422
FXUS64 KMRX 211705
AFDMRX
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE MORRISTOWN TN
105 PM EDT TUE JUL 21 2026
..NEW AVIATION
KEY MESSAGES
UPDATED AT 124 AM EDT TUE JUL 21 2026
- COLD FRONTAL PASSAGE TODAY INTO TOMORROW MAY BRING SEVERAL ROUNDS
OF SHOWERS AND STORMS, WITH A WIDE RANGE OF POTENTIAL OUTCOMES. SEE
DISC BELOW.
- THERE'S SOME UNCERTAINTY, BUT THE COLD FRONT MAY STALL TO THE
SOUTH, CONTINUING SHOWERS AND STORMS FOR PARTS OF THE FORECAST AREA
UNTIL THE LATTER PART OF THE WEEK. THIS COULD POSE SOME FLOODING
IMPACTS.
- BELOW NORMAL TEMPERATURES WILL FOLLOW BEYOND WEDNESDAY UNTIL THE
EARLY PART OF THE WEEKEND. GRADUAL WARMING TO NEAR NORMAL EARLY NEXT
WEEK.
DISCUSSION
ISSUED AT 124 AM EDT TUE JUL 21 2026
THE BULK OF THIS DISCUSSION WILL FOCUS ON THE TODAY THROUGH
TOMORROW TIMEFRAME. THERE IS A HIGH LEVEL OF UNCERTAINTY REGARDING
THE TIMING AND POTENTIAL IMPACTS DURING THIS TIMEFRAME, AS THERE
ARE VARIOUS MODEL SOLUTIONS. GENERALLY THOUGH, WE ARE LOOKING AT
THE POSSIBILITY OF SEVERAL ROUNDS OF SHOWERS AND STORMS WITH THE
POTENTIAL OF STRONG TO SEVERE STORMS FROM LATER THIS MORNING
THROUGH TOMORROW MORNING.
TROPICAL STORM BERTHA BECAME OFFICIALLY NAMED AS OF LAST NIGHT. EVEN
THOUGH SHE WILL REMAIN WELL TO OUR SOUTH IN THE GULF, HER PRESENCE
AND SLOW MOVEMENT WESTWARD MAY IMPACT HOW THINGS MOVE AND PROGRESS
FOR TODAY INTO TOMORROW. FROM HER CURRENT LOCATION OFF OF THE FL
PENINSULA COAST, SHE WILL BE LOCATED NEAR NEW ORLEANS TOMORROW
MORNING. PART OF THE REASON FOR HER MOVEMENT IS BECAUSE OF WEAK
FLOW/STEERING OVER MUCH OF THE SOUTHERN U.S.. THE HIGHEST HEIGHTS OF
THE UPPER RIDGE WILL SINK TOWARDS TEXAS WITH TIME, AIDING BERTHA TO
SOMEWHERE IN THE WESTERN GULF LATER THIS WEEK.
THE PATTERN OF HIGH AMPLITUDE RIDGING TO THE WEST AND TROUGHING WITH
SHORTWAVE IMPULSES TO THE EAST CONTINUES. MULTIPLE SHORTWAVE
IMPULSES WILL ROUND THE BOTTOM OF THE TROUGH BEFORE IT'S CARRIED
INTO FAR NE CANADA LATER TOMORROW INTO THURSDAY. AT THE SURFACE,
A COLD FRONT CURRENTLY DRAPED OVER IL TO IA TO NE/KS WILL
EVENTUALLY SHIFT OUR DIRECTION, IMPACTING US WELL BEFORE IT EVEN
ARRIVES. THE ACTUAL FRONT ITSELF MAY NOT ARRIVE UNTIL EARLY
TOMORROW.
THE POTENTIAL IMPACTS FROM TODAY MAY COME FROM AT LEAST THREE
SEPARATE ROUNDS OF SHOWERS AND THUNDERSTORMS. EACH ROUND MAY BECOME
STRONGER AS THE FRONT GETS CLOSER AND WE INTRODUCE HIGHER SHEAR.
BECAUSE OF THIS POSSIBILITY, IT MAY IMPACT THE SEVERITY AND
EVOLUTION OF THE NEXT ROUND, SO UNCERTAINTY IS ON THE LOWER SIDE.
RUNS OF RECENT CAMS CANNOT TOTALLY GRASP IT OR EVEN TRY TO ALIGN
WITH ONE ANOTHER. IN THE NEXT COUPLE OF HOURS OR SO, SOME ISOLATED
TO SCATTERED SHOWERS AND POSSIBLE THUNDERSTORMS MAY DEVELOP ACROSS
OUR NORTHERN TIER. THEY WILL MOST LIKELY MIMIC WHAT WE'VE SEEN THE
PAST COUPLE OF DAYS WITH HIGH PWATS AND LOW OVERALL SHEAR. THERE MAY
BE A PERIOD OF DRYING OR THERE COULD BE CONTINUING ACTIVITY UNTIL
THE NEXT ROUND.
ACTIVITY FOR THE MOST PART WILL BE SHIFTING DOWN FROM THE NORTH AND
NORTHWEST. LATER THIS AFTERNOON AND EVENING COULD INTRODUCE THE NEXT
ROUND WHERE WE WILL BE AT PEAK HEATING. EVERYTHING UP UNTIL THIS
POINT IS PRE-FRONTAL. THE MAIN THREATS FROM STORMS WILL BE DAMAGING
WIND GUSTS AND POTENTIAL FLOODING ISSUES. AFTER DARK, OR THE NEXT
ROUND, WILL CONFIDENTLY BE THE PERIOD WITH THE LEAST CONFIDENCE AND
CERTAINTY. BETTER SHEAR ROLLS IN AS WELL AS SRH, BUT SURFACE
INSTABILITY FALLS OFF SOME AFTER PEAK HEATING. CAMS DISAGREE ON
TIMING OF ARRIVAL AS WELL, WHICH BERTHA MAY BE PARTLY TO BLAME.
DAMAGING WIND GUSTS WILL CONTINUE TO BE THE GREATEST THREAT WITH A
GENERAL LINEAR STORM MODE. IF WE CAN GENERATE HAIL, IT WILL MOST
LIKELY BE OF THE SMALLER VARIETY. A LOW-END TORNADO THREAT DOES
EXIST, MAINLY FOR THE NORTHERN PLATEAU INTO SOUTHWEST VA. UNLESS
THERE'S SOME LOCALIZED EFFECTS, BACKED SURFACE WINDS MAY BE HARD
TO ACCOMPLISH.
THE "THIRD" ROUND MAY BEGIN AS EARLY AS 7 PM EDT, PERSISTING THROUGH
THE OVERNIGHT HOURS UNTIL IT WEAKENS. MOVEMENT DURING THE OVERNIGHT,
AT LEAST ACCORDING TO CAMS, DOESN'T SHOW MUCH SOUTHERN PROGRESSION,
SO THAT PUTS FLOODING ON THE FOREFRONT OF IMPACTS. GENERALLY, NORTH
OF I-40 AND THE HIGHER TERRAIN CAN EXPECT THE HIGHER END OF QPF.
LATER TOMORROW INTO THURSDAY, WHEN PREVIOUSLY THOUGHT THAT IT WOULD
DRY OUT, MAY KEEP CHANCES OF SHOWERS AND STORMS AROUND WITH THE
POTENTIALLY STALLED FRONT TO OUR SOUTH, BERTHA JUST OFF OF THE LA
COAST, AND HIGH PRESSURE DESPERATELY TRYING TO BARREL IN FROM THE
NORTH. WPC RECOGNIZES THIS, KEEPING MRGL TO SLGT ERO TOMORROW INTO
THURSDAY.
THE WEEKEND AS FAR AS PRECIPITATION GOES, DOES BECOME MORE UNCERTAIN
WITH A SHORTWAVE APPROACHING FROM THE NORTHWEST WHILE THE FRONT MAY
STILL BE HUNG UP TO OUR SOUTH. WE CAN SAY WITH CERTAINTY THOUGH,
THAT TEMPERATURES TOMORROW AND INTO THE FIRST PART OF THE WEEKEND
WILL BE NOTICEABLY BELOW NORMAL WITH LOW AND MID 80S. TEMPERATURES
GRADUALLY WARM TO NEAR NORMAL VALUES EARLY NEXT WEEK.
AVIATION
(18Z TAFS)
ISSUED AT 1257 PM EDT TUE JUL 21 2026
SHOWERS AND THUNDERSTORMS WILL BE MORE ISOLATED THIS AFTERNOON
AND MAINLY NORTH, THEN COVERAGE WILL INCREASE ESPECIALLY AROUND
THE TRI AND TYS AREAS TONIGHT INTO WEDNESDAY. WILL CARRY PROB30
THUNDER GROUPS WHEN THE BETTER CHANCE OF STORMS IS EXPECTED AT TYS
AND TRI. VFR CONDITIONS EXPECTED AT CHA AND VFR CONDITIONS ARE
LIKELY AT TYS OUTSIDE OF ANY HEAVIER SHOWER OR STORM, BUT
PREVAILING MVFR CONDITIONS LOOK LIKELY LATER TONIGHT INTO
WEDNESDAY AT TRI. LOWER CONDITIONS WILL BE AT LEAST BRIEFLY
POSSIBLE ESPECIALLY IN HEAVIER PRECIPITATION.
PRELIMINARY POINT TEMPS/POPS
CHATTANOOGA AIRPORT, TN 76 89 70 87 / 40 80 40 20
KNOXVILLE MCGHEE TYSON AIRPORT, TN 74 86 68 85 / 80 80 30 10
OAK RIDGE, TN 73 86 66 85 / 90 70 10 10
TRI CITIES AIRPORT, TN 69 83 63 83 / 90 80 20 20
MRX WATCHES/WARNINGS/ADVISORIES
NC...NONE.
TN...NONE.
VA...NONE.
DISCUSSION...KS
AVIATION...99
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