379  
FXUS21 KWNC 201852  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT APRIL 20 2018  
 
SYNOPSIS: THE 3-7 DAY PERIOD IS LIKELY TO BEGIN WITH MID-LEVEL LOW PRESSURE  
OVER THE SOUTHEAST, SUPPORTING A STRONG STORM SYSTEM WHICH IS FORECAST TO  
IMPACT THE EAST COAST. THE TEMPERATURE PATTERNS IN WEEK-2 ARE EXPECTED TO  
BECOME MORE MODERATE COMPARED TO PAST FEW WEEKS. MID -LEVEL HIGH PRESSURE IS  
LIKELY OVER MUCH OF THE CONUS, MINIMIZING CHANCES FOR HIGH IMPACT EVENTS. TWO  
SURFACE LOW PRESSURE SYSTEMS ARE EXPECTED TO IMPACT THE ALEUTIANS AND SOUTHERN  
COAST OF ALASKA, LEADING TO A FAIRLY ACTIVE 3-7 DAY PERIOD FOR THE REGION.  
MID-LEVEL LOW PRESSURE IS FORECAST TO WEAKEN OVER ALASKA FOR WEEK-2.  
 
HAZARDS  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE NORTHERN PLAINS.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY  
AND THE NORTHERN PLAINS.  
 
FLOODING LIKELY ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY AND THE  
NORTHERN PLAINS.  
 
HIGH WINDS ACROSS PORTIONS OF THE SOUTHEAST AND THE MID-ATLANTIC, MON-TUE, APR  
23-APR 24.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND  
ALASKA, MON-TUE, APR 23-APR 24.  
 
HIGH WINDS ACROSS PORTIONS OF THE ALASKA PANHANDLE AND MAINLAND ALASKA, MON,  
APR 23.  
 
HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS, MON-WED, APR  
23-APR 25.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF MAINLAND ALASKA AND THE  
ALEUTIANS, MON-WED, APR 23-APR 25.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE CENTRAL  
GREAT BASIN, THE NORTHERN PLAINS, THE SOUTHERN ROCKIES, CALIFORNIA, THE  
SOUTHEAST, THE SOUTHERN PLAINS, AND THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR MONDAY APRIL 23 - FRIDAY APRIL 27: AT THE BEGINNING OF THIS PERIOD, A  
STRONG LOW PRESSURE SYSTEM WILL BE MOVING NORTHWARD OUT OF THE SOUTHEAST ALONG  
THE EAST COAST, AFTER IMPACTING THE LOWER MISSISSIPPI VALLEY PRIOR TO THIS  
PERIOD. HEAVY RAIN (GREATER THAN 1.5 INCH IN 24 HOURS) IS FORECAST ALONG THE  
SOUTHEAST AND INTO THE MID-ATLANTIC FOR APR 23-24, WITH THE SOUTHERN  
APPALACHIANS MOST LIKELY TO RECEIVE UP TO 4 INCHES. MODEL GUIDANCE SHOWS THIS  
SYSTEM TRACKING ALONG THE COAST LONGER THAN PREVIOUSLY EXPECTED, SO THE  
AFFECTED AREA REACHES FURTHER NORTH THAN IN PRIOR FORECASTS. COASTAL REGIONS  
ARE ALSO FORECAST TO EXPERIENCE HIGH WINDS (GREATER THAN 30 KNOTS), APR 23-24.  
A SECOND STORM SYSTEM IS EXPECTED TO MOVE SOUTHEASTWARD OUT OF THE GREAT LAKES  
REGION IMMEDIATELY AFTER, POSSIBLY BRINGING MORE RAIN TO THE MID-ATLANTIC;  
HOWEVER, RAINFALL TOTALS FOR THAT SYSTEM ARE LIKELY TO REMAIN BELOW 1 INCH.  
 
THE REST OF THE PERIOD LOOKS RELATIVELY QUIET FOR THE MAJORITY OF THE LOWER 48.  
A FRONTAL SYSTEM IS LIKELY TO MOVE OVER THE CENTRAL U.S. DURING THE BEGINNING  
OF THE PERIOD, THOUGH ALL IMPACTS FROM THE SYSTEM ARE FORECAST TO REMAIN BELOW  
HAZARDOUS CRITERIA AT THIS TIME. SURFACE HIGH PRESSURE MOVING SOUTHWARD FROM  
CANADA IS EXPECTED RESULT IN A DRIER PATTERN FOR MUCH OF THE CENTRAL AND  
EASTERN CONUS.  
 
MID-LEVEL TROUGHING IS FORECAST TO MOVE OVER ALASKA DURING THE 3-7 DAY PERIOD,  
LIKELY SUPPORTING AN UNSETTLED PATTERN FOR THE REGION. AT THE BEGINNING OF THE  
PERIOD, SURFACE LOW PRESSURE IN THE GULF OF ALASKA IS FORECAST TO BRING HEAVY  
PRECIPITATION (GREATER THAN 2 INCHES PER 24 HOURS) ON APR 23-24 TO THE  
SOUTHEASTERN ALASKA COAST AND PARTS OF THE PANHANDLE. MOST OF THIS  
PRECIPITATION IS EXPECTED TO FALL AS RAIN, THOUGH SNOW IS POSSIBLE FOR AREAS AT  
HIGHER ELEVATIONS. HIGH WINDS ARE EXPECTED TO ACCOMPANY THE HEAVY PRECIPITATION  
ALONG THE COAST FOR APR 23. THE OTHER STRONG SURFACE LOW PRESSURE SYSTEM (976  
HPA) IN THE BERING SEA IS FORECAST TO MOVE EASTWARD ACROSS THE ALEUTIANS AND  
PARTS OF MAINLAND ALASKA. THE ALEUTIANS ARE LIKELY TO EXPERIENCE HIGH WINDS AND  
SIGNIFICANT WAVE HEIGHTS (EXCEEDING 20 FEET) AS THE SYSTEM MOVES THROUGH, APR  
23-25.  
 
FOR SATURDAY APRIL 28 - FRIDAY MAY 04: MID-LEVEL RIDGING AND A MORE ZONAL  
PATTERN LIMIT THE RISK OF IN HIGH IMPACT EVENTS FOR THE LOWER 48 IN WEEK-2.  
MODEL GUIDANCE DOES SHOW AGREEMENT IN A CLOSED LOW PRESSURE SYSTEM MOVING  
INLAND FROM THE WESTERN COAST TOWARD THE MIDDLE OF WEEK-2, WHICH COULD CAUSE  
SOME UNSETTLED PATTERNS FOR THE WESTERN HALF OF THE US. HOWEVER, SPREAD IN  
ENSEMBLE MEMBERS BETWEEN THE GFS AND ECMWF SHOWS UNCERTAINTY OF THE PLACEMENT  
OF THIS SYSTEM AS IT TRACKS ACROSS THE CONUS, PRECLUDING A FORECAST FOR ANY  
ASSOCIATED HAZARDS AT THIS TIME.  
 
THE MID-LEVEL PATTERN IS EXPECTED TO DEAMPLIFY FOR WEEK-2 OVER ALASKA, LEADING  
TO LESS STORMINESS FOR THE REGION. NO HAZARDS ARE CURRENTLY POSTED FOR WEEK-2  
IN ALASKA.  
 
THE US DROUGHT MONITOR, VALID ON APRIL 17, SHOWS A 1 CLASS IMPROVEMENT IN  
DROUGHT COVERAGE OVER THE NORTHERN PLAINS. THERE WAS DEGRADATION IN DROUGHT  
CONDITIONS OVER PARTS OF THE FOUR CORNERS REGION. OVERALL, THE SEVERE DROUGHT  
COVERAGE DURING THE PAST WEEK HAS SLIGHTLY DECREASED TO 16.33% FROM 16.69% LAST  
WEEK.  
 
FORECASTER: CHRISTINA FINAN  
 

 
 
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