Prognostic Meteorological Discussion
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FXUS21 KWNC 012003
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 01 2015

SYNOPSIS: SURFACE HIGH PRESSURE IS PREDICTED TO MOVE FROM EASTERN CANADA INTO
THE EASTERN UNITED STATES WITH A STRONG LOW PRESSURE MOVING THROUGH THE HIGH
PLAINS.  THIS PATTERN FAVORS PRECIPITATION FROM THE SOUTHWESTERN STATES INTO
THE DAKOTAS.  BELOW NORMAL TEMPERATURES ARE FORECAST FOR THE WESTERN STATES
WITH ABOVE NORMAL TEMPERATURES FAVORED FOR THE EASTERN STATES.

HAZARDS

SEVERE DROUGHT FOR PARTS OF THE WESTERN THIRD OF THE CONUS, SOUTHERN GREAT
PLAINS, LOWER MISSISSIPPI VALLEY, SOUTHEAST, AND HAWAII.

FLOODING POSSIBLE FOR PARTS OF WEST-CENTRAL FLORIDA.

DETAILED SUMMARY

FOR FRIDAY SEPTEMBER 04 - TUESDAY SEPTEMBER 08: THIS FORECAST PERIOD IS
EXPECTED TO BEGIN WITH AN UPPER-LEVEL TROUGH AMPLIFYING ALONG THE WEST COAST,
WITH AN UPPER-LEVEL RIDGE FROM EASTERN TEXAS TO THE NORTHERN GULF COAST.  THIS
PATTERN FAVORS BELOW NORMAL TEMPERATURES IN THE WESTERN STATES WITH ABOVE
NORMAL TEMPERATURES IN THE EASTERN STATES.  THE GREATEST CHANCE OF SIGNIFICANT
PRECIPITATION EXTENDS ALONG THE WESTERN PERIPHERY OF THE UPPER-LEVEL HIGH FROM
THE MOUNTAINS IN THE SOUTHWEST TO THE HIGH PLAINS AND THE DAKOTAS.



BY THE END OF THIS PERIOD, MOISTURE FROM THE REMNANTS OF TD 14E SOUTH OF BAJA
CALIFORNIA COULD GET DRAWN INTO THE CONUS, INCREASING THE POTENTIAL AMOUNTS OF
PRECIPITATION IN THE SOUTHWEST.  AT THIS TIME, NO LARGE-SCALE HAZARDS ARE
DENOTED ON THE MAP, BUT LOCALIZED FLOODING IS POSSIBLE IN ANY HEAVY DOWNPOURS
THAT MIGHT OCCUR.



SURFACE LOW PRESSURE IN THE PLAINS COMBINED WITH HIGH PRESSURE IN CANADA IS
EXPECTED TO LEAD TO STRONG NORTHEASTERLY UPSLOPE FLOW FROM IDAHO THROUGH
MONTANA INTO THE DAKOTAS.  WHILE SIGNIFICANT PRECIPITATION IS LIKELY, THE
FORECAST AMOUNTS DO NOT REACH HAZARDOUS CRITERIA, ALTHOUGH SOME LOCALIZED
FLOODING IS POSSIBLE.



IN THE WEST, AS INDIVIDUAL SHORTWAVES ROTATE AROUND THE BASE OF THE TROUGH,
ENHANCED WINDS ARE POSSIBLE, AND GIVEN THE DRY CONDITIONS, AN ENHANCED WILDFIRE
RISK FROM NEVADA INTO UTAH CANNOT BE RULED OUT.  HOWEVER, THERE IS TOO MUCH
MODEL UNCERTAINTY IN REGARDS TO THE MAGNITUDE OF THE SURFACE WINDS, THUS NO
HAZARDS ARE DENOTED ON THE MAP.

FOR WEDNESDAY SEPTEMBER 09 - TUESDAY SEPTEMBER 15: BY THE TIME THIS FORECAST
PERIOD BEGINS, THE REMNANTS OF HURRICANE IGNACIO ARE EXPECTED TO MERGE INTO THE
MID-LATITUDE WESTERLY FLOW.  HOW THIS WILL IMPACT THE DOWNSTREAM FLOW IS
UNCERTAIN.  AT THIS TIME, MODELS ARE FORECASTING THE AMPLIFICATION OF AN
UPPER-LEVEL TROUGH SOUTH OF THE ALEUTIANS.  THIS PATTERN FAVORS CONTINUED
CHANCES OF HEAVY RAIN FOR THE SOUTHERN AND SOUTHEASTERN COASTS OF ALASKA FOR
THE MIDDLE AND END OF THIS PERIOD.  HOWEVER, BECAUSE NUMERICAL MODELS HAVE A
NOTORIOUSLY HARD TIME IN FORECASTING THE CURVATURE OF TROPICAL SYSTEMS INTO THE
MID-LATITUDE JET STREAM, NO HAZARD IS PLACED ON THE MAP.  IF THE MODELS
CONTINUE TO FORECAST HEAVY RAIN OVER THE NEXT FEW DAYS, A HAZARD COULD BE
INTRODUCED WITH MORE CERTAINTY.



ACCORDING TO THE U.S. DROUGHT MONITOR MAP, VALID ON AUGUST 25, THE COVERAGE OF
SEVERE TO EXCEPTIONAL DROUGHT (D2 TO D4) DECREASED FROM 18.21 TO 18.07 PERCENT
ACROSS THE CONTIGUOUS U.S. SINCE THE PREVIOUS WEEK.

FORECASTER: KENNETH PELMAN

$$



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