677
FXUS02 KWBC 170614
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
114 AM EST FRI JAN 17 2025
VALID 12Z MON JAN 20 2025 - 12Z FRI JAN 24 2025
...STRONG ARCTIC SURGE WILL MOVE FROM THE CENTRAL U.S. INTO THE
SOUTH/EAST NEXT WEEK...
..OVERVIEW
MODELS AND ENSEMBLES CONTINUE TO SHOW A VERY AMPLIFIED MEAN
PATTERN THROUGH NEXT WEEK CONSISTING OF A DEEP TROUGH OVER MUCH OF
THE LOWER 48 WITH AN EASTERN PACIFIC RIDGE WHICH MAY EVENTUALLY
EDGE INTO THE WESTERN U.S. LATE NEXT WEEK. CONFIDENCE REMAINS HIGH
IN A SURGE OF ARCTIC AIR PROGRESSING FROM THE CENTRAL U.S. TO THE
EAST EARLY NEXT WEEK. BY MIDWEEK MOST OF THE PLAINS SHOULD SEE
MODERATING TEMPERATURES WHILE THE COLD WILL LIKELY LINGER OVER THE
SOUTH AND EAST. EMBEDDED SHORTWAVES WITHIN THE OVERALL MEAN TROUGH
HAVE LOW CONFIDENCE, BUT THE DETAILS OF WHICH WILL PLAY AN
IMPORTANT ROLE IN DETERMINING THE COVERAGE AND AMOUNTS OF POTENTIAL
WINTRY PRECIPITATION THE SOUTH INTO NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST MODELS AND ENSEMBLES GENERALLY SHOW GOOD AGREEMENT ON THE
OVERALL LARGE SCALE PATTERN ACROSS THE CONUS DURING THE MEDIUM
RANGE. HOWEVER, DESPITE THE SYNOPTIC AGREEMENT, THERE REMAINS QUITE
A BIT OF UNCERTAINTY IN THE DETAILS OF INDIVIDUAL SHORTWAVES
DROPPING INTO AND THROUGH THE MEAN TROUGH. THE FIRST OF THESE DIGS
INTO THE SOUTH AROUND TUESDAY AND SWINGS OFF THE SOUTHEAST COAST BY
WEDNESDAY. THERE IS CONSIDERABLE TIMING AND AMPLITUDE SPREAD IN
THIS WHICH IMPACTS HOW FAR SOUTH THE COLD AIR REACHES AND EXACT
PRECIPITATION TYPES EVEN AS FAR SOUTH AS THE GULF COAST. THE CMC
AND UKMET WERE THE DEEPEST/COLDEST (AND SLOWER) THAN THE BETTER
CONSENSUS AND WERE NOT THE PREFERRED SOLUTIONS EARLY IN THE PERIOD.
THE EARLY PERIOD WPC LEANED MOST HEAVILY ON THE GFS AND ECMWF.
A COMPACT AND CUT OFF CLOSED LOW OVER THE EAST PACIFIC MAY
GRADUALLY GET RE-ABSORBED INTO THE MEAN FLOW OVER THE CONUS AROUND
MID-WEEK BUT THE DETAILS OF THIS REMAINS VERY UNCERTAIN. THIS COULD
PUSH ANOTHER SHORTWAVE THROUGH THE SOUTH MID TO LATE WEEK, WITH
SOME INCREASING QPF ACROSS PARTS OF THE SOUTHERN PLAINS. YESTERDAYS
18Z GFS RUN WAS MOST BULLISH WITH THIS, BUT THE NEW 00Z RUN
TONIGHT (WHICH CAME IN AFTER THE WPC FORECAST WAS GENERATED) BACKED
OFF. ANOTHER SHORTWAVE DROPS THROUGH THE ROCKIES AND SURGES SOUTH
THURSDAY-FRIDAY, AND AGAIN THE SHAPE AND AMPLITUDE OF THE MEAN
TROUGH AT THIS TIME IS VERY UNCERTAIN AND HAS IMPLICATIONS ON
PRECIPITATION ACROSS THE SOUTH. FELT THE 12Z/JAN 16 ECMWF WAS THE
BEST MIDDLE GROUND CONSENSUS SO THIS COMBINED WITH THE ENSEMBLE
MEANS FORMED A GOOD LATE WEEK STARTING POINT FOR THE WPC FORECAST.
..WEATHER/HAZARDS HIGHLIGHTS
BY MONDAY, A BROAD AREA OF HAZARDOUSLY COLD ARCTIC AIR WILL
ALREADY COVER THE CENTRAL TO EASTERN U.S. WITH DAYTIME HIGHS AT
LEAST 20F BELOW NORMAL FOR MOST. THE COLDEST ANOMALIES ARE LIKELY
TO BE OVER THE HIGH PLAINS AND VICINITY WHERE HIGHS COULD BE 30-40F
BELOW NORMAL. COLDEST TEMPERATURES ON AN ABSOLUTE BASIS THOUGH
SHOULD BE OVER NORTHERN PLAINS AND UPPER MIDWEST WHERE SUBZERO
HIGHS AND LOWS IN THE -20S ARE LIKELY EARLY IN THE WEEK. WIND
CHILLS SHOULD BE EVEN COLDER AND MORE DANGEROUS. WPC IS POSTING KEY
MESSAGES REGARDING THIS COLD OUTBREAK. THE NORTHERN- CENTRAL
ROCKIES/PLAINS SHOULD MODERATE CONSIDERABLY BY TUESDAY- WEDNESDAY
(THOUGH WITH A POTENTIAL FOR GUSTY WINDS) WHILE ANOMALOUSLY COLD
WEATHER MAY PERSIST INTO WEDNESDAY AND POSSIBLY TO SOME EXTENT
THURSDAY ACROSS THE SOUTH AND EAST. THE WEST WILL SEE A PERIOD OF
COOL BUT NOT EXTREME TEMPERATURES INTO THE START OF NEXT WEEK, WITH
NEAR NORMAL AND THEN SLIGHTLY ABOVE NORMAL READINGS SLOWLY
BEGINNING TO PUSH EASTWARD FROM THE WEST COAST THEREAFTER.
EARLY IN THE WEEK THE PATTERN WOULD FAVOR LAKE EFFECT SNOW
ACROSS/DOWNWIND OF THE GREAT LAKES WITH SOME GENERALLY LIGHT AND
SCATTERED RAIN ACROSS FLORIDA ASSOCIATED WITH A LINGERING FRONT.
FARTHER WEST, A SHORTWAVE DIGGING INTO THE WEST EARLY NEXT WEEK MAY
PRODUCE SOME SCATTERED SNOW DEPENDING ON ITS EVOLUTION. WHAT THIS
SHORTWAVE DOES AFTER MONDAY WILL DETERMINE HOW MUCH PRECIPITATION
EMERGES OVER THE SOUTHERN TIER FROM TEXAS EASTWARD ON THE SOUTHERN
PERIPHERY OF THE OVERALL UPPER TROUGH AND SURFACE HIGH PRESSURE.
THE SOUTHERN EXTENT OF THE COLD AIR AT THE SURFACE MEANS THAT A
MAJORITY OF PRECIPITATION COULD BE WINTRY, PERHAPS ALL THE WAY TO
THE GULF COAST. FREEZING RAIN/ICE IS ALSO AN INCREASING CONCERN FOR
PARTS OF THE SOUTH GIVEN THE POSSIBILITY OF A WARM NOSE ATOP
ARCTIC COLD AIR. SOUTHERN TIER SNOW POTENTIAL CONTINUES TO SHOW UP
IN THE WINTER WEATHER PROBABILITIES FOR 0.25 INCH LIQUID IN THE
FORM OF SNOW, 10-20 PERCENT OVER AN AREA JUST NORTH OF THE WESTERN
GULF COAST FOR THE EARLY MONDAY- EARLY TUESDAY PERIOD AND 10-40
PERCENT ACROSS A MUCH BROADER SWATH OF THE SOUTH INTO SOUTHERN MID-
ATLANTIC EARLY TUESDAY INTO EARLY WEDNESDAY. SOME PRECIPITATION
POTENTIAL LINGERS THEREAFTER, BUT THROUGH THIS WHOLE PERIOD
CONFIDENCE IN DETAILS IS BELOW AVERAGE DUE TO CONSIDERABLE MODEL
DIFFERENCES AND VARIABILITY. MODERATE TO LOCALLY HEAVY RAIN IS
POSSIBLE ACROSS THE CENTRAL FLORIDA PENINSULA AS WELL MID-WEEK.
UNCERTAINTIES IN DETAILS ALOFT OVER THE SOUTHWEST INTO NEXT WEEK
MAKE THE SURFACE PATTERN UNCERTAIN AS WELL. HOWEVER, THERE IS SOME
POTENTIAL FOR A PERIOD OF RELATIVELY STRONGER WINDS OVER PARTS OF
CALIFORNIA AND VICINITY AROUND MONDAY-TUESDAY WHICH MAY INCREASE
FIRE WEATHER CONCERNS. CONTINUE TO MONITOR STORM PREDICTION CENTER
FIRE WEATHER FORECASTS FOR FURTHER INFORMATION.
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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