Severe Storm Outlook Narrative (AC)
Issued by NWS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14
000
ACUS03 KWNS 120748
SWODY3
SPC AC 120747

DAY 3 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0247 AM CDT SAT JUL 12 2014

VALID 141200Z - 151200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM MID MS VALLEY TO NJ/PA/NY
AND NRN DELMARVA AREAS...

...SUMMARY...
SEVERE THUNDERSTORMS WITH HIGH WINDS WILL BE POSSIBLE OVER AREAS OF
THE MID-ATLANTIC WEST TO THE OHIO RIVER VALLEY AND SOUTH TO THE
TENNESSEE RIVER VALLEY. MORE WIDELY DISPERSED STORMS WITH HAIL AND
STRONG GUSTY WINDS WILL BE POSSIBLE IN AN ARC FROM THE MIDDLE
MISSISSIPPI RIVER VALLEY WEST AND NORTHWEST TO THE NORTHERN ROCKIES.

...SYNOPSIS...
A TROUGH OF SUBSTANTIAL AMPLITUDE WILL EVOLVE ACROSS THE UPPER MS
VALLEY AND GREAT LAKES REGIONS THROUGH MONDAY WITH THE GREATEST
MID-LEVEL HEIGHT FALLS OF 60-90M PER 12H FORECAST TO SPREAD FROM
MN/WI TO MI/OH/INDIANA DURING THE PERIOD. A STRONG COLD FRONT
ASSOCIATED WITH THE AMPLIFYING TROUGH IS FORECAST TO SPREAD
EAST-SOUTHEAST FROM THE UPPER MIDWEST TO THE MIDDLE MS VALLEY
THROUGH THE PERIOD WITH CYCLOGENESIS POSSIBLE ALONG THE FRONT OVER
THE EASTERN GREAT LAKES...PER LATEST ECMWF. THE FORECAST IS MADE
MORE COMPLEX GIVEN A MORE DIFFUSE FRONT FROM NEW ENGLAND TO THE
MID-ATLANTIC WILL PRECEDE THE STRONGER COLD FRONT...AND THERE ARE
MODEL DIFFERENCES AS TO THE STRENGTH AND TIMING OF CYCLOGENESIS
ALONG THE TRAILING FRONT...AND THE DEGREE OF AIRMASS DESTABILIZATION
THAT WILL TAKE PLACE ALONG/NEAR BOTH BOUNDARIES AND THE DEVELOPING
FRONTAL LOW.

ELSEWHERE...AN EXTENSIVE ZONE OF STORM DEVELOPMENT WILL BE POSSIBLE
AHEAD OF THE FRONT...AND ACROSS THE HIGHER TERRAIN OF THE WEST AND
SOUTHWEST.

...MID MS VALLEY TO NJ/PA/NY AND NRN DELMARVA AREAS...
GIVEN THE AFOREMENTIONED FORECAST COMPLEXITIES ONLY A BROAD ZONE OF
RELATIVELY LOW SEVERE PROBABILITIES CAN BE DEPICTED IN THIS OUTLOOK.
THE LEADING FRONT WILL BE INTERSPERSED WITH CONVECTIVE OUTFLOW...AND
LIKELY ONGOING STORMS...THAT SHOULD SPREAD EAST/NORTHEAST INTO A
CORRIDOR OF INCREASING INSTABILITY. SHEAR AND FORCING AS DEPICTED IN
BOTH NAM AND PARALLEL NAM...AS WELL AS GFS AND ECMWF...WOULD SUPPORT
A FEW TO SEVERAL ORGANIZED STORMS WITH STRONG TO DAMAGING WINDS AND
ALSO SOME TORNADO POTENTIAL.

...MIDWEST/OH VALLEY...
ANOTHER CORRIDOR OF CONVECTIVE POTENTIAL WILL EVOLVE AHEAD OF THE
STRONGER COLD FRONT...FROM OH WEST-SOUTHWEST TO MO BOOTHEEL. THESE
STORMS MAY TAKE ON MORE LINEAR STRUCTURE GIVEN THE POTENTIAL FOR
STRONG AND FOCUSED ASCENT ALONG THE ADVANCING COLD FRONT. SUFFICIENT
INSTABILITY SHOULD EXIST FOR SOME HAIL/WIND EVENTS. TORNADO RISK MAY
ALSO EXIST IF STRONGER CYCLOGENESIS AS INDICATED ECMWF WERE TO OCCUR
ACROSS THE NORTHERN PORTION OF THE SLGT RISK AREA.

...PLAINS WEST AND NORTHWEST INTO THE NORTHERN ROCKIES...
ISOLATED TO SCATTERED STRONG STORMS DRIVEN PRIMARILY BY DIURNAL
HEATING AND/OR OROGRAPHIC ASCENT WILL BE POSSIBLE. SHORTWAVE TROUGH
CRESTING UPPER RIDGE IN THE NRN ROCKIES WILL LEND A BIT MORE FORCING
HERE FOR ORGANIZED STORMS WITH WIND/HAIL POTENTIAL.

...SOUTHWEST...
EASTERLY FLOW WILL PERSIST ALONG THE SOUTHERN FLANK OF THE GREAT
BASIN ANTICYCLONE AND ACT TO STEER MOUNTAIN CONVECTION WEST TO WHERE
DRY SUB-CLOUD LAYERS WILL SUPPORT ISOLATED DOWNBURSTS.

..CARBIN.. 07/12/2014



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