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526
FXUS21 KWNC 192021
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST DECEMBER 19 2014

SYNOPSIS: AT THE BEGINNING OF THE OUTLOOK PERIOD, A MAJOR STORM SYSTEM IS
PREDICTED TO DEVELOP ACROSS THE EAST-CENTRAL STATES JUST BEFORE CHRISTMAS,
BRINGING A VARIETY OF HAZARDOUS WEATHER CONDITIONS TO THE GREAT LAKES REGION
AND THE ATLANTIC COAST STATES. THERE IS ALSO THE POSSIBILITY OF STRONG TO
SEVERE THUNDERSTORMS AFFECTING THE FLORIDA PENINSULA, ON THE SOUTHERN END OF
THIS EXPANSIVE STORM SYSTEM. ANOTHER POWERFUL STORM IS ANTICIPATED TO MOVE
ACROSS THE CENTRAL BERING SEA BETWEEN DECEMBER 23-24, POSING A SIGNIFICANT
HAZARD TO COMMERCIAL SHIPPING. HOWEVER, IT DOES NOT LOOK LIKE HAZARDOUS
CONDITIONS ASSOCIATED WITH THIS STORM WILL REACH THE BERING SEACOAST OF ALASKA.

HAZARDS

HEAVY RAIN FROM FLORIDA TO DELAWARE, MON-TUE, DEC 22-23.

HEAVY RAIN FOR NEW ENGLAND AND NORTHERN NEW YORK, WED-THU, DEC 24-25.

HEAVY SNOW DOWNWIND OF THE GREAT LAKES, THU, DEC 25.

HIGH WINDS FROM THE GREAT LAKES AND OHIO VALLEY EASTWARD TO THE ATLANTIC COAST,
WED-THU, DEC 24-25.

FLOODING LIKELY IN SOUTHWEST WASHINGTON AND NORTHWEST OREGON, MON-WED, DEC
22-24.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FROM THE NORTHERN AND CENTRAL
ROCKIES TO THE UPPER MISSISSIPPI VALLEY, SAT-MON, DEC 27-29.

MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FROM THE NORTHERN AND CENTRAL
ROCKIES TO CENTRAL PORTIONS OF THE DAKOTAS AND NEBRASKA, SAT-MON, DEC 27-29.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, SOUTHEAST,
LOWER MISSISSIPPI VALLEY, PACIFIC NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR MONDAY DECEMBER 22 - FRIDAY DECEMBER 26: AN AMPLIFIED 500-HPA RIDGE IS
FORECAST FROM THE EASTERN PACIFIC NORTHWARD ACROSS ALASKA, AND A DEEP TROUGH IS
PREDICTED DOWNSTREAM ACROSS THE WEST-CENTRAL CONUS. THESE CIRCULATION FEATURES
ARE EXPECTED TO BE LOCATED 15-20 DEGREES LONGITUDE FARTHER WEST THAN WHAT WAS
ANTICIPATED DURING THE PAST FEW DAYS. THIS WILL, AMONG OTHER THINGS, CONTRIBUTE
TO A WESTWARD-SHIFTED STORM TRACK THROUGH THE OHIO VALLEY WITH RELATIVELY MILD
AIR ACROSS THE ATLANTIC COAST STATES, AND POSTPONE THE ARRIVAL OF SIGNIFICANTLY
COLDER AIR INTO THE NORTHEAST U.S.



DURING THIS PERIOD, A LOW PRESSURE CENTER IS EXPECTED TO MOVE INTO THE UPPER
MISSISSIPPI VALLEY BRINGING LIGHT SNOW TO THE REGION, WHILE A SECONDARY LOW
FORMS IN THE LOWER MISSISSIPPI VALLEY. WITH TIME, THE SECONDARY LOW IS
ANTICIPATED TO TRACK NORTHWARD AND STRENGTHEN, EVENTUALLY BECOMING THE DOMINANT
LOW PRESSURE CENTER IN THE VICINITY OF LOWER MICHIGAN, OR SLIGHTLY FARTHER
WEST. THIS SCENARIO IS PREDICTED BY BOTH THE 00Z UKMET AND 06Z GFS
DETERMINISTIC RUNS, WITH THE 00Z UKMET SOLUTION BEING ABOUT 12 HOURS SLOWER.
THE LATEST GFS RUN (INITIALIZED AT 12Z) SEEMS TO SPLIT THE DIFFERENCE, WITH ONE
LOW PRESSURE CENTER MOVING FROM THE MIDDLE MISSISSIPPI VALLEY TO THE CENTRAL
GREAT LAKES REGION. THOUGH THERE ARE DIFFERENCES AMONG THE VARIOUS DYNAMICAL
MODELS REGARDING TIMING AND OTHER DETAILS, THE GENERAL FORECAST DEPICTS LOW
PRESSURE OVER THE SOUTHERN OR SOUTHWESTERN GREAT LAKES REGION BY CHRISTMAS EVE.
HAZARDS ASSOCIATED WITH THIS PREDICTED STORM SYSTEM INCLUDE THE POSSIBILITY OF
STRONG TO SEVERE THUNDERSTORMS ACROSS THE FLORIDA PENINSULA, ESPECIALLY ON
TUESDAY, DECEMBER 23. AS OF 2PM EASTERN TIME TODAY (DEC 19), THE STORM
PREDICTION CENTER IN OKLAHOMA HAS NOT OFFICIALLY DESIGNATED A SEVERE WEATHER
RISK AREA, BUT THIS MAY CHANGE PENDING THE CONSISTENCY OF FUTURE MODEL RUNS.
OTHER HAZARDS INCLUDE HEAVY RAIN FROM FLORIDA TO DELAWARE IN ASSOCIATION WITH
THE STORM`S COLD FRONT, AND HEAVY RAIN OVER NEW ENGLAND AND NORTHERN NEW YORK
IN ASSOCIATION WITH THE OCCLUDED FRONT AND POSSIBLE TRIPLE-POINT LOW. WINDS OF
25-35 MPH ARE ALSO FORECAST ACROSS THE GREAT LAKES REGION, OHIO VALLEY, AND
ATLANTIC COAST STATES FROM NORTH CAROLINA TO MAINE. BY CHRISTMAS DAY, AS RAIN
DEPARTS THE NORTHEAST, LAKE-ENHANCED SNOW SQUALLS ARE EXPECTED TO SET UP
DOWNWIND OF THE GREAT LAKES, BRINGING LOCALIZED AREAS OF HEAVY SNOWFALL.



DIMINISHING WESTERLY FLOW ACROSS THE PACIFIC NORTHWEST IS EXPECTED TO RESULT IN
SIGNIFICANTLY REDUCED PRECIPITATION AMOUNTS ACROSS WESTERN SECTIONS OF BOTH
WASHINGTON AND OREGON DURING THE FIRST FEW DAYS OF THIS PERIOD. THE LATEST
PRECIPITATION FORECASTS FROM THE WEATHER PREDICTION CENTER (WPC) HAS
SIGNIFICANTLY LOWERED EXPECTED PRECIPITATION AMOUNTS TO 1-2 INCHES DURING
DECEMBER 22-23, PROMPTING THE REMOVAL OF ANY PRECIPITATION HAZARDS ACROSS THE
NORTHWEST.



LOCALIZED AREAS OF FLOODING ARE LIKELY WITHIN THE AREAS INDICATED ON THE MAP IN
SOUTHWEST WASHINGTON AND NORTHWEST OREGON DUE TO THE RECENT HEAVY PRECIPITATION
AND RUNOFF.



A MAJOR STORM SYSTEM IS FORECAST TO MOVE ACROSS THE BERING SEA DURING TUESDAY
AND WEDNESDAY, DECEMBER 23-24. AT THE STORM`S PEAK, 40-50 KNOT WINDS AND 8-9
METER SIGNIFICANT WAVE HEIGHTS ARE PREDICTED BY THE NOAA WAVEWATCH MODEL
(INITIALIZED AT 00Z) FOR THE BERING SEA, BEFORE THE STORM CURVES NORTHWESTWARD
INTO EXTREME EASTERN RUSSIA. THOUGH THIS STORM SYSTEM POSES SERIOUS HAZARDS FOR
COMMERCIAL SHIPPING IN THE BERING SEA, IT APPEARS THAT THE WEST COAST OF ALASKA
WILL BE SPARED THE WORST OF ITS IMPACTS.

FOR SATURDAY DECEMBER 27 - FRIDAY JANUARY 02: MODELS ARE IN AGREEMENT ON A
HIGHLY AMPLIFIED WAVE PATTERN OVER NORTH AMERICA IN THE WEEK-2 RANGE. A HIGHLY
AMPLIFIED RIDGE IS PREDICTED FROM THE EASTERN PACIFIC NORTHWARD ACROSS ALASKA,
WHILE A DEEP TROUGH IS EXPECTED OVER EAST-CENTRAL NORTH AMERICA. THERE IS A
SLIGHT CHANCE OF MUCH BELOW-NORMAL MINIMUM TEMPERATURES FROM THE NORTHERN AND
CENTRAL ROCKIES TO THE UPPER MISSISSIPPI VALLEY DURING THE FIRST THREE DAYS OF
THIS PERIOD. A MODERATE CHANCE OF MUCH BELOW-NORMAL MINIMUM TEMPERATURES IS
ANTICIPATED FROM THE NORTHERN AND CENTRAL ROCKIES TO THE CENTRAL PORTIONS OF
THE DAKOTAS AND NEBRASKA.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON DECEMBER 18, INDICATES A VERY
SLIGHT INCREASE IN THE AREAL COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2 TO
D4) FROM 17.09 TO 17.27 PERCENT ACROSS THE CONTINENTAL U.S.. PERHAPS THE
LARGEST AND MOST SIGNIFICANT CHANGE FROM LAST WEEK`S DROUGHT MONITOR IS THE
ONE-CLASS IMPROVEMENT (FROM D4 TO D3) ACROSS NORTHERN CALIFORNIA AND THE SAN
FRANCISCO AREA IN RESPONSE TO THE RECENT HEAVY RAINS IN THAT REGION.

FORECASTER: ANTHONY ARTUSA

$$




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