741
FXUS02 KWBC 120705
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
304 AM EDT TUE MAR 12 2024
VALID 12Z FRI MAR 15 2024 - 12Z TUE MAR 19 2024
...HEAVY SNOWS POSSIBLE ACROSS PARTS OF THE SOUTHERN ROCKIES INTO
FRIDAY...
...MULTI-DAY HEAVY RAINFALL EVENT LIKELY FOR PARTS OF THE SOUTH
LATE THIS WEEK AND WEEKEND...
..OVERVIEW
THE GENERAL FLOW OVER THE CONUS WILL BE SETTLING INTO A MUCH MORE
AMPLIFIED REGIME DURING THE MEDIUM RANGE PERIOD. BY THE START OF
THE PERIOD ON FRIDAY, A SHARP/AMPLIFIED UPPER RIDGE OFF THE WEST
COAST WILL SUPPORT A DEEP SOUTHWEST UPPER LOW THAT WILL LIKELY
MEANDER IN PLACE INTO EARLY NEXT WEEK. THIS FEATURE WOULD PROMOTE
A MULTI-DAY PERIOD OF HEAVY RAINFALL POTENTIAL ACROSS PARTS OF THE
SOUTHERN U.S. LATE THIS WEEK AND INTO THE WEEKEND WITH POSSIBLY
SIGNIFICANT SNOWFALL ONGOING THROUGH FRIDAY ACROSS PARTS OF THE
SOUTHERN ROCKIES. A LEADING PLAINS THROUGH NORTHEAST SYSTEM MAY
ALSO PRODUCE SOME ENHANCED RAINFALL NEAR ITS TRACK LATE THIS WEEK.
THE EAST PACIFIC INTO WESTERN CANADA UPPER RIDGE WILL HELP TO
AMPLIFY DOWNSTREAM TROUGHING INTO THE EASTERN HALF TO TWO-THIRDS
OF THE LOWER 48 BY THIS COMING WEEKEND INTO EARLY NEXT WEEK, WITH
A COLDER TREND BEHIND A NORTHERN TIER TO EAST COAST FRONT.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODEL GUIDANCE CONTINUES TO SHOW FAIRLY GOOD AGREEMENT ON
THE LARGE SCALE FORECAST, BUT A LOT OF DIFFERENCES IN THE DETAILS.
THERE REMAIN SOME MINOR DIFFERENCES IN TIMING AND STRENGTH OF AN
INITIAL WAVE TRACKING FROM THE MIDWEST THROUGH THE NORTHEAST LATE
THIS WEEK (THE GFS IS STILL A TAD FAST), BUT LATEST CLUSTERING
DOES SUGGEST THIS COULD BECOME A FAIRLY VIGOROUS (BUT PROGRESSIVE)
WAVE OFF THE NEW ENGLAND COAST BY EARLY FRIDAY. FOR THE SOUTHWEST
UPPER LOW, THERE IS VERY GOOD AGREEMENT THAT THIS LOW WILL
GENERALLY HANG AROUND THROUGH AT LEAST SUNDAY-MONDAY. AFTER THIS,
THE BIGGEST UNCERTAINTY BECOMES ANY KIND OF PHASING BETWEEN THIS
AND AN AMPLIFYING TROUGH OVER THE NORTH-CENTRAL U.S.. THE MODELS
HAVE SHOWN SOME RUN TO RUN VARIABILITY IN SHOWING THE NORTHERN
STREAM PHASING WITH THE SOUTHERN STREAM LOW AND DRAGGING IT
EASTWARD BY AROUND MONDAY, OR A FASTER PROGRESSION OF THE TROUGH
LEAVING THE UPPER LOW BEHIND. THE ECMWF HAS BEEN MOST CONSISTENT
IN SHOWING THE TWO PHASING, WHILE THE PAST FEW RUNS OF THE GFS
HAVE SUPPORTED THAT IDEA AS WELL. HOWEVER, THE ENSEMBLES ARE MORE
SUPPORTIVE OF THE UPPER LOW HANGING BACK THROUGH AT LEAST TUESDAY
AS THE NORTHERN STREAM TROUGH SPEEDS EASTWARD, AND THIS HAS
SUPPORT FROM MOST OF THE EC-INITIALIZED ML MODELS AS WELL AS THE
CMC. GIVEN THE SUPPORT FROM THE ENSEMBLE MEANS, THE WPC FORECAST
ALSO LEANED MORE ON HOLDING THE LOW BACK, AND INTERESTINGLY
ENOUGH, BOTH OF THE 00Z RUNS OF THE GFS AND ECMWF TONIGHT (WHICH
WAS AVAILABLE AFTER FORECAST GENERATION TIME) ALSO JUMPED BACK
INTO THIS CAMP AS WELL. BOTTOM LINE, THERE IS STILL A LOT OF
UNCERTAINTY IN HOW, IF AT ALL, THE TWO STREAMS WILL INTERACT AND
STILL PLENTY OF TIME FOR THE FORECAST TO CHANGE, ONE WAY OR THE
OTHER.
THE WPC FORECAST BLEND FOR TONIGHT USED A COMPOSITE BLEND OF THE
DETERMINISTIC SOLUTIONS DAYS 3-5 WHERE LARGE SCALE AGREEMENT WAS
GOOD. BY DAY 6 AND ESPECIALLY 7, THE BLEND PHASED OUT THE GFS AND
ECMWF AND QUICKLY INCREASED THE CONTRIBUTIONS FROM THE ENSEMBLE
MEANS. OVERALL, THIS MAINTAINED GOOD CONTINUITY WITH THE PREVIOUS
WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
A LONG-DURATION WINTER STORM WILL BE COMING TO AN END ACROSS PARTS
OF THE SOUTHERN ROCKIES ON FRIDAY, WITH THE SOME POSSIBLY
SIGNIFICANT STORM TOTAL ACCUMULATIONS ACROSS THE HIGHER TERRAIN.
FARTHER EAST, A MIDWEST THROUGH NORTHEAST WAVE AND FRONTAL SYSTEM
WILL SUPPORT SOME ENHANCED PRECIPITATION NEAR ITS PATH INTO
FRIDAY. ON DAY 4/FRIDAY, FAVORABLE MOISTURE/INSTABILITY IN THE
WARM SECTOR, A SUBSET OF OPERATIONAL MODELS WITH LOCALLY
SIGNIFICANT QPF, AND FAIRLY WET ANTECEDENT CONDITIONS/FFGS, SEEM
TO FAVOR HOLDING ON TO THE MARGINAL RISK INTO PARTS OF THE
NORTHEAST. SOME MOISTURE REACHING FAR NORTHERN NEW ENGLAND COULD
ALSO PRODUCE A LITTLE SNOW.
MEANWHILE THE MOISTURE STREAMING NORTHWARD AHEAD OF THE STAGNANT
UPPER LOW OVER THE SOUTHWEST AND INTERACTING WITH THE FRONT
TRAILING FROM THE AFOREMENTIONED NORTHERN WAVE WILL SUPPORT WHAT
SHOULD BE A MULTI-DAY HEAVY RAINFALL THREAT ACROSS THE SOUTH,
WHICH WILL START TOWARDS THE END OF THE SHORT RANGE PERIOD. THE
COLD FRONT MAY GET HUNG UP FOR A PERIOD OF TIME SUPPORTING
REPEAT/TRAINING THUNDERSTORMS ACROSS PARTS OF THE LOWER
MISSISSIPPI VALLEY INTO THE CENTRAL GULF COAST STATES, BUT THERE
IS PLENTY OF UNCERTAINTY IN THE EXACT PLACEMENT OF THE HIGHEST QPF
STILL. THE DAYS 4 AND 5 EXCESSIVE RAINFALL OUTLOOKS BOTH DEPICT
SLIGHT RISK AREAS ACROSS THIS REGION, AND THERE IS POTENTIAL FOR
AN UPGRADE AS THE EVENT GETS CLOSER IN TIME ESPECIALLY CONSIDERING
POSSIBLE OVERLAP IN THE HEAVIEST QPF. SOME HEAVY RAINFALL
POTENTIAL MAY EXTEND NORTHWARD ALONG THE BOUNDARY INTO THE
SOUTHERN/CENTRAL APPALACHIANS AS WELL. THE HEAVY RAINFALL THREAT
MAY LINGER ACROSS THE SOUTHEAST THROUGH THE WEEKEND. THE SYSTEM
TRACKING THROUGH SOUTHEASTERN CANADA SATURDAY-MONDAY AND TRAILING
FRONT MAY PRODUCE AREAS OF RAIN AND PERHAPS COLD SECTOR SNOW OVER
PARTS OF THE GREAT LAKES/NORTHEAST.
MEAN RIDGING ALOFT OVER THE EASTERN U.S. WILL CONTINUE TO SUPPORT
AN EXPANSIVE AREA OF ABOVE NORMAL TEMPERATURES, WITH THE CORE OF
THE WARMEST ANOMALIES OVER THE MID-ATLANTIC AND OHIO VALLEY ON
FRIDAY WHERE HIGH TEMPERATURES COULD REACH 15-20 DEGREES ABOVE
NORMAL. TEMPERATURES ACROSS THE EAST WILL TREND
COOLER WITH TIME AFTER FRIDAY, BUT SHOULD GENERALLY REMAIN ABOVE
NORMAL THROUGH THE WEEKEND. OVER THE WEST, MODERATELY BELOW
AVERAGE HIGHS AND NEAR/ABOVE AVERAGE LOWS WILL LINGER OVER THE
GREAT BASIN/SOUTHWEST FRIDAY-SATURDAY, BEFORE SHIFTING SLIGHTLY
EAST INTO THE PLAINS ON SUNDAY. STRONG SURFACE HIGH PRESSURE WILL
ALLOW FOR BELOW NORMAL TEMPERATURES TO EXPAND SOUTHWARD WITH TIME
EARLY NEXT WEEK INTO THE TENNESSEE VALLEY AND PARTS OF THE
SOUTHEAST, WITH SOME POSSIBLE FROST/FREEZE CONCERNS IN THE
TENNESSEE VALLEY FOR ANY AREAS WHICH MAY BE STARTING TO SEE THEIR
SPRING GREEN-UP ALREADY. OUT WEST, TEMPERATURES SHOULD INCREASE BY
FRIDAY AND THROUGH THE WEEKEND AS STRONG RIDGING BUILDS IN ALOFT,
WITH THE NORTHWEST SEEING THE BEST POTENTIAL FOR SOME HIGHS
REACHING 10-15 DEGREES ABOVE NORMAL.
SANTORELLI
ADDITIONAL 3-7 DAY HAZARD INFORMATION CAN BE FOUND ON THE WPC
MEDIUM RANGE HAZARDS OUTLOOK CHART AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,
QUANTITATIVE PRECIPITATION FORECAST, EXCESSIVE RAINFALL OUTLOOK,
WINTER WEATHER OUTLOOK PROBABILITIES, HEAT INDICES AND KEY
MESSAGES ARE AT:
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=ERO
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML
HTTPS://WWW.WPC.NCEP.NOAA.GOV/#PAGE=OVW
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