543
FXUS02 KWBC 210645
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
145 AM EST TUE JAN 21 2025
VALID 12Z FRI JAN 24 2025 - 12Z TUE JAN 28 2025
..OVERVIEW
MEAN TROUGHING OVER THE EAST-CENTRAL U.S. ON FRIDAY WILL PROGRESS
EASTWARD AND CROSS THE EAST COAST BY THE WEEKEND. BEHIND THIS, SOME
WEAK UPPER RIDGING OR AT LEAST FLATTER FLOW SHOULD MOVE IN,
FINALLY HELPING TO MODERATE THE BITTERLY COLD MID- WEEK
TEMPERATURES ACROSS THE EAST AND SOUTH. A SHORTWAVE INTO THE
NORTHERN ROCKIES WILL SPLIT, SENDING NORTHERN STREAM ENERGY THROUGH
THE NORTHERN U.S. TIER/GREAT LAKES/NORTHEAST AS TRAILING ENERGY
DIVES SOUTH AND LIKELY FORMS A CLOSED LOW OVER OR NEAR CALIFORNIA
INTO THE SOUTHWEST THIS WEEKEND. THE UPPER LOW SHOULD PERSIST INTO
NEXT WEEK, LIKELY BRINGING SOME MUCH NEEDED PRECIPITATION TO PARTS
OF SOUTHERN CALIFORNIA WHICH HAS BEEN STRICKEN WITH DEVASTATING
WILDFIRES LATELY. MEANWHILE A FRONT REACHING THE
MISSISSIPPI/TENNESSEE VALLEY REGION MAY SERVE TO ENHANCE RAINFALL
OVER PARTS OF THE SOUTHERN TIER BY SUNDAY.
..GUIDANCE/PREDICTABILITY ASSESSMENT
WITH GUIDANCE CLUSTERING BETTER FOR THE SHORTWAVE CROSSING THE
EASTERN PORTION OF THE COUNTRY FROM FRIDAY INTO EARLY SATURDAY, THE
PRIMARY FORECAST DISCREPANCIES INVOLVE THE POTENTIAL UPPER LOW
CLOSING OFF ALONG OR INLAND FROM THE WEST COAST DURING THE WEEKEND.
MODELS CONTINUE TO SHOW GOOD AGREEMENT ON THE PRESENCE OF AN UPPER
LOW, BUT UNCERTAINTY ON HOW LONG IT LINGERS OVER CALIFORNIA OR
SHIFTS GRADUALLY EASTWARD. THE 12Z/JAN 20 CMC WAS SLOWEST WITH THIS
FEATURE, BUT THE 00Z CMC CAME IN WEAKER AND MORE PROGRESSIVE. 00Z
GFS TRENDED A BIT FASTER TOO. SO STILL A LOT OF UNCERTAINTY LATE
PERIOD FOR THIS. TO THE NORTH, A SHORTWAVE SHOULD DROP INTO THE
NORTHERN PLAINS LATE WEEK AND PROGRESS EASTWARD WITH TIME. BUT BY
MONDAY, THERE IS A LOT OF DISCREPANCY IN THE TIMING AND AMPLITUDE
OF THE SHORTWAVE OVER THE EAST/MID-ATLANTIC AND ALSO IF/HOW
ADDITIONAL ENERGY DROPPING INTO THE MEAN TROUGH WILL AFFECT ITS
EVOLUTION/CHARACTERISTIC.
THE WPC PROGS FOR TONIGHT FEATURED A GENERAL MODEL BLEND THROUGH
DAY 5, INCREASING TO 60 PERCENT OF THE ENSEMBLE MEANS WITH 40
PERCENT OF THE GFS/ECMWF. THIS WORKED WELL AS A GOOD MIDDLE
GROUND/STARTING POINT FOR THE FORECAST AND MAINTAINED GOOD
CONTINUITY WITH THE PREVIOUS WPC FORECAST AS WELL.
..WEATHER/HAZARDS HIGHLIGHTS
COLDER THAN NORMAL TEMPERATURES WILL LINGER INTO FRIDAY OVER PARTS
OF THE EAST AND SOUTH, ESPECIALLY NEAR THE GULF COAST. READINGS OF
5-15 DEGREES BELOW NORMAL SHOULD NOT BE AS EXTREME AS EARLIER IN
THE WEEK AND TEMPERATURES SHOULD MODERATE, REACHING NEAR NORMAL
THIS WEEKEND. MEANWHILE, CALIFORNIA TO THE GREAT BASIN CAN EXPECT
WARMER THAN NORMAL TEMPERATURES THROUGH THE REST OF THE WORKWEEK
BEFORE THE WEST COOLS UNDERNEATH THE UPPER TROUGH NEXT WEEKEND. THE
EASTERN ROCKIES/HIGH PLAINS WILL ALSO SEE TEMPERATURES DROP BELOW
NORMAL (BY UP TO 15-20 DEGREES) THIS WEEKEND.
PRECIPITATION WISE, A COUPLE COLD FRONTS/CLIPPER SYSTEMS MAY
PRODUCE SOME LIGHT/SCATTERED PRECIPITATION FROM THE NORTHERN PLAINS
TO MIDWEST/GREAT LAKES AND OHIO VALLEY, BUT SPECIFICS FOR
LOCATIONS SEEING MEASURABLE TOTALS WILL LIKELY WAIT UNTIL THE SHORT
RANGE TO BE RESOLVED. MORE WIDESPREAD RAIN AND MOUNTAIN SNOWS WILL
MOVE INTO THE WEST BY THE END OF THE WEEK AND SHIFT SOUTH WITH
TIME, LIKELY PROVIDING SOME MUCH NEEDED RAIN TO SOUTHERN CALIFORNIA
NEXT WEEKEND. THE TIGHT GRADIENT BEHIND A COLD FRONT DROPPING
SOUTH THROUGH THE WEST AND PLAINS MAY PRODUCE AN EPISODE OF STRONG
WINDS ALONG PARTS OF THE ROCKIES LATE THIS WEEK AND OVER CALIFORNIA
AND VICINITY BY SATURDAY. FARTHER EAST, SOME GULF MOISTURE WILL
LIKELY INTERACT WITH A FRONT APPROACHING/REACHING THE LOWER
MISSISSIPPI VALLEY TO TENNESSEE AND OHIO VALLEYS BY THIS COMING
WEEKEND/EARLY NEXT WEEK. LATEST GUIDANCE CONTINUES TO TREND HEAVIER
WITH ENHANCED RAINFALL OVER PARTS OF THE SOUTHERN TIER. SNOW WILL
BE POSSIBLE FARTHER NORTH ACROSS THE GREAT LAKES, WITH A WINTRY MIX
POSSIBLE IN-BETWEEN DEPENDING ON CURRENTLY UNCERTAIN UPPER LEVEL
AND SURFACE DETAILS AT THAT TIME. SOME MOISTURE SPREADS BACK INTO
THE EASTERN U.S. NEXT WEEK.
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 (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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