Prognostic Meteorological Discussion
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FXUS21 KWNC 271939
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 27 2016

SYNOPSIS: A WEAKENING COLD FRONT IS EXPECTED TO MOVE OFF THE GULF AND ATLANTIC
COASTS EARLY IN THE OUTLOOK PERIOD. BROAD LOW PRESSURE AT THE SURFACE AND
ALOFT, ASSOCIATED WITH THE COLD FRONT, IS FORECAST TO LINGER OVER THE OHIO
VALLEY BEFORE FINALLY LIFTING OUT TO THE NORTH THIS SUNDAY. ANOTHER COLD FRONT
IS PREDICTED TO MOVE ACROSS THE WESTERN AND INTO THE CENTRAL CONTIGUOUS U.S.
DURING THIS SAME PERIOD. IN THE ALASKA DOMAIN, SEVERAL FRONTAL SYSTEMS ARE
ANTICIPATED TO AFFECT THE WESTERN PORTION OF THE STATE DURING THE FIRST HALF OF
THE OUTLOOK PERIOD. A WELL-ORGANIZED TROPICAL WAVE CURRENTLY ABOUT 350 MILES
AWAY FROM THE WINDWARD ISLANDS CONTINUES TO MOVE WEST-NORTHWEST. THIS SYSTEM
MAY HAVE A SIGNIFICANT IMPACT ON THE SOUTHEAST CONUS EARLY NEXT WEEK.

HAZARDS

LINGERING HEAVY RAIN FROM OHIO TO PENNSYLVANIA, FRI, SEP 30.

HEAVY RAIN FOR SOUTHWESTERN ALASKA, SAT-SUN, OCT 1-2.

FLOODING IS LIKELY, IMMINENT, OR OCCURRING IN PORTIONS OF THE MIDWEST, AND
SOUTHERN TEXAS.

SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE WEST-CENTRAL
CONUS, WED-THU, OCT 5-6.

SEVERE DROUGHT ACROSS PARTS OF THE EASTERN CONUS, MISSOURI RIVER VALLEY, GREAT
PLAINS, NORTHERN ROCKIES, INTERMOUNTAIN WEST, ARIZONA, CALIFORNIA, AND HAWAII.

DETAILED SUMMARY

FOR FRIDAY SEPTEMBER 30 - TUESDAY OCTOBER 04: A PRONOUNCED CUT-OFF LOW AT
500-HPA IS FORECAST TO BRING CLOUDY AND COOL CONDITIONS TO AREAS PRIMARILY EAST
OF THE MISSISSIPPI RIVER, AT LEAST INTO SUNDAY, OCT 2. BY THEN, THE CUT-OFF LOW
IS PREDICTED TO WEAKEN AND LIFT NORTHWARD INTO SOUTHERN QUEBEC. AT THE SURFACE,
A COLD FRONT IS EXPECTED TO PUSH OFF THE ATLANTIC AND GULF COASTS EARLY IN THE
PERIOD, THOUGH ASSOCIATED LOW PRESSURE (AND ATTENDANT CLOUDINESS) OVER THE OHIO
VALLEY AND MID-ATLANTIC IS PREDICTED TO LINGER ACROSS THIS REGION FOR SEVERAL
MORE DAYS. THOUGH MOST OF THE PRECIPITATION IS EXPECTED TO FALL PRIOR TO THE
BEGINNING OF THE HAZARDS PERIOD, THERE IS STILL THE POSSIBILITY OF HEAVY RAIN
CONTINUING ACROSS PORTIONS OF OHIO AND PENNSYLVANIA ON FRIDAY, SEP 30. THE COLD
FRONT IS FORECAST TO GET AS FAR SOUTH AS CENTRAL OR SOUTHERN FLORIDA BEFORE
STALLING, ENHANCING THE CHANCES FOR SHOWERS AND THUNDERSTORMS IN THAT AREA FROM
OCT 2-3.



A TROPICAL WAVE 350 MILES EAST OF THE WINDWARD ISLANDS (AS OF 2PM EDT 9/27) IS
PREDICTED TO CONTINUE ITS WEST-NORTHWEST HEADING TOWARDS THE SOUTHERN PORTION
OF THE CARIBBEAN SEA. A TRACK THIS FAR SOUTH IS UNUSUAL. THEN THE TRACK OF THIS
SYSTEM BECOMES HIGHLY UNCERTAIN, WITH THE ECMWF TAKING THE SYSTEM OVER WESTERN
CUBA OR THE YUCATAN CHANNEL, AND THE GFS AND CANADIAN MODELS RECURVING IT A BIT
EARLIER OVER/NEAR HAITI. MUCH WILL DEPEND ON THE EXACT EVOLUTION OF THE
UPPER-TROPOSPHERIC FLOW PATTERN ACROSS THE GULF OF MEXICO AND WESTERN
CARIBBEAN. AT THIS TIME, IT IS RECOMMENDED THAT RESIDENTS OF CENTRAL AND
SOUTHERN FLORIDA KEEP AN EYE ON THIS SYSTEM, WHICH THE NATIONAL HURRICANE
CENTER PREDICTS HAS A 90 PERCENT CHANCE OF DEVELOPING INTO A TROPICAL CYCLONE
IN THE NEXT 5-DAYS.



FLOODING IS LIKELY, IMMINENT, OR OCCURRING IN PORTIONS OF THE MIDWEST AND
SOUTHERN TEXAS FROM SEP 30-OCT 2. THIS IS PRIMARILY DUE TO RAIN THAT RECENTLY
FELL ACROSS THESE AREAS.



A CYCLONIC SYSTEM IS PREDICTED TO BRING HEAVY RAIN (2 INCHES OR GREATER) TO
SOUTHWESTERN ALASKA ON OCT 1-2. THE DETERMINISTIC 0Z ECMWF AND 6Z GFS RUNS
FORECAST IN EXCESS OF 4 INCHES DURING THIS PERIOD ACROSS THE VICINITY OF THE
EASTERN ALASKA PENINSULA.

FOR WEDNESDAY OCTOBER 05 - TUESDAY OCTOBER 11: THERE IS A SLIGHT (20 PERCENT)
CHANCE OF MUCH BELOW-NORMAL TEMPERATURES (AT OR BELOW THE 15TH PERCENTILE OF
THE HISTORICAL TEMPERATURE DISTRIBUTION) ACROSS MUCH OF THE WEST-CENTRAL CONUS
ON OCT 5-6, IN ASSOCIATION WITH A STRONG 500-HPA TROUGH. AT THE HIGHEST
ELEVATIONS, TEMPERATURES ARE EXPECTED TO BE COLD ENOUGH TO SUPPORT SNOW.



ACCORDING TO THE LATEST U.S. DROUGHT MONITOR (USDM) VALID ON SEPTEMBER 20, THE
COVERAGE OF SEVERE OR GREATER DROUGHT (FOR THE CONUS) INCREASED VERY SLIGHTLY
FROM 7.72 TO 7.76 PERCENT DURING THE PAST WEEK.  LESS THAN 1 PERCENT OF THE
HAWAIIAN ISLANDS IS DESIGNATED WITH SEVERE DROUGHT.

FORECASTER: ANTHONY ARTUSA

$$



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