929
FXUS02 KWBC 181900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SUN FEB 18 2024
VALID 12Z WED FEB 21 2024 - 12Z SUN FEB 25 2024
..OVERVIEW
UPPER TROUGHING COMING QUICKLY INTO THE WEST COAST AS THE PERIOD
BEGINS MIDWEEK WILL SPREAD SOME LINGERING PRECIPITATION TO
CALIFORNIA AND SNOW INTO THE INTERMOUNTAIN WEST. THE WEAKENING
SHORTWAVE ENERGY FROM THIS SYSTEM WILL THEN QUICKLY EJECT EASTWARD
AND MAY COMBINE WITH AMPLIFYING NORTHERN STREAM ENERGY TO DEVELOP
A CENTRAL-EASTERN U.S. SURFACE LOW/FRONTAL SYSTEM BY THE LATTER
HALF OF THE WEEK. THIS FEATURE SHOULD SPREAD RAIN AND NORTHERN
TIER SNOW TO PARTS OF THE EASTERN THIRD OF THE COUNTRY AS A LARGER
SCALE UPPER TROUGH SETTLES OVER THE EAST. MEANWHILE, PERIODS OF
UPPER RIDGING ACROSS THE WEST-CENTRAL U.S. WILL LEAD TO MUCH ABOVE
NORMAL TEMPERATURES ON AVERAGE THROUGH THIS WEEK INTO NEXT
WEEKEND. UPPER AND SURFACE LOWS MAY APPROACH THE WEST COAST AGAIN
BY NEXT WEEKEND BUT WITH UNCERTAINTY IN THEIR PLACEMENT AND TIMING.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST MODELS AND ENSEMBLES AGREE FAIRLY WELL ON THE LARGE SCALE
PATTERN EVOLUTION THROUGH THE PERIOD, BUT WITH CONTINUED
DIFFERENCES AND/OR TRENDING FOR DETAILS WITHIN THE DEEPENING
EASTERN U.S. UPPER TROUGH AND TIMING SPREAD FOR THE EAST PACIFIC
SYSTEM APPROACHING CALIFORNIA. BY NEXT WEEKEND THERE ARE
LOWER-PREDICTABILITY SHORTWAVE DIFFERENCES IN NORTHERN TIER
U.S./SOUTHERN CANADA FLOW THAT AFFECT THE DETAILS OF SURFACE
WAVES/FRONTS.
GUIDANCE MAINTAINS SOME DEGREE OF SPREAD FOR TIMING OF THE UPPER
TROUGH MOVING INTO THE SOUTHWEST ON THURSDAY, WITH ECMWF RUNS
TENDING TO BE SLOWEST AND GFS FASTEST AND A COMPROMISE LIKELY BEST
FOR A SINGLE DETERMINISTIC FORECAST. THE NEW 12Z ECMWF HAS NUDGED
A LITTLE CLOSER TO THE INTERMEDIATE 12Z UKMET/CMC. AS THIS FEATURE
ACCELERATES EASTWARD AND INTERACTS WITH AMPLIFYING NORTHERN STREAM
FLOW BY THURSDAY-FRIDAY, THERE IS STILL A PERSISTENT THEME OF A
DEFINED SURFACE WAVE TRACKING FROM THE SOUTH-CENTRAL PLAINS
THROUGH MID-ATLANTIC BUT WITH AN EMERGING HINT FROM RECENT GFS
RUNS AND THE 12Z CMC THAT THIS WAVE COULD TRACK FARTHER NORTH.
EVEN WITH THESE DIFFERENCES, THERE IS DECENT CLUSTERING TOWARD THE
SYSTEM TRACKING FAIRLY CLOSE TO THE NEW ENGLAND COAST AND THEN
INTO THE CANADIAN MARITIMES. THE 12Z UKMET/ECMWF HAVE STRAYED A
BIT TO THE SLOW SIDE RELATIVE TO THE MAJORITY MODEL/ENSEMBLE
CLUSTER WHILE SOME ECMWF RUNS (INCLUDING THE NEW 12Z VERSION AND
OTHER BEFORE THE 00Z CYCLE) HAVE BEEN A LITTLE MORE OFFSHORE NEW
ENGLAND FOR THE TRACK. A CONSENSUS APPROACH PROVIDES GOOD
CONTINUITY FOR THIS SYSTEM. HOWEVER THE MODELS/MEANS HAVE MADE A
NOTABLE CHANGE WITH THE CORE OF THE UPPER TROUGH OVER CANADA INTO
THE GREAT LAKES, NOW GRAVITATING TOWARD A DEEPER AND BETTER
DEFINED UPPER LOW TRACKING NEAR JAMES BAY. THIS CHANGES THE
FRONTAL DEPICTIONS BEHIND THE SYSTEM WITH A WELL-DEFINED COLD
FRONT DROPPING INTO THE UPPER MIDWEST/GREAT LAKES BY FRIDAY.
THE 00Z/06Z GUIDANCE MAINTAINED RECENT SPREAD FOR THE SYSTEM
OFFSHORE CALIFORNIA, WITH THE ECMWF/ECENS ON THE EASTERN SIDE OF
THE ENVELOPE AND THE GFS FARTHEST WEST. THE GEFS HAS GENERALLY
BEEN A TAD EAST OF THE OPERATIONAL RUN, WHILE THE CMC/CMCENS IS
CLOSER TO THE MIDDLE. ECMWF-INITIALIZED MACHINE LEARNING MODELS
ALSO ARGUE FOR A COMPROMISE APPROACH, AT TIMES MORE EMPHATICALLY
TRACKING EAST OF THE GFS BUT THEN BY THE END OF THE PERIOD
FAVORING SLOWER TIMING THAN THE ECMWF. THE NEW 12Z ECMWF HAS
ADJUSTED A LITTLE SLOWER TO NARROW THE SPREAD A BIT.
THE UPDATED FORECAST STARTED WITH A 00Z/06Z OPERATIONAL MODEL
COMPOSITE EARLY IN THE PERIOD AND THEN TRENDED TOWARD AN EVEN
BLEND OF THE 06Z GFS/GEFS MEAN AND 00Z ECMWF/ECENS MEAN. THE BLEND
PHASED OUT THE 00Z CMC AFTER FRIDAY AS ITS NORTHERN TIER FEATURES
BECAME OUT OF SYNC WITH MOST OTHER SOLUTIONS.
..WEATHER/HAZARDS HIGHLIGHTS
AN ATMOSPHERIC RIVER EVENT MAINLY IN THE SHORT RANGE PERIOD WILL
BE WINDING DOWN ACROSS CALIFORNIA BY WEDNESDAY. THERE REMAINS
SOMEWHAT LOW CONFIDENCE IN HOW MUCH PRECIPITATION MAY CONTINUE
ACROSS SOUTHERN CALIFORNIA WEDNESDAY BEHIND THE MAIN COLD FRONT.
OVERALL, TOTALS SHOULD BE REDUCED SIGNIFICANTLY FROM EARLIER DAYS,
BUT AS THE UPPER TROUGH COMES THROUGH, THE LOWERING HEIGHTS ALOFT
CAN STEEPEN LAPSE RATES AND ALLOW FOR SOME INSTABILITY TO PRODUCE
LOCALLY HIGHER RAIN RATES. THERE IS A PERSISTENT SIGNAL IN THE
GUIDANCE THAT THE ASSOCIATED AXIS OF DEEP MOISTURE MAY STILL BE
PROGRESSING THROUGH THE REGION VERY EARLY IN THE PERIOD AS WELL.
THUS HAVE MAINTAINED THE MARGINAL RISK IN THE DAY 4 EXCESSIVE
RAINFALL OUTLOOK COVERING SOUTHERN CALIFORNIA FOR EARLY WEDNESDAY
GIVEN THE LIKELY SENSITIVITY TO ADDITIONAL RAIN AT THE TAIL END OF
THE EVENT. SNOW COULD ALSO CONTINUE ACROSS THE SIERRA NEVADA
WEDNESDAY. FARTHER EAST, MODERATE SNOW IS LIKELY IN THE HIGHER
ELEVATIONS OF THE INTERMOUNTAIN WEST AND ROCKIES, PARTICULARLY IN
THE WASATCH TO CENTRAL ROCKIES BEFORE THE WEST DRIES OUT FOR LATE
WEEK. THE NEXT SYSTEM DROPPING INTO THE EAST PACIFIC LATE IN THE
WEEK MAY INCREASE PRECIPITATION CHANCES OVER CALIFORNIA BY NEXT
WEEKEND, BUT DETAILS DEPEND ON HOW CLOSE THE UPPER/SURFACE LOWS
GET TO THE COAST. THE CURRENT ARRAY OF GUIDANCE RANGES FROM
MEANINGFUL PRECIPITATION REACHING THE COAST AS EARLY AS FRIDAY
NIGHT (WITH MOISTURE SPREADING FARTHER INLAND THEREAFTER) TO EVEN
LIGHT AMOUNTS NOT REACHING THE COAST UNTIL SUNDAY.
PRECIPITATION SHOULD INCREASE IN COVERAGE/INTENSITY OVER THE OHIO
VALLEY TO GREAT LAKES WEDNESDAY AND ESPECIALLY THURSDAY UNDER THE
INFLUENCE OF A COUPLE OF LOW PRESSURE/FRONTAL SYSTEMS.
PRECIPITATION IS MOST LIKELY TO BE RAIN EXCEPT IN THE FAR NORTHERN
TIER. RAINFALL AMOUNTS OF AN INCH OR TWO ARE LIKELY IN THE OHIO
VALLEY ON THURSDAY, WITH LOCALLY HIGHER AMOUNTS. THE SURFACE LOW
AND SHORTWAVE HELPING TO FORCE THE PRECIPITATION SHOULD BE MOVING
RATHER QUICKLY, BUT THE WEST TO EAST TRACK MEANS THAT RAIN HAS THE
POTENTIAL TO TRAIN WEST TO EAST. SOME INSTABILITY COMBINED WITH
THE GOOD DYNAMICAL SUPPORT (LEFT EXIT REGION OF THE JET) MAY LEAD
TO HIGH RAINFALL RATES. HOWEVER, STREAMFLOWS AND SOIL MOISTURE ARE
WELL BELOW AVERAGE ALONG/NORTH OF THE OHIO RIVER BUT CLOSER TO
AVERAGE JUST TO THE SOUTH. LATEST GUIDANCE CONTINUES TO SHIFT
AROUND A LITTLE RELATIVE TO THE BEST OVERLAP OF ENSEMBLE
PROBABILITIES FOR MEANINGFUL QPF THRESHOLDS, FAVORING MAINTENANCE
OF THE CORE OF THE EXISTING MARGINAL RISK AREA DEPICTED OVER THE
OHIO VALLEY IN THE DAY 5/THURSDAY ERO. SOME OPERATIONAL
MODEL/ENSEMBLE SOLUTIONS SUPPORTED A SLIGHT EXPANSION ON THE
NORTHEAST AND WEST SIDES OF THE AREA FOR THE DAYTIME UPDATE. THE
PRECIPITATION SHOULD REACH THE EAST THURSDAY-FRIDAY WITH SNOW
POSSIBLE IN PARTS OF THE NORTHEAST. NORTHERN NEW ENGLAND HAS A
RELATIVELY HIGHER PROBABILITY OF SEEING NOTABLE SNOW ALONG WITH
THE POTENTIAL FOR A PERIOD OF BRISK WINDS. THE UNCERTAIN
INTERACTION OF SEPARATE FEATURES ULTIMATELY LEADS TO A WIDE RANGE
OF POSSIBILITIES FOR SENSIBLE WEATHER OVER THE NORTHEAST, BUT MOST
GUIDANCE SUGGESTS THAT THAT THE REGION SHOULD SEE AT LEAST SOME
PRECIPITATION/WIND FROM THIS SYSTEM. HOWEVER CONFIDENCE IN EXACT
MAGNITUDE REMAINS FAIRLY LOW. CONTINUE TO MONITOR FORECASTS OVER
THE COMING DAYS AS IMPORTANT DETAILS BECOME BETTER RESOLVED.
BEHIND THIS SYSTEM, PARTS OF THE GREAT LAKES MAY SEE MOSTLY LIGHT
SNOW FROM A COMBINATION OF LAKE EFFECT ACTIVITY AND ONE OR MORE
WAVES/FRONTAL SYSTEMS.
UPPER RIDGING PUSHING FROM THE CENTRAL U.S. WEDNESDAY TOWARD THE
EASTERN U.S. THURSDAY WILL PROMOTE ABOVE NORMAL TEMPERATURES IN
THOSE AREAS. TEMPERATURES AROUND 15-25F ABOVE NORMAL WILL BE IN
PLACE ACROSS THE PLAINS TO MIDWEST ON WEDNESDAY, AND 10-20F
ANOMALIES ARE LIKELY TO REACH INTO THE EAST BY THURSDAY WITH WILL
ABOVE NORMAL LOWS EXTENDING INTO FRIDAY MORNING ALONG THE EAST
COAST. HIGHS ARE FORECAST TO BE INTO THE 80S FOR MUCH OF TEXAS
WITH 70S STRETCHING INTO THE SOUTHEAST. TEMPERATURES SHOULD
MODERATE CLOSER TO NORMAL AFTER THE COLD FRONT COMES THROUGH AFTER
MIDWEEK (POSSIBLY DECLINING TO BELOW NORMAL FOR HIGHS OVER NEW
ENGLAND DURING THE WEEKEND) BUT REMAIN ABOVE NORMAL IN THE CENTRAL
U.S., ESPECIALLY OVER NORTHERN/CENTRAL PARTS OF THE REGION. THEN
EXPECT RENEWED WESTERN U.S. INTO PLAINS RIDGING DURING THE WEEKEND
TO RAISE TEMPERATURES TO 15-25F ABOVE NORMAL ONCE AGAIN OVER AN
EXPANDING AREA OF THE CENTRAL U.S. MEANWHILE THE WEST COAST SHOULD
BE NEAR AVERAGE FOR HIGHS FROM WEDNESDAY THROUGH NEXT WEEKEND BUT
A FEW DEGREES ABOVE NORMAL FOR LOWS AT TIMES.
RAUSCH/TATE
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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