385  
FXUS21 KWNC 212005  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST FEBRUARY 21 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. DURING THE  
3-7 DAY PERIOD. UPPER-LEVEL LOW PRESSURE IS FORECAST OVER THE WESTERN U.S.  
DURING MUCH OF THE HAZARDS PERIOD. THE COOLER TEMPERATURES THAT ARE PREDICTED  
OVER THE WESTERN PART OF THE LOWER 48 STATES EARLIER IN THE PERIOD ARE  
ANTICIPATED TO SHIFT EASTWARD LATER IN WEEK-2, WHILE SOME MODERATION IN  
TEMPERATURES IS PREDICTED OVER THE WEST. ACTIVE WEATHER IS FORECAST OVER MUCH  
OF THE EXTENSIVE SOUTHERN COAST OF ALASKA DURING THE HAZARDS OUTLOOK PERIOD.  
 
HAZARDS  
 
SEVERE WEATHER ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE LOWER  
MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE TENNESSEE VALLEY, SAT, FEB 24.  
 
HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY TO THE OHIO VALLEY,  
SAT-SUN, FEB 24-FEB 25.  
 
HEAVY SNOW FROM THE CENTRAL PLAINS TO THE UPPER GREAT LAKES, SAT-SUN, FEB  
24-FEB 25.  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
TENNESSEE VALLEY, THE GREAT LAKES, THE MIDDLE MISSISSIPPI VALLEY, THE  
NORTHEAST, THE UPPER MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, AND THE OHIO  
VALLEY.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE GREAT LAKES AND THE  
SOUTHERN PLAINS.  
 
FLOODING LIKELY ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY, THE GREAT  
LAKES, THE OHIO VALLEY, THE UPPER MISSISSIPPI VALLEY, AND THE TENNESSEE VALLEY.  
 
MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHERN AND CENTRAL  
PLAINS, THE ROCKIES, GREAT BASIN, CALIFORNIA,THE PACIFIC NORTHWEST, AND THE  
SOUTHWEST, SAT-WED, FEB 24-FEB 28.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FROM THE WEST COAST, ACROSS THE  
GREAT BASIN, SOUTHWEST, AND THE ROCKIES TO THE NORTHERN AND CENTRAL PLAINS,  
THU-MON, MAR 1-MAR 7.  
 
MODERATE RISK OF MUCH BELOW NORMAL TEMERPATURES FROM THE WEST COAST, ACROSS THE  
GREAT BASIN, SOUTHWEST, AND THE NORTHERN ROCKIES TO THE NORTHERN PLAINS,  
THU-MON, MAR 1-MAR 5.  
 
HIGH RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHERN  
PLAINS, THE NORTHERN ROCKIES, AND THE NORTHERN GREAT BASIN, THU-SUN, MAR 1-MAR  
4.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE SOUTHERN ROCKIES, THE  
CENTRAL GREAT BASIN, CALIFORNIA, AND THE SOUTHWEST, THU-SAT, MAR 1-MAR 3.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE LOWER MISSISSIPPI  
VALLEY, THE TENNESSEE VALLEY, MAINLAND ALASKA, THE MIDDLE MISSISSIPPI VALLEY,  
THE SOUTHERN APPALACHIANS, THE SOUTHEAST, THE SOUTHERN PLAINS, AND THE OHIO  
VALLEY, THU-FRI, MAR 1-MAR 2.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL PLAINS, THE  
MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, AND THE NORTHERN  
PLAINS, FRI-SAT, MAR 2-MAR 3.  
 
MODERATE RISK OF HEAVY PRECIPITATION FOR PORTIONS OF MAINLAND ALASKA, THU-FRI,  
MAR 1-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 SATURDAY FEBRUARY 24 - WEDNESDAY FEBRUARY 28: AT THE START OF THE PERIOD, A  
VERY SLOW-MOVING FRONTAL SYSTEM IS FORECAST TO STRETCH FROM TEXAS NORTHEASTWARD  
TO THE NORTHEAST CONUS. HEAVY RAIN (1.5-2.0 INCHES OR GREATER IN 48 HOURS) IS  
LIKELY OVER MUCH OF THIS REGION. IN ADDITION, SEVERE WEATHER IS FORECAST IN THE  
WARM SECTOR FOR PARTS OF THE SOUTHERN PLAINS, LOWER MISSISSIPPI AND TENNESSEE  
VALLEYS ON SATURDAY, FEB 24. VERTICAL WIND SHEAR PROFILES APPEAR FAVORABLE FOR  
ORGANIZED SEVERE STORMS, THOUGH THE ANTICIPATED SEVERITY OF THIS  
 
OUTBREAK MAY BE SOMEWHAT OFFSET BY WEAK LAPSE RATES AND WIDESPREAD CLOUDINESS.  
 
THE GFS DEVELOPS THE STRONGEST SURFACE LOW ASSOCIATED WITH THIS FRONTAL  
BOUNDARY THIS WEEKEND, AND PRODUCES A SWATH OF HEAVY SNOW (6 INCHES OR GREATER)  
TO THE NORTHWEST OF THE STORM TRACK OVER THE UPPER MIDWEST, FEB 24-25. TODAY'S  
0Z DETERMINISTIC ECMWF RUN HAS COME INTO BETTER AGREEMENT WITH THE MOST RECENT  
(0Z AND 6Z) GFS SOLUTIONS TODAY, WARRANTING THE DESIGNATION OF A  
 
HEAVY SNOW HAZARD FROM THE CENTRAL PLAINS NORTHEASTWARD ACROSS THE UPPER  
MIDWEST.  
 
SNOW MELT AND HEAVY RAINFALL DURING THE PERIOD IN AREAS THAT HAVE FROZEN GROUND  
LEAD TO POSSIBLE, LIKELY, IMMINENT OR OCCURRING 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 24-28. UPPER-LEVEL SHORTWAVES  
ARE FORECAST TO CROSS THE NORTHWESTERN CONUS RESULTING IN PERIODS OF HEAVY SNOW  
(AMOUNTS IN EXCESS OF 6 INCHES IN 24 HOURS) FOR PARTS OF  
 
THE CASCADES, FEB 24-25.  
 
AN OCCLUDED FRONTAL SYSTEM IS EXPECTED TO TRACK FROM THE BERING SEA TO THE GULF  
OF ALASKA, FEB 24-25. HOWEVER, PREDICTED WIND SPEEDS ASSOCIATED WITH THIS  
SYSTEM DO NOT APPEAR TO JUSTIFY A WIND HAZARD ON THE MAP. THERE COULD BE STRONG  
GAP WINDS THROUGH THE SHELIKOF STRAIT (NEAR KODIAK) AND LOWER COOK INLET, FEB  
24-25, BUT THEY SHOULD BE FAIRLY LOCALIZED IN NATURE.  
 
FOR THURSDAY MARCH 01 - WEDNESDAY MARCH 07: THE 8-14 DAY TIME PERIOD IS LIKELY  
TO FEATURE A TROUGH OVER THE WESTERN CONUS, WHICH IS LIKELY TO SHED SOME ENERGY  
DOWNSTREAM. A SLIGHT RISK OVER HEAVY PRECIPITATION IS INDICATED FOR THE  
SOUTHWEST, PORTIONS OF THE GREAT BASIN, AND THE SIERRA NEVADAS, FOR MAR 1-3.  
WIDESPREAD PRECIPITATION AMOUNTS ARE NOT LIKELY TO EXCEED HAZARDOUS THRESHOLDS,  
BUT IN HIGHER TERRAIN AND IN WEST AND SOUTHWARD FACING SLOPES, LOCAL AMOUNTS  
ARE LIKELY TO EXCEED 2 INCHES OF LIQUID EQUIVALENT. MODELS ARE PROGRESSING  
SOME OF THAT ENERGY TO THE LOWER MISSISSIPPI VALLEY, WHILE OTHER MODEL  
SOLUTIONS FAVOR ARE MORE NORTHWARD EXCURSION. THEREFORE A SLIGHT RISK OF HEAVY  
PRECIPITATION IS INDICATED FROM EASTERN TEXAS TO TENNESSEE AND OHIO, AS WELL AS  
OVER THE UPPER MISSISSIPPI VALLEY. THE SIGNAL IS WEAK, BUT GIVEN THE RECENT  
FLOODING IN THE TENNESSEE VALLEY, AND PREDICTED FLOODING IN THE 3-7 DAY PERIOD,  
THE POTENTIAL FOR MORE DAMAGING FLOODS WARRANTS THE POSTING OF A HAZARD.  
 
A MEAN STORM TRACK IS FORECAST TO STEER STORMS INTO WESTERN ALASKA DURING THE  
EARLY PORTIONS OF WEEK-2. A MODERATE RISK OF HEAVY PRECIPITATION IS INDICATED  
AS MODEL FORECASTS DEPICT A SLUG OF MOISTURE MOVING ACROSS WESTERN ALASKA ON  
MAR 1-2.  
 
THE TROUGHING FORECAST OVER THE WESTERN CONUS SUPPORTS HAZARDS FOR MUCH BELOW  
NORMAL TEMPERATURES. A HIGH RISK IS DELINEATED FROM NORTHERN IDAHO TO WESTERN  
NEBRASKA FOR DAYS 8-11 (MAR 1-4), WHILE MODERATE (MAR 1-5) AND SLIGHT (MAR 1-7)  
RISKS ARE POSTED FROM THE GREAT PLAINS TO THE WEST COAST.  
 
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: ANTHONY ARTUSA  
 

 
 
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