Threats Assessment Discussion

001 
FXUS21 KWNC 251911
PMDTHR
US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT SEPTEMBER 25 2017
SYNOPSIS: AT THE START OF THE HAZARDS OUTLOOK PERIOD, A COLD FRONT IS PREDICTED 
TO APPROACH THE ATLANTIC AND GULF COASTS. THIS FRONT IS FORECAST TO PUSH 
HURRICANE MARIA (PERHAPS TWO HUNDRED MILES OFF THE MID-ATLANTIC COAST AT THAT 
TIME) WELL OUT TO SEA. THE TRAILING (WESTERN) END OF THIS COLD FRONT IS 
ANTICIPATED TO LAG BACK OVER THE SOUTHERN GREAT PLAINS AND NEARBY ROCKIES, 
HELPING TO GENERATE UPSLOPE PRECIPITATION. ANOTHER COLD FRONT IS EXPECTED TO 
FOLLOW THE INITIAL FRONT ACROSS THE EASTERN LOWER 48 STATES, AND REINFORCE THE 
COOL, DRY AIRMASS THAT IS PREDICTED TO ALREADY BE IN PLACE. ELSEWHERE, SEVERAL 
LOW PRESSURE SYSTEMS ARE ANTICIPATED TO AFFECT THE SOUTHERN AND WESTERN COASTS 
OF ALASKA, THOUGH NONE OF THESE SYSTEMS APPEAR TO BE UNUSUALLY STRONG FOR THIS 
TIME OF YEAR. DURING WEEK-2, BROAD 500-HPA TROUGHS ARE EXPECTED ACROSS MUCH OF 
SOUTHERN ALASKA, AND NEAR BOTH COASTS OF THE LOWER 48 STATES, WITH A RIDGE 
CENTERED OVER APPROXIMATELY THE SOUTHERN HALVES OF BOTH THE GREAT PLAINS AND 
MISSISSIPPI VALLEY.
HAZARDS
HEAVY RAIN IN THE VICINITY OF THE EDWARDS PLATEAU IN SOUTHWEST TEXAS, THU-FRI, 
SEP 28-29.
PERIODS OF HEAVY RAIN IN EXTREME SOUTHERN FLORIDA, THU-SUN, SEP 28-OCT 1.
HEAVY RAIN FOR THE ALASKA PANHANDLE, THU, SEP 28.
FLOODING IS OCCURRING/IMMINENT IN NORTHERN AND CENTRAL PORTIONS OF FLORIDA.
FLOODING IS LIKELY OVER THE ALASKA PANHANDLE.
FLOODING IS POSSIBLE OVER PART OF THE EDWARDS PLATEAU IN SOUTHWEST TEXAS.
SEVERE DROUGHT ACROSS PORTIONS OF THE PLAINS AND MISSISSIPPI VALLEY, THE 
NORTHERN ROCKIES, AND HAWAII.
DETAILED SUMMARY
FOR THURSDAY SEPTEMBER 28 - MONDAY OCTOBER 02: A COLD FRONT IS FORECAST TO 
APPROACH THE ATLANTIC AND GULF COASTS AT THE START OF THE HAZARDS PERIOD. 
THOUGH GUSTY WINDS MAY STILL BE A FACTOR FOR THE OUTER BANKS OF NORTH CAROLINA 
THURSDAY MORNING (SEP 28) DUE TO HURRICANE MARIA OFFSHORE, THIS FRONT IS 
PREDICTED TO PUSH THE HURRICANE WELL OUT TO SEA. THE WESTERN END OF THE COLD 
FRONT IS ANTICIPATED TO BE DRAPED ACROSS THE SOUTHERN PLAINS AND ADJACENT 
ROCKIES, AND IS EXPECTED TO GENERATE UPSLOPE PRECIPITATION. HEAVY RAIN (1.5-2.5 
INCHES) IS PREDICTED OVER THE EDWARDS PLATEAU IN SOUTHWEST TEXAS ON SEP 28-29. 
SOME FLOODING IS POSSIBLE WITHIN THIS AREA. FARTHER EAST, THE COLD FRONT IS 
FORECAST TO STALL AS IT NEARS SOUTHERN FLORIDA, CAUSING PERIODS OF HEAVY RAIN 
(1.5-2.5 INCHES, LOCALLY GREATER) FROM SEP 28-OCT 1. RESIDUAL FLOODING PERSISTS 
ACROSS NORTHERN AND CENTRAL PORTIONS OF THE STATE, PRIMARILY DUE TO THE RECENT 
PASSAGE OF HURRICANE IRMA.
AT THE BEGINNING OF THIS PERIOD, HEAVY RAIN (1.5-3.0 INCHES) IS PREDICTED 
ACROSS THE ALASKA PANHANDLE. THOUGH THE RAINFALL REPRESENTS THE TAIL END OF 
THIS PRECIPITATION EVENT, RESIDENTS SHOULD BE AWARE OF THE POTENTIAL FOR 
MUDSLIDES AND FLOODING.
FOR TUESDAY OCTOBER 03 - MONDAY OCTOBER 09: THE ONLY FORESEEN HAZARDS AT THIS 
TIME RANGE ARE THE PERSISTENT LONG-TERM DROUGHT AREAS. 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.
THERE ARE MAJOR DIFFERENCES BETWEEN THE GEFS AND ECMWF MODELS OVER TEXAS DURING 
WEEK-2, WITH THE GEFS PREDICTING HEAVY RAIN OVER PORTIONS OF THE LONE STAR 
STATE, AND THE ECMWF PREDICTING MUCH DRIER CONDITIONS OVER THE SAME REGION. 
THIS MODEL DISAGREEMENT PRECLUDES THE SPECIFICATION OF ANY HAZARDOUS 
PRECIPITATION AREAS DURING WEEK-2 AT THIS TIME.
FORECASTER: ANTHONY ARTUSA 
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