Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 271855
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT AUGUST 27 2014

SYNOPSIS: A BROAD AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO DEVELOP
ACROSS THE NORTHWESTERN U.S., WHILE A SUBTROPICAL RIDGE OF HIGH PRESSURE BUILDS
ACROSS THE SOUTHEASTERN U.S. BY THE END OF AUGUST. A STRONG COLD FRONT IS
EXPECTED TO CROSS THE NORTH-CENTRAL U.S. ON SUNDAY AND MONDAY. A PAIR OF WEAK
LOW PRESSURE SYSTEMS ARE EXPECTED TO AFFECT SOUTHERN ALASKA AND THE ALASKAN
PANHANDLE DURING THE NEXT TEN DAYS.

HAZARDS

LOCALLY HEAVY RAIN FOR PARTS OF THE GULF COAST AND SOUTHEAST, SAT, AUG 30.

HEAVY RAIN SHIFTING EAST FROM THE NORTHERN/CENTRAL GREAT PLAINS TO THE GREAT
LAKES, SUN-MON, AUG 31-SEP 1.

SEVERE WEATHER FOR PARTS OF THE NORTHERN/CENTRAL PLAINS AND UPPER MISSISSIPPI
VALLEY, SUN, AUG 31.

HEAVY RAIN FOR SOUTH TEXAS, TUE-WED, SEP 2-3.

RIVER FLOODING POSSIBLE ACROSS PARTS OF THE MIDWEST.

RIVER FLOODING IS OCCURRING, IMMINENT, OR LIKELY ACROSS THE MISSOURI RIVER
VALLEY.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, PACIFIC
NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR SATURDAY AUGUST 30 - WEDNESDAY SEPTEMBER 03: TROPICAL MOISTURE FROM THE
GULF OF MEXICO IS FORECAST TO BECOME ESTABLISHED FROM THE GULF COAST NORTH TO
THE TENNESSEE VALLEY BY SATURDAY. THIS TROPICAL MOISTURE IS EXPECTED TO
INTERACT WITH A WEAKENING FRONT AND BRING LOCALLY HEAVY RAIN TO PARTS OF THE
GULF COAST AND SOUTHEAST ON SATURDAY.



AFTER AN INITIAL SHORTWAVE TROUGH EXITS THE GREAT LAKES ON SATURDAY, A SECOND
AND MORE VIGOROUS SHORTWAVE TROUGH IS FORECAST TO REACH THE NORTH-CENTRAL GREAT
PLAINS BY SUNDAY. THIS SHORTWAVE TROUGH AND ANOMALOUS LOW-LEVEL MOISTURE ARE
LIKELY TO RESULT IN ANOTHER ROUND OF HEAVY RAINFALL (1 TO 3 INCHES, LOCALLY
MORE) ACROSS PARTS OF THE GREAT LAKES, UPPER MISSISSIPPI VALLEY, AND MIDWEST ON
SUNDAY AND MONDAY. DUE TO RECENT HEAVY RAINFALL, THIS REGION IS VULNERABLE TO
FLASH FLOODING AND RIVER FLOODING. INSTABILITY, LOW-LEVEL MOISTURE, AND SHEAR
ARE PREDICTED TO BE SUFFICIENT ENOUGH TO SUPPORT SEVERE THUNDERSTORMS FROM THE
NORTH-CENTRAL GREAT PLAINS EAST TO THE UPPER MISSISSIPPI VALLEY ON SUNDAY.



AN AMPLIFIED TROUGH IS EXPECTED TO BRING RELATIVELY COOL TEMPERATURES AND
MOSTLY LIGHT PRECIPITATION TO THE NORTHERN ROCKIES DURING THE LABOR DAY
WEEKEND. ACCUMULATING SNOW IS POSSIBLE AT ELEVATIONS ABOVE 9,000 FEET. MAXIMUM
TEMPERATURES ARE FORECAST TO AVERAGE AROUND 10 DEGREES F BELOW-NORMAL FROM
SUNDAY THROUGH NEXT TUESDAY ACROSS THE NORTHERN ROCKIES. ALTHOUGH MINIMUM
TEMPERATURES ARE FORECAST TO REMAIN ABOVE FREEZING ACROSS THE LOWER ELEVATIONS
OF THE NORTHERN HIGH PLAINS, FREEZING TEMPERATURES ARE EXPECTED ACROSS THE
HIGHER ELEVATIONS OF THE NORTHERN ROCKIES.



A TROPICAL WAVE OVER THE EASTERN CARIBBEAN IS EXPECTED TO PROGRESS INTO THE BAY
OF CAMPECHE BY EARLY NEXT WEEK. THE 0Z/6Z/12Z GFS AND 0Z CANADIAN MODELS
INDICATE SURFACE LOW DEVELOPMENT ACROSS THIS REGION. REGARDLESS OF ANY TROPICAL
CYCLONE DEVELOPMENT, THIS TROPICAL WAVE INCREASES THE POTENTIAL FOR HEAVY
RAINFALL ACROSS SOUTH TEXAS NEXT WEEK.



OCCASIONAL RAIN IS FORECAST TO AFFECT THE ALEUTIANS, SOUTHERN ALASKA, AND THE
ALASKAN PANHANDLE THROUGHOUT THIS PERIOD, WHILE SOME SNOW IS EXPECTED NORTH OF
THE BROOKS RANGE. RAIN AND SNOW AMOUNTS ARE LIKELY TO REMAIN BELOW HAZARDOUS
CRITERIA.

FOR THURSDAY SEPTEMBER 04 - WEDNESDAY SEPTEMBER 10: THE 0Z GFS AND 0Z ECMWF
ENSEMBLE MEANS INDICATE SMALL 500-HPA HEIGHT ANOMALIES THROUGHOUT THE CONUS, IN
PART DUE TO INCREASING SPREAD AMONG THEIR ENSEMBLE MEMBERS. NO TEMPERATURE OR
PRECIPITATION HAZARDS ARE EXPECTED AT THIS TIME, BUT THE POTENTIAL EXISTS FOR
HEAVY RAIN TO CONTINUE ACROSS SOUTH TEXAS.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED ON AUGUST 21, SHOWS THE
PERCENTAGE OF CONUS IN SEVERE TO EXCEPTIONAL DROUGHT DECREASING VERY SLIGHTLY
FROM 22.03% TO 21.62%.

FORECASTER: BRAD PUGH

$$



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