midwest folks -- update on event / some changes

[wxguy25]

SORRY about not having the maps up and ready to go as promised. When I can get them online I will post the links here for you.

I suppose ill have to do this the old fashion way in the meantime w/ a good ole discussion.

Anyway, Latest WV imagery shows the PJ s/w dropping southward over the intermountain west, and the STJ s/w presently located over the southwest beginning to eject eastward. These two features will eventually phase over the 4-corners region and result in surface cyclogenesis along the QS frontal boundary/ inverted trough tomorrow over the WRN GOM/TX/LA. This boundary will also serve as a focal point for large scale ascent and overrunning precipitation.

BOTH the 18z ETA and GFS are back to the solutions from a day ago WRT to more rapid SLP intensification; this results in some MAJOR changes. Areas such as CLE which I originally thought would see the heaviest snowfall, now may not, and places such as DTW which the ETA virtually excluded from the event at 12z COULD now see the heaviest snow as the deepens below 1000mb and a well-defined deformation zone sets up.

Most of you know I don’t like making or changing forests based on the 06z or 18z model cycles, but this change cannot be ignored since BOTH the GFS and ETA are in close agreement.

Look for the following to determine who gets what and how much:

1. 850h low track which looks per 18z GFS to move from the AR/TX/LA region tomorrow afternoon and evening to the ERN lakes region by 18z THU.

2. SLP deepening below 999mb means that a strong deformation zone will develop and wraparound snows will be a problem.

3. Track of the 500mb s/w which will be from TX to the central lakes.

Favorable jet dynamics w/ most of the lower lakes under the influence of a coupled jet pattern at 200mb in the RRQ of an anticyclonically curved jet streak exiting over Ontario and the LFQ of another jet maximum coming out of the base of the trough means STRONG upper level divergence will develop helping to both cause the SLP to intensify more pronouncedly as a result of mass evacuation, and form a favorable environment for strong UVV w/ upper level divergence placed above low level convergence and baroclinicity (fronotgeneses/ Q vector convergence).

The next issue is dealing w/ how far west the heaviest precip extends given the nature of the Airmass (sharp precip gradients tend to develop when dealing w/ arctic airmasses). the 18z ETA has the .50” of liquid Isohyet running from SE MO through SE IL, Central IN, and eventually into SE lower MI, where the ETA would give DTW almost an inch of liquid all snow. This gradient is NOT as tight as what the 12z run had, but then again were dealing w/ a different scenario now.

The 18z GFS looks about the same BUT has the heaviest QPF further east. The 12z MM5 was furthest NW and would actually bring accumulating snow close to Chicago. This however appears to be TOO FAR WEST given the other solutions.

Long the NW periphery of the snow shield we will play the ratios game given the arctic air. THE 5400m thickness line runs right through the area of heaviest precipitation through much of the event, from the OV through the eastern lakes. The snow growth region (area of the atmosphere between -12 and -16 C where depositional growth is maximized and crystal type is normally dendrites) should be sufficiently saturated and w/ strong deep layer UVM developing there will be an area of maximized snowfall growth and > 10:1 ratios coinciding w/ the area of heavy snowfall.

With over an inch of liquid, near maximized snow growth, and higher ratios than you would normally see w/ a gulf system given the arctic air (less supercooled droplets in the clouds as a result of the airmass), I expect an area of 12-20” beginning across southern IN which moves north-northeastward into NW OH, just west of the Cleveland area. Totals will drop off quickly northwest of this area b/c of the arctic air. Mixing will limit totals to 8-14 inches (big deal) from NW KY through Cincinnati and into the CLE area, followed by 4-8 inches along the southern periphery where the predominant precip type WILL NOT be snow throughout >60% of the event. This would include NW PA and NW NY.

Changes may need to made to this based on tonight’s 0z runs so don’t get stuck on it.

Revised maps will be out IF I can get them out. The old ones based on the 12z data are into the crapper since the 18z cycle showed major changes.

[jkt21787]

Hey wxguy, nice updates, agreed on big changes on 18Z.

But of course I will ask, what are the implications for Memphis?

BUFKIT on both ETA and GFS showed a lengthy area of freezing rain and sleet with significant amounts over 1/4 inch then about an inch or two of snow. Is that realistic?

[wxguy25]

Hey wxguy, nice updates, agreed on big changes on 18Z.

But of course I will ask, what are the implications for Memphis?

BUFKIT on both ETA and GFS showed a lengthy area of freezing rain and sleet with significant amounts over 1/4 inch then about an inch or two of snow. Is that realistic?

MAJOR ice storm as it stands right now. Prolonged period of ZRA/IP. then some SN to end.

[jkt21787]

Although I have been hoping for winter weather, that is not what I wanted to hear, although I expected it looking at 18Z data.

Quite amazing to see the ZR/IP total from this as that low develops near New Orleans and heads NE.

Of course it is the 18Z and it could change right back on the 00Z. Winter Storm Watch already issued and that was before 18Z model data was out.

DO NOT want an ice storm, especially with snow afterwords. Always leads to problems, not to mention the wind which could exacerbate things.

Hope you can get a map up soon, even though I really dont want to see it given the current data.

[PurdueWx80]

GREAT non-model-based discussion - I think your amounts and their location look perfect as well. These snow amounts will be a huge deal in these parts (I'm near Louisville now where the record stands near 22-23" but many areas have never seen this much (Evansville, IN's record is 9" - they should come very close) in most people's lifetimes (save a few events like blizzard of '78). The interstates have been "brined" but with the precip expected to be light rain for the first few hours, it may have been a waste. Local tv mets are staying with the conservative NWS estimates of a max only near 8" - I imagine they'll wisen up in the morning, unless drastic changes in the modeling occur.

Of note is the excessive moisture return at the surface in the deep south with dewpoints in the 50s and 60s being widespread. MOS guidance is still too warm with surface temps, so that is another thing to take into consideration when forecasting where rain or snow (or ice) will fall. Can't wait for those 00Z models!

[wxguy25]

GREAT non-model-based discussion - I think your amounts and their location look perfect as well. These snow amounts will be a huge deal in these parts (I'm near Louisville now where the record stands near 22-23" but many areas have never seen this much (Evansville, IN's record is 9" - they should come very close) in most people's lifetimes (save a few events like blizzard of '78). The interstates have been "brined" but with the precip expected to be light rain for the first few hours, it may have been a waste. Local tv mets are staying with the conservative NWS estimates of a max only near 8" - I imagine they'll wisen up in the morning, unless drastic changes in the modeling occur.

Of note is the excessive moisture return at the surface in the deep south with dewpoints in the 50s and 60s being widespread. MOS guidance is still too warm with surface temps, so that is another thing to take into consideration when forecasting where rain or snow (or ice) will fall. Can't wait for those 00Z models!

Good observation about the MOS guidance. I always check that against the 1000-500mb thickness and 850h temp rules first but precip and cloudcover tend to complicate the situation if your using those two methods.

The 0z ETA had a good initialization w/ decent RAOB coverage so I can't pick on that if the 0z run is back to looking like 12z. i

it should be interesting

[wx247]

What impact does that have on areas farther to the NW like us here in Sw Missouri? Any??

[wxguy25]

I'll also be awaiting the 21z SREF. the 9z cycle looke similar to the 12z operational ETA and GFS cycles WRT to the placement of the heaviest QPF and coinciding snowfall.

http://wwwt.emc.ncep.noaa.gov/mmb/SREF/ ... p6h_42.gif

http://wwwt.emc.ncep.noaa.gov/mmb/SREF/ ... x24_54.gif

IF the 21z SREF looks similar to the 18z ETA/GFS then my confidence in the abovementioned totals will go up BIGTIME

[wxguy25]

What impact does that have on areas farther to the NW like us here in Sw Missouri? Any??

2-4" probably for you.

[jkt21787]

0Z Eta now through 18 hours, see no major changes from 18z at time, but I will leave that up to wxguy to make the final call for that.

[wxguy25]

0Z Eta now through 18 hours, see no major changes from 18z at time, but I will leave that up to wxguy to make the final call for that.

500h s/w looks somewhat stronger over W TX at 18hrs

[wxguy25]

Also more impressive over TX w/ .25-.50" of QPF. again somewhat more than 18z. 00z looks just as good as 18z.

[ALhurricane]

Taking a look at the 00z run coming in, I am increasingly concerned about a big ice event here in Memphis. What has me more concerned is the fact that the ETA is putting out a lot more QPF compared to earlier runs. Secondly, as mentioned above, the shortwave coming out of TX is stronger as well... not nearly as sheared as 00z last night.

It looks like there will be definite change over to snow sometime tomorrow evening in Memphis, with 1 to 2 inches of snow on top of the ice possible.

[jkt21787]

ALHurricane, I hate to hear that, but sure looks more likely with now the 18 and 0Z runs showing this.

What could be the potential amounts? BUFKIT put out almost 3/4 inch on 18Z.

Also, do you think a warning may be issued tonight, or wait till tomorrow?

[ALhurricane]

I am sure the office will review all the 00z guidance and if they feel confident of significant accumulations (ice totals > .25") then a warning will likely be issued.

As I said earlier, the only thing that will help out at first is the warmer temperatures and rain that will occur tonight. I think that will curtail any major road problems at first. If it is a prolonged event, which the ETA is now showing, then all bets are off.

[jkt21787]

I am sure they will have first insight of the 00Z data in the evening AFD, it may be too early to make an upgrade though until further analysis is done. This really came on fast, just this morning it was maybe an inch of snow, now a possible big ice event with a couple of inches of snow, just shows how the models always change!

Warm temps will be helpful, but that cold air is coming fast. Actually rising a bit tonight on my weather station at home ahead of this batch of rain.

BTW, 18Z ETA showed over 6 hours of ice, 0Z looks much the same, so this is not good. Of course 00Z GFS is coming, but at this point I am not sure it matters.

[wxguy25]

Personally I'm more interested in the 21z SREF. IF it supports the 18z operational models and now the 0z ETA WRT a stronger solution and more QPF then look out.

[wxguy25]

I am sure they will have first insight of the 00Z data in the evening AFD, it may be too early to make an upgrade though until further analysis is done. This really came on fast, just this morning it was maybe an inch of snow, now a possible big ice event with a couple of inches of snow, just shows how the models always change!

Warm temps will be helpful, but that cold air is coming fast. Actually rising a bit tonight on my weather station at home ahead of this batch of rain.

BTW, 18Z ETA showed over 6 hours of ice, 0Z looks much the same, so this is not good. Of course 00Z GFS is coming, but at this point I am not sure it matters.

What kind of weather station do you have?

[jkt21787]

Well after looking at the 0Z ETA, it looks like the 18Z trends could very well be verified.

Possibly Historic snows in the Ohio Valley, and Ice storm from KY into TN (including Memphis possibly).

Of course, I would rather listen to wxguy or even Purdue's comments than my own, LOL. I am sure they will be posting very soon.

[jkt21787]

New AFD out of Memphis, no warning yet, but they say one is very possible when all 00Z data is in.

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MEMPHIS TN
855 PM CST TUE DEC 21 2004

.DISCUSSION...
DO NOT SEE ANY REASON TO UPDATE THE FORECAST AT THIS TIME. COLD
FRONT BISECTS THE MIDSOUTH NORTHEAST TO SOUTHWEST FROM ABOUT PARIS
TN TO STUGGART AR. THE FRONT IS EXPECTED TO SAG SOUTHEASTWARD
OVERNIGHT. BAND OF WIDESPREAD RAIN OCCURRING ALONG AND BEHIND THE
FRONT IS ALSO EXPECTED TO SPREAD SOUTHEASTWARD OVERNIGHT WITH THE
FRONT. FREEZING RAIN AND SLEET IS STILL POSSIBLE LATER TONIGHT FROM
PARTS OF NORTHEAST AR INTO THE MO BOOTHEEL AS THE COLDER AIR SPREADS
IN. WILL LEAVE PRESENT WINTER STORMS WARNINGS AND WATCHES AS IS.

THERE HAVE BEEN SOME LIGHTNING STRIKES EARLIER THIS EVENING IN
EASTERN AR...BUT THESE HAVE DIMINISHED. THE MESOETA DID INDICATE
DECREASING CAPE THROUGH THIS AREA OVERNIGHT...SO DO NOT EXPECT
ANYMORE THAN ISOLATED THUNDER AT BEST.

18Z GFS/MESOETA SEEM DO BE COMING TOGETHER LITTLE BETTER THAN
PREVIOUS RUNS CONCERNING CONTINUED WINTER WEATHER THREAT WEDNESDAY
AND WEDNESDAY NIGHT. BOTH MODELS INDICATED A SURFACE LOW MOVING FROM
SOUTHWEST MS AT 00Z THU TO NORTHERN AL BY 06Z THU. THE GFS WAS A
LITTLE STRONGER WITH THE LOW AND A LITTLE WARMER.
NEVERTHELESS...BOTH MODELS INDICATED COULD BE SIGNIFICANT ICING IN A
BAND FROM AROUND MEMPHIS TO PARIS WITH HEAVY SNOW TO THE NORTHWEST
FROM PARTS OF NORTHEAST AR INTO THE MO BOOTHEEL. IF 00Z MODELS
CONTINUE THIS TREND...CONFIDENCE WILL INCREASE AND WINTER WEATHER
WATCHES WILL LIKELY BE UPGRADED TO WARNINGS AND POSSIBLY EXTENDED IN
AREA IN THE WED 4 AM PACKAGE. THE OUTLIER IS THE NGM WHICH SHOWS A
WARMER SCENARIO WITH LESS WINTRY PRECIPITATION.