Prognostic Meteorological Discussion
Issued by NWS

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FXUS21 KWNC 211939
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 21 2017

SYNOPSIS: EARLY IN THE PERIOD, TROPICAL STORM JOSE IS FORECAST TO REMAIN NEARLY
STATIONARY OFF THE COAST OF THE MID-ATLANTIC/NORTHEAST U.S. STRONG MID-LEVEL
HIGH PRESSURE IS ANTICIPATED OVER THE EASTERN U.S., WHILE STRONG MID-LEVEL LOW
PRESSURE IS EXPECTED OVER THE WEST. A FRONTAL SYSTEM OVER THE GREAT
PLAINS/CENTRAL ROCKIES/SOUTHWEST U.S. IS FORECAST TO MOVE VERY SLOWLY
EAST-SOUTHEASTWARD. SURFACE LOW PRESSURE IS FORECAST TO DEVELOP OVER THE GULF
OF ALASKA. HURRICANE MARIA IS EXPECTED TO MOVE NORTHWARD OVER THE WESTERN
ATLANTIC. DURING WEEK-2, AREAS OF MID-LEVEL LOW PRESSURE ARE ANTICIPATED OVER
THE EASTERN U.S. AND WESTERN AND CENTRAL MAINLAND ALASKA, WHILE MID-LEVEL HIGH
PRESSURE IS EXPECTED OVER THE WESTERN U.S. AND SOUTHEASTERN ALASKA.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE GREAT PLAINS AND UPPER MISSISSIPPI VALLEY,
SUN-MON, SEP 24-SEP 25.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, TUE-THU, SEP 26-SEP 28.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE MIDDLE MISSISSIPPI
VALLEY, THE GREAT LAKES, THE OHIO VALLEY, AND THE UPPER MISSISSIPPI VALLEY,
SUN-MON, SEP 24-SEP 25.

MUCH BELOW NORMAL TEMPERATURES ACROSS PORTIONS OF THE WEST, SUN-MON, SEP 24-SEP
25.

HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF THE MID-ATLANTIC AND THE
NORTHEAST, WED, SEP 27.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTH COAST OF ALASKA AND THE ALASKA
PANHANDLE, SUN-MON, SEP 24-25.

FLOODING LIKELY, OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, FRI, SEP 29.

SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE NORTHERN PLAINS, HAWAII, THE
NORTHERN ROCKIES, THE MIDDLE MISSISSIPPI VALLEY, CALIFORNIA, THE UPPER
MISSISSIPPI VALLEY, AND THE SOUTHERN PLAINS.

DETAILED SUMMARY

FOR SUNDAY SEPTEMBER 24 - THURSDAY SEPTEMBER 28: STRONG RIDGING OVER THE
EAST-CENTRAL CONUS LEADS TO MUCH ABOVE NORMAL TEMPERATURES (POSITIVE ANOMALIES
EXCEEDING 16-20 DEGREES F) ACROSS PORTIONS OF THE UPPER AND MIDDLE MISSISSIPPI
VALLEY, THE GREAT LAKES, AND THE OHIO VALLEY, SEP 24-25. DAY TIME MAXIMUM
TEMPERATURES ARE EXPECTED IN THE UPPER 80`S/LOW 90`S F FOR PARTS OF THESE
REGIONS. A DEEP TROUGH OVER THE WESTERN CONUS FAVORS MUCH BELOW NORMAL
TEMPERATURES (NEGATIVE ANOMLIES OF 12-16 DEGREES F) FOR PARTS OF THE INTERIOR
WEST SEP 24-25. SOME OF THESE REGIONS ARE EXPECTED TO SEE OVERNIGHT MINIMUM
TEMPERATURES IN THE HIGH TEEN`S/LOW 20`S F.



A STRONG MID-LEVEL TROUGH OVER THE WESTERN CONUS, IN COMBINATION WITH A FRONTAL
SYSTEM FORECAST TO MOVE EAST-SOUTHEASTWARD FROM THE UPPER MIDWEST/SOUTHWEST TO
THE EAST-CENTRAL CONUS FAVORS HEAVY RAIN (AMOUNTS OF 2-4 INCHES OVER 48 HOURS)
FOR PORTIONS OF THE GREAT PLAINS AND UPPER MISSISSIPPI VALLEY SEP 24-25. AS THE
SOUTHERN PORTION OF THIS COLD FRONT PROGRESSES SOUTHEASTWARD, PORTIONS OF THE
CENTRAL AND SOUTHERN PLAINS MAY RECEIVE HEAVY RAIN (AMOUNTS OF 5 INCHES OR
GREATER OVER 48 HOURS), SEP 26-28.



SURFACE HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS THE PACIFIC NORTHWEST AND
GREAT BASIN THROUGHOUT WEEK-1. THIS PATTERN MAY SUPPORT WINDY CONDITIONS ACROSS
SOUTHERN CALIFORNIA DURING THE EARLY PART OF NEXT WEEK. INCREASING DRYNESS IN
THE ATMOSPHERE AND FUELS IN COMBINATION WITH WINDY CONDITIONS MAY SUPPORT
INCREASED CHANCES FOR WILDFIRE RISK. HOWEVER, DUE TO UNCERTAINTY REGARDING THE
PATTERN AND RESULTING WIND SPEEDS, A SPECIFIC AREA IS NOT HIGHLIGHTED AT THIS
TIME.



HURRICANE MARIA IS FORECAST TO MOVE NORTHWARD OVER THE WESTERN ATLANTIC. HIGH
SIGNIFICANT WAVE HEIGHTS (IN EXCESS OF 20 FEET) ARE FORECAST FOR COASTAL
SECTIONS OF THE MID-ATLANTIC AND NORTHEAST SEP 27. PLEASE CONSULT THE LATEST
ADVISORIES FROM THE NATIONAL HURRICANE CENTER AT HTTP://WWW.NHC.NOAA.GOV/ FOR
THE LATEST FORECASTS REGARDING THIS SYSTEM.



RIVER FLOODING IS FORECAST TO CONTINUE FOR PARTS OF FLORIDA DUE TO ANTECEDENT
RAINFALL FROM HURRICANE IRMA.



A SURFACE LOW PRESSURE SYSTEM IS PREDICTED TO DEVELOP NEAR KODIAK ISLAND EARLY
IN THE PERIOD. HEAVY RAIN (AMOUNTS IN EXCESS OF 2 INCHES IN 24 HOURS) IS
ANTICIPATED ACROSS PORTIONS OF THE SOUTH COAST OF ALASKA AND THE ALASKA
PANHANDLE SEP 24-25. ANOTHER AREA OF SURFACE LOW PRESSURE IS EXPECTED TO
APPROACH THE ALASKA PANHANDLE SEP 27. HEAVY RAIN (AMOUNTS IN EXCESS OF 2 INCHES
IN 24 HOURS) IS FORECAST FOR PARTS OF THE REGION SEP 27. HOWEVER, DUE TO
SIGNIFICANT MODEL DIFFERENCES REGARDING THE LOCALIZED REGIONS OF HEAVY
RAINFALL, AN AREA IS NOT SPECIFIED AT THIS TIME.

FOR FRIDAY SEPTEMBER 29 - THURSDAY OCTOBER 05: THE FORECAST PATTERN IN WEEK-2
INDICATES MID-LEVEL TROUGHING OVER THE EASTERN CONUS AND MID-LEVEL RIDGING OVER
THE WEST. AT THE BEGINNING OF WEEK-2, SURFACE TROUGHING IS FORECAST ACROSS
WESTERN MEXICO, WITH SURFACE HIGH PRESSURE CENTERED OVER CENTRAL CONUS. THIS
PATTERN FAVORS MOIST SOUTHEASTERLY FLOW FROM THE GULF OF MEXICO INTO THE
SOUTHERN PLAINS. THE PROBABILISTIC PRECIPITATION TOOL, IN ADDITION TO THE 6Z
DETERMINISTIC GFS AND 0Z DETERMINISTIC ECMWF, INDICATE INCREASED CHANCES FOR
HEAVY RAIN (AMOUNTS OF 1.5 INCHES OR GREATER IN 24-HOURS) OVER PORTIONS OF
TEXAS ON SEP 29.



SOME MODEL SOLUTIONS INDICATE THE POSSIBILITY OF TROPICAL ACTIVITY OVER PARTS
OF THE CARIBBEAN LATE IN THE WEEK-2 PERIOD SO THIS REGION WILL NEED TO BE
MONITORED.



THE U.S. DROUGHT MONITOR, VALID ON SEP 19, INDICATES THAT SEVERE TO EXCEPTIONAL
(D2-D4) DROUGHT COVERS 5.60 PERCENT OF THE CONTINENTAL U.S.

FORECASTER: MELISSA OU

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