926
FXUS02 KWBC 201900
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
159 PM EST TUE DEC 20 2022
VALID 12Z FRI DEC 23 2022 - 12Z TUE DEC 27 2022
***A MAJOR WINTER STORM FROM THE MIDWEST TO THE NORTHEAST LATE IN
THE WEEK WILL LIKELY CAUSE BLIZZARD CONDITIONS AND TRAVEL
DISRUPTIONS, ALONG WITH BITTERLY COLD TEMPERATURES AND STRONG
WINDS TO CLOSE OUT THE WEEK***
..SYNOPTIC OVERVIEW
AN IMPRESSIVE DIP IN THE JET STREAM AND A HIGHLY ANOMALOUS UPPER
TROUGH/CLOSED LOW OVER THE OHIO VALLEY ON FRIDAY WILL SUSTAIN
EXPLOSIVE SURFACE CYCLOGENESIS ACROSS THE GREAT LAKES WITH CENTRAL
PRESSURES FALLING WELL BELOW 980 MB BY FRIDAY EVENING. THIS WILL
CAUSE AN INCREDIBLY STRONG COLD FRONT TO SWEEP ACROSS THE EASTERN
U.S. WITH FRIGID TEMPERATURES FROM THE PLAINS TO THE EAST COAST IN
TIME FOR CHRISTMAS WEEKEND. EXPECT THE LOW TO LIFT NORTHWARD
ACROSS WESTERN QUEBEC ON SATURDAY WITH LAKE EFFECT SNOW
CONTINUING, AND HEAVY RAINFALL EXITING NEW ENGLAND VERY EARLY IN
THE DAY. THE TRAILING ARCTIC SURFACE HIGH WILL SETTLE ACROSS THE
SOUTH-CENTRAL U.S. AND THEN MODIFY WITH GRADUALLY WARMING
TEMPERATURES GOING INTO CHRISTMAS DAY AND EARLY NEXT WEEK.
FARTHER WEST, MULTIPLE SHORTWAVE IMPULSES WILL PASS OVER THE
PACIFIC NORTHWEST AND RESULT IN PERIODS OF HEAVY RAIN AND HIGH
MOUNTAIN SNOW OVER WESTERN OREGON/WASHINGTON, WITH SOME SNOW
EXTENDING INTO THE NORTHERN ROCKIES. MODERATELY ABOVE NORMAL
TEMPERATURES SHOULD GRADUALLY SPREAD OVER MORE OF THE WEST AND
THEN EXTEND INTO THE HIGH PLAINS.
..GUIDANCE/PREDICTABILITY ASSESSMENT
LATEST GUIDANCE OFFERS GOOD AGREEMENT ON THE LARGE SCALE UPPER
PATTERN THAT FEATURES A WEST COAST RIDGE AND EASTERN TROUGH, WITH
PACIFIC SHORTWAVES ROUNDING THE RIDGE AND FEEDING INTO THE MEAN
TROUGH. CONSENSUS SHOWS THE MEAN RIDGE BEGINNING TO BROADEN AS IT
PUSHES INLAND BY DAY 7 NEXT TUESDAY WHILE TROUGHING APPROACHES THE
WEST COAST. DETAIL DIFFERENCES FOR THE INITIAL OHIO VALLEY/GREAT
LAKES STORM AND ASSOCIATED FRONTAL SYSTEM AS WELL AS NORTHEASTERN
PACIFIC FEATURES THAT BRUSH THE NORTHWEST THROUGH THE WEEKEND ARE
GENERALLY WITHIN THE TYPICAL SPREAD AND GUIDANCE ERROR FOR THE
TIME FRAME INVOLVED, SO AN OPERATIONAL MODEL COMPOSITE WORKED WELL
FOR DEPICTING SIGNIFICANT FEATURES IN THE UPDATED FORECAST. BY
DAYS 6-7 MONDAY-TUESDAY THERE ARE MORE NOTICEABLE DETAIL
DIFFERENCES THAT RECOMMEND A TREND TOWARD A MODEL/ENSEMBLE MEAN
BLEND. THESE INCLUDE SPECIFICS WITHIN THE EASTERN PACIFIC MEAN
TROUGH, AND WITHIN THE EASTERN NORTH AMERICA MEAN TROUGH ONE
SHORTWAVE DROPPING INTO THE CENTRAL/EASTERN U.S. AND POSSIBLY A
SEPARATE ONE DROPPING FROM CANADA INTO THE GREAT LAKES REGION.
RECENT ECMWF RUNS HAVE BEEN MORE PRONOUNCED WITH THIS NORTHERN
FEATURE THAN MOST OTHER MODELS BUT THE NEW 12Z CMC HAS TRENDED
MUCH CLOSER TO THE 00Z ECMWF, WHILE THE 12Z ECMWF HAS BACKED OFF
WITH THIS FEATURE'S STRENGTH SOMEWHAT. AN INTERMEDIATE SOLUTION
SEEMS REASONABLE AT THIS POINT GIVEN THE SPLIT IN THE GUIDANCE.
..WEATHER/HAZARD HIGHLIGHTS
THE MAIN WEATHER STORY IS THE EXPECTED DEVELOPMENT OF AN INTENSE
LOW PRESSURE SYSTEM OVER THE OHIO VALLEY INTO THE GREAT LAKES,
WITH THE SURFACE LOW THEN TRACKING INTO WESTERN QUEBEC BY EARLY
SATURDAY. THE EXPECTED INLAND TRACK OF THE MAIN LOW WILL RESULT
IN PERIODS OF MODERATE TO HEAVY RAIN SPREADING FROM THE
MID-ATLANTIC TO NEW ENGLAND LATE THURSDAY INTO LATE FRIDAY, AND
MODERATE TO HEAVY SNOW TO THE WEST WITH BLIZZARD CONDITIONS FROM
THE MIDWEST TO THE NORTHERN OHIO VALLEY AND GREAT LAKES. THERE IS
EVEN THE POTENTIAL FOR SOME MINOR FLOODING ACROSS PORTIONS OF
CENTRAL AND EASTERN NEW ENGLAND AS 2-3 INCHES OF RAINFALL IS
BECOMING MORE LIKELY WITH STRONG MOISTURE ADVECTION FROM THE
ATLANTIC AHEAD OF THE MAIN COLD FRONT, ESPECIALLY IF THIS RAINFALL
FALLS OVER REGIONS THAT MAY STILL HAVE A SNOW PACK FROM LAST
WEEK'S STORM. THEREFORE, A SLIGHT RISK OF EXCESSIVE RAINFALL
REMAINS IN EFFECT FOR THE DAY 4 PERIOD ON FRIDAY TO ACCOUNT FOR
THIS. STRONG AND POTENTIALLY DAMAGING WINDS ARE LIKELY ACROSS
PORTIONS OF OHIO, PENNSYLVANIA, AND WESTERN NEW YORK FRIDAY AND
INTO EARLY SATURDAY AS A STING JET MIXES STRONG WINDS ALOFT TO THE
SURFACE.
THE TRULY MASSIVE EXPANSE OF FRIGID TEMPERATURES ACROSS BASICALLY
ALL OF THE CENTRAL AND EASTERN U.S. EAST OF THE ROCKIES WILL ALSO
CONTINUE TO MAKE WEATHER HEADLINES TO CLOSE OUT THE WEEK, WITH
HARD FREEZES LIKELY FOR MUCH OF THE DEEP SOUTH AND WELL INTO
TEXAS. THERE WILL BE WIDESPREAD SUBZERO READINGS FOR OVERNIGHT
LOWS AND EVEN SOME DAYTIME HIGHS FROM THE NORTHERN ROCKIES TO THE
CENTRAL/NORTHERN PLAINS AND THE UPPER MIDWEST, ESPECIALLY ON
FRIDAY AND SATURDAY. ALTHOUGH THE FRIGID AIRMASS WILL MODIFY SOME
AS IT REACHES THE OHIO/TENNESSEE VALLEY REGION, IT WILL STILL BE
IMPRESSIVELY COLD WITH WIDESPREAD 0S AND 10S FOR HIGH
TEMPERATURES, AND SOME SUBZERO OVERNIGHT LOWS. HARD FREEZE
CONDITIONS ARE EXPECTED FOR MUCH OF THE DEEP SOUTH AND TEXAS
THURSDAY NIGHT THROUGH AT LEAST FRIDAY NIGHT, WITH LOWS WELL INTO
THE 10S AND LOW 20S, EVEN TO THE GULF COAST. COLD WEATHER WILL
ALSO REACH WELL INTO FLORIDA IN TIME FOR THE CHRISTMAS WEEKEND,
WITH LOWS FALLING INTO THE 30S AND 40S ACROSS MUCH OF THE
PENINSULA. THESE READINGS WILL EQUATE TO ANOMALIES OF 20-35F OR
SO BELOW NORMAL OVER A BROAD AREA, AND SOME DAILY RECORDS FOR
COLDEST MORNING LOWS/DAYTIME HIGHS APPEAR LIKELY EVEN WITH THE
CHALLENGING COMPARISONS TO EVENTS FROM 1989 AND 1983 (AMONG OTHER
YEARS DEPENDING ON LOCATION).
ELSEWHERE, THE PACIFIC NORTHWEST SHOULD SEE MULTIPLE EPISODES OF
RAIN AND HIGHER ELEVATION SNOW AS PERSISTENT ONSHORE FLOW ADVECTS
MOISTURE INLAND WHILE SHORTWAVES TRACK AROUND THE NORTHERN SIDE OF
THE MEAN RIDGE ALOFT NEAR THE WEST COAST. SOME MOISTURE SHOULD
EXTEND INTO THE NORTHERN ROCKIES WHERE MODERATE TO LOCALLY HEAVY
SNOW MAY FALL. BY LATE IN THE WEEKEND THE SOUTHERN PART OF THE
PRECIPITATION AREA SHOULD TREND LIGHTER AS THE UPPER RIDGE BRIEFLY
REBOUNDS. THEN DURING THE FIRST PART OF NEXT WEEK EXPECT THE RAIN
AND MOUNTAIN SNOW TO BECOME HEAVIER AND PUSH FARTHER SOUTHWARD,
EVENTUALLY REACHING INTO CALIFORNIA, AS A LARGER SCALE UPPER
TROUGH APPROACHES AND THE RIDGE AXIS PUSHES FARTHER INLAND. DRY
WEATHER SHOULD CONTINUE ACROSS THE SOUTHWESTERN U.S. UNDER THE
UPPER RIDGE.
RAUSCH/HAMRICK
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, EXPERIMENTAL EXCESSIVE RAINFALL
OUTLOOK, WINTER WEATHER OUTLOOK PROBABILITIES AND HEAT INDICES 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
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