Severe Storm Outlook Narrative (AC)
Issued by NWS

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000
ACUS02 KWNS 251724
SWODY2
SPC AC 251723

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1223 PM CDT MON JUL 25 2016

VALID 261200Z - 271200Z

...THERE IS A SLGT RISK OF SVR TSTMS ACROSS PORTIONS OF SD/NEB...

...THERE IS A MRGL RISK OF SVR TSTMS SURROUNDING THE SLGT ACROSS
PORTIONS OF THE NRN/CNTRL GREAT PLAINS TO THE UPPER MS VALLEY/UPPER
MI...

...THERE IS A MRGL RISK OF SVR TSTMS ACROSS PORTIONS OF THE
MID-ATLANTIC...

...SUMMARY...
THE GREATEST POTENTIAL FOR SEVERE THUNDERSTORMS ON TUESDAY WILL BE
ACROSS PORTIONS OF SOUTH DAKOTA AND NEBRASKA DURING THE AFTERNOON
AND EVENING. MORE ISOLATED SEVERE THUNDERSTORMS WILL BE POSSIBLE ON
TUESDAY ELSEWHERE ACROSS PORTIONS OF THE NORTHERN AND CENTRAL GREAT
PLAINS EASTWARD TO UPPER MICHIGAN...AND ACROSS PARTS OF THE
MID-ATLANTIC.

...SYNOPSIS...
IN THE MID LEVELS...A BAND OF MODESTLY ENHANCED QUASI-ZONAL FLOW
WILL EXTEND ACROSS THE NRN CONUS...WHICH WILL LIE BETWEEN RIDGING
CONCENTRATED OVER THE SRN CONUS AND LOWER HEIGHTS OVER CANADA. A
WEAKNESS IN THE SRN-CONUS RIDGE WILL EXTEND FROM PORTIONS OF THE
S-CNTRL CONUS TO THE LOWER MS VALLEY...WITH FLANKING ANTICYCLONES
CENTERED ACROSS THE SWRN CONUS AND THE SWRN N ATLANTIC.
A SHORTWAVE TROUGH WILL TRACK EWD ACROSS PARTS OF ONTARIO AND
QUEBEC...WITH AN ASSOCIATED SFC FRONT TRAILING WWD FROM PARTS OF
LAKE SUPERIOR/UPPER MI TO MT. ANOTHER SFC FRONT WILL EXTEND E-W FROM
THE MID-ATLANTIC TO THE MID MS VALLEY...ASSOCIATED WITH A MID-LEVEL
SHORTWAVE TROUGH MOVING OFF THE NERN CONUS COAST LATE D1/MON INTO
EARLY D2/TUE.

...PORTIONS OF THE NRN/CNTRL GREAT PLAINS...
A PLUME OF LOW-LEVEL MOISTURE WILL EXTEND NWD ACROSS PORTIONS OF THE
NRN/CNTRL GREAT PLAINS. THIS WILL BE FACILITATED BY POLEWARD MASS
FLUXES ACCOMPANYING SFC TROUGHING FOCUSED IN THE LEE OF THE ROCKIES.
THE LEE TROUGHING WILL BE AIDED BY THE MODEST CROSS-BARRIER FLOW
ALOFT...AND FURTHER ENCOURAGED BY SMALLER-SCALE ASCENT ACCOMPANYING
PERTURBATIONS EMBEDDED IN THE BAND OF ENHANCED FLOW ALOFT. AS SFC
DEWPOINTS IN THE LOWER/MIDDLE 60S EXTEND NWD TOWARD THE
MT-TO-UPPER-MI FRONT...AND MODERATELY STEEP MID-LEVEL LAPSE RATES
OVERSPREAD PORTIONS OF THE NRN/CNTRL GREAT PLAINS...MLCAPE AROUND
1500-2500 J/KG IS FORECAST TO BECOME ESTABLISHED FROM PORTIONS OF
CNTRL/WRN NEB INTO SD THROUGH THE AFTERNOON.

A MORE PROMINENT MID-LEVEL PERTURBATION IS PRESENTLY CROSSING PARTS
OF THE NRN GREAT BASIN PER WATER-VAPOR LOOPS...AND IS FORECAST TO
CONTINUE TRACKING EWD THROUGH THE D2/TUE PERIOD -- TOWARD/ACROSS THE
NRN GREAT PLAINS. PRESENT INDICATIONS ARE THAT RELATED ASCENT WILL
FOSTER AN EWD SPREADING AREA OF ELEVATED CONVECTION ACROSS PARTS OF
THE NRN PLAINS DURING D2/TUE MORNING. DIFFERENTIAL-HEATING-ENHANCED
BAROCLINICITY PERIPHERAL TO RELATED CLOUD SHIELDS...OROGRAPHIC
CIRCULATIONS INVOF THE BLACK HILLS...AND LOW-LEVEL ASCENT/DEEP
BOUNDARY-LAYER CIRCULATIONS IN PROXIMITY TO A N/S-ORIENTED LEE
TROUGH OVER THE HIGH PLAINS -- SHOULD ALL CONTRIBUTE TO
INTENSIFICATION OF CONVECTION AND/OR DEVELOPMENT OF SFC-BASED
CONVECTION DURING THE AFTERNOON. EFFECTIVE SHEAR AROUND 25-40 KT --
AIDED BY A VERTICALLY VEERING WIND PROFILE -- MAY SUPPORT A FEW
MULTICELL/SUPERCELL STRUCTURES WITH SVR WIND/HAIL POSSIBLE.
COLD-POOL AMALGAMATION COULD ENCOURAGE ONE OR TWO UPSCALE-GROWING
CONVECTIVE SYSTEMS BY LATE AFTERNOON/EARLY EVENING...WHICH WOULD
SUBSEQUENTLY SPREAD SEWD ACROSS PARTS OF SD/NEB MAINTAINING THE
SVR-WIND RISK.

THE SLGT-RISK AREA INDICATES THE AREA OF GREATEST POTENTIAL FOR SVR
WIND/HAIL. ELSEWHERE ACROSS PARTS OF THE NRN/CNTRL GREAT
PLAINS...THE SVR RISK IS FORECAST TO BE SOMEWHAT MORE
ISOLATED/CONDITIONAL. SOME NWD/NEWD EXTENSION OF THE SLGT MAY BE
NECESSARY IN SUBSEQUENT OUTLOOKS. HOWEVER...UNCERTAINTY REGARDING
THE EVOLUTION OF EARLY D2/TUE CONVECTION AND RELATED EFFECTS ON
DIURNAL DESTABILIZATION PRECLUDE ADJUSTMENTS TO THE SLGT AT THIS
TIME.

...PORTIONS OF THE UPPER MS VALLEY TO UPPER MI...
RELATIVELY RICH LOW-LEVEL MOISTURE AND SUFFICIENT SFC HEATING NEAR/S
OF THE MT-TO-UPPER-MI FRONT WILL SUPPORT MODERATE DESTABILIZATION.
THE PRESENCE OF 25-35 KT OF WLY FLOW THROUGH MUCH OF THE
CONVECTIVE-CLOUD LAYER MAY FACILITATE SMALL CONVECTIVE CLUSTERS
SPREADING EWD WITHIN A BAND OF PRE-FRONTAL MOISTURE DURING THE
AFTERNOON. ISOLATED DMGG WIND GUSTS MAY ACCOMPANY THIS ACTIVITY.

...PORTIONS OF THE MID-ATLANTIC...
TO THE S OF THE FRONT DRAPED E/W ACROSS THE MID-ATLANTIC...MODERATE
TO STRONG INSTABILITY IS FORECAST TO DEVELOP ACROSS PARTS OF THE
PIEDMONT AND COASTAL PLAIN OF VA AND NC. FRONTAL ASCENT...OROGRAPHIC
CIRCULATIONS OVER THE APPALACHIANS...AND SEA-BREEZE BOUNDARIES WILL
BE FOCI FOR CONVECTIVE DEVELOPMENT DURING THE DIURNAL HEATING CYCLE.
WHILE MID-LEVEL FLOW WILL BE MODEST -- E.G. H5 FLOW GENERALLY AROUND
15-20 KT -- SUFFICIENT HIGH-LEVEL FLOW IS FORECAST TO EXIST TO
ENCOURAGE CONVECTIVE VENTILATION. THIS COULD YIELD A FEW SUSTAINED
CONVECTIVE CLUSTERS. WITH PW AROUND 1.90-2.10 INCHES...AMPLE
PRECIPITATION LOADING IS EXPECTED TO ACCELERATE DOWNDRAFTS IN
SUPPORT OF LOCALLY STRONG WET MICROBURSTS CAPABLE OF ISOLATED DMGG
WIND GUSTS.

..COHEN.. 07/25/2016

$$



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