085
FXUS63 KPAH 151919
AFDPAH
AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE PADUCAH KY
119 PM CST SUN DEC 15 2024
KEY MESSAGES
- WIDESPREAD MODERATE TO HEAVY RAIN MOVES IN OVERNIGHT WITH
EMBEDDED THUNDERSTORMS. 1 TO 2 INCHES OF RAIN MAY OCCUR IN A
CORRIDOR THAT ALIGNS ABOUT 50 MILES EITHER SIDE OF THE OHIO
RIVER. SOME STORMS MAY CONTAIN HAIL OR GRAUPEL, AND THERE IS A
VERY SMALL RISK FOR A WIND/TORNADO THREAT EARLY MONDAY
MORNING.
- AFTER A DRY DAY ON TUESDAY, MORE RAIN MOVES THROUGH TUESDAY
NIGHT INTO WEDNESDAY. ANOTHER 0.5 TO 1.0 INCHES OF RAINFALL
IS POSSIBLE.
- AN ARCTIC COLD FRONT MOVES THROUGH WEDNESDAY NIGHT WITH A
REINFORCING SHOT OF COLD AIR ARRIVING FRIDAY. TEMPERATURES
WILL PLUMMET AND REMAIN BELOW NORMAL THROUGH NEXT WEEKEND,
WITH WIND CHILL VALUES FALLING INTO THE TEENS. A FEW SNOW
FLURRIES MAY EVEN RETURN FRIDAY AS AN ALBERTA CLIPPER PASSES
BY TO THE NORTH.
DISCUSSION
ISSUED AT 119 PM CST SUN DEC 15 2024
A THIN, BUT PERSISTENT LAYER OF CLOUDS IS HANGING ON THIS
AFTERNOON UNDERNEATH A TEMPERATURE INVERSION CENTERED AT AROUND
2400 FT. BY LATE AFTERNOON SKIES MAY BRIEFLY OPEN UP, BUT
ANOTHER SLUG OF MOISTURE AND LIFT WILL ARRIVE THIS EVENING. A
FAST MOVING SHORTWAVE TROUGH IS EMERGING OFF THE ROCKIES AND
YOU CAN ALREADY SEE THE LOWER LEVEL FLOW STARTING TO RESPOND.
THIS FLOW RAMPS UP TONIGHT AND STRONG MOISTURE AND LAYER WARM
AIR ADVECTION BEGINS AS A THE SAME TIME THE BROAD RIGHT REAR
QUADRANT OF A JET MAX AHEAD OF THE TROUGH MOVES OVER THE QUAD
STATE.
THIS LIFT OCCURS AS PWATS INCREASE TO 1.4 TO 1.5 INCHES, WHICH
IS 99TH PERCENTILE FOR CLIMATOLOGY. ELEVATED CONVECTIVE
INSTABILITY FORMS UP WITH MID LEVEL LAPSE RATES ABOUT 6.3-6.5
DEGC/KM. WET BULB ZERO HEIGHTS ARE ABOUT 9000 FT. DEEP AND LOW
LAYER SHEAR IS STRONG, WITH 850MB FLOW INCREASING TO 45-55KT
RESULTING IN LARGE LOOPED HODOGRAPHS.
WITH THAT, AREAS OF HEAVY RAIN APPEAR LIKELY. THE GUIDANCE IS
FOCUSING ON AN AREA FROM ABOUT CAIRO, ILLINOIS UP THROUGH
EVANSVILLE WHERE THE COMBO OF WARM ADVECTION, FRONTAL LIFT, AND
JET LEVEL LIFT LINE UP BEST. WE HAVE ABOUT 1.5 TO 2.0 INCHES OF
RAIN FORECAST IN THAT CORRIDOR AND HREF PROBABILITY MATCHED
MEANS SHOW AS MUCH AS 3 TO 4 INCHES. WE WOULD NEED ABOUT 2-3
INCHES IN 3 HOURS FOR FLASH FLOODING AND CONFIDENCE IN SUCH HIGH
AMOUNTS AND AREAL PLACEMENT PRECLUDES A FLOOD WATCH, BUT WILL
BUMP UP THE WORDING IN MESSAGING. THE LOW WET BULB ZERO HEIGHTS
AND ELEVATED INSTABILITY SUGGEST SOME HAIL POTENTIAL. IF
SURFACE TEMPERATURES GET ABOVE ABOUT 65 DEGREES, WITH DEWPOINTS
OVER 62 OR SO THEN SOME SURFACE-BASED INSTABILITY WILL DEVELOP
AND THE SHEAR PARAMETERS WOULD PRESENT A WIND/TORNADO THREAT.
WIDESPREAD RAIN MAY MAKE THAT A TALL ORDER. THE LOWER LEVEL
SHEAR SHOULD RELAX AS THE DAY PROGRESSES ALTHOUGH SOME SHOWERS
AND STORMS WILL BE POSSIBLE UNTIL THE FRONT CLEARS BY MID TO
LATE AFTERNOON.
THE FRONT CLEARS, WE GET A BREATH, AND THEN RIGHT BACK INTO IT
TUESDAY NIGHT AS ANOTHER SHORTWAVE EMERGES AND SPINS UP A LOW IN
THE VICINITY. THE ONLY NOTABLE TREND FOR THIS SYSTEM IS THAT THE
LIFT/QPF SEEMS TO BE MAXIMIZING MORE TO OUR SOUTH OVER
TENNESSEE, BUT ADDITIONAL SHOWERS AND STORMS SEEM QUITE LIKELY
REGARDLESS BEFORE A ANOTHER FRONT MOVES THROUGH WEDNESDAY.
WE WILL THEN DEAL WITH ONE MORE SHORTWAVE TROUGH THAT BRINGS AN
ALBERTA CLIPPER TO OUR NORTH. GFS/ECMWF ARE IN BETTER AGREEMENT
WITH THAT LOW TRACKING NORTH. MID-LEVEL LAPSE RATES ARE QUITE
STEEP AS THE TROUGH PASSES OVERHEAD AND WE GET ANOTHER SHOT OF
COLD AND DENSE AIR. HAVE ADDED A MENTION OF SNOW FLURRIES TO THE
FORECAST FRIDAY WITH THIS ACTIVITY AS THERE APPEARS TO BE ENOUGH
COLUMN MOISTURE TO WORK WITH THE LIFT TO PRODUCE AT LEAST SOME
PRECIP. THERE IS AN ODD BIFURCATION OF TEMPERATURES BETWEEN THE
GFS AND ECMWF THIS CYCLE, WITH THE GFS BREAKING MUCH WARMER THAN
WHAT WE SAW 24 HOURS AGO. THE SOURCE AIRMASS THIS FRONT IS
BRINGING IS STILL -35F, SO IT IS DIFFICULT TO SEE WHAT WOULD BE
MODIFYING/WARMING THE AIRMASS AS MUCH AS THE DETERMINISTIC GFS
ADVERTISES IN THE 12Z RUN. LEANED TOWARDS THE COLDER ECMWF AS IT
HAS BETTER RUN TO RUN CONTINUITY AND FROM THIS FORECASTERS
PERSPECTIVE MAKES BETTER SYNOPTIC SENSE. THE DETERMINISTIC
ECMWF IS STILL COLDER FOR SATURDAY HIGHS THAN THE NEW FORECAST,
WHICH WORKED WITHIN BLEND CONSTRAINTS.
AVIATION /18Z TAFS THROUGH 18Z MONDAY/
ISSUED AT 1121 AM CST SUN DEC 15 2024
FOG CONDITIONS ARE SLOWLY IMPROVING OVER MISSOURI AND MOSTLY LOW
MVFR CIGS ARE FORMING UP. FURTHER EAST LOW MVFR CLOUD DECKS ARE
MORE BROKEN TO SCATTERED. A FEW HOURS OF VFR CONDITIONS ARE
POSSIBLE AT VARIOUS SITES AND TIMES BUT THE OVERALL THEME WILL
BE FOR AT LEAST SCATTERED CLOUDS AT 1200-2200 FT.
AFTER SUNSET MORE UNSETTLED CONDITIONS BEGIN TO MOVE BACK INTO
THE AREA. PREVAILING LOW MVFR/IFR CEILINGS WITH VISIBILITY
REDUCING IN RAIN AND MIST CAN BE EXPECTED AREA-WIDE ONCE THIS
SETS IN. AREAS OF HEAVIER RAIN AND THUNDERSTORMS ARE ALSO
EXPECTED AT TIMES WITH THIS ACTIVITY. LOW-LEVEL WIND SHEAR
CONDITIONS WILL ALSO BE POSSIBLE WITH SOUTHWESTERLY WINDS AT
2000-3000 FT EXPECTED TO BE NEAR 50 KTS FOR A FEW HOURS IN THE
OVERNIGHT.
A FRONT THEN MOVES TOWARDS THE AREA AFTER SUNRISE MONDAY BUT AT
LEAST FOR NOW IFR CEILINGS LOOK TO PERSIST ALONG AND BEHIND THE
FRONT THROUGH THE NEW TAF PERIOD.
PAH WATCHES/WARNINGS/ADVISORIES
IL...NONE.
MO...NONE.
IN...NONE.
KY...NONE.
DISCUSSION...JGG
AVIATION...JGG
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