Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS01 KWNS 280602
SWODY1
SPC AC 280600

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0100 AM CDT SAT MAY 28 2016

VALID 281200Z - 291200Z

...THERE IS A MRGL RISK OF SVR TSTMS FROM THE WRN UPPER GREAT
LAKES/UPPER MS VALLEY SWWD TO THE RIO GRANDE VALLEY...

...SUMMARY...
ISOLATED SEVERE STORMS WILL BE POSSIBLE FROM TEXAS TO THE UPPER
MISSISSIPPI VALLEY...MAINLY ON SATURDAY AFTERNOON AND EVENING.

...SYNOPSIS...
SHORT-WAVE MID-LEVEL TROUGHING OVER THE CENTRAL PLAINS IS FORECAST
MAINTAIN NEGATIVE TILT AS IT SHIFTS NNEWD ACROSS THE MID MO VALLEY
THROUGH THE DAY...AND INTO THE UPPER MS VALLEY BY THE END OF THE
PERIOD.  MEANWHILE IN THE W...FAST WLY FLOW IS FORECAST ACROSS THE
PAC NW S OF A BRITISH COLUMBIA VORTEX...WHILE FARTHER S A WEAK
TROUGH LINGERS OVER THE CA/NV VICINITY THROUGH 29/12Z.

AT THE SURFACE...A RATHER WEAK/NONDESCRIPT PATTERN IS ANTICIPATED IN
GENERAL.  WEAK/DISORGANIZED LOW PRESSURE IS FORECAST TO SHIFT NNEWD
ACROSS THE UPPER MIDWEST THROUGH THE DAY...REACHING THE LK SUPERIOR
VICINITY OVERNIGHT.  THIS LOW -- AND A ZONE OF BROAD LOW-LEVEL WARM
ADVECTION AHEAD OF IT -- SHOULD SUPPORT AREAS OF SCATTERED TO
ISOLATED SHOWERS AND STORMS IN A ZONE STRETCHING FROM THE RIO GRANDE
TO THE WRN UPPER GREAT LAKES.

FINALLY...TROPICAL DEPRESSION NUMBER TWO IS FORECAST TO GRADUALLY
INTENSIFY TO TROPICAL STORM STRENGTH...AND APPROACH THE SERN U.S.
COAST TOWARD THE END OF THE PERIOD.  FOR ADDITIONAL TROPICAL
FORECAST INFORMATION...PLEASE REFER TO THE LATEST ADVISORIES FROM
THE NATIONAL HURRICANE CENTER.

...UPPER MS VALLEY/WRN UPPER GREAT LAKES SWWD TO THE RIO GRANDE
VALLEY OF TX...
SHOWERS AND A FEW THUNDERSTORMS -- ONGOING EARLY IN THE PERIOD INVOF
THE UPPER TROUGH SHIFTING NNEWD ACROSS THE MID MO VALLEY -- SHOULD
EXPAND IN COVERAGE/INTENSITY DURING THE AFTERNOON FROM PARTS OF
WI/MN SWD INTO MO...AS MODEST AFTERNOON DESTABILIZATION OCCURS.  THE
MOST WIDESPREAD CONVECTION SHOULD FOCUS ACROSS ERN SD/ERN NEB/SRN
MN/WI/IA...SPIRALING AROUND THE CENTER OF UPPER CIRCULATION.  MORE
ISOLATED STORMS MAY DEVELOP SSWWD ACROSS MO -- AND POSSIBLY EVEN
INTO PARTS OF ERN OK/WRN AR -- IN THE AFOREMENTIONED WARM ADVECTION
ZONE.  WITH SOMEWHAT ENHANCED -- THOUGH LARGELY UNIDIRECTIONAL --
FLOW ALOFT...A COUPLE OF THE STRONGER STORMS MAY BECOME CAPABLE OF
PRODUCING MARGINAL HAIL AND LOCALLY DAMAGING WIND GUSTS.  AN
ISOLATED/BRIEF TORNADO OR TWO MAY ALSO OCCUR IN THE IA VICINITY NEAR
THE UPPER CIRCULATION CENTER.

MEANWHILE FARTHER S INTO TX...RISING HEIGHTS ALOFT IN THE WAKE OF
THE TROUGH DEPARTING NNEWD ACROSS THE UPPER MIDWEST SUGGEST WEAK
BROAD-SCALE SUBSIDENCE.  FURTHER...WITH NWWD ADVECTION OF LOW-LEVEL
MOISTURE INTO W TX PROGGED WITH TIME THUS HINDERING ANY ADVANCE OF A
DRYLINE...LACK OF LOW-LEVEL FOCUS FOR UVV IS INDICATED.

HAVING SAID THAT...STEEP LAPSE RATES ALOFT RESIDING ABOVE A CAPPED
BOUNDARY LAYER WILL CONTRIBUTE TO SUBSTANTIAL AFTERNOON CAPE
DEVELOPMENT IN CONJUNCTION WITH DIURNAL HEATING/MIXING.  MODELS --
TO VARYING DEGREES -- FORECAST ISOLATED TO SCATTERED AFTERNOON STORM
INITIATION RANGING AREALLY FROM THE HIGHER TERRAIN OF NERN MEXICO
/AIDED BY HEATING AND WEAK UPSLOPE FLOW/ TO PARTS OF CENTRAL TX
/PRESUMABLY DUE TO VERY WEAK LOW-LEVEL WARM ADVECTION/.  WITH THE
LOW-LEVEL SELY FLOW EXPECTED ACROSS CENTRAL AND SRN TX VEERING TO
MODEST/WLY AT MID LEVELS...SHEAR SUPPORTIVE OF MID-LEVEL UPDRAFT
ROTATION IS EVIDENT...PARTICULARLY CONSIDERING THE THERMODYNAMIC
ENVIRONMENT.  THUS...LARGE HAIL AND LOCALLY DAMAGING WINDS WOULD BE
LIKELY WITH ANY STORM WHICH DOES DEVELOP.  HOWEVER...QUESTIONS
REGARDING THE NUMBER OF STORMS WHICH WILL ACTUALLY DEVELOP -- GIVEN
THE GENERALLY UNSUPPORTIVE BACKGROUND SYNOPTIC ENVIRONMENT --
PRECLUDES AN UPGRADE TO SLIGHT RISK ATTM.

..GOSS/MOSIER.. 05/28/2016

$$


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