Severe Storm Outlook Narrative (AC)
Issued by NWS

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ACUS02 KWNS 190604
SWODY2
SPC AC 190603

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0103 AM CDT FRI SEP 19 2014

VALID 201200Z - 211200Z

...THERE IS A SLGT RISK OF SVR TSTMS OVER PARTS OF THE LOWER GREAT
LAKES AND UPPER MIDWEST...

...SUMMARY...
STRONG TO SCATTERED SEVERE THUNDERSTORMS ARE EXPECTED DURING
SATURDAY OVER PARTS OF THE GREAT LAKES AND MIDWEST REGIONS. A FEW OF
THE SEVERE STORMS MAY PRODUCE HAIL AND HIGH WINDS. OTHER STRONG TO
ISOLATED SEVERE THUNDERSTORMS WITH GUSTY WINDS AND HAIL ARE POSSIBLE
FROM THE MID-MISSISSIPPI VALLEY WESTWARD ACROSS THE CENTRAL ROCKIES
TO THE SOUTHERN GREAT BASIN.

...SYNOPSIS...
PROGRESSIVE AND MODESTLY AMPLIFIED MID-LEVEL FLOW WILL EXIST FROM
THE NORTHERN PLAINS EAST ACROSS THE GREAT LAKES TO NEW ENGLAND ON
SATURDAY. A LEADING SHORTWAVE TROUGH CURRENTLY CROSSING THE NORTHERN
ROCKIES WILL MOVE EAST TO THE UPPER MS VALLEY THROUGH FRIDAY AND
THEN UNDERGO FURTHER AMPLIFICATION OVER THE GREAT LAKES ON SATURDAY
AS A STRONGER SHORTWAVE IMPULSE ACCELERATES SOUTHEAST OUT OF
SOUTH-CENTRAL CANADA. THE COLD FRONT ASSOCIATED WITH THE LEADING
DISTURBANCE IS FORECAST TO SPREAD SOUTHEAST INTO SOUTHERN WI/LOWER
MI AND PARTS OF INDIANA/IL COINCIDENT WITH DAYTIME
HEATING/DESTABILIZATION AND STRENGTHENING DEEP-LAYER WIND FIELDS.

A CLOSED MID/UPPER LOW NOW TAKING SHAPE OVER CA IS FORECAST TO DRIFT
INLAND/EASTWARD THROUGH LATE SATURDAY. WEAK HEIGHT FALLS ON THE
EASTERN FLANK OF THIS SYSTEM WILL IMPINGE UPON ANTECEDENT
SUB-TROPICAL MOISTURE PLUME ACROSS THE SOUTHERN GREAT BASIN.

...LOWER GREAT LAKES/UPPER MIDWEST...
SCATTERED CONVECTION MAY BE ONGOING AT THE START OF THE PERIOD ALONG
AND AHEAD OF A MODEST COLD FRONT SPREADING SOUTHEAST FROM THE UPPER
MS VALLEY AND NORTHERN LOWER MI. LIFT ALONG THE FRONT SHOULD
INCREASE THROUGH THE DAY AS STRONGER MID-LEVEL HEIGHT FALLS DEVELOP
OVER WI/LM. RELATIVELY STOUT WEST-SOUTHWESTERLY LOW-LEVEL FLOW
SHOULD AID MOISTURE TRANSPORT ACROSS THE UPPER MIDWEST/LOWER
MI...WITH SURFACE DEWPOINTS LIKELY CLIMBING INTO THE LOW-MID 60S F
BY AFTERNOON. WHILE EARLY DAY STORMS MAY STRUGGLE FROM LACK OF
STRONGER SURFACE-BASED DESTABILIZATION...SUFFICIENTLY STEEP
MID-LEVEL LAPSE RATES AROUND 7 C/KM MAY EXIST ACROSS SOUTHERN WI TO
SUPPORT STRONGER UPDRAFTS AND PERHAPS HAIL. STRONGER DESTABILIZATION
APPEARS LIKELY TO EVOLVE FROM MS VALLEY EASTWARD TO NORTHERN IL/IND
THROUGH THE AFTERNOON. A CORRIDOR OF SBCAPE ON THE ORDER OF 800-1200
J/KG AHEAD OF THE FRONT AND CO-LOCATED WITH STRENGTHENING
UNIDIRECTIONAL DEEP-LAYER SHEAR OF 35-40KT COULD SUPPORT THE
DEVELOPMENT OR MORE ORGANIZED/PERSISTENT STORMS FROM THE IL/WI
BORDER EAST TO NORTHERN IND AND LOWER MI. THIS ACTIVITY MAY EVOLVE
INTO FAST-MOVING LINE SEGMENTS AND OR A FEW SUPERCELLS THROUGH THE
EARLY EVENING HOURS. DESPITE A CONTINUATION OF LIFT ALONG THE
ADVANCING FRONT...ISOLATED TO SCATTERED HIGH WIND AND SEVERE HAIL
THREATS ARE LIKELY TO WANE BY EVENING AS EASTWARD-MOVING STORMS
ENCOUNTER DIMINISHING INSTABILITY.

...GREAT BASIN...
STRONGER QG FORCING FOR ASCENT IS INDICATED IN LATEST NAM ACROSS THE
SOUTHERN GREAT BASIN /EASTERN NV AND SOUTHWEST UT/ BY EARLY SATURDAY
EVENING AS MID/UPPER LOW DRIFTS EAST. LIFT WITH THIS SYSTEM WILL ACT
ON A RELATIVELY MOIST AIRMASS WHERE STRONGER DIURNAL HEATING WILL
LIKELY CONTRIBUTE TO A DEEPLY MIXED BOUNDARY LAYER. EXPECT SCATTERED
HIGH-BASED STORMS TO INCREASE/PERSIST AS LARGE-SCALE ASCENT SPREADS
EAST AND BELT OF 30-40KT SOUTHERLY MID-LEVEL FLOW SPREADS
NORTH/NORTHEAST FROM EASTERN NV INTO WESTERN UT. A COUPLE OF
STRONGER CORES MAY RESULT IN MARGINAL HAIL AND/OR STRONG DOWNBURST
WINDS.

...MN/UPPER MS VALLEY...
AS A STRONG SHORTWAVE TROUGH DEVELOPS SOUTHEAST OUT OF CANADA
THROUGH LATE AFTERNOON...DEEP-LAYER ASCENT AND LOWERING STATIC
STABILITY WITHIN LEFT EXIT REGION OF 70-80KT MID-LEVEL JET STREAK
WILL MOVE FROM NORTHERN MN TO NORTHWEST WI. RESIDUAL LOW-LEVEL
MOISTURE IN THE WAKE OF LEADING FRONTAL PASSAGE...IN COMBINATION
WITH COLDER TEMPERATURES ALOFT...SHOULD BE ADEQUATE FOR AT LEAST
LOW-TOPPED CONVECTION AMIDST INTENSIFYING WIND FIELDS. IT SEEMS
POSSIBLE THAT A COUPLE OF STORMS COULD PRODUCE HAIL AND GUSTY WINDS
BEFORE NIGHTFALL.

..CARBIN.. 09/19/2014



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