Prognostic Meteorological Discussion
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FXUS21 KWNC 171846
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 17 2014

SYNOPSIS: THE REMNANT LOW OF FORMER HURRICANE ODILE IS FORECAST TO TRACK INTO
THE SOUTH-CENTRAL GREAT PLAINS THIS WEEKEND. A COLD FRONT IS FORECAST TO
PROGRESS FROM THE GREAT PLAINS AND MISSISSIPPI VALLEY TO THE EAST COAST EARLY
IN THE PERIOD. ON SUNDAY AND MONDAY, AN AREA OF UPPER-LEVEL LOW PRESSURE IS
FORECAST TO TRACK ACROSS THE GREAT BASIN AND CENTRAL ROCKIES. ONSHORE FLOW IS
EXPECTED TO INCREASE ACROSS THE PACIFIC NORTHWEST BY THE MIDDLE PART OF NEXT
WEEK. AN AREA OF UPPER-LEVEL LOW PRESSURE IS FORECAST TO PERSIST ACROSS ALASKA
DURING THE NEXT TWO WEEKS.

HAZARDS

HEAVY RAIN ACROSS THE CENTRAL AND SOUTHERN GREAT PLAINS, SAT-SUN, SEP 20-21.

FLASH FLOODING POSSIBLE ACROSS THE CENTRAL ROCKIES, SUN-MON, SEP 21-22.

HEAVY RAIN FOR THE NORTHERN/CENTRAL ALASKA PANHANDLE, SAT-SUN, SEP 20-21.

RIVER FLOODING LIKELY FOR PARTS OF ARIZONA AND NEW MEXICO.

RIVER FLOODING POSSIBLE FOR PARTS OF NEW MEXICO AND WEST TEXAS.

SEVERE DROUGHT FOR THE CENTRAL AND SOUTHERN GREAT PLAINS, SOUTHWEST, SOUTHERN
GEORGIA, PACIFIC NORTHWEST, GREAT BASIN, AND CALIFORNIA.

DETAILED SUMMARY

FOR SATURDAY SEPTEMBER 20 - WEDNESDAY SEPTEMBER 24: A COLD FRONT INTERACTING
WITH MID-LEVEL MOISTURE FROM THE REMNANT OF ODILE AND ABUNDANT LOW-LEVEL
MOISTURE FROM THE GULF OF MEXICO IS LIKELY TO BRING HEAVY RAINFALL TO THE
CENTRAL AND SOUTHERN GREAT PLAINS THIS WEEKEND. THE 6Z GFS MODEL INDICATES THAT
PRECIPITABLE WATER VALUES INCREASE TO AROUND 2 INCHES ACROSS THE SOUTHERN GREAT
PLAINS ON SATURDAY. SEVERE THUNDERSTORMS COULD DEVELOP ALONG AND AHEAD OF THE
COLD FRONT AS IT CROSSES THE UPPER MISSISSIPPI VALLEY AND GREAT LAKES ON
SATURDAY, BUT UNCERTAINTY ON SUFFICIENT INSTABILITY PRECLUDES DESIGNATION OF A
SEVERE WEATHER HAZARD AT THIS TIME. EARLY NEXT WEEK, EASTERLY FLOW ELEVATES THE
THREAT OF HEAVY RAINFALL ACROSS WEST TEXAS AND THE UPPER RIO GRANDE VALLEY. IF
MODEL AGREEMENT ON RAINFALL AMOUNTS AND LOCATION IMPROVE, THEN A HEAVY RAIN
HAZARD WILL BE POSTED ON FUTURE OUTLOOKS.



THE HIGH RESOLUTION 0Z ECMWF MODEL TRENDED TOWARDS THE 0Z/6Z GFS REGARDING THE
MOVEMENT OF A MID-LEVEL TROUGH CROSSING THE GREAT BASIN AND CENTRAL ROCKIES
EARLY IN THE PERIOD. THIS MID-LEVEL TROUGH COMBINED WITH ANOMALOUS LOW-LEVEL
MOISTURE IS EXPECTED TO RESULT IN LOCALLY HEAVY RAIN AND POSSIBLE FLASH
FLOODING ACROSS THE CENTRAL ROCKIES ON SUNDAY AND MONDAY.



AN UPPER-LEVEL RIDGE IS EXPECTED TO RESULT IN MAXIMUM TEMPERATURES AVERAGING
AROUND 12 DEGREES F ABOVE-NORMAL ACROSS THE INTERIOR PACIFIC NORTHWEST ON
SUNDAY AND MONDAY. SINCE MAXIMUM TEMPERATURES ARE FORECAST TO REMAIN BELOW 90
DEGREES F, A MUCH-ABOVE NORMAL TEMPERATURE HAZARD IS NOT DEEMED NECESSARY FOR
THIS REGION.



NUMEROUS WILDFIRES ARE BURNING ACROSS OREGON AND CALIFORNIA WITH THE LARGEST
WILDFIRE (MORE THAN 113,000 ACRES BURNED) IN SISKIYOU COUNTY OF NORTHERN
CALIFORNIA. DURING THE MIDDLE PART OF NEXT WEEK, THE HIGH RESOLUTION 0Z ECMWF
AND 12 GFS MODELS INDICATE A TROUGH MOVING ONSHORE INTO THE PACIFIC NORTHWEST
WHICH WOULD BRING MUCH NEEDED RAIN TO THIS REGION.



MODEL GUIDANCE CONTINUES TO INDICATE THE POTENTIAL FOR LOW PRESSURE DEVELOPMENT
OFFSHORE OF THE SOUTHEAST COAST THIS WEEKEND. NO HAZARDOUS WEATHER IS CURRENTLY
EXPECTED ALONG THE EAST COAST IF THIS SURFACE LOW FORMS.



A PAIR OF SURFACE LOWS ARE EXPECTED TO AFFECT SOUTHEAST ALASKA AND THE ALASKA
PANHANDLE DURING THE WEEKEND. A HEAVY PRECIPITATION HAZARD IS POSTED TODAY DUE
TO THE BETTER AGREEMENT BETWEEN THE HIGH RESOLUTION 0Z ECMWF AND 12Z GFS MODELS
WHICH INDICATE RAINFALL AMOUNTS EXCEEDING 5 INCHES ACROSS THE NORTHERN/CENTRAL
ALASKA PANHANDLE SEPTEMBER 20-21.

FOR THURSDAY SEPTEMBER 25 - WEDNESDAY OCTOBER 01: LARGE SPREAD AMONG THE 0Z GFS
AND 0Z ECMWF ENSEMBLE MEMBERS FOR THE SECOND CONSECUTIVE DAY PRECLUDES
DESIGNATION OF ANY SPECIFIC HAZARDS DURING WEEK-2, EXPECT THE ONGOING SEVERE
DROUGHT. MUCH ABOVE-NORMAL TEMPERATURES MAY AFFECT CALIFORNIA EARLY IN WEEK-2,
BUT MODEL DIFFERENCES ON THE RIDGE AMPLITUDE PRECLUDE DESIGNATION OF THIS
HAZARD.



THE MOST RECENT U.S. DROUGHT MONITOR, RELEASED LAST THURSDAY, INDICATES THE
PERCENTAGE OF THE CONUS IN SEVERE TO EXCEPTIONAL DROUGHT DECREASING FROM THE
PREVIOUS WEEK`S (SEPTEMBER 4) 20.93 PERCENT TO 20.31 PERCENT. THIS IS ALSO DOWN
SUBSTANTIALLY FROM BOTH 2013 AND 2012 AT THIS TIME OF YEAR (32.40 AND 42.48
PERCENT, RESPECTIVELY).

FORECASTER: BRAD PUGH

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