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Jan 4th 2018 Fish Bomb

Rjay

By Rjay,
in New York City Metro

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LongBeachSurfFreak

LongBeachSurfFreak

Posted
Posted
1 hour ago, SnoSki14 said:

The models are really trying this morning to make this storm happen. It may just be off hour fluke runs though, the afternoon runs should be the nail in the coffin.

If they don't shift west/trend notably better then the fate of this storm is sealed. 

Come on, “should be the nail in the coffin”?????? You do realize people in the forum live on Long Island right? I thought you finally wanted a storm...

that NAM run would be an extremely dangerous blizzard on the east end. Life threatening. Hurricane fource gusts and snow is a pretty serious situation. Then it only gets worse if power is out over the weekend with temps Near zero

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donsutherland1

donsutherland1

Posted
Posted

The 6z runs provided perhaps some early hints that the guidance may finally be moving slowly toward agreement. The RGEM went east with the snow shield. The 12 km and 3 km NAM went west. These mesoscale models are now in some agreement over a large part of the area (biggest snows over a portion of New England including the Boston Metro Area, potentially the biggest snows in this subforum over Long Island, accumulating snows back to west of New York City). It will be interesting to see if the 12z global models move toward what may be an emerging mesoscale model consensus or if the seemingly emerging mesoscale model agreement falls apart at 12z.

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bluewave

bluewave

Posted
Posted

The whole forecast comes down to getting the convection right later Wednesday near Florida. The Euro and other globals pop the best convection further east of Florida with the LP development. The NAM is currently further west closer to the coast with the convection and LP. This results in a further west track and the southern vort closing off. Convection can be the most poorly forecast part of a storms evolution especially so close to the tropics. So the future forecasts and radar confirmation will tell the tale. 

 

ecmwf_slp_precip_east_8.thumb.png.1d3cd2fac42f8454a0c2f7f5f7593c75.png

nam_precip_mslp_east_13.thumb.png.a13c20d0580353c9169943e28ff800a2.png

 

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tdp146

tdp146

Posted
Posted

Pretty nice summary from Upton of where things currently stand this morning.  

LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
** Accumulating snow expected Wed Night into Thursday **
** Potentially dangerous cold for Friday into Saturday **

Models continue in good agreement with the polar jet digging down
into the SE US Wednesday, following a strong shortwave/jet streak
diving south from the Canadian Plains this morning, and interacting
with a separate vigorous PAC shortwave diving through the southern
plains today. Although there is good agreement in the mass fields,
subtle differences in the timing/location of phasing of the above
shortwave energies as they round the base of the digging trough, as
well as the interaction of the polar trough with the second
shortwave (determining trough tilt), will be key in track/timing of
an explosively developing northward moving southern low on Thursday.

Consensus operational/ensemble track takes a 970-975 mb low, located
about 200 miles east of Cape Hatteras Thursday morning, down to a
955-960 mb low about 100 miles se of the 40/70 benchmark by Thursday
afternoon, and then about 150 mile e/ne of Cape Cod by Thu evening
as a 950-955 mb low. Very impressive deepening! But looking at
GEFS/ECMWF ensemble members there is about a 100 miles radius of
track/timing differences, predicated on the subtle mid-level
differences mentioned earlier. So although there is high confidence
in the explosive strengthening of the low, there is still quite a
bit of wiggle room with how close/far from the coast that the low
tracks. Trend over the last 24 hours has been slightly closer to the
coast.

Taking into account the above uncertainty and an operational and
GEFS/ECMWF ensemble consensus, the probability for at least a light
accumulating snowfall event for the area is high for Wed Night into
Thu Night. Have increased pops to categorical for east of the Hudson
River and likely to the west, based on GEFS/ECWMF ensembles
probs for 1/10th inch QPF over the region late Wed Night into
early Thu Night. Potential for 6 inches of snow has trended
higher over the last 24 hrs for LI/SE CT as well, looking at the
24 hr prob of 1/2 inch qpf. For E LI/SE CT, 00z ECMWF ensembles
indicating 40-50 % chance, while 00Z GEFS 20-30 percent over
eastern LI. Meanwhile, the SREF is very aggressive with QPF,
averaging anywhere from 50 to 80 prob of over 1/2 inch qpf. Of
note, the 06z NAM has shifted close to the 40/70 benchmark with
3/4 to 1 1/4 inches qpf for much of the region, which is within
the spread seen with the SREF/ECMWF ensembles. Meanhwile the 06z
GFS is at the low end if not lower than all the 06z ensemble
members.

So at this point, a good compromise for likely qpf is staying close
to the ECMWF ensemble mean (reflected well in WPC qpf), which is in
between the wetter and typically over-dispersed SREF and the drier
and typically under-dispersed GEFS. This results in 1/4 to 1/2
inch qpf across LI/SE CT, 1/10th to 1/4 inch across NYC/NJ metro
and SW CT, and up to 1/10th to the NW. Based on blend of snow
ratio algorithms and WPC, this points towards a likelihood of 4
to 6 inch snowfall for E LI/SE CT, 2 to 4 inches westward to
the Hudson River, and less than 2 inches to the NW. This is a
fluid situation though based on model spread, with potential for
these numbers to go down, but it seems moreso upwards based on
model trends and mode of SREF/GEFS/ECMWF ensemble members
compared to operational runs. This potential is reflected in
latest WFO/WPC snow probs, with low-moderate prob of greater
than 6 inches of snow across E LI/SE CT, and a 1 in 10 chance of
seeing more than 10-12 inches of snow across the entire area.

The other potential hazard with this storm will be strong winds,
with a blend between GFS/NAM profiles pointing to potential for
30 to 40 mph winds along the coast Thu aft/eve. There is
potential for 45-50 mph gusts for eastern coastal areas, if
closer NAM track and stronger NAM wind field verifies. This
would also lead to blowing and drifting snow and reduced vsby
issues.

Finally, after the storm, the hazard once again becomes the arctic
cold. In fact, this could be the coldest air thus far, with signal
for 850 temps of -25 to -30c into the region for Friday into the
weekend. This would likely have temps struggling to get out of the
single digits to lower teens Fri/Sat, with widespread wind chills of
-10 to -20 degrees early Fri morning, and potentially dangerously
cold wind chills of -15 to -25 degrees Sat morning. Of note, 40-50
mph NW gusts are possible on Friday as well.
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DaveTinNY

DaveTinNY

Posted
Posted
2 minutes ago, tdp146 said:

Pretty nice summary from Upton of where things currently stand this morning.  


LONG TERM /WEDNESDAY NIGHT THROUGH MONDAY/...
** Accumulating snow expected Wed Night into Thursday **
** Potentially dangerous cold for Friday into Saturday **

Models continue in good agreement with the polar jet digging down
into the SE US Wednesday, following a strong shortwave/jet streak
diving south from the Canadian Plains this morning, and interacting
with a separate vigorous PAC shortwave diving through the southern
plains today. Although there is good agreement in the mass fields,
subtle differences in the timing/location of phasing of the above
shortwave energies as they round the base of the digging trough, as
well as the interaction of the polar trough with the second
shortwave (determining trough tilt), will be key in track/timing of
an explosively developing northward moving southern low on Thursday.

Consensus operational/ensemble track takes a 970-975 mb low, located
about 200 miles east of Cape Hatteras Thursday morning, down to a
955-960 mb low about 100 miles se of the 40/70 benchmark by Thursday
afternoon, and then about 150 mile e/ne of Cape Cod by Thu evening
as a 950-955 mb low. Very impressive deepening! But looking at
GEFS/ECMWF ensemble members there is about a 100 miles radius of
track/timing differences, predicated on the subtle mid-level
differences mentioned earlier. So although there is high confidence
in the explosive strengthening of the low, there is still quite a
bit of wiggle room with how close/far from the coast that the low
tracks. Trend over the last 24 hours has been slightly closer to the
coast.

Taking into account the above uncertainty and an operational and
GEFS/ECMWF ensemble consensus, the probability for at least a light
accumulating snowfall event for the area is high for Wed Night into
Thu Night. Have increased pops to categorical for east of the Hudson
River and likely to the west, based on GEFS/ECWMF ensembles
probs for 1/10th inch QPF over the region late Wed Night into
early Thu Night. Potential for 6 inches of snow has trended
higher over the last 24 hrs for LI/SE CT as well, looking at the
24 hr prob of 1/2 inch qpf. For E LI/SE CT, 00z ECMWF ensembles
indicating 40-50 % chance, while 00Z GEFS 20-30 percent over
eastern LI. Meanwhile, the SREF is very aggressive with QPF,
averaging anywhere from 50 to 80 prob of over 1/2 inch qpf. Of
note, the 06z NAM has shifted close to the 40/70 benchmark with
3/4 to 1 1/4 inches qpf for much of the region, which is within
the spread seen with the SREF/ECMWF ensembles. Meanhwile the 06z
GFS is at the low end if not lower than all the 06z ensemble
members.

So at this point, a good compromise for likely qpf is staying close
to the ECMWF ensemble mean (reflected well in WPC qpf), which is in
between the wetter and typically over-dispersed SREF and the drier
and typically under-dispersed GEFS. This results in 1/4 to 1/2
inch qpf across LI/SE CT, 1/10th to 1/4 inch across NYC/NJ metro
and SW CT, and up to 1/10th to the NW. Based on blend of snow
ratio algorithms and WPC, this points towards a likelihood of 4
to 6 inch snowfall for E LI/SE CT, 2 to 4 inches westward to
the Hudson River, and less than 2 inches to the NW. This is a
fluid situation though based on model spread, with potential for
these numbers to go down, but it seems moreso upwards based on
model trends and mode of SREF/GEFS/ECMWF ensemble members
compared to operational runs. This potential is reflected in
latest WFO/WPC snow probs, with low-moderate prob of greater
than 6 inches of snow across E LI/SE CT, and a 1 in 10 chance of
seeing more than 10-12 inches of snow across the entire area.

The other potential hazard with this storm will be strong winds,
with a blend between GFS/NAM profiles pointing to potential for
30 to 40 mph winds along the coast Thu aft/eve. There is
potential for 45-50 mph gusts for eastern coastal areas, if
closer NAM track and stronger NAM wind field verifies. This
would also lead to blowing and drifting snow and reduced vsby
issues.

Finally, after the storm, the hazard once again becomes the arctic
cold. In fact, this could be the coldest air thus far, with signal
for 850 temps of -25 to -30c into the region for Friday into the
weekend. This would likely have temps struggling to get out of the
single digits to lower teens Fri/Sat, with widespread wind chills of
-10 to -20 degrees early Fri morning, and potentially dangerously
cold wind chills of -15 to -25 degrees Sat morning. Of note, 40-50
mph NW gusts are possible on Friday as well.

Me eyes picked up on the 10% chance of 10-12" area wide.  We shall see. 

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jbenedet

jbenedet

Posted
Posted
1 hour ago, bluewave said:

The whole forecast comes down to getting the convection right later Wednesday near Florida. The Euro and other globals pop the best convection further east of Florida with the LP development. The NAM is currently further west closer to the coast with the convection and LP. This results in a further west track and the southern vort closing off. Convection can be the most poorly forecast part of a storms evolution especially so close to the tropics. So the future forecasts and radar confirmation will tell the tale. 

 

ecmwf_slp_precip_east_8.thumb.png.1d3cd2fac42f8454a0c2f7f5f7593c75.png

nam_precip_mslp_east_13.thumb.png.a13c20d0580353c9169943e28ff800a2.png

 

Disagree here. Convection itself will not produce the best surface pressure falls. What we're interested in is how convection results in UL height rises, impacting the orientation of the Jet and downstream UL ridge. To my eye the 6z Nam is making a critical error here in collocating the best surface pressure falls with the deepest convection rather than the location further east where the best upper level divergence exists. 

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