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 041258
SWODY1
SPC AC 041256

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0756 AM CDT FRI SEP 04 2015

VALID 041300Z - 051200Z

...THERE IS A MRGL RISK OF SVR TSTMS PORTIONS ERN DAKOTAS AND
WRN/NRN MN...

...SUMMARY...
ISOLATED LARGE HAIL AND/OR DAMAGING GUSTS MAY OCCUR FROM
THUNDERSTORMS OVER THE EASTERN DAKOTAS AND PARTS OF MINNESOTA TODAY.

...SYNOPSIS...
HIGHLY AMPLIFIED SYNOPTIC-SCALE PATTERN WILL PERSIST IN MID/UPPER
LEVELS...WITH MEAN TROUGHING OVER WRN STATES AND RIDGING FROM TX TO
HUDSON BAY.  EMBEDDED WITHIN THAT RIDGE...QUASISTATIONARY 500-MB LOW
OVER LOWER MI SHOULD DRIFT ERRATICALLY NEAR ITS PRESENT POSITION
THROUGH MOST OF PERIOD...WHILE GRADUALLY FILLING/WEAKENING INTO
OPEN-WAVE TROUGH.  MEANWHILE...BROAD CYCLONE OVER SRN BC AND PAC NW
SHOULD CONSOLIDATE AROUND VORTICITY MAXIMA NOW LOCATED NEAR WA AND
SWRN ORE COASTS...RESULTING IN LOW PIVOTING CYCLONICALLY ACROSS ORE
FROM W-E DURING 00Z-12Z TIME FRAME AND TROUGH SHIFTING SLOWLY EWD
OVER CENTRAL/NRN CA.  SWLY FLOW FETCH E OF THAT TROUGH...FROM NWRN
MEX ACROSS SRN ROCKIES TO NRN PLAINS...WILL HOST 3 PRIMARY SHORTWAVE
PERTURBATIONS PERTINENT TO CONVECTIVE POTENTIAL...
1.  TROUGH NOW EVIDENT IN MOISTURE-CHANNEL IMAGERY OVER WRN PORTIONS
SD/NEB...FCST TO EJECT NEWD TO ERN ND/NWRN MN AREA BY 00Z THEN
WRN-MOST AREAS OF NWRN ONT BY 12Z.
2.  VERY WEAK RIPPLE NOW OVER SONORA...WHICH SHOULD AMPLIFY AS IT
MOVES NEWD OVER CO ROCKIES AROUND 00Z THEN REACH WRN SD AROUND 12Z.

3.  VORTICITY FIELD ASSOCIATED WITH ERN PAC TS KEVIN.  PER NHC
DISCUSSIONS...MID/UPPER-LEVEL REPRESENTATION OF THIS FEATURE SHOULD
SEPARATE FROM ITS LOW-LEVEL CENTER AND MOVE NEWD.  SOME ASSOCIATED
500-MB VORTICITY MAY REACH SRN/ERN AZ LATE TONIGHT ACCORDING TO
SYNOPTIC PROGS SUCH AS SPECTRAL/NAM.

AT SFC...11Z ANALYSIS SHOWED WEAK LOW OVER CENTRAL/SWRN SD WITH
TROUGH SWD ACROSS WRN KS THEN SSWWD OVER ERN NM.  COLD FRONT WAS
DRAWN SEPARATELY FROM THAT LOW...FROM N-CENTRAL/NERN ND SWWD OVER
EXTREME SERN MT TO S-CENTRAL WY.  COLD FRONT SHOULD BECOME
QUASISTATIONARY TODAY...LIKELY REMAINING SOMEWHAT REMOVED FROM SFC
LOW THAT ITSELF WILL LINGER OVER CENTRAL/WRN SD.  WAVY FRONTAL ZONE
EXTENDS FROM NWRN/SERN MN ACROSS NRN PORTIONS IL/INDIANA TO WEAK LOW
OVER S-CENTRAL LOWER MI.  THAT LOW SHOULD WEAKEN FURTHER AS
SUPPORTIVE MID/UPPER PERTURBATION BECOMES MORE DIFFUSE...LEADING TO
WEAKER LOW-LEVEL FLOW/CONVERGENCE THAN YESTERDAY.  WHILE SCATTERED
TSTMS MAY FORM OVER LOWER MI/OH/INDIANA/IL REGION...POTENTIAL FOR
SVR/50-KT GUSTS APPEARS TOO WEAK TO ASSIGN UNCONDITIONAL SVR
PROBABILITIES.

...UPPER MIDWEST/NERN PLAINS...
CONVECTIVE FCST ACROSS THIS REGION IS COMPLICATED BY PRESENCE OF
EXTENSIVE/ONGOING PRECIP PLUME...WITH WIDELY SCATTERED EMBEDDED
TSTMS...FROM ERN NEB ACROSS CENTRAL SD TO WRN ND.  THIS ACTIVITY IS
OCCURRING IN ZONE OF LOW-LEVEL WAA/ISENTROPIC ASCENT TO
LFC....CONSIDERABLY JUXTAPOSED WITH DCVA PRECEDING LEADING SHORTWAVE
TROUGH DESCRIBED ABOVE.  ASSOCIATED CLOUD COVER SHOULD RESTRICT
PACE/INTENSITY OF DIABATIC HEATING DOWNSHEAR ACROSS OUTLOOK
AREA...COMBINING WITH LACK OF WELL-FOCUSED SFC BOUNDARIES AHEAD OF
CONVECTIVE PLUME TO CAST DOUBT UPON LIFT IN WARM SECTOR.  ADDITIONAL
TSTMS MAY FORM ALONG/AHEAD OF LEADING EDGE OF THIS PRECIP
PLUME...MOVING OVER DESTABILIZING BOUNDARY LAYER WITH UPPER-60S TO
LOW-70S F SFC DEW POINTS SUPPORTING MLCAPE 1500-2500 J/KG...LOCALLY
HIGHER.  COMBINATION OF MUTED INSOLATION AND RICH LOW-LEVEL
MOISTURE/THETAE ALREADY IN PLACE SHOULD RESULT IN REDUCTION OF
MLCINH SUFFICIENT TO SUPPORT SFC-BASED EFFECTIVE-INFLOW PARCELS BY
EARLY AFTN.  HOWEVER...HIGH CONVECTIVE TEMPS ON 12Z RAOBS SUGGEST
CONSIDERABLE LARGE-SCALE COOLING AND/OR BOUNDARY-RELATED LIFT WILL
BE NEEDED NEAR BASE OF EML FOR WIDESPREAD SFC-BASED TSTMS.

KINEMATICALLY...SUBTLE INCREASE IN DEEP SHEAR SHOULD OCCUR WITH APCH
OF LEADING SHORTWAVE TROUGH...CONTRIBUTING TO EFFECTIVE-SHEAR
MAGNITUDES 30-40 KT.  ALTHOUGH MIDLEVEL WIND PROFILES IN FCST
SOUNDINGS EXHIBIT SOME SPEED WEAKNESSES AND ERRATIC DIRECTIONAL
SHIFTS...LOW-LEVEL VEERING/STRENGTHENING  WITH HEIGHT IN THIS
ENVIRONMENT SHOULD LEAD TO HODOGRAPHS SUITABLE FOR AT LEAST
TRANSIENT SUPERCELL STRUCTURES.

...CENTRAL MT TO WRN ND OVERNIGHT...
ISOLATED TO WIDELY SCATTERED ELEVATED TSTMS MAY DEVELOP AFTER
00Z...AND ESPECIALLY AFTER 03Z...WITH CONDITIONAL HAIL RISK.  ATTM
COVERAGE/INTENSITY CONCERNS OFFER ENOUGH UNCERTAINTY TO HOLD OFF
UNCONDITIONAL SVR PROBABILITIES FOR NOW...BUT SOME MAY NEED TO BE
ADDED AS MESOSCALE FOCI BECOME BETTER-DEFINED AND IF SHORTER-FUSED
MODEL GUIDANCE TRENDS THAT WAY.  ANY SUCH ACTIVITY WOULD DEVELOP ON
ELEVATED FRONTAL SLOPE W OF SFC BOUNDARY...AND WITHIN WRN LIMB OF
LOW-LEVEL WAA/MOISTURE TRANSPORT ZONE CHARACTERIZED BY ISENTROPIC
LIFT TO LFC.  UPPER-LEVEL SUPPORT APPEARS NEBULOUS WITH BIG PAC NW
CYCLONE REMAINING WELL-REMOVED...AND AFOREMENTIONED TRAIN OF
LOWER-AMPLITUDE/SW-FLOW PERTURBATIONS ON TRACKS S THROUGH E OF THIS
AREA.

..EDWARDS/PICCA.. 09/04/2015



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