIBLE.

...SYNOPSIS...
IN MID-UPPER LEVELS...CURRENT ARRANGEMENT OF HIGH-AMPLITUDE RIDGING
OVER NERN PAC WILL AMPLIFY THROUGH DAY-2...WITH CLOSED 500-MB HIGH
DEVELOPING DAY-1 W OF BC COAST AND MIGRATING NEWD TOWARD SRN AK
PANHANDLE. THIS WILL LEAD TO ADDITIONAL AMPLIFICATION OF DOWNSTREAM
TROUGHING OVER WRN CONUS ON SYNOPTIC SCALE...WHILE SEVERAL EMBEDDED
SHORTWAVES MODULATE GEOMETRY OF HEIGHT FIELD. MOST IMPORTANT OF
THOSE FOR THIS FCST WILL BE CYCLONE CURRENTLY EVIDENT IN MOISTURE-
CHANNEL IMAGERY OVER SIERRAS AND WRN GREAT BASIN. CYCLONE IS FCST
TO FILL SOMEWHAT BUT STILL BE EVIDENT AT START OF PERIOD OVER NRN
CO...WITH STG TROUGH SWWD ACROSS LAS AREA THEN WWD OVER CENTRAL/SRN
CA. SEVERAL BASAL SHORTWAVES MIGRATING THROUGH ASSOCIATED CYCLONIC
FLOW WILL HELP TO MAINTAIN DECIDEDLY POSITIVE TILT TO SWRN TROUGH
THROUGH PERIOD...AS IT SHIFTS SEWD TO 31/12Z POSITION FROM NRN NM
ACROSS CENTRAL AZ AND NRN BAJA.

MEANWHILE...SHORTWAVE TROUGH NOW ENTERING SWRN/S-CENTRAL AK IS FCST
TO MOVE THROUGH LARGE-SCALE RIDGE DAY-1...THEN TURN RAPIDLY SEWD
FROM NW TERRITORIES ACROSS SK DAY-1...REACHING ERN MT AND WRN
DAKOTAS NEAR END OF PERIOD. ASSOCIATED HEIGHT FALLS WILL OVERSPREAD
CENTRAL/NRN PLAINS...LEADING TO ENEWD EJECTION AND OPEN-WAVE
TRANSITION OF 30/12Z CO CYCLONE. BY 31/00Z...THAT 500-MB LOW SHOULD
BE LOCATED OVER NERN CO/CENTRAL NEB...SEPARATING ITS SHORTWAVE
TROUGH FROM LARGER SWRN-CONUS HEIGHT ANOMALY. BY 31/12Z -- END OF
PERIOD -- RESULTING POSITIVELY TILTED SHORTWAVE TROUGH SHOULD EXTEND
FROM CENTRAL/SRN MN ACROSS CENTRAL/WRN IA...NERN/S-CENTRAL KS...AND
WRN OK/ERN TX PANHANDLE. DESPITE THIS COMPLEX PATTERN EVOLUTION ON
SUBSYNOPTIC SCALES...REASONABLE AGREEMENT EXISTS ON THAT SCENARIO TO
THIS POINT AMONGST AVAILABLE OPERATIONAL AND SREF UPPER-AIR
GUIDANCE...WHEN ZOOMING BACK FROM MESOSCALE DETAILS.

IN LOW LEVELS...RETURN FLOW NOW UNDERWAY ACROSS SRN PLAINS WILL GET
PROGRESSIVELY MORE MOIST WITH TIME...CONTRIBUTING TO BROAD PLUME OF
LATE-AFTN SFC DEW POINTS IN MID 50S F FROM SRN IA TO OZARKS AND NERN
OK...WITH LOW-MID-60S VALUES SWD FROM ERN OK ACROSS E TX...AND 70S
POSSIBLE OVER PORTIONS E AND S TX. DRYLINE SHOULD SHARPEN THROUGH
PERIOD...BECOMING WELL-DEFINED FROM SFC LOW OVER SERN NEB SSWWD
ACROSS E-CENTRAL KS...CENTRAL/W-CENTRAL OK...TO DRT AREA. COLD
FRONT AT 31/00Z SHOULD EXTEND FROM LOW SWWD ACROSS SERN CO...
OVERTAKING DRYLINE FROM N-S OVERNIGHT AND REACHING SRN MO...ERN OK
AND CENTRAL TX BY 31/12Z. PROGS DO DIVERGE DURING LAST HALF OF
PERIOD REGARDING SPEED/DEPTH OF SFC CYCLONE...WITH GFS GIVEN MINIMAL
CREDENCE WHILE TRENDING FASTER THAN MOST SREF MEMBERS...00Z
OPERATIONAL NAM...AND PRIOR 12Z ECMWF.

...CENTRAL/SRN PLAINS TO WRN GULF COAST -- GENERAL THOUGHTS...
GIVEN POSITIVE TILT OF TROUGH...ASSOCIATED FLOW/MASS-FIELD
GEOMETRIES...AND POTENTIAL FOR EARLY-PERIOD CONVECTION TO ERUPT OVER
PARTS OF TX/OK...SCENARIO REGARDING TIMING/PLACEMENT/EVOLUTION OF
GREATEST SVR POTENTIAL REMAINS FRAUGHT WITH UNCERTAINTIES FOR MOST
OF SLGT-RISK AREA. AS SUCH...WILL CONTINUE WITH BROAD BRUSH ON
UNCONDITIONAL PROBABILITIES...ACKNOWLEDGING THAT 30%/TOTAL-SVR
CONCENTRATION ULTIMATELY IS LIKELY TO BECOME APPARENT ON MESOSCALE
SOMEWHERE BETWEEN ERN NEB AND UPPER TX COAST. RELATIVE GAP MAY BE
PRESENT IN SVR POTENTIAL OVER SOME PARTS OF SRN KS OR OK BETWEEN
REGIMES DISCUSSED BELOW...HOWEVER UNCERTAINTY IS TOO GREAT ATTM TO
DRAW EITHER TWO SEPARATE OUTLOOKS OR AREAL INDENTATION.

...CENTRAL LOW PLAINS AND MID MS VALLEY TO WRN GULF COAST -- EARLY
PERIOD...
THOUGH LLJ WILL BE WEAKENING THROUGH MORNING...BROAD AREA OF
40-50-KT FLOW AND ASSOCIATED MOISTURE TRANSPORT WILL SUPPORT
SCATTERED TO LOCALLY NUMEROUS TSTMS FROM MORNING THROUGH MID AFTN.
THIS ACTIVITY IS POSSIBLE ALMOST ANYWHERE FROM SRN KS AND MO SSWWD
ACROSS CENTRAL/ERN OK...AR...ARKLATEX AND CENTRAL/E TX...IN REGIME
OF SLOWLY STRENGTHENING DEEP SHEAR. SPORADIC LARGE HAIL IS
POSSIBLE...AND ALSO STG GUSTS WITH TX CONVECTION WHERE LESS STATIC
STABILITY SHOULD BE PRESENT IN RELATIVELY MOIST BOUNDARY LAYER.
MULTIPLE ROUNDS OF TSTMS ARE POSSIBLE OVER TX AND PERHAPS SERN
OK/AR. ELEVATED/PRECONVECTIVE MUCAPE 1000-2500 J/KG AND 35-40 KT
EFFECTIVE-SHEAR MAGNITUDES WILL SUPPORT AT LEAST MRGL SVR RISK WITH
THIS ACTIVITY...WHICH MAY ACCESS POCKETS OF STEEP MIDLEVEL LAPSE
RATES RELATED TO RESIDUAL EML.

...CENTRAL PLAINS/ADJACENT MO VALLEY...AFTN/EVENING...
WIDELY SCATTERED TO SCATTERED AFTN TSTMS SHOULD FORM NEAR
DRYLINE...IN ARC EXTENDING GENERALLY SWD FROM VICINITY OF SFC LOW
ACROSS ERN KS. THIS ACTIVITY MAY INCLUDE SUPERCELLS WITH FULL
SPECTRUM OF SVR THREATS SHIFTING NEWD ACROSS ERN KS...SERN NEB AND
W-CENTRAL/NWRN MO...BEFORE LOSING ORGANIZATION DURING EVENING/
OVERNIGHT HOURS. FCST SOUNDINGS SUGGEST SUFFICIENTLY LARGE LOW-
LEVEL HODOGRAPHS FOR SUPERCELLS AMIDST 40-60 KT EFFECTIVE-SHEAR
MAGNITUDES...AND POTENTIALLY UP TO 2000 J/KG MLCAPE. UNCERTAINTIES
INCLUDE EWD EXTENT OF THIS REGIME INTO MO AND ANY SWD BACKBUILDING
INTO OK...GIVEN POTENTIAL FOR
1. LIMITED/NARROW CORRIDOR OF DESTABILIZATION BEHIND MORNING
ACTIVITY AND
2. EXTENT/MAGNITUDE OF RELATIVELY STABLE AIR ADVECTED NWD FROM
BENEATH RECURRING TSTM CLUSTERS OVER TX/SERN OK.

...SRN PLAINS...MID-LATE PERIOD...
ISOLATED TO WIDELY SCATTERED TSTMS MAY DEVELOP ALONG/AHEAD OF SFC
COLD FRONT AND DRYLINE IN RELATIVELY PRISTINE RETURN-FLOW AIR
ADVECTED NWD OFF GULF AND PAST OUTFLOW FROM EARLIER-PERIOD TSTMS
ACROSS THIS REGION. TIMING/COVERAGE REMAINS VERY UNCERTAIN ATTM...
AND STRONGLY DEPENDENT ON LOCATION/GEOMETRY OF RESULTING MESOSCALE
BOUNDARIES. FAVORABLE DEEP SHEAR AND CURVED LOW-LEVEL HODOGRAPHS
WILL SUPPORT SUPERCELL POTENTIAL WITH ANY CONVECTION THAT DOES
DEVELOP IN THIS REGIME.

 

[IllinoisWedges]

They wrote an essay for the day 2 outlook. Literally 5 pages of double-spaced text... almost 1,000 words.

Yea, he deserves an award. 

 

SPC not diggin' it. 

[HillsdaleMIWeather]

Day 3 marginal introduced into the areas where all the models agree on the minimum of a marginal threat, will be adjusted when the models change.

[IWXwx]

They wrote an essay for the day 2 outlook. Literally 5 pages of double-spaced text... almost 1,000 words.

 

Yeah, Roger Edwards really loves his job.

[hm8]

Yea, he deserves an award.

SPC not diggin' it.

Is... Is that map flipping me off?

[Hoosier]

Day 3 outlook touched on the uncertainty

 

..MID MS VALLEY...LOWER OH VALLEY AND SRN UPPER GREAT LAKES    NARROW CORRIDOR OF DIURNAL DESTABILIZATION MAY DEVELOP AHEAD OF SFC  COLD FRONT...AMIDST SHEAR FIELDS SUPPORTING SVR POTENTIAL.   HOWEVER...GIVEN WEAKENING OF MID/UPPER-LEVEL SUPPORT...POTENTIALLY  STABLE TRAJECTORIES FROM PROFUSE CONVECTION FARTHER S...AND  LIKELIHOOD OF SOMEWHAT VEERED FLOW AHEAD OF FRONT...UNCERTAINTIES  APPEAR TOO GREAT ATTM TO DRAW OUTLOOK AREA WITH UNCONDITIONAL  PROBABILITIES AOA 15%.  NARROW CORRIDOR OF MRGL PROBABILITIES IS  BEING INTRODUCED...HOWEVER.  

[Hoosier]

Looks like the 12z GFS slowed down some and the 12z NAM sped up some.

[Stebo]

Looks like the 12z GFS slowed down some and the 12z NAM sped up some.

NAM looks really weird with the low pressure orientation, really strung out.

[Hoosier]

NAM looks really weird with the low pressure orientation, really strung out.

 

 

Yeah, noticed that

 

All in all it seems like we're converging toward a solution that has IN/KY in play, and possibly into OH and northward into MI if there's enough instability.

[ClicheVortex2014]

So... how 'bout that 12z 4km NAM?