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2017 Severe Thread


mappy

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17 minutes ago, Kmlwx said:

4k NAM is not particularly exciting at all for DC proper anymore. Has a good cell go south of the area, though. 

3km looks better with a squall coming through. 

Yeah, the line @high risk has been talking about is more south on the 18Z 3km NAM, thus killing severe chances even for those of us near 64. However, seasonal trend has been to the NW, so that would buck that trend to happen. Can't wait to get in the HRRR window in a few hours. 

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3 minutes ago, Eskimo Joe said:

Yes.  I only go for high end potential.  I'm still "in" on this event, but I'm not liking the direction things are headed.  Today seems pretty 'meh' out in the Midwest thus far.

:huh:

Already reports of at least one fatality in Ottawa IL and large tornadoes in IL.... but yeah, guess that's "meh" to you

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Both the ops and para NAM nests shown a significant threat between 00 and 03z, but they arrive at it in different ways.  The ops brings the lead squall line through the area (mostly DC north) during the afternoon with major regeneration of storms behind it during the evening.   The para washes out the squall line and has the evening cells as the only show.

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NAM suite definitely trended toward the cloud cover not abating, which is why we see the forecast soundings suck until late afternoon/early evening. Will be interesting to see how things play out around here tomorrow, specially with how strong some of the storms out west have been the past several hours. 

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Area Forecast Discussion
National Weather Service Baltimore MD/Washington DC
837 PM EST Tue Feb 28 2017

.SYNOPSIS...
A warm front will lift to our north tonight and a strong cold
front will pass through the area late Wednesday and Wednesday
night. After a brief period of high pressure Thursday, an area
of weak low pressure will cross the region Friday. High pressure
returns for Saturday.

&&

.NEAR TERM /UNTIL 6 AM WEDNESDAY MORNING/...
A warm front located over the area late this evening will lift
to the north overnight. Southerly flow behind the boundary will
allow for more unusually mild conditions. Temps will hold steady
or even rise overnight due to the southerly flow.

An upper-level disturbance has triggered showers this evening.
The upper-level disturbance will move away from the area
overnight...causing coverage of showers to diminish across most
areas. However...more upper-level energy is expected to move
across the northern CWA late this evening and again toward
morning. Elevated instability has increased across these areas
due to the southerly flow. Latest mesoanalysis shows around 100
J/KG of MUCAPE approaching from the south and west. The
instability along with the upper-level energy will trigger some
showers and isolated thunderstorms. The best chance for
precipitation will be across northern Maryland...eastern West
Virginia and northern Virginia late this evening into the
overnight...and then again toward morning.

&&

.SHORT TERM /6 AM WEDNESDAY MORNING THROUGH THURSDAY NIGHT/...
..Significant weather day expected on Wednesday with strong to
severe thunderstorms...

Cold front will approach the region during the day on Wednesday
with deep moist southwest flow out ahead of the front. Expecting
temperatures to surge well into the 70s to near 80F, with dew
points in the 50s to around 60F, which should help generate
500-1000 J/KG of MLCAPE. This combined with 0-6KM shear of 60-70
knots and 850-mb flow of 50-60 knots will set the stage for
strong to severe thunderstorm development.

Exact evolution of thunderstorms will be dependent on how
remnant activity from today plays out, but expecting some
morning activity across our northern zones to give way to main
convective period from about 18z-03z. It should be noted that
some solutions depict an earlier start time, beginning about
16z. Main threat is expected to be damaging winds associated
with a squall line, but large hail and perhaps an isolated
tornado are also possible given steep lapse rates and impressive
shear profiles.
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The gradual intensification of the upper level winds across the northeast U.S. overnight and Wednesday will allow any squall line development to accelerate and I think that severe wind gusts will develop along the entire frontal zone because of the extreme thermal gradient developing -- that part is only in a formative stage around IA-nwMO-eKS now and debris from all the action out ahead could spark sporadic severe threats in MD and PA at any time from late tonight to mid-day. Then I think it clears for a time with temps near 80 F, strong WSW winds, still fairly high dews, and the front, in whatever form, blasts through -- even if echo presentation is weak (and it may be strong) there will likely be gusts to 60-70 mph anyway, the 500-mb gradient is constantly tightening next 24h and there's also a downsloping factor with the very cold air rushing in to replace the warm sector. I would say 40% chance of a tornado somewhere in the MA forum, 70% chance of a severe thunderstorm and 99.9% chance of damaging wind gusts. 

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Please keep the Midwest chatter in it's appropriate regional forum.



Wish I had seen this last night. Dude, you brought up the Midwest, of course people are going to reply in kind. lol at you then policing people over reply to you over it. Come on man...
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Been working the overnights and keeping track of how the models are handling the setup out in the Ohio Valley. The HRRR has been doing a pretty nice job overall with the placement of the precip shield and particular cells at times. The 3km NAM has been a little innocuous at times with some of the precip field, so I think it maybe under playing it to a degree. I still don't mind the look given the parameters its spitting out, so could be a time to ignore the future radar composite and look at the parameters at hand. Both the HRRR and 3km show a decent wave of precip motioning to the east-northeast out of SW PA and Western MD into the remainder of PA and the northern fringes of the forum getting scrapped as it passes. The main line will march east from the Ohio Valley with anticipated weakening of the shield somewhat as it reaches the mountains. That's when we'll have to watch what happens on the eastern side of the BR with regard to cloud cover and diurnal heating in the morning and afternoon. Current HRRR at 9z (Latest completed run) shows a break in the clouds toward noon with the line preparing to pass through the BR. The result of the clearing caused a sharp increase in SBCAPE and MUCAPE with indices shooting between 1-2k j/kg, as well as steady uptick in the LI to around -4. certainly a good sign if you want strong to severe cells. As the line passes through the 81 corridor, the destabilization ahead of the line allows the segment to congeal and increase in intensity as it interacts with the more favorable environment. It's noticeable that when there is a decrease in sky cover prior to the line, the proposed reflectivity looks more impressive with a good structure and a better organization of cells. We've mentioned repetitively about sky cover being important and its no secret that the key to anything substantial would be for a period of destabilization prior to the main line reaching past the 81 corridor. The one constant is no matter the case, temps should be into the low to mid 70's at minimum with DP's into the 50's to near 60 at the onset of any convection. It's a pretty nice setup for straight-line winds and possibly a spin up or two within any line that develops with a strong LLJ into the 50's and steep ML LR's around 7-8C/km. HRRR was showing potential for 60-70 knots mixing down with the passage of the line, so I think its safe to say that we should be on the lookout for potential outages if we were to get hit. The one saving grace is probably the lack of leaves on the trees. If this were later in spring or summer, it would be more worrisome. Here's a glimpse at the HRRR for KGAI this afternoon just prior to the line moving through the area. Not a bad look. 

 

KGAI HRRR 9z.PNG

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Yeah HRRR does clear us out around 16z to 17z. The NAM4km looked less impressive with clearing but still some breaks in the clouds. Battle of the sun today. Looking forward to sun obs ;)

The 10z HRRR is pretty early too with the line. Has it plowing through around 19-20z. Makes it all the more important to get clearing as early as possible. The way the HRRR brings in the convection makes it look like it'll minimize the TOR threat (more squall line in nature vs cellular)

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9 minutes ago, H2O said:

delay the squall line more and it will give more time for clearing ahead and heating.  P standard look this morning.  Clouds until 10ish or later then a quick warm up

The bad news is our squall line events like to come in earlier than expected. Either that or we tend to get pop up activity that ruins our priming before hand. 

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3 minutes ago, Kmlwx said:

The bad news is our squall line events like to come in earlier than expected. Either that or we tend to get pop up activity that ruins our priming before hand. 

was just thinking that.  We do see cells pop early before the main show and it clears out the juiced atmosphere.  But all we can do is wait and see.  i think today might surprise some.

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