109
FXUS02 KWBC 160700
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 AM EST TUE JAN 16 2024
VALID 12Z FRI JAN 19 2024 - 12Z TUE JAN 23 2024
...ANOTHER ARCTIC AIRMASS COMES INTO THE CENTRAL U.S. LATE WEEK,
BUT NOT AS EXTREME AS THE FIRST ONE...
...MULTIPLE ROUNDS OF POTENTIALLY HEAVY PRECIPITATION WILL AFFECT
THE WEST...
..OVERVIEW
THE LARGE SCALE PATTERN FINALLY BECOMES MORE PROGRESSIVE BY LATE
WEEK INTO EARLY NEXT WEEK, AS THE DEEP AND BROAD UPPER TROUGH THAT
SHOULD DOMINATE MUCH OF THE LOWER 48 DURING THE SHORT RANGE PERIOD
WILL FINALLY GET DISPLACED INTO THE EAST AND THEN THE ATLANTIC
OVER THE WEEKEND. THIS IS DUE TO AN UPPER RIDGE SHIFTING ACROSS
THE WESTERN AND THEN CENTRAL U.S. BY LATE WEEK/WEEKEND AND INTO
THE EASTERN U.S. EARLY NEXT WEEK. AHEAD OF THE RIDGE, MEAN
NORTHWESTERLY FLOW WILL BRING IN ANOTHER ARCTIC SURFACE HIGH,
PRODUCING MUCH BELOW NORMAL TEMPERATURES ACROSS THE CENTRAL U.S.
AND EASTERN U.S. ESPECIALLY FRIDAY AND SATURDAY BEFORE GRADUALLY
MODERATING. WHILE TEMPERATURES ARE FORECAST TO BE GENERALLY BE
15-30F BELOW AVERAGE, AT MOST LOCATIONS THIS SECOND ROUND OF COLD
TEMPERATURES SHOULD BE LESS EXTREME THAN THE CURRENT COLD WAVE.
MEANWHILE, ROUNDS OF PRECIPITATION ARE EXPECTED FOR THE WEST
COAST, AND IN THE EAST POSSIBLE LOW DEVELOPMENT ALONG A SURFACE
FRONTAL SYSTEM OR TWO COULD PRODUCE SOME WINTER WEATHER
PARTICULARLY FRIDAY, BUT WITH CONTINUED UNCERTAINTY FOR DETAILS.
RETURN FLOW FROM THE GULF OF MEXICO WILL INCREASE PRECIPITATION
CHANCES ACROSS THE CENTRAL U.S. FOR THE EARLY PART OF NEXT WEEK.
..GUIDANCE/PREDICTABILITY ASSESSMENT
MODEL GUIDANCE SEEMS TO BE HANDLING THE LARGE SCALE PATTERN WELL,
WITH GOOD MODEL AGREEMENT ON MOST FEATURES INCLUDING THE INITIAL
EAST UPPER TROUGH, SURFACE HIGH PRESSURE DIVING INTO THE
CENTRAL/EASTERN U.S. LATE WEEK, THE RIDGE PROGRESSING ACROSS THE
LOWER 48, AND MEAN TROUGHING COMING IN BEHIND THAT. ONE ASPECT OF
THE FORECAST WITH SOME POTENTIALLY IMPACTFUL MODEL DIFFERENCES IS
WITH THE EXACT PATTERN IN THE EAST/WESTERN ATLANTIC ON FRIDAY.
MODELS ARE AGREEABLE THAT A SHORTWAVE SHOULD CONSOLIDATE IN THE
EAST-CENTRAL U.S. BY FRIDAY AS ENERGIES FROM THE NORTHWEST AND
NORTH COMBINE WITHIN THE BROAD TROUGH, AND THIS STRONG SHORTWAVE
PIVOTS EAST AND SUPPORTS LOW PRESSURE FORMATION. BUT A SURFACE LOW
TRYING TO CONSOLIDATE IN THE WESTERN ATLANTIC MAY HAVE A MORE
COMPLEX EVOLUTION THAN NORMAL BECAUSE OF ANOTHER LOW
PRESSURE/FRONTAL SYSTEM JUST TO THE WEST ONSHORE IN THE EAST. ONCE
THE COASTAL LOW FORMS IT LOOKS TO TRACK QUICKLY NORTHEASTWARD,
LIMITING IMPACTS TO THE EAST COAST TOO MUCH, BUT SOME SNOW/WIND
COULD PRODUCE SOME ISSUES. AFTER SOME CMC RUNS SHOWED THE LOW
CLOSEST TO THE COAST, THE 12Z AND NOW 00Z RUNS ARE AMONG THE
FARTHEST EAST SOLUTIONS. ALSO REGARDING THE CMC, ITS RUNS HAD BEEN
PERSISTENT IN SHOWING TROUGHING LINGERING ACROSS THE EAST TO
WESTERN ATLANTIC SUNDAY-MONDAY WHILE OTHER GUIDANCE SHIFTS IT AWAY
MORE QUICKLY. THE 00Z CMC HAS NOW JOINED WITH THE BETTER CONSENSUS
FOR A FASTER TROUGH. BUT LEANED AWAY FROM THE 12Z CMC AT THE TIME
OF FORECAST GENERATION.
ADDITIONAL DETAILS OF SHORTWAVES WITHIN THE MEAN TROUGH MARCHING
INTO THE WEST BEHIND THE RIDGE ALSO SHOW SOME VARIABILITY IN
TIMING, THOUGH CERTAINLY WITHIN TYPICAL SPREAD DURING THE MID-LATE
MEDIUM RANGE TIMEFRAME. THESE WILL TAKE ADDITIONAL TIME TO RESOLVE
ESPECIALLY SINCE THEY ARE TRACKING FROM THE DATA-POOR PACIFIC THAT
CAUSES MODELS TO STRUGGLE. A MODEL/ENSEMBLE MEAN BLEND SEEMED BEST
TO HANDLE THESE FEATURES.
THE WPC FORECAST WAS BASED ON A MULTI-MODEL DETERMINISTIC BLEND
EARLY IN THE FORECAST PERIOD. GRADUALLY INCORPORATED THE GEFS AND
EC ENSEMBLE MEAN GUIDANCE WHILE PHASING OUT THE CMC (AND OF COURSE
THE TIME-LIMITED UKMET) AS THE PERIOD PROGRESSED, ENDING UP WITH
AN EVEN BLEND OF THE 18Z GFS AND GEFS MEAN AND 12Z ECMWF AND EC
MEAN BY DAY 7. THIS SMOOTHED OUT MODEL DIFFERENCES BUT MAINTAINED
SOME STRENGTH IN INDIVIDUAL SYSTEMS.
..WEATHER/HAZARDS HIGHLIGHTS
ARCTIC HIGH PRESSURE WILL PROVIDE A REINFORCING SURGE OF COLD AIR
THAT IS FORECAST TO PUSH WELL INTO THE CENTRAL AND EAST-CENTRAL
U.S. BY FRIDAY AND INTO THE EAST ON SATURDAY. BELOW NORMAL
TEMPERATURES BY 15-30 DEGREES SHOULD BE WIDESPREAD, WITH LOCALIZED
ANOMALIES MORE THAN 30F BELOW NORMAL, AND THIS COLD EPISODE WILL
STILL BE NOTABLE EVEN IF NOT QUITE AS EXTREME AS THE CURRENT COLD
EVENT OVER MOST AREAS. THE HIGHEST POTENTIAL FOR HAZARDOUS COLD IS
ACROSS THE NORTH-CENTRAL PLAINS INTO PARTS OF THE UPPER MIDWEST.
TEMPERATURES ARE FORECAST TO START MODERATING CLOSER TO NORMAL
SUNDAY AND BECOME NEAR TO ABOVE AVERAGE IN THE CENTRAL AND EASTERN
U.S. BY MONDAY-TUESDAY AS THE SURFACE HIGH SHIFTS AWAY INTO THE
ATLANTIC AND THE UPPER RIDGE ALLOWS FOR MORE SOUTHERLY FLOW. FROM
THE ROCKIES WESTWARD, NEAR TO ABOVE NORMAL TEMPERATURES ARE
EXPECTED, WITH HIGHER ANOMALIES (GENERALLY 10-20F ABOVE AVERAGE)
FOR LOWS THAN HIGHS.
THE WEST COAST STATES CAN EXPECT ROUNDS OF PRECIPITATION FOR THE
LATTER PART OF THIS WEEK INTO EARLY NEXT WEEK. BY LATE FRIDAY, A
ROUND OF PRECIPITATION LOOKS TO AFFECT CALIFORNIA ALONG AND AHEAD
OF A FRONTAL SYSTEM. MODELS INDICATE THAT RAIN RATES COULD BE OVER
HALF AN INCH PER HOUR AS INSTABILITY MAY SNEAK ONSHORE, ALONG WITH
GOOD DYNAMICAL SUPPORT FOR HEAVY RAIN FROM A STRONG SHORTWAVE
ALOFT. THUS THE MARGINAL RISK IN THE EXCESSIVE RAINFALL OUTLOOK
FOR PORTIONS OF NORTHERN CALIFORNIA ON FRIDAY-FRIDAY NIGHT STILL
LOOKS REASONABLE. AS PRECIPITATION GENERALLY EXPANDS SOUTHEASTWARD
OVER THE WEEKEND, A SIMILAR MARGINAL RISK IS NOW IN PLACE FOR
SATURDAY-SATURDAY NIGHT BUT WITH SOME SOUTHWARD EXPANSION COMPARED
TO FRIDAY'S OUTLOOK. THESE MULTIPLE ROUNDS OF PRECIPITATION SHOULD
CONTINUE INTO EARLY NEXT WEEK FROM THE WEST COAST INTO THE
INTERMOUNTAIN WEST. SOME LOCALLY MODERATE/HEAVY TOTALS ARE
POSSIBLE OVER FAVORED TERRAIN, DEPENDING ON UPPER LEVEL AND
SURFACE DETAILS THAT WILL BE BETTER RESOLVED IN COMING DAYS. PARTS
OF THE INTERIOR NORTHWEST COULD SEE CONDITIONS FAVORABLE FOR
FREEZING RAIN FOR MULTIPLE DAYS. EVENTUALLY BY EARLY NEXT WEEK,
THE PATTERN SHOULD ALLOW FOR GULF RETURN FLOW TO PRODUCE RAIN
CHANCES FIRST FOR THE SOUTHERN PLAINS SUNDAY. MODELS INDICATE
HEAVIER RAIN THERE BY MONDAY WHILE THE PRECIPITATION SHIELD ALSO
EXPANDS NORTHEASTWARD MONDAY-TUESDAY, WITH SOME POSSIBLE WINTRY
WEATHER ON THE NORTHERN SIDE.
A FRONTAL SYSTEM WITH EMBEDDED LOW PRESSURE REACHING THE EAST
DURING THE LATTER PART OF THE WEEK MAY PRODUCE SOME PRECIPITATION
ACROSS THE APPALACHIANS AND PARTS OF THE EAST COAST FRIDAY. SNOW
SHOULD BE THE PRIMARY PRECIPITATION TYPE CONSIDERING THE COLD AIR
IN PLACE. THE CENTRAL APPALACHIANS WILL LIKELY SEE THE HEAVIEST
SNOW WITH UPSLOPE FLOW HELPING TO CONTRIBUTE TO AMOUNTS. FARTHER
EAST THE MOST LIKELY AXIS FOR NOTABLE SNOW LOOKS TO BE MAINLY
ACROSS THE NORTHERN MID-ATLANTIC INTO SOUTHERN PARTS OF THE
NORTHEAST, BUT AMOUNTS DO NOT LOOK TO BE TOO HEAVY. EXPECT
CONTINUED PERIODS OF LAKE EFFECT SNOW WITH PERSISTENCE OF COLD AIR
AND BREEZY CONDITIONS INTO SATURDAY. LAKE EFFECT SNOW WILL LIKELY
TAPER OFF BY SUNDAY AS SURFACE HIGH PRESSURE BUILDS INTO THE EAST.
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
CLICK HERE TO GO TO PREVIOUS BULLETINS.
Main Text Page