Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 301813
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 30 2016

SYNOPSIS: SURFACE HIGH PRESSURE IS FORECAST TO BECOME CENTERED OVER NEW ENGLAND
EARLY IN THE PERIOD AS HURRICANE MATTHEW TRACKS NORTH FROM THE CARIBBEAN SEA. A
STRONG AREA OF UPPER-LEVEL LOW PRESSURE IS EXPECTED TO ADVANCE ACROSS THE
WEST-CENTRAL U.S. ON OCTOBER 3 AND 4. AN AREA OF UPPER-LEVEL HIGH (LOW)
PRESSURE IS FORECAST TO DEVELOP ACROSS EASTERN ALASKA (BERING SEA AND NORTHEAST
PACIFIC) DURING THE FIRST TWO WEEKS OF OCTOBER.

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 SOUTHERN MONTANA AND NORTHERN WYOMING,
MON-TUE, OCT 3-4.

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

ENHANCED WILDFIRE RISK ACROSS PARTS OF THE CENTRAL AND SOUTHERN HIGH PLAINS,
MON, OCT 3.

HIGH WINDS AND SIGNIFICANT WAVES FOR PARTS OF THE EAST COAST, TUE-FRI, OCT 4-7.

MUCH BELOW-NORMAL TEMPERATURES FOR MUCH OF THE INTERMOUNTAIN WEST AND GREAT
BASIN, TUE-WED, OCT 4-5.

FLOODING IS OCCURRING, LIKELY, OR POSSIBLE ACROSS PARTS OF THE MIDWEST AND
SOUTH TEXAS.

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

DETAILED SUMMARY

FOR MONDAY OCTOBER 03 - FRIDAY OCTOBER 07: AS OF 11AM EDT ON SEPTEMBER 30, THE
CENTER OF HURRICANE MATTHEW IS LOCATED AT 14N/70W (SOUTH-CENTRAL CARIBBEAN
SEA). MATTHEW IS EXPECTED TO TURN NORTH AS A SUBTROPICAL RIDGE SHIFTS EAST AND
IT 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 ITS 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 TO AT LEAST LONG ISLAND. A
HEAVY RAIN HAZARD IS NOT POSTED DUE TO CONTINUED DIFFERENCES ON THE PROXIMITY
OF THE TROPICAL CYCLONE TO THE EAST COAST. PLEASE REFER TO THE LATEST
STATEMENTS AND FORECASTS FROM THE NATIONAL HURRICANE CENTER AT WWW.NHC.NOAA.GOV.



MODEL GUIDANCE REMAINS IN REASONABLY GOOD AGREEMENT WITH THE EVOLUTION OF AN
AMPLIFYING 500-HPA TROUGH ENTERING THE WESTERN U.S. 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 SOUTHERN MONTANA AND NORTHERN
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/12Z GFS AND 0Z ECMWF MODELS ON SEPTEMBER 30
INDICATE 48-HOUR PRECIPITATION AMOUNTS, ENDING AT 12Z OCTOBER 5, OF 1 TO 3
INCHES (LIQUID EQUIVALENT) CENTERED ON EASTERN MONTANA AND NORTHERN WYOMING.



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 OCTOBER 3, THE
MOST LIKELY AREA FOR SEVERE THUNDERSTORMS EXISTS FROM KANSAS TO NORTHWEST TEXAS
ON OCTOBER 4 DUE TO HIGHER INSTABILITY.



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 MUCH OF THE
GREAT BASIN, ROCKIES, AND GREAT PLAINS ON OCTOBER 3 AND 4. THE GUSTY WINDS
COUPLED WITH DRY FUELS RESULT IN AN ENHANCED RISK FOR CRITICAL FIRE WEATHER
CONDITIONS ACROSS THE CENTRAL AND SOUTHERN HIGH PLAINS ON OCTOBER 3. MUCH
BELOW-NORMAL TEMPERATURES ARE ALSO EXPECTED TO ACCOMPANY THE UPPER-LEVEL
TROUGH. THIS HAZARD IS HIGHLIGHTED ACROSS THE INTERMOUNTAIN WEST AND GREAT
BASIN WHERE MINIMUM TEMPERATURES ARE FORECAST TO AVERAGE NEAR 10 DEGREES F
BELOW NORMAL AND SUBFREEZING TEMPERATURES ARE MOST LIKELY ON OCTOBER 4 AND 5.



HEAVY RAINFALL DURING THE PREVIOUS WEEK TRIGGERED MODERATE TO MAJOR FLOODING
ALONG THE CEDAR AND IOWA RIVERS IN SOUTHEAST IOWA, MIDDLE MISSISSIPPI RIVER,
AND NUECES RIVER IN SOUTH TEXAS. THIS RIVER FLOODING IS EXPECTED TO LINGER INTO
THE BEGINNING OF OCTOBER.

FOR SATURDAY OCTOBER 08 - FRIDAY OCTOBER 14: MODEL GUIDANCE ON SEPTEMBER 30
INDICATES THAT THE UPPER-LEVEL TROUGH, SHIFTING INTO THE EAST-CENTRAL U.S.,
STEERS MATTHEW AWAY FROM THE EAST COAST BY THE BEGINNING OF WEEK-2. HOWEVER,
UNCERTAINTY REMAINS RATHER HIGH GIVEN THE LARGE SPREAD AMONG 0Z ECMWF ENSEMBLE
MEMBERS.



AN UPPER-LEVEL TROUGH OVER THE BERING SEA IS EXPECTED TO MAINTAIN ABOVE-MEDIAN
PRECIPITATION ACROSS THE ALEUTIANS AND SOUTHWEST ALASKA. RECURVING TYPHOON
CHABA, OVER THE NORTHWEST PACIFIC, MAY FURTHER AMPLIFY THIS UPPER-LEVEL TROUGH
DURING WEEK-2. MODEL SOLUTIONS ON SEPTEMBER 30 HAVE TRENDED TOWARDS A MORE
AMPLIFIED TROUGH ACROSS THE NORTHEAST PACIFIC. ALTHOUGH THERE IS AN INCREASING
POTENTIAL FOR HEAVY RAINFALL ACROSS THE COASTAL PACIFIC NORTHWEST DURING
WEEK-2, MODERATE TO LARGE SPREAD AMONG GFS AND ECMWF ENSEMBLE MEMBERS PRECLUDE
DESIGNATION OF A HEAVY RAIN HAZARD AT THIS TIME.



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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