Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 291629
SWODY1
SPC AC 291627

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1127 AM CDT SUN MAR 29 2015

VALID 291630Z - 301200Z

...THERE IS A MRGL RISK OF SVR TSTMS FROM SOUTHEAST OKLAHOMA AND
NORTHEAST TEXAS EASTWARD TO THE MID-SOUTH...

...SUMMARY...
A FEW THUNDERSTORMS MAY PRODUCE SEVERE HAIL THIS EVENING AND TONIGHT
WITHIN AN AREA EXTENDING FROM SOUTHEAST OKLAHOMA AND NORTHEAST
TEXAS...EASTWARD TO THE MID-SOUTH.

...SYNOPSIS...
RECENT WATER VAPOR LOOPS INDICATE A MIDLEVEL SHORTWAVE TROUGH FROM
THE UPPER MS VALLEY TO THE CNTRL PLAINS. THIS TROUGH WILL CONTINUE
TRACKING EWD TOWARD THE APPALACHIANS WHILE BEING OVERTAKEN BY A
DISTURBANCE AMPLIFYING FROM SRN MANITOBA. A FRONT ASSOCIATED WITH
THESE MIDLEVEL FEATURES WILL TRACK EWD ACROSS PORTIONS THE MS VALLEY
TO THE OH VALLEY AND TRAIL SWWD TO THE SRN PLAINS.

...SERN OK/NERN TX EWD TO THE MID-SOUTH...
THE RETURN OF PARTIALLY MODIFIED GULF MOISTURE AHEAD OF THE
AFOREMENTIONED FRONT IS UNDERWAY ACROSS THE SRN PLAINS...WITH
50S-LOWER-60S SFC DEWPOINTS ANALYZED ACROSS MUCH OF SRN/ERN TX.
PREFRONTAL SFC SLYS WILL CONTINUE TO MAINTAIN A STEADY INFLUX OF
SIMILAR MOISTURE TOWARD THE RED RIVER OF THE SOUTH TO THE LOWER MS
VALLEY THROUGH THE DAY. HOWEVER...SUBSTANTIAL CAPPING ALOFT AT THE
BASE OF AN EML SAMPLED BY THE 12Z OUN AND FWD RAOBS WILL LIKELY KEEP
DIURNAL THUNDERSTORM CHANCES MINIMAL DESPITE THE INCREASE IN
CONVECTIVE INSTABILITY.

BY THIS EVENING...THE FRONT WILL BE INTERCEPTING THE AFOREMENTIONED
MODEST RETURN MOISTURE ACROSS THE REGION...FAVORABLY COINCIDENT WITH
GLANCING DCVA/FORCING FOR ASCENT ATTENDANT TO THE SHORTWAVE
TROUGH...TO ENCOURAGE TSTM DEVELOPMENT. FURTHERMORE...WITH A
STRENGTHENING NOCTURNAL BOUNDARY-LAYER WIND MAXIMUM AUGMENTING
FRONT-PRECEDING WAA ALONG A LLJ /STRONGEST ACROSS THE LOWER MS
VALLEY/...ISOLATED TO SCATTERED THUNDERSTORMS WILL LIKELY DEVELOP
INVOF THE FRONTAL ZONE IN THE 00Z-04Z PERIOD. THIS ACTIVITY WILL
LIKELY BE ELEVATED ABOVE A NOCTURNALLY STABILIZING PBL LAYER AND
PERHAPS UNDERCUTTING BAROCLINIC ZONE.

THE LATEST FORECAST SOUNDINGS SUGGEST THAT 500-1000 J/KG OF MUCAPE
WILL BE COMMON ACROSS THE AREA...WHICH WILL SUPPORT SOME HAIL
POTENTIAL GIVEN 25-40 KT OF EFFECTIVE BULK SHEAR YIELDING ORGANIZED
CONVECTIVE STRUCTURES /POSSIBLE SUPERCELLS/. GIVEN H7-H5 LAPSE RATES
AROUND 7-8 C/KM SAMPLED BY 12Z FWD/OUN RAOBS...WITH SIMILAR VALUES
SPREADING EWD WITH TIME...NORMALIZED CAPE/UPDRAFT ACCELERATIONS WILL
BE SUFFICIENTLY ROBUST -- IN THE PRESENCE OF THE AFOREMENTIONED DEEP
SHEAR -- FOR ISOLATED SVR-HAIL POTENTIAL THIS EVENING INTO TONIGHT.
THIS SCENARIO IS AFFIRMED BY THE LATEST AVAILABLE
CONVECTION-PERMITTING MODEL GUIDANCE...AND WARRANTS THE UPGRADE TO
MARGINAL-RISK DELINEATION.

HOWEVER...GIVEN THE UNDERCUTTING NATURE OF THE SFC BOUNDARY...AND
THE PROPENSITY FOR INCREASING CELL INTERACTIONS TO EVENTUALLY IMPEDE
INDIVIDUAL-CELL INFLOW IN THIS REGIME OF BOUNDARY-PARALLEL DEEP
FLOW...A MORE SUBSTANTIAL SVR-TSTM RISK IS NOT EXPECTED TO EVOLVE.

..COHEN.. 03/29/2015



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