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 300535
SWODY1
SPC AC 300534

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1234 AM CDT SAT AUG 30 2014

VALID 301200Z - 311200Z

...THERE IS A SLGT RISK OF SVR TSTMS LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE NORTHERN HIGH PLAINS...

...SUMMARY...
A FEW SEVERE STORMS ARE POSSIBLE LATE THIS AFTERNOON AND EVENING
ACROSS PARTS OF THE NORTHERN HIGH PLAINS.  OTHER STRONG STORMS ARE
POSSIBLE TODAY IN A CORRIDOR ARCING FROM THE CENTRAL GULF COAST INTO
THE TENNESSEE VALLEY...AND ACROSS LOWER MICHIGAN AND ADJACENT
PORTIONS OF THE GREAT LAKES REGION.

...SYNOPSIS...
LARGER SCALE MID/UPPER TROUGHING WITHIN THE WESTERLIES IS FORECAST
TO CONTINUE PROGRESSING INLAND DURING THIS FORECAST PERIOD...EAST OF
THE CANADIAN ROCKIES...AND ACROSS NORTHERN AND CENTRAL PORTIONS OF
THE U.S. INTERMOUNTAIN REGION AND ROCKIES.  AS THIS OCCURS...THE
REMNANTS OF A CLOSED LOW WITHIN THE SOUTHERN BRANCH OF THE SPLIT
DOWNSTREAM WESTERLIES ARE EXPECTED TO TURN EASTWARD ACROSS THE GREAT
LAKES REGION...AROUND THE NORTHWESTERN PERIPHERY OF PROMINENT
SUBTROPICAL RIDGING CENTERED NEAR THE SOUTH ATLANTIC COAST.  AT THE
SAME TIME...MODELS SUGGEST THAT THE REMNANTS OF AN IMPULSE EMERGING
FROM THE WESTERN GULF OF MEXICO WILL GRADUALLY CONTINUE
NORTHEASTWARD AROUND THE WESTERN PERIPHERY OF THE RIDGE...ACROSS THE
CENTRAL GULF COAST/LOWER MISSISSIPPI VALLEY...TOWARD THE CENTRAL
APPALACHIANS.  FORCING ASSOCIATED WITH THESE FEATURES IS EXPECTED TO
CONTRIBUTE TO THE DEVELOPMENT OF CONSIDERABLE THUNDERSTORM ACTIVITY
TODAY...ACROSS THE NORTHERN AND CENTRAL ROCKIES INTO THE NORTHERN
PLAINS...AND ACROSS THE LOWER MISSISSIPPI VALLEY...NORTHWARD THROUGH
THE LOWER GREAT LAKES REGION.  SOME OF THESE STORMS PROBABLY WILL BE
ACCOMPANIED BY AT LEAST SOME SEVERE WEATHER POTENTIAL.

...CENTRAL GULF COAST INTO LOWER OHIO/TENNESSEE VALLEYS...
MODELS CONTINUE TO INDICATE THE NORTHEASTWARD ADVECTION OF A PLUME
OF SEASONABLY HIGH PRECIPITABLE WATER CONTENT /2 TO 2.25 INCHES/ IN
ASSOCIATION WITH THE IMPULSE EMERGING FROM THE GULF OF MEXICO.  THIS
APPEARS LIKELY TO COINCIDE WITH A LOWER/MID TROPOSPHERIC BELT OF
SOUTHERLY FLOW STRENGTHENING TO 25-35+ ACROSS LOUISIANA AND
MISSISSIPPI DURING THE DAY.  ALTHOUGH INSOLATION MAY BE
LIMITED...AND LAPSE RATES GENERALLY WEAK WITH THIS
REGIME...SUFFICIENT CAPE AND FORCING FOR ASCENT SHOULD EXIST TO
SUPPORT VIGOROUS UPDRAFTS.  GIVEN MODESTLY LARGE AND CLOCKWISE
CURVED LOW-LEVEL HODOGRAPHS...IN THE PRESENCE OF HIGH BOUNDARY LAYER
MOISTURE CONTENT AND RELATIVE HUMIDITY...THE RISK OF ISOLATED BRIEF
TORNADOES DOES NOT APPEAR OUT OF THE QUESTION.  OTHERWISE...HEAVY
PRECIPITATION LOADING AND DOWNWARD MOMENTUM TRANSPORT IN THE MORE
PERSISTENT CONVECTION COULD EVENTUALLY POSE A MORE SUBSTANTIVE RISK
FOR STRONG WIND GUSTS AT LEAST APPROACHING...IF NOT BRIEFLY
EXCEEDING...SEVERE LIMITS.  THIS THREAT MAY SPREAD NORTHEASTWARD
INTO PARTS OF WESTERN/MIDDLE TENNESSEE AND KENTUCKY THIS EVENING.

...MICHIGAN AND ADJACENT PORTIONS OF THE GREAT LAKES REGION...
STRENGTHENING LOWER/MID TROPOSPHERIC FLOW...ON THE ORDER OF 30-50
KT...APPEARS LIKELY ACROSS LOWER MICHIGAN DURING THE DAY WITH THE
APPROACH OF THE MID/UPPER IMPULSE.  EARLY PERIOD CONVECTIVE CLOUD
COVER AND PRECIPITATION MAY HAMPER BOUNDARY LAYER DESTABILIZATION
...BUT WITH SURFACE DEW POINTS NEAR 70F...SUBSEQUENT INSOLATION
BENEATH AN EASTWARD ADVECTING MID-LEVEL DRY SLOT COULD CONTRIBUTE TO
MODERATELY LARGE MIXED LAYER CAPE BY LATE AFTERNOON.  IT DOES NOT
APPEAR OUT OF THE QUESTION THAT THERE WILL BE A WINDOW OF
OPPORTUNITY FOR SCATTERED VIGOROUS CONVECTIVE DEVELOPMENT...WITH
ISOLATED SUPERCELLS POSSIBLE...ACCOMPANIED BY THE RISK FOR LOCALLY
DAMAGING WIND GUSTS...PERHAPS A TORNADO OR TWO.

...NORTHERN HIGH PLAINS...
MODELS SUGGEST THAT THE CYCLONIC BELT OF FLOW SPREADING INTO WESTERN
NORTH AMERICA MAY BECOME INCREASINGLY SPLIT DURING THIS
PERIOD...WITH ONE PROMINENT IMPULSE WITHIN ONE STREAM PROGRESSING
EAST OF THE CANADIAN ROCKIES...WHILE ANOTHER DIGS WITHIN ANOTHER
STREAM ACROSS THE NORTHERN GREAT BASIN.  HOWEVER...GUIDANCE DOES
GENERALLY INDICATE THAT AN AREA OF SUBSTANTIVE LARGE-SCALE FORCING
FOR ASCENT WILL SPREAD EAST NORTHEASTWARD ACROSS THE MOUNTAINS OF
SOUTHWEST MONTANA THROUGH THE NORTHERN PLAINS BY LATE TONIGHT.  AS
THIS ENCOUNTERS A MOISTENING BOUNDARY LAYER BENEATH STEEP MID-LEVEL
LAPSE...NEAR A DEVELOPING SURFACE LOW ACROSS THE NORTHERN HIGH
PLAINS...POTENTIAL APPEARS TO EXIST FOR STRONG/SEVERE STORM
DEVELOPMENT LATE THIS AFTERNOON AND EVENING.  AIDED BY INCREASING
SHEAR ASSOCIATED WITH A STRENGTHENING SOUTHERLY LOW-LEVEL
JET...SUPERCELLS ARE POSSIBLE...AT LEAST INITIALLY.  IT DOES NOT
APPEAR OUT OF THE QUESTION THAT LARGE-SCALE FORCING COULD SUPPORT AN
UPSCALE GROWING CONVECTIVE SYSTEM WHICH COULD GENERATE A FEW SEVERE
WIND GUSTS BEFORE WEAKENING ACROSS THE CENTRAL DAKOTAS THIS EVENING.

..KERR/LEITMAN.. 08/30/2014



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