549  
FXUS02 KWBC 191547  
PMDEPD  
 
EXTENDED FORECAST DISCUSSION  
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD  
1146 AM EDT FRI OCT 19 2018  
 
VALID 12Z MON OCT 22 2018 - 12Z FRI OCT 26 2018  
 
...GUIDANCE/PREDICTABILITY ASSESSMENT AND WEATHER  
HIGHLIGHTS/THREATS...  
 
LATEST MODELS AND ENSEMBLES ARE WELL CLUSTERED THROUGH MIDWEEK IN  
A PATTERN WITH ABOVE NORMAL FORECAST CONFIDENCE. PREFER A  
COMPOSITE GUIDANCE SOLUTION TO SMOOTH OUT LINGERING SMALL SCALE  
VARIANCE. PREFER TO LEAN MORE ON ENSEMBLE GUIDANCE AND CONTINUITY  
BY DAYS 6/7 AS VARIANCE GRADUALLY GROWS.  
 
THE PATTERN IS HIGHLY AMPLIFIED AT HIGHER LATITUDES WITH A MEAN  
MID-UPPER LEVEL TROUGH AND SURFACE LOW/STORM SOLUTION INTO ALASKA  
DOWN TO THE NORTHEAST PACIFIC...INCLUDING POWERFUL SURFACE LOWS  
CRASHING INTO COASTAL BRITISH COLUMBIA. LEAD HEIGHT FALLS INTO  
WESTERN CANADA AND THE PACIFIC NORTHWEST ALONG WITH AN  
INCREASINGLY PRECIPITATION AMOUNT AND CHANCE OF MODERATE  
PRECIPITATION. DOWNSTREAM, HIGHLY AMPLIFIED FLOW WILL BE IN PLACE  
WITH A MEAN UPPER LOW SPINNING OVER THE UPPER REACHES OF NUNAVUT.  
SHORTWAVES EMBEDDED IN THIS FLOW ARE PRIMED TO INTENSIFY AND  
EVENTUALLY BECOME NEGATIVELY-TILTED NEAR NEW ENGLAND. MANY  
SOLUTIONS SHOW A RATHER DEEP SURFACE CYCLONE OVER THE CANADIAN  
MARITIMES BY MIDWEEK.  
 
WELL SOUTH IN SPLIT FLOW THAT INITIALLY SETS UP ACROSS NORTH  
AMERICA, A WEAK AND STRETCHED OUT SOUTHERN STREAM TROUGH ANCHORS  
FROM THE DESERT SOUTHWEST. THIS FEATURE SHOULD GRADUALLY PRESS  
EASTWARD IN RESPONSE TO A LOWERING OF UPSTREAM HEIGHTS.  
DOWNSTREAM, TOWARD THE GULF OF MEXICO, A LINGERING FRONTAL ZONE  
AND EVENTUAL WAVE OF LOW PRESSURE SHOULD IMPACT THE GULF COAST  
STATES THEN SOUTHEAST WITH A THREAT FOR HEAVY REPEAT RAINFALL.  
EXPECT MORE MODEST PRECIPITATION ON THE BACKSIDE UP NORTHWARD  
THROUGH THE SOUTHERN AND CENTRAL ROCKY STATES WITH PROGRESSION OF  
A MAIN SOUTHERN STREAM TROUGH FROM CA/NW MEXICO.  
 
A HEAVY RAINFALL THREAT WILL REMAIN ALONG THE WESTERN/CENTRAL GULF  
COASTS WITH THE AXIS MOVING EASTWARD IN TIME ACCOMPANYING THE WEAK  
AREA OF LOW PRESSURE. IT REMAINS TO BE SEEN HOW MUCH INSTABILITY  
WILL APPROACH THE COAST BUT HEFTY QPF IS NOTED IN THE GUIDANCE  
JUST OFFSHORE. THE FORECAST ITSELF TENDS TO KEEP THIS AXIS RIGHT  
ALONG THE COAST BUT THE ULTIMATE PLACEMENT WITH BE HEAVILY DRIVEN  
BY WHERE THE INSTABILITY SETS UP. ACROSS THE PACIFIC NORTHWEST,  
SEMI-PERSISTENT ONSHORE FLOW WILL KEEP CONDITIONS WET OVER THE  
OLYMPICS AND CASCADES THROUGHOUT THE PERIOD. PACIFIC DOMINATED AIR  
MASSES WILL PRECLUDE ANY NOTABLE WINTER WEATHER THREATS. ACROSS  
NEW ENGLAND, SOME SNOW MAY FALL OVER NORTHERN SECTIONS IF THE LOW  
PRESSURE WERE TO DEEPEN ENOUGH TO PULL IN COLDER AIR DOWN FROM  
EASTERN CANADA. REGARDING TEMPERATURES, BELOW AVERAGE NUMBERS WILL  
PREVAIL OVER MUCH OF THE CENTRAL/EASTERN U.S. DURING THE EARLY TO  
MIDDLE PART OF NEXT WEEK, READINGS COULD BE AROUND 10 TO 15  
DEGREES BELOW CLIMATOLOGY OVER THE SOUTHERN PLAINS WITH PERSISTENT  
NORTHERLY FLOW AND ACTIVE PRECIPITATION. OVER THE NORTHWESTERN  
U.S., AIR MASSES OF PACIFIC ORIGIN WILL KEEP MILD AIR IN PLACE  
THROUGH AT LEAST THE MIDDLE OF NEXT WEEK.  
 
SCHICHTEL  
 
WPC MEDIUM RANGE 500 MB HEIGHTS, SURFACE SYSTEMS, WEATHER GRIDS,  
QUANTITATIVE PRECIPITATION, WINTER WEATHER OUTLOOK PROBABILITIES  
AND HEAT INDEXES ARE FOUND 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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