Issued by NWS Jackson, MS
000 FXUS64 KJAN 210229 AFDJAN AREA FORECAST DISCUSSION...UPDATED NATIONAL WEATHER SERVICE JACKSON MS 825 PM CST FRI NOV 20 2009 .UPDATE...LATEST SATELLITE IMAGERY SHOWED A SHORT WAVE OVER THE SOUTHERN PLAINS WITH AN ASSOCIATED SURFACE WAVE OVER THE NORTHWEST GULF OF MEXICO. THE ARKLAMISS WAS WELL NORTH IN THE COOLER AND STABLE AIRMASS. AREA RADARS WERE PICKING UP SOME PATCHY VERY LIGHT RAIN TO THE WEST AND SOUTH OF THE REGION. STILL EXPECT SOME VERY LIGHT RAIN TO IMPACT THE REGION LATER TONIGHT FROM THE SOUTH. THIS WILL NOT BE A SHOWERY TYPE SYSTEM FOR THIS REGION IN THIS COOL STABLE AIRMASS. SO FOLLOWING RADAR TRENDS OF DEVELOPMENT. HAVE PUSHED BACK THE FIRST WAVE OF VERY LIGHT RAIN IN THE SOUTH UNTIL NEAR MIDNIGHT...THEN PUT PULLED BACK RAIN CHANCES FOR THE REST OF THE NIGHT. GOING FROM A SLIGHT CHANCE ALONG AND NORTH OF INTERSTATE 20 TO CHANCE POPS SOUTH. ALSO DELAYED HIGH POPS UNTIL THE LATER HALF OF SATURDAY MORNING FOR THE REGION. CURRENT LOWS IN THE 40S LOOKS TO BE ON TRACK. WILL KEEP THE BEST CHANCE POPS ACROSS THE SOUTH HALF WHERE THE LIGHT RAIN WILL ORIGINATE FROM./17/ .PREV DISCUSSION...352 PM CST FRI NOV 20 2009 .SHORT TERM...TONIGHT THROUGH SUNDAY NIGHT...PRIMARY CONCERN THIS PERIOD REVOLVES AROUND WIND SPEEDS AND PRECIP ACCUMULATIONS THROUGH SUNDAY AFTERNOON. THIN UPPER LEVEL CLOUD COVER IS ON THE INCREASE THIS AFTERNOON AHEAD OF A S/WV TROUGH CROSSING THE RIO GRANDE VALLEY. THIS S/WV WILL DEEPEN AN AREA OF SFC LOW PRESSURE LOCATED OVER THE WESTERN GULF OF MEXICO AS IT ADVANCES EAST THROUGH THE NIGHT TONIGHT. AS A RESULT...PRECIP CHANCES WILL INCREASE FROM THE SW OVERNIGHT AS THE SFC LOW TRANSLATES TOWARD THE LA COAST. SOME DIFFERENCES EMERGE AMONG THE NWP GUIDANCE AT THIS POINT CALLING THE EVENTUAL PROGRESSION OF THIS SYSTEM INTO QUESTION. THE GFS REMAINS ON THE FAST EDGE OF THE ENVELOPE THROUGH THE WEEKEND AND MAINTAINS A WEAKER MORE PERSISTENT SFC LOW RIGHT ALONG THE COAST. THE ECMWF DEVELOPS A MUCH DEEPER SURFACE LOW WITH SOME UNUSUAL BULLS EYES IN THE PRECIP FIELDS LIKELY ASSOCIATED WITH GRID SCALE FEEDBACK PROBLEMS. SREF CAME IN MORE WITH THE GFS IN TERMS OF SURFACE LOW TRACK ALTHOUGH WAS NOT AS FAST PUSHING THE LOW INTO THE AL COAST. FOR THIS PACKAGE...LEANED MORE ON THE SREF IN TERMS OF OVERALL SPEED OF THE SYSTEM WITH A GFS/ECMWF/SREF BLEND FOR THE TRACK. THIS DID MEAN SOME DIVERGENCE FROM THE 12Z MAV GUIDANCE POPS...PRIMARILY ON SATURDAY AFTERNOON/NIGHT WHERE ALL AREAS GOT BUMPED ABOVE GUIDANCE. GFS REALLY KEEPS THE RAIN ISOLATED SE OF THE NATCHEZ TRACE. THIS IS NOT SUPPORTED BY THE ECMWF OR SREF WHICH BOTH SHOW MEASURABLE RAINFALL ACROSS THE AREA DURING THESE TIMES. DO FEEL THE HEAVIEST RAINFALL WILL BE SE OF THE TRACE...BUT NOT LIMITED TO THIS AREA. AT THIS POINT...HEAVY RAINFALL WARRANTING ANY FLOOD PRODUCTS IS NOT NEEDED AS PW VALUES STRUGGLE TO CLIMB ABOVE 1.25 IN...EVEN ACROSS SOUTHEASTERN AREAS. RAINFALL TOTALS ON THE ORDER OF 0.50 TO 1 INCH ARE PROBABLE ACROSS THE CWA WITH THE HIGHEST AMOUNTS SE OF THE TRACE. THAT BEING SAID...LOCALIZED AREAS RECEIVING A LITTLE OVER AN INCH IS NOT OUT OF THE QUESTION. EASTERLY WINDS ARE STILL EXPECTED TO INCREASE TOMORROW AFTERNOON AS THE SFC LOW NEARS. STRONGEST WINDS WILL BE LIMITED TO AREAS S AND E...AND WILL GO AHEAD AND ISSUE A LAKE WIND ADVISORY FOR THE ROSS BARNETT RES AND LAKE OKATIBBEE STARTING LATE TOMORROW MORNING. THIS IS A MARGINAL EVENT CONSIDERING THE SYNOPTIC SET-UP AND WILL BE WATCHED CLOSELY FOR POSSIBLE TEMPORAL AND AREAL CHANGES AS THIS SYSTEM EVOLVES. IN ADDITION... WENT AHEAD AND LEFT A SLIGHT CHANCE OF A THUNDERSTORM OR TWO DEVELOPING ACROSS SERN AREAS TOMORROW AFTERNOON INTO THE EARLY EVENING. GFS HINTS AT 100-200 J/KG OF MUCAPE SLIDING ACROSS THE AREA AS THE LOW MAKES ITS CLOSEST POINT OF APPROACH AND COUPLED WITH DEEP LAYER LIFT IN PLACE AHEAD OF THE UPPER LEVEL S/WV...FEEL THE CHANCES ARE NON-ZERO. PRECIP WILL CONTINUE INTO THE OVERNIGHT HOURS SAT NIGHT BEFORE BEGINNING TO TAPER OFF FROM W TO E LATE SUN MORNING INTO THE AFTERNOON AS THE BEST LIFT AND LOW LEVEL MOISTURE FEED MOVE INTO AL. S/WV RIDGING AND SFC HIGH PRESSURE MOVE INTO THE ARKLAMISS LATE SUNDAY AND SHOULD PROVIDE SOME CLOUD CLEARING AS A RESULT. WINDS LOOK TO GO VERY LIGHT OR EVEN CALM MONDAY NIGHT...AND CONSIDERING THE LACK OF A COOL/DRY PUSH AND RESIDUAL SFC MOISTURE FROM THE RAINS, ADDED SOME PATCHY FOG FOR MONDAY MORNING. MAV TEMPS LOOKED GOOD EXCEPT FOR SUN AFTERNOON HIGHS WHERE GFS APPEARED TOO WARM CONSIDERING THE LINGERING RAIN AND CLOUD COVER. WENT AHEAD AND LOWERED TEMPS A DEGREE OR TWO AREAWIDE AT THAT TIME. /BK/ .PREVIOUS LONG TERM...FOR MID- TO LATE-WEEK...A SERIES OF SHORTWAVE TROUGHS AND ASSOCIATED SURFACE COLD FRONTS WILL DIVE SOUTHEASTWARD ACROSS THE MIDWEST AND OHIO VALLEY REGIONS...CARVING OUT A MEAN TROUGH OVER THE EASTERN CONUS. NWP MODEL GUIDANCE HAS COME INTO BETTER AGREEMENT IN DROPPING ONE OF THESE COLD FRONTS SOUTHWARD ACROSS THE REGION ON TUESDAY. THE FRONT WILL BECOME MORE SHALLOW AS IT APPROACHES AND MOVES ACROSS THE ARKLAMISS AS THE ASSOCIATED UPPER TROUGH AND STRONGER DEEP-LAYER SYNOPTIC-SCALE ASCENT REMAIN WELL NORTH OF THE AREA. NEVERTHELESS... MOISTURE POOLING ALONG THE BOUNDARY RESULTING IN PWATS NEAR ONE INCH WILL BE SUFFICIENT FOR ISOLATED LIGHT SHOWERS ALONG OR JUST BEHIND THE SURFACE FRONT...ALONG WITH AN INCREASE IN CLOUDS. POPS WERE LOWERED FROM MEX GUIDANCE TO SLIGHT CHANCE FOR LATE MONDAY NIGHT OVER NORTHWESTERN AREAS...AS THE OPERATIONAL GFS APPEARS TO MOVE THE FRONT TOO QUICKLY TO THE SOUTH RELATIVE TO GFS ENSEMBLE MEMBERS AND ECMWF...AND WITH WEAK UPPER SUPPORT OVER THE ARKLAMISS. BEHIND THE FRONT...WINDS WILL BECOME NORTHERLY AND ADVECT COOLER AIR ACROSS THE REGION...WITH HIGH PRESSURE BUILDING IN THE WAKE OF THE FRONT. FOR WEDNESDAY NIGHT OR THURSDAY...A REINFORCING COLD FRONT WILL QUICKLY SURGE SOUTH ACROSS THE REGION...THOUGH DEEP-LAYER DRY AIR WILL BE IN PLACE /PWATS OF ONLY 0.3 INCHES/ PRECLUDING PRECIP CHANCES WITH THIS FRONT. THE ONLY IMPACTS TO SENSIBLE WEATHER WITH THE FRONT WILL BE AN INCREASE IN NORTH WINDS ALONG WITH THE POTENTIAL FOR MUCH COOLER CONDITIONS LATE IN THE WEEK. THE CORE OF THE COLD AIRMASS WILL REMAIN NORTH OF THE CWA...THOUGH GFS AND ECMWF INDICATE 850-MB TEMPS FALLING TO 3C ACROSS NORTHERN AREAS BEHIND THE FRONT... POTENTIALLY SUPPORTING TEMPERATURES SEVERAL DEGREES BELOW SEASONAL AVERAGES. HOWEVER...SIGNIFICANT DIFFERENCES BETWEEN GFS AND ECMWF IN THE CHARACTERISTICS OF THE ASSOCIATED UPPER TROUGH SUGGEST LOW CONFIDENCE IN THE TIMING OF THE CORRESPONDING SURFACE FRONT...AS WELL AS HOW COLD TEMPERATURES GET. /COHEN/ && .AVIATION...A LOW PRESSURE SYSTEM APPROACHING FROM THE WEST KEPT THE CIRRUS SHIELD OVER THE REGION FOR THIS EVENING. THIS CLOUD DECK WILL GRADUALLY LOWER TONIGHT...BUT CEILINGS SHOULD REMAIN ABOVE 8000 FT THROUGH THE NIGHT GIVEN THE VERY DRY LOW LEVEL AIR IN PLACE. AS RAIN DEVELOPS OVER THE AREA NORTH OF A WARM FRONT...CEILINGS AND VISIBILITY WILL DETERIORATE...ESPECIALLY AT JAN/HBG/MEI WHERE IFR CEILINGS MAY BECOME PREVALENT PRIOR TO NOON SATURDAY. ALL SITES COULD EXPERIENCE MVFR/IFR RESTRICTIONS DUE TO LOWER CEILINGS AND RAIN AS WE GO INTO SATURDAY AFTN/NIGHT. GREATER INSTABILITY IN THE MEI/HBG AREA WILL SUPPORT A FEW TSTMS FROM SATURDAY AFTERNOON INTO SATURDAY EVENING. /17/ && .PRELIMINARY POINT TEMPS/POPS... JACKSON 46 58 45 61 / 22 89 63 13 MERIDIAN 44 57 45 61 / 22 86 80 24 VICKSBURG 46 58 45 62 / 22 89 58 9 HATTIESBURG 48 58 49 63 / 49 90 56 12 NATCHEZ 47 57 44 63 / 47 90 45 5 GREENVILLE 46 60 44 63 / 18 80 69 13 GREENWOOD 45 60 45 62 / 13 83 80 19 && .JAN WATCHES/WARNINGS/ADVISORIES... MS...LAKE WIND ADVISORY FROM 9 AM SATURDAY TO MIDNIGHT CST SATURDAY NIGHT FOR MSZ043-049-052. LA...NONE. AR...NONE. && $$
