243
FXUS02 KWBC 030704
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
204 AM EST MON FEB 3 2025
VALID 12Z THU FEB 06 2025 - 12Z MON FEB 10 2025
...ANOTHER ROUND OF POTENTIALLY HEAVY PRECIPITATION FOR CALIFORNIA THURSDAY...
...WINTRY WEATHER FORECAST FOR THE NORTHEAST THURSDAY AND AGAIN
OVER THE WEEKEND...
..OVERVIEW
LATEST MODELS AND ENSEMBLES CONTINUE TO SHOW NEARLY ZONAL FLOW
ACROSS MOST OF THE LOWER 48 INTO LATE WEEK, FOLLOWED BY A TREND
TOWARD BROAD MEAN TROUGHING FROM NORTHEASTERN CANADA INTO THE
WESTERN U.S. OVER THE WEEKEND AS ALASKA UPPER RIDGING REGAINS
AMPLITUDE. THIS TREND SHOULD FINALLY LEAD TO A DRIER PATTERN FOR
CALIFORNIA AFTER A SYSTEM BRINGS ANOTHER EPISODE OF SIGNIFICANT
RAIN AND SNOW AROUND THURSDAY. MOISTURE FARTHER INLAND WILL SUPPORT
PRECIPITATION ACROSS THE GREAT BASIN AND ROCKIES, WITH SIGNIFICANT
SNOW POSSIBLE FOR HIGHER ELEVATIONS. THE EASTERN HALF OF THE
COUNTRY WILL LIKELY SEE TWO EVENTS WITH THE FULL RANGE OF
PRECIPITATION TYPES, ONE LASTING INTO THURSDAY AND THEN ANOTHER
OVER THE WEEKEND. EACH SYSTEM MAY PRODUCE SOME AREAS OF MODERATE TO
HEAVY RAIN AND/OR SNOW (POSSIBLY SEPARATED BY A WINTRY MIX)
DEPENDING ON LATITUDE AND SYSTEM DETAILS. THE SOUTHERN TIER WILL
SEE THE MOST PERSISTENT WARMTH DURING THE PERIOD, THOUGH INDIVIDUAL
SURFACE LOW/FRONTAL SYSTEMS WILL BRIEFLY PULL WELL ABOVE NORMAL
TEMPERATURES SOMEWHAT FARTHER NORTHWARD, ESPECIALLY ON THURSDAY.
THE EVOLVING UPPER PATTERN AND CANADIAN SURFACE HIGH PRESSURE
SHOULD PROMOTE BELOW NORMAL TEMPERATURES FROM THE NORTHWEST INTO
THE NORTHERN PLAINS WITH THE COLDEST ANOMALIES CENTERED OVER
MONTANA THURSDAY AND PERHAPS AGAIN EARLY NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MOST GUIDANCE CONTINUES TO SHOW GOOD AGREEMENT FOR THE LARGE SCALE
PATTERN EVOLUTION THROUGH MUCH OF THE PERIOD, WHILE MODELS SLOWLY
COME INTO BETTER AGREEMENT ON SOME SMALLER SCALE FEATURES AS THE
PERIOD BEGINS THURSDAY. THE CALIFORNIA AR ON THURSDAY IS SUPPORTED
BY A SURFACE LOW TRACKING FROM THE EASTERN PACIFIC TOWARD THE
STATE. THE 12Z ECMWF WAS SLOWER THAN CONSENSUS WITH THIS SURFACE
LOW, WHICH LED TO LESS PRECIPITATION ON THURSDAY COMPARED TO OTHER
GUIDANCE, BUT THE NEWER 00Z RUN HAS TRENDED FASTER. MEANWHILE THE
OTHER FEATURE OF NOTE THURSDAY IS A SHORTWAVE SUPPORTING A GREAT
LAKES SURFACE LOW OR TWO THAT HAVE SHOWN SPREAD AND PLACEMENT AND
DEPTH. GFS RUNS HAVE BEEN FAVORING A SURFACE LOW DEVELOPING OVER
THE EASTERN SEABOARD THAT BECOMES THE DOMINANT FEATURE, BUT THE 00Z
GFS FINALLY BECAME BETTER ALIGNED WITH OTHER GUIDANCE FAVORING THE
GREAT LAKES LOWS AS THEY TRACK NORTHEASTWARD THURSDAY-FRIDAY.
BY LATE WEEK, MOST MODELS SHOW REASONABLE AGREEMENT FOR THE
PACIFIC UPPER TROUGH TO PIVOT EASTWARD INTO THE WEST AND QUICKLY
INTO THE CENTRAL U.S. OVER THE WEEKEND. THE EXCEPTION WAS THE 12Z
CMC, WHICH HAD ITS TROUGH AXIS SLOWER/FARTHER OUT INTO THE EASTERN
PACIFIC, BUT THE 00Z CMC HAS TRENDED FAVORABLY TOWARD OTHER
GUIDANCE. SURFACE LOW PRESSURE IS FORECAST TO DEVELOP IN THE SOUTH-
CENTRAL U.S. BY SATURDAY AND MOVE QUICKLY NORTHEASTWARD. THERE IS
ONCE AGAIN SPREAD FOR THE LOW TRACK AND GFS RUNS ARE FARTHER
EAST/FASTER THAN THE 12Z EC, CMC, AND MANY OF THE AI/ML MODELS. THE
00Z EC AND CMC ARE STILL FARTHER WEST THAN THE GFS BUT HAVE JUMPED
FARTHER NORTH, AROUND THE LOWER GREAT LAKES RATHER THAN THE
CENTRAL APPALACHIANS. SO THESE DETAILS WILL TAKE ADDITIONAL TIME TO
RESOLVE.
UPSTREAM, PACIFIC AND NORTHWESTERN CANADIAN ENERGIES COMPLICATE
THE GENERAL PATTERN ACROSS THE WEST INTO EARLY NEXT WEEK AS MODELS
HAVE VARYING IDEAS ON HOW TO COMBINE AND ABSORB THE VORT MAXES INTO
THE MEAN FLOW. IT IS DIFFICULT TO DETERMINE CLEAR OUTLIERS IN THIS
PATTERN, BUT THE NEW 00Z GFS DID SEEM DEEPER THAN OTHER GUIDANCE
WITH ITS WEST TROUGH AND ALSO WITH A CLOSED LOW WEST OF HAIDA GWAII
EARLY MONDAY. GENERALLY PREFERRED TO USE THE ENSEMBLE MEANS FOR AN
INTERMEDIATE SOLUTION.
THE WPC FORECAST USED A MULTI-MODEL DETERMINISTIC BLEND EARLY IN
THE FORECAST, WITHOUT TOO MUCH EMPHASIS ON ANY PARTICULAR MODEL
GIVEN THE VARIOUS ISSUES OF EACH. AS THE PERIOD PROGRESSED,
INCREASED THE PROPORTION OF ENSEMBLE MEANS TO NEAR/OVER HALF BY
DAYS 6-7 AS MODEL SPREAD CONTINUED TO INCREASE.
..WEATHER/HAZARDS HIGHLIGHTS
ANOTHER ATMOSPHERIC RIVER IS FORECAST TO TAKE AIM AT CALIFORNIA ON
THURSDAY, SUPPORTED BY TROUGHING ALOFT AND SURFACE LOW PRESSURE
MOVING INLAND. THIS AR EVENT SHOULD BE SHORTER-LIVED THAN THE
CURRENT AR, BUT SOME LOCALLY HEAVY RAIN AMOUNTS ARE POSSIBLE OVER
AREAS THAT WILL HAVE QUITE WET ANTECEDENT CONDITIONS BY THAT TIME.
A MARGINAL RISK STILL LOOKS GOOD FOR THE DAY 4/THURSDAY ERO, AS
FASTER MOVEMENT OF THIS AR SHOULD TEMPER RAIN AMOUNTS SOME AND
PRECLUDE AN EMBEDDED SLIGHT RISK AREA FOR NOW. RISK UPGRADES MAY
STILL BE POSSIBLE AS GUIDANCE BETTER REFINES SYSTEM DETAILS IN THE
SHORTER RANGE. LIGHTER PRECIPITATION SHOULD PERSIST INTO FRIDAY
OVER CALIFORNIA BUT THEN THE PATTERN EVOLUTION WILL LIKELY SHIFT
THE BEST POTENTIAL FOR ORGANIZED (BUT FAIRLY LIGHT) ACTIVITY INTO
THE PACIFIC NORTHWEST DURING THE WEEKEND, WHILE CALIFORNIA FINALLY
DRIES OUT.
SNOW WILL ALSO BE LIKELY FROM HIGHER ELEVATIONS OF THE CASCADES
AND SIERRA NEVADA ACROSS MUCH OF THE INTERMOUNTAIN WEST INTO THE
NORTHERN/CENTRAL ROCKIES THURSDAY INTO FRIDAY. THE HEAVIEST SNOW
AMOUNTS ARE LIKELY IN HIGHER ELEVATIONS, BUT THE NORTHERN GREAT
BASIN MAY SEE SNOW AS WELL. THE PATTERN WILL ALSO PROMOTE STRONG
WINDS ESPECIALLY ON MOUNTAIN RIDGES LIKE THE SIERRA AND CENTRAL
ROCKIES, BUT SOME GUSTY CONDITIONS MAY REACH LOWER ELEVATIONS OF
THE GREAT BASIN AND FOUR CORNERS TOO.
MEANWHILE FARTHER EAST, PRECIPITATION IS LIKELY IN ASSOCIATION
WITH A LOW PRESSURE SYSTEM LOCATED OVER THE GREAT LAKES BY EARLY
THURSDAY. RAIN IS FORECAST ACROSS THE TENNESSEE VALLEY TO
SOUTHERN/CENTRAL APPALACHIANS, BUT RAIN TOTALS ARE FORECAST TO
DECREASE BY THURSDAY (COMPARED TO WEDNESDAY) AND LIKELY STAY BELOW
THRESHOLDS FOR ANY EXCESSIVE RAINFALL AREA ON DAY 4. WILL CONTINUE
TO MONITOR THOUGH AS INSTABILITY MAY STILL BE IN PLACE FOR SOME
LOCALLY HEAVY RAIN RATES. FARTHER NORTH, COLD AIR IN PLACE WILL
BRING THE POTENTIAL FOR WINTRY WEATHER TO THE NORTHEAST.
PROBABILITIES FOR PLOWABLE SNOW/SLEET ARE INCREASING ACROSS THE
ADIRONDACKS INTO NORTHERN NEW ENGLAND, WHILE SOUTH OF THE GREATEST
SNOW AMOUNTS, A TRANSITION ZONE OF SLEET AND/OR FREEZING RAIN IS
LIKELY PERHAPS AROUND THE NORTHERN MID-ATLANTIC TO SOUTHERN NEW
YORK/NEW ENGLAND. BY FRIDAY-SATURDAY SOME LIGHT TO MODERATE SNOW IS
FORECAST FOR THE NORTHERN TIER, BUT AS A LOW PRESSURE SYSTEM
ORGANIZES OVER THE WEEKEND, INCREASING PRECIPITATION WILL SPREAD TO
THE EAST-CENTRAL AND EASTERN U.S. AGAIN. THE CURRENT FORECAST HAS
THE GREATEST PROBABILITIES FOR IMPACTFUL SNOW ACROSS MUCH OF
PENNSYLVANIA AND NEW YORK INTO NEW ENGLAND DURING THE WEEKEND. ONCE
AGAIN RAIN IS LIKELY FARTHER SOUTH ACROSS THE OHIO AND TENNESSEE
VALLEYS INTO THE CENTRAL APPALACHIANS, AND A BAND OF WINTRY MIX MAY
SEPARATE THE TWO PRIMARY PRECIPITATION TYPES.
COLDER THAN AVERAGE TEMPERATURES ARE FORECAST FOR NORTHWESTERN AND
NORTH-CENTRAL PARTS OF THE LOWER 48 THROUGH THE PERIOD. THE COLD
WILL BE ESPECIALLY PRONOUNCED ACROSS MONTANA AND NORTH DAKOTA, WITH
SINGLE DIGIT HIGHS INTO THURSDAY. THESE AREAS WILL LIKELY REMAIN
BELOW AVERAGE BUT WITH SOME MODERATION FRIDAY INTO THE WEEKEND, BUT
ANOTHER SURGE OF COLD AIR IS LIKELY BY NEXT MONDAY. MEANWHILE,
AREAS FROM THE FOUR CORNERS STATES THROUGH THE EAST SHOULD SEE
ABOVE TO WELL ABOVE NORMAL TEMPERATURES FOR MOST OF THE PERIOD.
SOME AREAS WILL LIKELY SEE ONE OR MORE DAYS OF MIN/MAX TEMPERATURES
REACHING 20 OR MORE DEGREES ABOVE NORMAL (PERHAPS EVEN A NARROW
BAND OF PLUS 30F OR GREATER ANOMALIES FOR MORNING LOWS AROUND THE
MID-SOUTH). THESE ANOMALIES COULD SET DAILY RECORDS ESPECIALLY ON
THURSDAY. EXACT TEMPERATURES/ANOMALIES VARY SOMEWHAT AT ANY
PARTICULAR PLACE FRIDAY-SATURDAY, BUT BY SUNDAY-MONDAY THERE SHOULD
BE A MORE PRONOUNCED COOLING TREND ACROSS THE FOUR CORNERS AND
SOUTH-CENTRAL U.S. TO THE MID-ATLANTIC BEHIND A STRONG COLD FRONT.
TATE/RAUSCH
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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