789  
FXUS02 KWBC 272120  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
419 PM EST WED FEB 27 2019  
 
VALID 12Z SAT MAR 02 2019 - 12Z WED MAR 06 2019  
   
..PATTERN OVERVIEW
 
 
BROADLY CYCLONIC MEAN FLOW ACROSS THE CONUS AT THE START OF THE  
WEEKEND SHOULD TRANSITION TOWARD INCREASINGLY AMPLIFIED TROUGHING  
OVER THE EAST BY THE MIDDLE OF NEXT WEEK AS AN UPPER RIDGE REACHES  
THE ROCKIES AND A TRAILING TROUGH APPROACHES THE WEST COAST.  
 
   
..GUIDANCE EVALUATION/PREFERENCES
 
 
FORECAST WAS KEPT FAIRLY CLOSE TO CONTINUITY IN THIS UPDATE WITH  
ONLY MINOR ADJUSTMENTS. MODELS CONTINUE TO SHOW GOOD AGREEMENT AT  
THE LARGER SCALES THROUGH THE PERIOD, BUT WITH SOME SIGNIFICANT  
DIFFERENCES SURROUNDING SMALLER-SCALE FEATURES. FAST-MOVING AND  
LOW AMPLITUDE SHORTWAVE ENERGY ARRIVING AT THE WEST COAST ON DAY 3  
(SAT) IS KEY IN THE EVOLUTION OF A WAVE OF LOW PRESSURE ACROSS THE  
EASTERN U.S. SUN-MON. THE DETERMINISTIC 00Z ECMWF WAS A BIT FASTER  
WITH THIS ENERGY THAN THE CONSENSUS THROUGHOUT THIS TIME FRAME,  
WHICH ENDS UP RESULTING IN A SURFACE WAVE TRACKING FARTHER  
NORTH/WEST ACROSS THE EASTERN U.S. BY SUN. MODELS HAVE SHOWN A  
TREND TOWARD A LESS SUPPRESSED SYSTEM ACROSS THE EAST SUN, WITH  
THE GFS LAGGING THE TREND. THE SOLUTIONS BEST CLUSTERED WITH THE  
ENSEMBLE CONSENSUS THROUGHOUT WITH RESPECT TO THIS FEATURE SEEMED  
TO BE THE 00Z UKMET/CMC AND 06Z FV3-GFS, AND A BLEND OF THESE  
SOLUTIONS FORMED A BASIS FOR THE FORECAST DURING DAYS 3-5. THE  
EVENTUAL TRACK OF THIS SURFACE LOW BY SUN-MON WILL HAVE  
SIGNIFICANT IMPLICATIONS IN TERMS OF P-TYPE FOR PORTIONS OF THE  
MID-ATLANTIC AND NORTHEAST, INCLUDING THE MAJOR CITIES, THE  
FORECAST FOR WHICH IS HIGHLY UNCERTAIN AT THIS TIME. LATER IN THE  
FORECAST PERIOD, AS ARCTIC HIGH PRESSURE CONTINUES TO SPREAD COLD  
AIR SOUTH INTO THE CENTRAL AND PORTIONS OF THE EASTERN U.S., THE  
MOST ACTIVE WEATHER WILL SHIFT TO THE WEST COAST, WITH GENERAL  
CONSENSUS THAT A LOW PRESSURE SYSTEM SHOULD APPROACH THE COAST BY  
THE MIDDLE OF NEXT WEEK. SOLUTIONS DIFFER RATHER SUBSTANTIALLY ON  
TIMING, HOWEVER, WHILE THE ENSEMBLE MEANS SHOW A BIT MORE  
CONSENSUS. THUS, THE FORECAST DURING DAYS 6-7 (TUE-WED) PLACED  
HEAVY EMPHASIS ON THE 00Z ECENS/06Z GEFS ENSEMBLE MEANS.  
 
   
..WEATHER HIGHLIGHTS/HAZARDS
 
 
ACROSS THE WEST THE PRIMARY AXIS FOR HEAVIEST RAIN AND HIGHER  
ELEVATION SNOW WILL EXTEND FROM CALIFORNIA EASTWARD THROUGH THE  
CENTRAL/SOUTH-CENTRAL ROCKIES WITH THE SIERRA NEVADA LIKELY SEEING  
THE HIGHEST 5-DAY TOTALS. TWO SYSTEMS WILL AFFECT THE REGION  
DURING THE PERIOD, ONE ARRIVING EARLY IN THE WEEKEND AND SPREADING  
MOISTURE RAPIDLY EASTWARD THEN FOLLOWED BY A SECOND ARRIVING  
TUE-WED. AS MOISTURE FROM THE SECOND SYSTEM SPREADS NORTHWARD  
THERE MAY BE POTENTIAL FOR WINTRY PRECIPITATION AT LOW ELEVATIONS  
OVER INTERIOR PORTIONS OF THE NORTHWEST GIVEN THE COLD AIR LIKELY  
TO BE IN PLACE.  
 
THE SYSTEM AFFECTING THE NORTHEAST DURING THE WEEKEND SHOULD BRING  
SOME SNOWFALL TO THE REGION BUT WEAKENING AND POSSIBLY OFFSHORE  
TRENDS FOR LOW PRESSURE AS WELL AS FAST PROGRESSION MAY LIMIT  
ACCUMULATIONS. SOUTHERN STREAM ENERGY INTERACTING WITH THE  
TRAILING FRONT MAY PRODUCE A PERIOD OF HEAVY RAINFALL OVER PARTS  
OF THE SOUTHEAST WITH THE WEEKEND INTO EARLY MON TIME FRAME THE  
MOST LIKELY PERIOD FOR THIS ACTIVITY. GUIDANCE HAS NOT YET FULLY  
CONVERGED FOR DETAILS SO CONFIDENCE IS ONLY MODERATE THUS FAR.  
SNOW WILL BE POSSIBLE IN THE NORTHERN PART OF THE MOISTURE  
SHIELD--FROM THE SOUTH-CENTRAL MISSISSIPPI VALLEY INTO THE  
MID-ATLANTIC. LIGHTER RAINFALL COULD LINGER OVER PARTS OF THE  
EXTREME SOUTHEAST/FLORIDA INTO NEXT WEEK.  
 
WITHIN THE WIDESPREAD AREA OF EXTREMELY COLD AIR OVER THE CENTRAL  
U.S., EXPECT THE MOST EXTREME ANOMALIES TO BE OVER THE  
NORTHERN-CENTRAL PLAINS DURING SAT-MON WITH ANOMALIES OF 30-45F  
BELOW NORMAL. ESPECIALLY ON SUN-MON MANY PLACES OVER THE PLAINS  
AND MIDWEST SHOULD CHALLENGE OR EXCEED DAILY RECORD  
VALUES--ESPECIALLY FOR COLD HIGHS BUT ALSO FOR MORNING LOWS AT  
SOME LOCATIONS. LESS EXTENSIVE COVERAGE OF DAILY RECORDS MAY  
CONTINUE INTO TUE. THE EASTERN U.S. WILL SEE A MODIFIED FORM OF  
THIS COLD AIR BY THE FIRST HALF OF NEXT WEEK WITH READINGS "ONLY"  
10-20F BELOW NORMAL. LOCALIZED PARTS OF THE INTERIOR NORTHWEST  
MAY SEE TEMPERATURES 10-30F BELOW NORMAL. RELATIVE WARMTH WILL BE  
CONFINED TO THE SOUTHERN HALF OF THE WEST AND MORE SO FOR MORNING  
LOWS THAN AFTERNOON HIGHS.  
 
RYAN/RAUSCH  
 
HAZARDS:  
- HEAVY PRECIPITATION ACROSS PORTIONS OF THE NORTHEAST, THE  
CENTRAL APPALACHIANS, THE MIDDLE MISSISSIPPI VALLEY, THE  
MID-ATLANTIC, THE GREAT LAKES, AND THE OHIO VALLEY, SUN-MON, MAR  
3-MAR 4.  
- HEAVY RAIN ACROSS PORTIONS OF CALIFORNIA, THE CENTRAL GREAT  
BASIN, THE PACIFIC NORTHWEST, AND THE SOUTHWEST, SAT-WED, MAR  
2-MAR 6.  
- HEAVY RAIN ACROSS PORTIONS OF THE LOWER MISSISSIPPI VALLEY, THE  
TENNESSEE VALLEY, THE MID-ATLANTIC, THE SOUTHERN APPALACHIANS, THE  
SOUTHEAST, AND THE OHIO VALLEY, SAT-SUN, MAR 2-MAR 3.  
- HEAVY SNOW ACROSS PORTIONS OF THE NORTHEAST, THE CENTRAL GREAT  
BASIN, THE PACIFIC NORTHWEST, THE NORTHERN GREAT BASIN,  
CALIFORNIA, THE GREAT LAKES, AND THE SOUTHWEST, SAT, MAR 2.  
- HEAVY SNOW ACROSS PORTIONS OF THE SOUTHERN ROCKIES, THE CENTRAL  
ROCKIES, THE CENTRAL GREAT BASIN, THE CENTRAL PLAINS, AND THE  
SOUTHWEST, SAT-SUN, MAR 2-MAR 3.  
- FLOODING POSSIBLE ACROSS PORTIONS OF THE SOUTHEAST AND THE  
MID-ATLANTIC.  
- FLOODING OCCURRING OR IMMINENT ACROSS PORTIONS OF THE LOWER  
MISSISSIPPI VALLEY, THE TENNESSEE VALLEY, THE GREAT LAKES, THE  
MIDDLE MISSISSIPPI VALLEY, THE MID-ATLANTIC, THE UPPER MISSISSIPPI  
VALLEY, THE SOUTHEAST, THE PACIFIC NORTHWEST, AND THE OHIO VALLEY.  
- FLOODING LIKELY ACROSS PORTIONS OF THE SOUTHEAST, THE  
MID-ATLANTIC, AND CALIFORNIA.  
- MUCH BELOW NORMAL TEMPERATURES ACROSS MUCH OF THE EASTERN  
TWO-THIRDS OF THE COUNTRY INCLUDING THE INTERIOR SECTIONS OF THE  
PACIFIC NORTHWEST, SAT-WED, MAR 2-MAR 6.  
- HIGH WINDS ACROSS PORTIONS OF MAINLAND ALASKA AND THE ALEUTIANS,  
MON-TUE, MAR 4-MAR 5.  
- HIGH WINDS ACROSS PORTIONS OF THE ALEUTIANS, SUN-MON, MAR 3-MAR  
4.  
AND WED, MAR 6.  
- HIGH SIGNIFICANT WAVE HEIGHTS FOR COASTAL PORTIONS OF MAINLAND  
ALASKA, MON-TUE, MAR 4-MAR 5.  
 
ADDITIONAL 3-7 DAY HAZARDS INFORMATION CAN BE FOUND ON THE WPC  
MEDIUM RANGE HAZARDS CHART AT:  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/THREATS/THREATS.PHP  
 
WPC MEDIUM RANGE 500MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDICES ARE AT:  
 
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST500_WBG.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/MEDR/5DAYFCST_WBG_CONUS.GIF  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/5KM_GRIDS/5KM_GRIDSBODY.HTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/QPF/DAY4-7.SHTML  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/WWD/PWPF_D47/PWPF_MEDR.PHP?DAY=4  
HTTPS://WWW.WPC.NCEP.NOAA.GOV/HEAT_INDEX.SHTML  
 

 
 
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