364  
FXUS21 KWNC 202222  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST FEBRUARY 20 2018  
 
SYNOPSIS: A NEARLY STATIONARY FRONTAL BOUNDARY IS EXPECTED TO SERVE AS A FOCAL  
POINT FOR HAZARDOUS WEATHER ACROSS PARTS OF THE EAST-CENTRAL U.S. AT THE START  
OF THE PERIOD. UPPER-LEVEL LOW PRESSURE IS FORECAST OVER THE WESTERN U.S.  
DURING MUCH OF THE PERIOD. A COOLER WEATHER PATTERN IS LIKELY TO EVOLVE OVER  
MUCH OF THE EASTERN U.S. BY THE END OF THE PERIOD. ACTIVE WEATHER IS FORECAST  
OVER PARTS OF SOUTHERN ALASKA AND THE ALEUTIANS EARLY IN WEEK-1.  
 
HAZARDS  
 
HEAVY RAIN ACROSS PORTIONS OF THE LOWER AND MIDDLE MISSISSIPPI VALLEY, THE  
CENTRAL AND SOUTHERN APPALACHIANS, THE TENNESSEE VALLEY, THE GREAT LAKES, THE  
MID-ATLANTIC, THE SOUTHERN PLAINS, AND THE OHIO VALLEY, FRI-SAT, FEB 23-FEB 24.  
 
HEAVY SNOW ACROSS PORTIONS OF THE CASCADES, FRI-MON, FEB 23-FEB 26.  
 
SEVERE WEATHER ACROSS PORTIONS OF THE SOUTHEAST, THE MIDDLE AND LOWER  
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE TENNESSEE VALLEY, SAT, FEB 24.  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE LOWER AND MIDDLE MISSISSIPPI VALLEY,  
THE TENNESSEE VALLEY, THE SOUTHERN PLAINS, THE NORTHEAST, THE GREAT LAKES, AND  
THE OHIO VALLEY.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE OHIO VALLEY.  
 
FLOODING LIKELY ACROSS PORTIONS OF THE MIDDLE AND UPPER MISSISSIPPI VALLEY, THE  
GREAT LAKES, AND THE OHIO VALLEY.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE CENTRAL AND NOTHERN  
PLAINS, THE ROCKIES, AND THE WESTERN U.S., FRI-TUE, FEB 23-FEB 27.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND ALASKA, FRI,  
FEB 23.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS, FRI-SUN, FEB  
23-FEB 25.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE ALEUTIANS, FRI-MON,  
FEB 23-FEB 26.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL AND  
WESTERN U.S., WED-TUE, FEB 28-MAR 6.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL AND  
NORTHERN PLAINS, THE GREAT BASIN, THE ROCKIES, AND THE WESTERN U.S., WED-MON,  
FEB 28-MAR 5.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN  
PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN, WED-SUN, FEB 28-MAR  
4.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL GREAT BASIN,  
CALIFORNIA, AND THE SOUTHWEST, WED-SAT, FEB 28-MAR 3.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHEAST, THE LOWER  
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE TENNESSEE VALLEY, WED-FRI, FEB  
28-MAR 2.  
 
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF CALIFORNIA, THU-FRI, MAR  
1-MAR 2.  
 
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI  
VALLEY AND THE SOUTHERN PLAINS, WED-FRI, FEB 28-MAR 2.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE LOWER  
MISSISSIPPI VALLEY, THE CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE SOUTHERN  
ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, CALIFORNIA, THE SOUTHERN PLAINS, AND  
THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR FRIDAY FEBRUARY 23 - TUESDAY FEBRUARY 27: AT THE START OF THE PERIOD, A  
VERY SLOW MOVING FRONTAL SYSTEM IS FORECAST TO STRETCH FROM EAST TEXAS  
NORTHEASTWARD TO THE GREAT LAKES. HEAVY RAIN (AMOUNTS IN EXCESS OF 2 INCHES IN  
48 HOURS) IS LIKELY OVER MUCH OF THIS REGION. PEAK TWO-DAY RAINFALL TOTALS IN  
EXCESS OF 4 INCHES ARE LIKELY IN SOME FAVORED REGIONS. IN ADDITION, SEVERE  
WEATHER IS FORECAST IN THE WARM SECTOR FOR PARTS OF THE SOUTHERN PLAINS, AND  
LOWER MISSISSIPPI AND TENNESSEE VALLEYS ON SUNDAY.  
 
THE GFS DEVELOPS THE STRONGEST SURFACE LOW ASSOCIATED WITH THIS FRONTAL  
BOUNDARY THIS WEEKEND, AND PRODUCES A SWATH OF HEAVY SNOW TO THE NORTHWEST OF  
THE STORM TRACK OVER THE UPPER MIDWEST. THE 12Z CANADIAN AND ECMWF  
DETERMINISTIC RUNS EACH DEPICT A MUCH WEAKER SOLUTION, AND SO NO HAZARD IS  
DEPICTED AT THIS TIME.  
 
SNOW MELT AND HEAVY RAINFALL DURING THE PERIOD ON AREAS THAT HAVE FROZEN GROUND  
LEAD TO POSSIBLE AND LIKELY RIVER FLOODING ACROSS PORTIONS OF THE SOUTHERN  
PLAINS, MISSISSIPPI VALLEY, THE OHIO VALLEY AND GREAT LAKES.  
 
UPPER-LEVEL LOW PRESSURE AND AREAS OF SURFACE HIGH PRESSURE RESULT IN PERIODS  
OF MUCH-BELOW NORMAL TEMPERATURES (NEGATIVE ANOMALIES OF 15-25 DEGREES F) FOR  
MUCH OF THE WESTERN AND NORTH-CENTRAL CONUS FEB 23-27. UPPER-LEVEL SHORTWAVES  
ARE FORECAST TO CROSS THE NORTHWEST CONUS RESULTING IN PERIODS OF HEAVY SNOW  
(AMOUNTS IN EXCESS OF 6 INCHES IN 24 HOURS) FOR PARTS OF THE CASCADES FEB 23-26.  
 
STRONG OFFSHORE WINDS (SPEEDS IN EXCESS OF 40 KNOTS) ARE FORECAST FOR PARTS OF  
THE ALASKA PENINSULA, SOUTHWESTERN AND SOUTH COASTAL MAINLAND ALASKA, KODIAK  
ISLAND, AND THE KENAI PENINSULA FEB 23. A SERIES OF FRONTAL SYSTEMS CROSSING  
THE ALEUTIANS LEADS TO PERIODS OF HIGH WINDS (SPEEDS IN EXCESS OF 40 KNOTS) FEB  
23-25, AND HIGH SIGNIFICANT WAVE HEIGHTS (IN EXCESS OF 20 FEET) FEB 23-26.  
 
FOR WEDNESDAY FEBRUARY 28 - TUESDAY MARCH 06: THE WEEK-2 MID-LEVEL FLOW PATTERN  
ACROSS THE FORECAST DOMAIN IS EXPECTED TO UNDERGO SIGNIFICANT CHANGES FROM THE  
EARLY PERIOD, LARGELY DUE TO THE EVOLUTION OF A STRONG DOWNSTREAM BLOCKING  
PATTERN FORECAST OVER THE DAVIS STRAIT. UPSTREAM RIDGING IS FORECAST TO REMAIN  
IN PLACE OVER THE NORTH PACIFIC DURING WEEK-2, WITH DOWNSTREAM TROUGHING OVER  
WESTERN NORTH AMERICA. THIS LEADS TO MUCH BELOW NORMAL TEMPERATURES BEING  
FAVORED OVER MUCH OF THE WESTERN CONUS DURING WEEK-2, WITH TEMPERATURES OVER  
THE EASTERN CONUS TRANSITIONING TOWARD A MUCH COLDER PATTERN RELATIVE TO NORMAL  
BY THE END OF WEEK-2.  
 
THE TROUGH OVER THE WESTERN CONUS LEADS TO AN ENHANCED RISK OF HEAVY  
PRECIPITATION OVER CALIFORNIA AND PARTS OF THE SOUTHWEST EARLY IN WEEK-2. A  
MODERATE RISK IS INDICATED FOR COASTAL CALIFORNIA ON DAYS 9-10, MAR 1-2.  
FARTHER EAST, DYNAMICAL MODEL GUIDANCE IS IN GOOD AGREEMENT ON A MODERATE RISK  
OF HEAVY RAIN FOR PARTS OF THE SOUTHERN PLAINS AND LOWER MISSISSIPPI VALLEY ON  
DAYS 8-10, FEB 28-MAR 2.  
 
 
 
THE U.S. DROUGHT MONITOR, VALID ON FEB 13, 2018 INDICATES A SLIGHT DECREASE IN  
THE COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 18.44% LAST WEEK TO  
18.04% THIS WEEK. A FEW OF THE MORE SUBSTANTIAL REVISIONS MADE TO THE MAP THIS  
WEEK INCLUDE AN INCREASE IN D2 COVERAGE ACROSS SOUTHERN CALIFORNIA, THE  
ELIMINATION OF ALL D2 AREAS ACROSS THE GULF COAST STATES FROM LOUISIANA TO  
FLORIDA, AND SIGNIFICANT 1-CATEGORY IMPROVEMENTS RENDERED ACROSS THE CAROLINAS,  
MID-ATLANTIC, AND NORTHEAST.  
 
FORECASTER: STEPHEN BAXTER  
 

 
 
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