217  
FXUS21 KWNC 212015  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT APRIL 21 2017  
 
SYNOPSIS: AN ACTIVE STORM TRACK IS FORECAST FROM THE PACIFIC NORTHWEST TO THE  
CENTRAL PLAINS AND TO THE NORTHEAST. THEREFORE, MULTIPLE LOW-PRESSURE SYSTEMS  
ARE FORECAST TO TRAVERSE THE PACIFIC NORTHWEST AND GREAT PLAINS DURING THE  
FIRST PORTION OF THE OUTLOOK PERIOD. THE FOCUS OF THE ACTIVE WEATHER DURING THE  
LATTER PORTION OF THE OUTLOOK PERIOD REMAINS IN THE GREAT PLAINS. SOUTHERN  
ALASKA LOOKS TO BECOME WETTER WHILE THE PACIFIC NORTHWEST IS LIKELY TO  
EXPERIENCE A BREAK IN ACTIVE WEATHER. NO WEATHER HAZARDS ARE LIKELY OVER ALASKA  
DURING THE ENTIRE PERIOD, DESPITE THE SHIFT TOWARD WETTER WEATHER IN WEEK-2.  
 
HAZARDS  
 
SEVERE WEATHER ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE SOUTHERN PLAINS,  
FRI, APR 28.  
 
HEAVY PRECIPITATION ACROSS PORTIONS OF THE PACIFIC NORTHWEST AND THE NORTHERN  
GREAT BASIN, MON-WED, APR 24-APR 26.  
 
HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA AND THE PACIFIC NORTHWEST, MON-WED,  
APR 24-APR 26.  
 
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY,  
THE NORTHERN PLAINS, THE GREAT LAKES, THE CENTRAL ROCKIES, THE MIDDLE  
MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS,  
WED-THU, APR 26-APR 27.  
 
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI  
VALLEY, THE SOUTHERN PLAINS, AND THE UPPER MISSISSIPPI VALLEY, FRI, APR 28.  
 
HEAVY RAIN ACROSS PORTIONS OF THE NORTHEAST, TUE, APR 25.  
 
HEAVY RAIN ACROSS PORTIONS OF THE MID-ATLANTIC, MON, APR 24.  
 
HEAVY SNOW ACROSS PORTIONS OF THE NORTHERN ROCKIES AND THE NORTHERN GREAT  
BASIN, MON-TUE, APR 24-APR 25.  
 
HEAVY SNOW ACROSS PORTIONS OF THE CENTRAL ROCKIES, WED-THU, APR 26-APR 27.  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI  
VALLEY, THE SOUTHERN PLAINS, THE OHIO VALLEY, AND THE UPPER MISSISSIPPI VALLEY.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE NORTHERN PLAINS AND THE  
NORTHERN GREAT BASIN.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI VALLEY.  
 
FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI  
VALLEY, THE LOWER MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS.  
 
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI VALLEY,  
THE TENNESSEE VALLEY, THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHEAST, THE  
SOUTHERN PLAINS, AND THE OHIO VALLEY, SAT-SUN, APR 29-APR 30.  
 
HIGH WINDS ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE SOUTHERN PLAINS, THE  
SOUTHWEST, THE CENTRAL GREAT BASIN, AND THE CENTRAL ROCKIES, MON-FRI, APR  
24-APR 28.  
 
HIGH WINDS ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE CENTRAL PLAINS, THE  
SOUTHERN PLAINS, AND THE NORTHERN PLAINS, MON, APR 24.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE  
SOUTHERN PLAINS, AND THE SOUTHWEST, TUE-WED, APR 25-APR 26.  
 
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE SOUTHERN APPALACHIANS,  
THE GREAT LAKES, THE MID-ATLANTIC, THE CENTRAL APPALACHIANS, AND THE OHIO  
VALLEY, THU-FRI, APR 27-APR 28.  
 
SLIGHT RISK OF MUCH BELOW NORMAL TEMPERATURES FOR PORTIONS OF THE CENTRAL  
PLAINS, THE CENTRAL ROCKIES, THE CENTRAL GREAT BASIN, THE NORTHERN PLAINS, THE  
SOUTHERN PLAINS, MAINLAND ALASKA, THE NORTHERN GREAT BASIN, THE SOUTHERN  
ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, CALIFORNIA, THE NORTHERN ROCKIES, THE  
UPPER MISSISSIPPI VALLEY, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, SAT-SUN,  
APR 29-APR 30.  
 
SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHERN  
PLAINS, SAT-SUN, APR 29-APR 30.  
 
MODERATE RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHERN  
PLAINS, SAT-SUN, APR 29-APR 30.  
 
SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE SOUTHEAST AND  
THE TENNESSEE VALLEY, SAT-TUE, APR 29-MAY 2.  
 
SLIGHT RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST,  
THE CENTRAL APPALACHIANS, THE TENNESSEE VALLEY, THE MID-ATLANTIC, THE GREAT  
LAKES, AND THE OHIO VALLEY, SAT-MON, APR 29-MAY 1.  
 
MODERATE RISK OF MUCH ABOVE NORMAL TEMPERATURES FOR PORTIONS OF THE NORTHEAST,  
THE CENTRAL APPALACHIANS, THE SOUTHERN PLAINS, THE MID-ATLANTIC, THE GREAT  
LAKES, AND THE OHIO VALLEY, SAT-SUN, APR 29-APR 30.  
 
SEVERE DROUGHT ACROSS THE LOWER MISSISSIPPI VALLEY, THE TENNESSEE VALLEY,  
HAWAII, THE NORTHEAST, CALIFORNIA, THE SOUTHEAST, THE SOUTHERN APPALACHIANS,  
THE SOUTHERN PLAINS, AND THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR MONDAY APRIL 24 - FRIDAY APRIL 28: A LOW-PRESSURE SYSTEM IS FORECAST TO  
MOVE ACROSS THE SOUTHEAST AT THE START OF THE PERIOD, BEFORE MOVING TOWARD THE  
NORTHEAST. HEAVY RAINS ARE LIKELY OVER THE CAROLINAS (APPROXIMATELY 2 INCHES IN  
24 HOURS), THEN OVER THE NORTHEAST (2-3 INCHES IN 24 HOURS), APRIL 24-25.  
 
A STRONG LOW-PRESSURE SYSTEM IS FORECAST TO MOVE FROM THE NORTHERN GREAT PLAINS  
ON MONDAY, APR 24, TO THE NORTHEAST BY APR 27, WITH THE ASSOCIATED COLD FRONT  
MOVING SOUTHWARD TO THE SOUTHERN PLAINS. THIS LOW-PRESSURE SYSTEM IS LIKELY TO  
SUPPORT HIGH WINDS (GREATER THAN 35 MPH, SUSTAINED) ACROSS THE GREAT PLAINS  
EARLY IN THE PERIOD.  
 
WITH AN ACTIVE STORM TRACK INTO THE PACIFIC NORTHWEST, HEAVY RAIN IS EXPECTED  
AT LOWER ELEVATIONS, WHILE HIGHER ELEVATIONS ARE LIKELY TO EXPERIENCE  
FLUCTUATING SNOW LEVELS, APRIL 24-26. AS THE SYSTEMS MOVE EASTWARD, SOME AREAS  
OF HEAVY SNOW (6 INCHES IN 24 HOURS) ARE LIKELY IN THE NORTHERN ROCKIES AND  
COLORADO.  
 
A MID-LEVEL SHORTWAVE IS FORECAST TO MOVE SOUTHWARD FROM THE PACIFIC NORTHWEST  
TO THE CENTRAL GREAT PLAINS ON WED, APR 26. THE SHORTWAVE AND REMNANT COLD  
FRONT, ALONG WITH STRONG SOUTHERLY FLOW EAST OF THE FRONT, ARE LIKELY TO  
SUPPORT HEAVY RAINS (2 INCHES IN 24 HOURS, WITH LOCALLY HIGHER AMOUNTS WHERE  
STRONGER THUNDERSTORMS OCCUR) ACROSS THE GREAT PLAINS AND MIDWEST. AS THE  
MID-LEVEL SHORTWAVE AND ATTENDANT SURFACE LOW-PRESSURE SYSTEM DEEPEN, THEY ARE  
LIKELY TO SUPPORT SEVERE WEATHER FOR THE CENTRAL AND SOUTHERN GREAT PLAINS AND  
MORE HEAVY RAIN FOR THE MISSISSIPPI VALLEY, APRIL 28.  
 
SOUTH OF THE ACTIVE STORM TRACK, WARM AND WINDY CONDITIONS ARE LIKELY ACROSS  
MUCH OF THE SOUTHWEST AND TEXAS. HIGH WINDS (GREATER THAN 35 MPH, SUSTAINED)  
ARE LIKELY OVER THE SOUTHWEST (APRIL 24-28), WHILE TEMPERATURES 12 DEGREES  
ABOVE NORMAL ARE POSSIBLE OVER WESTERN TEXAS AND NEW MEXICO (APRIL 25-26). EAST  
OF THE ACTIVE WEATHER OVER THE GREAT PLAINS, TEMPERATURES ARE EXPECTED TO BE  
ABOVE NORMAL OVER THE OHIO VALLEY AND MID-ATLANTIC. DAILY MAXIMUM TEMPERATURES  
ARE LIKELY TO APPROACH 90 DEG F, WITH ISOLATED, TRADITIONALLY WARMER AREAS  
SURPASSING 90 DEG F ON APR 28.  
 
FOR SATURDAY APRIL 29 - FRIDAY MAY 05: MODEL GUIDANCE REMAINS CONSISTENT WITH  
ITS FORECAST OF AN UPPER-LEVEL TROUGH CENTERED OVER THE WEST-CENTRAL U.S. AT  
THE BEGINNING OF WEEK-2. THE POSITION AND AMPLITUDE OF THIS UPPER-LEVEL TROUGH  
COUPLED WITH ENHANCED MOISTURE RETURN FROM THE GULF OF MEXICO SIGNAL AN  
INCREASING RISK OF HEAVY RAINFALL (1 TO 2 INCHES, LOCALLY MORE) AND THE  
POTENTIAL FOR SEVERE THUNDERSTORMS ACROSS THE CENTRAL U.S. ON APRIL 29-30. THE  
OUTLINED HAZARD AREA FOR HEAVY RAINFALL IS BASED ON 48-HOUR PRECIPITATION  
AMOUNTS FROM THE DETERMINISTIC 0/6Z GFS AND 0Z ECMWF MODELS AND THEIR ENSEMBLE  
MEANS WHICH ARE IN GOOD AGREEMENT FOR DAYS 8 AND 9 AS WELL AS THE GEFS  
REFORECAST TOOL. THE GEFS REFORECAST TOOL INDICATES INCREASED CHANCES FOR  
POTENTIAL HEAVY RAIN SHIFTING EASTWARD FROM THE SOUTHERN PLAINS, THOUGH MODEL  
DISAGREEMENT BEGINS TO INCREASE BY DAY 9. MODELS SHOW THE TROUGH BECOMING LESS  
AMPLIFIED TOWARD THE MIDDLE OF WEEK-2. THIS REGION WILL BE MONITORED IN THE  
UPCOMING DAYS. THIS TROUGH ALSO SUPPORTS A SLIGHT RISK OF MUCH BELOW NORMAL  
TEMPERATURES ACROSS PARTS OF THE WESTERN HALF OF THE CONUS APRIL 29 TO 30. THE  
HIGHLIGHTED AREA INDICATES AT LEAST A 20 PERCENT CHANCE OF FREEZING  
TEMPERATURES WHICH COULD HAVE AN IMPACT TO SENSITIVE VEGETATION.  
 
DOWNSTREAM OF THE AMPLIFIED MID-LEVEL TROUGH, AMPLIFIED MID-LEVEL RIDGING IS  
EXPECTED TO BUILD ACROSS THE EASTERN HALF OF THE CONUS. THIS PATTERN SUPPORTS A  
SLIGHT TO MODERATE CHANCE OF MUCH ABOVE NORMAL TEMPERATURES ACROSS THE SOUTHERN  
PLAINS APRIL 29 TO 30. FURTHER EAST, TEMPERATURES ACROSS THE SOUTHEAST ARE  
LIKELY TO EXCEED THE 85TH PERCENTILE, WITH DAILY MAXIMUM TEMPERATURES REACHING  
90 DEG F OR GREATER. ACROSS THE GREAT LAKES, MID-ATLANTIC, AND NORTHEAST,  
TEMPERATURES ARE LIKELY TO BE MUCH ABOVE NORMAL, WITH ISOLATED PORTIONS OF THE  
MID-ATLANTIC APPROACHING 90 DEG F.  
 
SURFACE HIGH PRESSURE IS PREDICTED TO DEVELOP ACROSS NORTHERN MAINLAND ALASKA  
FROM THE BEGINNING OF WEEK-2 UNTIL AT LEAST THE MIDDLE OF WEEK-2. THIS SUPPORTS  
A SLIGHT CHANCE OF MUCH BELOW NORMAL TEMPERATURES ACROSS THE NORTH SLOPE OF  
ALASKA AND THE NORTHWEST COAST OF ALASKA APRIL 29 TO 30. THE GEFS REFORECAST  
TOOL INDICATES THE POTENTIAL FOR THIS AREA EXPERIENCING MINIMUM TEMPERATURES  
REACHING THE LOWEST 15TH PERCENTILE AND LESS THAN ZERO DEGREES F.  
 
ACCORDING TO THE U.S. DROUGHT MONITOR RELEASED ON APRIL 20TH (USING DATA  
THROUGH 8AM EASTERN TIME, APRIL 18TH), COVERAGE OF SEVERE, OR GREATER  
INTENSITY, DROUGHT THROUGHOUT THE CONUS REMAINS THE SAME AS LAST WEEK (1.44  
PERCENT). THIS REMAINS THE LOWEST COVERAGE OF D2-D4 DROUGHT OVER THE CONUS  
SINCE AUG 2010.  
 
FORECASTER: MATTHEW ROSENCRANS  
 

 
 
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