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Winter Storm Feb 25 and 26


nrgjeff

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I've been just sitting back and reading for this one. There isn't much more I can add that y'all have went over and showed. I would go 4-6 for KTRI and KTYS. 6-8 for KCHA. I think the next few hours will be very telling on radar for how far northwest the band gets. HRRR and RAP have the northern shield not moving past the state line below Memphis/Nashville. It is knocking on the borders door right now. I wouldn't be concerned in Chatty. Dynamical cooling and wet bulbs should keep you mostly snow. Maybe some rain/sleet at the start of the event. Charlotte to RDU are going to get crushed.

 

Sounds right to me man (TRI).  I can't imagine we have the upside of the last big system that busted dramatically, but I don't think we have much downside bust potential either, looks to be a perfect hone in on 4-6 inches.  As I type this I am amazed at my lack of excitement for 4-6 haha after experiencing the last few weeks

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I've been just sitting back and reading for this one. There isn't much more I can add that y'all have went over and showed. I would go 4-6 for KTRI and KTYS. 6-8 for KCHA. I think the next few hours will be very telling on radar for how far northwest the band gets. HRRR and RAP have the northern shield not moving past the state line below Memphis/Nashville. It is knocking on the borders door right now. I wouldn't be concerned in Chatty. Dynamical cooling and wet bulbs should keep you mostly snow. Maybe some rain/sleet at the start of the event. Charlotte to RDU are going to get crushed.

I like your projections!!  I feel comfortable with those, and Jeff's and maybe a blend of the two.

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The question I have...Have the models caught-up or is this a case where the precip is growing so quick on the western side that models don't catch real time. This trend has been the case all winter with precip not being robust enough. Approaching spring time helps. Makes them juicier.

I don't think they will catch on until it is almost happening. To be honest after last weekend's event I don't have much trust in the HRRR and RAP. They were advertising 1-3 inches and I ended up with 8. With all that said this is a much different situation than last week. Last week was a thermal problem that those short term models had. They were trying to warm us up too quick. Here in this situation most of us are concerned with precip shield placement and intensity. Last week the HRRR and RAP were a little bit weak on the intensity but overall did okay.

I wouldn't trust those models too much around Chattanooga. They will probably show too much rain mixing in. At least in my experience last weekend they were too warm.

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I don't think they will catch on until it is almost happening. To be honest after last weekend's event I don't have much trust in the HRRR and RAP. They were advertising 1-3 inches and I ended up with 8. With all that said this is a much different situation than last week. Last week was a thermal problem that those short term models had. They were trying to warm us up too quick. Here in this situation most of us are concerned with precip shield placement and intensity. Last week the HRRR and RAP were a little bit weak on the intensity but overall did okay.

I wouldn't trust those models too much around Chattanooga. They will probably show too much rain mixing in. At least in my experience last weekend they were too warm.

 

My knock on the RAP is it is usually too low for the northern Valley.  I really want to see the 18z NAM before locking in...but 3-6" for the eastern Valley seems about right...w/ locally higher amounts further south. 

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17z HRRR is beefy, considering it's still snowing plateau eastward:

 

H1AKO2p.gif

 

 

I am going to leave the map up w/ these comments.  The precip shield has backed westward about 100 miles today on this model.  It isn't so much that the storm is moving northward, though it has a tad.  It has more to do w/ the models recognizing an expanding precip shield for a deepening slp.  Remember, we get pretty good snows when lows track just north of the GOM through southern GA and to Hatteras, preferably inside Hatteras.  Prob won't go inside Hatteras this time, but the storm may be strong enough to overcome that distance as it strengthens. 

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are there any current reports of precip reaching the ground in TN yet?

AREA FORECAST DISCUSSION

NATIONAL WEATHER SERVICE NASHVILLE TN

134 PM CST WED FEB 25 2015

.DISCUSSION...CURRENT RADAR LOOP SHOWS LIGHT ECHOES NOW MOVING

INTO SOUTHERN MIDDLE TENNESSEE, ALTHOUGH TEMPS ACROSS THE MID

STATE ARE FOR THE MOST PART SLIGHTLY ABOVE FREEZING. HOWEVER,

LARGE DEW POINT SPREADS (15-20F) DO LEAVE SOME ROOM FOR

EVAPORATIVE COOLING. TEMPS UPSTREAM WHERE IT HAS ALREADY BEEN

PRECIPITATING ARE RIGHT AROUND FREEZING, SO BELIEVE MOST OF THE

PRECIPITATION WE SEE THIS AFTERNOON WILL BE SNOW. LATEST HPC

SNOWFALL PROGS ARE CONSISTENT WITH THE AMOUNTS WE HAVE BEEN

FORECASTING, SO AM GOING TO LEAVE THE SNOW GRIDS ALONE THIS

FORECAST. NAM BRINGS THE DEEPEST MOISTURE THROUGH MIDDLE TENNESSEE

BETWEEN 00Z & 06Z, WITH SNOW TAPERING OFF FROM WEST TO EAST AFTER

06Z. LOOK FOR SOME LINGERING LIGHT SNOW OR FLURRIES TOMORROW AS A

SECONDARY WAVE PUSHES THROUGH BUT WE SHOULD REMAIN DRY UNTIL LATER

IN THE WEEKEND WHEN THE NEXT ACTIVE SYSTEM MOVES IN. MODELS ARE

HINTING AT A SPRING-LIKE FRONTAL SYSTEM ON TUESDAY AS MUCH WARMER

TEMPERATURES AND A STRONG LOW-LEVEL JET APPEAR TO SET THE TABLE

FOR THUNDERSTORMS BEFORE WE TURN COLDER AGAIN.

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15z SREF Means

TRI: 4.71 (Large cluster of members between 2 and 5, and another smaller cluster right around 8 inches)
TYS: 5.02 (Also a large cluster of members between 2 and 5, and another cluster of members from 7-8.5)
CHA: 7.03 (Every member but 3 clustered between 5.24-10.61. Lowest member still 2.45)
BNA: 0.93 (A lot of members between .24-.74. Seven members between 1-2.67, bringing up the mean)

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HRRR seems to dry slot us, because of the convection down south?

 

Yao6kZD.gif

Lets just hope that convective banding across the gulf, FL and GA doesn't get that strong.  Right now the precip shield has a lot of convection but fairly disorganized, if it can stay disorganized I think we will be ok.  We'll have to watch for that.

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MRX:

 

 

 

000
FXUS64 KMRX 252008
AFDMRX

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
308 PM EST WED FEB 25 2015

.SHORT TERM (TONIGHT THROUGH THURSDAY NIGHT)...
A LOW LEVEL DRY LAYER IS DELAYING PRECIP AT THE GROUND OVER SOUTHERN
AREAS...BUT GRADUAL MOISTENING OF THIS LAYER SHOULD RESULT IN SNOW
BEGINNING NEAR CHATTANOOGA AROUND 22-23Z...WITH ACCUMULATIONS
STARTING AN HOUR OR TWO LATER AS TEMPERATURES DROP FROM EVAPORATIVE
COOLING. HEAVY TO MODERATE SNOWFALL IS EXPECTED AT TIMES THIS
EVENING AS AGEOSTROPHIC FORCING BETWEEN UPPER JET STREAKS PROVIDES
STRONG VERTICAL ASCENT. THIS LIFT APPEARS STRONGEST OVER SE TN...SW
NC..AND THE MOUNTAINS THIS EVENING. BY 06Z WE START TO SEE DRIER
AIR MOVING INTO SOUTHERN AREAS AT THE DENDRITE GROWTH LEVEL...AND
THE AREA OF BEST FORCING MOVES INTO NE TN AND SW VA. POPS WILL DROP
BACK TO A CHANCE NORTH TO SLIGHT CHANCE SOUTH BY EARLY THURSDAY
MORNING...WITH LITTLE TO NO ADDITIONAL ACCUMULATION EXPECTED AFTER
THIS TIME. THE WINTER STORM WARNING AND WINTER WEATHER ADVISORY
AREAS AND TIMING WILL REMAIN UNCHANGED.

A NW UPSLOPE FLOW AND SOME STEEPENING LAPSE RATES MAY KEEP SOME SNOW
SHOWERS AND FLURRIES IN NORTHERN AREAS AND THE MOUNTAINS THURSDAY
AFTERNOON AND NIGHT. IT DOES NOT APPEAR THAT THIS WILL ADD MUCH
ADDITIONAL SNOW ACCUMULATION TO THE TOTAL...AS UPSLOPE WINDS ARE
ONLY 10-15 KTS AND MOISTURE IS SHALLOW. FOR TEMPERATURES...WILL
UNDERCUT MOS GUIDANCE BY A FEW DEGREES TO ACCOUNT FOR THE SNOW
COVER...AND FOR THE EXPECTED OVERCAST CLOUD COVER THAT IS EXPECTED
TO LINGER THROUGH THURDAY.

 

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Afternoon disco from MRX: 

 

.SHORT TERM (TONIGHT THROUGH THURSDAY NIGHT)...
A LOW LEVEL DRY LAYER IS DELAYING PRECIP AT THE GROUND OVER SOUTHERN
AREAS...BUT GRADUAL MOISTENING OF THIS LAYER SHOULD RESULT IN SNOW
BEGINNING NEAR CHATTANOOGA AROUND 22-23Z...WITH ACCUMULATIONS
STARTING AN HOUR OR TWO LATER AS TEMPERATURES DROP FROM EVAPORATIVE
COOLING. HEAVY TO MODERATE SNOWFALL IS EXPECTED AT TIMES THIS
EVENING AS AGEOSTROPHIC FORCING BETWEEN UPPER JET STREAKS PROVIDES
STRONG VERTICAL ASCENT. THIS LIFT APPEARS STRONGEST OVER SE TN...SW
NC..AND THE MOUNTAINS THIS EVENING. BY 06Z WE START TO SEE DRIER
AIR MOVING INTO SOUTHERN AREAS AT THE DENDRITE GROWTH LEVEL...AND
THE AREA OF BEST FORCING MOVES INTO NE TN AND SW VA. POPS WILL DROP
BACK TO A CHANCE NORTH TO SLIGHT CHANCE SOUTH BY EARLY THURSDAY
MORNING...WITH LITTLE TO NO ADDITIONAL ACCUMULATION EXPECTED AFTER
THIS TIME. THE WINTER STORM WARNING AND WINTER WEATHER ADVISORY
AREAS AND TIMING WILL REMAIN UNCHANGED.

A NW UPSLOPE FLOW AND SOME STEEPENING LAPSE RATES MAY KEEP SOME SNOW
SHOWERS AND FLURRIES IN NORTHERN AREAS AND THE MOUNTAINS THURSDAY
AFTERNOON AND NIGHT. IT DOES NOT APPEAR THAT THIS WILL ADD MUCH
ADDITIONAL SNOW ACCUMULATION TO THE TOTAL...AS UPSLOPE WINDS ARE
ONLY 10-15 KTS AND MOISTURE IS SHALLOW. FOR TEMPERATURES...WILL
UNDERCUT MOS GUIDANCE BY A FEW DEGREES TO ACCOUNT FOR THE SNOW
COVER...AND FOR THE EXPECTED OVERCAST CLOUD COVER THAT IS EXPECTED
TO LINGER THROUGH THURDAY.

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Is the ULL modeled to track across East TN?

Parts of the the 500 mb low should track over east TN. Here is the current position of the upper low and the forecasted positions. I will say the NAM has been pretty darn good with this system so far.

9c6781d28f52452857f991b32e4e3860.jpg

6c7fcf09eb156d37d06ac4c7aff30ae0.jpg

This storm would of been a doozy if the 500mb low would of stayed intact more and stayed negative tilt over the Carolinas.

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Thank you for the feedback on my previous post. All snow HSV to CHA is settled. Dual polarization radar correlation coefficient shows all snow at/north of the blue line. Shows up best out of KBMX. Dual pole physics are superior to some grid based algorithms, so I am now really rest assured no debacle in Chattanooga. Everybody enjoy!

post-2545-0-71388700-1424895518_thumb.pn

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