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> July 27-29, 2017 Severe Weather / Heavy Rains MidAtl/NE, Forecasts, Discussions
phillyfan
post Jul 25 2017, 08:50 AM
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Time to open a thread for the Thursday - Friday period.
SPC:
Attached Image


QUOTE
Day 3 Convective Outlook
NWS Storm Prediction Center Norman OK
0231 AM CDT Tue Jul 25 2017

Valid 271200Z - 281200Z

...THERE IS A SLIGHT RISK OF SEVERE THUNDERSTORMS FROM THE MID AND
UPPER OHIO VALLEY EAST THE MID ATLANTIC COAST...

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS SURROUNDING THE
SLIGHT RISK AREA...AND EXTENDING INTO THE SOUTHEAST U.S....

...THERE IS A MARGINAL RISK OF SEVERE THUNDERSTORMS ACROSS PORTIONS
OF THE NORTHERN INTERMOUNTAIN REGION...

...SUMMARY...
Strong/locally severe storms are forecast to spread across the
central Appalachians and mid Atlantic region and vicinity Thursday
afternoon and evening. Isolated severe risk may also evolve across
the northern Intermountain region Thursday afternoon/evening.

...Synopsis...
Larger-scale mid-level troughing is forecast to expand across the
eastern U.S. this period, as a short-wave trough digs southeast
across the Great Lakes area into the mid and upper Ohio Valley
through the period. Meanwhile to the west, ridging will prevail,
though a short-wave trough moving eastward out of the Pacific
Northwest will suppress ridging to some degree as it moves through
the northern Intermountain region.

At the surface, a cold front will shift southeast across eastern and
southern portions of the country through the period, while high
pressure prevails across the central and northern portions of the
country.

...Mid and upper Ohio Valley east to the mid Atlantic coast...
Widespread precipitation is forecast to be ongoing across western
and northern portions of the risk area, which -- along with clouds
streaming east ahead of the convection -- should hinder diurnal
destabilization across a large portion of the risk area. Still,
with a belt of strong flow aloft expected to spread east across the
region in conjunction with a lead short-wave trough ahead of the
main system crossing the Great Lakes, any storms which can
form/organize would likely evolve into fast-moving bands, posing a
damaging wind risk. Therefore, while uncertainty remains relatively
high, will introduce slight risk across a broad zone from the mid
and upper Ohio Valley east the mid Atlantic area to cover this
potential risk -- which could extend through the evening and into
the overnight hours.

Lesser risk -- due to weaker shear -- is expected along the trailing
cold front as it shifts southeast across the mid South region during
the day, aided by greater CAPE. Local severe risk may linger
through the evening, spreading south into the Southeast states
before weakening overnight.

...Northern Intermountain region...
As the weakening upper short-wave trough shifts east-northeast
across the area, modestly enhanced mid-level southwesterlies along
with ample large-scale ascent will favor afternoon thunderstorm
development, as modest CAPE develops through peak diurnal heating.
Though modest instability in most areas should limit hail potential,
damaging wind gusts -- aided by sub-cloud evaporation -- may occur
locally with stronger storms through the evening.

..Goss.. 07/25/2017


Also this HWO from Mount Holly:

QUOTE
.DAYS TWO THROUGH SEVEN...Wednesday through Monday.

There is a potential for heavy rainfall Thursday night into Friday.
Areas that were impacted by heavy rainfall earlier this week will be
particularly susceptible to another round of flooding. Additionally,
a few thunderstorms may become severe.


This post has been edited by phillyfan: Jul 27 2017, 08:52 AM


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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phillyfan
post Jul 25 2017, 11:55 AM
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Ok, 12z GFS just came out with nothing on Thursday. Instead it had Friday into Saturday, so I guess stay tuned.


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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MD Blue Ridge
post Jul 25 2017, 12:45 PM
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QUOTE(phillyfan @ Jul 25 2017, 12:55 PM) *
Ok, 12z GFS just came out with nothing on Thursday. Instead it had Friday into Saturday, so I guess stay tuned.


Weather Model Flip Flopery?!!!!

I feel misled.


--------------------
Blue Ridge Bouncer

Cascade, MD
Elevation: 1625'


90 Degree Days in 2017: 0
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phillyfan
post Jul 25 2017, 01:30 PM
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QUOTE(MD Blue Ridge @ Jul 25 2017, 01:45 PM) *
Weather Model Flip Flopery?!!!!

I feel misled.

What else is new.... laugh.gif


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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CentralJerseySno...
post Jul 25 2017, 02:15 PM
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So I have a flight out of Newark Friday night [655p] to Venice Italy that I cannot afford to have canceled. What are the odds that the weather is so bad that delays force the flight to be canceled?

Should I start trying to bump the flight to Thursday night?
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NorEaster07
post Jul 25 2017, 05:07 PM
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Anomalous High. Anomalous Low.


QUOTE
Area Forecast Discussion
National Weather Service Taunton MA
338 PM EDT Tue Jul 25 2017

Thu night into Fri...
Potentially most unsettled period of the forecast. Very robust
shortwave, especially by July standards, will be carving out a
trof across the NE.
Exactly how this plays out at the sfc
remains somewhat uncertain, as both ensembles and operational
guidance suggest anywhere from a standard cold frontal passage,
to as deep as a 992mb low pres passage directly over New
England.


Attached Image

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grandpaboy
post Jul 25 2017, 10:06 PM
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Is this July..? blink.gif


Attached Image



Attached Image




Attached Image



wheres winter when you need it..




--------------------
just a guy who despises weather but loves the drama....


whats going to happen when weather is predictable:...-me
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NorEaster07
post Jul 25 2017, 10:49 PM
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QUOTE(grandpaboy @ Jul 25 2017, 11:06 PM) *
Is this July..? blink.gif
Attached Image

Attached Image


Attached Image

wheres winter when you need it..


Feels like we been in this pattern since May? Maybe not. What are the odds it remains in place next 7 months? Lol. Or at least comes bavk for winter?

QUOTE
National Weather Service Charleston WV
724 PM EDT Tue Jul 25 2017

Although there are differences in the specifics, models are in
very good agreement signaling an unseasonably strong low
pressure system and attending strong cold front
dropping
southeast across the area for the later part of the work week.

This is in response to the western upper ridge building,
allowing for a vigorous upper low to drop southeast across the
Great Lakes into the Mid Atlantic states
by Friday. Dry high
pressure will rapidly give way Wednesday night and Thursday to
an increasingly moist and unstable airmass feeding northward
ahead of the cold front. All the ingredients are there for
strong to severe thunderstorms, especially Thursday afternoon
ahead of the cold front.

Behind the front, an unusually cooler
Canadian airmass moves in
during Friday, but upper dynamics and
wraparound moisture from the upper low will keep showers and
storms going Thurday night and much of Friday, especially in
the north. Because of this, given the recent heavy rains,
flooding is also possible across the north Thursday night into
friday. So look for a dramatic weather change from Thursday to
Friday from very warm and humid to much cooler and damp.

&&

.LONG TERM /SATURDAY THROUGH TUESDAY/...
As of 350 PM Tuesday...

The aforementioned upper low and wraparound rains lift out
early Saturday, with dry Canadian high pressure quickly taking
firm hold over the region for the weekend. Unusually dry air
will now be the rule for this time of year, with a slow warming
under summer time sunshine.
Still, temperatures for the weekend
will be below normal, especially at night with the drier air.
Early next week, although some heat and humidity will return as
high pressure moves east, dry weather will still hold.
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NorEaster07
post Jul 25 2017, 11:03 PM
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GFS00z

Northern New England misses out

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KENNYP2339
post Jul 26 2017, 04:19 AM
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So how much snow for KFWN? Oh sorry I went into default mode because its chilly up here this morning.
Lets see how this plays out, it could be interesting but since we don't have a ton of warm juicy air to play with, this might be more rain then severe.
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grandpaboy
post Jul 26 2017, 08:10 AM
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QUOTE(NorEaster07 @ Jul 25 2017, 11:49 PM) *
Feels like we been in this pattern since May? Maybe not. What are the odds it remains in place next 7 months? Lol. Or at least comes bavk for winter?



Pattern has been "active" due to northern stream playing with us thus far ...but the Bermuda high has flexed enough to keep it summer like since may...

Going foward ...next 12 to 14 days will be unsummer like for the NE and northern MidAtl which was seen coming weeks ago...


As far as winter...IMHO...looking rather interesting ..but that's about as far as I'll take that bait...

Bermuda high will continue to flex its muscle well into Oct., so thats not going anywhere anytime aoon...also should play an interesting role in the tropics... rolleyes.gif


--------------------
just a guy who despises weather but loves the drama....


whats going to happen when weather is predictable:...-me
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phillyfan
post Jul 26 2017, 08:44 AM
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6z GFS Rainfall map courtesy of EPAWA:

QUOTE
Late week heavy rainfall projection from the latest GFS... both the Euro and NAM are farther south with this heavy axis by ~50-75 miles.


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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Undertakerson
post Jul 26 2017, 10:51 AM
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QUOTE(grandpaboy @ Jul 26 2017, 09:10 AM) *
Pattern has been "active" due to northern stream playing with us thus far ...but the Bermuda high has flexed enough to keep it summer like since may...

Going foward ...next 12 to 14 days will be unsummer like for the NE and northern MidAtl which was seen coming weeks ago...
As far as winter...IMHO...looking rather interesting ..but that's about as far as I'll take that bait...

Bermuda high will continue to flex its muscle well into Oct., so thats not going anywhere anytime aoon...also should play an interesting role in the tropics... rolleyes.gif

The repeated assault, by the northern stream, on the Atl Ridge, is starting to show up as gradual weakening or eastern displacement of the ridge (in some instances, squashing it to the southeast).

Hence the unsummer like next 10 days (or so) as you say.

It has (so far this summer) been able to withstand the assaults from the continental troughs that move through, but it does seem to be very resilient and has, to this point, been keeping the tropics at bay. I expect that will slowly change due to intermittent, and then more sustained, displacement and slight weakening of the SER influence.

Back to the matter at hand, I would not be shocked if the QPF output on the models starts to show some increase over the next 24 hours. It may, (as it often does in cold months) back off the higher end - towards the starting point. Of course, what we don't want is too much at once, on the heels of last week's disaster in So. Dauphin County, PA etc.
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Undertakerson
post Jul 26 2017, 10:56 AM
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QUOTE(phillyfan @ Jul 26 2017, 09:44 AM) *
6z GFS Rainfall map courtesy of EPAWA:

12z (12K) NAM paints it like this:


Attached Image
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Undertakerson
post Jul 26 2017, 10:58 AM
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QUOTE(Undertakerson @ Jul 26 2017, 11:56 AM) *
12z (12K) NAM paints it like this:


Attached Image

Honestly think the models are "guessing mode" at present. The situation will have to watched closely for unpleasant surprises.

For the record, 3K NAM (at 12z) paints a stripe of 2-4 from Pgh to MDBR's house - with some lollipops of 6" mixed in here and there.
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Undertakerson
post Jul 26 2017, 11:02 AM
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Just like a coastal system in winter - except for the convection part that is...

QUOTE
LONG TERM /FRIDAY THROUGH TUESDAY/...
The last cycle or two of model run shows a highly anomalous
northeasterly flow in the sfc-850 mb layer developing Friday
into Saturday as a strengthening wave (or two) of low pressure
at the sfc develops/moves east from the Ohio River Valley and
passes near the Mason/Dixon.

Thick clouds and a strengthening north to nwrly ageostropic
llvl flow will combine with moderately strong llvl cold
advection to bring a quite chilly day for late July. Highs
Friday could struggle to climb above the mid 60s across the
higher terrain of the north and west, while highs in the Central
valleys come out to be in the low-mid 70s. The strength of the
expected sfc low shown by multiple models and EFSs and the
approximate -3 sigma 925-850 mb wind will be quite a rarity in
the Mid Atlantic region for Mid Summer. A significant severe
weather outbreak will likely occur near and just to the south of
the aforementioned sfc low track.

Q widespread light to moderate, chilly rain event (with locally
heavy amounts and elevated instability/thunder across the
south) is expected for Friday afternoon into Saturday morning
,
followed by a chilly airmass for later Saturday into Sunday as
the northerly llvl wind anomaly strengthens to -3 to -4 sigma in
the wake of the deepening low just off the southern New England
coast.

Conditions eventually dry out later Saturday and Saturday night
with a gusty north to northwest wind as high pressure builds
in.
Sunday and Monday appear mainly dry at this time as the
sharp mid level thermal trough slides off the Mid Atlantic
Seaboard.
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grandpaboy
post Jul 26 2017, 11:09 AM
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QUOTE(Undertakerson @ Jul 26 2017, 11:51 AM) *
The repeated assault, by the northern stream, on the Atl Ridge, is starting to show up as gradual weakening or eastern displacement of the ridge (in some instances, squashing it to the southeast).

Hence the unsummer like next 10 days (or so) as you say.

It has (so far this summer) been able to withstand the assaults from the continental troughs that move through, but it does seem to be very resilient and has, to this point, been keeping the tropics at bay. I expect that will slowly change due to intermittent, and then more sustained, displacement and slight weakening of the SER influence.

Back to the matter at hand, I would not be shocked if the QPF output on the models starts to show some increase over the next 24 hours. It may, (as it often does in cold months) back off the higher end - towards the starting point. Of course, what we don't want is too much at once, on the heels of last week's disaster in So. Dauphin County, PA etc.



Agreed...models will play with QPF amounts next 24hrs and get a better idea of the bullseye...

But this system is juiced...coming with Monsoon moisture seeds and add the extra energy dropping in from the north, spells flooding rains for someone...

Get the canoes ready...



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whats going to happen when weather is predictable:...-me
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phillyfan
post Jul 26 2017, 11:31 AM
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QUOTE(Undertakerson @ Jul 26 2017, 11:56 AM) *
12z (12K) NAM paints it like this:


Attached Image

12z GFS is south a bit of 6z. Keeps NEPA completely out of it, follow the bouncing ball. I feel like we're tracking a winter storm. laugh.gif


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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Undertakerson
post Jul 26 2017, 11:39 AM
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QUOTE(Undertakerson @ Jul 26 2017, 12:02 PM) *
Just like a coastal system in winter - except for the convection part that is...



QUOTE(phillyfan @ Jul 26 2017, 12:31 PM) *
12z GFS is south a bit of 6z. Keeps NEPA completely out of it, follow the bouncing ball. I feel like we're tracking a winter storm. laugh.gif

Yep - very much like that. Wonder what the ensembles look like?
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phillyfan
post Jul 26 2017, 11:39 AM
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WFMZ going with a fairly dry Friday....

QUOTE
Thursday will be a bit more humid and warmer as highs bounce back into the 80s. Most of Thursday will be dry with periods of clouds and sun. Late in the day or at night, showers and t-storm may cross the area as a front approaches and sinks just south of the area. These have the potential to produce heavy rain and gusty winds.

That front will stay near or south of the Mason-Dixon line on Friday and act as a corridor for a wave of low pressure to ride along. This wave of low pressure will bring a period of rain and possibly a few thunderstorms to the area. Now, that track of the low pressure may trend farther south of the area and we may end up being fairly dry. If the trend continues to take the frontal boundary and low pressure farther south then Friday may end up being fairly dry. Otherwise, Friday will be humid with highs once again reaching into the 80s. Please stayed tuned as we continue to monitor the models for the latest trends.


--------------------
Severe Weather 2017:

High Wind Watch: 2/13
High Wind Warning: 3/2
Severe T-Storm Watch: 2/25, 3/1, 6/19, 6/23, 7/1, 7/13, 7/20, 8/12, 8/18, 8/22, 9/5
Severe T-Storm Warning: 2/25, 2/25, 3/1, 6/19, 8/5, 8/12, 8/18, 8/19, 8/22, 9/5
Tornado Warning: 7/13
Flood Watch: 3/31-4/1, 4/6
Flash Flood Watch: 6/19, 7/14, 7/23-24, 7/28-29(Cancelled), 8/18
Flash Flood Warning: 7/13, 7/23-24, 7/28-29, 8/18, 9/5
Pea Size Hail: 2/25, 9/5

90 Degree Days: 17 / Heat Waves: 3
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