July 20-22 MidAtl/NE Severe Weather, SPC Risk Level: Moderate - Forecasts & OBS Options

[WeatherDudeNYC]

The gfs has been showing these 3 days to have high cape with high LI and some shear( some is better than none lol)

Here are the cape values

This post has been edited by jdrenken: Jul 19 2010, 02:11 PM

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[NYCSuburbs]

Upton seems to be expecting strong/severe storms for Tuesday night as they mention a MCS moving into the area (Source).

Tuesday Night: A chance of showers and thunderstorms, mainly between 8pm and 2am. Some of the storms could produce gusty winds and heavy rain. Mostly cloudy, with a low around 72. South wind at 5 mph becoming northwest. Chance of precipitation is 40%.

[NYCSuburbs]

I'm surprised there's no activity in this thread... a MCS is expected for parts of the Mid Atlantic/NE tomorrow, and while there is uncertainty on what areas it affects, ranging from central NY/New England to the northern/central Mid Atlantic, SPC included a slight risk for the southern end of that range. Most of tomorrow's reports should likely be wind reports.

...CNTRL PLNS TO OH VLY...
SHORTWAVE IMPULSE OVER ERN SD/NEB SHOULD SUPPORT MCS
DEVELOPMENT/MAINTENANCE TONIGHT OVER IA/MO. THE CONVECTIVE SYSTEM
SHOULD TRACK ESE TO SE INTO IL/IND/OH AND NRN KY BY 12Z TUE. THE
SYSTEM MAY PRODUCE AN MCV THAT...GIVEN EXPECTED PRESENCE OF HIGH
PW...MODERATE SFC HEATING...AND MODERATE UNIDIRECTIONAL WLY
FLOW...MAY FOSTER STORM REJUVENATION/INTENSIFICATION OVER PARTS OF
PA/MD/WV TUE AFTN...WITH AN ATTENDANT THREAT FOR DMGG WINDS.

Source

In addition, SPC has a slight risk for Wednesday in western PA/WV, also in this thread's time frame.

[windman]

The outlook looks promising, but the models are not showing even a bit of LI or CAPE for tomorrow... I can't see how we can get much of anything without at least marginal instability. I'm thinking Wednesday will easily be the better day.

[phillyfan]

I'm surprised there's no activity in this thread... a MCS is expected for parts of the Mid Atlantic/NE tomorrow, and while there is uncertainty on what areas it affects, ranging from central NY/New England to the northern/central Mid Atlantic, SPC included a slight risk for the southern end of that range. Most of tomorrow's reports should likely be wind reports.


Source

In addition, SPC has a slight risk for Wednesday in western PA/WV, also in this thread's time frame.

Any idea when the MCS will occur?

I hope it comes here cause I could use the rain to help fill the pool up.

[NYCSuburbs]

Any idea when the MCS will occur?

I hope it comes here cause I could use the rain to help fill the pool up.

The timing is uncertain, but Mt. Holly IMO gives a good explanation of their thoughts on this event, also expecting most of it to stay to your north:

IT WOULD APPEARS AS THOUGH THE BEST OF THE WARM AIR ADVECTION WILL
OCCUR TUESDAY NIGHT. THE LOW TO MID LEVEL WARM AIR ADVECTION WILL
FOCUS ITSELF ON A WEAK WARM FRONT CROSSING THE SOUTHERN TIER OF NEW
YORK STATE AND NORTHWEST NEW JERSEY. PRECIPITABLE WATER VALUES SURGE
TO OVER 2 INCHES IN THIS AREA FOR TUESDAY NIGHT...AND LOCALLY HEAVY
RAINFALL IS POSSIBLE WITH ANY CONVECTION THAT DEVELOPS TUESDAY
NIGHT. WILL NOT ADD ANY ENHANCED WORDING AT THIS DISTANCE...BUT
LATER FORECASTS MAY HAVE TO INCLUDE THE MENTION.

TIMING WOULD PLACE THE BEST CHANCE OF CONVECTION ACROSS THE
NORTHERN AREAS BETWEEN 0900 UTC AND 1200 UTC WEDNESDAY. WILL INCLUDE
THE MENTION OF THUNDER TUESDAY NIGHT IN ALL AREAS...SINCE MODEL
SOUNDINGS INDICATED ELEVATED INSTABILITY...WITH THE BEST CHANCE
ACROSS NORTHERN AREAS.

IT WOULD APPEAR AS THOUGH THE BEST LOW TO MID LEVEL MOISTURE COULD
BE SCOURED IN THE WARM AIR ADVECTION PROCESS LATE TUESDAY NIGHT AND
WEDNESDAY MORNING. IF THIS IS INDEED THE CASE...THIS WOULD CUT DOWN
ON THE CONVECTIVE POTENTIAL FOR WEDNESDAY. A WEAK SHORT WAVE PASSES
IN IN THE MID LEVELS DURING THE AFTERNOON...WITH THE LOWER LEVEL
THERMAL FIELDS SUGGESTING A WEAK COLD FRONTAL PASSAGE AFTER 2100
UTC.

Source

[windman]

The timing is uncertain, but Mt. Holly IMO gives a good explanation of their thoughts on this event, also expecting most of it to stay to your north:
Source

Wow thats interesting... The way those MCS's always have that SEward trajectory I would think it would stay to the south of our area. Also, coming through at 09-12z is not the best time for anything severe... Would probably be more of a heavy rain threat than anything. Then again, we could get lucky and have what happened this morning...

[Removed_Member_OHweather2_*]

Here is the MLWX severe weather outlook for Tuesday...look out Snowshoe...

Categorical risk area(s):


Tornado probabilities:


Large hail probabilities:


Damaging wind probabilities:


Discussion:

The is a slight risk for severe storms from central OH/southern PA/western MD points south…

At the start of the period…ongoing convection (a potential MCS) is expected to be ongoing over parts of west-central/southwest OH with a weak wave of low pressure riding along a quasi-stationary front. This wave of low pressure is extected to track east (potentially slightly south of east) through far northern WV/extreme SW PA into far northern VA during the afternoon into the evening…with the MCS likely tracking ESE along the warm front and near the low through the day.

The MCS will be riding along a developing instability gradient due to a front in the vicinity…south of the front, the airmass will be characterized by dew points in the lower 70s and MLCAPEs in excess of 2000 J/KG, and shearing along and just south of the front will be on the order of 30-40 knots (similar greater north of front, but this will be displaced from best instability). This should allow for either the MCS to strengthen by early afternoon, or for outflow boundaries it leaves behind to fire new storms, depending on if the MCS stays somewhat organized or not. We believe enough shear and instability exist from about the Apps west for some scattered wind reports out of this MCS during the early to mid afternoon as it moves over SE OH, WV, SW PA, and western VA, and thus will introduce a 15% risk for damaging winds here. East of the Apps, shear remains modest at 30 or so knots, but instability drops off, so will lower wind probabilities to 5% east of the Apps in VA/MD/extreme S. PA, as we believe the MCS will be in a weakening phase by that point. In addition to wind…with over 2000 J/KG of MLCAPE and decent shear, an isolated large hail threat appears possible with the stronger storms over the Virginias/western MD/southern PA, so will introduce minimal (5%) hail probs here to accommodate for this threat. Also, with the front being near by and a weak wave of low pressure on it, believe enough low level turning on top of 30-40 knots of bulk shear will exist in tandem with moderate instability for the potential to exist for a couple weak/brief tornadoes to develop across southern OH, N. KY into the Virginias/southern PA with this MCS from the late morning into the mid afternoon as it moves through the region, so will add a broad 2% tornado risk area to cover this. Will again cut probs east of the Apps due to instability dropping off.

By evening, the front will be located from central OH into extreme N. WV/VA, with another wave and mid level speed max moving towards OH from the west. For this reason, extended 15% wind, 5% hail, and 2% tornado probabilities west along the front all the way through Ohio, as conditions upstream appear favorable for strong to potentially severe activity to develop/moving into OH overnight, and eventually approach western PA.

Another area for potential strong to locally severe storms exists over a small portion of southern/eastern New England ahead of a weak cold front. This front will move into locally 1000 J/KG of MLCAPE and be in a strongly sheared environment, with 40+ knot of bulk shear being present. Due to the shear and modest instability, believe fast storm motions and potential formation of storms into small line segments could support isolated damaging wind gusts across the region, and will accordingly introduce 5% wind probabilities. Due to rather weak instability, will not add any hail probs at this time.

[WeatherDudeNYC]

Here is our little rain maker

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[phillyfan]

Here is our little rain maker

Got that knocking on my door step

[WeatherDudeNYC]

Here is our little rain maker

Update: Looks like the rain is splitting

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[LoganTyler]

Will just start by saying that NONE of the models have a good handle on the current non-severe upstream MCS over the IL / MO / KY vicinity. Currently extrapolation would take this feature over the Southern portions of our outlook area, and this was something last night's 0z models were noticeably off on as for as placement goes. There is expected to be a rejuvenation in the intensity with this upstream MCS later this Afternoon into this Evening as supporting perameters downwind across Eastern KY / Southern WV / Southern VA continue to increase with normal diurnal processes.

As such, will be amending the Slight Risk placement and pull it a bit to the south to include the corridor from Eastern KY / Southern WV / Southern VA. Other 5% probabilities will be re-aligned accordingly.

EDIT: The newly released SPC 1630z Update looks nearly spot on for 15% Wind / Slight Risk placement from previous outlooks.

This post has been edited by LoganTyler: Jul 20 2010, 11:27 AM

[rapidsingleflux]

Here is our little rain maker

Or not?

[NYCSuburbs]

Latest radar loop really doesn't look impressive. Only areas of notable rain should be in the Hudson Valley (which was also flooded yesterday) into central CT, and for SE PA into northeastern Maryland, northern Delaware and S NJ.

Today's not looking like a very good day for widespread severe weather, but tomorrow could be much better, especially if the GFS verifies, which has good CAPE/LI, lapse rates and wind shear. The NAM, however, is completely horrible for severe weather chances, with much lower CAPE/LI, and it has less activity than the GFS.



This post has been edited by NYCSuburbs: Jul 20 2010, 12:15 PM

[LoganTyler]

Discussion:

The is a slight risk for severe storms from central OH/southern PA/western MD points south…

At the start of the period…ongoing convection (a potential MCS) is expected to be ongoing over parts of west-central/southwest OH with a weak wave of low pressure riding along a quasi-stationary front. This wave of low pressure is extected to track east (potentially slightly south of east) through far northern WV/extreme SW PA into far northern VA during the afternoon into the evening…with the MCS likely tracking ESE along the warm front and near the low through the day.

The MCS will be riding along a developing instability gradient due to a front in the vicinity…south of the front, the airmass will be characterized by dew points in the lower 70s and MLCAPEs in excess of 2000 J/KG, and shearing along and just south of the front will be on the order of 30-40 knots (similar greater north of front, but this will be displaced from best instability). This should allow for either the MCS to strengthen by early afternoon, or for outflow boundaries it leaves behind to fire new storms, depending on if the MCS stays somewhat organized or not. We believe enough shear and instability exist from about the Apps west for some scattered wind reports out of this MCS during the early to mid afternoon as it moves over SE OH, WV, SW PA, and western VA, and thus will introduce a 15% risk for damaging winds here. East of the Apps, shear remains modest at 30 or so knots, but instability drops off, so will lower wind probabilities to 5% east of the Apps in VA/MD/extreme S. PA, as we believe the MCS will be in a weakening phase by that point. In addition to wind…with over 2000 J/KG of MLCAPE and decent shear, an isolated large hail threat appears possible with the stronger storms over the Virginias/western MD/southern PA, so will introduce minimal (5%) hail probs here to accommodate for this threat. Also, with the front being near by and a weak wave of low pressure on it, believe enough low level turning on top of 30-40 knots of bulk shear will exist in tandem with moderate instability for the potential to exist for a couple weak/brief tornadoes to develop across southern OH, N. KY into the Virginias/southern PA with this MCS from the late morning into the mid afternoon as it moves through the region, so will add a broad 2% tornado risk area to cover this. Will again cut probs east of the Apps due to instability dropping off.

By evening, the front will be located from central OH into extreme N. WV/VA, with another wave and mid level speed max moving towards OH from the west. For this reason, extended 15% wind, 5% hail, and 2% tornado probabilities west along the front all the way through Ohio, as conditions upstream appear favorable for strong to potentially severe activity to develop/moving into OH overnight, and eventually approach western PA.

Another area for potential strong to locally severe storms exists over a small portion of southern/eastern New England ahead of a weak cold front. This front will move into locally 1000 J/KG of MLCAPE and be in a strongly sheared environment, with 40+ knot of bulk shear being present. Due to the shear and modest instability, believe fast storm motions and potential formation of storms into small line segments could support isolated damaging wind gusts across the region, and will accordingly introduce 5% wind probabilities. Due to rather weak instability, will not add any hail probs at this time.

Will just start by saying that NONE of the models have a good handle on the current non-severe upstream MCS over the IL / MO / KY vicinity. Currently extrapolation would take this feature over the Southern portions of our outlook area, and this was something last night's 0z models were noticeably off on as for as placement goes. There is expected to be a rejuvenation in the intensity with this upstream MCS later this Afternoon into this Evening as supporting perameters downwind across Eastern KY / Southern WV / Southern VA continue to increase with normal diurnal processes.

As such, will be amending the Slight Risk placement and pull it a bit to the south to include the corridor from Eastern KY / Southern WV / Southern VA. Other 5% probabilities will be re-aligned accordingly.

EDIT: The newly released SPC 1630z Update looks nearly spot on for 15% Wind / Slight Risk placement from previous outlooks.

Couple brief updates…

1) As mentioned, re-aligned the previous Slight Risk accordingly per this Mornings nowcast observations combined with short-term model forecasts. Last night’s 0z runs were off somewhat with placement of important mesoscale features, which will impact how the rest of the day’s events play out, and thus, an update was needed. Scattered strong storms have initiated along weak surface boundary over the southwest… aided by high terrain orographic lift. These storms will pose risk for damaging winds and isolated severe hail (mainly to either side of the Appalachians) as they translate eastward across the Virginia’s thru the Afternoon into the Evening.

2) Also kept, but tweaked the low 2% tornado probability according to latest and future placement of stationary / to-be retreating warm front across the central Mid-Atlantic per latest short-term model forecasts. This threat is somewhat conditional upon instability and discrete storm initiation along this feature, so this is more of a ‘just-to-be-safe’ strategy as helicity values are indicative of a low 2% probability IOO.

This also includes Eastern Virginia vicinity ahead of pre-frontal surface front where RUC indicating some moderate helicity values developing later on with associated storm activity in the area.

3) Axed the 5% wind over New England as instability should keep the threat below severe limits.






This post has been edited by LoganTyler: Jul 20 2010, 12:41 PM

[yankees]

Updated SPC Day 2 Outlook

SPC AC 201728

DAY 2 CONVECTIVE OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1228 PM CDT TUE JUL 20 2010

VALID 211200Z - 221200Z

...THERE IS A SLGT RISK OF SVR TSTMS FROM THE NRN HI PLNS THROUGH
THE CNTRL PLNS/MID MS VLY INTO THE OH VLY/NORTHEAST...

...SYNOPSIS...
SRN STATES RIDGE EXPECTED TO SHIFT SLIGHTLY E AND BECOME CENTERED
OVER THE LWR MS VLY DURING THE NEXT 36-48 HRS...S AND E OF TROUGH
NOW BEGINNING TO AMPLIFY OVER THE PACIFIC NORTHWEST. THE TROUGH
LIKELY WILL EJECT ENE ACROSS NRN RCKYS LATER WED AS UPSTREAM JET
STREAK NOW OVER THE ALEUTIANS CONTINUES SE INTO BC. FARTHER E...UPR
VORT COMPLEX NOW OVER SRN SK/ERN MT SHOULD REACH THE UPR GRT LKS
EARLY IN THE PERIOD. THE TROUGH MAY SOMEWHAT AMPLIFY AS IT
CONTINUES E BEYOND UPR RIDGE AXIS INTO NY/NEW ENGLAND LATER
WED/EARLY THU.

THE DISTURBANCES MENTIONED ABOVE WILL TO A LARGE EXTENT MODULATE
TSTM/MCS ACTIVITY IN THE SLIGHT RISK AREA THROUGH THE PERIOD. BUT
DEVELOPMENT ALSO WILL BE IMPACTED BY THE PRESENCE OF
CONVECTIVELY-INDUCED VORTS IMMEDIATELY S OF THE STRONGER BAND OF
WLYS...AND BY THE DIURNAL CYCLE OF THE LLJ.

...MT/WY SE INTO CNTRL PLNS/MID MS VLY...
NOCTURNALLY-ENHANCED SWLY LLJ LIKELY WILL SUPPORT ANOTHER ROUND OF
OVERNIGHT CONVECTIVE CLUSTERS ALONG THE SRN FRINGE OF THE WLYS.
THESE SYSTEMS...LIKELY IN A WEAKENED STATE...SHOULD EXTEND FROM THE
LWR MO VLY ESE TO THE CNTRL APPALACHIANS AT 12Z WED.

SFC HEATING ALONG CONVECTIVE OUTFLOW...AND WEAK BUT STRENGTHENING
UPSLOPE FLOW SHOULD SUPPORT NEW STORM DEVELOPMENT OVER ERN WY/NE CO
ESE INTO SRN NEB/NRN KS BY LATE AFTN. COMBINATION OF 35-40 KT DEEP
WSWLY SHEAR WITH A SIZABLE DIRECTIONAL COMPONENT AND SBCAPE TO 2000
J/KG SHOULD SUPPORT A FEW SUPERCELLS WITH LARGE HAIL AND POSSIBLY A
COUPLE TORNADOES. THE STORMS LIKELY WILL MERGE INTO ONE OR TWO
OVERNIGHT MCSS THAT MOVE ESEWD AS LLJ/ASCENT STRENGTHEN DOWNSTREAM
FROM EJECTING UPR TROUGH.

FARTHER NW...LOW LVL MOISTURE WILL CONTINUE TO SPREAD NW ACROSS THE
NRN HI PLNS BETWEEN NOW AND WED AHEAD OF AMPLIFYING UPR TROUGH.
COUPLED WITH STRONG HEATING...UPSLOPE FLOW...AND SEASONABLY STRONG
ASCENT BENEATH DEVELOPING UPR JET ENTRANCE REGION...SETUP SHOULD
SUPPORT ISOLD TO SCTD SUPERCELL DEVELOPMENT BY MID/LATE AFTN. THESE
WILL BE CAPABLE OF LARGE HAIL...DMGG WINDS...AND POSSIBLY A COUPLE
TORNADOES...DESPITE MORE LIMITED MOISTURE AVAILABILITY RELATIVE
POINTS FARTHER S. CONTINUED EWD MOVEMENT OF UPR TROUGH AND 50 KT
DEEP WSWLY SHEAR SUGGEST THAT THE STORMS WILL CONSOLIDATE INTO A
STRONG...ESE-MOVING MCS. THIS COULD EXTEND THE SVR THREAT INTO THE
WRN DAKOTAS BY EARLY THU.

...OH VLY INTO NERN STATES...
DEEP/LARGELY UNIDIRECTIONAL WLY FLOW...AND ASCENT...WILL INCREASE
OVER THE UPR OH VLY AND NERN STATES ON WED AS AFOREMENTIONED UPR
TROUGH AMPLIFIES ESE FROM THE UPR GRT LKS. WITH 500 MB WLY FLOW
EXPECTED TO BE AROUND 50 KTS ACROSS PA/NJ AND NY...AMPLE SHEAR WILL
BE PRESENT FOR SUSTAINED STORMS WITH BOWING SEGMENTS AND SUPERCELLS.
LOW LVL DESTABILIZATION IS THE MAIN UNCERTAINTY AS FAR AS SVR
POTENTIAL IS CONCERNED...GIVEN LIKELIHOOD FOR ONGOING STORM
CLUSTERS/CLOUD DEBRIS IN THE OH VLY AT THE START OF THE PERIOD. IT
DOES SEEM LIKELY...NEVERTHELESS...THAT AT LEAST A FEW POCKETS OF
STRONGER SFC HEATING WILL DEVELOP BENEATH THE STRENGTHENING UPR
FLOW/ASCENT...ESPECIALLY FROM ERN NY/WRN NEW ENGLAND SSW INTO ERN
PA/NJ AND PERHAPS MD/DE. SOME OF THESE STORMS COULD PERSIST INTO
WED NIGHT.

..CORFIDI.. 07/20/2010

CLICK TO GET WUUS02 PTSDY2 PRODUCT

NOTE: THE NEXT DAY 2 OUTLOOK IS SCHEDULED BY 0600Z
CURRENT UTC TIME: 1732Z (1:32PM), RELOAD THIS PAGE TO UPDATE THE TIME

http://www.spc.noaa.gov/products/outlook/day2otlk.html

This post has been edited by yankees: Jul 20 2010, 12:40 PM

[NYCSuburbs]

Updated SPC Day 2 Outlook






http://www.spc.noaa.gov/products/outlook/day2otlk.html

If the GFS verifies, a 30% risk may very well be possible for parts of the Mid Atlantic/NE tomorrow, especially with supportive shear and lapse rates. It will be interesting to see what happens with tomorrow's update...

[yankees]

If the GFS verifies, a 30% risk may very well be possible for parts of the Mid Atlantic/NE tomorrow, especially with supportive shear and lapse rates. It will be interesting to see what happens with tomorrow's update...

Agreed 60-70 knot shear and cape up to 3000 in the 30 percent risk area on GFS. NAM has similar shear but lower cape. So we can assume that this will be a high shear event just cape seems a little bit uncertain.

[NYCSuburbs]

Agreed 60-70 knot shear and cape up to 3000 in the 30 percent risk area on GFS. NAM has similar shear but lower cape. So we can assume that this will be a high shear event just cape seems a little bit uncertain.

The NAM was also much lower with the CAPE during the other events, so that may also be the case tomorrow. The next few runs of the GFS and NAM will be interesting to see.

[STEVE392]

Long time looker, first time poster.

Was watching the rain approach using the NWS site at work, got me excited to see some tstorms brewing but everything dried out as it approached northern nj. is there any potential for some more storms this evening?