Threats Assessment Discussion

191 
FXUS21 KWNC 191916
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EST JANUARY 19 2018
SYNOPSIS: A MODERATELY STRONG SURFACE LOW IS FORECAST TO TRACK FROM THE CENTRAL 
GREAT PLAINS TO THE GREAT LAKES AT THE BEGINNING OF THE PERIOD. AN AREA OF 
MID-LEVEL LOW PRESSURE IS EXPECTED TO MOVE INLAND INTO THE WESTERN U.S. DURING 
THE NEXT WEEK, WHILE A STRONG AREA OF MID-LEVEL HIGH PRESSURE BECOMES 
ESTABLISHED ACROSS THE CARIBBEAN AND SOUTHWEST ATLANTIC. A STRONG AREA OF 
MID-LEVEL HIGH PRESSURE, EXTENDING FROM THE NORTH PACIFIC TO THE BERING STRAIT, 
IS FORECAST TO PERSIST THROUGH THE END OF JANUARY.
HAZARDS
HEAVY SNOW SHIFTING NORTHEAST FROM THE CENTRAL GREAT PLAINS TO THE UPPER 
MISSISSIPPI VALLEY AND GREAT LAKES, MON-TUE, JAN 22-23.
HEAVY SNOW FOR NORTHERN NEW ENGLAND, MON-TUE, JAN 22-23.
HEAVY RAIN FOR NEW ENGLAND AND THE HUDSON VALLEY OF NEW YORK, MON-TUE, JAN 
22-23.
HEAVY SNOW FOR THE CASCADES, NORTHERN SIERRA NEVADA MOUNTAINS, AND PARTS OF THE 
NORTHERN AND CENTRAL ROCKIES, WED-THU, JAN 24-25.
HEAVY SNOW FOR PARTS OF THE NORTHERN AND CENTRAL ROCKIES, FRI, JAN 26.
HIGH WINDS SHIFTING EAST FROM THE DESERT SOUTHWEST TO THE CENTRAL AND SOUTHERN 
HIGH PLAINS, THU-FRI, JAN 25-26. 
MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF MAINLAND ALASKA, MON-FRI, JAN 22-26.
PERIODS OF HIGH WINDS FOR THE ALASKA PENINSULA, PARTS OF SOUTHERN COASTAL 
ALASKA, AND THE KENAI PENINSULA, MON-FRI, JAN 22-26.
A SLIGHT TO MODERATE RISK OF HEAVY PRECIPITATION FOR PARTS OF THE EASTERN AND 
CENTRAL U.S., SAT-MON, JAN 27-29. 
A SLIGHT RISK OF HEAVY PRECIPITATION FOR PARTS OF THE PACIFIC NORTHWEST AND 
NORTHERN ROCKIES, SAT-TUE, JAN 27-30.
A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR SOUTHWEST MAINLAND 
ALASKA, SAT-SUN, JAN 27-28.
A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF MAINLAND ALASKA, 
THE ALASKA PENINSULA, AND THE NORTHERN ALASKA PANHANDLE, SAT-FRI, JAN 27-FEB 2.
A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR THE NORTHERN GREAT PLAINS, 
WED-FRI, JAN 31-FEB 2.
SEVERE DROUGHT FOR PARTS OF THE GREAT PLAINS, SOUTHWEST, MIDDLE AND LOWER 
MISSISSIPPI VALLEY, AND SOUTHEAST.
DETAILED SUMMARY
FOR MONDAY JANUARY 22 - FRIDAY JANUARY 26: A MAJOR WINTER STORM IS LIKELY TO 
IMPACT AREAS FROM THE CENTRAL GREAT PLAINS NORTHEAST TO THE UPPER MISSISSIPPI 
VALLEY AND GREAT LAKES ON JAN 22 AND 23. THE DETERMINISTIC 6Z/12Z GFS AND 0Z 
ECMWF MODELS ARE IN EXCELLENT AGREEMENT WITH THE TRACK OF A 996-HPA SURFACE LOW 
FROM NEAR KANSAS CITY ON MONDAY MORNING TO LAKE HURON BY TUESDAY MORNING. HEAVY 
SNOW IS LIKELY ALONG AND TO THE NORTHWEST OF THE SURFACE LOW TRACK. THE 
HEAVIEST SNOW (6 TO 12 INCHES, OR MORE) IS EXPECTED TO EXTEND FROM SIOUX CITY, 
IOWA NORTHEAST TO THE MINNEAPOLIS AREA. 
WARM AIR ADVECTION, AHEAD OF THE LOW PRESSURE SYSTEM ACROSS THE MIDWEST, IS 
FORECAST TO SUPPORT HEAVY SNOW (TOTAL AMOUNTS OF 4 TO 8 INCHES) ACROSS NORTHERN 
NEW ENGLAND ON JAN 22 AND 23. HEAVY RAIN (1 TO 1.5 INCHES) IS EXPECTED IN THE 
WARMER LOW-LEVEL AIR ACROSS NEW ENGLAND AND THE HUDSON RIVER VALLEY OF NEW 
YORK. HEAVY RAIN, SNOW MELT, AND ICE JAMS CONTINUE TO MAINTAIN FLOODING 
CONCERNS IN THESE AREAS.
AN AMPLIFYING 500-HPA TROUGH IS FORECAST TO ENTER THE WESTERN U.S. DURING 
MID-WEEK. HEAVY SNOW IS EXPECTED TO BE THE MAJOR PRECIPITATION HAZARD DUE TO 
DECREASING 500-HPA HEIGHTS AND LOWERING SNOW LEVELS WITH TIME. BASED ON 
REASONABLY GOOD AGREEMENT AMONG THE DETERMINISTIC MODEL RUNS WITH THE TIMING 
AND AMPLITUDE OF THE 500-HPA TROUGH, HEAVY SNOW (6 INCHES OR MORE PER 24 HOURS) 
IS FORECAST TO SHIFT FROM THE CASCADES AND NORTHERN SIERRA NEVADA MOUNTAINS ON 
JAN 24 TO THE NORTH-CENTRAL ROCKIES ON JAN 26. HEAVY SNOW MAY RETURN TO THE 
CENTRAL GREAT PLAINS BY JAN 26, BUT UNCERTAINTY EXISTS ON WHEN A SHORTWAVE 
TROUGH EJECTS FROM THE WESTERN U.S. THE DETERMINISTIC 0Z ECMWF ON JAN 19 
INDICATES 850-HPA TEMPERATURES FALLING TO -6 DEGREES C ACROSS THE PACIFIC 
NORTHWEST BY JAN 25 WHICH WOULD SUPPORT SNOW LEVELS DECREASING TO THE FOOTHILLS 
IN WESTERN OREGON. 
HIGH WINDS (ABOVE 40 MPH) ARE LIKELY TO ACCOMPANY THE AMPLIFYING 500-HPA TROUGH 
ACROSS THE SOUTHWESTERN U.S. ON JAN 25 AND 26. SOIL MOISTURE IS CURRENTLY IN 
THE LOWEST 10TH PERCENTILE ACROSS PARTS OF THE FOUR CORNERS REGION. THE GUSTY 
WINDS COMBINED WITH VERY LOW SOIL MOISTURE INCREASES THE RISK FOR BLOWING DUST 
FROM THE SOUTHWEST EAST TO THE CENTRAL AND SOUTHERN HIGH PLAINS. 
MUCH COLDER TEMPERATURES ARE LIKELY TO OVERSPREAD MAINLAND ALASKA BY JAN 22 AS 
AN AMPLIFIED 500-HPA RIDGE BECOMES ESTABLISHED OVER THE BERING SEA AND AN 
ANOMALOUS NORTHEAST SURFACE LOW DEVELOPS. MUCH BELOW-NORMAL TEMPERATURES ARE 
FORECAST THROUGHOUT MUCH OF MAINLAND ALASKA FROM JAN 22-26 WITH THE LARGEST 
NEGATIVE ANOMALIES OF MORE THAN -30 DEGREES F FORECAST ACROSS SOUTHWEST 
MAINLAND ALASKA. A 1044-HPA SURFACE HIGH NEAR THE BERING STRAIT COUPLED WITH 
SURFACE LOW PRESSURE OF MODERATE STRENGTH OVER THE GULF ALASKA IS EXPECTED TO 
PROMOTE PERIODS OF HIGH WINDS (SPEEDS OF 40 MPH OR MORE) ACROSS THE ALASKA 
PENINSULA AND KENAI PENINSULA. 
FOR SATURDAY JANUARY 27 - FRIDAY FEBRUARY 02: THE HIGHLY AMPLIFIED 500-HPA 
RIDGE OVER THE BERING SEA AND ANOMALOUS NORTHEAST SURFACE FLOW ACROSS MAINLAND 
ALASKA ARE EXPECTED TO PERSIST INTO THE WEEK-2 PERIOD. THEREFORE, A SLIGHT RISK 
OF MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR MAINLAND ALASKA, THE ALASKA 
PENINSULA, AND THE NORTHERN ALASKA PANHANDLE, LASTING INTO THE BEGINNING OF 
FEBRUARY. ON JAN 27 AND 28, A MODERATE RISK OF MUCH BELOW-NORMAL TEMPERATURES 
IS POSTED FOR SOUTHWEST MAINLAND ALASKA WHERE THE GFS ENSEMBLE MEANS INDICATE 
LARGE NEGATIVE TEMPERATURE ANOMALIES. MODEL GUIDANCE INDICATES THAT THE 
BITTERLY COLD TEMPERATURES OVER THE HIGHEST LATITUDES OF WESTERN NORTH AMERICA 
MAY BEGIN TO SHIFT SOUTHEAST BY THE END OF JANUARY. THEREFORE, A SLIGHT RISK OF 
MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR THE NORTHERN GREAT PLAINS FROM JAN 
31-FEB 2.
THE EVOLVING LONGWAVE PATTERN WITH THE LIKELIHOOD OF ABOVE-NORMAL TEMPERATURES 
ACROSS THE EASTERN U.S. DURING LATE JANUARY IS CONSISTENT WITH THE RECENT 
EASTWARD PROPAGATION OF THE ENHANCED PHASE OF THE MADDEN-JULIAN OSCILLATION 
(MJO) FROM THE INDIAN OCEAN TO THE MARITIME CONTINENT. THE STRENGTHENING 
SUBTROPICAL RIDGE OVER THE CARIBBEAN IS EXPECTED TO RESULT IN ANOMALOUS 
LOW-LEVEL MOISTURE ACROSS THE EASTERN HALF OF THE CONTINENTAL U.S. EARLY IN 
WEEK-2. GIVEN THE EXPECTATION THAT A SHORTWAVE TROUGH EJECTS FROM THE WESTERN 
U.S., THERE IS A MODERATE RISK OF HEAVY PRECIPITATION FROM THE MISSISSIPPI 
VALLEY TO THE EAST COAST FROM JAN 27 TO 29. A BROADER AREA OF A SLIGHT RISK IS 
HIGHLIGHTED FURTHER WESTWARD. INCREASING INSTABILITY MAY SUPPORT SEVERE 
THUNDERSTORMS ACROSS THE GULF COAST STATES AND SOUTHEAST DURING THIS TIME 
PERIOD. A SLIGHT RISK OF HEAVY PRECIPITATION, MOST LIKELY IN THE FORM OF SNOW, 
IS POSTED FROM THE CENTRAL GREAT PLAINS TO THE UPPER MISSISSIPPI VALLEY AND 
GREAT LAKES FROM JAN 27 TO 29, AS ANOTHER WINTER STORM MAY AFFECT THESE AREAS. 
PERSISTENT, ONSHORE FLOW RESULTS IN A SLIGHT RISK OF HEAVY PRECIPITATION (RAIN 
AND HIGH-ELEVATION) FOR THE PACIFIC NORTHWEST AND NORTHERN ROCKIES FROM JAN 27 
TO 30.
THE U.S. DROUGHT MONITOR, VALID ON JANUARY 16, 2018 INDICATES AN INCREASE IN 
THE COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 8.70% LAST WEEK TO 
10.03% THIS WEEK. SEVERE DROUGHT CONTINUED TO EXPAND ACROSS THE SOUTHERN GREAT 
PLAINS WITH NEARLY HALF OF OKLAHOMA DESIGNATED WITH SEVERE DROUGHT.
FORECASTER: BRAD PUGH 
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