Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 291824
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 29 2016

SYNOPSIS: AN AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO WEAKEN AS IT
PROGRESSES SLOWLY NORTH INTO SOUTHEAST CANADA EARLY IN THE PERIOD. A STRONG
AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST TO ENTER THE WESTERN U.S. THIS
WEEKEND, RESULTING IN A COLD FRONT PUSHING EAST ACROSS THE GREAT PLAINS TO THE
MISSISSIPPI VALLEY ON OCTOBER 4 AND 5. AN AREA OF UPPER-LEVEL HIGH PRESSURE IS
FORECAST TO PERSIST ACROSS MAINLAND ALASKA THROUGH THE EARLY PART OF WEEK-2.
HURRICANE MATTHEW, CURRENTLY OVER THE EASTERN CARIBBEAN SEA, IS FORECAST TO
STRENGTHEN AND TURN NORTH DURING THE NEXT FIVE DAYS AND COULD EVENTUALLY RESULT
IN MULTIPLE HAZARDS ALONG THE EAST COAST.

HAZARDS

SEVERE WEATHER FOR PARTS OF THE CENTRAL AND SOUTHERN GREAT PLAINS, TUE, OCT 4.

HEAVY RAIN FOR THE NORTHERN HIGH PLAINS, MON-TUE, OCT 3-4.

HEAVY SNOW AT THE HIGHER ELEVATIONS OF WYOMING, MON-TUE, OCT 3-4.

HIGH WINDS FOR PARTS OF THE WESTERN AND CENTRAL U.S., MON-TUE, OCT 3-4.

HIGH WINDS AND SIGNIFICANT WAVES FOR PARTS OF THE EAST COAST, TUE-THU, OCT 4-6.

FLOODING IS OCCURRING ACROSS PARTS OF THE MIDWEST AND SOUTH TEXAS, WITH
POSSIBLE FLOODING FOR PARTS OF THE MID-ATLANTIC.

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

DETAILED SUMMARY

FOR SUNDAY OCTOBER 02 - THURSDAY OCTOBER 06: THE CLOSED 500-HPA LOW, INITIALLY
CENTERED OVER THE OHIO VALLEY AND CENTRAL APPALACHIANS, IS FORECAST TO
GRADUALLY FILL AS IT MOVES NORTH INTO SOUTHEAST CANADA. RAINFALL INTENSITY OVER
THE EASTERN U.S. IS LIKELY DECREASE IN TIME, BUT RIVER FLOODING MAY LINGER INTO
THE BEGINNING OF THIS PERIOD ACROSS PARTS OF THE MID-ATLANTIC. ELSEWHERE, HEAVY
RAINFALL PRIOR TO THIS PERIOD TRIGGERED MODERATE TO MAJOR FLOODING ALONG THE
CEDAR, IOWA, AND WAPSIPICNIC RIVERS IN SOUTHEAST IOWA, MIDDLE MISSISSIPPI
RIVER, AND NUECES RIVER IN SOUTH TEXAS.



MODEL GUIDANCE REMAINS IN REASONABLY GOOD AGREEMENT WITH THE EVOLUTION OF AN
AMPLIFYING 500-HPA TROUGH ENTERING THE WESTERN U.S. DURING THE WEEKEND. AS THE
VIGOROUS TROUGH ALOFT PROGRESSES INLAND TO THE ROCKIES, HEAVY SNOW (MORE THAN 6
INCHES IN 24 HOURS) IS MOST LIKELY ABOVE 6,000 FEET ACROSS WYOMING ON OCTOBER 3
AND 4. HEAVY RAIN (AROUND 1 INCH PER 24 HOURS) ASSOCIATED WITH THE SURFACE LOW
IS EXPECTED ACROSS THE NORTHERN HIGH PLAINS AT THE SAME TIME.  THE
DETERMINISTIC 0Z GFS AND 0Z ECMWF MODELS INDICATE 48-HOUR PRECIPITATION
AMOUNTS, ENDING AT 12Z OCTOBER 5, OF 1 TO 4 INCHES (LIQUID EQUIVALENT) CENTERED
ON SOUTHEAST MONTANA AND NORTHERN WYOMING ON OCTOBER 3 AND 4.



A LEE SIDE SURFACE LOW IS EXPECTED TO DEVELOP ACROSS THE NORTH-CENTRAL HIGH
PLAINS ON MONDAY, OCTOBER 3, DUE TO THE APPROACHING 500-HPA TROUGH. ALTHOUGH A
FEW SEVERE THUNDERSTORMS MAY AFFECT THE DAKOTAS AND NEBRASKA ON MONDAY
AFTERNOON AND EVENING, COVERAGE IS EXPECTED TO BE LIMITED BY MARGINAL
INSTABILITY. ON OCTOBER 4, INSTABILITY IS EXPECTED TO BE SUFFICIENT TO SUPPORT
SEVERE THUNDERSTORMS ALONG THE DRYLINE, EXTENDING FROM KANSAS SOUTH TO THE
TEXAS PANHANDLE AND SOUTHWEST TEXAS. THE AMPLIFYING TROUGH AND THE DEVELOPMENT
OF THE LEE SIDE LOW PRESSURE SYSTEM ARE LIKELY TO RESULT IN HIGH WINDS (GUSTS
ABOVE 40 MPH) ACROSS PARTS OF THE GREAT BASIN, ROCKIES, AND HIGH PLAINS ON
OCTOBER 3 AND 4.



AS OF 11AM EDT ON SEPTEMBER 29, HURRICANE MATTHEW IS LOCATED AT 14.2N/65.3W
(EASTERN CARIBBEAN SEA). MATTHEW IS EXPECTED TO TURN NORTH AS IT MOVES TO THE
WESTERN EDGE OF A SUBTROPICAL RIDGE AND PERHAPS BEGINS TO BE INFLUENCED BY A
MID-LEVEL TROUGH OVER THE GULF OF MEXICO. MODEL SOLUTIONS CONTINUE TO DIFFER ON
WHERE AND HOW FAST THIS NORTHWARD TURN OCCURS. REGARDLESS OF THE EVENTUAL
TRACK, A TIGHT PRESSURE GRADIENT BETWEEN A 1032-HPA SURFACE HIGH OVER NEW
ENGLAND AND TROPICAL CYCLONE MATTHEW IS FORECAST TO BRING THE POTENTIAL OF HIGH
WINDS (GUSTS ABOVE 40 MPH) TO COASTAL AREAS OF THE SOUTHEAST AND MID-ATLANTIC.
AN INCREASE IN SWELLS AND WAVE HEIGHTS ARE ALSO EXPECTED FROM THE ATLANTIC
BEACHES OF FLORIDA NORTH AT LEAST TO LONG ISLAND. A HEAVY RAIN HAZARD IS NOT
POSTED DUE TO THE CONTINUED LARGE DIFFERENCES AMONG THE DETERMINISTIC MODELS
AND LARGE SPREAD AMONG THE 0Z ECMWF ENSEMBLE MEMBERS ON THE TRACK OF MATTHEW.
PLEASE REFER TO THE LATEST STATEMENTS AND FORECASTS FROM THE NATIONAL HURRICANE
CENTER AT WWW.NHC.NOAA.GOV.

FOR FRIDAY OCTOBER 07 - THURSDAY OCTOBER 13: THE FORECAST ALONG THE EAST COAST
DURING THE EARLY PART OF WEEK-2 REMAINS HIGHLY UNCERTAIN DUE TO THE LARGE MODEL
SPREAD WITH THE EVENTUAL TRACK OF TROPICAL CYCLONE MATTHEW. THE 0Z/6Z GFS AND
0Z ECMWF ENSEMBLE MEANS FEATURE A WEAK UPPER-LEVEL TROUGH OVER THE NORTHWESTERN
CONUS AND A SUBTROPICAL RIDGE CENTERED OVER THE SOUTH-CENTRAL CONUS. THE ECMWF
MODEL FAVORS BELOW-NORMAL TEMPERATURES ACROSS THE NORTHERN GREAT PLAINS, BUT
MINIMUM TEMPERATURES ARE NOT EXPECTED TO BE TOO ANOMALOUS. AN UPPER-LEVEL
TROUGH OVER THE BERING SEA IS EXPECTED TO MAINTAIN ABOVE-MEDIAN PRECIPITATION
ACROSS SOUTHWEST ALASKA.



ACCORDING TO THE LATEST U.S. DROUGHT MONITOR (USDM) VALID ON SEPTEMBER 27, THE
COVERAGE OF SEVERE OR GREATER DROUGHT (FOR THE CONUS) INCREASED FROM 7.76 TO
8.10 PERCENT DURING THE PAST WEEK. LESS THAN 1 PERCENT OF THE HAWAIIAN ISLANDS
IS DESIGNATED WITH SEVERE DROUGHT.

FORECASTER: BRAD PUGH

$$



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