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beell

Severe Outlook Friday, 09/23

Rating: 2 votes, 5.00 average.
by on 09-23-2011 at 12:37 PM (1514 Views)
Severe potential over the coastal mid-Atlantic seems rather small this morning despite very good wind profiles conducive to rotating updrafts. Primary negative factor would appear to be extensive cloud cover and precipitation placing a limit on instability. A small risk for hail over WV and eastern PA-closer to the colder temperatures aloft associated with the cut-off upper low over WI.

But we'll keep one eye open anyway.



Day 1 Tornado Outlook



DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1204 AM CDT FRI SEP 23 2011
VALID 231200Z - 241200Z

...NO SVR TSTM AREAS FORECAST...

...SYNOPSIS...
MODELS INDICATE THAT THE UPPER MIDWEST CLOSED LOW WILL BECOME
CUT-OFF FROM THE STRONGER WESTERLIES DURING THIS PERIOD. THE CENTER
OF THE LARGE CYCLONIC CIRCULATION ENCOMPASSING MUCH OF THE CENTRAL
AND EASTERN U.S. IS EXPECTED TO SHIFT INTO NORTHERN ILLINOIS BEFORE
BEGINNING TO RETROGRADE LATE FRIDAY NIGHT INTO SATURDAY. UPSTREAM
...MID/UPPER RIDGING LIKELY WILL PERSIST ACROSS EASTERN PORTIONS OF
THE INTERMOUNTAIN WEST AND ROCKIES...WHILE A TROUGH CONTINUES TO
SLOWLY LIFT NORTHWARD NEAR THE SOUTHERN AND CENTRAL CALIFORNIA
COAST...AHEAD OF A LARGER AND MUCH MORE SIGNIFICANT TROUGH SHIFTING
EASTWARD WITHIN THE WESTERLIES...ACROSS THE EASTERN PACIFIC.

THE EVOLVING PATTERN DOES NOT APPEAR ANY MORE CONDUCIVE TO
SIGNIFICANT DESTABILIZATION THAN THE PAST FEW DAYS.
..BUT POTENTIAL
FOR CONVECTION AND SCATTERED THUNDERSTORM ACTIVITY WILL CONTINUE
AHEAD OF A COLD FRONT ASSOCIATED WITH UPPER LOW AND TROUGH IN THE
EAST. A FEW THUNDERSTORMS MAY ALSO ACCOMPANY THE CALIFORNIA
IMPULSE.

...WRN SLOPES OF THE CNTRL APPALACHIANS INTO LWR GREAT LAKES...
STRENGTHENING SOUTHWESTERLY MID/UPPER FLOW...COUPLED WITH FORCING
AND LOW-LEVEL SHEAR ASSOCIATED WITH A WEAK FRONTAL WAVE PROGGED TO
LIFT NORTHWARD ACROSS THE REGION...MAY ENHANCE CONVECTIVE POTENTIAL
TODAY. WITH THE MID-LEVEL COLD CORE REMAINING GENERALLY UPSTREAM OF
THE WARM SECTOR...LAPSE RATES ARE NOT EXPECTED TO STEEPEN
SUBSTANTIALLY. HOWEVER...GUIDANCE IS SUGGESTIVE THAT BREAKS IN
CLOUD COVER COULD ALLOW FOR ENOUGH BOUNDARY LAYER WARMING TO SUPPORT
MIXED LAYER CAPE UP TO AROUND 500 J/KG. IF THIS OCCURS...ORGANIZED
CONVECTIVE DEVELOPMENT DOES NOT APPEAR OUT OF THE
QUESTION...INCLUDING A LOW RISK FOR STRONG/SEVERE STORMS.

...LEE OF THE CENTRAL APPALACHIANS...
MODELS SUGGEST THAT SOUTHERLY LOW-LEVEL FLOW WILL BECOME MODERATELY
STRONG /30-40+ KTS AT 850 MB/ TODAY IN A BELT NEAR THE MID ATLANTIC
COAST
...ON THE WESTERN PERIPHERY OF RIDGING OVER THE WESTERN
ATLANTIC. GIVEN AT LEAST WEAK CONDITIONAL INSTABILITY WITHIN A
PLUME OF HIGH MOISTURE CONTENT AIR /CHARACTERIZED BY PRECIPITABLE
WATER IN EXCESS OF 2 INCHES AND 70F+ SURFACE DEW
POINTS/...ENLARGING...CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS APPEAR
SUPPORTIVE OF LOW POTENTIAL FOR STORMS CAPABLE OF PRODUCING DAMAGING
WINDS...PERHAPS ISOLATED TORNADOES
. HOWEVER...MUCH WILL DEPEND ON
THE EXTENT OF THE BOUNDARY LAYER DESTABILIZATION...WHICH REMAINS
UNCLEAR DUE TO THE POTENTIAL FOR CONSIDERABLE CLOUD COVER AND
ASSOCIATED AREAS OF PRECIPITATION.

..KERR.. 09/23/2011

Additional SPC graphics for hail/wind available here:
http://www.spc.noaa.gov/products/out...0923_1200.html

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Comments

  1. beell's Avatar
    Da Hodograph


    A few quick notes regarding the "oddly named, ripe for a joke" hodograph. A graphical look at wind shear-a clockwise turning of wind with height. Something supercells require. A supercell is simply a thunderstorm with a persistent, rotating, updraft. It does not guarantee a tornado.

    The above diagram is a simple representation of a hodograph. The wind direction and wind speed are obtained from weather balloons. Direction and speed can also be derived from a model for a forecast hodograph.

    The center of the graph is the origin. The place where the balloon is launched or the forecast point for a model.
    The arrows represent the wind direction but it is backwards from the norm. Towards the top is south. North is at the bottom, west on the right, and east on the left side.

    A south wind would point straight up from the origin. The longer the arrow, the stronger the wind. The circles are used to estimate wind speed. Usually in knots.

    On the diagram, the first arrow (the surface wind) indicates a SE wind (161 degrees) at 25knots.
    1 kilometer up, winds are almost due south (175 degrees) at 42 knots.
    And so on and so forth. After each level is plotted, draw a line connecting each arrowhead and evaluate the shape of the "line".

    In this case, mets would call this a "strongly curved" hodograph and with a little study, you can visualize the curving of the wind field with height. If there is a substantial increase in wind speed with height the "curve" of the severe hodograph extends farther and farther away from the origin at each level. In addition to "strongly curved" descriptor, we can add "enlarging" to our assesment of the hodograph.

    This example, real world would catch the eye of any stormchaser. Strong winds curving with height will cause a regular, old updraft to "rotate". The first step towards the production of a tornado. Instability and a few other parameters are also required.

    From the 12Z SPC Day 1 posted in the blog entry:

    ENLARGING...CLOCKWISE CURVED LOW-LEVEL HODOGRAPHS APPEAR
    SUPPORTIVE OF LOW POTENTIAL FOR STORMS CAPABLE OF PRODUCING DAMAGING
    WINDS...PERHAPS ISOLATED TORNADOES


    The Velocity Azimuth Display or VAD is a useful tool for real time evaluation of wind speed and direction above a particular area-with the added benefit of tracking the change in these values over time. Pretty sure most of you have seen a few of them. The wind direction is conventional. North is up, etc. Ok, enough of that.

    Here's one from the Raleigh/Durham, NC VAD

    Updated 09-23-2011 at 12:46 PM by beell
  2. P451's Avatar
    Morning beell. Feels awfully juicy out there this AM in NY (~30mi north of NYC).

    First good shot of rain is progressing through southern/central NJ as we speak. Trying to get some outside stuff done in the two hours or so I have left before it moves in. Got my firewood stacked just gotta cover it some.


    24hr WV Imagery, East Coast:

  3. beell's Avatar
    And the latest (13Z) Day 1 Outlook which is in pretty good sync with the unofficial slight tornado risk area posted yesterday morning.

    Valid 4PM
    Friday, 09/23






    DAY 1 CONVECTIVE OUTLOOK
    NWS STORM PREDICTION CENTER NORMAN OK
    0734 AM CDT FRI SEP 23 2011

    VALID 231300Z - 241200Z

    ...NO SVR TSTM AREAS FORECAST...

    ...LOWER GREAT LAKES/UPPER OH VALLEY...

    STRONG VORTICITY MAXIMUM OVER THE LOWER OH VALLEY WILL ROTATE NNEWD
    THROUGH ERN PERIPHERY OF UPPER LOW...SUPPORTING AN INCREASE IN
    FORCING FOR ASCENT AND MIDLEVEL FLOW ACROSS THE REGION TODAY. IN
    THE LOW LEVELS...WEAK FRONTAL WAVE WILL DEVELOP NWD THROUGH THE
    UPPER OH VALLEY INTO SWRN ONTARIO WHILE TRAILING COLD FRONT ADVANCES
    EWD THROUGH THE LOWER GREAT LAKES AND CNTRL APPALACHIANS.

    WHILE WIDESPREAD CLOUDS AND MARGINAL BOUNDARY LAYER MOISTURE CONTENT
    WILL LIMIT AIR MASS DESTABILIZATION TODAY...THE NEWD PROGRESSION OF
    MIDLEVEL DRY SLOT MAY YIELD SOME CLOUD BREAKS AND POCKETS OF WEAK
    INSTABILITY. FRONTAL ASCENT COUPLED WITH INCREASED LARGE-SCALE
    FORCING ATTENDANT TO ABOVE-MENTIONED VORTICITY MAXIMUM MAY FOSTER AN
    INCREASE IN TSTM COVERAGE BY AFTERNOON FROM WRN PARTS OF NY/PA INTO
    THE CNTRL APPALACHIANS. DESPITE STRENGTHENING MID- AND HIGH-FLOW
    FLOW AND RESULTANT LENGTHENING HODOGRAPHS...FORECAST SOUNDINGS
    SUGGEST THAT BULK OF POTENTIAL BUOYANCY WILL RESIDE GENERALLY BELOW
    500 MB WHERE WIND FIELD WILL BE WEAKER. THIS COMBINED WITH THE WEAK
    INSTABILITY WILL LIKELY LIMIT ORGANIZED SEVERE WEATHER POTENTIAL
    LATER TODAY.

    ...CAROLINAS TO MID-ATLANTIC COAST...

    MORNING WATER VAPOR IMAGERY SHOWS A WEAK VORTICITY MAXIMUM OVER THE
    SRN APPALACHIANS WHICH WILL CONTINUE NNEWD TODAY WITHIN
    DEEP-MERIDIONAL FLOW REGIME PRESENT DOWNSTREAM FROM GREAT LAKES
    UPPER LOW. FORCING FOR ASCENT ASSOCIATED WITH THIS IMPULSE IS
    EXPECTED TO SUPPORT AN INCREASE IN TSTM ACTIVITY THROUGH THE DIURNAL
    HEATING CYCLE WITHIN A MOIST AIR MASS CHARACTERIZED BY DEW POINTS IN
    THE UPPER 60S TO LOWER 70S AND PW VALUES OF 1.5-2.0+ INCHES. HERE
    TOO...WIDESPREAD CLOUDS AND WEAK LAPSE RATES WILL LIMIT AIR MASS
    DESTABILIZATION...WITH MLCAPE VALUES REMAINING GENERALLY BELOW 1000
    J/KG ACROSS THE WARM SECTOR.

    LATEST MODEL GUIDANCE INDICATES AN INCREASE IN LOW-LEVEL WINDS BY
    AFTERNOON ALONG THE MID-ATLANTIC COAST...RESULTING IN VERTICALLY
    VEERING WIND PROFILES AND SUFFICIENT SHEAR FOR ROTATING STORMS.
    WHILE LOCALLY DAMAGING WET MICROBURSTS AND/OR A BRIEF TORNADO ARE
    POSSIBLE...THE MARGINAL INSTABILITY IS EXPECTED TO PRECLUDE A MORE
    SUBSTANTIAL SEVERE WEATHER THREAT.

    ..MEAD/ROGERS.. 09/23/2011
    Updated 09-23-2011 at 04:45 PM by beell
  4. beell's Avatar
    Morning, P.

    Noted some pretty close T/Td spreads earlier this morning on the surface charts. Odd for late September for yall?

    Oh, and we try not to use the word "firewood" here in TX

    Thanks for the WV loop. Pretty strong looking low swinging strongly to a negative tilt. Not exactly stationary either. Be thankful for the cloud cover I guess. Forced ascent is not an issue!
  5. P451's Avatar
    I-95 running through from Philly into CT is a good dividing line to use in this area for many weather events.

    Anything South and East of that line? Not unusual. North and West of that line? Getting late for that.


    Interestingly enough they took out the "Heavy Rain" wording from the local products - but have kept the same flood watches up with the same wording of "one and a half to three inches, up to four inches of rain" in that particular product.

    A bit conflicting?


    Three day QPF seems there although this is down quite a bit from two days ago.

  6. beell's Avatar
    Maybe the lower QPF represents a little bit more of a progressive modeled cut-off and eastward moving dry slot.
  7. MSGAL's Avatar
    Looky here.....I've found Beell......what a good find..
  8. beell's Avatar
    Oops. I missed ya'll on the changeover to the new blog. I'm learning.

    Morning, aqua,
    Most of my work is done from the home office nowdays. I miss the RBF's. MIL and the dog are my only targets-and they're both slow.

    Welcome stormwatcher. The more the merrier. Ophelia is not prime-time material

    Thanks for picking up the slack on the welcome, Grill!
    And even an Admin that travels to your location! What a concept.

  9. beell's Avatar
    Quote Originally Posted by MSGAL
    Looky here.....I've found Beell......what a good find..
    hmmm...I used to know a weather blogger gal from MS. I think I still do!

    Thanks for checking in.
  10. beell's Avatar
    Not much change from the previous outlook.



    DAY 1 CONVECTIVE OUTLOOK
    NWS STORM PREDICTION CENTER NORMAN OK
    1113 AM CDT FRI SEP 23 2011

    VALID 231630Z - 241200Z

    ...NO SVR TSTM AREAS FORECAST...

    ...ERN CAROLINAS/VA TIDEWATER AREA THIS AFTERNOON...

    A MIDLEVEL LOW CENTERED NEAR LAKE MI WILL MOVE LITTLE THROUGH THIS
    FORECAST PERIOD. A WEAK EMBEDDED SPEED MAX WILL ROTATE NNEWD THIS
    AFTERNOON/EVENING FROM THE SRN APPALACHIANS TO PA...AROUND THE SERN
    PERIPHERY OF THE LOW. AT THE SURFACE...THE PRIMARY SYNOPTIC LOW
    WILL DRIFT NWD INVOF LAKE ERIE...WHILE A FRONT WILL REMAIN
    QUASISTATIONARY FROM ERN SC/CENTRAL NC INTO THE CHESAPEAKE BAY AREA.
    THIS FRONTAL SEGMENT WILL FOCUS THE MAIN CONVECTIVE DEVELOPMENT
    THROUGH THE PERIOD...IN ADVANCE OF THE EJECTING SPEED MAX OVER THE
    SRN APPALACHIANS.

    BOUNDARY LAYER DEWPOINTS IN THE LOW-MID 70S HAVE SPREAD INLAND
    ACROSS THE ERN CAROLINAS AND THE LOWER CHESAPEAKE BAY AREA.
    HOWEVER...SURFACE HEATING WILL CONTINUE TO BE LIMITED THROUGH THE
    AFTERNOON BY WIDESPREAD CLOUDS...AND THE DEGREE OF INSTABILITY WILL
    ALSO BE LIMITED BY POOR MIDLEVEL LAPSE RATES.
    MEANWHILE...DEEP-LAYER VERTICAL SHEAR IN THE WARM SECTOR WILL BE
    SUFFICIENT FOR ORGANIZED CLUSTERS/EMBEDDED SUPERCELLS
    IN CONJUNCTION
    WITH A BELT OF 30-40 KT SSWLY MIDLEVEL FLOW...AND EFFECTIVE SRH ON
    THE ORDER OF 150 M2/S2. THE COMBINATION OF RELATIVELY WEAK
    INSTABILITY/POOR LAPSE RATES/MOIST PROFILES WITH MODEST VERTICAL
    SHEAR APPEARS MARGINALLY SUPPORTIVE OF DAMAGING WINDS AND AN
    ISOLATED/BRIEF TORNADO
    . WILL MAINTAIN LOW WIND/TORNADO
    PROBABILITIES IN THIS UPDATE...BUT THIS AREA WILL CONTINUE TO BE
    MONITORED CLOSELY THROUGH THE AFTERNOON
    .

    ...WRN NY/PA TO THE SRN APPALACHIANS THIS AFTERNOON...
    THE PRIMARY EMBEDDED SPEED MAX WILL ROTATE NNEWD FROM KY TO OH THIS
    AFTERNOON...ROUGHLY ALONG THE SYNOPTIC COLD FRONT NEAR THE W SLOPE
    OF THE APPALACHIANS. WIDESPREAD CLOUDS AND RELATIVELY COOL SURFACE
    TEMPERATURES WILL KEEP INSTABILITY WEAK THROUGH THE AFTERNOON IN
    ADVANCE OF THE FRONT...THOUGH THERE WILL BE SUFFICIENT MIDLEVEL
    MOMENTUM TO SUPPORT A SMALL RISK FOR ISOLATED DAMAGING GUSTS THIS
    AFTERNOON.

    ..THOMPSON/HURLBUT.. 09/23/2011
  11. MSGAL's Avatar
    Quote Originally Posted by beell
    hmmm...I used to know a weather blogger gal from MS. I think I still do!

    Thanks for checking in.

    o
    Yes you do, glad you're here...cant imagine bad weather and tornado season without Beell.....now just need Keep... ....my Eyes will be watching.........and these little icons will get ya in trouble, if you don't look closely......been there , done that..
  12. Cos's Avatar
    Hope it's not too wet in WV.
    Everyone I've ever known from there claims they grew up barefoot and dirt poor.
  13. P451's Avatar
    Had some moderate steady rain for awhile today. Most of it has been light as it is now. Looks like the intensity will increase in an hour or so however. Looks like it will be heavy.

    Looks like an embedded low between Baltimore and Philly riding up I-95 - enhancing rainfall quite good.
  14. shoreacres's Avatar
    Lookie what washed up on your shore! No, wait.... I'm shore. No, wait....

    Tell you what, I'm "shore" glad to have found you and some of the others over here. Place feels so comfortable I kicked my shoes off first thing. I promise not to cause trouble. I'll just lurk around and smile.

  15. beell's Avatar
    Evening, Cos.
    The youth of today just does not know what poor is.



    Hello, P.
    And they don't know what weather is either!The new normal for them.

    I'd rather be poor and shoeless than have this kind of forecast.

    ...HIGHS IN THE UPPER 90S TO AROUND 100 DEGREES BY SUNDAY ACROSS MUCH OF SOUTHEAST TEXAS...

    ...SOUTH TO SOUTHWEST WINDS INCREASING SUNDAY WITH CRITICAL FIRE WEATHER CONDITIONS. WINDSPEEDS
    INCREASING TO 15-20 MPH AND GUSTS TO 25 MPH...

    ...THE TEXAS COMMISSION ON ENVIRONMENTAL QUALITY...HAS ISSUED AN OZONE WATCH FOR THE HOUSTON...GALVESTON...AND BRAZORIA AREAS FOR
    SATURDAY...SEPTEMBER 24TH. ATMOSPHERIC CONDITIONS ARE EXPECTED TO BE FAVORABLE FOR PRODUCING HIGH LEVELS OF OZONE POLLUTION IN THE HOUSTON...GALVESTON...AND BRAZORIA AREAS...

    3-4 tornado warnings in extreme northeast NC/southeast VA.
    Nothing reported on the ground. Good news.

    Thanks, MSGAL. Good luck on the rain next mid-week!
    Updated 09-24-2011 at 12:13 AM by beell
  16. beell's Avatar
    Quote Originally Posted by shoreacres
    Lookie what washed up on your shore! No, wait.... I'm shore. No, wait....

    Tell you what, I'm "shore" glad to have found you and some of the others over here. Place feels so comfortable I kicked my shoes off first thing. I promise not to cause trouble. I'll just lurk around and smile.

    OK!
    Welcome freshly washed and shoeless shore! I have blogged with you for several years. Cause trouble? You? Well, only if the cause is just & righteous, maybe a little trouble, lol.

    Would love to see your latest blog show up here somewhere. It's a good one.

    Thanks for the smile you brought.
  17. aqua's Avatar
    a late night good evening to all. Good to see shore among us.
    Three days they predicted heavy rains; two of those days haven't yielded but a spit.
    As if I have room to complain to a Texan....
  18. Cos's Avatar
    Beell...that skit's too funny.
    Great find.
  19. P451's Avatar
    I've got to say that so far we've had maybe two long duration bouts of moderate showers. A few heavy moments. Today it's been dry...even some peeks of sun at times.

    Seems like the meat of the matter is down over the outer banks of NC right now. When that disturbance rides north we could have some heavy weather.

    Also should be watching 91L over the Bahamas...as that could be absorbed into the trough and enhance rainfall up the coast. Question is... will it be far enough west when it does to affect NC to NYC or will this be a concern for SE New England instead?
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