Heavy Rain and T-storm threat Mid Week

[Dark Energy]

From my discussion this AM on the nyc metro weather blog. This will have to be watched.

The main show looks like it is on WED. The southern part of the deep trof swings up this way and goes negatively tilted. This will form a wave of low pressure on the incoming front. When this happens, it usually slows the front down. A very mild air mass will be in place with increasing humidity ahead of the front. Highs could get over 60F in this setup. I put in for scattered t-storms given the -tilted upper trof. They usually lead to some convection, but i will note that the forecast soundings as of now are stable. With such strong winds aloft over the area, any storms can mix down those winds so we will have to keep an eye on a damaging wind threat if the convection is realized. Heavy rain is possible as a strong low level jet over 60 knots comes in and precipitable water values shoot up to 1.5 inches. I went with likely (60%) pops. Kind of unusual to go that high this far out but the ensembles are very supportive of the other guidance so it was warranted. The only thing that may go wrong here is if the front slows down further due to the frontal wave. If that happens then the rain may be delayed bit.

http://nymetrowx.blo...discussion.html

[bluewave]

Great thread.With good blocking to our NE, it looks like the front will really slow down with a wave of low pressure developing near our region as the trough goes negative tilt.

The potential for heavy rains is there in addition to the threat of strong winds being brought down during the heavier downpours as the really strong LLJ moves overhead.

[NYCSuburbs]

Wednesday looks like a very interesting day... a slow moving cold front with a lot of moisture and a wave of low pressure forming and enhancing the rainfall as it becomes negatively tilted, leading to a heavy wind-driven rain. Temperatures look like they should warm up on Tuesday night as the warm air mass moves in ahead of the rain with 850 mb temps rising above 10c, peaking on Wednesday in the lower 60s, followed by the heavy rain and wind in the second half of the day. While it looks like the heaviest rain will fall in PA/NY, heavy rain should still fall in NJ and may approach/pass 2 inches with the high precipitable water values.

[Dark Energy]

Upton starting to pick up on the idea in this afternoon diso.

IN TERMS OF SENSIBLE WEATHER...GOOD MODEL AGREEMENT WITH STRONG LOW

PRESSURE TRACKING TOWARDS HUDSON BAY TUESDAY NIGHT AHEAD OF

STRONG UPPER TROUGH ENERGY. ITS ASSOCIATED COLD FRONT WILL WORK

TOWARDS THE COAST WED WITH WAVE DEVELOPMENT ALONG IT...PUSHING

EAST OF THE REGION WED NIGHT. RETURN FLOW STRENGTHENS TUESDAY

NIGHT AHEAD OF APPROACHING TROUGH AND FRONTAL SYSTEM...WITH

INCREASING CHANCE FOR RAIN FROM W TO E. BEST MODEL/ENSEMBLE

CONSENSUS OVER SEVERAL RUNS HAS BEEN FOR RAIN ON WED AS

TROUGH/FRONTAL SYSTEM APPROACH THE COAST...SO HAVE PROCEEDED WITH

CAT/HIGH LIKELY POPS FOR THIS TIME PERIOD. AN AXIS OF HEAVY

RAINFALL POSSIBLE WITH LONGITUDINALLY DEEP TROUGH TAPPING INTO

GULF MOISTURE DURING THIS TIME. IN ADDITION...MODELS ARE POINTING

TOWARDS A STRONG LLJ (80+KT) AHEAD OF THE COLD FRONT BRINGING THE

POSSIBILITY OF A PERIOD OF WIND ADVISORY WINDS OR WITH THE STRONG

DYNAMICS A LOW END SEVERE THREAT IN THE FORM OF A FINE LINE OF

HEAVY SHRA/ISOL TSRA AHEAD OF COLD FRONT. THIS WILL HAVE TO BE

FURTHER EVALUATED AS THE EVENT NEARS. TEMPS ARE EXPECTED TO BE

WELL ABOVE NORMAL IN THE ANOMALOUS SETUP...WITH LOWS TUES NIGHT IN

THE VICINITY OF NORMAL HIGHS FOR THIS TIME OF YEAR...AND MAX TEMPS

LIKELY WELL INTO THE 50S TO POSSIBLY LOWER 60S ON WED.

[MGorse]

Upton starting to pick up on the idea in this afternoon diso.

So is Mount Holly.

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...

THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN AMPLIFIED RIDGE

CONTINUING TO SHIFT OFF THE EAST COAST TUESDAY NIGHT. THIS IS IN

RESPONSE TO A HIGHLY AMPLIFIED TROUGH ACROSS THE CENTRAL UNITED

STATES THAT WILL BE MOVING EASTWARD AND DRIVING A STRONG COLD

FRONT ACROSS OUR AREA WEDNESDAY. THE MODEL GUIDANCE CONTINUES TO

BE IN GOOD AGREEMENT OVERALL ON THE EVOLUTION OF THE PATTERN AND

EVEN THE TIMING OF THE COLD FRONTAL PASSAGE. OF COURSE FARTHER OUT

IN TIME, THERE IS MORE UNCERTAINTY WITH THE DETAILS. HPC WENT WITH

A BLEND OF THE ECMWF ENSEMBLE MEAN AND THE GFS ENSEMBLE MEAN. WE

INITIALIZED THE DATABASE WITH HPC GUIDANCE BUT THEN MADE SOME

ADJUSTMENTS AFTER ADDITIONAL COLLABORATION.

BASED ON THE ABOVE, A SURFACE LOW WILL BE LIFTING NORTHEASTWARD

TO NEAR JAMES BAY WEDNESDAY MORNING. A HIGHLY AMPLIFIED TROUGH

WILL DRIVE ITS ASSOCIATED COLD FRONT EASTWARD AND ACROSS OUR AREA

WEDNESDAY. THERE IS AMPLE MOISTURE FORECAST TO BE ADVECTING

NORTHWARD AHEAD OF THE FRONT AS A DEEP AND STRENGTHENING SOUTHERLY

FLOW REGIME OCCURS. THIS SOUTHERLY FLOW IS FORECAST TO BE NEAR 60

KNOTS AT 925 MB TUESDAY NIGHT AND WEDNESDAY AHEAD OF THE COLD

FRONT. THE 925 MB TEMPERATURES ARE FORECAST TO SURGE TO NEAR +13C

AHEAD OF THE FRONT. THERE MAY BE A TRIPLE POINT MOVING ACROSS A

PORTION OF THE CWA WITH THE DEVELOPMENT OF A WEAK SURFACE LOW.

THIS WILL HAVE AN INFLUENCE ON HOW FAR NORTH THE WARM SECTOR GETS,

BUT GIVEN THE STRONG SOUTHERLY FLOW FORECAST, THE WARM FRONT MAY

END UP LIFTING NORTH OF OUR ENTIRE AREA. A CONCERN IS THE STRONG

SOUTHERLY FLOW MIXING DOWN TO THE SURFACE IN THE WARM SECTOR.

THEREFORE, WE DID INCREASE HPC WINDS UP TUESDAY NIGHT AND

WEDNESDAY MORNING AS THE DEW POINTS ARE FORECAST TO CLIMB INTO THE

50S ACROSS A GOOD PART OF THE CWA. THERE CONTINUES TO BE STRONG

FRONTAL FORCING WITH THIS SYSTEM, THEREFORE A BAND OF MODERATE TO

POSSIBLY HEAVY RAIN SHOULD MOVE THROUGH THE AREA. SOME OF THE

MODEL GUIDANCE IS HINTING AT A LITTLE BIT OF INSTABILITY AHEAD OF

THE FRONT, BUT NOT ENOUGH AT THIS POINT TO INTRODUCE THUNDER. IF

ENOUGH INSTABILITY OCCURS, THERE COULD BE A NARROW CONVECTIVE LINE

/LOW-TOPPED/ AHEAD OF THE COLD FRONT AS THE UPPER TROUGH IS

FORECAST TO TAKE ON A NEGATIVE TILT. WE SLOWED DOWN THE INCREASE

IN POPS FROM WEST TO EAST AS THE FORCING WILL PROBABLY ALLOW FOR

THE BEST LIFT CLOSER TO THE FRONT. THERE IS ENOUGH MODEL CONSENSUS

TO GO WITH LOW END CATEGORICAL POPS FROM WEST TO EAST WITH THE

FRONT.

[CooL]

Great stuff guys - gfs and the canadian are really slowing down the front right before it reaches I-95. Could be a nice 1-3" event for alot of us.

[Sundog]

Good we need the rain. It hasn't been the wettest November ever so let's start off December with a good sized system.

[Dark Energy]

So is Mount Holly.

.LONG TERM /TUESDAY NIGHT THROUGH SATURDAY/...

THE OVERALL SYNOPTIC SETUP IS COMPRISED OF AN AMPLIFIED RIDGE

CONTINUING TO SHIFT OFF THE EAST COAST TUESDAY NIGHT. THIS IS IN

RESPONSE TO A HIGHLY AMPLIFIED TROUGH ACROSS THE CENTRAL UNITED

STATES THAT WILL BE MOVING EASTWARD AND DRIVING A STRONG COLD

FRONT ACROSS OUR AREA WEDNESDAY. THE MODEL GUIDANCE CONTINUES TO

BE IN GOOD AGREEMENT OVERALL ON THE EVOLUTION OF THE PATTERN AND

EVEN THE TIMING OF THE COLD FRONTAL PASSAGE. OF COURSE FARTHER OUT

IN TIME, THERE IS MORE UNCERTAINTY WITH THE DETAILS. HPC WENT WITH

A BLEND OF THE ECMWF ENSEMBLE MEAN AND THE GFS ENSEMBLE MEAN. WE

INITIALIZED THE DATABASE WITH HPC GUIDANCE BUT THEN MADE SOME

ADJUSTMENTS AFTER ADDITIONAL COLLABORATION.

BASED ON THE ABOVE, A SURFACE LOW WILL BE LIFTING NORTHEASTWARD

TO NEAR JAMES BAY WEDNESDAY MORNING. A HIGHLY AMPLIFIED TROUGH

WILL DRIVE ITS ASSOCIATED COLD FRONT EASTWARD AND ACROSS OUR AREA

WEDNESDAY. THERE IS AMPLE MOISTURE FORECAST TO BE ADVECTING

NORTHWARD AHEAD OF THE FRONT AS A DEEP AND STRENGTHENING SOUTHERLY

FLOW REGIME OCCURS. THIS SOUTHERLY FLOW IS FORECAST TO BE NEAR 60

KNOTS AT 925 MB TUESDAY NIGHT AND WEDNESDAY AHEAD OF THE COLD

FRONT. THE 925 MB TEMPERATURES ARE FORECAST TO SURGE TO NEAR +13C

AHEAD OF THE FRONT. THERE MAY BE A TRIPLE POINT MOVING ACROSS A

PORTION OF THE CWA WITH THE DEVELOPMENT OF A WEAK SURFACE LOW.

THIS WILL HAVE AN INFLUENCE ON HOW FAR NORTH THE WARM SECTOR GETS,

BUT GIVEN THE STRONG SOUTHERLY FLOW FORECAST, THE WARM FRONT MAY

END UP LIFTING NORTH OF OUR ENTIRE AREA. A CONCERN IS THE STRONG

SOUTHERLY FLOW MIXING DOWN TO THE SURFACE IN THE WARM SECTOR.

THEREFORE, WE DID INCREASE HPC WINDS UP TUESDAY NIGHT AND

WEDNESDAY MORNING AS THE DEW POINTS ARE FORECAST TO CLIMB INTO THE

50S ACROSS A GOOD PART OF THE CWA. THERE CONTINUES TO BE STRONG

FRONTAL FORCING WITH THIS SYSTEM, THEREFORE A BAND OF MODERATE TO

POSSIBLY HEAVY RAIN SHOULD MOVE THROUGH THE AREA. SOME OF THE

MODEL GUIDANCE IS HINTING AT A LITTLE BIT OF INSTABILITY AHEAD OF

THE FRONT, BUT NOT ENOUGH AT THIS POINT TO INTRODUCE THUNDER. IF

ENOUGH INSTABILITY OCCURS, THERE COULD BE A NARROW CONVECTIVE LINE

/LOW-TOPPED/ AHEAD OF THE COLD FRONT AS THE UPPER TROUGH IS

FORECAST TO TAKE ON A NEGATIVE TILT. WE SLOWED DOWN THE INCREASE

IN POPS FROM WEST TO EAST AS THE FORCING WILL PROBABLY ALLOW FOR

THE BEST LIFT CLOSER TO THE FRONT. THERE IS ENOUGH MODEL CONSENSUS

TO GO WITH LOW END CATEGORICAL POPS FROM WEST TO EAST WITH THE

FRONT.

Mike, sorry about that. I first saw the OKX afd and then read the PHI one later on and didn't get to post it. It's good to see everyone is on the same page. Good potential here.

[Dark Energy]

Negative tilted trof is the key here folks. If that holds true. Watch the forcing and radar light up with a fine line. This happened not too long ago and we had 60 mph gusts across the area ovn with warnings galore. It's still early in the game, but potential is there and will be interesting to plot the next couple of days.

[tmagan]

I'm surprised this storm system isn't getting more attention in this subforum, I think this is a really interesting storm system. I still surprised the SPC isn't more bullish with their outlooks.

[earthlight]

I'm surprised this storm system isn't getting more attention in this subforum, I think this is a really interesting storm system. I still surprised the SPC isn't more bullish with their outlooks.

SPC won't be bullish in the long range unless it's a serious, high probability threat. That being said, given the kinematics I would be entirely surprised if they didn't eventually have a Slight Risk area over the Mid Atl/Northeast should the event unfold as modeled.

[weatherwiz]

Made a thread a few nights ago in the SNE subforum regarding this potential.

I agree, could be a pretty fun weather day on Wednesday. The models have been trending to move slower and slower with the cold front, as one might have expected with the trough really becoming negatively tilted, the front becoming parallel to the UL flow and the blocking to the east. I think the slower timing really helps us out some.

With the slower eastward advancement of the cold front this may allow the primary low to also track a bit more to the north and west which would give us a better shot at not only getting into the better part of the warm sector but it also prolongs the time spent in the warm sector, this could mean a period of potentially strong winds alone with mixing going on given how strong the wind fields become aloft.

This system is packed with a ton of forcing and a ton of dynamical support, with some cooling aloft to help generate some weak elevated instability it isn't out of the question we see a forced low-topped line of convection just out ahead of the front with an axis of extremely heavy rainfall out ahead of it.

Then as the front passes strong CAA works in from the NW and this could create a several hour period of some strong winds as well.

[weatherwiz]

SPC won't be bullish in the long range unless it's a serious, high probability threat. That being said, given the kinematics I would be entirely surprised if they didn't eventually have a Slight Risk area over the Mid Atl/Northeast should the event unfold as modeled.

Totally agree.

[weatherwiz]

Looks like the best potential for strongest winds in the WAA out ahead of the cold front could be right across NJ. Here it looks like temperatures will spike into the lower to the middle 60's which could tend to weaken any inversion that will be in place. Then an area of extremely heavy rainfall, possibly with embedded convection works in and given the strength of the LLJ and how close to the sfc some of the winds are it may not take much to draw these closer to the sfc.

[NYCSuburbs]

Upton is catching up with the expected scenario for this event, also showing heavy rain in the forecast. I'm not sure though why they don't mention "Windy" in the forecast for Tuesday night and Wednesday, this has the potential to produce strong winds, and they also have dropping, not rising temperatures on Tuesday night when temperatures should rise as 850 mb temps rise to 10c.

The GFS seems to have backed down from the rain amounts, with its 06z run showing only 1 inch in NYC, though I think it should be higher than that, somewhere between 1 and 2 inches. SPC also doesn't seem to really mention anything about this event, though they usually do that in their Day 4-8 range, and as others said here, I also wouldn't be surprised if they end up adding a slight risk in parts of the Mid Atlantic/NE.

[earthlight]

18z NAM is still pretty robust, although a bit less amplified and a bit cooler at H85

[MGorse]

Negative tilted trof is the key here folks. If that holds true. Watch the forcing and radar light up with a fine line. This happened not too long ago and we had 60 mph gusts across the area ovn with warnings galore. It's still early in the game, but potential is there and will be interesting to plot the next couple of days.

Yeah, I remember that event back on the 17th of this month. I was working the night shift as the narrow squall line raced across the area. This upcoming event still looks interesting.

[Grothar]

Yeah, I remember that event back on the 17th of this month. I was working the night shift as the narrow squall line raced across the area. This upcoming event still looks interesting.

I see a lot of straight line wind damage reports and perhaps calls to your office to investigate F0-F1 possible tornadoes by Wed evening? Will spotters be asked to be on duty Mike?

http://msiegelweatherman.blogspot.com/

[MGorse]

I see a lot of straight line wind damage reports and perhaps calls to your office to investigate F0-F1 possible tornadoes by Wed evening? Will spotters be asked to be on duty Mike?

http://msiegelweatherman.blogspot.com/

Spotters may need to be activated, but it will just depend on the amount of convective elements that can develop. Keep monitoring the forecast and also the hazardous weather outlook.

[NJwinter23]

Why isn't this thread pinned anymore? I know a snow threat Dec. 5th-10th is stealing the show, but this looks like a hell of a cold front coming through still. 12z gfs has a LLJ maxing at 85kts 2pm Wednesday at EWR. 80 kts as low as 925mb, surface pressure at 998mb. Still doesnt look like much instability but the potential remains for a wild frontal passage for our area.

[tmagan]

I'm surprised this storm system isn't getting more attention in this subforum, I think this is a really interesting storm system. I still surprised the SPC isn't more bullish with their outlooks.

Hate to toot my own horn, as I have certainly been wrong in the past, but I thought this was pretty much close to a slam dunk.

[earthlight]

00z NAM has 25-30kt winds at 10m

[phlwx]

Hate to toot my own horn, as I have certainly been wrong in the past, but I thought this was pretty much close to a slam dunk.

it's not snow...if this were a severe snow squall the thread would be pages long.

Anyways, I agree on the wind threat...I would tend to place it anywhere along and southeast of the surface wave (assuming it develops) as it rides the front.

Nice pattern changing front coming in though no matter how you slice it...

[weatherwiz]

This is certainly one helluva potent system but of course since it isn't snow it doesn't get much attention. Looks like sfc temperatures will end up being warmer down in NJ than they will here in SNE so I'd assume that low-level lapse rates will be a bit on the steeper side here...I haven't looked at soundings for this area so I could be wrong but if they are steeper here this will be a HUGE boost with drawing those stronger winds just above the sfc down.

Right now it appears as if any convection will go offshore but some embedded convection can't be ruled out either, or at least some convective elements in extremely heavy pockets of rainfall. While there isn't much in the way of elevated instability to work with there certainly is enough forcing and lift.

Another thing to consider is the pressure gradient that will be developing, you have a deepening sfc low traversing up along the boundary and you have a system offshore, this gradient alone will not only help to maintain and strengthen the LL wind fields but will also act to create windy conditions at the sfc. If sfc temps do get into the middle 60's this as well would certainly help with mixing as well as steepening those LL lapse rates and could make for some fun times wind wise.

[jggearhead]

The wind advisory is up! Who thinks the winds are going to mix down?

[phlwx]

Impressive line setting up in VA that's moving NE along the front...

[bluewave]

Not surprised to see this moved further north this morning.

...ERN NC/SE VA NWD INTO ERN PA/NJ/SERN NY... VERY STRONG WIND FIELD PROFILES WILL EXIST AHEAD OF THE FRONT...AND SFC DEWPOINTS WILL RISE INTO THE MID/UPR 50S NWD INTO DELAWARE VLY OF NJ/ERN PA. SATELLITE TRENDS AND SFC DATA SUGGEST THAT COLD FRONT IS INTENSIFYING ATTM FROM CNTRL MD NWD INTO CNTRL PA...IN ZONE OF STRONG FORCING FOR ASCENT DOWNSTREAM FROM APPROACHING UPR VORT. WHILE AREA SOUNDINGS SHOW LITTLE OR NO CAPE...MOIST ADIABATIC PROFILES MAY SUPPORT DEEPENING CONVECTION AND POSSIBLY A FEW SPOTS OF THUNDER ALONG THE FRONT AS THE FRONTAL CIRCULATION CONTINUES TO STRENGTHEN. GIVEN INTENSITY OF LOW LVL WIND FIELD /60+ KTS AT 1 KM/...ANY MORE SUSTAINED CONVECTION MAY ENHANCE DOWNWARD TRANSPORT OF WINDS AND COULD YIELD A FEW DMGG GUSTS THROUGH ABOUT MIDDAY.

Storm report

0755 AM TSTM WND DMG HARMONY HILL 39.51N 77.40W12/01/2010 FREDERICK MD TRAINED SPOTTER

[Dark Energy]

negatively tilted trofs do it every time. don't bet against them.