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Freeze to Thaw, Winter Wx, Feb. 20th-21st, 2015


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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
950 AM EST THU FEB 19 2015

.DISCUSSION...SOME LINGERING LOW LEVEL MOISTURE COULD STILL PRODUCE
A FEW FLURRIES INTO THIS AFTERNOON...WHICH IS WELL COVERED IN
TODAY`S GRIDS.

OTHERWISE...THE MAIN STORY IS THE BITTERLY COLD AIR MASS OVER THE
REGION...AS NOTED BY THE -25 DEGREES CELSIUS TEMPS OVER ERN KY AND
SW VA THIS MORNING AT 850 MBS. SUB ZERO AND SINGLE DIGIT LOWS THIS
MORNING WON`T RISE MUCH TODAY...BUT I MAY NEED TO TWEAK A FEW MAX
TEMPS BASED ON LATEST OBSERVATIONS.

WIND SPEEDS ARE MUCH LIGHTER THAN YESTERDAY...AND AS TEMPS WARM A
FEW DEGREES THIS MORNING...THE WIND CHILL WARNING VALUES SHOULD BE
LIMITED TO THE ERN MTNS AND HIGHER TERRAIN OF SW VA. HOWEVER...NRN
PLATEAU AND NRN VALLEY AREAS DID BRIEFLY DIP BELOW -15 DEGREES FOR
WIND CHILLS EARLY THIS MORNING. CURRENT WIND CHILL ADVISORY AND
WARNING PRODUCTS LOOK GOOD ON AREAL COVERAGE AND DURATION.

LOOKING FURTHER AHEAD...WINTER WEATHER LOOMS FOR FRIDAY NIGHT INTO
SATURDAY. AFTER VIEWING 06Z MODEL DATA...OUR LATEST FORECAST GRIDS
LOOK ON TRACK FOR THOSE PERIODS ON POTENTIAL ICE AND/OR SNOW
AMOUNTS. WILL VIEW 12Z MODEL DATA AND COORDINATE ON THE NEED TO
EXPAND THE WINTER STORM WATCH NORTH INTO NE TN AND SW VA.

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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
921 AM CST THU FEB 19 2015

.UPDATE...FRIGID TEMPERATURES WERE REPORTED THIS MORNING ACROSS
MID TN. SUNSHINE WAS HELPING...WITH MID MORNING READINGS "WARMING"
INTO THE 5 TO 10 RANGE FOR MOST LOCATIONS. WIND CHILLS WERE IN THE
SINGLE DIGITS BELOW ZERO...AND A WIND CHILL ADVISORY WILL CONTINUE
UNTIL NOON. THE FORECAST HAS BEEN ADJUSTED FOR HOURLY TRENDS...AND
GIVEN FULL SUNSHINE...BUMPED UP HIGHS A DEGREE OR 2.

WE CONTINUE TO BE CONCERNED ABOUT MORE WINTRY WX FOR MID TN FROM
MIDDAY FRIDAY THROUGH FRIDAY NIGHT. 06Z DATA AND FIRST GLANCE AT
12Z DATA SHOW AN INCH OR 2 OF SNOW FOLLOWED BY SIGNIFICANT...
LIKELY DAMAGING...ICE IN THE FORM OF HEAVY FREEZING RAIN. THE GOOD
NEWS ABOUT THIS SYSTEM IS THAT TEMPS WILL WARM UP CONSIDERABLY ON
SATURDAY. BUT ANOTHER DOWNER...WE MAY HAVE SOME LOCALIZED FLOOD
PROBLEMS TO DEAL WITH THEN. BUCKLE UP...ITS GOING TO BE A BUMPY
RIDE.

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The RGEM came south at the last minute with this last storm. It also seemed to miss the ice threat...but I may be misremembering. I think most short range models(minus he NAM) over estimated surface warming to a large degree. The switch by the NAM and GFS is significant because this is when we saw the models shift drastically north last time around. This time the shift is south in apparent response to an approaching cold front and cold air that won't move easily. The RGEM is a valid solution as are the NAM/GFS solutions. I think a blend of the two would be wise.

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OHX upgraded their entire CWA to a winter storm warning. 1-2 inches of snow, 1/2 inch of ice. Says areas East of 65 will be hardest hit and will likely be changed to an Ice Storm Warning after the snow passes.

...WINTER STORM WARNING IN EFFECT FROM NOON FRIDAY TO 9 AM CST

SATURDAY...

THE NATIONAL WEATHER SERVICE IN NASHVILLE HAS ISSUED A WINTER

STORM WARNING FOR ICE AND SNOW...WHICH IS IN EFFECT FROM NOON

FRIDAY TO 9 AM CST SATURDAY. THE WINTER STORM WATCH IS NO LONGER

IN EFFECT.

* TIMING...NOON FRIDAY TO 9 AM SATURDAY.

* ACCUMULATIONS...1 TO 2 INCHES OF SNOW FRIDAY...FOLLOWED BY ONE

  TENTH TO ONE HALF INCH OF ICE IN THE FORM OF FREEZING RAIN

  FRIDAY EVENING THROUGH EARLY SATURDAY MORNING. AREAS ALONG AND

  EAST OF INTERSTATE 65 WILL BE THE HARDEST HIT...WITH NEW ICE

  AMOUNTS UP TO ONE HALF INCH. THE EAST HALF OF MID TENNESSEE MAY

  LATER BE PLACED UNDER AN ICE STORM WARNING.

* MAIN IMPACT...ICE AND SNOW WILL MAKE TRAVEL HAZARDOUS. FREEZING

  RAIN WILL ADD TO ICE THAT IS ALREADY ON TREES AND OTHER SURFACES

  TO CAUSE DAMAGE. TREE LIMBS ARE LIKELY TO FALL...AND POWER

  OUTAGES ARE LIKELY.

* OTHER IMPACTS...MAJOR DISRUPTIONS TO TRAVEL ARE EXPECTED FRIDAY

  AFTERNOON THROUGH EARLY SATURDAY MORNING. GUSTY WINDS WILL ADD

  TO THE THREAT FOR FALLING LIMBS AND POWER OUTAGES. WARMING

  TEMPERATURES AND HEAVY RAINFALL WILL BRING THE POTENTIAL FOR

  LOCALIZED FLOODING ON SATURDAY.

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URGENT - WINTER WEATHER MESSAGE

NATIONAL WEATHER SERVICE HUNTSVILLE AL

206 PM CST THU FEB 19 2015

 

...ICE AND SNOW WILL BRING HAZARDOUS CONDITIONS TO SOUTHERN MIDDLE

TENNESSEE AND NORTHERN ALABAMA FROM FRIDAY MORNING UNTIL SATURDAY

MORNING...

 

.A DEVELOPING STORM SYSTEM WILL QUICKLY SPREAD MOISTURE INTO THE AREA

BY EARLY FRIDAY MORNING. WITH ABUNDANT COLD AIR IN PLACE...IT IS

EXPECTED THAT THE PRECIPITATION WILL BEGIN AS A PERIOD OF SNOW. AS

WARM AIR MOVES NORTHEAST INTO THE AREA...THE SNOW SHOULD TRANSITION

TO A SLEET AND FREEZING RAIN MIXTURE BY AFTERNOON AND CONTINUE INTO

FRIDAY NIGHT. NORTHEAST ALABAMA AND SOUTHERN MIDDLE TENNESSEE MAY

HAVE A LONGER DURATION OF SLEET AND FREEZING RAIN FROM FRIDAY

AFTERNOON UNTIL SATURDAY MORNING. ICE AMOUNTS AROUND A TENTH OF AN

INCH ARE EXPECTED ALONG AND SOUTH OF A LINE FROM FLORENCE TO CULLMAN

ALABAMA. ICE AMOUNTS GREATER THAN A QUARTER OF AN INCH ARE EXPECTED

ALONG AND NORTH OF A LINE FROM HUNTSVILLE TO FORT PAYNE ALABAMA...

EXTENDING NORTHWARD INTO SOUTHERN MIDDLE TENNESSEE.

 

MADISON-JACKSON-DEKALB-MOORE-LINCOLN-FRANKLIN TN- INCLUDING THE CITIES OF...HUNTSVILLE...SCOTTSBORO...FORT PAYNE... LYNCHBURG...FAYETTEVILLE...WINCHESTER

206 PM CST THU FEB 19 2015

 

...WINTER STORM WARNING IN EFFECT FROM NOON FRIDAY TO 9 AM CST

SATURDAY...

 

THE NATIONAL WEATHER SERVICE IN HUNTSVILLE HAS ISSUED A WINTER

STORM WARNING FOR ICE AND SNOW...WHICH IS IN EFFECT FROM NOON FRIDAY

TO 9 AM CST SATURDAY. THE WINTER STORM WATCH IS NO LONGER IN EFFECT.

 

* TIMING AND AREAS AFFECTED...NORTHEAST ALABAMA AND SOUTHERN MIDDLE

  TENNESSEE FROM NOON CST FRIDAY UNTIL 9 AM CST SATURDAY.

 

* IMPACTS...MIXED WINTRY PRECIPITATION WILL CAUSE SIGNIFICANT TRAVEL

  PROBLEMS FROM AROUND NOON FRIDAY THROUGH SUNDAY MORNING.

 

* ACCUMULATIONS...AROUND A HALF AN INCH OF SNOW OR SLEET...AND

  GREATER THAN A QUARTER OF AN INCH OF ICE.

 

PRECAUTIONARY/PREPAREDNESS ACTIONS...

 

A WINTER STORM WARNING MEANS SIGNIFICANT AMOUNTS OF SNOW...

SLEET...AND ICE ARE EXPECTED. THIS WILL MAKE TRAVEL VERY HAZARDOUS.

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I am going with faster NAM guidance on change over timing from HSV to Chatty, both snow to ice and ice to rain. Believe GFS, slower on both transitions, will work out from the Plateau into northeast Tenn. Knoxville is in my GFS zone. Nashvegas maybe a blend of all 3 including the Euro. Agreement seems better farther west into the Mid South and Memphis area. I may write more later. Hope everyone over achieves on snow and keeps power in ice. Cheers!

 

EDIT: Bearman thanks for the report (next post). Good to know with more coming.

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hmm, so two nice runs of the nam now, and the 12z GFS backed it up.  Seems like every big storm always has these last minute slight shifts that when you get 2-3 of them in a row means honing in.  But I suppose we have a little battle between Euro vs Nam/GFS?

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AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE NASHVILLE TN
247 PM CST THU FEB 19 2015

.SHORT TERM...TONIGHT THROUGH SATURDAY NIGHT.

RECORD SETTING COLD AIR IS IN PLACE OVER MID TN. THE CENTER OF
THE ARCTIC HIGH PRESSURE SYSTEM WILL MOVE EAST OF THE AREA TONIGHT
AS A LOW PRESSURE SYSTEM BEGINS TO TAKE SHAPE OVER THE PLAINS.
WARM ADVECTION WILL DEVELOP BETWEEN THESE SYSTEMS...SPREADING
MOISTURE ACROSS THE COLD AIR IN PLACE. THIS COULD MEAN SOME
FLURRIES OR VERY LIGHT SNOW MOVING INTO OUR WEST COUNTIES BY
DAYBREAK. LITTLE OR NO ACCUM THROUGH DAYBREAK.

ON FRIDAY...MOISTURE AND LIFT WILL INCREASE...ESPECIALLY IN THE
AFTERNOON AS 850 MB WINDS BACK TO THE SOUTHWEST AND INCREASE. THIS
WILL SPREAD ACCUMULATING SNOWFALL ACROSS THE MID STATE...WITH
AMOUNTS OF 1 TO 2 INCHES. FRIDAY AFTERNOON RUSH HOUR IS LIKELY TO
BE SIGNIFICANTLY IMPACTED.

BY FRIDAY NIGHT...THE LOW PRESSURE SYSTEM WILL BE MOVING TOWARD
THE MS VALLEY REGION. OUT AHEAD OF IT...850 MB WINDS WILL
STRENGTHEN TO 70KT...BRINGING A SURGE OR WARMER AIR. THE QUESTION
IS HOW QUICKLY THIS WARMING WILL OCCUR AT VARIOUS LEVELS IN THE
ATMOSPHERE. WE EXPECT THE SNOW TO QUICKLY TRANSITION TO SLEET AND
FREEZING RAIN FRIDAY EVENING...THEN OVER TO ALL LIQUID FROM WEST
TO EAST. THE CHANGE TO ALL RAIN IS EXPECTED TO OCCUR AROUND 10 PM
ALONG THE TN RIVER...AROUND 2 AM ALONG THE I 65 CORRIDOR...AND BY
9 AM SATURDAY ALONG THE PLATEAU. SURFACE TEMPS WILL BE CRITICAL
TO THE AMOUNT OF ICE (FREEZING RAIN) WE RECEIVE. GENERALLY...WE
EXPECT THE SURFACE WARMING TO BE SLOWER THAN ADVERTISED BY THE
GUIDANCE...GOING MORE WITH THE NAM 2 METER TEMPS. EVEN WHEN TEMPS
DO CLIMB ABOVE FREEZING...THE ICE WILL TAKE A LITTLE WHILE TO STOP
ACCRUING AND START MELTING SINCE SURFACES ARE SO COLD GOING INTO
THIS EVENT. WE EXPECT ICE AMOUNTS TO BE GENERALLY ONE TENTH TO ONE
QUARTER WEST HALF...AND UP TO ONE HALF INCH IN THE EAST HALF. THIS
SIGNIFICANT ICE WILL ADD TO ICE THAT IS ALREADY ON TREES...POWER
LINES...BUILDINGS...ETC. TO CAUSE DAMAGE AND POWER OUTAGES. WE MAY
UPDATE SOME AREAS TO ICE STORM WARNING LATER ON. FORTUNATELY...THIS
EVENT WILL BE RELATIVELY BRIEF WITH ALL OF MID TN CHANGING OVER TO
RAIN BY 9 AM SATURDAY.

A FEW THOUGHTS ABOUT CONFIDENCE...
CONFIDENCE IN THE GENERAL EVOLUTION OF THIS EVENT IS
HIGH...MEANING WE ARE HIGHLY CONFIDENT THAT LIGHT SNOW WILL
DEVELOP...THEN PRECIPITATION WILL INCREASE AS IT TRANSITIONS TO
SLEET...FREEZING RAIN AND RAIN. WE HAVE MEDIUM CONFIDENCE
REGARDING THE EXACT AMOUNTS OF EACH TYPE THAT WILL OCCUR. IT IS
POSSIBLE THAT THE INITIAL MOISTURE MAY BE SLOWER COMING INTO THE
VERY DRY AIR IN PLACE...AND THAT SNOW AMOUNTS WOULD BE LOWER THAN
INDICATED. ALSO...THE WARM AIR SURGE MAY BE SO STRONG THAT THE ICE
LASTS ONLY A SHORT TIME. THIS WOULD ALSO CUT EXPECTED TOTALS...BUT
THIS WOULD BE A GOOD THING. ON THE OTHER HAND...SFC TEMPS MAY STAY
COLD LONGER...MEANING MORE WIDESPREAD ICE PROBLEMS (MAJOR ICE
STORM). THIS POTENTIAL LOOKS GREATEST OVER THE EAST HALF. THIS
FORECAST SITUATION IS DIFFERENT THAN MOST BECAUSE OF THE EXISTING
ICE AND FRIGID AIR. OUR CURRENT CONDITIONS GOING INTO THIS EVENT
HAVE PLAYED A BIG ROLE IN THE DECISION TO GO AHEAD WITH THE
WARNING. EVEN IF WW MANAGE TO AVOID MAJOR ICE DAMAGE...TRAVEL IS
HIGHLY LIKELY TO BECOME QUITE DANGEROUS BY FRIDAY EVENING.

AFTER THE WINTRY MESS...HEAVY RAINFALL AND LOCALIZED FLOODING WILL
BE A CONCERN. WE ARE NOT GOING TO ADD ANOTHER HEADLINE AT THIS
TIME...BUT DEPENDING ON FUTURE QPF...WE MAY EVENTUALLY NEED A
FLOOD WATCH FOR SATURDAY AND SATURDAY NIGHT. 1 TO 2 INCHES OF
RAINFALL IS EXPECTED.

13

.EXTENDED DISCUSSION...

...COLD NORTHWESTERLY FLOW WILL CONTINUE NEXT WEEK...

ON SUNDAY ANOTHER ARCTIC BLAST WILL MOVE THROUGH THE MID STATE WITH
LIGHT SNOW AND LOWS SUNDAY NIGHT IN THE TEENS AND LOWER 20S. ON
MONDAY A 1040 MBAR HIGH PRESSURE CENTER WILL BUILD DOWN THIS WAY
FROM THE NORTHWEST WITH TEMPS NOT REACHING THE FREEZING MARK MOST
AREAS. A FEW FLURRIES COULD FLY ON MONDAY BUT SHOULD NOT AMOUNT TO
MUCH. LOWS MONDAY NIGHT IN THE TEENS. HIGHS ON TUESDAY WILL BE IN
THE 30S WITH YET ANOTHER ARCTIC SHOT OF COLD AIR DIVING DOWN THROUGH
THE AREA TUESDAY NIGHT FOLLOWED BY LOWS IN THE LOWER 20S.
UNSEASONABLY COLD WEATHER WILL CONTINUE THROUGH THE WORK WEEK.

.CLIMATE...RECORD LOW PREVIOUSLY SET BACK IN 1958 TIED THIS MORNING
WHEN THE TEMPERATURE FELL TO 5 DEGREES ABOVE ZERO.

SO FAR TODAY`S HIGH HAS BEEN 19 DEGREES. THE RECORD FOR THE LOWEST
DAILY HIGH IS 26 DEGREES SET IN 2006.

BB

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