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The official 2014 Summer Discussion Thread

Marion_NC_WX

By Marion_NC_WX,
in Southeastern States

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mackerel_sky

mackerel_sky

Posted
Posted

The 18z NAM has really come in with some higher precip amounts for NC. Here's a comparison of the last for NAM runs (all 84 hr total precip accum). Even Snowstorm should like this run!

It's the 18z NAM, throw it out! I

My gut tells me to not expect much rainfall in my area. I'm still going < .50 total

TWC local forecast has 80% chance of rain tomorrow and 60% on Sat.! The kiss of death

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Cold Rain

Cold Rain

Posted
Posted

It's the 18z NAM, throw it out! I

My gut tells me to not expect much rainfall in my area. I'm still going < .50 total

TWC local forecast has 80% chance of rain tomorrow and 60% on Sat.! The kiss of death

Yeah, take the NAM amounts and chop them by at 4 and then you're in the ballpark....works that way in the winter, at least!

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calculus1

calculus1

Posted
Posted

Something is really wrong with this picture. None of the operational models support this depiction. I guess this is their in-house model. Then even his text is wrong for RDU. It should be .8 (not.08) to match the color banding.  

 

**even so, if it was right we would actually benefit from less rain.

 

That map is probably off by 100-200 miles. That big heavy area will probably be from Roanoke Va to Richmond and Norfolk VA. Raleigh should get 1-2 inches of rain.The Charlotte metro WELL LESS than half of what that shows.

 

That model was run at 15Z.  The same model three hours later,  18Z, gave Charlotte a whopping 0.13".

 

Yep, Brad P had two pictures in the same post.  The 15Z and the 18Z were both shown.  He was trying to show how difficult it was to forecast the actual rainfall this weekend when the RPM produced vastly different results within a 3-hour span.  Here's both images side-by-side:

 

Edit:  I did just realize that Brad P did release only the first image when it first came out, which was when Solak first posted.  This compiled image was released later in the afternoon.

 

KYI4rIB.png

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downeastnc

downeastnc

Posted
Posted

Looks like its going to rain

 

post-141-0-71108100-1407464062_thumb.gif

 

 

The headwaters of the Tar River are going to get a lot of water apparently and this could end up being trouble if this pattern persist. Would be bad if a cane forms and sneaks in between the troughs we are getting in this pattern....ground is soaked, ditches are not drying out hardly at all so ground water table is high.

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jshetley

jshetley

Posted
Posted

Looks like its going to rain

 

attachicon.gifp168i.gif

 

 

The headwaters of the Tar River are going to get a lot of water apparently and this could end up being trouble if this pattern persist. Would be bad if a cane forms and sneaks in between the troughs we are getting in this pattern....ground is soaked, ditches are not drying out hardly at all so ground water table is high.

That map says we all win. Hopefully it'll be right.

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WxJordan

WxJordan

Posted
Posted

Here is the post me, another meteorologist I graduated with from UNCA (Thomas W.), and a couple of other forecasters (Nathan H. and Michael M.) posted on my websites WxCarolina.com and WxJordan.com. This has the potential to be a very big rain event for a large chunk of the area. This post concentrates on NC, but the synoptics apply to SC and VA as well. Wherever these storms develop will see over a month's worth of rain through the weekend. I expect the highest totals to be out of central NC and VA. Regardless, I expect widespread totals of 1-2 inches by the end of the weekend, with higher amounts likely in parts of NC and VA. Northwest SC could do very well in this event too, with isolated areas picking up 3+ inches of rain. 

 

This forecast is not as easy as previous forecasts because it depends where the upper level energy tracks. The storms will be aided by upper level jet divergence, which can cause large clusters of intense storms and heavy rain to break out. The models have the heaviest rain right in the right entrance region of the jet, and rightly so with this begin the area with the best upper level divergence.

 

It will be fun to track over the weekend for sure, but it will ruin a lot of people's outdoor plans, especially Saturday.

 

 

Heavy Rain Threat This Weekend

Very heavy showers and storms are expected Friday and into the weekend as waves of upper level energy slide through the eastern United States.

 

SYNOPTICS

A weak warm front will lift from the south Friday, bringing a surge of rich Gulf of Mexico moisture northward. Widespread showers and thunderstorms are expected to develop over the southeast and mid-Atlantic Friday morning. The storms will move out of Tennessee and the Ohio Valley through the morning hours, and will begin to redevelop Friday afternoon.
 
Low level moisture will continue to increase through the day on Friday with southerly winds due to an area of high pressure off the coast of northern Virginia. Precipitable water values are expected to climb over 2 inches Friday evening and Saturday morning, which is 175% above normal for this time of year. Precipitable water is a measure of how much moisture is available in the atmosphere, where higher amounts can help contribute to heavy rain.
 
The best upper level forcing moves into the state on Saturday. The 500 mb upper level energy will slide across the North Carolina / Virginia border through the day on Saturday, and this will help to produce very heavy rain.  This energy will be aided by a 60 knot upper level jet which will in turn act to increase forcing and lift over the northern Piedmont. The highest rain totals are expected along the I-85 corridor from Charlotte to Greensboro and then over to Raleigh where the increased forcing and lift will help reinforce the heavy rain threat.
 
Here is the upper level energy shown on the NAM Saturday afternoon. It will continue to move eastward through the evening and overnight hours.
Slide4.PNG
 
By Sunday, another piece of energy will roll into the Carolinas, so expect another round of showers and storms. The area of high pressure will persist off the coast of Virginia and will continue to transport very moist air into the Carolinas. There will not be as much upper level forcing on Sunday, so storms and showers will not be as widespread but flash flooding will definitely be a concern, especially in areas that receive copious amounts of rain on Friday and Saturday.
 

ESTIMATED RAIN TOTALS

As far as rain totals come, there is still some inconsistency in the models in regards to who will see the most rain. Widespread amounts of 2-3 inches are likely across the state with higher amounts closer to the Virginia/N​orth Carolina line possible.
 
Locally higher amounts could be as high as 6 inches, but it is hard to say where that area will be due to the uncertainty and the potential for training storms. 
 
The Weather Prediction Center is showing widespread 2-3 inches of rain, with higher amounts in the central Carolinas over the next three days.
Slide1.PNG
 
Here is the Thursday 18z GFS forecast rain totals...
Slide2.PNG
 
Here is the Thursday 18z GFS Ensemble forecast...
Slide3.PNG
 
The GFS is likely under estimated the precipitation because a majority of the precipitation will be convective in nature.
 

FLOODING CHANCE

With high precipitable water values and relatively slow storm movement, flash flooding is likely across the state. Any thunderstorms that develop have the potential to drop 1-2 inches of rain in 30 minutes.
 
The storms will likely train over the same areas, so these areas could see 2-3 inches of rain in an hour. It is impossible to say where this will occur, but we expect some areas across North Carolina to see a month’s worth of rain in a few days.
 

SEVERE CHANCE

Severe weather will not be a big threat this weekend as shear and substantial instability will be lacking. Typically, in environments characteristic of deep rich moisture there is not enough cooler air aloft to result in sufficient instability. With that being said, Sunday has the most potential for an isolated wet downburst but the threat will be isolated. There is potential for some more organized clusters of storms along the stationary front in eastern NC on Sunday but there is still too much uncertainty to determine whether there will be an elevated severe threat at this point. However, we will keep you updated if the severe threat increases for Sunday.
 

TEMPERATURES

Temperatures will remain below average with abundant clouds and frequent downpours. Many areas will struggle to eclipse the 80° mark on Saturday. Areas west of I-77 will stay in the 70s on Friday for highs. Dew points will also be in the 70s, helping to aid shower and thunderstorm development.
 

INTO NEXT WEEK

While the showers and thunderstorm chance remains into next week, most of the storms will be the afternoon pop-up variety. We expect a 30-40% chance of afternoon storms, with the best chance in the western part of the state.

Very heavy showers and storms are expected Friday and into the weekend as waves of upper level energy slide through the eastern United States.

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Marion_NC_WX

Marion_NC_WX

Posted
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Posted

I look at it this way...areas like the Northern Piedmont of NC and Southside VA, you're almost guaranteed to be jinxed as the models have been focusing on your area over the past 24 hours in regards to where the heaviest rain is supposed to occur.

 

It happened to me last weekend along the Blue Ridge...we were progged to get the most rainfall because of southeast flow but it was like a brick wall kept everything along I-85 in South Carolina.

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Cold Rain

Cold Rain

Posted
Posted

 

Rainfall has quickly blossomed across the SoApps in the last 2 hours...in fact the SPC has a current meso discussion posted for WNC. I am on phone right now so I can't attach any of it on here

 

I gotcha, Marion. By the way, the 12z NAM really scaled back the precip totals.

 

MESOSCALE PRECIPITATION DISCUSSION 0256

NWS WEATHER PREDICTION CENTER COLLEGE PARK MD

1027 AM EDT FRI AUG 08 2014

AREAS AFFECTED...EASTERN TN...WESTERN NC...NORTHWEST SC...NORTHERN

GA

CONCERNING...HEAVY RAINFALL...FLASH FLOODING POSSIBLE

VALID 081425Z - 081845Z

SUMMARY...SLOW-MOVING AND REPEATING WARM-TOPPED CONVECTION WILL

FOSTER INTENSE RAINFALL RATES AND POTENTIALLY EXCESSIVE TOTALS

THROUGH MIDDAY.

DISCUSSION...A WELL-DEFINED MCV AND ASSOCD SFC LOW CENTER OVER SRN

IL THIS MORNING IS VERY SLOWLY MOVING EASTWARD ALONG A FRONTAL

ZONE INVOLVING THE OH/TN VALLEYS. THE FRONT ACTUALLY EXTENDS SEWD

INTO CNTRL GA AND THEN EAST INTO THE SOUTHEAST COASTAL PLAIN.

MEANWHILE...A LARGE AREA OF DEEP MOISTURE WITH PWATS NEAR 2 INCHES

ARE POOLED ALONG AND JUST NORTH OF THE FRONT AS PER LATEST

GPS-DERIVED PWATS ARE NEAR 2 INCHES.

MODEST LOW LEVEL SWLY FLOW UP TO ABOUT 20 KTS IS OVERRUNNING THE

BNDRY...BUT THERE IS SUFFICIENT ELEVATED CAPE GIVEN THE LARGER

SCALE FORCING AHEAD OF THE MCV FOR NUMEROUS SHWRS/TSTMS. THE

ACTIVITY IS TENDING TO REPEAT GIVEN THE PERSISTENT LOW LVL FEED OF

MOIST/UNSTABLE AIR FROM THE TN VLY.

THE ONGOING CONVECTION IS WARM-TOPPED IN NATURE...AND AS A RESULT

RAINFALL PRODUCTION WILL BE PARTICULARLY EFFICIENT AND GIVEN THE

VERY HIGH PWAT ENVIRONMENT...RAINFALL RATES WILL BE QUITE INTENSE.

ALREADY RAINFALL RATES UPWARDS OF 2 INCHES/HR HAVE BEEN

NOTED...AND GIVEN THE SLOW-MOVEMENT AND REPETITIVE NATURE TO THE

CONVECTION...THERE WILL BE CONCERN FOR EXCESSIVE AMTS THROUGH

MIDDAY.

THE LATEST HI-RES MODEL GUIDANCE IS GENERALLY NOT HANDLING THE

CURRENT ACTIVITY TOO WELL...WITH THE 06Z NAM-CONEST AND 09Z HRRR

CONSIDERABLY UNDERDONE WITH THE CONVECTIVE COVERAGE. THE 00Z ARW

AND 00Z NMMB ARE AT LEAST BETTER IN IDENTIFY THE RELATIVE

PLACEMENT OF CONVECTIVE BANDS.

EXPECT THE ACTIVITY TO PERSIST FOR THE NEXT FEW HOURS AT LEAST AND

ESP WITH THE AID OF OROGRAPHIC FORCING. FLASH FLOODING WILL BE

POSSIBLE.

ORRISON

post-987-0-07800200-1407510794_thumb.gif

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griteater

griteater

Posted
Posted

the 12z NAM really scaled back the precip totals.

 

Those 9 words give me winter flashbacks.....any winter.

 

If you like rain (I don't), I'm having a hard time seeing how this is going to bust for the vast majority of North Carolina.  The wedge is going to be established.  But it's not the dry dewpoint kind.  The frontal boundaries are going to be close by, from TN extending ESE through SC, and meandering north and south over the next 3 days.  Just looking at the 12z GFS, what sticks out to me is that this wedge pattern holds through the 3 day period with waves of precip moving through NC.  For example, there is a weak sfc low in northern SC still there early Monday morning...that says to me that it's going to be an extended period of elevated rain chances...through the weekend and into Monday.

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Cold Rain

Cold Rain

Posted
Posted

 

Those 9 words give me winter flashbacks.....any winter.

 

If you like rain (I don't), I'm having a hard time seeing how this is going to bust for the vast majority of North Carolina.  The wedge is going to be established.  But it's not the dry dewpoint kind.  The frontal boundaries are going to be close by, from TN extending ESE through SC, and meandering north and south over the next 3 days.  Just looking at the 12z GFS, what sticks out to me is that this wedge pattern holds through the 3 day period with waves of precip moving through NC.  For example, there is a weak sfc low in northern SC still there early Monday morning...that says to me that it's going to be an extended period of elevated rain chances...through the weekend and into Monday.

Yeah, I agree. I think everyone is pretty much going to get in on the action. A widespread 1-2" is a good forecast. Of course, some locales will do much, much better. The models have been pretty inconsistent on where they put the QPF max (it was SE VA/NE NC but now Central VA/Central/Western NC), probably due to convective feedback, I would guess. I like lots of rain, so I will be happy to sit on the porch and watch the water pile up in the ditches.

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frazdaddy

frazdaddy

Posted
Posted

Yeah, I agree. I think everyone is pretty much going to get in on the action. A widespread 1-2" is a good forecast. Of course, some locales will do much, much better. The models have been pretty inconsistent on where they put the QPF max (it was SE VA/NE NC but now Central VA/Central/Western NC), probably due to convective feedback, I would guess. I like lots of rain, so I will be happy to sit on the porch and watch the water pile up in the ditches.

Yepp me too. Reading Roberts thoughts this am, there are too many variables to nail down a bullseye for this one. I'll have my Radar scope on the porch with me.

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