Area Forecast Discussion
Issued by NWS Jackson, MS

Home | Current Version | Previous Version | Text Only | Print | Product List | Glossary On
Versions: 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50
000
FXUS64 KJAN 271620 AAA
AFDJAN

AREA FORECAST DISCUSSION...UPDATED
NATIONAL WEATHER SERVICE JACKSON MS
1020 AM CST SAT DEC 27 2014

.UPDATE...PRECIPITATION HAS BEEN SLOW TO DEVELOP THIS MORNING OTHER
THAN A SCATTERING OF SHOWERS. AS OF 16Z...HOWEVER...COOLING CLOUP TOPS AND
MORE WIDESPREAD CONVECTION BEGINNING TO DEVELOP OVER SE LA/S MS. THIS
IS THE BEGINNING OF MUCH MORE RAIN THAT WILL OVERSPREAD THE AREA AS
ADVERTISED BY THE LATEST HIRES MODELS. BLENDED TOTAL PRECIPITABLE
WATER SATELLITE IMAGERY IS SHOWING 1.6-1.8 INCH AIR OVER SE LA AND
JUST OFFSHORE. THESE VALUES ARE GREATER THAN 200% OF NORMAL. WHILE
ADIABATIC FORCING WILL BE AS SUCH TO MAKE RAINFALL PRODUCTION QUITE
EFFICIENT...CONVECTIVE DEVELOPMENT SHOULD ENSURE FRENETIC RAINFALL
RATES LEADING TO AN ENHANCED POTENTIAL FOR FLOODING. /26/


&&

.AVIATION...CONDITIONS HAVE BEEN DETERIORATING OVER LAST SEVERAL
HOURS WITH MVFR/IFR CONDITIONS NOW WIDESPREAD ACROSS AREA DUE TO
CIGS. EXPECT COVERAGE OF RAIN/TSRA TO CONTINUE TO EXPAND INTO THIS
EVENING RESULTING IN FURTHER DETERIORATION OF VSBYS. POOR FLYING
CONDITIONS WITH WIDESPREAD IFR/OCNL LIFR EXPECTED INTO SUNDAY. /AEG/

&&

.PREV DISCUSSION... /ISSUED 524 AM CST SAT DEC 27 2014/

..HEAVY RAINFALL AND POTENTIAL FOR FLASH FLOODING THIS WEEKEND...

DISCUSSION...

TODAY THROUGH SUNDAY NIGHT...

THE ADVERTISED HEAVY RAIN SET-UP IS UNFOLDING WITH NUMEROUS SHOWERS
BREAKING OUT OVER THE LOWER MS VALLEY REGION...AND SOME LOCALLY HEAVY
RAINFALL HAS ALREADY DEVELOPED OVER SOUTH CENTRAL/EAST CENTRAL MS
WITH INITIAL WARM ADVECTION ACTIVITY. THE KEY FEATURES LEADING TO THE
HEAVY RAINFALL PATTERN ARE A STRONG TROUGH-TO-RIDGE PATTERN WITH A
DEEP LONGWAVE TROUGH OVER THE WESTERN CONUS AND AN ANOMALOUS
SUBTROPICAL RIDGE AXIS JUST OFF THE SOUTHEAST ATLANTIC COAST. THE
RESULTING DEEP SOUTHWEST FLOW OVER THE LOWER MS VALLEY REGION WILL
SEND TWO SIGNIFICANT SHORTWAVE PERTURBATIONS ACROSS THE FORECAST
AREA.

STRONGEST MOISTURE FLUX WITH ANOMALOUS PRECIPITABLE WATER AIR
(1.5-2.0 INCHES --- +2 TO 3 SDS) SURGING NORTH INTO THE FORECAST AREA
WILL ACCOMPANY THE FIRST WAVE OF LIFT/HEAVIEST RAIN POTENTIAL LATE
THIS AFTERNOON AND TONIGHT. LIFT WILL BE FURTHER ENHANCED BY
IMPRESSIVE UPPER JET ENTRANCE REGION DYNAMICS AND ASSOCIATED UPPER
LEVEL DIVERGENCE. WHILE THERE WILL LIKELY BE A BREAK IN THE ACTION
AFTER THE EARLY MORNING CONVECTION...EXPECT WIDESPREAD SHOWER/TSTM
ACTIVITY TO DEVELOP THIS AFTERNOON AND BECOME WIDESPREAD BY THE
EVENING WITH LOCALIZED INTENSE RAINFALL RATES DEVELOPING PER HIGH-RES
GUIDANCE. ANOTHER BREAK IS EXPECTED PERHAPS SUNDAY MORNING BEFORE THE
NEXT SHORTWAVE TROUGH AXIS APPROACHES SUNDAY AFTERNOON
RESULTING IN ADDITIONAL HEAVY RAIN POTENTIAL WITH ANOMALOUS MOISTURE
TRANSPORT...BUT WILL NOTE THAT MODELS HAVE BACKED OFF A LITTLE FOR
SUNDAY QPF GIVEN A SLIGHTLY FLATTER TROUGH AND MORE STRUNG OUT LOOK
TO THE MOISTURE PLUME.

VERY MOIST AIR WILL RESULT IN HIGH PRECIPITATION EFFICIENCY...ESPECIALLY
WHERE DEEP CONVECTION CAN DEVELOP. LATEST ECMWF/GFS PROG SUFFICIENT
CONVECTIVE INSTABILITY WITH NEGATIVE SHOWALTER INDICES TODAY AND
TONIGHT...WITH LAPSE RATES AND CONVECTIVE POTENTIAL DECREASING
SUNDAY. SEE HYDROLOGY SECTION BELOW FOR DISCUSSION ON IMPACTS OF
HEAVY WEEKEND RAINFALL AND MORE CONCERNING THE FLASH FLOOD WATCH
ISSUANCE.

AS FOR THE SEVERE WEATHER POTENTIAL...IT IS NON-ZERO GIVEN THE
EXPECTATION OF AT LEAST NEAR-SFC BASED INSTABILITY AND POTENTIAL FOR
STRONGER WINDS TO MIX DOWN IN DOWNDRAFTS. BUT POOR LOW LEVEL LAPSE
RATES AND OVERALL LACK OF SIGNIFICANT INSTABILITY WILL GREATLY LIMIT
THE POTENTIAL. SLU CIPS ANALOGS DO SHOW A FEW SEVERE REPORTS AND WILL
KEEP THE LIMITED POTENTIAL GOING FOR AREAS ALONG THE HWY 84
CORRIDOR...MAINLY FOCUSING ON LATER TODAY AND TONIGHT. THERE HAS BEEN
A FASTER TREND WITH THE COLD FRONT FOR SUNDAY AND THIS WILL LIMIT
SFC-BASED INSTABILITY POTENTIAL OVER SOUTHEAST PORTIONS OF THE
FORECAST AREA. EXPECT DIMINISHING RAINFALL POTENTIAL AS WE GO INTO
SUNDAY NIGHT. /EC/

MONDAY THROUGH SATURDAY...SURFACE HIGH PRESSURE RIDGING
WILL BUILD IN ON MONDAY ACROSS THE ARKLAMISS WITH COOLER HIGHS
RANGING FROM THE LOW TO MID 50S. LITTLE CHANGE IS EXPECTED TUESDAY...
BUT COLDER AIR WILL MOVE IN TUESDAY NIGHT AS COLD HIGH PRESSURE NOSES
INTO THE REGION. NEW YEARS EVE DAY TEMPERATURES WILL ONLY CLIMB INTO
THE 40S. NEW YEARS EVE WILL BE COLD WITH LOWS WEDNESDAY NIGHT FALLING
INTO THE UPPER 20S/LOW 30S. HAVE KEPT PRECIPITATION OUT OF THE
FORECAST FOR WEDNESDAY NIGHT AND THURSDAY...BUT THERE COULD BE SOME
POTENTIAL AS WE GET CLOSER.

THE PATTERN OVER THE AREA WILL BEGIN TO CHANGE ON THURSDAY AS THE
SURFACE HIGH SHIFTS TO THE EAST AND AN UPPER TROUGH DEEPENS OVER THE
SOUTHERN PLANES. MOISTURE WILL INCREASE OVER THE AREA THURSDAY NIGHT
INTO FRIDAY WITH SHOWERS ON THE INCREASE FRIDAY AFTERNOON. THE
GLOBAL MODELS DIVERGE ON THEIR SOLUTIONS FRIDAY NIGHT INTO SATURDAY
WITH THE GFS TAKING THE SURFACE LOW NORTH AND THE ECMWF FURTHER
SOUTH. EITHER WAY SHOWERS AND STORMS WILL BE ON THE INCREASE AS WE
GET INTO THE WEEKEND WITH ANOTHER ROUND OF HEAVY RAINFALL AND
POSSIBLY SOME SEVERE STORMS./15/

HYDROLOGY...WET ANTECEDENT SOIL CONDITIONS OVER MAINLY CENTRAL/EASTERN
MS WILL SUPPORT EXCESSIVE RUN-OFF AND FLASH FLOODING POTENTIAL WHERE
HEAVIER RAINFALL RATES DEVELOP THIS WEEKEND...AND A FLASH FLOOD WATCH
HAS BEEN ISSUED ACCORDINGLY. RIVER FLOODING IS NOT ANTICIPATED PER
PREVIOUS DISCUSSION...BUT IF RAINFALL AMOUNTS ARE A BIT HEAVIER THAN
EXPECTED (CERTAINLY POSSIBLE GIVEN ANOMALOUS MOISTURE) THEN A FEW
RIVER POINTS COULD REACH MINOR FLOOD STAGE BASED ON LMRFC CONTINGENCY
FORECASTS. /EC/

&&


.PRELIMINARY POINT TEMPS/POPS...
JACKSON       66  54  57  42 / 100 100  86  82
MERIDIAN      61  57  65  47 / 100 100  88  89
VICKSBURG     68  50  53  40 / 100 100  88  62
HATTIESBURG   66  62  69  49 / 100  95  70  65
NATCHEZ       68  53  55  42 / 100 100  88  64
GREENVILLE    63  44  49  38 / 100 100  85  41
GREENWOOD     62  48  51  39 / 100 100  88  51

&&

.JAN WATCHES/WARNINGS/ADVISORIES...
MS...FLASH FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR MSZ026>033-
     036>039-042>066-072>074.

LA...FLASH FLOOD WATCH THROUGH SUNDAY AFTERNOON FOR LAZ026.

AR...NONE.
&&

$$






USA.gov is the U.S. government's official web portal to all federal, state and local government web resources and services.