909  
FXUS21 KWNC 212243  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EDT JUNE 21 2018  
 
SYNOPSIS: A BROAD AREA OF HIGH PRESSURE ALOFT IS EXPECTED TO PERSIST OVER THE  
LOWER 48 THROUGHOUT MUCH OF THE NEXT TWO WEEKS. FRONTAL ACTIVITY IS LIKELY OVER  
THE CENTRAL AND EASTERN U.S. IN THE 3-7 DAY PERIOD, WITH POSSIBLE EXTENSION  
INTO WEEK-2. EXCESSIVE HEAT IS FORECAST TO BE A CONCERN FOR MANY PARTS OF THE  
LOWER 48 STATES THROUGHOUT THE 3 TO 7 DAY AND WEEK-2 PERIOD. FOR ALASKA,  
PRECIPITATION IS EXPECTED THROUGHOUT THE 3 TO 7 DAY PERIOD ASSOCIATED WITH  
MID-LEVEL LOW PRESSURE, THOUGH LIKELY WILL NOT BE HAZARDOUS.  
 
HAZARDS  
 
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL CONUS, SUN-TUE, JUN 24-JUN 26.  
 
HEAVY RAIN ACROSS COASTAL PORTIONS OF THE CAROLINAS, MON, JUN 25.  
 
EXCESSIVE HEAT ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL GREAT BASIN, THE  
PACIFIC NORTHWEST, AND THE NORTHERN GREAT BASIN, SUN, JUN 24.  
 
EXCESSIVE HEAT ACROSS PORTIONS OF THE SOUTHWEST, SUN, JUN 24.  
 
EXCESSIVE HEAT ACROSS PORTIONS OF THE EASTERN HALF OF THE CONUS, SUN-THU, JUN  
24-JUN 28.  
 
HIGH WINDS ACROSS PORTIONS OF THE CENTRAL PLAINS AND THE SOUTHERN PLAINS,  
SUN-MON, JUN 24-JUN 25.  
 
FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI  
VALLEY, THE GREAT LAKES, THE OHIO VALLEY, AND THE UPPER MISSISSIPPI VALLEY.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE UPPER MISSISSIPPI VALLEY,  
THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN PLAINS, THE NORTHERN PLAINS, AND  
THE NORTHERN ROCKIES.  
 
FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL PLAINS, THE CENTRAL GREAT BASIN,  
THE NORTHERN PLAINS, THE NORTHERN ROCKIES, THE CENTRAL ROCKIES, THE MIDDLE  
MISSISSIPPI VALLEY, AND THE UPPER MISSISSIPPI VALLEY.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE CENTRAL  
GREAT BASIN, THE NORTHERN PLAINS, THE NORTHERN GREAT BASIN, THE SOUTHERN  
ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, CALIFORNIA, THE SOUTHERN PLAINS, AND  
THE SOUTHWEST.  
 
SLIGHT RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE DESERT SOUTHWEST, FRI-THU,  
JUN 29-JUL 5.  
 
SLIGHT RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE EASTERN QUARTER OF THE CONUS,  
FRI-THU, JUN 29-JUL 5.  
 
MODERATE RISK OF EXCESSIVE HEAT ACROSS PARTS OF THE GREAT LAKES, OHIO VALLEY,  
NORTHEAST, AND MID-ATLANTIC, FRI-SUN, JUN 29-JUL 1.  
 
SLIGHT RISK OF HEAVY PRECIPITATION FOR PORTIONS OF THE CENTRAL PLAINS, THE  
MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, AND THE GREAT LAKES,  
FRI-SUN, JUN 29-JUL 1.  
 
DETAILED SUMMARY  
 
FOR SUNDAY JUNE 24 - THURSDAY JUNE 28: 500-HPA RIDGING IS ANTICIPATED ACROSS  
THE WESTERN THIRD OF THE CONUS AT THE BEGINNING OF THE PERIOD, INCREASING  
CHANCES FOR EXCESSIVE HEAT ACROSS THE DESERT SOUTHWEST (MAXIMUM TEMPERATURES  
REACHING 90S DEG F OR GREATER) AND CALIFORNIA, THE CENTRAL GREAT BASIN, THE  
PACIFIC NORTHWEST, AND THE NORTHERN GREAT BASIN (MAXIMUM TEMPERATURES REACHING  
MID 100S DEG F), JUNE 24. THE MID-LEVEL RIDGE IS EXPECTED TO FLATTEN  
THEREAFTER, PROVIDING A RESPITE FROM THE HEAT. MODERATE TO STRONG MID-LEVEL  
WINDS MIXING TO THE SURFACE COMBINED WITH ARID CONDITIONS, MAY INCREASE  
WILDFIRE RISK ACROSS PARTS OF THE SOUTHWEST JUNE 24. THE STORM PREDICTION  
CENTER HAS HIGHLIGHTED A 40% CHANCE OF CRITICAL FIRE WEATHER IN THIS AREA FOR  
JUNE 24.  
 
A SERIES OF FRONTAL BOUNDARIES ARE EXPECTED TO PERSIST THROUGH THE 3-7 DAY  
PERIOD OVER THE EASTERN AND CENTRAL CONUS. THESE FRONTS ARE FORECAST TO  
PROGRESS SOUTHEASTWARD THROUGHOUT THE 3 TO 7 DAY PERIOD, BRINGING HEAVY RAIN TO  
PARTS OF THE CENTRAL CONUS JUNE 24 TO 26 AND COASTAL PARTS OF THE CAROLINAS  
JUNE 25. LOCALIZED AREAS WITHIN THE PARTS HIGHLIGHTED MAY RECEIVE 2 INCHES OR  
GREATER OF RAINFALL IN A 24-HOUR PERIOD.  
 
MID-LEVEL RIDGING IS EXPECTED TO DOMINATE THE EASTERN HALF OF THE CONUS DURING  
THE 3 TO 7 DAY PERIOD, AS WELL AS WEEK-2. THIS PATTERN FAVORS INCREASED CHANCES  
FOR EXCESSIVE HEAT, INITIALLY ACROSS THE SOUTHEASTERN QUARTER OF THE CONUS JUNE  
24 TO 26, SHIFTING NORTHWESTWARD TO THE MISSISSIPPI, OHIO, AND TENNESSEE  
VALLEYS, JUNE 27 TO 28. LOCALIZED AREAS HIGHLIGHTED MAY EXPERIENCE HEAT INDEX  
VALUES REACHING 110 DEG F OR GREATER.  
 
A SURFACE TROUGH IS PREDICTED TO FORM ACROSS THE GREAT PLAINS FROM THE  
BEGINNING TO MIDDLE OF THE 3 TO 7 DAY PERIOD. THIS PATTERN MAY SUPPORT  
INCREASED CHANCES FOR HIGH WINDS ACROSS PARTS OF PORTIONS OF THE CENTRAL PLAINS  
AND THE SOUTHERN PLAINS, JUNE 24 TO 25. SOME AREAS MAY EXPERIENCE SUSTAINED  
WINDS REACHING 30 KNOTS OR GREATER.  
 
WIDESPREAD MID-LEVEL TROUGHING IS EXPECTED FOR ALASKA THROUGH THE 3 TO 7 DAY  
PERIOD. SEVERAL SURFACE LOW PRESSURE SYSTEMS ARE FORECAST TO MOVE OVER THE  
MAINLAND AND PARTS OF THE SOUTHERN COAST; HOWEVER, ALL IMPACTS FROM THESE  
SYSTEMS ARE CURRENTLY FORECAST TO REMAIN BELOW HAZARDOUS CRITERIA.  
 
FOR FRIDAY JUNE 29 - THURSDAY JULY 05: AMPLIFIED MID-LEVEL RIDGING IS FORECAST  
TO PERSIST FROM THE 3 TO 7 DAY PERIOD THROUGHOUT MOST OF WEEK-2, SUPPORTING  
MANY AREAS OF INCREASED RISK OF EXCESSIVE HEAT. A SLIGHT RISK FOR EXCESSIVE  
HEAT IS HIGHLIGHTED ACROSS PARTS OF THE NORTHEASTERN QUARTER OF THE CONUS  
THROUGHOUT WEEK-2, AS WELL AS A MODERATE AREA ACROSS THE NORTHEAST AND GREAT  
LAKES, EXCLUDING PARTS OF THE APPALACHIANS, JUNE 29 TO JULY 1. SOME AREAS MAY  
EXPERIENCE HEAT VALUES REACHING 100 DEG F, IN THE UPPER 90TH PERCENTILE,  
COMPARED TO CLIMATOLOGY.  
 
A SURFACE LOW IS ANTICIPATED TO FORM OVER THE CENTRAL PLAINS AND INTO THE  
MISSISSIPPI RIVER VALLEY, ALONG THE FRONTAL BOUNDARY FROM THE 3 TO 7 DAY  
PERIOD. THE GEFS REFORECAST TOOL HIGHLIGHTS A SLIGHT RISK FOR HEAVY  
PRECIPITATION AREA FURTHER SOUTH ACROSS THE MIDDLE AND LOWER MISSISSIPPI  
VALLEY, WHEREAS THE ECMWF REFORECAST TOOL SHOWS INCREASED CHANCES OVER THE  
UPPER AND MIDDLE MISSISSIPPI VALLEY. THERE IS THEREFORE, SIGNIFICANT  
UNCERTAINTY REGARDING SPECIFIC REGIONS WITH THE GREATEST RISK. A BROAD AREA IS  
HIGHLIGHTED THAT INCORPORATES MAIN AREAS OF OVERLAP BETWEEN THE TWO MODEL  
GUIDANCE TOOLS.  
 
THE OVERALL WEEK-2 PATTERN FOR ALASKA IS PREDICTED TO BE DOMINATED BY NEAR TO  
ABOVE NORMAL 500-HPA HEIGHTS. NO HAZARDS ARE EXPECTED FOR ALASKA AT THIS TIME.  
 
THE US DROUGHT MONITOR, VALID ON JUNE 19, INDICATES THAT THE COVERAGE OF SEVERE  
TO EXCEPTIONAL DROUGHT DECREASED SLIGHTLY FROM 16.97 PERCENT TO 16.54.  
EXCEPTIONAL DROUGHT REMAINS ENTRENCHED OVER THE FOUR CORNERS REGION. SOME  
IMPROVEMENT IN CONDITIONS IS SEEN IN THE OKLAHOMA PANHANDLE AND INTO  
SOUTHWESTERN KANSAS.  
 
FORECASTER: MELISSA OU  
 

 
 
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