Prognostic Meteorological Discussion
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FXUS21 KWNC 221748
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 22 2017

SYNOPSIS: 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 UPPER MISSISSIPPI VALLEY/GREAT PLAINS/SOUTHWEST U.S. IS FORECAST TO
MOVE VERY SLOWLY EAST-SOUTHEASTWARD. HURRICANE MARIA IS EXPECTED TO MOVE
NORTHWARD OVER THE WESTERN ATLANTIC. SURFACE LOW PRESSURE IS FORECAST TO
DEVELOP OVER THE GULF OF ALASKA. DURING THE BEGINNING TO MIDDLE OF 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. THE MIDDLE TO END OF WEEK-2 IS
ANTICIPATED TO BE DOMINATED BY A MORE ZONAL PATTERN ACROSS THE LOWER 48 STATES.

HAZARDS

HEAVY RAIN ACROSS PORTIONS OF THE CENTRAL PLAINS AND SOUTHERN PLAINS, MON, SEP
25.

HEAVY RAIN ACROSS PORTIONS OF THE SOUTHERN PLAINS, TUE-FRI, SEP 26-SEP 29.

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

HEAVY RAIN ACROSS PORTIONS OF THE ALASKA PANHANDLE, TUE-WED, SEP 26-SEP 27.

MUCH ABOVE NORMAL TEMPERATURES ACROSS PORTIONS OF THE NORTHEAST, THE CENTRAL
APPALACHIANS, THE MID-ATLANTIC, THE UPPER MISSISSIPPI VALLEY, THE GREAT LAKES,
AND THE OHIO VALLEY, TUE-WED, SEP 26-SEP 27.

FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE SOUTHEAST.

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 MONDAY SEPTEMBER 25 - FRIDAY SEPTEMBER 29: STRONG RIDGING OVER THE
EAST-CENTRAL CONUS FAVORS MUCH ABOVE NORMAL TEMPERATURES (POSITIVE ANOMALIES
EXCEEDING 20-24 DEGREES F) ACROSS PORTIONS OF THE NORTHEAST, THE CENTRAL
APPALACHIANS, THE MID-ATLANTIC, THE UPPER MISSISSIPPI VALLEY, THE GREAT LAKES,
AND THE OHIO VALLEY, SEP 26-27. DAY TIME MAXIMUM TEMPERATURES ARE EXPECTED IN
THE UPPER 80`S/LOW 90`S F FOR PARTS OF THESE REGIONS.



A STRONG MID-LEVEL TROUGH OVER THE WESTERN CONUS, IN COMBINATION WITH A FRONTAL
SYSTEM FORECAST TO MOVE EAST-SOUTHEASTWARD FROM THE UPPER MISSISSIPPI
VALLEY/GREAT PLAINS/SOUTHWEST TO THE EAST-CENTRAL CONUS INCREASES THE
LIKELIHOOD FOR HEAVY RAIN (AMOUNTS OF 3-4 INCHES OVER 48 HOURS) FOR PORTIONS OF
THE CENTRAL PLAINS AND SOUTHERN PLAINS SEP 25, SHIFTING SOUTHEASTWARD TO THE
SOUTHERN PLAINS FROM SEP 26 TO 29.



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.



SURFACE HIGH PRESSURE IS ANTICIPATED TO BUILD ACROSS THE GREAT BASIN AT THE
BEGINNING OF THE PERIOD. THIS PATTERN MAY SUPPORT SEVERAL DAYS OF INCREASED
PROBABILITY FOR WINDY CONDITIONS. HIGH TEMPERATURES, LOW RELATIVE HUMIDITY, AND
DRY FUELS MAY LEAD TO INCREASED CHANCES FOR WILDFIRE RISK. HOWEVER, DUE TO
FORECAST SURFACE WIND SPEEDS NOT REACHING CRITICAL CRITERIA, A SPECIFIC AREA IS
NOT HIGHLIGHTED AT THIS TIME.

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 OVER THE GULF OF ALASKA
EARLY IN THE PERIOD. HEAVY RAIN (AMOUNTS IN EXCESS OF 2 INCHES IN 24 HOURS) IS
ANTICIPATED ACROSS PORTIONS OF THE ALASKA PANHANDLE SEP 26 TO 27.

FOR SATURDAY SEPTEMBER 30 - FRIDAY OCTOBER 06: THE 6Z DETERMINISTIC GFS
INDICATES THE POTENTIAL FOR A SURFACE LOW TO DEVELOP OFF THE COAST OF THE
CAROLINAS BY OCT 1. THIS MODEL SOLUTION THEN INDICATES THE LOW WOULD INTENSIFY
AND TRACK ALONG THE COAST OF THE MID-ATLANTIC, BRINGING HEAVY RAIN TO COASTAL
AREAS. HOWEVER, THE 6Z GEFS AND 0Z DETERMINISTIC AND ENSEMBLE ECMWF DOES NOT
SHOW DEVELOPMENT OF THIS STORM, PRECLUDING ANY RELATED HAZARDS FROM BEING
DETERMINED AT THIS TIME.



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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