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 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 300601
SWODY1
SPC AC 300600

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT THU JUL 30 2015

VALID 301200Z - 311200Z

...THERE IS A MRGL RISK OF SVR TSTMS FROM NEW ENGLAND TO PART OF THE
MID-ATLANTIC STATES...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS THE SOUTHEAST AND
CENTRAL GULF COAST STATES...

...SUMMARY...
ISOLATED STRONG TO MARGINALLY SEVERE THUNDERSTORMS WILL BE POSSIBLE
ACROSS THE NORTHEAST INTO THE MID-ATLANTIC STATES THIS
AFTERNOON...WITH A SIMILAR SEVERE THREAT FROM THE SOUTHEAST STATES
TO THE LOWER MISSISSIPPI VALLEY.

...SYNOPSIS...
A CLOSED LOW...CURRENTLY MOVING TO THE NORTHEAST ACROSS NORTHERN
ONTARIO PER WATER VAPOR IMAGERY...WILL BECOME STATIONARY THIS
FORECAST PERIOD ACROSS HUDSON BAY AS IT DEEPENS AND AMPLIFIES.  THIS
EVOLUTION WILL OCCUR AS AN UPPER RIDGE CENTERED OVER THE
SOUTH-CENTRAL STATES SHIFTS WEST TO THE SOUTHERN HIGH PLAINS.  THE
CYCLONIC-FLOW REGIME WITHIN THE SOUTHERN PERIPHERY OF THE HUDSON BAY
LOW WILL ENCOMPASS THE UPPER MS TO UPPER OH VALLEYS INTO THE
NORTHEAST STATES.  A SERIES OF MIDLEVEL SHORTWAVE TROUGHS EMBEDDED
WITHIN THIS FLOW REGIME WILL TRACK THROUGH THE GREAT LAKES TO THE
NORTHEAST...WHILE HEIGHT FALLS ATTENDANT TO THESE TROUGHS AND THE
ENLARGEMENT OF THE HUDSON BAY LOW AID IN SHIFTING AN UPPER RIDGE
EAST OF THE NORTHEAST STATES.  AT THE SURFACE...A COLD FRONT SHOULD
EXTEND FROM WESTERN NY/PA THROUGH EASTERN TN...AND THEN WESTWARD
THROUGH SOUTHERN AR TO THE RED RIVER VALLEY AT 12Z TODAY.  THIS
FRONT WILL ADVANCE EAST THROUGH THE EASTERN STATES...WHILE THE
TRAILING PORTION MOVES SOUTHWARD THROUGH THE CENTRAL GULF COAST
STATES...LOWER MS VALLEY AND INTO CENTRAL TX.

...NEW ENGLAND TO PARTS OF THE MID-ATLANTIC STATES...
SHOWERS AND A FEW EMBEDDED TSTMS SHOULD BE ONGOING ALONG THE COLD
FRONT AT THE START OF THE FORECAST PERIOD FROM WRN NY/PA TO THE
CENTRAL APPALACHIANS.  SURFACE HEATING MAY BE LIMITED THROUGH THE
DAY AHEAD OF THE COLD FRONT AND MIDLEVEL LAPSE RATES SHOULD BE WEAK.
DESPITE THESE FACTORS...A MOISTENING WARM SECTOR AIR MASS FROM SOUTH
TO NORTH SHOULD RESULT IN MODERATE INSTABILITY IN THE MID-ATLANTIC
STATES...WHILE INSTABILITY IS FORECAST TO BE WEAKER WITH NORTHWARD
EXTENT.  MODEST HEIGHT FALLS /30-50 METERS AT 500-MB PER 12 HR/
ACROSS THE NORTHEAST STATES WITH THE APPROACH OF A LEAD SHORTWAVE
TROUGH AND UPLIFT ALONG THE COLD FRONT SHOULD PROVE FAVORABLE FOR
SCATTERED TSTM DEVELOPMENT INTO THE AFTERNOON.

ALTHOUGH BULK SHEAR WILL BE STRONGER ACROSS NY INTO NEW
ENGLAND...GIVEN STRENGTHENING WEST-SOUTHWESTERLY 500-MB WINDS TO 40
KT...WEAKER INSTABILITY WITH NORTHWARD EXTENT PRECLUDES THE
INTRODUCTION OF HIGHER SEVERE PROBABILITIES...MAINTAINING THE
MARGINAL SEVERE RISK.  FARTHER SOUTH INTO EASTERN PA/NJ TO MD/VA...
INSTABILITY WILL BE STRONGER...THOUGH WEAKER FORCING FOR ASCENT AND
WEAKER BULK SHEAR SHOULD LIMIT STORM ORGANIZATION.  GIVEN THE DEGREE
OF DESTABILIZATION...A FEW STRONGER WIND GUSTS CANNOT BE RULED OUT
WITH SOUTHERN EXTENT...RESULTING IN THIS REGION BEING INCLUDED IN A
MARGINAL SEVERE RISK FOR LOCALLY STRONG WIND GUSTS.

...SOUTHEAST STATES TO LOUISIANA...
STRONG SURFACE HEATING WITHIN A MOIST ENVIRONMENT /PRECIPITABLE
WATER OF 1.75 TO AROUND 2 INCHES/ WILL RESULT IN MODERATELY STRONG
INSTABILITY WITH MLCAPE RANGING FROM 1500-2500 J/KG THIS AFTERNOON.
DESPITE WEAK LARGE-SCALE FORCING FOR ASCENT ACROSS THESE STATES...
STORM DEVELOPMENT IS EXPECTED ALONG THE SOUTHWARD-MOVING COLD
FRONT...LEE TROUGH FROM SC TO SOUTHERN GA...AND SEA BREEZE
BOUNDARIES.  THE DEGREE OF INSTABILITY COMBINED WITH STEEPENING
SURFACE TO 3-KM LAPSE RATES WILL RESULT IN A FEW STRONG/DAMAGING
WIND GUSTS THIS AFTERNOON INTO THE EARLY EVENING.

...SOUTHWEST STATES TO PART OF THE SOUTHERN PLAINS...
TSTMS ARE EXPECTED AGAIN FOR MUCH OF THIS FORECAST FROM PARTS OF
EASTERN AZ THROUGH NM WHERE THE GREATEST STORM COVERAGE IS EXPECTED
WITHIN A PLUME OF MOISTURE PER WATER VAPOR IMAGERY.  MEANWHILE...
MORE OF A DIURNAL-TSTM THREAT WILL EXIST EASTWARD INTO SOUTHERN KS
AND OKLAHOMA AND ALSO WESTWARD INTO PARTS OF SOUTHERN AND CENTRAL
CA.  WEAK INSTABILITY ACROSS THESE AREAS IS EXPECTED TO PRECLUDE A
SEVERE WEATHER THREAT.

..PETERS/MARSH.. 07/30/2015



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