SPC Mesoscale Discussion Changes
As part of SPCs efforts to more efficiently convey critical forecast information, standardized content structure
within the Mesoscale Discussion (MD) product will increase, including new information on the probability of watch
issuance for severe potential MDs.
Starting May 1, 2012, MDs will include the following sections:
For Severe Potential MDs (click here to download an example product text.)
AREAS AFFECTED...(PORTION OF STATES OR GEOGRAPHICAL AREAS)
CONCERNING...(TYPE OF MD)
VALID DDHHMMZ - DDHHMMZ
PROBABILITY OF WATCH ISSUANCE...[increments of 20% from 20-80%,
including 5% and 95%]
SUMMARY...A concise statement regarding the forecast
(timing, coverage, intensity, and mode) severe threat.
DISCUSSION...The description of significant mesoscale features and
atmospheric processes which will likely result in the expected event.
Definitions:
PROBABILITY OF WATCH ISSUANCE in percent...5 and 20 for Unlikely,
40 and 60 for Possible, 80 and 95 for Likely, 95 for Needed Soon.
For all other MDs (click to download a Watch MD, or a Winter MD example product text.)
AREAS AFFECTED...(PORTION OF STATES OR GEOGRAPHICAL AREAS)
CONCERNING...(TYPE OF MD)
VALID DDHHMMZ - DDHHMMZ
SUMMARY...A concise statement regarding the forecast
(timing, coverage, intensity, and mode) severe threat.
DISCUSSION...The description of significant mesoscale features and
atmospheric processes which will likely result in the expected event.
Example of Severe Potential Mesoscale Discussion - Watch Possible
MESOSCALE DISCUSSION 2046
NWS STORM PREDICTION CENTER NORMAN OK
0247 AM CST TUE NOV 16 2010
AREAS AFFECTED...THE FL PANHANDLE
CONCERNING...SEVERE POTENTIAL...WATCH POSSIBLE
VALID 160847Z - 161115Z
PROBABILITY OF WATCH ISSUANCE...40 PERCENT
SUMMARY...SHORT-LINE SEGMENT MAY GROW UPSCALE AND BRUSH COAST WITH
ATTENDENT INCREASE IN SEVERE THREAT AFTER 10Z.
DISCUSSION...CONVECTIVELY ENHANCED BOUNDARY STRETCHES FROM SOUTH OF
APALACHICOLA WWD AND INTERSECTS A NE-SW ORIENTED BAND OF THUNDERSTORMS
EXTENDING FROM SOUTH OF GULF SHORES SWWD TO JUST OFF SERN TIP OF LA.
ACTIVITY IS DEVELOPING WITHIN A PRE-FRONTAL CONFLUENCE ZONE ASSOCIATED
WITH A STRENGTHENING SWLY LOW-LEVEL JET. THIS FEATURE WILL DEVELOP NWD
THROUGH THE WRN FL PANHANDLE INTO AL AS PRIMARY SURFACE LOW DEEPENS
AND LIFTS NWD INTO THE TN VALLEY IN RESPONSE TO FORCING ASSOCIATED
WITH NEWD EJECTING VORT MAX. BUOY OBSERVATIONS SHOW A RESERVOIR OF 70F
DEWPOINTS OVER THE NRN GULF SOUTH OF E-W BOUNDARY. THIS FEATURE WILL
MOVE SLOWLY NWD AS THE LOW LEVEL JET STRENGTHENS...AND IS ALREADY
APPROACHING THE COAST NEAR APALACHICOLA. REMAINING PORTIONS OF THE
BOUNDARY WILL LIKELY NOT MOVE INLAND UNTIL AFTER 11Z. BOUNDARY LAYER
DESTABILIZATION AND POTENTIAL FOR SURFACE BASED STORMS WILL INCREASE
MARKEDLY WHERE THE MOIST WARM SECTOR MOVES ONSHORE....WHILE LARGE
HODOGRAPHS ACCOMPANYING THE LOW-LEVEL JET WILL PROMOTE SEVERE
POTENTIAL. HOWEVER...THE COASTAL BOUNDARY WILL MAKE ONLY LIMITED
INLAND PROGRESS THIS MORNING SUGGESTING THE THREAT AREA SHOULD REMAIN
SMALL.
..DIAL/MEAD.. 11/16/2010
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...TAE...
LAT...LON 30118348 30058436 29738509 30168565 30498617 30838606
30858543 30658468 30578344 30118348
Example of Severe Potential Mesoscale Discussion - Watch Likely
MESOSCALE DISCUSSION 0589
NWS STORM PREDICTION CENTER NORMAN OK
0111 PM CDT TUE APR 26 2011
AREAS AFFECTED...NERN TX AND FAR SERN OK/NRN LA/SRN AR
CONCERNING...SEVERE POTENTIAL...TORNADO WATCH LIKELY
VALID 261811Z - 262015Z
PROBABILITY OF WATCH ISSUANCE...80 PERCENT
SUMMARY...DISCRETE SUPERCELLS EXPECTED TO FORM AFTER 20Z WITH AN
INCREASING LARGE HAIL/TORNADO THREAT INTO THIS EVENING. A RELATIVELY LONG
LEAD TIME/DURATION PDS TORNADO WATCH WILL BE ISSUED BY 20Z.
DISCUSSION...WITH SURFACE CYCLOGENESIS UNDERWAY ACROSS THE SRN HIGH
PLAINS...THE WARM SECTOR AIRMASS...EAST OF A NEAR I-35 CENTRAL TX
DRYLINE...AND ALONG/SOUTH OF A SLOW NORTHWARD-RETURNING
SOUTHWEST-NORTHEAST ORIENTED FRONTAL BOUNDARY FROM THE SOUTH DFW
METRO INTO SOUTHERN AR...HAS ALREADY BECOME MODERATE TO STRONGLY
UNSTABLE IN THE PRESENCE OF LITTLE CINH. AFTER A BRIEF BOUT OF
SHORTWAVE RIDGING AT MIDDAY...THE LEADING EDGE OF AN UPPER JET
STREAK APPEARS TO HAVE REACHED THE SOUTHERN HIGH PLAINS...WITH
LIKELY-ASSOCIATED DEEP MIXED CUMULIFORM DEVELOPMENT NOW EVIDENT
ACROSS EASTERN NM/NORTHWEST TX PER VISIBLE SATELLITE IMAGERY.
INCREASING DEEP LAYER WIND FIELD ATOP THE MOIST/UNSTABLE WARM SECTOR
WILL BE HIGHLY FAVORABLE FOR SUPERCELLS. STRENGTHENING LOWER
TROPOSPHERIC WINDS THIS EVENING WILL ACCENTUATE THE RISK OF STRONG
TORNADOES ESPECIALLY ACROSS THE ARKLATEX VICINITY/ADJACENT FAR
SOUTHEAST OK.
..GUYER/HART.. 04/26/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...JAN...LZK...SHV...TSA...HGX...FWD...OUN...
LAT...LON 31739772 32889727 34059625 34489432 34559322 34019166
32609213 31619336 30579640 31739772
Example of Severe Potential Mesoscale Discussion - Watch Unlikely
MESOSCALE DISCUSSION 0026
NWS STORM PREDICTION CENTER NORMAN OK
0345 PM CST TUE JAN 17 2012
AREAS AFFECTED...PARTS OF CENTRAL/SRN LA AND SRN MS
CONCERNING...SEVERE POTENTIAL...WATCH UNLIKELY
VALID 172145Z - 172245Z
PROBABILITY OF WATCH ISSUANCE...20 PERCENT
SUMMARY...POTENTIAL FOR ISOLATED STRONG TO SEVERE STORMS WILL PERSIST
LATE THIS AFTERNOON. IN ADDITION...STORMS DEVELOPING OVER CENTRAL/SWRN
LA WILL TEND TO TRACK ENEWD INTO FAR SRN MS WHERE STORMS ARE ALREADY IN
PROGRESS...WITH HEAVY RAINFALL RATES POSSIBLE WITH THESE TRAINING STORMS.
DISCUSSION...MID-AFTERNOON SURFACE ANALYSES SHOWED A COLD FRONT STEADILY
ADVANCING EWD THROUGH THE LOWER MS VALLEY AND TOWARD THE TX COAST.
STORMS OVER CENTRAL LA WERE LOCATED ALONG AND E OF THE FRONT...WHILE
THE STORMS OVER FAR SRN MS WERE LOCATED ALONG AN APPARENT
DIFFERENTIAL HEATING BOUNDARY. DESPITE SURFACE DEWPOINTS IN THE 60S
AND STEEP MIDLEVEL LAPSE RATES...EXTENSIVE CLOUDINESS HAS CONTINUED
TO INHIBIT GREATER SURFACE HEATING AND THUS MAINTAINING WEAK
INSTABILITY /MLCAPE 500-1000 J PER KG/. STRONG EFFECTIVE BULK SHEAR
/AROUND 50 KT/ IS SUPPORTIVE FOR ORGANIZED STORMS...BUT VEERED
PRE-FRONTAL LOW LEVEL WINDS WILL CONTINUE TO LIMIT CONVERGENCE AND
OVERALL TSTM COVERAGE. GIVEN STEEP MIDLEVEL LAPSE RATES AND DEEP
LAYER SHEAR...HAIL AND STRONG WIND GUSTS WILL BE POSSIBLE WITH THE
MORE SUSTAINED UPDRAFTS.
CONCERN ALSO EXISTS FOR HEAVY RAINFALL RATES...AS STORMS TRAIN ENEWD
FROM CENTRAL LA THROUGH EXTREME SRN MS...WITH THE GREATEST THREAT
AREA EXTENDING WSW-ENE WITHIN A 30-40 MILE WIDE CORRIDOR FROM NRN
EVANGELINE PARISH LA TO LAMAR COUNTY MS. PRECIPITABLE WATER VALUES
TO AROUND 1.5 INCH WILL SUPPORT THIS THREAT.
..PETERS/RACY.. 01/17/2012
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...JAN...LIX...LCH...SHV...
LAT...LON 30619347 31479216 31879144 31919007 31468922 30938971
30709100 30379241 30329316 30619347
Example of Severe Potential Mesoscale Discussion - Watch in Effect
MESOSCALE DISCUSSION 2049
NWS STORM PREDICTION CENTER NORMAN OK
1027 PM CST TUE NOV 16 2010
AREAS AFFECTED...PORTIONS CNTRL/ERN SC/NC/VA...SRN MD
CONCERNING...TORNADO WATCH 741...
VALID 170427Z - 170630Z
THE SEVERE WEATHER THREAT FOR TORNADO WATCH 741 CONTINUES.
SUMMARY...SVR POTENTIAL WILL CONTINUE OVER ERN PORTIONS WW WITH BOWS
EMBEDDED WITHIN SEVERAL BROKEN LINE SEGMENTS...AND MAY SHIFT SOMEWHAT
E OR NE OF WW INTO LOWER POTOMAC REGION AND COASTAL PLAIN SWD TO SC
BY 06-07Z.
DISCUSSION...SFC ANALYSIS INDICATES COLD FRONT CONTINUING TO MOVE EWD
ACROSS W-CENTRAL PORTIONS SC/NC AND FROM SWRN INTO CENTRAL
VA...IMMEDIATELY BEHIND LAST BANDS OF CONVECTION IN THESE AREAS.
TSTMS HAVE PRODUCED SEVERAL REPORTS OF TREES DOWN DURING PAST 2 HOURS.
MEASURED GUSTS UP TO 58 KT ALSO WERE REPORTED IN APPOMATTOX COUNTY VA
AT 0331Z...WITH BOW NOW MOVING NEWD ABOUT 50 KT TOWARD TIDAL POTOMAC
REGION. AIR MASS AHEAD OF TSTM BANDS HAS BEEN DESTABILIZING TO AT
LEAST MRGL LEVELS FOR CONTINUE CONVECTIVE POTENTIAL...AS LOW-LEVEL
THETAE ADVECTION OFFSETS SFC DIABATIC COOLING...WHICH ALSO IS KEEPING
LIFTED PARCELS EITHER SFC-BASED OR NEARLY SO IN IMMEDIATE INFLOW
REGION. MODIFIED RAOBS AND FCST SOUNDINGS SUGGEST ONLY 200-500 J/KG
MLCAPE IN NARROW STRIP FROM CENTRAL NC TO CENTRAL/ERN VA. 45-55 KT
EFFECTIVE SHEAR MAGNITUDE SHOULD BE MAINTAINED ALONG CORRESPONDING
INSTABILITY AXIS. WHILE BUOYANCY GENERALLY WILL DIMINISH WITH TIME
AND WITH EWD EXTENT...THIS PROCESS WILL BE GRADUAL ENOUGH THAT SVR
POTENTIAL MAY EXTEND SOMEWHAT PAST CURRENT ERN BOUNDS OF WW.
PRIND SVR POTENTIAL WILL CONTINUE TO CLEAR OUT OF WW FROM W-E BEHIND
COLD FRONT AS LOW-LEVEL FLOW VEERS...AND AS BOUNDARY LAYER AIR MASS
STABILIZES DUE TO COMBINATION OF CAA AND DIABATIC SFC COOLING.
..EDWARDS.. 11/17/2010
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...AKQ...MHX...LWX...RAH...ILM...RNK...CAE...
LAT...LON 33238181 35167990 36677932 37557849 38277795 38877656
38297604 37137648 35307800 33827943 33508062 33238181
Example of Severe Potential Mesoscale Discussion - Winter Weather
MESOSCALE DISCUSSION 0088
NWS STORM PREDICTION CENTER NORMAN OK
1222 PM CST SAT FEB 05 2011
AREAS AFFECTED...S-CNTRL/SERN NY
CONCERNING...FREEZING RAIN
VALID 051822Z - 052215Z
SUMMARY...FREEZING RAIN RATES ARE EXPECTED TO INCREASE TO 0.05-0.10
IN/HR AFTER 20Z. EMBEDDED CONVECTIVE BURSTS MAY YIELD LOCALLY
HIGHER RATES AT TIMES.
DISCUSSION...LARGE SWATH OF LIGHT-MODERATE PRECIPITATION CONTINUES TO
EXPAND N/EWD INTO CNTRL/ERN NY AHEAD OF AN APPROACHING MIDLEVEL CYCLONE
POSITIONED OVER THE CNTRL OH RIVER VALLEY. STRENGTHENING LOW-LEVEL
WAA PROFILES /AHEAD OF 50-60 KT 850 MB LLJ/ AND ISENTROPIC UPGLIDE
MAXIMIZED IN THE 285-295 K LAYER ATOP SUBFREEZING SURFACE
TEMPERATURES...COMBINED WITH INCREASING MID-LEVEL DCVA...WILL ACT TO
INCREASE PRECIPITATION RATES ACROSS THE REGION.
ADDITIONALLY...MODERATELY STEEP MIDLEVEL LAPSE RATES OVER THE REGION
WILL FAVOR OCCASIONAL EMBEDDED CONVECTIVE ELEMENTS LEADING TO
LOCALLY HIGHER RATES. NAMKF AND RUC POINT FORECAST SOUNDINGS
INDICATE SIGNIFICANT WARMING WILL OCCUR IN THE 2-6 KFT AGL LAYER
ACROSS SERN NY...REINFORCING A FAVORED P-TYPE OF FREEZING RAIN. SURFACE
FREEZING LINE IS EXPECTED TO SHIFT NWD WITH TIME...AND WILL YIELD
POCKETS OF ABOVE FREEZING TEMPERATURES ACROSS SRN PORTIONS OF THE
AREA BY THIS AFTERNOON.
..ROGERS.. 02/05/2011
...PLEASE SEE WWW.SPC.NOAA.GOV FOR GRAPHIC PRODUCT...
ATTN...WFO...ALY...BGM...BUF...
LAT...LON 41697383 42037599 42237684 42757654 43237577 43347510
43297394 42897333 42747317 42337328 41727358 41697383
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