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Nov. 27th - Nov. 29th Upper Level Low


LithiaWx

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the latest run of GFS is shifting back west and closer to the latest ECMWF and GGEM. Its not quite there but its a substantial difference. It would be just like the model to find a major storm, lose it , then inch back to it.

Old run:

post-38-0-72325500-1322216907.gif

New, valid same time: Notice the trough axis is well back from Toledo to Mobile.

post-38-0-95342100-1322216945.gif

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From HPC this morning

...COMMA HEAD SNOWS ANTICIPATED FROM THE MID-SOUTH THROUGH THE UPPER OHIO VALLEY

INTO THE EASTERN GREAT LAKES EARLY NEXT WEEK... THE GENERAL FLOW PATTERN IS EXPECTED

TO FEATURE A TROUGH BROADENING ACROSS NORTH AMERICA DOWNWIND OF AN EASTERN PACIFIC

RIDGE. THE GUIDANCE SHARES THESE IDEAS. DETAIL-WISE...THERE ARE MAJOR ISSUES OUT EAST

WITH HOW FAR SOUTH A CLOSED CYCLONE IS EXPECTED TO FORM NEAR THE BASE OF THE TROUGH

DURING THE SHORT RANGE PERIOD AND HOW DEEP IT WILL GET. THE NCEP GUIDANCE WAS ALONE

WITH THEIR MORE NORTHERLY SOLUTIONS NEAR THE GREAT LAKES WHILE THE INTERNATIONAL

GUIDANCE WAS SETTLING UPON A MORE SOUTHERN/SLOWER SOLUTION. WHILE THE INTERNATIONAL

GUIDANCE WAS MORE BELIEVABLE WITH THEIR MORE SOUTHERN SOLUTIONS CONSIDERING THE

AMPLIFICATION EXPECTED UPSTREAM DURING THE SHORT RANGE PERIOD...THE 00Z CANADIAN FIT

TELECONNECTIONS BEST /THE APEX OF THE NORTHERN STREAM RIDGE IN NORTHERN QUEBEC

IMPLIES A CLOSED LOW IN THE NEIGHBORHOOD OF TENNESSEE/. HOWEVER... THE CANADIAN LOOKS

QUITE DEEP AS ITS 500 HPA STANDARDIZED ANOMALIES ARE 5-6 SIGMAS BELOW CLIMATOLOGY...WHICH

IS IMPROBABLE. THIS IS ANOTHER REASON WHY A COMPROMISE OF THE 12Z ECMWF ENSEMBLE MEAN/00Z

CANADIAN WAS NEEDED WITH THIS SYSTEM...WHICH SLOWED ITS PROGRESSION AT LEAST 12 HOURS

WHEN COMPARED TO CONTINUITY /THE ECMWF AND UKMET SOLUTIONS WOULD HAVE FORCED ADDITIONAL

SLOWING/. DEPENDING ON ITS DEPTH AND TRACK...COMMA HEAD SNOWS SHOULD SPREAD FROM THE

MID-SOUTH NORTHWARD INTO THE GREAT LAKES AND POTENTIALLY UP THE SPINE OF THE APPALACHIANS.

THERE IS AN OUTSIDE CHANCE OF SNOW ACROSS THE SOUTHEAST IF THE DEEPER/UNCLIMATOLOGICAL

SOLUTIONS VERIFY EARLY NEXT WEEK.

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Yep, I am thinking the cutoff is the way to go. To me, it's amazing to see the GFS ensembles so clearly show the cutoff while the operational still isn't there. Like Robert said, the 6z operational GFS is stepping in that direction.

Even with that said, the 6z operational still isn't there. Compare 18z Monday on the operational vs. the ensemble mean. Remember, that is an ensemble MEAN...pretty impressive.

Operational

post-390-0-53168400-1322221915.png

Ensemble mean

post-390-0-01733200-1322221929.png

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Yep, I am thinking the cutoff is the way to go. To me, it's amazing to see the GFS ensembles so clearly show the cutoff while the operational still isn't there. Like Robert said, the 6z operational GFS is stepping in that direction.

Even with that said, the 6z operational still isn't there. Compare 18z Monday on the operational vs. the ensemble mean. Remember, that is an ensemble MEAN...pretty impressive.

Operational

post-390-0-53168400-1322221915.png

Ensemble mean

post-390-0-01733200-1322221929.png

good post Matt. The mean has it squarely over MEM, same place op. had it for days until recently. If I had any guts I'd make a first call map with regard to specifics on this one, but that's too dangerous and I'm still chicken right now.:lol:

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I hear ya for sure. To say it's a challenge is an understatement. I guess right now if I were to pick any one model to go with it would be the 0z GEM operational. Looks about the best fit to me.

good post Matt. The mean has it squarely over MEM, same place op. had it for days until recently. If I had any guts I'd make a first call map with regard to specifics on this one, but that's too dangerous and I'm still chicken right now.:lol:

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Got to love this line from RAH's afternoon discussion after a good in depth overview of the model differences. :D

"BOTTOM LINE IS... MINIMAL CHANGES TO THE FORECAST DUE TO NO CONFIDENCE IN BEING ABLE TO IMPROVE IT."

That reminds me of a storm last winter where GSP was struggling and the disco says, "some days I wish I were a farmer"

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The Canadian and Euro 0z show quite interesting solutions. The American models, including the current NAM, seem to show nothing more than a glorified frontal passage. Will be interesting to see how this plays out... Is this a classic case of the American models losing the storm only to regain it as the event nears, or are they leading the way like much of last winter? I bet we'll have a good idea by the 0z runs tonight. The pessimist in me says it won't happen, but I am truly hoping for some wild weather. There is pretty good evidence to support either solution.

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The Canadian and Euro 0z show quite interesting solutions. The American models, including the current NAM, seem to show nothing more than a glorified frontal passage. Will be interesting to see how this plays out... Is this a classic case of the American models losing the storm only to regain it as the event nears, or are they leading the way like much of last winter? I bet we'll have a good idea by the 0z runs tonight. The pessimist in me says it won't happen, but I am truly hoping for some wild weather. There is pretty good evidence to support either solution.

the NAM is now coming around..surprise. I'd bet the GFS begins to revert to the major cutoff again.

post-38-0-67931400-1322234135.gif

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That reminds me of a storm last winter where GSP was struggling and the disco says, "some days I wish I were a farmer"

One of the funniest lines in a afd I have ever read. I have it saved.

NEAR TERM /THROUGH TONIGHT/...

-- Changed Discussion --SOMETIMES I THINK I SHOULD HAVE BEEN A FARMER. AT LONG LAST...WE

/THINK/ WE ARE GETTING A SOLID HANDLE ON THE UNFOLDING WINTER

WEATHER EVENT ACROSS THE WESTERN CAROLINAS/NORTHEAST GEORGIA.

HOWEVER...IT SHOULD BE NOTED THAT CONFIDENCE DROPS OFF SHARPLY AFTER

THE FIRST 6 HOURS OR SO...AS MUCH OF THIS EVENT WILL BE DOMINATED BY

MESOSCALE AND EVEN CONVECTIVE SCALE PROCESSES.

AS OF 16Z...A BAND OF MODERATE TO HEAVY SNOW WAS WELL ESTABLISHED

OVER THE MOUNTAINS AND ALONG THE I-40 CORRIDOR EAST OF THE BLUE

RIDGE. THIS WILL ONLY GRADUALLY DRIFT/EXPAND TO THE SOUTH AND EAST

WITH TIME. IN FACT...THE BACK EDGE OF THE FRONTOGENETICALLY FORCED

PRECIP WILL PROBABLY NOT MAKE SIGNIFICANT EASTWARD PROGRESS UNTIL

THE SURFACE LOW MAKES THE JUMP TO OFF THE SOUTHEAST COAST THIS

EVENING. THEREFORE...THE SNOW WILL CONTINUE TO PILE UP WHERE ITS

ALREADY FALLING...AND ACCUMULATIONS WILL NEED AN UPWARD ADJUSTMENT.

WE WILL NOW ADVERTISE 8-12 INCHES THROUGH TONIGHT ACROSS A GOOD

CHUNK OF THE MOUNTAINS...AND BUMP THE I-40 PORTION OF THE

PIEDMONT/FOOTHILLS TO 5 TO 8 INCHES. AS USUAL...THE LOCALLY HIGHER

AMOUNTS CAVEAT APPLIES.

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9z SREF @ 72hrs, agree with what others have postulated this morning, Memphis (mid MS River Valley) seems a reasonable starting place, as the low closes off at the base of the trough. Thereafter tracking through N AL/N GA, upstate of SC near GSP, maybe GSO and out near the Chesapeake. That would place TN on the favored NW side, with -SN chances for N AL, N GA, and western SC & NC, depending on how deep. Dryslot should punch into the area from about Macon to Charlotte as the main pva sweeps through, but still a potential for a few convective type squalls as the greatest delta-heights pass overhead. Still somewhat uncertain on strength and whether actual surface reflection will ride up the Apps, or attempt to occlude back into the upper level over SC/NC, maybe the TN Valley? Best conservative guess on strength would be a peak in the 540-543 range, somewhere between ATL and GSP, as that looks to be the area where the cutoff turns hard right, and at its most mature point. Still lots of uncertainty, but a general picture is starting to emerge now that we are within 72hrs... What a ride this was in the 3-7 day range :)

09zsref500mbHGHTUS072.gif

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9z SREF @ 72hrs, agree with what others have postulated this morning, Memphis (mid MS River Valley) seems a reasonable starting place, as the low closes off at the base of the trough. Thereafter tracking through N AL/N GA, upstate of SC near GSP, maybe GSO and out near the Chesapeake. That would place TN on the favored NW side, with -SN chances for N AL, N GA, and western SC & NC, depending on how deep. Dryslot should punch into the area from about Macon to Charlotte as the main pva sweeps through, but still a potential for a few convective type squalls as the greatest delta-heights pass overhead. Still somewhat uncertain on strength and whether actual surface reflection will ride up the Apps, or attempt to occlude back into the upper level over SC/NC, maybe the TN Valley? Best conservative guess on strength would be a peak in the 540-543 range, somewhere between ATL and GSP, as that looks to be the area where the cutoff turns hard right, and at its most mature point. Still lots of uncertainty, but a general picture is starting to emerge now that we are within 72hrs... What a ride this was in the 3-7 day range :)

09zsref500mbHGHTUS072.gif

Good post and thoughts there. And yet SREF has made a stout halt on the eastward progression. So now we have all the models going back west it appears. It would be something for the initial GFS to have latched on to this in the approx. correct spot, after all this.:lol: 12z GFS coming in now, and it too is already further west and south through 42 hours. We'll see where it makes the cutoff. Exciting storm to say the least.

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And sure enough by 60 hours its closed off (546) around west TN/KY, with thkns of 534 and 850 temps -4. Heavy rain in western Carolnas and GA through 66 hours, and moisture beginning to wrap into the colder air over Middle Tennessee. (snow showers at that point there).

By 72, the closed off low is deepening to 540 heights over middle Tenn, so its a pretty cold cutoff low for November. Snow in Ky, Tn so far not shown to be that much but remember as the low develops aloft, moisture will wrap around, and this is a cold enough one for snow probably.

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Thickness drops to 528 over Nashville. The model (and others did this) do something strange and thats make it a colder as you go type storm. Very dynamic cutoff. Pretty nice to see this work like that, so obviously snow showers galore under that thing in the TENN valley, including n. Ala, and nw GA I'd think. Probably a situation where its raining in Pittsburg, and there's snow showers in Nashville and Chattanooga Monday Night.

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Thickness drops to 528 over Nashville. The model (and others did this) do something strange and thats make it a colder as you go type storm. Very dynamic cutoff. Pretty nice to see this work like that, so obviously snow showers galore under that thing in the TENN valley, including n. Ala, and nw GA I'd think. Probably a situation where its raining in Pittsburg, and there's snow showers in Nashville and Chattanooga Monday Night.

I smell a snow chase for me if this continues! :snowman:

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Boy that dry slot is killer for Robert and I's area. This is a good run for folks in TN and WNC

Yeah, an upper closed off low is never good for us, if your wanting wrap around precip. I never was looking for snow east of the mtns in NC on this one..its all west of the Apps and up to the chain. In fact, we'd have a less shot at some flakes on the wraparound than say CLT or GSO would. We get dryslotted rapidly . But boy do we get the rain before the cold comes in!

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