AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE NEW ORLEANS LA 432 PM CST SAT JAN 25 2014
.SYNOPSIS...
HIGH PRESSURE OVER THE WESTERN GULF THIS AFTERNOON. SKIES HAVE CLEARED AND THE REMNANTS OF THE WINTRY PRECIPITATION FROM YESTERDAY ARE ONLY A MEMORY...AND NOT NECESSARILY A POSITIVE ONE. TEMPERATURES REBOUNDED INTO THE 50S TODAY...AND DEW POINTS ARE MAINLY IN THE 30S.
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.SHORT TERM...
HIGH PRESSURE SHIFTS RAPIDLY EASTWARD TONIGHT AND SUNDAY TO BE CENTERED ALONG THE ATLANTIC COAST BY SUNDAY EVENING. SOME POTENTIAL FOR FOG OVERNIGHT...DRYING NEAR THE SURFACE TODAY SHOULD HAVE EASED THE THREAT SOMEWHAT. A PARTLY SUNNY DAY SUNDAY AS COLD FRONT ADVANCES TOWARD AREA...WITH MOST AREAS WARMING INTO THE 60S.
BEYOND SUNDAY EVENING...THE FORECAST...AND THE FORECAST CONFIDENCE BOTH GO DOWNHILL. FRONTAL PASSAGE OCCURS DURING THE DAY MONDAY...WITH HIGH TEMPERATURES GENERALLY DURING THE MORNING HOURS. EXPECT SOME SHOWERS WITH THE FRONTAL PASSAGE WITH RAIN AMOUNTS RATHER LIGHT. QUESTION THEN BECOMES THE SPEED AND STRENGTH OF THE COLD AIR IMPACT. ECMWF AND GFS PUSH THE COLDER AIR SOUTHEASTWARD MORE AGGRESSIVELY MONDAY NIGHT THAN DOES THE 12Z NAM. HOW COLD AND HOW FAR SOUTHEAST THE COLD AIR GETS HAS A SIGNIFICANT IMPACT ON POSSIBLE PRECIPITATION ON TUESDAY. DURING MONDAY NIGHT...PRECIPITATION WOULD BE RAIN DURING THE EVENING WITH POTENTIAL FOR A MIX OR CHANGE TO SLEET FOR MOST OF THE AREA. AMOUNTS ARE EXPECTED TO BE RATHER LIGHT...BUT AS SEEN YESTERDAY...IT DOESNT TAKE A LOT TO CAUSE PROBLEMS. AS A JET IMPULSE MOVES ALONG THE FRONT TUESDAY...PRECIPITATION WILL BREAK OUT ALONG AND NORTH OF THE FRONT. THE 12Z GFS AND ECMWF OPERATIONAL SOLUTIONS INDICATE THAT THE COLD AIR WOULD BE ENTRENCHED ENOUGH WHERE LIGHT PRECIPITATION WOULD FALL AS SLEET OR SNOW. THE 12Z NAM DOES NOT DIG THE COLD AIR AS DEEPLY...AND SHOWS QUITE A WARM NOSE OF AIR BETWEEN 800 AND 900 MB THROUGH MUCH OF TUESDAY. THAT MODEL ALSO PAINTS A SIGNIFICANT AMOUNT OF PRECIPITATION ACROSS ABOUT THE SOUTHERN HALF OF THE CWA ON TUESDAY AND MUCH OF THAT COULD FALL AS FREEZING RAIN...LOOKING AT NAM SOUNDINGS. ALL THREE SOLUTIONS HAVE AT LEAST SOME SUPPORT FROM VARIOUS MEMBERS OF 00Z AND 12Z ENSEMBLES. HOPEFULLY...LATER RUNS WILL COME INTO BETTER AGREEMENT ON THE MONDAY NIGHT AND TUESDAY PORTIONS OF THE FORECAST. LATER FORECASTS WILL NEED TO BE MONITORED FOR ANY SIGNIFICANT CHANGES IN THINKING REGARDING PRECIPITATION TYPES AND AMOUNTS. SO STAY TUNED.
IN ANY CASE...IT WILL BE COLD TUESDAY AND TUESDAY NIGHT WITH TEMPERATURES 20-25 DEGREES BELOW NORMAL. 35
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.LONG TERM...
ON THE BRIGHTER SIDE...IT APPEARS THAT THE COLD AIR EARLY IN THE WEEK MAY BE THE LAST IN THE CURRENT SERIES OF COLD AIR PLUNGES. BOTH MEDIUM RANGE MODELS DIG A TROF ALONG THE WEST COAST FOR THE MIDDLE AND END OF THE WEEK...WHICH FORCES RIDGING DOWNSTREAM OVER THE GULF OF MEXICO AND EASTERN STATES. ONSHORE FLOW DEVELOPS...WITH A CHANCE OF SHOWERS BY THURSDAY NIGHT OR FRIDAY...WITH AT LEAST SMALL CHANCES OF RAIN IN THE FORECAST THROUGH NEXT WEEKEND. THE ECMWF IS SLIGHTLY SLOWER ON THE MOISTURE RETURN AND WARMING...BUT CARRIES THE SAME GENERAL MESSAGE. TEMPERATURES WILL REMAIN VERY MUCH BELOW NORMAL FOR WEDNESDAY THROUGH THURSDAY MORNING BEFORE MODERATING. BY THE WEEKEND...HIGH TEMPERATURES ARE LIKELY TO BE IN THE 60S...AND POSSIBLY THE 70S. AND THERE ARE SOME INDICATIONS THAT THE TEMPERATURES WE CURRENTLY HAVE IN THE FORECAST MAY NOT BE WARM ENOUGH. THIS PATTERN CHANGE...UNFORTUNATELY...APPEARS TO BE TRANSITORY AS THE GFS BEYOND 240 HOURS DOES REBUILD THE RIDGE OVER THE EASTERN PACIFIC. 35
Here's the 18z NAM's forecast sounding for Lockport late Tuesday night. There's a small warm layer in there but wet bulbing should help with the snow. NAM's snow depth on twisterdata.com looks like a 1 - 4" snowfall total from Lockport to Thibodaux.
Here's the 18z NAM's forecast sounding for Lockport late Tuesday night. There's a small warm layer in there but wet bulbing should help with the snow. NAM's snow depth on twisterdata.com looks like a 1 - 4" snowfall total from Lockport to Thibodaux.
Loving it
60 miles southwest of New Orleans) Thibodaux, La
SKYSUMMIT President | Director of OperationsAdministrator
AREA FORECAST DISCUSSION NATIONAL WEATHER SERVICE HOUSTON/GALVESTON TX 508 PM CST SAT JAN 25 2014
.AVIATION... VFR FOR THE NEXT 24+ HOURS, WITH THE EXCEPTION OF MAYBE LBX WHERE THERE MIGHT BE SOME TYPICAL PATCHY LATE NIGHT FOG ONCE WINDS DIMINISH. AN UPPER LEVEL DISTURBANCE WILL MOVE ACROSS THE AREA OVERNIGHT BRINGING SOME MID/HIGH LEVEL CIGS. COULD BE SOME RETURNS ON RADAR AS WELL...BUT DRY SUB CLOUD LAYER WILL KEEP ANYTHING FROM REACHING THE GROUND. CLEARING SKIES SUN AFTN. 47
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.PREV DISCUSSION... /ISSUED 351 PM CST SAT JAN 25 2014/ WHAT A DIFFERENCE A DAY MAKES. WEST SOUTHWEST WINDS AND PARTLY CLOUDY SKIES HAVE ALLOWED TEMPERATURES TO WARM TO NEAR 60 DEGREES THIS AFTERNOON. EXPECT SIMILAR CONDITIONS ON SUNDAY...WITH TEMPERATURES LIKELY NEARING 70 ACROSS MUCH OF THE REGION.
AFTER OUR BRIEF RESPITE OLD MAN WINTER WILL RETURN ON MONDAY AS A STRONG FRONT BRINGS ARCTIC AIR BACK TO THE REGION. HIGH TEMPERATURES WILL LIKELY OCCUR IN THE MORNING AS THE FRONT SHOULD BE MOVING THROUGH COLLEGE STATION BY DAYBREAK AND INTO THE HOUSTON METRO AREA BY LUNCHTIME. TEMPERATURES TUESDAY MORNING WILL FALL BELOW FREEZING ACROSS ALL BUT THE IMMEDIATE COASTLINE WITH NORTHERN AREAS FALLING INTO THE MID 20S. OF GREATER CONCERN IS THE APPROACH OF AN UPPER LEVEL SHORTWAVE WHICH WILL LEAD TO THE POTENTIAL FOR SOME FROZEN PRECIPITATION TUESDAY INTO WEDNESDAY. MODELS HAVE TRENDED SLIGHTLY SLOWER WITH THE APPROACH OF THIS FEATURE ALLOWING SURFACE AND NEAR SURFACE TEMPERATURES TO COOL FURTHER. WHILE THERE REMAINS GREAT UNCERTAINTY WITH THIS EVENT THERE IS ENOUGH MODEL CONSENSUS TO INTRODUCE A MENTION OF FROZEN PRECIPITATION INTO THE FORECAST. TEMPERATURES LOOK TO BE COLDER THAN LAST WEEK WHICH WOULD SHIFT THE THREAT MORE TOWARD SLEET AND SNOW...RATHER THAN FREEZING RAIN. GREATEST IMPACTS WILL LIKELY BE CONFINED TO AN AREA ALONG AND SOUTH OF A LINE FROM COLLEGE STATION TO HOUSTON TO WINNIE. FURTHER NORTH...MOISTURE WILL BE SOMEWHAT LIMITED AND SNOW FLURRIES ARE POSSIBLE. ONE CONCERN WITH THIS SOLUTION WILL BE THE AMOUNT OF INTERACTION WITH THE SHORTWAVE AND THE UPPER LEVEL LOW WHICH IS FORECAST TO HANG BACK OVER NORTHERN MEXICO...WHICH COULD CHANGE THE AMOUNT OF MOISTURE AVAILABLE TO WORK WITH. AGAIN...EXPECT TO SEE CHANGES IN THE FORECAST AS WE GET CLOSER BUT ANOTHER BRUSH WITH WINTER WEATHER LOOKS POSSIBLE THIS WEEK.
PRECIPITATION WILL EXIT THE REGION BY WEDNESDAY AFTERNOON WITH ANOTHER QUICK WARMUP EXPECTED MUCH AS WE ARE SEEING NOW. ANOTHER FRONT WILL ARRIVE NEXT WEEKEND BRINGING RAIN CHANCES FOR MUCH OF THE REGION BUT TEMPERATURES WILL NOT NEARLY BE AS COLD.
Post by thibodauxwx on Jan 25, 2014 17:24:12 GMT -6
This is what Larry Cosgrove thinks is happening to the model, and why they don't show the winter precip here: this was with for the models and yesterdays weather, but it would be the same for the next round:
Larry Cosgrove The data is relatively plentiful...but climatology says "it should not ice in Louisiana"...which I think is the reason the models showed a very limited shortwave. If you look at radar displays of intensity and basic amount, NOTHING of this nature was predicted by the equations....through later the NAM and RGEM outlooks seemed to grasp some the threat.
Last Edit: Jan 25, 2014 17:26:35 GMT -6 by thibodauxwx
Here is the HPC latest discussion. Still there are uncertainties.
...GULF COAST/SOUTHEAST/FL...
THE MODELS ARE IN RATHER POOR CORRELATION WITH THE QPF...CERTAINLY MORE SO COMPARED TO THEIR MASS FIELD DIFFERENCES. THE MAIN DIFFERENCE DEALS WITH TO WHAT DEGREE THE SRN STREAM WILL BECOME INVOLVED IN TERMS OF BOTH THE DISTRIBUTION OF THE PCPN (I.E. HOW FAR N INTO THE GULF COAST/SOUTHEAST/SOUTHERN MID-ATLANTIC REGION THE PCPN WILL GET) AS WELL AS AMOUNTS...PARTICULARLY NEAR THE GULF COAST. THE NAM TRENDED MUCH WETTER AT 12Z COMPARED TO PRIOR RUNS...INDICATIVE OF A MORE PROGRESSIVE SRN STREAM WAVE AND THUS A BROADER EXPANSION OF WAA/OVERRUNNING PCPN...HOWEVER THE 18Z NAM HAS SINCE BACKED OFF ON THIS IDEA CONSIDERABLY (ESPECIALLY WITH RESPECT TO THE NRN EXTENT). HOWEVER...GIVEN THE LACK OF CONSISTENCY WITH THE NAM (AND THE SREF MEAN FOR THAT MATTER)...WPC STAYED FAIRLY CLOSE TO A BIAS-CORRECTED GEFS MEAN...WHICH IS STILL SOMEWHAT WETTER THAN THE OPERATIONAL GFS/UKMET/ECMWF...BUT NEVERTHELESS INCORPORATES THE IDEA OF MORE SRN STREAM INTERACTION TOWARD THE END OF DAY 3...WHICH IS WHERE THE OPERATIONAL ECMWF IS TRENDING (THOUGH AGAIN...NOT TO THE BULLISH EXTENT AS THE NAM OR SREFMEAN). EXPECT A LLVL BOUNDARY (INVERTED SFC TROUGH) TO GET FRONTOGENETIC SUPPORT VIA THE RIGHT ENTRANCE REGION OF THE UPPER LEVEL JET STREAK...ANY SRN STREAM SUPPORT WOULD ONLY AMPLIFY THE FORCING AND EXTEND THE OVERRUNNING PCPN FARTHER N INTO THE COLDER AIR. FOR FURTHER DETAILS REGARDING THE WINTER WEATHER PROBABILITIES ASSOCIATED WITH THIS SYSTEM...PLEASE REFER TO THE WPC'S SUITE OF WINTER WEATHER PRODUCTS... INCLUDING THE LATEST QPFHSD DISCUSSION.
