743
FXUS64 KMRX 091228
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
728 AM EST THU JAN 9 2025
..NEW UPDATE
UPDATE
ISSUED AT 715 AM EST THU JAN 9 2025
QUICK UPDATE TO EXTEND SNOW FLURRIES AND LIGHT SNOW
SHOWERS A FEW MORE HOURS INTO THE MORNING AND MORE
CLOUD COVER OVER NORTHEAST TENNESSEE AND SOUTHWEST
VIRGINIA.
SHORT TERM
(TODAY AND TONIGHT)
ISSUED AT 335 AM EST THU JAN 9 2025
KEY MESSAGES:
1. LIGHT SNOW SHOWERS/FLURRIES HAS CONTINUED INTO THE OVERNIGHT
HOURS IN NORTHEAST TN AND SOUTHWEST VA.
2. COLD TEMPERATURES THIS MORNING. HIGHS TODAY SLIGHTLY WARMER THAN
WEDNESDAY.
3. SLOWLY CLEARING SKIES THIS MORNING NE AND POSSIBLY INTO EARLY
AFTERNOON BEFORE SKIES SUNNY EVERYWHERE.
4. COLD AGAIN TONIGHT BUT INCREASING CLOUDS AFTER MIDNIGHT FROM
SOUTHWEST TO NORTHEAST. SNOW STARTING SOUTHERN PLATEAU JUST BEFORE
SUNRISE.
DISCUSSION:
WEAK NORTHWEST FLOW STILL CONTINUING ACROSS SOUTHEAST KY/WV INTO
EXTREME SOUTHWEST VA AND NORTHEAST TN WITH SNOW SHOWERS AT WISE, AND
ABINGDON VA AND FLURRIES AT TRI AND CARTER COUNTY AIRPORT IN
ELIZABETHTON IN THE PAST FEW HOURS. ACCUMULATIONS THE REST OF THE
NIGHT ARE EXPECTED TO BE AROUND A TRACE TO A TENTH OR SO. THERE
COULD BE A LIGHT DUSTING AND ENOUGH TO CAUSE SOME SLICK ROADWAYS
WHERE THE FLURRIES AND SNOW SHOWERS OCCUR. ELSEWHERE ACROSS THE
FORECAST AREA CLOUDS WERE DECREASING AND MOSTLY CLEAR EAST CENTRAL
TENNESSEE AND POINTS SOUTH. TEMPERATURES AT 300 AM EST WERE IN
THE TEENS TO LOWER 20S, SEVERAL DEGREES COLDER THAN WEDNESDAY
MORNING WITH THE OVERCAST SKIES. WINDS ARE MOSTLY LIGHT TO CALM
WHICH IS KEEPING WIND CHILLS NEAR TO JUST BELOW ACTUAL
TEMPERATURES.
THE FORECAST NOW FOR THIS MORNING THROUGH TONIGHT. SKIES WILL BE
MOSTLY SUNNY WITH EXCEPTION OF DECREASING CLOUDS NORTHEAST. HIGH
PRESSURE AT THE SURFACE WILL BE MOVING OVER THE EASTERN OHIO AND
TENNESSEE VALLEYS DURING THE DAY TODAY. WITH THE CLOUDS GONE AND
WINDS VERY LIGHT TEMPERATURES WILL BE A FEW DEGREES WARMER TODAY,
GENERALLY UPPER 20S NORTHEAST WHERE THERE IS STILL SOME SNOW COVER
TO THE LOWER TO MID 30S ACROSS MOST OF EAST TENNESSEE AND SOUTHWEST
NORTH CAROLINA. USED A BLEND OF CONSHORT AND NBM FOR HIGHS TODAY.
FOR TONIGHT THE SURFACE HIGH SHIFTS NORTHEAST TO THE CENTRAL
APPALACHIANS/MID ATLANTIC STATES.
EARLY TODAY A LOW PRESSURE CENTER IS FORECAST TO DEVELOP OFF THE
SOUTH TEXAS COAST EAST OF A VERY DEEP UPPER TROUGH OVER THE SOUTHERN
ROCKIES AND NORTHERN MEXICO AND THEN BE NEAR THE TX/LA COASTLINE
THIS EVENING. MOISTURE WILL BEGIN STREAMING NORTHEAST INTO THE LOWER
MISSISSIPPI VALLEY EARLY THIS EVENING AND MOVE INTO THE WESTERN
TENNESSEE VALLEY AFTER MIDNIGHT. THE SURFACE LOW WILL BE NEAR THE
MISSISSIPPI MOUTH EARLY FRIDAY MORNING. THIS DEEPENING SOUTHWEST
FLOW WILL REACH THE SOUTHERN PLATEAU JUST BEFORE SUNRISE WITH LIGHT
SNOW DEVELOPING THERE. NO SIGNIFICANT SNOWFALL AMOUNTS SHOULD OCCUR
BEFORE 12Z. LOWS WILL BE REACHED EARLY IN THE SOUTHWESTERN FORECAST
AREA AROUND MIDNIGHT IN THE MID TO UPPER 20S AND THEN STEADY BEFORE
THE SNOW STARTS. ELSEWHERE TEMPERATURES WILL DROP INTO THE HIGHER
TEENS NORTHEAST AND LOWER TO MID 20S CENTRAL SECTIONS BEFORE CLOUDS
INCREASE.
LONG TERM
(FRIDAY THROUGH WEDNESDAY)
ISSUED AT 335 AM EST THU JAN 9 2025
KEY MESSAGES:
1. A WINTER STORM WILL IMPACT THE AREA FRIDAY INTO SATURDAY WITH
WIDESPREAD ACCUMULATING SNOW AND POSSIBLE MIXED PRECIPITATION IN
SOUTHERN SECTIONS.
2. A WINTER STORM WATCH REMAINS IN EFFECT FOR THE ENTIRE FORECAST
AREA FOR POTENTIAL TRAVEL IMPACTS.
3. TEMPERATURES WILL REMAIN BELOW NORMAL THROUGH NEXT WEEK. SLIGHTLY
WARMER TEMPERATURES FOR SUNDAY AND MONDAY, BUT ANOTHER SHOT OF COLD
AIR ARRIVES MONDAY NIGHT.
DISCUSSION:
BOTTOM LINE UP FRONT: NO CHANGE WILL BE MADE TO THE WINTER STORM
WATCH AT THIS TIME, DUE TO THE LOWERED CONFIDENCE IN P-TYPES AND
SNOW AMOUNTS. TO ISSUE A WARNING BEYOND 24 HOURS, CONFIDENCE MUST BE
HIGH THAT WARNING CRITERIA WILL BE MET AND THAT IMPACTS WILL BE
SIGNIFICANT.
MODEL TRENDS AND DIFFERENCES:
THE NAM HAS THROWN A WRENCH IN THE FORECAST WITH ITS DEPICTION OF A
WARM NOSE SPREADING WELL NORTHWARD INTO OUR AREA, DUE TO ITS STRONG
SOUTHERLY LOW LEVEL JET. THIS POTENTIAL FOR MIXED P-TYPES ADDS MUCH
UNCERTAINTY TO THE FORECAST SNOW AMOUNTS IN SOUTHERN SECTIONS AND IN
THE LEE OF THE MOUNTAINS. THE MAIN DIFFERENCE IN THE NAM IS THAT IT
DEVELOPS A SECONDARY SURFACE LOW IN NORTHERN AL ON FRIDAY AFTERNOON,
WHICH TRACKS NE ALONG THE CUMBERLAND PLATEAU TO WV THROUGH THE
EVENING. THIS CREATES A STRONG PRESSURE GRADIENT ACROSS THE TN
MOUNTAINS, AND A 40-50 KT LLJ. HOWEVER, IT IS NOTEWORTHY THAT THIS
IS NOT A TYPICAL MOUNTAIN WAVE/DOWNSLOPE ENHANCEMENT PATTERN, WHICH
IS USUALLY CHARACTERIZED BY A 850 MB JET MAX TO OUR NW, SO PERHAPS
THE NAM IS OVERDONE WITH THE DOWNSLOPE WARMING. ALSO, THE NAM IS AN
OUTLIER IN ITS SOLUTION, AS THE GFS AND ECMWF DO NOT DEVELOP THIS
SECONDARY LOW AND LLJ, AND KEEP WARM ADVECTION TO OUR SOUTH. THE
HRRR SEEMS TO BE A COMPROMISE SOLUTION, AND IS NOT AS AGGRESSIVE
WITH THE WARM NOSE AND LLJ AS THE NAM.
PRECIPITATION TYPES:
AT ONSET FRIDAY MORNING, TEMPERATURES PROFILES WILL SUPPORT ALL SNOW
AS TOP-DOWN MOISTENING EVAPORATIVELY COOLS A DRY LOW LEVEL LAYER.
HREF P-TYPE PROBS SHOW A SNOW/SLEET/FZRA MIX ENTERING SOUTHERN
SECTIONS BETWEEN 1 PM AND 4 PM EST. THE NORTHWARD EXTENT OF THIS MIX
IS A BIG UNCERTAINTY, BUT FOR THIS FORECAST, THE HREF PROBS LOOK
REASONABLE, AND KEEP THE MIX MAINLY TO THE SOUTH OF I-40. THE
STRENGTH OF THE DOWNSLOPE WIND WILL AFFECT THE P-TYPE IN THE
FOOTHILLS NORTH OF I-40 AND THE TRI-CITIES, AND THE POTENTIAL FOR A
BRIEF PERIOD OF MIXED P-TYPES MAY RESULT IN LOWERED SNOW AMOUNTS
THERE.
SNOW AMOUNTS AND CONFIDENCE:
THE AREA OF HIGHEST CONFIDENCE IN THE SNOW AMOUNT FORECAST IS NORTH
OF I-40 AND WEST OF I-81, IN THE NORTHERN CUMBERLAND PLATEAU AREA
AND KY BORDER COUNTIES, WHERE THE P-TYPE IS HIGHLY LIKELY TO REMAIN
ALL SNOW. IN THIS AREA, AMOUNTS ARE EXPECTED TO BE IN THE 4-6"
RANGE. AS WE GO SOUTH AND EAST FROM THERE, CONFIDENCE LOWERS DUE TO
THE ABOVE MENTION P-TYPE ISSUES. IN THE SOUTHERN VALLEY AND SW NC, 1-
3 INCHES OF SNOW IS EXPECTED, MAINLY DURING FRIDAY MORNING AND EARLY
AFTERNOON BEFORE THE MIX TAKES OVER, WITH THE POTENTIAL FOR UP TO A
TENTH OF AN INCH OF ICE ACCUMULATION IN THE MID/LATE AFTERNOON AND
EVENING. ANOTHER FACTOR IN THE SNOW AMOUNTS WILL BE THE LOSS OF
MOISTURE IN THE DENDRITIC GROWTH ZONE FROM THE DRY SLOT FRIDAY
EVENING, WHICH MAY SHUT OFF ACCUMULATING SNOWFALL SOONER THAN
PREVIOUSLY FORECAST. THE CHANCE OF ACCUMULATING PRECIP DROPS RAPIDLY
BETWEEN 7 PM AND MIDNIGHT EST AS THE DRY SLOT MOVES OVERHEAD.
FREEZING DRIZZLE MAY BE A CONCERN DURING THIS PERIOD.
TIMING:
NOT MUCH HAS CHANGED FROM PREVIOUS FORECASTS REGARDING THE TIMING OF
SNOW ONSET FRIDAY MORNING. EXPECT THAT THE MORNING COMMUTE IN THE
CHATTANOOGA AREA COULD BE IMPACTED BY SNOW, POTENTIALLY STARTING AS
EARLY AS 7 AM EST BUT ACCUMULATING MAINLY IN THE 9-11 AM TIME FRAME
AS SNOWFALL RATES INCREASE. IN KNOXVILLE, 10 AM TO NOON APPEARS TO
BE THE LIKELY TIME FRAME FOR SNOW TO START ACCUMULATING, WITH TRI-
CITIES BEING IN THE NOON TO 2 PM WINDOW. PEAK PRECIP INTENSITY
APPEARS TO BE DURING THE AFTERNOON, FROM AROUND 1 PM EST TO 7 PM
EST. PRECIP WILL BEGIN TO END NEAR OR AFTER 7 PM FROM SW TO NE AS
THE DRY SLOT MOVES ACROSS THE AREA AND BRINGS DRYING IN THE DENDRITE
GROWTH ZONE. THIS END TIME IS FASTER THAN PREVIOUSLY FORECAST, BUT
THE END TIME OF THE WINTER STORM WATCH WILL BE KEPT AT 7 AM EST
SATURDAY. WE TRANSITION TO A NW FLOW PATTERN FRIDAY NIGHT, WHICH MAY
RESULT IN SOME ADDITIONAL LIGHT SNOW ACCUMULATION IN SW VA AND THE
TN MOUNTAINS INTO SATURDAY MORNING.
FOR THE REMAINDER OF THE LONG TERM PERIOD, WE WILL HAVE A SLIGHT
WARMING TREND ON SUNDAY AND MONDAY, WITH HIGHS IN THE MID/UPPER 30S
TO LOWER 40S BOTH DAYS. A CLIPPER-TYPE SYSTEM WILL BRING A SHOT OF
COLDER AIR AND A CHANCE OF SNOW SHOWERS IN SW VA MONDAY NIGHT, WITH
TEMPERATURES ON TUESDAY ONLY REACHING THE UPPER 20S TO MID 30S,
AND LOWS IN THE TEENS TUESDAY MORNING AND WEDNESDAY MORNING.
AVIATION
(12Z TAFS)
ISSUED AT 630 AM EST THU JAN 9 2025
THE LIGHT SNOW HAS FINALLY ENDED OVER EAST TENNESSEE AS LOW CLOUDS
HAVE CLEARED THE REGION. SOME SCATTERED LOWER LEVEL CLOUDS ARE
POSSIBLE THIS MORNING BUT SKIES SHOULD STAY MOSTLY CLEAR THROUGH
THE EVENING. WINDS WILL BE LIGHT. LATE TODAY HIGH LEVEL CLOUDS
INCREASE AND CONTINUE TO LOWER OVERNIGHT BUT STAY VFR WITH SNOW
AND LOWER CLOUDS NOT MOVING IN UNTIL AFTER 12Z FRIDAY.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 37 26 33 30 / 0 20 100 60
KNOXVILLE MCGHEE TYSON AIRPORT, TN 33 21 32 28 / 0 0 100 90
OAK RIDGE, TN 32 22 31 27 / 0 10 100 80
TRI CITIES AIRPORT, TN 29 18 33 27 / 10 0 90 100
MRX WATCHES/WARNINGS/ADVISORIES
NC...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING
FOR CHEROKEE-CLAY.
TN...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING
FOR ANDERSON-BLEDSOE-BLOUNT SMOKY MOUNTAINS-BRADLEY-
CAMPBELL-CLAIBORNE-COCKE SMOKY MOUNTAINS-EAST POLK-GRAINGER-
HAMBLEN-HAMILTON-HANCOCK-HAWKINS-JEFFERSON-JOHNSON-KNOX-
LOUDON-MARION-MCMINN-MEIGS-MORGAN-NORTH SEVIER-NORTHWEST
BLOUNT-NORTHWEST CARTER-NORTHWEST COCKE-NORTHWEST GREENE-
NORTHWEST MONROE-RHEA-ROANE-SCOTT TN-SEQUATCHIE-SEVIER
SMOKY MOUNTAINS-SOUTHEAST CARTER-SOUTHEAST GREENE-SOUTHEAST
MONROE-SULLIVAN-UNICOI-UNION-WASHINGTON TN-WEST POLK.
VA...WINTER STORM WATCH FROM FRIDAY MORNING THROUGH SATURDAY MORNING
FOR LEE-RUSSELL-SCOTT VA-WASHINGTON VA-WISE.
SHORT TERM...TD
LONG TERM....DGS
AVIATION...TD
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