554
FXUS02 KWBC 191901
PMDEPD
EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
200 PM EST SUN NOV 19 2023
VALID 12Z WED NOV 22 2023 - 12Z SUN NOV 26 2023
..PATTERN OVERVIEW
BEHIND A SYSTEM FORECAST TO TRACK OVER/NEAR NEW ENGLAND ON
WEDNESDAY, AN UPPER RIDGE OVER THE WEST WILL QUICKLY GIVE WAY TO A
SHORTWAVE TROUGH WHILE AN UPPER RIDGE SETTING UP OVER THE EASTERN
PACIFIC/NORTHWESTERN NORTH AMERICA WILL ULTIMATELY TEND TO FAVOR
INCREASINGLY LARGE SCALE TROUGHING THAT SHOULD BE ALIGNED FROM
NEAR HUDSON BAY SOUTHWEST INTO THE WESTERN U.S. BY THE END OF NEXT
WEEKEND. EXPECT THIS EVOLUTION TO BRING COLDER TEMPERATURES TO THE
CENTRAL U.S. IN PARTICULAR BY FRIDAY-SUNDAY, WITH MANY OTHER AREAS
TRENDING COOLER AS WELL. THE NEW ENGLAND SYSTEM WILL BRING SOME
PRECIPITATION TO THE EAST COAST WHILE THE TROUGH REACHING THE WEST
BY THANKSGIVING WILL SPREAD AN AREA OF SNOW ACROSS THE
NORTH-CENTRAL ROCKIES. THERE IS ALSO SOME UNCERTAIN POTENTIAL FOR
ADDITIONAL SOUTHERN-EASTERN U.S. RAINFALL FROM A SECOND WAVE UP
THE EAST COAST LATE THIS WEEK.
..GUIDANCE EVALUATION/PREDICTABILITY ASSESSMENT
THE MODELS AND ENSEMBLES CONTINUE TO STRUGGLE WITH RESOLVING
IMPORTANT DETAILS OF THE INITIAL TROUGH ENERGY REACHING THE
EASTERN U.S. MIDWEEK AND HOW CORRESPONDING COASTAL LOW PRESSUE
EVOLVES. THE 00Z UKMET CONTINUES TO BE MUCH SLOWER WITH SOUTHERN
STREAM ENERGY THROUGH THE SOUTHEAST, RESULTING IN A SLOWER AND
MORE SOUTH WAVE OFF THE EAST COAST. THE GFS IS ALSO
STRONGER/SLOWER BUT USABLE AND NOT LIKE THE UKMET WHICH APPEARS TO
BE AN OUTLIER AT THIS POINT. THE UPPER LOW THAT MEANDERS OVER
NORTHERN MEXICO EARLY IN THE WEEK SHOULD BEGIN TO PUSH EAST AS
ADDITIONAL TROUGHING ENTERS THE WEST. THERE ARE TIMING DIFFERENCES
WITH THIS FEATURE AND THAT IMPACTS POTENTIAL ADDITIONAL COASTAL
LOW DEVELOPMENT OFF THE SOUTHEAST COAST LATE IN THE WEEK AND
RESULTING QPF. TROUGHING INTO THE WEST AROUND THANKSGIVING BECOMES
QUITE UNCERTAIN AND RELATED TO A BUILDING RIDGE UPSTREAM WHICH
ALSO AFFECTS SHORTWAVES ROUNDING THE BASE OF AN UPPER LOW
MEANDERING NEAR HUDSON BAY.
..WEATHER/HAZARDS HIGHLIGHTS
WHILE THERE IS STILL LOWER THAN AVERAGE CONFIDENCE FOR HOW THE
SYSTEM AFFECTING NEW ENGLAND ON WEDNESDAY (AND WITH LOWER
PROBABILITY INTO THANKSGIVING) MAY EVOLVE/TRACK, POTENTIAL STILL
EXISTS FOR A PERIOD OF MODEST RAINFALL OVER PARTS OF EASTERN NEW
ENGLAND. HOWEVER, GIVEN VERY DRY ANTECEDENT CONDITIONS AND A
GENERAL LACK OF SUFFICIENT INSTABILITY AND ANOMALOUS MOISTURE,
OPTED TO REMOVE (WITH SUPPORT FROM THE AFFECTED WFOS) THE MARGINAL
RISK ON THE DAY 4 EXCESSIVE RAINFALL OUTLOOK. SNOW WILL BE
POSSIBLE OVER PARTS OF INTERIOR NEW ENGLAND WITH THE WEDNESDAY
SYSTEM AS WELL AND A BRIEF PERIOD OF LAKE EFFECT SNOW WILL BE
POSSIBLE AFTER SYSTEM PASSAGE. WITH VERY UNCERTAIN DETAILS, A
TRAILING WAVE MAY PRODUCE SOME RAINFALL OVER PARTS OF THE
SOUTH/EAST DURING THE LATTER HALF OF THE WEEK. OVER THE WEST, A
SYSTEM MOVING INTO THE REGION LATE IN THE WEEK SHOULD BRING AN
AREA OF SNOW ACROSS THE NORTH-CENTRAL ROCKIES ESPECIALLY AROUND
THANKSGIVING, WITH SOME LOCALIZED ENHANCEMENT POSSIBLE. SOME
RAIN/SNOW MAY EXTEND EAST OF THE ROCKIES THEREAFTER ALONG A WEAK
AND WAVY FRONTAL SYSTEM, WITH SOME RAINFALL POSSIBLE ALONG PARTS
OF THE GULF COAST.
COLDER AIR DROPPING SOUTH OVER THE PLAINS/EASTERN SLOPES OF THE
ROCKIES FROM FRIDAY INTO THE WEEKEND SHOULD SHOULD BRING HIGHS
DOWN TO 10-20F BELOW NORMAL OVER THAT REGION. BELOW NORMAL
ANOMALIES WILL SPREAD ELSEWHERE AS WELL, WITH THE INTERIOR WEST
HIGHS TRENDING TO 5-10F BELOW NORMAL LATE WEEK INTO THE WEEKEND
AND THE MISSISSIPPI VALLEY PLUS PARTS OF THE OHIO VALLEY AT LEAST
10F BELOW NORMAL BY SUNDAY. THIS WILL BE A SIGNIFICANT CHANGE FROM
ABOVE NORMAL TEMPERATURES OVER THE HIGH PLAINS INTO THE WEST ON
WEDNESDAY. THE SOUTH AND EAST WILL SEE A BRIEF PERIOD OF BELOW
NORMAL TEMPERATURES FOLLOWED BY A REBOUND TOWARD NORMAL VALUES.
SANTORELLI/RAUSCH
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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