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Feb 25-26 Discussion/pbp


Wow

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Our local ch 4 met still has a swath of 4-7" basically about 25 miles either side of 85!

The radar he showed had the finger of rain streaking ahead of the storm and near or east of ATL by around noon and here by 5 as rain! I think BL temps will matter, if we get to high of 47 as forecast , that will be a problem. Get clouds in here early and drop some temps tonight, and we will be good!

47? WYFF had 39. :huh:

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Most already know this type info but it relates to this storm and all storms. Thought I would share. Credit: Weather Brains

 

1. Not everyone in a winter storm warning will get a lot of snow and ice. Some will get nothing at all.

2. It’s very unlikely that any snow amount forecast – especially days in advance – will be exactly right. Consider it to be a range of possibilities. Also, those lines on maps dividing snow from sleet from rain look very precise, but they actually have very fuzzy edges.

3. In many cases, we’re better at forecasting the general location of where the heaviest snow will happen rather than the exact forecast amounts. Don’t focus so much on the exact numbers.

4. We try to provide you with our best forecast of snow/sleet/ice amounts as far in advance as we can. The first forecast numbers won’t usually be as good as the ones closer to the event. That’s just the way it is.

5. Often there will be a very small area, maybe a county wide, of heavy snow embedded within the main snow band. It is very difficult to pinpoint exactly where this will set up in advance. That’s what we mean when we say “isolated higher amounts.”

6. If you want the most accurate and up-to-date information, you will have to check the forecast several times a day. Otherwise, you’re working with old information.

7. People tend to focus on and remember the highest number, even if it’s from a forecast they heard days ago. This is especially true if they want it to happen. If you want it to snow, you’ll probably focus on the 6 inch amount if the forecast says “3 to 6 inches”.

8. Forecasts from the media, NWS, armchair social media forecasters, and the guy who cuts your hair who knows someone who took a meteorology course in college often get lumped together, and attributed to the generic “they”. If the haircut guy says he heard it could snow 8 inches, and everyone else says 2 to 4, many people will remember only that “they say we’re going to get 8 inches of snow.” And if there’s not 8 inches of snow, all the forecasters get the blame.

9. The volume of social media posts about snow is not necessarily directly proportional to the amount of snow we’re actually going to get. It seems like the more people are talking about it, the worse it’s going to be, but that’s not always the case.

10. Having too much snow forecast information can be confusing. Anyone can post an image of the computer model’s snow forecast. That doesn’t make it accurate or reliable. Social media has made it too to easy to share this kind of information. Choose your information sources wisely and don’t blindly share forecasts with big numbers.

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Jon Cash, former WAVY-TV Met says:

 

"...Some models paint 2-5” of snow while others bring in a foot! Which one is correct? This is where meteorologists earn their paychecks! Here’s my thinking. Almost every storm coming from this direction this year has moved further north than advertised. Hence, the higher snow totals are the more likely scenario. The rain snow line will be located on a line from just south of Elizabeth City and Kill Devil Hills. Hence, it appears this will be a snow event for the metro Hampton Roads area with parts of Carolina possibly mixing with rain if that line moves a bit further north than predicted. Temps will be in the upper 20s during the event and the snow will stick to all the roads. It is highly doubtful there will be school Thursday or Friday and even tomorrow it will be in question due to the snow currently falling. Here’s my first attempt at snowfall totals. I will adjust this again sometime tomorrow before the storm moves in..."

 

Snow Totals for Wednesday night into Thursday morning.
Southside (VA Beach, Norfolk, Chesapeake, Portsmouth) 8-12”
Suffolk 6-10”
Franklin 5-9”
Smithfield 4-8”
Hampton 6-10”
Newport News 6-10”
Williamsburg 4-8”
Gloucester 3-7”
Eastern Shore 6-12”
Elizabeth City 4-12” (dependent on switch to rain?)
Edenton 4-12” (dependent on switch to rain?)
Outer Banks 1-12” lowest Hatteras and highest Corolla

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Mike Maze FB Post:
Whew! Round one is on its way out....Round #2 arrives tomorrow evening. Should start off as rain tomorrow evening then transition to a snow, sleet and rain mix through the overnight. It doesn't look like there will be enough cold air for the entire event to be snow which could dramatically cut down on snowfall totals. Also cold air will be limited near the ground to keep this from being a freezing rain issue. An interesting setup indeed!

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Stop being pessimistic Cheeznado. I know you are a meteorologist, but FFC knows what they are talking about. You honestly think being this close to the even that we could end up with mostly rain even though 3-6" is being forecast ?

It could go either way at ATL, the thermal profiles are so close in both directions it's going to be a nowcast there ultimately. The RGEM has them right on the edge of heavy snow and it's been 30-50 miles warm biased on all events this winter, if it's doing that again they will get hit hard

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Stop being pessimistic Cheeznado. I know you are a meteorologist, but FFC knows what they are talking about. You honestly think being this close to the event that we could end up with mostly rain even though 3-6" is being forecast ? It would be a bust of epic proportions.

I really hope I am wrong and they are correct. But it is not a matter of being pessimistic or optimistic, I feel that ITP has only a small chance of any accumulations. And an inch well south of ATL- that is laughable. I will gladly chow down on a big meal of crow if FFC is right, but I just do not see it.

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I really hope I am wrong and they are correct. But it is not a matter of being pessimistic or optimistic, I feel that ITP has only a small chance of any accumulations. And an inch well south of ATL- that is laughable. I will gladly chow down on a big meal of crow if FFC is right, but I just do not see it.

 

Just out of curiosity and also seeing that it may help others to understand what Cheez and Snowgoose are forecasting/explaining.....when you guys reference Atlanta verbatim, are you talking about KATL at Hartsfield Int. Airport, downtown Atlanta, or the metro area in general?  It may help those not totally familiar with how big Atlanta is to throw out your definition when you say Atlanta.  I know Cheez has referenced ITP which to us Atlanta folks means Inside the Perimeter (the perimeter being I-285). 

 

- Buck

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God that is a horrible overdone map. FFC continues to do a bad job. I live east of downtown, will be lucky to get 3.6 flakes of snow.

probably a bit over done on their part for southern areas but I think you are being way too pessimistic. i took a close look at the soundings on the gfs and it's extremely close. Literally just one degree will make the difference between an epic hit and going back and forth with all precip types.

 

this is from near lawrencville but soundings all along the northern burbs of atlanta look the same as this pretty much the entire storm. It's mostly snow anyway but throw in heavy rates and it's almost certain. It's way too soon to be writing it off.

GFS Text Sounding | 21 UTC Wed 25 Feb 2015 |
PRES	HGHT	TEMP	DWPT	RELH	MIXR	DRCT	SKNT	TWTB	TVRT	THTA	THTE	THTV
970.8	313	2.1	1.5	96	4.4	63	5	1.9	2.8	277.5	289.8	278.3
950.0	487	0.9	-0.2	92	4.0	63	12	0.4	1.5	278.0	289.2	278.7
925.0	701	-1.0	-1.2	99	3.8	61	15	-1.1	-0.4	278.2	288.9	278.9
900.0	919	-1.8	-1.9	98	3.7	56	14	-1.8	-1.1	279.7	290.2	280.3
850.0	1376	-0.4	-0.8	97	4.3	73	4	-0.6	0.3	285.6	298.0	286.4
800.0	1862	0.7	-0.3	93	4.7	206	9	0.2	1.4	291.8	305.7	292.6
750.0	2380	-0.2	-0.3	99	5.0	223	19	-0.3	0.6	296.3	311.2	297.1
700.0	2932	-1.5	-1.6	99	4.9	244	34	-1.6	-0.7	300.7	315.6	301.6
650.0	3522	-2.5	-2.6	99	4.9	241	55	-2.6	-1.8	306.0	321.2	306.9
600.0	4155	-4.8	-4.9	100	4.5	234	69	-4.9	-4.1	310.4	324.6	311.3
550.0	4836	-8.2	-8.3	100	3.7	234	80	-8.3	-7.6	314.2	326.4	314.9
500.0	5570	-12.8	-12.8	100	2.9	235	89	-12.8	-12.3	317.4	327.0	31
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It could go either way at ATL, the thermal profiles are so close in both directions it's going to be a nowcast there ultimately. The RGEM has them right on the edge of heavy snow and it's been 30-50 miles warm biased on all events this winter, if it's doing that again they will get hit hard

 

That's a sick gradient for Atlanta...what is that 20 miles from 6"?  

post-2311-0-01358400-1424823531_thumb.pn

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Looks overly optimistic in the southern metro, but the northern metro can certainly see 3-5". North of Marietta-Alpharetta-Suwanee should do well.

This I agree with. I am mainly talking about the heart of Atlanta- I live near downtown and FFC has me getting 3.6" I feel that is almost certainly overdone. North of I285- different story, anything from an inch or two to maybe 3-6" is possible- this where the real uncertainty lies.

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That start time map is pretty hilarious. I feel confident this over performs for most involved. I'll gladly take my 3-6 and end the winter on a good note.

I'm not far from his 8-10. If you follow DT then you know he was probably rushing to get it done. I am sure he meant WED instead of TH on that. Even so, pretty humorous.

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btw, snow could get an early start per rap with the finger of snow. I wouldn't be too surprised if far western areas of georgia saw something as early as 15z.

also...the rap is south of the nam at 18 hours with the surface low

As with most system, the earlier the better !

Sent from my iPhone

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This I agree with. I am mainly talking about the heart of Atlanta- I live near downtown and FFC has me getting 3.6" I feel that is almost certainly overdone. North of I285- different story, anything from an inch or two to maybe 3-6" is possible- this where the real uncertainty lies.

 

Yeah, my (meteo) roommate and I are tracking this pretty closely and we have an over/under bet of 1" for KATL. I took the under and unfortunately am thinking I might win the bet. With the northward trend today I can't help but think the writing is on the wall for folks ITP and south. Maybe a sloppy inch or two downtown but I certainly would want to be up in Cherokee/northern Forsyth county if I was looking to see warning-criteria snow.

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The 540 thickness line is not as valuable in this part of the country as is 1000-850mb and 850-700mb thickness values

 

Great point and for those who want to learn more about using thickness values to determine dominant type, or just need a refresher checkout the link below.

 

http://www4.ncsu.edu/~nwsfo/storage/trend/

 

Based on this technique, you want to stay below 1300m for 1000-850mb thick, and 1550m for 850-700mb (preferably 1540m), to remain SN dominant type.  There are exceptions as you can see below, GSO stayed SN (or dominant) with 850-700mb thick as high as 1556m back in 97 but with a very deep isothermal layer.  

 

post-382-0-04109100-1424824346_thumb.jpg

 

My guess based on looking at skew T's for RWI and PGV is that we are very close maintaining an deep isothermal layer for the bulk of what falls.  Ceiling is probably capped at 8-10" somewhere between RWI and ORF.

 

18z RGEM at 36hrs (credit http://www.americanwx.com/models)

post-382-0-45518600-1424824535_thumb.png

 

18z NAM at 36hrs for PGV, or about thereto

post-382-0-32867800-1424824558_thumb.jpg

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Jon Cash, former WAVY-TV Met says:

 

"...Some models paint 2-5” of snow while others bring in a foot! Which one is correct? This is where meteorologists earn their paychecks! Here’s my thinking. Almost every storm coming from this direction this year has moved further north than advertised. Hence, the higher snow totals are the more likely scenario. The rain snow line will be located on a line from just south of Elizabeth City and Kill Devil Hills. Hence, it appears this will be a snow event for the metro Hampton Roads area with parts of Carolina possibly mixing with rain if that line moves a bit further north than predicted. Temps will be in the upper 20s during the event and the snow will stick to all the roads. It is highly doubtful there will be school Thursday or Friday and even tomorrow it will be in question due to the snow currently falling. Here’s my first attempt at snowfall totals. I will adjust this again sometime tomorrow before the storm moves in..."

 

Snow Totals for Wednesday night into Thursday morning.

Southside (VA Beach, Norfolk, Chesapeake, Portsmouth) 8-12”

Suffolk 6-10”

Franklin 5-9”

Smithfield 4-8”

Hampton 6-10”

Newport News 6-10”

Williamsburg 4-8”

Gloucester 3-7”

Eastern Shore 6-12”

Elizabeth City 4-12” (dependent on switch to rain?)

Edenton 4-12” (dependent on switch to rain?)

Outer Banks 1-12” lowest Hatteras and highest Corolla

Thanks for the post. Personally, I think the totals will be more in-line with his thinking, which seems to be on the heavier side of guidance.

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