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September 1st and Beyond Severe Thread


andyhb

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New discussion for upcoming severe threats as we move out of August into September, starting with the new Day 4-8 outlook.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0327 AM CDT SUN AUG 28 2011

VALID 311200Z - 051200Z

...DISCUSSION...

ECMWF AND GFS ARE IN REASONABLE AGREEMENT IN THE LARGE SCALE PATTERN

DURING THE EARLY PART OF THE MEDIUM RANGE PERIOD. BOTH SUGGEST A

FAIRLY SIGNIFICANT UPPER TROUGH WILL EJECT ACROSS THE NRN ROCKIES

INTO THE NRN PLAINS BY THURSDAY. AS A RESULT...A PACIFIC COLD FRONT

WILL ADVANCE ACROSS THE REGION LIKELY PROVIDING THE LOW LEVEL

CONVERGENCE NECESSARY FOR TSTM DEVELOPMENT. IF SUFFICIENT

MOISTURE/INSTABILITY CAN DEVELOP ACROSS ERN MT/ND WEDNESDAY THEN

ORGANIZED CONVECTION AND POSSIBLE SEVERE MAY BE NOTED. SUBSEQUENT

CONVECTIVE THREAT WOULD THEN ADVANCE ACROSS ND INTO MN ON FRIDAY.

AT THIS TIME WILL NOT INCLUDE AN ORGANIZED SEVERE RISK ACROSS THIS

REGION AS TIMING OF UPPER TROUGH COULD BE DELAYED...OR WARM SECTOR

CAPPING/INSTABILITY COULD PROVE DETRIMENT FOR PRE-FRONTAL SEVERE

THREAT.

..DARROW.. 08/28/2011

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Here we go, day 4-8.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0400 AM CDT MON AUG 29 2011

VALID 011200Z - 061200Z

...DISCUSSION...

THE POTENTIAL FOR MORE WIDESPREAD AND ORGANIZED SEVERE TSTMS IS

EXPECTED TO INCREASE OVER THE NRN PLAINS AND UPPER MS RIVER VALLEY

AS A PROGRESSIVE SHORTWAVE TROUGH DEVELOPS EAST ON THURSDAY/D4.

BETWEEN LATEST DETERMINISTIC GFS AND EURO MODELS...THERE ARE SLIGHT

TIMING DIFFERENCES IN THE SPEED OF THE UPPER TROUGH EMERGING FROM

THE NRN ROCKIES/HIGH PLAINS DURING D4 AND INTO D5/FRIDAY.

HOWEVER...THESE DIFFERENCES ARE RELATIVELY MINOR WITH THE EURO BEING

CHARACTERISTICALLY SLOWER BY ABOUT 12H. DESPITE THE DIFFERENCE WITH

THE SPEED/TIMING OF THE UPPER TROUGH BETWEEN THE MODELS...THE

DEEP-LAYER FRONTAL ZONE AND LOW LEVEL JET CONFIGURATION APPEAR VERY

SIMILAR OVER THE PLAINS AND SUGGEST THE POSSIBILITY FOR STORMS TO

DEVELOP AND BECOME FOCUSED AHEAD OF THE FRONT...AND ON THE NOSE OF

LLJ IN THE FORM OF AN MCS. THE FORECAST INSTABILITY AND SHEAR

INDICATE THAT SEVERE WILL BE MOST LIKELY FROM NERN NEB INTO THE ERN

DAKOTAS AND MN. IT IS POSSIBLE THAT THIS SCENARIO MAY EVOLVE THROUGH

LATE THURSDAY...OR THE GREATER POTENTIAL MAY COME ABOUT LATE IN THE

D4 PERIOD AND CONTINUE INTO D5/FRIDAY. AT PRESENT...WILL OTLK D4

ONLY WITH FORECAST UNCERTAINTY INCREASING THEREAFTER.

..CARBIN.. 08/29/2011

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New day 4-8 hinting at something more potentially substantial past this oncoming trough.

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0350 AM CDT TUE AUG 30 2011

VALID 021200Z - 071200Z

...DISCUSSION...

NUMERICAL MODELS PRESENT CHALLENGES IN THE D4 THROUGH D8

PERIOD....FRIDAY THROUGH NEXT TUESDAY. WHILE THE LATEST GUIDANCE

APPEARS TO BE IN REMARKABLY GOOD AGREEMENT IN THE OVERALL EVOLUTION

OF UPPER AIR PATTERN AND RESULTING WEATHER SYSTEMS ACROSS THE CONUS

INTO THE WEEKEND...RUN TO RUN CONSISTENCY AMONGST THE MODELS

REVIEWED FOR THIS FORECAST REMAINS LOW. THIS INTRODUCES ENOUGH

UNCERTAINTY IN THE FORECAST TO BE WARY OF OUTLINING DAILY SEVERE

WEATHER AREAS FROM D5 AND BEYOND.

A LEADING SHORT WAVE TROUGH IS FORECAST TO DEAMPLIFY WHILE EJECTING

NEWD ACROSS THE GREAT LAKES ON D4/FRIDAY. THIS SYSTEM IS FORECAST TO

BE FOLLOWED BY A STRONGER TROUGH AND COLD FRONT THAT WILL MOVE

ACROSS THE NRN PLAINS AND INTO MIDWEST ON DAYS 5-6/SATURDAY INTO

SUNDAY. IT APPEARS POSSIBLE THAT THE FRONT WILL MOVE INTO AN

EXTENSIVE CORRIDOR OF VERY WARM AND POTENTIALLY UNSTABLE AIR FROM

THE PLAINS EAST TO THE OH VALLEY. HOWEVER...QUESTIONS REGARDING

FRONTAL TIMING...CAPPING/INHIBITION...AND STRENGTH OF FLOW/SHEAR

PRECLUDE DELINEATING A REGION MORE PRONE TO NUMEROUS ORGANIZED

SEVERE STORMS AT THIS STAGE.

THE MID-LEVEL RIDGE STRETCHING FROM COAST TO COAST ACROSS THE SRN

U.S. IS ALSO EXPECTED TO BE INFLUENCED AND POSSIBLY WEAKENED/SPLIT

BY A DISTURBANCE EVOLVING ACROSS THE NW GULF OF MEXICO IN THE MEDIUM

RANGE. THERE IS SOME SPREAD IN THE GUIDANCE AS TO HOW THIS SYSTEM

DEVELOPS OVER THE GULF AND WHAT INFLUENCE IT MAY HAVE ON THE

FRONT/TROUGH ACTING TO WEAKEN THE RIDGE FROM THE NORTH.

..CARBIN.. 08/30/2011

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The AFDs around the region are starting to squawk about the potential..

GRR

AFTER A VERY HOT DAY...RAIN CHANCES ARE NOT EXPECTED UNTIL FRIDAY NIGHT. IN SPITE OF EXPECTED WEAK UPPER FORCING...WE BELIEVE THAT SEVERE WEATHER IS QUITE POSSIBLE AHEAD OF THE COLD FRONT AS MLCAPE MAY REMAIN QUITE HIGH / 1500+ J PER KG / AFTER DARK. THIS IS ASSUMING A DEEP RESIDUAL MIXED LAYER...WHICH FREQUENTLY BECOMES WELL-ESTABLISHED AFTER A SERIES OF DAYS WITH STRONG INSOLATION.

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Interesting...

DAY 4-8 CONVECTIVE OUTLOOK

NWS STORM PREDICTION CENTER NORMAN OK

0416 AM CDT WED AUG 31 2011

VALID 031200Z - 081200Z

...DISCUSSION...

RELATIVE RUN-TO-RUN CONSISTENCY AND GOOD AGREEMENT AMONGST THE

MODELS AND ENSEMBLES REVIEWED FOR THIS FORECAST SUGGEST SOMEWHAT

HIGHER-END SEVERE POTENTIAL MAY EVOLVE ACROSS THE MIDWEST/OH VALLEY

REGION ON D4/SATURDAY INTO D5/SUNDAY. THIS SHOULD OCCUR AS ANOTHER

STRONG SHORTWAVE TROUGH PROVIDES A REINFORCING SURGE OF COOLER AIR

ACROSS THE UPPER MIDWEST AND RESULTING LIFT ALONG THE ADVANCING COLD

FRONT ENCOUNTERS WARMING AND MOIST AIRMASS. THE AREA DEPICTED FOR D4

IS THE REGION WHERE ENSEMBLE OUTPUT SUGGESTS THE HIGHER PROBABILITY

OF CONVECTIVE QPF WILL COINCIDE WITH A MEAN MUCAPE AROUND 1000 J PER

KG. THIS WILL ALSO BE THE AREA LIKELY TO EXPERIENCE SOMEWHAT

STRONGER DEEP-LAYER FLOW ON THE EDGE OF THE STRONGER WLYS ALOFT.

THE TRAILING PORTION OF THE COLD FRONT...ESPECIALLY THAT SEGMENT

INTO THE HIGHER TERRAIN OF THE FRONT RANGE AND SRN HIGH PLAINS WILL

ALSO SERVE AS A FOCUS FOR SCATTERED TSTMS. HOWEVER...DEEP-LAYER FLOW

ACROSS THESE AREAS IS MORE MARGINAL TO SUPPORT A RISK AREA AT THIS

TIME.

BEYOND D4...A WIDE DISPARITY IN MODEL SCENARIOS BEGINS TO

EVOLVE...ESPECIALLY WITH EVOLUTION OF GULF OF MEXICO LOW PRESSURE.

GIVEN THE WIDE SPREAD IN THE FORECASTS...UNCERTAINTY IN SEVERE STORM

DEVELOPMENT AND COVERAGE IS HIGH. HOWEVER...LARGER SCALE PATTERN

DEPICTED IN THE 00Z NCEP MREF SOLUTIONS SUGGESTS THAT THE EVOLVING

PATTERN WILL GENERALLY ACT TO SUPPRESS SEVERE WEATHER ACTIVITY GOING

INTO NEXT WEEK.

..CARBIN.. 08/31/2011

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Looking forward to a nice elevated MCS overnight here.

good luck

R.M. of Rhineland including Altona Plum Coulee and Gretna

1:49 AM CDT Thursday 01 September 2011

Severe thunderstorm warning for

R.M. of Rhineland including Altona Plum Coulee and Gretna issued

At 1:45 AM weather radar is showing a line of severe thunderstorms centred over Brandon extending southward into North Dakota. Wind gusts to 100 km/h, rainfall in excess of 50 mm, intense lightning and loonie-sized hail are possible with the stronger cells located in this line of intense thunderstorms. The thunderstorms are travelling eastward at approximately 70 km/h and will begin to affect the Morden/Winkler area within the next hour.

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Lord, that's some big hail!

SEVERE WEATHER BULLETIN
ISSUED BY ENVIRONMENT CANADA
AT 11:28 AM EDT FRIDAY 2 SEPTEMBER 2011.
---------------------------------------------------------------------
WATCHES/WARNINGS IN EFFECT FOR NORTHERN ONTARIO...

SEVERE THUNDERSTORM WARNING FOR:
     MANITOUWADGE - HORNEPAYNE
     WHITE RIVER - DUBREUILVILLE
     KAPUSKASING - HEARST - SMOOTH ROCK FALLS
     FRASERDALE - PLEDGER LAKE
     LITTLE ABITIBI - KESAGAMI LAKE.

     WEATHER RADAR AT 10:50 AM EDT INDICATED AN AREA OF SEVERE
     THUNDERSTORMS EXTENDING FROM FORT ALBANY SOUTH TO KAPUSKASING
     AND WEST TO WHITE RIVER. STORM MOTION IS TO THE NORTHEAST AT
     AROUND 75 KM/H. THESE STORMS ARE CAPABLE OF PRODUCING UP TO
     SOFTBALL SIZE HAIL. HEAVY RAINFALL OF 50 MILLIMETRES AND BRIEF
     WIND GUSTS TO 90 KM/H ARE ALSO QUITE POSSIBLE.

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FWIW the 14/15z runs of the HRRR develop a line of storms from Kenosha to Clinton and pushes it southeast but weakening and then more storms firing after that from Dixon to southern IA....then weaken moving east, the another complex develops ENE of DSM (the most impressive complex this run) and move it east.

Basically, I get screwed here lol

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Q

FWIW the 14/15z runs of the HRRR develop a line of storms from Kenosha to Clinton and pushes it southeast but weakening and then more storms firing after that from Dixon to southern IA....then weaken moving east, the another complex develops ENE of DSM (the most impressive complex this run) and move it east.

Basically, I get screwed here lol

Not seeing anything to push things into our area until tomorrow aft.

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MESOSCALE DISCUSSION 2097

NWS STORM PREDICTION CENTER NORMAN OK

0241 PM CDT FRI SEP 02 2011

AREAS AFFECTED...ERN NEB THROUGH CNTRL IA INTO SRN WI/NRN IL

CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE

VALID 021941Z - 022115Z

THE THREAT FOR SEVERE STORMS CAPABLE OF MAINLY DAMAGING WINDS AND

HAIL IS EXPECTED TO INCREASE ACROSS DISCUSSION AREA THROUGH MID-LATE

AFTERNOON. CONVECTIVE TRENDS ARE BEING MONITORED FOR A WATCH.

CURRENT SURFACE ANALYSIS AND REGIONAL VAD/PROFILER DATA INDICATE

THAT DEEPER-LAYER BAROCLINIC ZONE EXTENDS FROM NERN WI SWWD THROUGH

SWRN MN INTO S-CNTRL NEB...WITH MULTIPLE CONVECTIVE OUTFLOW

BOUNDARIES OBSERVED ACROSS PRE-FRONTAL WARM SECTOR. THOUGH DENSER

CLOUDINESS HAS PERSISTED INVOF SYNOPTIC FRONT...THE CORRIDOR FROM

E-CNTRL NEB EWD THROUGH CNTRL IA INTO NRN IL HAS EXPERIENCED

COMPARABLY STRONGER INSOLATION. HERE...BOUNDARY LAYER DEWPOINTS IN

THE MID 60S TO UPPER 70S AND STEEP MIDLEVEL LAPSE RATES HAVE

COMBINED WITH THE DAYTIME HEATING TO YIELD MLCAPE OF 2000-3500 J/KG

AND A WEAKENING CAP.

LARGE-SCALE FORCING IS FORECAST TO REMAIN RATHER WEAK ACROSS THE

REGION THROUGH THE REMAINDER OF THE DIURNAL HEATING CYCLE...CASTING

UNCERTAINTY ON WHERE AND WHEN SURFACE-BASED STORMS WILL DEVELOP.

ONE POSSIBLE LOCATION IS ALONG AN OUTFLOW BOUNDARY EXTENDING FROM E

OF FOD SWWD TO NEAR OMA WHERE VISIBLE SATELLITE DOES INDICATE SOME

DEEPENING CUMULUS.

SHOULD STORMS DEVELOP AND BECOME SUSTAINED...THE PRESENCE OF 30-35

KT WLY WINDS IN THE MIDLEVELS ATOP WEAK SELY/ELY SURFACE WINDS WILL

RESULT IN A KINEMATIC ENVIRONMENT SUPPORTIVE OF ORGANIZED STORM

MODES /INCLUDING SUPERCELLS/ CAPABLE OF MAINLY DAMAGING WINDS AND

HAIL.

..MEAD.. 09/02/2011

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URGENT - IMMEDIATE BROADCAST REQUESTED

SEVERE THUNDERSTORM WATCH NUMBER 824

NWS STORM PREDICTION CENTER NORMAN OK

1025 PM CDT FRI SEP 2 2011

THE NWS STORM PREDICTION CENTER HAS ISSUED A

SEVERE THUNDERSTORM WATCH FOR PORTIONS OF

CENTRAL AND EAST CENTRAL IOWA

EFFECTIVE THIS FRIDAY NIGHT AND SATURDAY MORNING FROM 1025 PM

UNTIL 400 AM CDT.

HAIL TO 1 INCH IN DIAMETER...THUNDERSTORM WIND GUSTS TO 70

MPH...AND DANGEROUS LIGHTNING ARE POSSIBLE IN THESE AREAS.

THE SEVERE THUNDERSTORM WATCH AREA IS APPROXIMATELY ALONG AND 40

STATUTE MILES NORTH AND SOUTH OF A LINE FROM 70 MILES WEST OF DES

MOINES IOWA TO 50 MILES EAST NORTHEAST OF CEDAR RAPIDS IOWA. FOR

A COMPLETE DEPICTION OF THE WATCH SEE THE ASSOCIATED WATCH

OUTLINE UPDATE (WOUS64 KWNS WOU4).

REMEMBER...A SEVERE THUNDERSTORM WATCH MEANS CONDITIONS ARE

FAVORABLE FOR SEVERE THUNDERSTORMS IN AND CLOSE TO THE WATCH

AREA. PERSONS IN THESE AREAS SHOULD BE ON THE LOOKOUT FOR

THREATENING WEATHER CONDITIONS AND LISTEN FOR LATER STATEMENTS

AND POSSIBLE WARNINGS. SEVERE THUNDERSTORMS CAN AND OCCASIONALLY

DO PRODUCE TORNADOES.

DISCUSSION...THERE WILL BE SOME RISK FOR THE CONVECTIVE CLUSTERS

MOVING INTO W CENTRAL/CENTRAL IA TO PERSIST FOR A FEW MORE

HOURS...WITH AN ATTENDANT RISK FOR DAMAGING WINDS. THE ENVIRONMENT

IS SUPPORTIVE OF STRONG DOWNDRAFTS WITH STEEP MIDLEVEL LAPSE RATES

AND LARGE DCAPE/MODERATE CAPE...AS WELL AS EFFECTIVE BULK SHEAR

AROUND 35 KT TO MAINTAIN ORGANIZED CONVECTIVE STRUCTURES. THE

UNCERTAINTY CENTERS ON INCREASING CONVECTIVE INHIBITION AND RATHER

MODEST FORCING FOR ASCENT ALONG THE WSW-ENE SURFACE FRONT IN IA.

AVIATION...A FEW SEVERE THUNDERSTORMS WITH HAIL SURFACE AND ALOFT

TO 1 INCH. EXTREME TURBULENCE AND SURFACE WIND GUSTS TO 60 KNOTS.

A FEW CUMULONIMBI WITH MAXIMUM TOPS TO 550. MEAN STORM MOTION

VECTOR 26035.

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MESOSCALE DISCUSSION 2101

NWS STORM PREDICTION CENTER NORMAN OK

1156 PM CDT FRI SEP 02 2011

AREAS AFFECTED...IA TO FAR SOUTHERN WI/NORTHERN IL

CONCERNING...SEVERE THUNDERSTORM WATCH 824...

VALID 030456Z - 030630Z

THE SEVERE WEATHER THREAT FOR SEVERE THUNDERSTORM WATCH 824

CONTINUES.

SEVERE TSTM WATCH 824 CONTINUES UNTIL 09Z...WITH A CONTINUED THREAT

FOR DAMAGING WINDS AND SOME SEVERE HAIL ON AN ISOLATED BASIS. A

SEVERE THREAT COULD SPREAD EAST-NORTHEASTWARD INTO FAR SOUTHERN

WI/NORTHERN IL OVERNIGHT...AND A WATCH MAY BE NEED TO BE CONSIDERED

FOR THESE AREAS.

TWO RELATIVELY DISTINCT CLUSTERS OF STRONG/SEVERE TSTMS CONTINUE TO

STEADILY SPREAD EAST-NORTHEASTWARD EARLY IN THE OVERNIGHT...ONE NEAR

THE WATERLOO AREA IN ADDITION TO ANOTHER NEAR THE DES MOINES/AMES

VICINITIES AS OF 0445Z. IN FACT...A 51 KT WIND GUST WAS RECENTLY

MEASURED AT WATERLOO IA. THESE STORMS WILL CONTINUE TO FAVOR A

CORRIDOR NEAR/JUST NORTH OF A SURFACE FRONT...WHERE A FAVORABLE

COLLOCATION OF VERTICAL SHEAR/MODERATE INSTABILITY JUST ABOVE THE

SURFACE EXISTS. WHILE THE LONGEVITY OF THE SEVERE THREAT IS

QUESTIONABLE GIVEN FACTORS SUCH AS INCREASING NEAR-SURFACE

CINH...WEAK WARM ADVECTION AND EXISTING ORGANIZATION OF THESE STORMS

MAY ALLOW AT LEAST AN ISOLATED SEVERE THREAT TO SPREAD INTO PORTIONS

OF SOUTHERN WI/NORTHERN IL OVER THE NEXT FEW HOURS.

..GUYER.. 09/03/2011

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Yep. It looks like it's well behind the outflow though so it shouldn't be a tornadic threat.

Could it affect storm motion though? Might the cell start to turn more easterly? The latest MCD seemed to indicate the severe potential overnight being further south than the region the cell appears to be heading toward.

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