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March 20-23 Severe Threat


Jim Martin

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Bingo, in summary. Look at the NAM 500mb vorticity, 500mb height, and 700mb VV charts closely by 00z tomorrow in central IL...

SPC WRF tries to fire something in that area. It's a risky setup but worth mentioning so there's not a wtf moment tomorrow.

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Looking at things a little more closely, this run of the NAM, unlike previous runs, does indicate a nonzero tornado threat south of the cold core (in E KS, MO, etc.), with nice low-lvl lapse rates and decent hodograph curvature. Td's of 60-61F might just do it for that area. The cap erodes rapidly between 21Z and 0Z and significant forcing swings across during the 0Z timeframe.

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Looking at things a little more closely, this run of the NAM, unlike previous runs, does indicate a nonzero tornado threat south of the cold core (in E KS, MO, etc.), with nice low-lvl lapse rates and decent hodograph curvature. Td's of 60-61F might just do it for that area. The cap erodes rapidly between 21Z and 0Z and significant forcing swings across during the 0Z timeframe.

as a low-topped sup produces tors in central lol :)

due to class I get to play the "secondary" more conditional target.

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That cold-core looks prolific. It has a ton more instability than many cold-core events do. I would not be shocked to see something intense happen in NE/NW IA with that at all.

Great setup--very stout EML and a great height field config for deep low/mid level height falls as that embedded S/W trough at the base of the upper low progresses over the area. These tanking mid level lows always need to be watched for more significant potential. Looks interesting no doubt.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

1239 AM CDT TUE MAR 22 2011

VALID 221200Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM ERN NEB/KS ACROSS NRN AND

WRN MO...IA...AND NRN IL...

..SYNOPSIS

A STRONG UPPER SHORTWAVE TROUGH WITH A 90+ KT MID LEVEL JET MAX WILL

MOVE FROM THE FOUR CORNERS AREA NEWD ACROSS THE PLAINS AND INTO THE

MID MO/MS VALLEY DURING THE EVENING. AT THE SURFACE...LOW PRESSURE

WILL DEEPEN OVER NEB AND MOVE INTO WRN IA BY 00Z WITH A DRYLINE

EXTENDING SWD ALONG THE KS/MO BORDER AND INTO E CNTRL OK/NRN TX. SLY

FLOW ACROSS A LARGELY CAPPED WARM SECTOR WILL MAINTAIN BOUNDARY

LAYER DEWPOINTS IN THE MID TO UPPER 50S F AS FAR N AS IA AND CNTRL

IL NEAR A WARM FRONT. FORCING WITH THE LOW AND HEATING ALONG AND W

OF THE DRYLINE WILL LIKELY LEAD TO AN ACTIVE SEVERE WEATHER DAY OVER

A RELATIVELY FOCUSED AREA.

..ERN NEB/KS INTO IA/NRN MO/NWRN IL

ELEVATED/PERHAPS MARGINALLY SEVERE CONVECTION WITH HAIL WILL BE

ONGOING FROM ERN SD INTO SRN MN WHERE STRONG ISENTROPIC LIFT WILL

EXIST N OF THE WARM FRONT AND BENEATH STEEP LAPSE RATES ALOFT. TO

THE S...CAPPING WILL INHIBIT CONVECTION UNTIL AROUND 21Z WHEN STRONG

HEIGHT FALLS AND DEEP MIXING ERODE INHIBITION OVER ERN NEB. STRONG

UVVS AND ADVECTION OF STEEP LAPSE RATES WILL ALLOW FOR MUCAPE ON THE

ORDER OF 1000 J/KG TO DEVELOP FROM ERN NEB INTO IA AND FAR NRN MO BY

LATE AFTERNOON.

THE GREATEST THREAT FOR TORNADOES...LARGE HAIL AND DAMAGING WINDS

WILL BE FROM FAR ERN NEB ACROSS MUCH OF IA...PERHAPS EXTENDING INTO

FAR NRN MO. THIS AREA...BOUNDED BY THE DRYLINE TO THE W AND WARM

FRONT TO THE N...WILL HAVE VERY STRONG SHEAR PROFILES FAVORABLE FOR

SUPERCELLS AND TORNADOES. JUXTAPOSITION OF GREATEST SHEAR AND

INSTABILITY IS LIKELY TO BE OVER IA...PERHAPS EXTREME ERN NEB IF THE

DRYLINE MOVES MORE SLOWLY. HOWEVER...FAST STORM MOTIONS WILL LIMIT

TEMPORAL WINDOW AVAILABLE FOR TORNADOES AS STORMS BECOME ELEVATED AS

THEY CROSS THE WARM FRONT. WHILE SYNOPTIC SETUP AND SHEAR WOULD

APPEAR TO FAVOR STRONG TORNADOES...BOUNDARY LAYER MOISTURE QUALITY

AND INSTABILITY ARE LIKELY TO BE A LIMITING FACTOR IN THIS REGARD.

LARGE HAIL WILL REMAIN LIKELY WITH ANY STORMS N OF THE WARM

FRONT...FROM NERN IA INTO NRN IL AND NWRN IND LATE.

FARTHER S...THE THREAT BECOMES MORE CONDITIONAL ACROSS ERN KS...WRN

MO...AND FAR NERN OK...WHERE LAPSE RATE PROFILES WILL BE POOR. SHEAR

WILL BE QUITE STRONG...AND THERE WILL BE SOME LIFT ALONG THE

DRYLINE. ANY THREAT IN THESE AREAS IS EXPECTED TO BE RELATIVELY

SHORT LIVED AS CAPPING QUICKLY OCCURS AFTER SUNSET...AND THE THREAT

OF FURTHER SEVERE WEATHER DIMINISHES. LARGE HAIL AND PERHAPS A BRIEF

TORNADO WOULD BE THE MAIN THREATS IN THESE AREAS.

..JEWELL.. 03/22/2011

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BULLETIN - EAS ACTIVATION REQUESTED

SEVERE THUNDERSTORM WARNING

NATIONAL WEATHER SERVICE QUAD CITIES IA IL

1236 AM CDT TUE MAR 22 2011

THE NATIONAL WEATHER SERVICE IN THE QUAD CITIES HAS ISSUED A

* SEVERE THUNDERSTORM WARNING FOR...

SOUTHEASTERN WHITESIDE COUNTY IN NORTHWEST ILLINOIS...

* UNTIL 130 AM CDT.

* AT 1233 AM CDT...NATIONAL WEATHER SERVICE DOPPLER RADAR INDICATED A

SEVERE THUNDERSTORM CAPABLE OF PRODUCING QUARTER SIZE HAIL. THIS

STORM WAS LOCATED APPROXIMATELY NEAR PROPHETSTOWN...OR 12 MILES

SOUTH OF MORRISON...AND MOVING EAST AT 40 MPH.

* THE SEVERE THUNDERSTORM WILL BE NEAR...

TAMPICO AROUND 1245 AM CDT...

DEER GROVE AROUND 1250 AM CDT...

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here is the culprit, it probably produce a bit bigger hail to your east as it shot up to 70dbz for a scan and then it got warned.

Looks like an elevated sup.

It was almost as if there were two hail cores that affected us. The first one only had pea sized hail, and it was solid white looking. That shut off almost completely, and then BAM, a wall of much larger hail hit. It was mainly clear, almost like sleet.

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Im tempted to go out to western iowa now, even have the day off work :) still debating if its worth the gas money

-anyone going out tuesday with a laptop setup? (i currently dont have one) :( just a cell phone

Tempting for me, But I'm going to pass. Reminds of the April 6th setup last year in eastern Iowa..limited surface based potential as they become elevated as they race across the warm front.

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DAY 1 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0748 AM CDT TUE MAR 22 2011

VALID 221300Z - 231200Z

...THERE IS A SLGT RISK OF SVR TSTMS THIS AFTERNOON INTO TONIGHT FOR

ERN KS/NEB INTO IA...MO...AND NRN IL...

..ERN NEB/KS INTO IA...MO AND NRN IL THIS AFTERNOON INTO TONIGHT

A MIDLEVEL SHORTWAVE TROUGH OVER NM/CO THIS MORNING WILL EJECT NEWD

OVER KS/NEB TODAY AND REACH NRN MO/IA THIS EVENING...AS A LARGER

SCALE MIDLEVEL LOW DEVELOPS EWD FROM THE NRN HIGH PLAINS TO MN/IA BY

THE END OF THE PERIOD. AN ASSOCIATED SURFACE CYCLONE IN CENTRAL NEB

WILL DEVELOP EWD ALONG A BAROCLINIC ZONE THAT EXTENDS EWD INTO

IA...WITHIN THE LEFT EXIT REGION OF A 90-130 KT MID-UPPER JET MAX.

THIS KINEMATIC ENVIRONMENT WILL CONTRIBUTE TO FOCUSED ASCENT NEAR

AND IMMEDIATELY E OF THE SURFACE LOW THIS AFTERNOON/EVENING...AND

VERTICAL SHEAR PROFILES FAVORABLE FOR SUPERCELLS IN THE WARM SECTOR

OF THE CYCLONE.

THE PRIMARY LIMITING FACTOR FOR A MORE WIDESPREAD/SIGNIFICANT SEVERE

STORM EPISODE WILL BE THE MODEST BOUNDARY LAYER MOISTURE IN THE WARM

SECTOR. LARGE SCALE SUBSIDENCE OVER THE GULF BASIN AND PERSISTENT

TRAJECTORIES FROM WITHIN THE RIDGE HAVE INHIBITED APPRECIABLE WARM

SECTOR MOISTENING OVER THE PAST SEVERAL DAYS...AND ALLOWED BOUNDARY

LAYER MOISTURE QUALITY TO BE REDUCED EACH AFTERNOON VIA MIXING

INLAND FROM THE COAST. THUS...DEWPOINTS ARE UNLIKELY TO INCREASE

FROM THE MID-UPPER 50S ALREADY PRESENT. DESPITE THE MODEST

MOISTURE...AFTERNOON TEMPERATURES WELL INTO THE 70S/LOW 80S ALONG

THE DRYLINE...AND STEEP MIDLEVEL LAPSE RATES ALONG AND N OF THE JET

CORE...WILL CONTRIBUTE TO MLCAPE VALUES APPROACHING 1500 J/KG NEAR

AND IMMEDIATELY SE OF THE TRIPLE POINT /WITH WEAKER INSTABILITY

FARTHER TO THE S/.

PRESENT INDICATIONS ARE THAT THUNDERSTORMS WILL DEVELOP AROUND 21Z

NEAR THE TRIPLE POINT INVOF THE KS/NEB BORDER AS THE CAP

WEAKENS...WITH CONVECTION EXPECTED TO INCREASE IN COVERAGE AND

SPREAD EWD/NEWD INTO IA DURING THE EVENING. OTHER MORE ISOLATED

STORMS MAY ALSO FORM FARTHER S ALONG THE DRYLINE INTO ERN KS AND

EXTREME NE OK. THE MODERATE INSTABILITY AND STRONG DEEP-LAYER

VERTICAL SHEAR WILL FAVOR SUPERCELLS CAPABLE OF PRODUCING LARGE HAIL

AND A FEW DAMAGING GUSTS. A FEW TORNADOES WILL ALSO BE POSSIBLE

GIVEN THE RELATIVELY STRONG LOW-LEVEL SHEAR /EFFECTIVE SRH IN EXCESS

OF 250 M2 PER S2/ AND SUFFICIENT BOUNDARY LAYER MOISTURE E OF THE

SURFACE CYCLONE THIS EVENING. THE WINDOW OF OPPORTUNITY FOR SEVERE

STORMS WILL BE WIDER ALONG THE PATH OF THE CYCLONE ACROSS IA INTO

THE EARLY OVERNIGHT HOURS...WHILE ANY DRYLINE STORMS FARTHER S

SHOULD WEAKEN JUST AFTER SUNSET AS CONVECTIVE INHIBITION INCREASES.

..THOMPSON/GRAMS.. 03/22/2011

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Looking at things a little more closely, this run of the NAM, unlike previous runs, does indicate a nonzero tornado threat south of the cold core (in E KS, MO, etc.), with nice low-lvl lapse rates and decent hodograph curvature. Td's of 60-61F might just do it for that area. The cap erodes rapidly between 21Z and 0Z and significant forcing swings across during the 0Z timeframe.

I would think mid-upper 50s to low 60s dews would cut it for this time of the year. If it was May you would probably want at least mid 60s.

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