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September 2011 General Discussion/Obs


Chicago Storm

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FROPA in Madison, it's completely sunny and the winds are picking up. I can see the clouds coming in from the north associated with the center of the low already though. They look convective on radar and may mix serious winds down to the surface, though the strongest winds so far are being recorded in the clear area south of the precipitation.

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FROPA in Madison, it's completely sunny and the winds are picking up. I can see the clouds coming in from the north associated with the center of the low already though. They look convective on radar and may mix serious winds down to the surface, though the strongest winds so far are being recorded in the clear area south of the precipitation.

There's a good amount of lightning with that activity.

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Interesting updated ILN AFD concerning severe weather this evening and possible sleet/ice pellets tomorrow.

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE WILMINGTON OH

303 PM EDT THU SEP 29 2011

&&

.NEAR TERM /UNTIL 6 AM FRIDAY MORNING/...

PLENTY OF WEATHER IN THIS 12-HR PERIOD. VERY DYNAMIC WEATHER

SYSTEM CLEARLY SEEN ON WATER VAPOR LOOPS THIS AFTERNOON DIGGING

SOUTHEAST AND AMPLIFYING INTO SRN WISCONSIN. RUC ANALYSIS SHOWING

THE 1.5 POTENTIAL VORTICITY SURFACE IS ALL THE WAY DOWN TO 600MB

NORTH OF MADISON...WITH LIGHTNING UNDER THE CORE OF THIS

SIGNIFICANT PERTURBATION. SIGNIFICANT HEIGHT FALLS /12-HR/

APPROACHING 200 METERS ARE ON THE LEADING EDGE OF THIS

ANOMALY...AND THE SURFACE RESPONSE/REFLECTION IS NOW UNDERWAY AS

SIGNIFICANT 3-HR PRESSURE FALLS ARE NOW DEVELOPING DOWNSTREAM IN

THE STRONG WARM ADVECTION REGIME OVER LAKE MICH AND INDIANA. THIS

IS INDUCING AN INCREASE SWLY BOUNDARY LAYER FLOW AND VERY MODEST

MOISTURE TRANSPORT...BUT DUE TO THE SHORT WAVELENGTH BETWEEN THE

PESKY UPPER LOW WHICH IS STILL JUST TO OUR EAST...AND RAPIDLY

INBOUND WAVE...THERE JUST ISN/T SUFFICIENT TIME TO ADVECT IN

DEEPER MOISTURE.

HAVING SAID THAT...HOWEVER...SYSTEM HAS TREMENDOUS LIFT AS

EVIDENCED BY OBSERVATIONAL DATASETS /RADAR AND SATELLITE/ AND WILL

MAKE THE MOST OF ITS ARRIVAL INTO THE FORECAST AREA NEAR/JUST AFTER

PEAK HEATING. LATEST AMALGAM OF CONVECTION-ALLOWING DATA SETS

/INCLUDING EXPERIMENTAL 4KM SPC WRF AND 3KM HRRR/ IN STRONG

AGREEMENT WITH COARSER 12-30KM PARAMETERIZED MODELS /29.12Z GFS

AND NAM/ INDICATE THAT CURRENT BAND OF RAIN OVER IL/NRN IND WILL

CONTINUE TO PRESS QUICKLY SOUTHEAST...WHILE FRONTOGENETICAL

CIRCULATION TIED TO THE ADVANCING COLD FRONT WILL INITIATE

SHALLOW /LOW-TOPPED/ CONVECTION IMMEDIATELY AHEAD OF THIS BAND OF

RAIN ACROSS CNTL IND. THERE SEEMS TO BE A GROWING SIGNAL

THAT...DESPITE MLCAPE REMAINING ON THE ORDER OF 500-700 J/KG/...A

RATHER CONCENTRATED BUT NARROW BAND OF STORMS WILL DEVELOP AND

REACH MATURITY AS IT CROSSES INTO WRN OH VERY NEAR 23Z/00Z. THIS

BAND OF STORMS SHOULD RACE QUICKLY EAST...WITH GOOD COVERAGE

ACROSS THE ENTIRE AREA. HIGH RAIN CHANCES WARRANTED WITH

INCREASING CONFIDENCE IN THIS SCENARIO.

SEVERE POTENTIAL HAS BEEN LAID OUT WELL BY SPC VIA SWODY1 PRODUCT.

VERY STRONG WIND FIELDS...ESPECIALLY IN THE MID LEVELS WHERE 90KT

/500MB/ WLY JETLET WILL OVERSPREAD THE NRN-MOST PORTIONS OF THE

INSTABILITY AXIS THIS EVENING. DESPITE THE RATHER UNIDIRECTIONAL

WIND PROFILE...THERE IS ENOUGH BACKING IN THE LOW LEVELS DUE TO

THE DEEPENING LOW PRESSURE TO OUR NORTH THAT VERTICAL AND SPEED

SHEAR CONSIDERATIONS ARE IMPRESSIVE...AND CONTRIBUTE TO EFFECTIVE

SHEARS IN EXCESS OF 55KTS ALONG THE COLD FRONT THIS EVENING.

THIS DEEPER SHEAR...AND THE WLY ORIENTATION OF THE 0-3KM SHEAR

VECTOR /SOMEWHAT ORTHOGONAL TO THE FRONTAL ZONE/ SUGGEST LINE

SEGMENTS WITH EMBEDDED SUPERCELLS ARE POSSIBLE...WITH PRIMARY

THREATS OF WIND DAMAGE. IN FACT...29.12Z SPC WRF...AND RECENT HRRR

RUNS HAVE BEEN SHOWING CONCENTRATED 2-5KM UPDRAFT HELICITY

MAXIMUMS IN THEIR MODELED FIELDS FOR EARLY THIS EVENING FROM

DAYTON THROUGH CVG INTO NRN KY...SUGGESTING THE STRONGER RELATIVE INSTABILITY

ON THIS PORTION OF THE CONVECTIVE LINE MAY BE ENOUGH TO ALLOW

UPDRAFTS TO FEEL THE STRONGER FLOW ALOFT. AS MUCH OF THIS

CONVECTION WILL BE QUITE SHALLOW OWING TO MEAGER INSTABILITY...MOST ACTIVITY

MAY VERY WELL REMAIN BELOW SEVERE LEVELS ACROSS NORTHERN AREAS AND

POSE WIND GUST POTENTIAL TO 40-45 KTS.BUT THE SOUTHWEST 1/3 OF THE

ILN CWA MAY GET A CONCENTRATED SWATH OF SEVERE STORMS GIVEN THE

CLEARING/WARMING GOING ON THIS AFTERNOON. THIS PATTERN ANALOGS

VERY WELL TO THIS EXACT DATE IN 2009 WHEN A HANDFUL OF SEVERE

STORMS AFFECTED WESTERN OHIO. BUT OVERALL SETUP HERE IS MORE

FAVORABLE DESPITE LIMITED MOISTURE...SO WILL MONITOR SEVERE THREAT

CLOSELY.

THERE IS ALSO LIKELY TO BE A BURST OF STRONG WINDS IN THE WAKE OF

THE FRONT AS THE STRONG COLD ADVECTION ENSUES. WILL HIGHLIGHT ALL

OF THESE ITEMS IN HAZARDOUS WEATHER OUTLOOK.

&&

.SHORT TERM /6 AM FRIDAY THROUGH SUNDAY/...

THE STORY IN THIS PORTION OF THE FORECAST WILL BE LOW CLOUDS AND

SHOWERS...AND STRONG GUSTY WINDS FRIDAY AND FRIDAY NIGHT AS THE

LONGWAVE TROUGH AND DEEP CYCLONIC FLOW ONCE AGAIN RESUME THEIR

HOLD ON THE AREA. WITH WEAK COLD ADVECTION CONTINUING ON

FRIDAY...AND WHAT SHOULD BE PLENTY OF CLOUDS...TEMPERATURE

FORECAST IS VERY CONSERVATIVE AND LIES AT THE VERY LOW END OF THE

MODEL SPECTRUM. IN FACT...SOME AREAS OF WCNTL/CNTL OH MAY STRUGGLE

TO GET ABOVE 50 IF CLOUDS REMAIN THICK. A SECONDARY AND EQUALLY

IMPRESSIVE PV ANOMALY WILL DIG DOWN AND SPREAD CONTINUED FORCING

FOR ASCENT...ESPECIALLY INTO THE AFTERNOON WHEN STATIC STABILITY

WILL MINMIZE UNDER THE TROP FOLD. FORECAST SOUNDINGS SUGGEST

PLENTY OF STEEP LAPSE RATES FOR GUSTY WINDS DESPITE THE LOW

CLOUDS...AND LOW TOPPED SHOWERS THAT COULD EVEN SPIT OUT SOME

SLEET/ICE PELLETS GIVEN CAPE CONSIDERATIONS...WHICH ARE RATHER

IMPRESSIVE UNDER THE PV ANOMALY. MODELS OFTEN VERY MUCH

UNDERESTIMATE THE AMOUNT/COVERAGE OF SHOWERS UNDER THESE DYNAMIC

PV/S...AND THUS HAVE INCREASED RAIN COVERAGE SOME FOR

TOMORROW...AND WOULD NOT BE SURPRISED IF TEMPS ARE EVEN STILL TOO

OPTIMISTIC. BETTER CHANCES FOR SUN WILL BE FAR SWRN FORECAST

AREA...WHERE WARMEST TEMPS ARE INDICATED NEAR CVG AND TO

SOUTHWEST. WIND GUSTS EASILY COULD TOP 30KTS AT TIMES IN WIND

PRONE AREAS ON FRIDAY.

THEREAFTER...THINGS START TO SLOWLY BUDGE EAST ON FRIDAY

NIGHT/SAT. KEPT MINS A LITTLE WARMER THAN GUIDANCE GIVEN CONTINUED

WINDS...CLOUDS...AND MIXING. ACTUALLY NEAR THE TOP END OF THE

GUIDANCE SPREAD IN SOME CASES. EXPECT SHOWERS TO CONTINUE IN THE

SCIOTO VALLEY MUCH OF FRIDAY EVENING AND EVEN INTO SATURDAY

MORNING BEFORE ENOUGH PUSH BY RISING HEIGHTS ON THE BACKSIDE OF

THE TROUGH ALLOWS HIGH PRESSURE IN THE LOW LEVELS TO COME IN.

SATURDAY IS A TOUGH FORECAST...COULD BE A TALE OF DAYS FROM AREAS

SOUTHWEST OF CVG /MOSTLY SUNNY AND NEAR 60/ TO CNTL OH WHERE

CLOUDS MAY BE STUBBORN TO MOVE OUT...AND TEMPERATURES MAY NOT

BREACH THE 40S.

SATURDAY NIGHT...COULD BE A SETUP FOR FROST...BUT AM A LITTLE

CONCERNED THAT POSITION OF HIGH PRESSURE WELL TO THE WEST MAY NOT

ALLOW GRADIENT TO RELAX ENOUGH TO GO WHOLE HOG ON THIS SCENARIO.

THIS...AND CLOUDS OVER CNTL OHIO MAY STILL BE STUBBORN ENOUGH TO

KEEP THAT AREA FROST FREE. BUT THINK THE CHANCES ARE LOOKING

RATHER HIGH FOR FROST ESPECIALLY ACROSS THE WHITEWATER AND MIAMI VALLEYS.

SUNDAY LOOKS DRY...COOL...CRISP AND SUNNY.

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Getting very windy out there now. Probably on the order of 40-45mph gusts. Unfortunately my weather station sits a little too low to get a good sampling of the wind gusts, but it's still picking up some 30+mph gusts. The sky has a hazy brown color to it. Must be a lot of dirt getting lifted aloft over Iowa.

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Latest shower band just ripped through here. Almost as quickly as it came, we are back with the golden sunlight.

Going to bike over to the city park on the west side of town and see what greets. We have a ten foot "thunderfoil" kite that has been up before in probably 35+. I am tempted now, but also don't want to invest in the repairs should things go haywire. I am going to bring it with.

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