724
FXUS62 KCAE 271852
AFDCAE
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE COLUMBIA SC
252 PM EDT WED OCT 27 2021
SYNOPSIS
SEASONABLE TEMPERATURES ARE EXPECTED TODAY AS AIR MASS REMAINS
DRY. A STRONG LOW PRESSURE SYSTEM WILL DEVELOP OVER THE
SOUTHEASTERN STATES THURSDAY WITH WIDESPREAD SHOWERS AND A FEW
THUNDERSTORMS THROUGH THURSDAY NIGHT. SOME STRONG
SHOWERS/STORMS ARE POSSIBLE, BUT WIDESPREAD SEVERE WEATHER IS
NOT EXPECTED AT THIS TIME. CONDITIONS WILL SLOWLY IMPROVE OVER
THE WEEKEND BUT TEMPERATURES WILL REMAIN BELOW NORMAL.
NEAR TERM /THROUGH TONIGHT/
AREA REMAINS UNDER THE INFLUENCE OF TRANSITORY RIDGE OF HIGH
PRESSURE BOTH AT THE SURFACE AND ALOFT IN A VERY AMPLIFIED
PATTERN WITH STRONG UPPER LOW PRESSURE OFF THE COAST OF NEW
ENGLAND AND A DEEP TROUGH OVER THE SOUTHERN PLAINS. BIT DRIER
AIRMASS IN PLACE THAN MODELS INDICATED WITH DEW POINTS IN THE
MID TO UPPER 30S ACROSS THE FORECAST AREA. WITH WEAK FLOW OVER
THE AREA, TEMPERATURES WILL BE A FEW DEGREES COOLER AS WE LOSE
OUT ON DOWNSLOPE WINDS WE HAD YESTERDAY. TONIGHT, THE UPPER
RIDGE AXIS WILL BEGIN TO SHIFT OFFSHORE WITH DEEPER SW
DEVELOPING. WITH SUCH DRY AIR IN PLACE, IT WILL TAKE SOME TIME
FOR ATMOSPHERE TO MOISTEN, AND AS A RESULT LIGHT WINDS AND CLEAR
SKIES EARLY WILL LEAD TO FAVORABLE RADIATIONAL COOLING
CONDITIONS BEFORE CLOUDS BEGIN TO INCREASE AROUND 10KFT AND
ABOVE, FIRST IN THE CSRA AND THEN IN THE REST OF THE FORECAST
AREA. LOWS DROP INTO THE MID 40S IN THE NORTHERN FORECAST AREA
TO NEAR 50 IN THE CSRA AS CLOUDS INTERFERE WITH RADIATIONAL
COOLING. WITH MOISTURE LACKING BELOW 10KFT, NO PRECIPITATION IS
EXPECTED TONIGHT.
SHORT TERM /THURSDAY THROUGH FRIDAY NIGHT/
SUMMARY: A POTENT UPPER LEVEL SYSTEM AND ASSOCIATED COLD FRONT
WILL MOVE THROUGH THE AREA THURSDAY. WIDESPREAD MODERATE-HEAVY
IS EXPECTED THROUGHOUT THE DAY THURSDAY AND THURSDAY NIGHT.
CONFIDENCE IN THE SEVERE RISK REMAINS RELATIVELY LOW, WITH
EXTREMELY IMPRESSIVE WIND PROFILES BUT UNFAVORABLE
THERMODYNAMICS. THE EASTERN CWA REMAINS MOST FAVORABLE IF SEVERE
WEATHER DOES DEVELOP. SOME SHOWERS ARE POSSIBLE AGAIN FRIDAY AS
THE UPPER LOW MOVES OVERHEAD. THERE IS OVERALL LITTLE CHANGE IN
THE FORECAST FOR THE SYSTEM THURSDAY. THE MOST RECENT SUITES OF
HI- RES MODELS ARE IN REASONABLE AGREEMENT WITH A COMPLEX AND
INHERENTLY TRICKY SETUP.
THURSDAY MORNING: THE CWA WILL QUICKLY COME UNDER THE FORCING
OF THE DEEP UPPER LOW BY EARLY THURSDAY AS MID LEVEL HEIGHTS
FALL AND BROAD DIVERGENCE ALOFT BEGINS. THE CORRESPONDING
OCCLUDING SURFACE LOW WILL STILL BE POSITIONED OVER ARKANSAS BY
THIS TIME BUT THE SURFACE OCCLUDED/COLD FRONT WILL BE QUICKLY
PUSHING THROUGH MS AND AL BY THURSDAY MORNING. A SECONDARY
OCCLUDED LOW CENTER WILL FORM ALONG THE FRONTAL BOUNDARY
THROUGHOUT THURSDAY WHICH ADDS TO THE COMPLEXITY OF THE EVENT.
STRONG ISENTROPIC LIFT WILL BEGIN BY THE LATE MORNING THURSDAY
AS WARM ADVECTION AHEAD OF THE SECONDARY LOW AND WARM FRONT
RAMPS OUT. PWATS BY THIS TIME WILL HAVE REBOUNDED TO OVER 1.5"
SO COMBINED WITH THE STRONG ISENTROPIC LIFT, THIS IS EXPECTED TO
PRODUCE A BROAD AREA OF MODERATE SHOWERS AND SOME ISOLATED
THUNDERSTORMS BY THE EARLY AFTERNOON.
THURSDAY AFTERNOON/EVENING: SEVERE POTENTIAL INCREASES IN THE
AFTERNOON AS THE BEST KINEMATICS WILL BE OVERSPREADING THE AREA, A
100+ KNOT 250MB JET OVERHEAD, RAPIDLY FALLING MID-LEVEL HEIGHTS
AND PVA, AND 45+ KNOT 850MB SOUTHERLY FLOW. THE SECONDARY LOW
DEVELOPMENT WILL HELP BACK SURFACE FLOW AND KEEP BOUNDARY LAYER
WINDS FROM THE EAST- SOUTHEAST. THIS ALL COMBINES FOR IMPRESSIVE
HODOGRAPHS WITH SUBSTANTIAL SPEED AND DIRECTIONAL SHEAR IN THE
LOW LEVEL LAYERS, 0-1KM BULK SHEAR OVER 30+ KNOTS AND 50+ KNOTS
OF 0-3 BULK SHEAR. SO KINEMATICS ARE EASILY SUPPORTIVE OF
SEVERE HAZARDS. THE THERMODYNAMICS REMAIN THE LIMITING FACTOR
WITH PERSISTENT MORNING CLOUD COVER AND PRECIP THAT WILL LIMIT
THE NORTHWARD EXPANSION OF THE WARM SECTOR. SO ONLY VERY WEAK
SURFACE AND/OR MIXED LAYER INSTABILITY IS EXPECTED TO DEVELOP,
WITH GOOD AGREEMENT ACROSS THE HI-RES SUITE IN THIS. THE INTENSE
WARM ADVECTION ALOFT WILL ONLY ADD TO THE UNFAVORABLE LOW LEVEL
THERMODYNAMICS, ACTING AS A WEAK CAP FROM 850-700MB. SO
COMBINING EVERYTHING, THE EASTERN HALF OF THE CWA CONTINUES TO
REMAIN THE MOST FAVORABLE FOR SEVERE WEATHER SINCE LATE
AFTERNOON THERMODYNAMICS WILL BE MOST FAVORABLE THERE, TO GO
ALONG WITH IMPRESSIVE KINEMATICS. SPC HAS EXPANDED THE SLIGHT
AND MARGINAL RISKS TO INCLUDE MOST OF THE CWA NOW, FOR SEVERE
WIND AND TORNADOES.
THE MAIN AREAS OF UNCERTAINTIES ARE RELATED TO THE
THERMODYNAMIC SETUP (AS THE KINEMATICS ARE MUCH MORE CONFIDENT):
WHERE DOES THE OCCLUDED LOW EXACTLY TRACK?, HOW DOES THE WARM
SECTOR DEVELOP?, AND HOW WIDESPREAD IS THE MORNING GULF COAST
CONVECTION?.
DRIER AIR FILLS IN BEHIND THE FRONTAL PASSAGE LATE THURSDAY AND
INTO FRIDAY. THE UPPER LOW WILL MOVE OVER THE CWA FRIDAY AND, COMBINED
WITH THE ENHANCED LOW-MID LAPSE RATES AND SOME DIURNAL HEATING,
ISOLATED SHOWERS ARE EXPECTED THROUGHOUT THE AFTERNOON. HIGH
TEMPS WILL REMAIN IN THE UPPER 60S ACROSS THE AREA THANKS TO
WEAK COLD ADVECTION.
LONG TERM /SATURDAY THROUGH TUESDAY/
GOOD AGREEMENT ACROSS GUIDANCE THAT THE SLIGHT CHANCE OF
SHOWERS CONTINUES ON SATURDAY AS THE UPPER LOW WILL FINALLY
LIFT TO OUR NORTHEAST. A NORTHWEST FLOW REGIME THEN DEVELOPS
AND USHERS IN A MUCH DRIER AND SEASONAL PERIOD FOR THE REMAINDER
OF THE LONG TERM. BLEND AND ENSEMBLES ARE IN REASONABLE
AGREEMENT, NEAR AVERAGE TEMPERATURES WITH ZONAL FLOW ALOFT AND
LITTLE CHANCE FOR PRECIP UNTIL LATER NEXT WEEK.
AVIATION /18Z WEDNESDAY THROUGH SUNDAY/
HIGH PRESSURE OVER THE AREA WITH VFR CONDITIONS AT ALL TERMINALS
WITH PASSING HIGH CLOUDS AND LIGHTER WINDS, GENERALLY OUT OF
THE NW AROUND 5 KNOTS. WINDS DECREASE TONIGHT, BECOMING LIGHT
AND VARIABLE WITH INCREASING MOISTURE. BY TOMORROW MORNING
EXPECT AN OVERCAST DECK AROUND 8KFT AND SOUTHEASTERLY WINDS
BETWEEN 5 TO 10 KNOTS AS LOW PRESSURE APPROACHES FROM THE WEST.
MAY GET SOME LOWER CLOUDS TO DEVELOP LATE IN THE TAF PERIOD BUT
CONFIDENCE IN RESTRICTIONS BEFORE 18Z IS LOW. PRECIPITATION
CHANCES WILL ALSO BE HIGHEST AFTER 18Z AS WELL, ALTHOUGH CAN'T
COMPLETELY RULE OUT CHANCES, ESPECIALLY AT AGS/DNL.
EXTENDED AVIATION OUTLOOK... EXPECT INCREASING MOISTURE
THURSDAY AFTERNOON WITH RAIN AND ASSOCIATED RESTRICTIONS AS A
STRONG LOW PRESSURE SYSTEM MOVES INTO THE REGION. CHANCE OF
SHOWERS AND ASSOCIATED RESTRICTIONS FRI/SAT DUE TO UPPER LEVEL
LOW OVER THE AREA. UPPER LOW MOVING NORTHEAST OF THE AREA SUNDAY
WITH IMPROVING CONDITIONS INTO EARLY NEXT WEEK.
CAE WATCHES/WARNINGS/ADVISORIES
GA...NONE.
SC...NONE.
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