718  
FXUS21 KWNC 071936  
PMDTHR  
US HAZARDS OUTLOOK  
NWS CLIMATE PREDICTION CENTER COLLEGE PARK MD  
300 PM EST MARCH 07 2018  
 
SYNOPSIS: A SURFACE LOW IS FORECAST TO PROGRESS EAST ACROSS THE TENNESSEE  
VALLEY THIS WEEKEND WITH THE POTENTIAL FOR A SECONDARY COASTAL STORM TO DEVELOP  
NEAR THE MID-ATLANTIC. AN AREA OF MID-LEVEL LOW PRESSURE IS EXPECTED TO  
PROGRESS SHIFT FROM THE EAST PACIFIC TO CALIFORNIA AND THE SOUTHWEST DURING THE  
NEXT WEEK TO TEN DAYS. A BROAD AREA OF SURFACE LOW PRESSURE IS FORECAST OVER  
SOUTHERN MAINLAND ALASKA AT THE BEGINNING OF THE PERIOD, WHILE AN AREA OF  
MID-LEVEL HIGH PRESSURE PERSISTS NEAR THE ALEUTIANS DURING THE NEXT TWO WEEKS.  
 
HAZARDS  
 
HEAVY RAIN FOR PARTS OF THE SOUTHEAST, SAT, MAR 10.  
 
HEAVY SNOW FOR THE HIGHER ELEVATIONS OF THE CENTRAL AND SOUTHERN APPALACHIANS,  
SAT-SUN, MAR 10-11.  
 
HEAVY SNOW FOR PARTS OF THE SIERRA NEVADA MOUNTAINS OF CALIFORNIA, TUE-WED, MAR  
13-14.  
 
HIGH WINDS FOR PARTS OF THE ALEUTIANS AND ALASKA PENINSULA, SAT, MAR 10.  
 
HIGH SIGNIFICANT WAVE HEIGHTS FOR PARTS OF THE ALEUTIANS AND ALASKA PENINSULA,  
SAT, MAR 10.  
 
FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER AND MIDDLE  
MISSISSIPPI VALLEY, NORTHEAST TEXAS, AND THE MIDWEST.  
 
A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE SOUTHEAST AND  
MID-ATLANTIC, THU, MAR 15.  
 
A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES FOR PARTS OF THE NORTHERN GREAT  
PLAINS, SAT-WED, MAR 17-21.  
 
A SLIGHT TO MODERATE RISK OF HEAVY PRECIPITATION FOR PARTS OF THE WESTERN U.S.,  
THU-SAT, MAR 15-17.  
 
SEVERE DROUGHT ACROSS THE CENTRAL PLAINS, THE CENTRAL ROCKIES, THE CENTRAL  
GREAT BASIN, THE NORTHERN PLAINS, THE SOUTHERN ROCKIES, CALIFORNIA, THE  
SOUTHERN PLAINS, AND THE SOUTHWEST.  
 
DETAILED SUMMARY  
 
FOR SATURDAY MARCH 10 - WEDNESDAY MARCH 14: A SHORTWAVE TROUGH IN THE SOUTHERN  
STREAM IS FORECAST TO SPAWN A WEAK SURFACE LOW OVER THE SOUTHERN GREAT PLAINS  
BY MARCH 10. AS THIS SURFACE LOW INTERACTS WITH MODEST GULF INFLOW, MODERATE TO  
HEAVY RAIN (LOCAL AMOUNTS UP TO 2 INCHES) IS EXPECTED FROM THE TENNESSEE VALLEY  
SOUTH TO THE GULF COAST ON MARCH 10. ANY HEAVY RAINFALL IS LIKELY TO BE BRIEF  
AND MOSTLY OCCUR TO THE EAST OF THE ONGOING FLOOD AREAS. ALTHOUGH ISOLATED  
SEVERE THUNDERSTORMS MAY AFFECT PARTS OF THE LOWER MISSISSIPPI VALLEY AND GULF  
COAST STATES ON MARCH 10, A WIDESPREAD OUTBREAK OF SEVERE WEATHER IS NOT  
ANTICIPATED DUE TO THE LOW AMPLITUDE OF THE SHORTWAVE TROUGH AND LIMITED  
INSTABILITY.  
 
THE GFS MODEL REMAINS THE MOST BULLISH ON THE POTENTIAL FOR A LATE SEASON  
WINTER STORM TO AFFECT THE MID-ATLANTIC. THE RECENT DETERMINISTIC GFS MODEL  
RUNS, INCLUDING 12Z/MAR 7 AND MANY OF ITS ENSEMBLE MEMBERS, INDICATE A  
SECONDARY COASTAL STORM FORMING ON MARCH 11 NEAR THE LOWER CHESAPEAKE BAY,  
WHICH WOULD BRING HEAVY SNOW AT LEAST TO THE HIGHER ELEVATIONS OF THE  
MID-ATLANTIC. HOWEVER, THE DETERMINISTIC 0Z ECMWF MODEL FAVORS A WEAKER AND  
MORE SUPPRESSED SURFACE LOW TRACK. THE DETERMINISTIC 12Z ECMWF MODEL INDICATES  
A STRENGTHENING LOW OFFSHORE OF THE EAST COAST. DUE TO LARGE DIFFERENCES AMONG  
DETERMINISTIC MODEL SOLUTIONS, A HEAVY SNOW HAZARD (4 INCHES OR MORE) IS POSTED  
ONLY FOR THE HIGHER ELEVATIONS OF THE CENTRAL AND SOUTHERN APPALACHIANS AT THIS  
TIME.  
 
SURFACE HIGH PRESSURE IS FORECAST TO BECOME CENTERED OVER THE SOUTHEAST BY THE  
MIDDLE PART OF NEXT WEEK. A FREEZE OR FROST IS EXPECTED TO OCCUR ON MARCH 14 IN  
THE AREA OUTLINED WITH A MUCH BELOW-NORMAL TEMPERATURE HAZARD. GIVEN THE  
ABOVE-NORMAL TEMPERATURES DURING LATE FEBRUARY, THESE FREEZING TEMPERATURES  
COULD DAMAGE PEACH TREES THAT ARE IN BLOOM ACROSS THE SOUTHEAST.  
 
HEAVY SNOW (6 INCHES OR MORE PER 24 HOURS) REMAINS LIKELY FOR THE SIERRA NEVADA  
MOUNTAINS OF CALIFORNIA ON MARCH 13 AND 14 AS AN AMPLIFIED 500-HPA TROUGH  
APPROACHES THE WEST COAST NEXT WEEK. THE 0Z ECMWF ENSEMBLE MEAN INDICATES  
48-HOUR PRECIPITATION AMOUNTS OF 1.5 TO 2 INCHES (LIQUID EQUIVALENT) ACROSS  
THESE AREAS.  
 
WIDESPREAD MODERATE TO MAJOR FLOODING CONTINUES ALONG THE SOUTHERN THIRD OF THE  
MISSISSIPPI RIVER AND LOWER OHIO RIVER AND MANY OF THE TRIBUTARIES. FLOOD  
LEVELS ALONG THE LOWER MISSISSIPPI RIVER ARE FORECAST TO CONTINUE TO INCREASE  
THROUGH NEXT WEEK AND MAY NEAR MAJOR FLOOD STAGE.  
 
A SURFACE LOW NEAR THE KENAI PENINSULA IS EXPECTED TO PROMOTE HIGH WINDS  
(SPEEDS IN EXCESS OF 40 KNOTS) AND HIGH SIGNIFICANT WAVE HEIGHTS (ABOVE 24  
FEET) THROUGH MARCH 10. WIND SPEEDS AND WAVE HEIGHTS ARE LIKELY TO EASE QUICKLY  
THIS WEEKEND AS THE TIGHT PRESSURE GRADIENT OVER THE ALEUTIANS RELAXES.  
 
FOR THURSDAY MARCH 15 - WEDNESDAY MARCH 21: THE DETERMINISTIC MODEL RUNS  
INDICATE SURFACE HIGH PRESSURE OVER THE SOUTHERN APPALACHIANS ON MARCH 15 WHICH  
COULD RESULT IN A DAMAGING FROST OR FREEZE TO ANY EARLY VEGETATIVE GROWTH.  
THEREFORE, A SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES IS POSTED FOR PARTS  
OF THE SOUTHERN APPALACHIANS AND SOUTHERN MID-ATLANTIC ON MARCH 15.  
 
UPPER-LEVEL RIDGING (TROUGHING) OVER THE NORTH PACIFIC (WESTERN U.S.) ARE THE  
MOST STABLE LONGWAVE FEATURES DURING WEEK-2. SPREAD IS LARGE AMONG ENSEMBLE  
MEMBERS ACROSS THE CENTRAL AND EASTERN U.S. WHERE MODEL SOLUTIONS CONTINUE TO  
DIFFER ON HOW VARIOUS SHORTWAVE TROUGHS INTERACT. BLOCKING AT THE HIGHER  
LATITUDES OVER EASTERN NORTH AMERICA AND THE NORTHERN ATLANTIC IS EXPECTED TO  
WEAKEN DURING MID-MARCH. THE GFS MODEL INDICATES THAT THE ARCTIC OSCILLATION  
(AO) INDEX BECOMES MORE NEUTRAL DURING THE THIRD WEEK OF MARCH AFTER IT REACHED  
ITS LOWEST VALUE AT THE BEGINNING OF THE MONTH.  
 
BASED ON THE AMPLIFYING UPPER-LEVEL TROUGH MOVING INLAND FROM THE EAST PACIFIC  
BY THE BEGINNING OF WEEK-2, A SLIGHT TO MODERATE RISK OF HEAVY PRECIPITATION IS  
POSTED FOR PARTS OF THE WESTERN U.S. FROM MARCH 15-17. HEAVY SNOW IS LIKELY TO  
CONTINUE FOR THE SIERRA NEVADA MOUNTAINS AND MAY AFFECT THE HIGHER ELEVATIONS  
OF THE FOUR CORNERS REGION. THE SLIGHT RISK OF MUCH BELOW-NORMAL TEMPERATURES  
POSTED FOR THE NORTHERN GREAT PLAINS FROM MARCH 17-21 IS CONSISTENT WITH  
UPSTREAM RIDGING NEAR THE ALEUTIANS. A DEVELOPING UPPER-LEVEL TROUGH OVER THE  
BERING SEA AND ASSOCIATED ONSHORE FLOW ARE EXPECTED TO INCREASE THE RISK OF  
HIGH SURF/COASTAL FLOODING ALONG THE SOUTHWEST ALASKA COAST WHERE SEA ICE IS  
LOW.  
 
THE U.S. DROUGHT MONITOR, VALID ON FEB 27, 2018 INDICATES A DECREASE IN THE  
COVERAGE OF SEVERE TO EXCEPTIONAL DROUGHT (D2-D4) FROM 17.76% LAST WEEK TO  
14.31% THIS WEEK. A FEW OF THE MORE SUBSTANTIAL REVISIONS MADE TO THE MAP THIS  
WEEK INCLUDE A DECREASE IN THE D1 COVERAGE OVER PENNSYLVANIA AND A DECREASE IN  
THE D2 COVERAGE OVER OKLAHOMA AND ARKANSAS.  
 
FORECASTER: BRAD PUGH  
 

 
 
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