Valid Saturday, October 05, 2013 to Wednesday, October 16, 2013

Summary of Forecasts and Hazards

US HAZARDS OUTLOOK
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD
300 PM EDT OCTOBER 02 2013

SYNOPSIS: A FAIRLY ACTIVE OCTOBER PATTERN IS FORECAST OVER THE NEXT WEEK, COMPLETE WITH A RAPIDLY INTENSIFYING LOW-PRESSURE SYSTEM ACROSS THE NORTH-CENTRAL U.S. AND THE POTENTIAL INVOLVEMENT OF A TROPICAL STORM SYSTEM ACROSS THE SOUTHEASTERN U.S. IN THE WAKE OF AN ACTIVE PERIOD ACROSS THE WESTERN U.S., HIGH PRESSURE IS FORECAST TO TAKE HOLD LATER THIS WEEK. A SERIES OF LOW-PRESSURE SYSTEMS IS EXPECTED TO IMPACT ALASKA THROUGHOUT THE PERIOD.

HAZARDS

• SEVERE WEATHER FOR PARTS OF THE CENTRAL PLAINS AND MIDWEST, FRI, OCT 4.
• HEAVY RAIN FOR PARTS OF THE NORTHERN PLAINS AND UPPER MIDWEST, FRI-SAT, OCT 4-5.
• HIGH WINDS FOR PARTS OF THE HIGH PLAINS AND UPPER MIDWEST, FRI-SAT, OCT 4-5.
• MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF WYOMING, MONTANA, AND IDAHO, FRI-SAT, OCT 4-5.
• HIGH WINDS FOR PARTS OF SOUTHERN CALIFORNIA, FRI-SAT, OCT 4-5.
• ENHANCED WILDFIRE RISK FOR PARTS OF SOUTHERN CALIFORNIA, FRI-SAT, OCT 4-5.
• HEAVY RAIN FOR PARTS OF THE SOUTHEAST, TENNESSEE VALLEY, AND GULF COAST, FRI-SAT, OCT 4-5.
• HEAVY RAIN FOR PARTS OF THE EASTERN SEABOARD, SUN-TUE, OCT 6-8.
• SEVERE DROUGHT FOR PARTS OF THE MIDWEST, GREAT PLAINS, RIO GRANDE VALLEY, ROCKIES, SOUTHWEST, GREAT BASIN, CALIFORNIA, ALASKA, AND HAWAII.

DETAILED SUMMARY

FOR SATURDAY OCTOBER 05 - WEDNESDAY OCTOBER 09: A STRONG UPPER-LEVEL TROUGH IS FORECAST TO MOVE SLOWLY EASTWARD ACROSS THE CONUS LATE THIS WEEK AND THROUGH THE WEEKEND. AT THE BEGINNING OF THE PERIOD, LEE CYCLOGENESIS IS FORECAST IN EARNEST, PRODUCING A LOW PRESSURE AT PEAK INTENSITY NEAR 990 HPA ACROSS THE UPPER MIDWEST. HEAVY RAIN AND HIGH WIND HAZARDS ARE DEPICTED IN ASSOCIATION WITH THIS SYSTEM LATE IN THE WEEK AND EARLY THIS WEEKEND ACROSS THE NORTH-CENTRAL CONUS. AHEAD OF THE BEST UPPER-LEVEL DYNAMICS, WHERE SHEAR AND INSTABILITY ARE SUFFICIENT, A SUBSTANTIAL OUTBREAK OF SEVERE WEATHER IS POSSIBLE. AN AREA IS DEPICTED ACROSS PARTS OF THE PLAINS AND MIDWEST WHERE THE GREATEST THREAT EXISTS ON FRIDAY. THE THREAT OF SEVERE WEATHER WILL CONTINUE ALONG THE FRONT AS IT MOVES SLOWLY EASTWARD, THOUGH CHANCES ARE DIMINISHED AS THE BEST UPPER-LEVEL DYNAMICS ARE LIKELY TO MOVE NORTHWARD RAPIDLY.

AS HIGH PRESSURE BUILDS IN BEHIND THE STORM ACROSS THE NORTHERN ROCKIES ON FRIDAY AND SATURDAY, MINIMUM TEMPERATURE ANOMALIES IN EXCESS OF 12 DEGREES F BELOW NORMAL ARE EXPECTED, PRODUCING WIDESPREAD SUBFREEZING TEMPERATURES ACROSS PARTS OF MONTANA, WYOMING, AND IDAHO.

THE STORM IS EXPECTED TO MOVE RAPIDLY NORTHEASTWARD ALONG WITH THE BEST UPPER-LEVEL FORCING OVER THE WEEKEND, BUT COULD PRODUCE A SWATH OF WET SNOW ON THE NORTHWEST SIDE FROM NORTHERN MINNESOTA NORTHEASTWARD. THIS POTENTIAL WINTERY WEATHER DOES NOT APPEAR PARTICULARLY HAZARDOUS AT THIS TIME, THOUGH IT WOULD BE EARLY IN THE SEASON FOR SUCH AN EVENT.

AS THE UPPER-LEVEL RIDGE BUILDS ACROSS THE WEST IN THE WAKE OF THE DEEP TROUGH, SURFACE HIGH PRESSURE IS FORECAST TO STRENGTHEN IN A FAVORABLE LOCATION TO SUPPORT A SANTA ANA WIND EVENT ACROSS SOUTHERN CALIFORNIA ON FRIDAY AND SATURDAY. THIS ALSO ENHANCES WILDFIRE RISK IN THAT REGION.

A TROPICAL WAVE IS MOVING NORTHWESTWARD ACROSS THE CARIBBEAN AND IS FORECAST TO MOVE INTO THE GULF OF MEXICO OVER THE NEXT COUPLE OF DAYS, POTENTIALLY DEVELOPING INTO A TROPICAL CYCLONE. THERE IS FAIRLY GOOD MODEL AGREEMENT THAT A SIGNIFICANT AMOUNT OF TROPICAL MOISTURE COULD BE TRANSPORTED NORTHWARD AHEAD OF THE COLD FRONT ORIGINATING WITH THE EXTRATROPICAL CYCLONE ACROSS THE NORTHERN CONUS. AS IS TYPICAL FOR THIS TIME OF YEAR, THE BEST UPPER-LEVEL FORCING WILL LIFT NORTHWARD INTO CANADA, WHILE A WEAKER TROUGH SPLITS OFF TO THE SOUTHWEST ACROSS THE SOUTHERN CONUS. THIS WILL LIKELY SLOW THE EASTWARD PROGRESSION OF THE COLD FRONT, INTRODUCING THE POSSIBILITY OF A PROLONGED RAIN EVENT ACROSS PARTS OF THE EASTERN CONUS. THERE IS SOME UNCERTAINTY AS TO WHERE THE HEAVIEST RAINFALL WILL OCCUR, SO THE SHAPES DEPICTED ON THE MAP ARE FAIRLY LARGE IN ORDER TO ACCOUNT FOR SOME OF THIS UNCERTAINTY. LARGE AREAS OF 2-4 (LOCALLY MORE) INCHES OF RAIN ARE POSSIBLE WITHIN THE DEPICTED REGIONS. ADDITIONALLY, FOR EACH DEPICTED HEAVY RAIN HAZARD ASSOCIATED WITH THIS SYSTEM, THE SOUTHERN PART OF THE SHAPES ARE FAVORED EARLIER IN THE PERIOD, WHILE THE NORTHERN PARTS ARE FAVORED LATER IN THE PERIOD.

A STRONG SYSTEM IS FORECAST TO IMPACT PARTS OF NORTHERN AND WESTERN ALASKA LATE IN THE WEEK AND EARLY THIS WEEKEND, POTENTIALLY BRINGING HIGH WINDS/WAVES FRIDAY INTO SATURDAY. HOWEVER, IT APPEARS THAT THAT THE LOW WILL OCCLUDE AT PEAK INTENSITY TOO FAR WEST TO POSE SERIOUS HAZARDS TO LAND.

FOR THURSDAY OCTOBER 10 - WEDNESDAY OCTOBER 16: A LARGE SPREAD AMONG THE 6Z GFS AND 0Z ECMWF ENSEMBLE MEMBERS PRECLUDES DESIGNATION OF ANY HAZARDS ACROSS THE CONUS EXCEPT FOR THE ONGOING SEVERE TO EXCEPTIONAL DROUGHT AREAS. ACCORDING TO THE U.S. DROUGHT MONITOR VALID ON SEPTEMBER 24, SEVERE TO EXCEPTIONAL DROUGHT COVERS A QUARTER OF THE CONUS WHICH IS THE LOWEST COVERAGE SINCE JUNE 2012.

A MORE FAVORABLE MJO PHASE SUPPORTS ENHANCED TROPICAL ACTIVITY IN THE ATLANTIC BASIN DURING WEEK-2. U.S. INTERESTS SHOULD MONITOR UPDATES FROM THE NATIONAL HURRICANE CENTER FOR THE LATEST ON ANY POTENTIAL TROPICAL DEVELOPMENT.

AS MANY AS THREE RECURVING TROPICAL CYCLONES ARE POSSIBLE IN THE WEST PACIFIC OVER THE NEXT ONE TO TWO WEEKS. THIS INTRODUCES THE LIKELIHOOD OF EXTRATROPICAL AMPLIFICATION DOWNSTREAM, LIKELY ACCOUNTING FOR THE UNCERTAINTY CURRENTLY OBSERVED IN THE GLOBAL ENSEMBLES.

A LONGWAVE TROUGH IS EXPECTED TO MAINTAIN INCLEMENT WEATHER ACROSS MUCH OF ALASKA. UNCERTAINTY IN TIMING AND INTENSITY OF SURFACE LOWS PRECLUDES DESIGNATION OF ANY SPECIFIC HAZARDS DURING THIS TIME RANGE.

FORECASTER: STEPHEN BAXTER

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