838
FXUS02 KWBC 171859
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST MON FEB 17 2025
VALID 12Z THU FEB 20 2025 - 12Z MON FEB 24 2025
..INTENSE CENTRAL TO EASTERN U.S. ARCTIC BLAST THIS WEEK
..OVERVIEW AND GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE AGREES UPON MODERATE PROGRESSION OF INDIVIDUAL
SHORTWAVES ALOFT WITHIN AN EVOLUTION TOWARD A LARGER SCALE MEAN
PATTERN CONSISTING OF A WESTERN RIDGE AND EASTERN TROUGH BY THE
START OF NEXT WEEK. THIS TRANSITION WILL BRING THE BEST POTENTIAL
FOR MEANINGFUL PRECIPITATION TO THE PACIFIC NORTHWEST FROM THE
WEEKEND INTO EARLY NEXT WEEK, ALONG WITH A PRONOUNCED WARMING
TREND OVER THE WESTERN-CENTRAL U.S. AFTER THE VERY COLD
TEMPERATURES FORECAST EAST OF THE ROCKIES INTO LATE THIS WEEK. THE
SOUTHERN TIER MAY SEE SOME PRECIPITATION BUT WITH MUCH LOWER
CONFIDENCE FOR SPECIFICS, DUE TO THE LOWER PREDICTABILITY OF
MEDIUM TO SMALLER SCALE LEADING SHORTWAVES AND ASSOCIATED SURFACE
FEATURES.
THE UPDATED FORECAST STARTED WITH AN OPERATIONAL MODEL EARLY IN
THE PERIOD (MORE 06Z GFS/00Z ECMWF WEIGHT RELATIVE TO THE
CMC/UKMET) AND THEN TRENDED TOWARD A MODEL/ENSEMBLE MEAN MIX (06Z
GEFS/00Z ECENS FOR THE MEANS) WITH THE INCREASE OF DETAIL
UNCERTAINTY LATER IN THE PERIOD. GULF INTO WESTERN ATLANTIC
DETAILS WILL DEPEND ON SPECIFICS OF SHORTWAVE ENERGY EMERGING FROM
THE WEST AND A SEPARATE NORTHERN SHORTWAVE DROPPING INTO THE GREAT
LAKES BY SATURDAY, WITH SOME POSSIBLE INDIRECT INFLUENCE OF AN
UPSTREAM SHORTWAVE REACHING WESTERN NORTH AMERICA AT THAT TIME.
MACHINE LEARNING (ML) MODELS GENERALLY REFLECT THE DYNAMICAL MODEL
SPREAD AT THE SURFACE DURING THE WEEKEND, WITH THE SHARPER SUBSET
FOR THE WESTERN ENERGY YIELDING A BETTER DEFINED GULF COAST SURFACE
WAVE (COMPARABLE TO THE 00Z CMC AND LATEST ICON RUNS) VERSUS A
MORE DIFFUSE/SUPPRESSED WAVE. BY NEXT MONDAY THERE IS A DIFFUSE
SIGNAL FOR WAVINESS OVER THE WESTERN ATLANTIC BUT POOR AGREEMENT
FOR THE DETAILS, WITH A RANGE OF POSSIBILITIES INCLUDING
SUPPRESSION OF THE GULF WAVE WHILE THERE IS A MERE FRONT OFF THE
SOUTHEAST COAST OR INSTEAD PROGRESSION OF THE GULF WAVE INTO THE
ATLANTIC. GFS RUNS HAVE BEEN LEANING ON THE WESTERN SIDE OF THE
ENVELOPE FOR THEIR DEFINED SURFACE SYSTEM. THERE IS DECENT
AGREEMENT ON THE SERIES OF FRONTS EXPECTED TO AFFECT THE PACIFIC
NORTHWEST, THOUGH THE FAST FLOW PUSHING THE FRONTS ALONG WILL LEAD
TO SOME DECREASE IN PREDICTABILITY.
..WEATHER/HAZARDS HIGHLIGHTS
AN EXITING COASTAL STORM WITH LIFT ROBUSTLY OFFSHORE THE EAST
COAST THURSDAY AS MAINLY A MARITIME THREAT. HIGH WINDS AND SURF
WILL IMPACT EASTERN NEW ENGLAND, WHILE RECENT TRENDS ARE DECREASING
THE POTENTIAL FOR MEANINGFUL SNOW. IN THE WAKE OF THIS STORM,
QUITE AN IMPRESSIVE ARCTIC AIRMASS IS TAKING HOLD OVER THE CENTRAL
AND EASTERN U.S. THIS WEEK WITH STRONG CANADIAN HIGH PRESSURE
COVERING PLAINS AS OF THURSDAY. ENTRENCHED COLD AIR WILL MAINTAIN
SOME LAKE EFFECT SNOWS AND OFFER A WIDESPREAD EXTREME COLD THREAT.
DURING THURSDAY INTO FRIDAY, WIDESPREAD RECORD TEMPERATURES FOR
MORNING LOWS/COLD DAYTIME HIGHS ARE LIKELY FROM THE SOUTHERN TWO-
THIRDS OF THE PLAINS THROUGH THE MID-LOWER MISSISSIPPI VALLEY AND
THE SOUTH. THE MOST EXTREME TEMPERATURE ANOMALIES WILL BE ON
THURSDAY, RANGING FROM 30 TO 40 DEGREES BELOW NORMAL OVER THE
CENTRAL PLAINS/MID-MISSISSIPPI VALLEY AND 10-30 DEGREES BELOW
NORMAL OVER MUCH OF THE EASTERN U.S. THE AIRMASS WILL SLOWLY
MODERATE LATE WEEK THROUGH THE WEEKEND WHILE ABOVE NORMAL
TEMPERATURES SPREAD INTO THE WESTERN AND EVENTUALLY CENTRAL U.S. BY
NEXT MONDAY, EXPECT MOST LOCATIONS WEST OF THE MISSISSIPPI RIVER TO
BE ABOVE NORMAL WITH DECENT COVERAGE OF PLUS 10-25 DEGREE
ANOMALIES. BEST POTENTIAL FOR HIGHEST ANOMALIES WILL BE OVER AND
NEAR THE NORTHERN PLAINS. TEMPERATURES OVER THE EAST SHOULD FINALLY
REACH NEAR NORMAL BY NEXT MONDAY.
THE WEST WILL SEE A LEADING THURSDAY SYSTEM BRING A SWATH OF
TERRAIN/MOUNTAIN ENHANCED SNOW OVER THE NORTH-CENTRAL
INTERMOUNTAIN WEST/ROCKIES. ACCUMULATIONS SHOULD NOT BE ESPECIALLY
HEAVY THOUGH, WITH PROBABILITIES FOR 0.25 INCH LIQUID IN THE FORM
OF SNOW IN THE 10-50 PERCENT RANGE. FROM SATURDAY ONWARD THE
PATTERN BECOMES INCREASINGLY FAVORABLE FOR LONGER FETCH MOISTURE
FEED TO FUEL ROUNDS OF MODERATE TO HEAVY LOW ELEVATION RAIN AND
MOUNTAIN SNOW PRIMARILY INTO THE PACIFIC NORTHWEST, BUT ALSO INLAND
TO THE NORTHERN ROCKIES. THERE IS SOME UNCERTAINTY OVER THE EXACT
SOUTHWARD EXTENT OF THIS PRECIPITATION BUT THE BEST POTENTIAL FOR
HIGHEST TOTALS CURRENTLY EXISTS OVER THE FAVORED TERRAIN AND
COASTAL AREAS OF WESTERN WASHINGTON AND NORTHWESTERN OREGON.
FARTHER EAST, NO CONSENSUS EXISTS FOR ANY STRONGLY ORGANIZED STORM
SYSTEM DURING THURSDAY-MONDAY BUT MULTIPLE UNCERTAIN IMPULSES
FEEDING INTO AN EVENTUAL LARGER SCALE EASTERN U.S. MEAN TROUGH
ALOFT MAY PRODUCE SOME LIGHT AND UNHERALDED BUT LOCALLY DISRUPTIVE
WINTRY WEATHER IN THE ARCTIC AIRMASS. ONE SUCH FEATURE IS EMERGING
WESTERN U.S. ENERGY THAT MAY SUPPORT PERIODIC MODERATE RAINFALL
OVER THE GULF AND POSSIBLY EXTENDING INTO THE GULF COAST STATES IN
ASSOCIATION WITH A PERSISTENT AND SLOW MOVING WAVY FRONTAL ZONE.
MOST PRECIPITATION SHOULD BE RAIN, BUT THOUGH A LITTLE WINTRY
WEATHER COULD BE POSSIBLE IN THE NORTHERN FRINGE OF THE MOISTURE
SHIELD IF IT EXTENDS FAR ENOUGH NORTH. CONFIDENCE IS LOW REGARDING
HOW THE WAVINESS MAY EVOLVE OVER THE GULF DURING THE WEEKEND, AND
WHAT THE SURFACE PATTERN MAY LOOK LIKE OFF THE EAST COAST BY NEXT
MONDAY. AT THAT LATTER TIME THE MAJORITY (THOUGH NOT ALL) OF
GUIDANCE SUGGESTS THAT MOST PRECIPITATION SHOULD STAY OFFSHORE THE
MID-ATLANTIC/NEW ENGLAND COAST. MEANWHILE A SERIES OF WAVES MAY
SPREAD LIGHT PRECIPITATION (MOSTLY SNOW) ACROSS PARTS OF THE GREAT
LAKES INTO WESTERN NEW ENGLAND FROM THE WEEKEND INTO EARLY NEXT
WEEK.
RAUSCH/SCHICHTEL
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 (QPF), EXCESSIVE RAINFALL
OUTLOOK (ERO), WINTER WEATHER OUTLOOK (WWO) PROBABILITIES, HEAT
INDICES, AND KEY MESSAGES CAN BE ACCESSED FROM:
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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