818
FXUS64 KMRX 192302
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
602 PM EST THU DEC 19 2024
..NEW AVIATION
SHORT TERM
(THIS EVENING THROUGH FRIDAY)
ISSUED AT 313 PM EST THU DEC 19 2024
KEY MESSAGES:
1. WINTER STORM WATCH ISSUED FOR THE MOUNTAIN ZONES OF SOUTHWEST
VIRGINIA AND EAST TENNESSEE FROM FRIDAY AFTERNOON THROUGH SATURDAY
AFTERNOON.
2. MUCH COOLER TEMPERATURES FRIDAY WITH BREEZY CONDITIONS IN THE
AFTERNOON. WIND GUSTS NEAR 45 MPH POSSIBLE IN THE HIGHER TERRAIN.
DISCUSSION:
OVERCAST CONDITIONS MAY PERSIST INTO THE NIGHT AND INTO FRIDAY. A
FAIRLY POTENT TROUGH WILL ROTATE THROUGH ON FRIDAY, EVENTUALLY SENDING
ANOTHER COLD FRONT ACROSS THE AREA. CONFIDENCE IS INCREASING FOR
A NORTHWEST FLOW SNOWFALL EVENT FRIDAY INTO SATURDAY.
NWLY LOW-LEVEL FLOW IS EXPECTED TO RUN AROUND 20 TO 35 KT ACROSS
THE HIGHER TERRAIN TOMORROW. TANKING 850 TEMPS, MOISTURE SOARING
TO NEARLY 700 MB ACCORDING TO FORECAST SOUNDINGS, AND SUFFICIENT
CONDITIONS WITHIN THE DGZ, WILL PROVIDE THE BEST CASE FOR
ACCUMULATING SNOWFALL ACROSS THE SOUTHERN APPALACHIANS, NORTHERN
PLATEAU, AND HIGHER TERRAIN OF SOUTHWEST VIRGINIA.
PRECIPITATION WILL BEGIN TO ENTER THE REGION MID TO LATE MORNING
TOMORROW WHERE IT WILL LIKELY FALL AS RAIN FIRST ACROSS
NORTHWESTERN PARTS OF THE FORECAST AREA. ODDLY AS TEMPERATURES
FALL INTO THE AFTERNOON, CHANGEOVER WILL OCCUR OVER HIGHER
ELEVATION SPOTS. THE LONG TERM FORECAST BELOW GOES INTO THIS MORE
IN DETAIL, BUT EXPECT COLDER TEMPERATURES TOMORROW FROM LOWERING
UPPER LEVEL HEIGHTS AND THE FROPA. WINDS WILL ALSO INCREASE OUT
OF THE NORTHWEST INTO THE AFTERNOON HOURS WHERE GUSTS CAN RANGE
BETWEEN 20 TO 30 MPH IN THE VALLEY AND HIGHER THAN THAT TO NEAR 45
MPH ACROSS THE HIGHER TERRAIN.
LONG TERM
(FRIDAY NIGHT THROUGH NEXT THURSDAY)
ISSUED AT 313 PM EST THU DEC 19 2024
KEY MESSAGES:
1. NORTHWEST FLOW SNOW EVENT WILL BE ONGOING FRIDAY NIGHT. LIKELY
WRAPS UP AROUND MIDDAY SATURDAY.
2. DRY, WITH GRADUALLY MODERATING TEMPERATURES LATE SATURDAY THROUGH
MONDAY.
3. HIGH DEGREE OF UNCERTAINTY FOR CHRISTMAS EVE AND CHRISTMAS DAY.
LOOKS RAINY AT THE MOMENT, BUT CONFIDENCE IS VERY LOW.
DISCUSSION:
MAIN CONCERN FOR THE LONG TERM PERIOD WILL BE THE NORTHWEST FLOW
SNOW EVENT THAT WILL BE ONGOING AT THE START OF THE PERIOD. AFTER
THAT WINDS DOWN SATURDAY MORNING, CONDITIONS LOOK DRY THROUGH AT
LEAST EARLY TUESDAY (CHRISTMAS EVE) IF NOT TUESDAY NIGHT INTO
WEDNESDAY (CHRISTMAS DAY). WILL FOCUS THE DISCUSSION ON FRIDAY NIGHT
INTO SATURDAY AS IT WILL IMPACT HOLIDAY TRAVEL OVER THE MOUNTAINS.
FRIDAY AFTERNOON AND INTO THE EVENING, A SHARP UPPER TROUGH WILL
ROTATE THROUGH THE SOUTHERN APPALACHIAN REGION, LEAVING OUR FORECAST
AREA BENEATH NORTHWESTERLY FLOW ALOFT AND NNW LOW LEVEL H85 FLOW
UNTIL ROUGHLY MIDDAY SATURDAY. THIS WILL PROMOTE NORTHWEST FLOW
SNOWFALL DURING THE OVERNIGHT HOURS AND THROUGH AT LEAST SATURDAY
MORNING, IF NOT THE MIDDAY OR EARLY AFTERNOON TIME FRAME. A CURSORY
GLANCE AS 1000-850MB RH SHOWS THAT THERE'S AT LEAST A BRIEF
CONNECTION TO LOW LEVEL MOISTURE STREAMING IN FROM THE WESTERN GREAT
LAKES REGION. MODEL SOUNDINGS OVER KNOXVILLE AND TRI-CITIES SHOW
THAT THE SATURATED LAYER WILL EXTEND UP ABOVE 800MB THROUGH SHORTLY
AFTER DAYBREAK SATURDAY AS WELL. ALL OF THIS TO SAY THAT
ACCUMULATING SNOWFALL WILL CONTINUE INTO SATURDAY MORNING BEFORE
ABATING. WHEN ALL IS SAID AND DONE, FOR AREAS MOSTLY ABOVE 2,500 FT
IN ELEVATION IN THE MOUNTAINS OF VIRGINIA AND EAST TENNESSEE, WE'RE
EXPECT ROUGHLY 3-5" OF SNOW FOR THE ENTIRE EVENT, WITH SOME AMOUNTS
OF AROUND 7" FOR THE USUAL SUSPECTS LIKE MOUNT LECONTE IN THE
SMOKIES FOR EXAMPLE. WE HAVE HOISTED UP A WINTER STORM WATCH TO
ACCOUNT FOR THIS AND WILL LET THE INCOMING NIGHT SHIFT LOOK AT THE
LATEST 00Z GUIDANCE AND REFINE ACCUMULATIONS AND DECIDE WHETHER A
CONVERSION TO ADVISORY OR WARNING IS WARRANTED. LASTLY, WE MAY
VERY WELL NEED SOME SORT OF HEADLINES OUTSIDE OF THE MOUNTAIN
ZONES, BUT CONFIDENCE WAS NOT HIGH ENOUGH TO PINPOINT EXACTLY WHAT
ALL AREAS TO INCLUDE JUST YET.
OTHERWISE, THE SNOW WINDS DOWN BY MIDDAY SATURDAY OR THEREABOUTS,
AND DRY HIGH PRESSURE MOVES IN FOR THE REMAINDER OF THE WEEKEND.
MODELS DISAGREE ON HOW THE UPPER LEVELS EVOLVE NEXT WEEK. GOOD
AGREEMENT THAT WE REMAIN DRY WITH MODERATING TEMPERATURES SUNDAY
INTO MONDAY. FOR TUESDAY ONWARD, THERE'S GOOD AGREEMENT IN A
COMPLICATED PATTERN ACROSS THE CONUS, WITH SOME SORT OF SOUTHERN
STREAM TROUGH MOVING ALONG THE GULF STATES BY MIDWEEK. BUT HOW THAT
INTERACTS WITH NORTHERN STREAM TROUGHS AND HOW QUICKLY RAIN SPREADS
BACK NORTH TO OUR CWA IS UNCERTAIN. FOR THIS REASON, THE NBM
GUIDANCE SEEMED VERY REASONABLE FOR THE TIME BEING.
AVIATION
(00Z TAFS)
ISSUED AT 600 PM EST THU DEC 19 2024
VFR AND MOSTLY CLEAR SKY CONDITIONS ARE FORECAST TO CONTINUE AT
CHA TONIGHT WITH MVFR CIGS REMAINING AT TYS AND TRI FOR MUCH OF
THE NEXT 6 TO 12 HOURS. THERE SHOULD BE SOME GRADUAL IMPROVEMENT
IN CIGS AT TYS AND TRI ON FRIDAY MORNING PRIOR TO A LOW PRESSURE
SYSTEM BRINGING A RETURN OF SCATTERED RAIN AND SNOW SHOWERS AND
LOWER CIGS. MAIN IMPACTS ON FRIDAY AFTERNOON ARE EXPECTED AT TRI
AND TYS WITH THE POTENTIAL OF IFR CIGS DEVELOPING AT TRI LATE
FRIDAY.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 36 47 32 44 / 0 0 10 0
KNOXVILLE MCGHEE TYSON AIRPORT, TN 35 43 30 40 / 0 40 20 0
OAK RIDGE, TN 33 42 30 40 / 0 40 20 0
TRI CITIES AIRPORT, TN 34 42 28 36 / 20 70 50 0
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
AFTERNOON FOR BLOUNT SMOKY MOUNTAINS-COCKE SMOKY MOUNTAINS-
JOHNSON-SEVIER SMOKY MOUNTAINS-SOUTHEAST CARTER-SOUTHEAST
GREENE-UNICOI.
VA...WINTER STORM WATCH FROM FRIDAY AFTERNOON THROUGH SATURDAY
AFTERNOON FOR LEE-RUSSELL-WASHINGTON VA-WISE.
SHORT TERM...KS
LONG TERM....CD
AVIATION...JB
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