Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Graphics & Text | Print | Product List | Glossary Off
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50

000
ACUS01 KWNS 190457
SWODY1
SPC AC 190456

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1156 PM CDT THU SEP 18 2014

VALID 191200Z - 201200Z

...NO SVR TSTM AREAS FORECAST...

...SUMMARY...
A FEW THUNDERSTORMS MAY BECOME MARGINALLY SEVERE FROM EASTERN
PORTIONS OF NEBRASKA AND SOUTH DAKOTA NORTHEASTWARD INTO PORTIONS OF
MICHIGAN FOR THIS EVENING INTO TONIGHT.

...SYNOPSIS...
THE SRN INFLUENCE OF THE POLAR MID/UPPER-LEVEL STREAM WILL GLANCE
THE NRN STATES WITH EMBEDDED/PROGRESSIVE LOW-AMPLITUDE PERTURBATIONS
FROM THE NRN PLAINS TO THE NE STATES. MEANWHILE...A MID-LEVEL
CYCLONIC CIRCULATION NEAR THE CA COAST WILL BECOME INCREASINGLY
DISASSOCIATED FROM THE AFOREMENTIONED STREAM...AS A RIDGE BUILDS
OVER THE PACIFIC NW. AT THE SFC...A MODEST COLD FRONT WILL ADVANCE
SEWD ACROSS PORTIONS OF THE NRN/CNTRL PLAINS TO THE UPPER MS
VALLEY...WHILE AN ANTICYCLONE COVERS PORTIONS OF THE NERN STATES.

...ERN PORTIONS OF NEB/SD NEWD INTO PORTIONS OF MI...
A QUASI-ZONAL SPEED MAX AT THE SRN EDGE OF THE POLAR STREAM WILL
ADVANCE FROM THE NRN PLAINS TO THE ERN GREAT LAKES REGION. SHOWERS
AND ISOLATED THUNDERSTORMS WILL LIKELY BE SPREADING EWD AT THE
BEGINNING OF THE PERIOD FROM PORTIONS OF ND INTO MN...IN RESPONSE TO
ASCENT ACCOMPANYING THE SPEED MAX AND WAA RELATED TO A SWLY LLJ. THE
LLJ WILL PERSIST THROUGH THE PERIOD WHILE GRADUALLY SHIFTING
EWD...ROUGHLY EXTENDING FROM THE CNTRL PLAINS TO THE GREAT LAKES
REGION. THE COMBINATION OF WARMING ALOFT ASSOCIATED WITH
LLJ-ENHANCED WAA AND THE INFLUX OF AN EML FROM THE WRN-CONUS PLATEAU
WILL ENCOURAGE STRONG CAPPING AMIDST A PRE-FRONTAL WARM SECTOR.
DESPITE RICH BOUNDARY-LAYER MOISTURE AHEAD OF THE FRONT CONTRIBUTING
TO STRONG CONDITIONAL INSTABILITY FROM PORTIONS OF ERN NEB/SD INTO
SRN MN...ASCENT ALONG/AHEAD OF THE COLD FRONT IS NOT EXPECTED TO
INCREASE SUFFICIENTLY FOR MORE ROBUST CONVECTIVE DEVELOPMENT UNTIL
THE EVENING HOURS.

BY EARLY EVENING...MODEST MID-LEVEL HEIGHT FALLS SHOULD BECOME MORE
PREVALENT ACROSS THE N-CNTRL STATES DOWNSTREAM OF A SHORTWAVE
IMPULSE CROSSING THE CANADIAN PRAIRIE PROVINCES. RELATED COOLING
ALOFT MAY BE SUFFICIENT FOR LOW-LEVEL PARCELS TO BREACH A WEAKENING
CAP AS FRONT/LLJ-ENCOURAGED ASCENT CONTINUES. THIS SHOULD SUPPORT
TSTM DEVELOPMENT/INTENSIFICATION FROM PORTIONS OF ERN NEB/SD NEWD TO
PORTIONS OF MI INTO THE OVERNIGHT HOURS. CLOUD-BEARING SHEAR AND
MODERATELY STEEP MID-LEVEL LAPSE RATES MAY SUPPORT ISOLATED
INSTANCES OF MARGINALLY SVR HAIL WITH CONVECTION...WHICH IS
GENERALLY EXPECTED TO BE ROOTED ATOP A NOCTURNALLY STABILIZING
BOUNDARY LAYER. THERE MAY ALSO EXIST A BRIEF WINDOW OF OPPORTUNITY
FOR NEAR-SFC-BASED CONVECTION TO EVOLVE FROM ERN NEB/SERN SD INTO
SRN MN/NRN IA THROUGH MID-EVENING. THIS REGIME COULD FEATURE
RELATIVELY WARMER SFC CONDITIONS WELL S OF EARLIER
PRECIPITATION...TO LOCALLY ENHANCE REDUCTIONS TO SFC-BASED
CINH...AND SUPPORT ISOLATED DMGG WIND GUSTS. CONFIDENCE IN
GREATER-COVERAGE SVR-TSTM POTENTIAL OWING TO ANTECEDENT CAPPING
PRECLUDES HIGHER PROBABILITIES AT THIS TIME.

...NERN ND AND NRN MN...
A FEW STRONG TO PERHAPS LOCALLY/MARGINALLY SVR STORMS CANNOT BE
RULED OUT ACROSS THE AREA IN THE WAKE OF EARLIER-DAY
PRECIPITATION...AND AHEAD OF A MID-LEVEL VORT MAX CROSSING THE
INTERNATIONAL BORDER REGION. MODERATE DEEP SHEAR WILL PERSIST.
UNCERTAINTY IN THE EVOLUTION OF THE PRECEDING PRECIPITATION EXTENDS
TO THE PROPENSITY FOR LATER-DAY DESTABILIZATION TO SUPPORT A
SVR-TSTM RISK. AS SUCH...SVR-TSTM PROBABILITIES HAVE NOT BEEN
INCLUDED AT THIS TIME.

..COHEN/DARROW.. 09/19/2014




USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.