710
FXUS02 KWBC 140701
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 AM EST SUN JAN 14 2024
VALID 12Z WED JAN 17 2024 - 12Z SUN JAN 21 2024
...RECORD-BREAKING COLD COULD LINGER IN THE SOUTH-CENTRAL U.S.
MIDWEEK, WITH ANOTHER ARCTIC AIRMASS COMING INTO THE CENTRAL U.S.
LATE WEEK...
..OVERVIEW
A DEEP AND BROAD MEAN TROUGH ALOFT WILL STAY ATOP MUCH OF THE
LOWER 48 THROUGH LATE WEEK, AHEAD OF A MEAN RIDGE THAT TRACKS FROM
THE EASTERN PACIFIC EASTWARD INTO THE WESTERN AND CENTRAL U.S.
LATE WEEK INTO THE WEEKEND AND DISPLACES THE TROUGH EAST. THIS
PATTERN WILL ALLOW FOR A COUPLE OF ARCTIC HIGH PRESSURE CENTERS AT
THE SURFACE TO SUPPORT VERY COLD TEMPERATURES FIRST LINGERING IN
THE EASTERN TWO-THIRDS OF THE COUNTRY FOR MIDWEEK, AHEAD OF
ANOTHER SURGE OF COLD AIR THAT PUSHES INTO THE CENTRAL U.S. AND
EVENTUALLY THE EAST LATE WEEK INTO THE WEEKEND. AT MOST LOCATIONS
THIS SECOND ROUND OF COLD TEMPERATURES SHOULD BE LESS EXTREME THAN
THE THE FIRST. SNOW AND SOME LOWER ELEVATION RAIN ARE FORECAST
ACROSS THE NORTHERN HALF OR SO OF THE WEST ESPECIALLY ON WEDNESDAY
AND LINGERING INTO THURSDAY, WITH A PRECIPITATION FOCUS MORE ALONG
THE WEST COAST BY FRIDAY INTO THE WEEKEND FROM MOISTURE ON THE
LEADING SIDE OF AN APPROACHING UPPER TROUGH. IN THE EAST, A
POSSIBLY DEVELOPING LOW PRESSURE/FRONTAL SYSTEM COULD PRODUCE SOME
WINTER WEATHER FOR THURSDAY-SATURDAY, BUT WITH CONSIDERABLE
UNCERTAINTY FOR DETAILS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS/MEANS AGREE WELL ON THE LARGE SCALE EVOLUTION DURING
THE PERIOD, WITH SOME REASONABLE CONSENSUS ON SOME DETAILS EARLY
IN THE PERIOD BUT LESS SO BY LATE WEEK INTO THE WEEKEND. AS THE
PERIOD BEGINS EARLY WEDNESDAY, SHORTWAVE ENERGY ENHANCING THE
BROAD TROUGH WITH ITS FOCUS AROUND THE APPALACHIANS OR SO WILL
SUPPORT A SURFACE LOW OVER ATLANTIC CANADA WITH FINALLY SOME
BETTER AGREEMENT IN PLACEMENT/STRENGTH IN THE INCOMING 00Z SUITE
OF GUIDANCE. THIS SHORTWAVE PIVOTS QUICKLY EAST INTO THE ATLANTIC.
IN THE WEST, MODELS SHOW TWO SHORTWAVES EARLY WEDNESDAY WITH ONE
ATOP THE NORTHWEST AND ONE IN BRITISH COLUMBIA. THESE SUPPORT A
REASONABLY AGREEABLE FAIRLY COMPACT BUT VIGOROUS SURFACE LOW NEAR
VANCOUVER ISLAND/NORTHERN WASHINGTON. THESE SHORTWAVES LOOK TO GET
ABSORBED INTO THE BACKSIDE OF THE BROAD TROUGH INTO THURSDAY.
MODELS CONTINUE TO SHOW THE UPPER RIDGE MARCHING INTO THE WEST
COAST THURSDAY AND AMPLIFYING AS IT TRACKS EAST FRIDAY, PUSHING
FARTHER INTO THE CENTRAL U.S. OVER THE WEEKEND. THIS HAS BEEN VERY
CONSISTENT FOR MULTIPLE MODEL CYCLES. NORTHWEST FLOW BETWEEN THE
RIDGE AND TROUGH BRINGS IN COLD SURFACE HIGH PRESSURE TO THE HIGH
PLAINS WITH JUST SOME TYPICAL DIFFERENCES IN EXACT PLACEMENT AND
STRENGTH. AHEAD OF THIS SURFACE HIGH IS WHERE THE MOST IMPACTFUL
MODEL DIFFERENCES ARE, NAMELY LOW PRESSURE/FRONTAL SYSTEMS IN THE
EAST LATE WEEK INTO THE WEEKEND. MODELS SEEM TO BE HAVING TROUBLE
DEFINING A LOW CENTER WITHIN THIS BROAD AREA OF LOW PRESSURE IN
THE EASTERN THIRD OF THE U.S. INTO THE WESTERN ATLANTIC AROUND
FRIDAY, BUT THERE IS SOME SIGNAL FOR A SURFACE LOW TRACKING
NORTHEAST THROUGH THE ATLANTIC EAST OF THE MID-ATLANTIC AND
NORTHEAST LATE FRIDAY INTO SATURDAY. THE 18Z GFS WAS ON THE FAST
SIDE WITH THE LOW TRACK WHILE THE 12Z GFS WAS SLOW; ENSEMBLE MEANS
AND THE ECMWF AND CMC POSITION SEEMED TO BE THE BEST MIDDLE GROUND
AT THIS TIME, BUT WITH RELATIVELY LOW CONFIDENCE. UPSTREAM OF THE
RIDGE, TROUGHING IN THE EASTERN PACIFIC POSSIBLY AFFECTING THE
WEST COAST BY THE WEEKEND HAS SOME TYPICAL MODEL DIFFERENCES FOR
THE LATE MEDIUM RANGE PERIOD.
THE WPC FORECAST WAS BASED ON A BLEND OF THE DETERMINISTIC
GUIDANCE FAVORING THE 18Z GFS AND 12Z ECMWF EARLY IN THE MEDIUM
RANGE PERIOD. GIVEN THE INCREASING MODEL DIFFERENCES PARTICULARLY
WITH THE EASTERN SYSTEM, BLENDED IN SOME GEFS AND EC ENSEMBLE
MEANS BY DAY 5 AND INCREASED THE ENSEMBLE PROPORTION TO 40 PERCENT
BY THE LATE PERIOD, WHICH MAINTAINED SOME STRENGTH OF SYSTEMS BUT
MINIMIZED TOO MANY INDIVIDUAL MODEL DETAILS.
..WEATHER/HAZARDS HIGHLIGHTS
THOUGH THE COLDEST AIR NOW PHASES INTO THE SHORT RANGE PERIOD
EARLY THIS WEEK, CHILLY TEMPERATURES REMAIN ACROSS THE PLAINS TO
EAST COAST WEDNESDAY, AROUND 10-25F BELOW AVERAGE. LOW
TEMPERATURES WEDNESDAY MORNING COULD SET RECORDS IN THE SOUTHERN
PLAINS/LOWER MISSISSIPPI VALLEY. THESE AREAS WILL WARM CLOSER TO
NORMAL THURSDAY, BUT ANOTHER REINFORCING SURGE OF COLD AIR IS
FORECAST TO PUSH INTO THE NORTH-CENTRAL U.S. THURSDAY, WELL INTO
THE PLAINS/MISSISSIPPI VALLEY FRIDAY, AND INTO THE EAST-CENTRAL
U.S. SATURDAY. BELOW NORMAL TEMPERATURES BY 15-30 DEGREES SHOULD
BE WIDESPREAD, SO STILL NOTABLE EVEN THOUGH NOT QUITE AS COLD AS
THE CURRENT/SHORT RANGE COLD EVENT. MEANWHILE WEST OF THE ROCKIES,
RIDGING ALOFT WILL PROMOTE ABOVE NORMAL TEMPERATURES INCREASING IN
MAGNITUDE AND COVERAGE LATE WEEK INTO THE WEEKEND.
A SURFACE LOW PRESSURE SYSTEM AND A SHORTWAVE ALOFT COMING INTO
THE NORTHWEST BY WEDNESDAY WILL HELP CAUSE WIDESPREAD
PRECIPITATION ACROSS THE NORTHERN HALF OF CALIFORNIA INTO THE
PACIFIC NORTHWEST AND EAST TO THE ROCKIES. THIS EVENT WILL LIKELY
SEE SNOW CONFINED TO HIGHER ELEVATIONS THAN IN THE SHORTER TERM,
BUT INLAND AREAS WHERE COLD AIR PERSISTS LONGER COULD STILL SEE
SOME LOWER ELEVATION WINTER WEATHER ISSUES, INCLUDING POTENTIAL
FOR FREEZING RAIN IN THE NORTHERN GREAT BASIN. SNOW AMOUNTS COULD
BE HEAVY IN HIGHER ELEVATION AREAS INCLUDING THE CASCADES TO
NORTHERN/CENTRAL ROCKIES. MEANWHILE COASTAL AREAS OF THE PACIFIC
MAY SEE OCCASIONAL ENHANCED RAINFALL AMOUNTS FOR PERHAPS A NONZERO
POTENTIAL FOR FLOODING CONCERNS. ON WEDNESDAY COASTAL OREGON COULD
BE A FOCUS FOR HEAVY RAIN WHILE ON THURSDAY COASTAL WASHINGTON
SEEMS MORE LIKELY. HOWEVER, A LACK OF INSTABILITY, GUIDANCE NOT
SHOWING ANY FOCUSED ATMOSPHERIC RIVER TAKING AIM AT THE REGION,
AND CONTINUED MODEL DIFFERENCES FOR AMOUNTS/PLACEMENT OF HEAVIEST
RAIN PRECLUDE US FROM INTRODUCING ANY MARGINAL RISKS (WHICH ARE
FOR A 5 PERCENT OR GREATER CHANCE OF FLOODING) IN THE EXCESSIVE
RAINFALL OUTLOOKS AT THIS TIME. ADDITIONAL ROUNDS OF PRECIPITATION
FOR THE WEST COAST STATES ARE POSSIBLE LATE WEEK.
FARTHER EAST, EXPECT CONTINUED PERIODS OF LAKE EFFECT SNOW WITH
PERSISTENCE OF COLD AIR AND BREEZY CONDITIONS. THEN A FRONT AND
POSSIBLE LOW PRESSURE SYSTEM REACHING THE EAST DURING THE LATTER
PART OF THE WEEK MAY PRODUCE SOME PRECIPITATION. THIS SYSTEM COULD
INITIALLY SPREAD SOME LIGHT SNOW ACROSS THE NORTHERN-CENTRAL
PLAINS BY THURSDAY WHILE SOME LIMITED GULF MOISTURE COMES INTO THE
EAST-CENTRAL U.S., SHIFTING INTO THE EAST COAST FRIDAY. THE
PRECIPITATION TYPE IN THE SOUTHEAST SHOULD STAY RAIN WHILE
GENERALLY FROM THE OHIO VALLEY INTO THE APPALACHIANS AND THE
NORTHERN MID-ATLANTIC TO NORTHEAST SHOULD HAVE SNOW. AREAS IN
BETWEEN ARE MORE UNCERTAIN WITH PRECIPITATION TYPE WHILE
UNCERTAINTY ALSO REMAINS WITH THE COVERAGE AND AMOUNTS OF
PRECIPITATION, WHICH WILL CONTINUE TO BE REFINED IN FUTURE
FORECASTS.
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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