Aug 21 Mid-Atl/NE Severe Weather, SPC Risk Level: Day 1 Slight Risk Forecasts & OBS Options

[yankees]

SPC and Upton are saying that this could be a pretty nice outbreak of severe weather not only in uptons area but north into new england. Isolated Tornado threat is even in play although the biggest threat is wind with any clusters that form.

SPC Forecast

SPC AC 210557

DAY 1 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1257 AM CDT SUN AUG 21 2011

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE UPPER OH VALLEY AND
MID ATLANTIC STATES INTO NEW ENGLAND...

...SYNOPSIS...
AN UPPER TROUGH CURRENTLY EXTENDING SWD THROUGH THE GREAT LAKES AND
ANCHORED BY A VORTEX OVER HUDSON BAY WILL UNDERGO FURTHER
AMPLIFICATION AS A SHORTWAVE TROUGH TRACKS ESEWD FROM THE UPPER
GREAT LAKES TO NY/PA THIS FORECAST PERIOD. AT 12Z SUNDAY...A COLD
FRONT ATTENDANT TO THE PARENT LONGWAVE TROUGH SHOULD EXTEND SWWD
FROM SRN ONTARIO THROUGH THE LOWER OH VALLEY TO CENTRAL AR AND WWD
INTO OK. THIS BOUNDARY WILL PROGRESS E/SEWD MOVING THROUGH MUCH OF
THE NERN AND MID-ATLANTIC STATES...AND EXTEND WSWWD INTO THE CENTRAL
GULF COAST STATES BY 12Z MONDAY.

FARTHER W...AN IMPULSE EMANATING FROM AN UPPER LOW ALONG THE NRN CA
COAST IS EXPECTED TO MOVE INTO WRN/NRN MT THIS AFTERNOON AIDING IN
SOME TSTM DEVELOPMENT OVER THE HIGHER TERRAIN. MEANWHILE...HEIGHT
RISES ARE EXPECTED ACROSS THE NRN HIGH PLAINS...TENDING TO LIMIT
TSTM DEVELOPMENT.

...MID-ATLANTIC STATES TO NEW ENGLAND...
00Z NAM/GFS AND 12Z ECMWF AGREE WITH THE TIMING OF THE COLD FRONT
TODAY...REACHING NRN NY TO WRN PA/UPPER OH VALLEY DURING THE
EARLY-MID AFTERNOON. GIVEN THE TIMING OF THE FRONT ALLOWING FOR
SURFACE HEATING/DESTABILIZATION AND THE ARRIVAL OF FORCING ALOFT
DURING THE AFTERNOON/EVENING...THE FORECAST CONFIDENCE REMAINS GOOD
FOR THE DEVELOPMENT OF SEVERE STORMS TODAY INTO TONIGHT ACROSS THE
SLIGHT RISK AREA. SWLY LOW LEVEL WINDS ACROSS THE OH VALLEY TO WRN
PA AND SSWLY LOW LEVEL WINDS IN LEE OF THE CENTRAL APPALACHIANS TO
THE HUDSON VALLEY/NEW ENGLAND WILL EACH SUPPORT MOISTURE ADVECTION
INTO THESE REGIONS. ALTHOUGH MIDLEVEL LAPSE RATES ARE FORECAST TO
BE MODEST /AOB 6.5 C PER KM/ ACROSS THE SLIGHT RISK AREA...SURFACE
HEATING COMBINED WITH THE MOISTURE RETURN WILL RESULT IN MODERATE
INSTABILITY FROM MD/D.C./DELMARVA TO SERN/ERN NY AND SWRN NEW
ENGLAND THIS AFTERNOON. MLCAPE ACROSS THIS CORRIDOR WILL BE UP TO
1500-2000 J/KG WHILE FURTHER W OVER THE UPPER OH VALLEY VALUES WILL
BE UP TO 1000 J/KG.

DIFFLUENT FLOW ALOFT AND HEIGHT FALLS WITH THE APPROACH OF THE UPPER
GREAT LAKES SHORTWAVE TROUGH...AND CONVERGENCE/ASCENT ALONG THE COLD
FRONT AND PRE-FRONTAL/LEE TROUGH EXTENDING FROM VA TO ERN NY WILL
SUPPORT TSTM DEVELOPMENT BY EARLY-MID AFTERNOON IN VICINITY AND
AHEAD OF THESE SURFACE BOUNDARIES. STRENGTHENING WIND FIELDS AND
EFFECTIVE BULK SHEAR OF 40-50 KT COMBINED WITH THE AVAILABLE
INSTABILITY WILL SUPPORT ORGANIZED STORMS. SHEAR VECTORS MORE
NORMAL TO THE LEE TROUGH SUGGEST A GREATER POTENTIAL FOR DISCRETE
STORMS...INCLUDING SUPERCELLS. VERTICALLY VEERING WINDS AND HIGHER
THETAE EXTENDING FROM MD/ERN PA TO SERN NY/SWRN NEW ENGLAND SUPPORT
AN ISOLATED TORNADO THREAT ALONG WITH DAMAGING WINDS AND HAIL.
FARTHER W INTO THE UPPER OH VALLEY...ORGANIZED STRONG TO SEVERE
STORMS WILL BE POSSIBLE BY EARLY-MID AFTERNOON WITH STRONG WIND
GUSTS AND HAIL THE PRIMARY THREATS.

ALTHOUGH INSTABILITY SHOULD BE WEAKENING THIS EVENING...A FURTHER
INCREASE IN DEEP LAYER WIND FIELDS INTO THE NERN STATES AND 60-90
METER HEIGHT FALLS ACROSS THIS REGION SHOULD COMPENSATE THE WEAKER
THERMODYNAMICS FOR AT LEAST A CONTINUED THREAT FOR DAMAGING WINDS
INTO PARTS OF NEW ENGLAND. FORECAST SOUNDINGS SUGGEST A TORNADO
CANNOT BE RULED OUT ACROSS SRN NEW ENGLAND AS STRENGTHENING SLY LLJ
SUPPORTS AN INCREASE IN LOW LEVEL HODOGRAPH CURVATURE.

...WV/VA/CAROLINAS SWWD TO TN/CENTRAL GULF COAST STATES...
A MIDLEVEL SHORTWAVE TROUGH...CURRENTLY MOVING ACROSS IL/IND TO THE
MID SOUTH PER WATER VAPOR IMAGERY...IS EXPECTED TO WEAKEN TODAY AND
MOVE TOWARD THE SRN HALF OF THE APPALACHIANS /WRN VA TO NRN GA/NERN
AL/. ASCENT WITH THIS FEATURE COMBINED WITH MODERATE INSTABILITY
SHOULD SUPPORT TSTM DEVELOPMENT FROM THE TN VALLEY/NRN EXTENT OF THE
CENTRAL GULF COAST STATES INTO THE WRN CAROLINAS AND VA. THE FOCUS
FOR GREATER STORM COVERAGE IS UNCERTAIN AT THIS TIME..AND THUS WILL
MAINTAIN LOW SEVERE PROBABILITIES.

...NRN HIGH PLAINS INTO SRN SD/NRN NEB...
A SURFACE FRONT WILL MOVE SWD TODAY REACHING THE VICINITY OF THE
SD/NEB BORDER. SLY LOW LEVEL WINDS S OF THIS BOUNDARY WILL RETURN
MOISTURE NWD BENEATH A PLUME OF STEEP LEVEL LAPSE RATES/EML
SPREADING EWD INTO SD/NEB. ALTHOUGH MODELS ARE INDICATING MODERATE
INSTABILITY FROM NEB/WRN SD INTO PARTS OF THE ADJACENT NRN HIGH
PLAINS ALONG WITH STRONG EFFECTIVE BULK SHEAR...HEIGHT RISES ACROSS
THIS REGION AND LACK OF SUFFICIENT FORCING ALOFT SUGGEST TSTM
DEVELOPMENT SHOULD BE MINIMAL. THIS OUTLOOK WILL MAINTAIN A LOW
PROBABILITY FOR SEVERE STORMS...GIVEN THE FAVORABLE
INSTABILITY/SHEAR...BUT CONFIDENCE IN GREATER STORM/SEVERE COVERAGE
REMAINS LOW.

..PETERS/SMITH.. 08/21/2011

CLICK TO GET WUUS01 PTSDY1 PRODUCT

NOTE: THE NEXT DAY 1 OUTLOOK IS SCHEDULED BY 1300Z
CURRENT UTC TIME: 1212Z (8:12AM), RELOAD THIS PAGE TO UPDATE THE TIME

http://www.spc.noaa.gov/products/outlook/day1otlk.html

Upton

.SHORT TERM /NOON TODAY THROUGH 6 AM MONDAY/...
UPR LOW SPINNING OVER HUDSON BAY WITH THE JET APPROACHING THE NRN
GREAT LAKES PER WATER VAPOR. H25 U COMPONENT WINDS AND H5 HEIGHT
ANOMALIES WITH THIS SYSTEM ABOUT 2-3 STD/S. 00Z SUITE OF MODELS
CONTINUE TO PROG SCT TSTMS DEVELOPING THIS AFTN ACROSS THE
W...EVOLVING INTO WIDESPREAD TSTMS THIS EVE AND THRU THE OVERNIGHT
AS THE COLD FRONT AND INCREASING DYNAMICS CATCH UP. THIS SOLN HAS
BEEN ACCEPTED FOR THE FCST.

PARAMETERS REMAIN IN PLACE FOR A SEVERE OUTBREAK. 00Z NAM CAME IN
A BIT HIGHER WITH THE BRN...RESULTING IN A TENDENCY TOWARDS
MULTICELLULAR. SYNOPTIC LLVL DIRECTIONAL SHEAR IS
LIMITED...HOWEVER AS STORMS DEVELOP ALLOWING FOR LLVL
INFLOW...EXPECT THIS SHEAR TO BE ENHANCED RESULTING IN AN
ENVIRONMENT MORE SUPPORTIVE OF SUPERCELLS.

ALTHOUGH THERE ISN/T A WARM FRONT INVOF THE CWA WITH THIS
EVENT...EHI STILL IN THE 1-2 RANGE SUPPORTING A TOR POTENTIAL.
INFLOW MAY ENHANCE THESE NUMBERS AS WELL BUT COMPUTATION IS BASED
ON SRH SO CONFIDENCE NOT AS HIGH AS IN THE BRN. ANY OUTFLOW
BOUNDARIES WILL ELEVATE THE SPIN UP RISK...AND AS THE CONVECTION
CONSOLIDATES TONIGHT THE RISK COULD SHIFT TO LI WITH COASTAL
BOUNDARY DEVELOPMENT.

PW/S STILL ON TRACK TO REACH JUST UNDER 2 INCHES SO HVY RAIN HAS
BEEN INCLUDED IN THE FCST. SEE HYDRO SECTION FOR ADDITIONAL INFO.

MODERATE RIP RISK TODAY. THREAT HIGHEST IN THE AFTN AND EVE.

NW WINDS BEHIND THE FRONT TONIGHT. BOUNDARY LOOKS TO CLEAR THE CWA
BY 12Z MON.

http://forecast.weather.gov/product.php?si...p;highlight=off

[Dave12308]

After a long, severe weather-free summer; I am really hoping we get something decent out of this IMBY. And I hope it involves some lightning after dark this evening.

[Dave12308]

Hmmm, TWC's hour-by-hour forecast doesn't show precip coming in until 1:45PM or so; up until then it's "mostly cloudy" - meaning at least SOME sun. The other thing it means is that we won't have a round of non-severe convection come through early and hamper instability. We should have at least some heating. Temps are generally on the rise, as it's sitting at 73 right now, and was 71 last I checked. On the hour-by-hour; the hours of 4, 5, and 6 PM are all inside a red box marked severe, and it just says "strong storms'.

If things go the way they seem to be going, this might be the first time a frontal passage like this hasn't been marred by early convection.

[STEVE392]

NYCSuburbs should go on vacation more often....No more bubble when he's gone. LOL


Im just bustin ya.


But back on top, Bear, DE is about to get hit head on by that cell that just exited Baltimore.

[Undertakerson]

SKEW-T

Look like rock and roll for my region after 1400!

[Dave12308]

SKEW-T

Look like rock and roll for my region after 1400!

How in the world do you read those charts? In other words, what should I be looking for?

[Niyologist]

The Parameters I have here is becoming very intense. I'll post it when it gets really good.

[Dave12308]

Small cell headed right toward me as I write this. See what happens. Shouldn't be much; bad stuff predicted later on this afternoon/evening.

[Niyologist]

There's an intensifying Rotating T-Storm going over me now. The parameters support major intensification and possible supercell activity.

[Niyologist]

Now that cell turned into a Significant Hail Storm.

[Dave12308]

I hope this (not so) little cell that just hit me directly is a predictor of what to expect today. Because, my friends, we just had the overall most impressive storm of the summer. Was strong, not severe; but it contained impressive winds, heavy rain, and some very loud thunder. The cell with the hail core missed me, but what we did get was impressive enough; sort of like the type of weather you'd expect during a tropical storm/depression.

And considering I wasn't expecting anything before noon, it was a nice surprise.


Edit: And, it looks like the sun is coming back out; to make things nice for later on!

This post has been edited by Dave12308: Aug 21 2011, 10:55 AM

[WeatherDudeNYC]

Nice little gift from the weather gods with this pop up storm. A big heavy down pour and no wind.

[phillyfan]

Severe Thunderstorm Watch Likely to be issued soon:

MESOSCALE DISCUSSION 2030
NWS STORM PREDICTION CENTER NORMAN OK
1054 AM CDT SUN AUG 21 2011

AREAS AFFECTED...PARTS OF NRN VA...THE DELMARVA...SRN AND ERN
PA...NJ...INTO THE LWR HUDSON VALLEY

CONCERNING...SEVERE POTENTIAL...WATCH LIKELY

VALID 211554Z - 211800Z

TRENDS ARE BEING MONITORED FOR AN INCREASING SEVERE THREAT THAT
COULD REQUIRE ONE OR MORE WATCHES DURING THE 17-19Z TIME FRAME.

BENEATH DIFLUENT UPPER FLOW DOWNSTREAM OF A VIGOROUS SHORT WAVE
TROUGH NOW TURNING EASTWARD THROUGH THE GREAT LAKES REGION...
SCATTERED THUNDERSTORM ACTIVITY IS ONGOING THROUGH MUCH OF THE
NORTHEAST. ASSOCIATED CLOUD COVER AND PRECIPITATION ARE SLOWING
BOUNDARY LAYER DESTABILIZATION IN BROAD POCKETS...COMPLICATING THE
SEVERE WEATHER POTENTIAL...WITH SOUTHWESTERLY DEEP LAYER MEAN FLOW
AND SHEAR STILL SOMEWHAT MODEST ACROSS MUCH OF THE REGION.

IT DOES APPEAR ONE AREA OF FORCING FOR ASCENT ASSOCIATED WITH A
SMALLER SCALE IMPULSE/WEAK AREA OF MID-LEVEL HEIGHT FALLS IS
BEGINNING TO SHIFT EAST NORTHEAST OF THE CENTRAL APPALACHIANS. THIS
COULD SUPPORT INCREASING STORM DEVELOPMENT WITHIN THE NEXT FEW HOURS
ACROSS NORTHERN VIRGINIA INTO PARTS OF SOUTH CENTRAL/ SOUTHEAST
PENNSYLVANIA...WHERE STRONGEST SURFACE HEATING IS OCCURRING. LATEST
RUC GUIDANCE SUGGESTS INHIBITION FOR MOIST BOUNDARY LAYER PARCELS
CHARACTERIZED BY 70F+ SURFACE DEW POINTS IS DIMINISHING...AND MIXED
LAYER CAPE COULD EXCEED 2000 J/KG TOWARD THE 18-20Z.

THEREAFTER...THE SEVERE WEATHER POTENTIAL...INCLUDING THE RISK FOR
ISOLATED SUPERCELLS AND ORGANIZED STORM CLUSTERS...APPEARS LIKELY TO
GRADUALLY INCREASE THROUGH THE REMAINDER OF THE AFTERNOON. THIS
PROBABLY WILL INCLUDE AREAS FROM THE LEE OF THE LOWER GREAT LAKES
EASTWARD INTO NEW ENGLAND...BUT IT REMAINS UNCLEAR WHETHER THE
THREAT WILL BECOME WIDESPREAD...OR REMAIN RELATIVELY LOCALIZED
ACROSS THESE AREAS.

[STEVE392]

Now that cell turned into a Significant Hail Storm.

that cell opened up its flood gates and just dumped buckets of rain on eastern bergen county from the bergen/hudson county border and then right to you in the BX.

[Dave12308]

Another cell trying to fire up along the same path the last one took. The cells to the north of me are training, looks like our batch of cells is trying to copy them.

Not only have I already seen my best storm this season, it's beginning to look like this will be the first day this year that mutiple cells go through my area. And we're not even in the thick of it yet.

[stilko4]

idk but i have afeeling this wont be a big event for li

[Dave12308]

This cell not as intense as the last, as it lacks wind. However, lightning and thunder is more impressive. The thunder sounds like those nuclear explosions they show in those bomb test documentaries on TV.

Rain coming down REAL hard.

[STEVE392]

This cell not as intense as the last, as it lacks wind. However, lightning and thunder is more impressive. The thunder sounds like those nuclear explosions they show in those bomb test documentaries on TV.

Rain coming down REAL hard.

it looks like the storm is just sitting on top of your area and developing even more.

[Dave12308]

it looks like the storm is just sitting on top of your area and developing even more.

It came in as a moderate rain shower, and just exploded into a blossom of red on radar. It looked like it was weakening as it came in, and then BAM! I just came inside from watching it rain harder than I can remember in recent memory. And the thunder was crazy. This has already been an awesome day for me after the way the entire summer was going storm wise. And according to the forecasts, the bad stuff isn't even here yet; this is only round one.

The Schenectady, NY anti-storm bubble has burst today; in a dramatic fashion. It is now raining down on us, hard.

Edit: And it didn't have any gust front to it, probably because it developed out of nowhere. There was essentially no wind during the entire storm. Looks like it's clearing up a bit now, as the sun is shining through the clouds. Which just helps things out for late this afternoon into this evening.

This post has been edited by Dave12308: Aug 21 2011, 11:44 AM

[phillyfan]

Watch Issued now:

SEVERE THUNDERSTORM WATCH OUTLINE UPDATE FOR WS 794
NWS STORM PREDICTION CENTER NORMAN OK
1255 PM EDT SUN AUG 21 2011

SEVERE THUNDERSTORM WATCH 794 IS IN EFFECT UNTIL 900 PM EDT
FOR THE FOLLOWING LOCATIONS

PAC001-009-011-013-017-021-025-027-029-033-035-037-041-043-045-
055-057-061-067-071-075-077-081-087-089-091-093-095-097-099-101-
107-109-111-113-119-133-220100-
/O.NEW.KWNS.SV.A.0794.110821T1655Z-110822T0100Z/

PA
. PENNSYLVANIA COUNTIES INCLUDED ARE

ADAMS BEDFORD BERKS
BLAIR BUCKS CAMBRIA
CARBON CENTRE CHESTER
CLEARFIELD CLINTON COLUMBIA
CUMBERLAND DAUPHIN DELAWARE
FRANKLIN FULTON HUNTINGDON
JUNIATA LANCASTER LEBANON
LEHIGH LYCOMING MIFFLIN
MONROE MONTGOMERY MONTOUR
NORTHAMPTON NORTHUMBERLAND PERRY
PHILADELPHIA SCHUYLKILL SNYDER
SOMERSET SULLIVAN UNION
YORK