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Windspeed

Winter Storm Threat: Feb. 16th-18th, 2015

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I know temps are forecast to remain below freezing for the next few days, but maybe if we get some sunshine on Tuesday the roads will improve a bit. The sun angle is getting stronger so even with temps below freezing there may be some melting on roads.

Hopefully we can switch over to snow here as there is alot of moisture still to move across. Not sure that I want three inches of sleet lol

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Crazy dewpoints in E TN....21 over 1 at KTRI, 25 over 4 at KTYS, and 32 over 4 at KCHA....I know it will be overwhelmed down here in Chatt but it may take a little while. I remember Jan 29, 2010 very well...although there won't be any snow here.

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mcd0069.gif

 

 

MESOSCALE DISCUSSION 0069
   NWS STORM PREDICTION CENTER NORMAN OK
   0909 AM CST MON FEB 16 2015

   AREAS AFFECTED...A LARGE PART OF TN

   CONCERNING...WINTER MIXED PRECIPITATION

   VALID 161509Z - 162015Z

   SUMMARY...FREEZING RAIN AND SLEET WILL CONTINUE SUPPORTING
   SUBSTANTIAL ICING ACROSS MUCH OF TN INTO THE AFTERNOON...WITH THE
   PRECIPITATION SPREADING EWD WITH TIME.

   DISCUSSION...SFC OBSERVATIONS ARE INDICATING WIDESPREAD SLEET AND
   FREEZING RAIN ASSOCIATED WITH A CONTINUOUS SHIELD OF PRECIPITATION
   EXTENDING FROM THE MID-SOUTH REGION TO MIDDLE TN. WITH NQA AND OHX
   VWPS DEPICTING NOTABLE VEERING OF WIND DIRECTION WITH HEIGHT IN THE
   LOWER TROPOSPHERE...WAA IS STRONG ACROSS THE AREA. RELATED STRONG
   ISENTROPIC ASCENT WILL CONTINUE IN PROXIMITY TO A LLJ THAT WILL
   GRADUALLY SHIFT EWD INTO THE AFTERNOON...WITH THE
   ASCENT/PRECIPITATION SPREADING TOWARD THE APPALACHIANS.

   THE 12Z BNA RAOB SAMPLES AN ELEVATED WARM LAYER JUST ABOVE H85
   SURMOUNTING DEEP SUB-FREEZING AIR...SUPPORTING SLEET.
   HOWEVER...ELEVATED WAA-ENHANCED WARMING WILL ALSO HAVE A PROPENSITY
   TO MELT DESCENDING HYDROMETEORS TO SUPPORT AREAS OF FREEZING RAIN
   ACROSS THE REGION...AND LOCAL-AREA/UPSTREAM OBSERVATIONS SUGGEST
   FREEZING RAIN RATES OF 0.05-0.10 INCH PER HOUR THIS MORNING. SLEET
   ACCUMULATION RATES MAY REACH NEAR A QUARTER INCH PER HOUR.
   SUBSTANTIAL ICING WILL LIKELY RESULT FROM THESE FREEZING RAIN/SLEET
   RATES...ESPECIALLY IN ANY CONVECTIVE ELEMENTS.

   SHORT-RANGE FORECAST SOUNDINGS DO INDICATE NEAR-SFC WARMING
   SUPPORTING A TRANSITION TO PURE LIQUID RAIN ACROSS SRN PARTS OF
   MIDDLE AND SERN TN THIS AFTERNOON. HOWEVER...OBSERVATIONS SHOW A
   VERY DRY AIR MASS IN PLACE -- AS REPRESENTED BY SFC DEWPOINTS FROM
   THE UPPER SINGLE DIGITS TO THE TEENS -- AND RELATED WET-BULB COOLING
   MAY OFFSET SFC-LOW PRECEDING WAA AND VERY MODEST DIURNAL HEATING. AS
   SUCH...IT IS POSSIBLE THAT FROZEN PRECIPITATION MAY PREDOMINATE
   REGION-WIDE. ELSEWHERE...PRECIPITATION WILL BEGIN TAPERING OFF FROM
   WEST TO EAST ACROSS PARTS OF THE MID-SOUTH BY MID-AFTERNOON...AS
   LARGE-SCALE ASCENT SHIFTS EWD.

 

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I'll give the RAP and HRRR credit for one thing, they've been consistent since last night about rain for most of east TN.  I don't buy it based on the real world analysis but there is definately a line drawn in the sand about this.  It'll be facinating to watch unfold.

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The warming issue isn't currently at 850, it's well above there between 750 and 800. Thus the lack of snow even with 850s below freezing. I'm somewhat surprised to see freezing rain being able to fall in areas with 850s below freezing. I'd have figured that would be enough for sleet in that whole area.

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124 PM EST MON FEB 16 2015

...ICE STORM WARNING IN EFFECT UNTIL 7 AM EST /6 AM CST/

TUESDAY...

...WINTER STORM WARNING IS CANCELLED...

THE NATIONAL WEATHER SERVICE IN MORRISTOWN HAS ISSUED AN ICE

STORM WARNING, WHICH IS IN EFFECT UNTIL 7 AM EST /6 AM CST/

TUESDAY. THE WINTER STORM WARNING HAS BEEN CANCELLED.

* EVENT, A MIX OF MOSTLY FREEZING RAIN AND SLEET WILL PICK UP IN

INTENSITY THIS AFTERNOON, RESULTING IN WIDESPREAD SIGNIFICANT

ICE ACCUMULATION ACROSS THE CENTRAL VALLEY, THE CENTRAL SMOKY

MOUNTAINS AND PORTIONS OF THE SOUTHERN VALLEY, BEFORE TAPERING

OFF LATE TONIGHT. TOTAL ICE ACCUMULATIONS OF A QUARTER TO A HALF

INCH POSSIBLE, WITH SOME LOCALLY HIGHER AMOUNTS ARE POSSIBLE. 1

TO 3 INCHES OF SLEET AND SNOW ACCUMULATION ARE POSSIBLE THROUGH

LATE TONIGHT.

* TIMING, PRECIPITATION WILL CONTINUE THROUGHOUT THE DAY AND

EVENING... AND WILL TAPER OFF AFTER MIDNIGHT TONIGHT.

* IMPACTS, ICE AND SNOW ACCUMULATION MAY BRING WIDESPREAD

HAZARDOUS TRAVEL CONDITIONS ON ROADWAYS, AS WELL AS POWER

OUTAGES AND TREE DAMAGE.

* ICE ACCUMULATIONS, WIDESPREAD AMOUNTS OF ONE THIRD OF AN INCH

TO ONE HALF OF AN INCH OF ICE ACCRETION, WITH LOCALLY HIGHER

AMOUNTS WILL BE POSSIBLE. IN ADDITION, SLEET ACCUMULATION OF 1

TO 2 INCHES WILL BE POSSIBLE IN SOME AREA, ALONG WITH LIGHT

SNOWFALL AMOUNTS.

* OTHER IMPACTS, SIGNIFICANT ICE AND SLEET ACCUMULATION WILL BRING

WIDESPREAD HAZARDOUS TRAVEL CONDITIONS ON ROADWAYS, AS WELL AS

RESULT IN SOME POWER OUTAGES AND TREE DAMAGE.

PRECAUTIONARY/PREPAREDNESS ACTIONS...

AN ICE STORM WARNING MEANS SEVERE WINTER WEATHER CONDITIONS ARE

EXPECTED OR OCCURRING. SIGNIFICANT AMOUNTS OF ICE ACCUMULATIONS ARE

EXPECTED, WHICH WILL LIKELY LEAD TO DOWNED POWER LINES AND FALLING

TREE BRANCHES, AS WELL AS MAKING TRAVEL VERY HAZARDOUS OR

IMPOSSIBLE. TRAVEL IS STRONGLY DISCOURAGED. IF TRAVEL IS

UNAVOIDABLE, KEEP AN EXTRA FLASHLIGHT, FOOD, AND WATER IN YOUR

VEHICLE IN CASE OF AN EMERGENCY.

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I'm gonna give hat's off to the NAM. It's been very close on precip types. It gave me the least snow accumulation by far and showed this as a sleet storm all day. It's gotten both right so far. It has the peak of warming in about an hour or two, then the collapse of cold into the back side around 6-7 that causes the change to snow to begin as the precip pulls away. If it's correct, the valley from JC to Chattanooga will switch to rain for a little while this evening.

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I think its safe to say Euro lost on this storm. Not that any model did great, but NAM seemed to snif out this warm nose first.

 

Part of it was the data ingest that happend a couple of nights ago.  We saw it on SREF first as that rolled out first, then NAM, then GFS, then I think even Euro started showing the warm push north.  But yes Euro/Ukie were consistent with a colder more southern solution for many days so we'll have to keep that in mind going forward.  I'm going to always bet on an eventual nothern trend on these things.

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I noticed that on Saturday the open 850 mb wave progged over the Valley for Monday turned into a closed or nearly closed 850 low tracking north of us, which was the death knell for snow in the Valley. South winds ahead of the 850 low pull in warm air aloft. With the surface low/trough still south, holding in cold air, it became a classic ice storm signature. The system is very slanted from south to north, with the 500 mb vort max at/north of the Ohio River. Kentucky pulled off a miracle snow with the vort max north. Surface high also retreated faster this side of the Apps but I think that was more an effect, than a cause of the weather pattern.

 

I've seen a couple other nice posts about this storm. Maybe a discussion thread? Otherwise we can let the end of this thread be the discussion, esp if only a few more posts. No whining outside the Banter thread; but, certainly discuss what went wrong, or just what happened. Our Kentucky friends sure enjoyed both the 850 low and surface low tracking to their south - in spite of 500 mb issues! I think kissing jets upstairs helped Kentucky cash in. Go Big winter Blue? Cheers!

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Probably better to continue the post-analysis of the storm here just to make searching easier on how the storm evolved from a model and synoptic standpoint. We may have a few more storm threads before February is done.

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I noticed that on Saturday the open 850 mb wave progged over the Valley for Monday turned into a closed or nearly closed 850 low tracking north of us, which was the death knell for snow in the Valley. South winds ahead of the 850 low pull in warm air aloft. With the surface low/trough still south, holding in cold air, it became a classic ice storm signature. The system is very slanted from south to north, with the 500 mb vort max at/north of the Ohio River. Kentucky pulled off a miracle snow with the vort max north. Surface high also retreated faster this side of the Apps but I think that was more an effect, than a cause of the weather pattern.

 

I've seen a couple other nice posts about this storm. Maybe a discussion thread? Otherwise we can let the end of this thread be the discussion, esp if only a few more posts. No whining outside the Banter thread; but, certainly discuss what went wrong, or just what happened. Our Kentucky friends sure enjoyed both the 850 low and surface low tracking to their south - in spite of 500 mb issues! I think kissing jets upstairs helped Kentucky cash in. Go Big winter Blue? Cheers!

Great post, Jeff. Thanks for the explanation.

I see no reason for whining from anyone. Understandably, those suffering damages and power outages have reason to be upset with the way this turned out. From a meteorological standpoint, however, this storm was absolutely fascinating. As I mentioned, I have never seen a sleet storm of this magnitude. Typically, it's either rain or snow here.

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