Threats Assessment Discussion

257 
FXUS21 KWNC 221953
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT JUNE 22 2017
SYNOPSIS: A COLD FRONT IS PREDICTED TO STRETCH ACROSS THE SOUTHERN TIER OF THE 
LOWER 48 STATES AT THE BEGINNING OF THE PERIOD, EVOLVING INTO A STATIONARY 
FRONT ACROSS FLORIDA ON JUNE 28TH. MEANWHILE, SURFACE LOW PRESSURE IS EXPECTED 
TO DOMINATE MOST OF THE WESTERN THIRD OF THE CONTIGUOUS U.S. DURING THE 3 TO 7 
DAY PERIOD. SURFACE LOW PRESSURE IS ANTICIPATED TO DEVELOP OVER THE BERING SEA 
AND GULF OF ALASKA DURING THE 3 TO 7 DAY PERIOD. SOUTHERLY FLOW ASSOCIATED WITH 
SURFACE LOW PRESSURE MAY BRING UNSETTLED WEATHER TO THE KENAI PENINSULA BY THE 
END OF THE 3 TO 7 DAY PERIOD.
HAZARDS
HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN ROCKIES AND SOUTHERN PLAINS, CENTRAL 
AND WESTERN GULF COAST, AND COASTAL PARTS OF THE SOUTHEAST AND SOUTHERN 
MID-ATLANTIC, SUN-MON, JUN 25-JUN 26.
MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE GREAT BASIN, THE PACIFIC 
NORTHWEST, AND  THE NORTHERN ROCKIES, SUN-MON, JUN 25-JUN 26.
EXCESSIVE HEAT ACROSS PORTIONS OF THE DESERT SOUTHWEST, SUN-TUE, JUN 25-JUN 27.
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI 
VALLEY, AND THE UPPER MISSISSIPPI VALLEY, WED-THU, JUN 28-JUN 29.
HEAVY RAIN ACROSS COASTAL PORTIONS OF THE KENAI PENINSULA, WED-THU, JUN 28-JUN 
29.
FLOODING POSSIBLE ACROSS PORTIONS OF THE CENTRAL PLAINS, THE LOWER MISSISSIPPI 
VALLEY, THE CENTRAL APPALACHIANS, THE NORTHERN PLAINS, THE TENNESSEE VALLEY, 
THE MIDDLE MISSISSIPPI VALLEY, THE SOUTHERN APPALACHIANS, THE UPPER MISSISSIPPI 
VALLEY, THE SOUTHEAST, THE GREAT LAKES, AND THE OHIO VALLEY.
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST AND THE 
NORTHERN GREAT BASIN.
FLOODING LIKELY ACROSS PORTIONS OF THE CENTRAL ROCKIES, THE SOUTHEAST, THE 
LOWER MISSISSIPPI VALLEY, THE CENTRAL GREAT BASIN, AND THE NORTHERN ROCKIES.
SEVERE DROUGHT ACROSS CALIFORNIA, HAWAII, THE NORTHERN PLAINS, AND THE 
SOUTHWEST.
HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS, THE SOUTHERN PLAINS, THE 
MIDDLE MISSISSIPPI VALLEY, THE UPPER MISSISSIPPI VALLEY, THE GREAT LAKES, AND 
THE OHIO VALLEY, FRI-SUN, JUN 30-JUL 2.
DETAILED SUMMARY
FOR SUNDAY JUNE 25 - THURSDAY JUNE 29: ON JUN 25, A FRONTAL SYSTEM IS EXPECTED 
TO STRETCH FROM ALONG COASTAL SECTIONS OF THE SOUTHERN TIER OF THE CONUS FROM 
THE MID-ATLANTIC TO THE SOUTHWEST. THIS WILL SERVE TO ACT AS A FOCUSING 
MECHANISM FOR SHOWERS AND THUNDERSTORMS. HEAVY RAIN IS ANTICIPATED FOR PARTS OF 
THE CENTRAL AND WESTERN GULF COAST JUNE 25 TO 26. SURFACE TROUGHING ACROSS THE 
SOUTHWEST IS ALSO EXPECTED TO SUPPORT STRONG MOIST SOUTHERLY FLOW, BRINGING 
HEAVY RAINFALL TO THE SOUTHERN ROCKIES AND SOUTHERN PLAINS JUNE 25 AND 26. IN 
ADDITION, MOISTURE ASSOCIATED WITH THE REMNANTS OF TROPICAL SYSTEM CINDY ARE 
FORECAST TO INTERACT WITH THE FRONTAL SYSTEM LEADING TO HEAVY RAIN FOR COASTAL 
PORTIONS OF THE SOUTHEAST AND SOUTHERN MID-ATLANTIC JUNE 25 TO 26. AS THE FRONT 
MOVES SOUTHEASTWARD AND STALLS OVER THE FLORIDA PENINSULA JUN 27, HEAVY RAIN IS 
POSSIBLE FOR PARTS OF THE STATE. HOWEVER, DUE TO SIGNIFICANT MODEL UNCERTAINTY 
REGARDING THE AMOUNT OF RAINFALL, AN ADDITIONAL HEAVY RAIN HAZARD IS NOT 
INCLUDED AT THIS TIME. RAINFALL AMOUNTS IN EXCESS OF 1 INCH IN 24 HOURS ARE 
POSSIBLE FOR THE AFOREMENTIONED AREAS.
HEAT-RELATED HAZARDS CONTINUE TO BE FORECAST ACROSS PARTS OF THE WESTERN THIRD 
OF THE CONUS DURING THE 3-7 DAY PERIOD, DUE IN PART TO SUBSIDENCE ASSOCIATED 
WITH 500-HPA RIDGING THAT IS ANTICIPATED OVER THE WESTERN CONUS. MUCH ABOVE 
NORMAL TEMPERATURES (POSITIVE ANOMALIES OF 16-20 DEGREES F) ARE EXPECTED FOR 
PARTS OF THE GREAT BASIN, THE PACIFIC NORTHWEST, AND THE NORTHERN ROCKIES, JUN 
25-26. MAXIMUM TEMPERATURES ARE EXPECTED TO BE IN THE TRIPLE DIGITS ACROSS 
PARTS OF WESTERN OREGON AND SOUTHERN WASHINGTON. EXCESSIVE HEAT (HEAT INDEX 
VALUES ABOVE 105 F) IS FORECAST ACROSS PORTIONS OF THE SOUTHWEST JUN 25-27. 
SURFACE LOW PRESSURE IS PREDICTED TO FORM ACROSS A FRONTAL BOUNDARY STRETCHING 
FROM THE NORTHERN PLAINS SOUTHWESTWARD TO THE SOUTHWEST BY JUNE 29. AS THIS 
STORM MOVES EASTWARD, PARTS OF THE CENTRAL PLAINS, THE MIDDLE MISSISSIPPI 
VALLEY, AND THE UPPER MISSISSIPPI VALLEY MAY RECEIVE HEAVY RAINFALL (1.5 INCHES 
OR GREATER IN 24-HOURS) JUNE 28 TO 29.
A SURFACE LOW IS ANTICIPATED TO FORM OVER THE GULF OF ALASKA BY JUNE 28. STRONG 
ONSHORE FLOW ASSOCIATED WITH THIS SYSTEM MAY SUPPORT HEAVY RAINFALL ACROSS 
COASTAL PORTIONS OF THE KENAI PENINSULA JUNE 28 TO 29. LOCALIZED AREAS MAY 
RECEIVE UP TO 2 INCHES OF RAINFALL IN A 24-HOUR PERIOD. BESIDES THIS FEATURE, 
ALASKA IS FORECAST TO BE RELATIVELY WARM AND DRY THROUGHOUT BOTH WEEKS WITH 
HIGH PRESSURE FORECAST TO THE SOUTH OF THE STATE AND MID-LEVEL RIDGING IN THE 
GULF OF ALASKA. THIS SCENARIO SUGGESTS INCREASED RISKS FOR FIRE ACTIVITY FOR 
THE STATE WHICH BEAR MONITORING THROUGHOUT THE PERIOD, DESPITE SOME INITIALLY 
MOIST CONDITIONS FROM ANTECEDENT RAINS ACROSS THE INTERIOR.
FOR FRIDAY JUNE 30 - THURSDAY JULY 06: THE AFOREMENTIONED SURFACE LOW PRESSURE 
ALONG A FRONTAL BOUNDARY ACROSS CENTRAL CONUS FROM THE 3 TO 7 DAY PERIOD IS 
EXPECTED TO MOVE EASTWARD ACROSS THE CONUS INTO THE BEGINNING TO MIDDLE OF 
WEEK-2. PASSAGE OF THIS COLD FRONT MAY BRING HEAVY RAINFALL TO PARTS OF THE 
CENTRAL PLAINS, THE SOUTHERN PLAINS, THE MIDDLE MISSISSIPPI VALLEY, THE UPPER 
MISSISSIPPI VALLEY, THE GREAT LAKES, AND THE OHIO VALLEY JUNE 30 TO JULY 2. THE 
GEFS REFORECAST TOOL INDICATES A 20% CHANCE OR GREATER OF RAINFALL REACHING THE 
85TH PERCENTILE OF ACCUMULATED 3-DAY PRECIPITATION COMPARED TO CLIMATOLOGY IN 
HIGHLIGHTED AREAS. THE GEFS SHOWS THE GREATEST CHANCE FOR HEAVY RAINFALL OVER 
THE UPPER MISSISSIPPI VALLEY AND UPPER GREAT LAKES, WHEREAS THE ECMWF ENSEMBLE 
INDICATES THE AXIS OF HEAVY RAINFALL SHIFTED SOUTHEASTWARD, MAINLY ACROSS THE 
MIDDLE MISSISSIPPI VALLEY. THE HIGHLIGHTED HEAVY RAINFALL AREA INCORPORATES A 
BROAD RISK AREA TAKING INTO ACCOUNT THESE MODEL DIFFERENCES. BEYOND THIS 
POSSIBLE AREA OF UNSETTLED WEATHER, A MOSTLY ZONAL FLOW PATTERN IS FORECAST 
ACROSS MOST OF THE CONUS DURING THE WEEK-2 PERIOD, WITH WEAK TROUGHS OVER THE 
NORTHEAST, WESTERN CONUS AND ALEUTIANS, AND A WEAK RIDGE OVER THE INTERIOR 
WESTERN CONUS.
THE U.S. DROUGHT MONITOR RELEASED ON JUNE 22ND SHOWS D2-D4 DROUGHT COVERAGE 
OVER THE CONUS NOW AT 2.13%, A SLIGHT INCREASE FROM 1.57% ONE WEEK AGO.
FORECASTER: MELISSA OU 
$$