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Extended Forecast Discussion
 
(Caution: Version displayed is not the latest version. - Issued 0446Z Feb 13, 2018)
 
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Abbreviations and acronyms used in this product
 
Geographic Boundaries -  Map 1: Color  Black/White       Map 2: Color  Black/White


EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
1146 PM EST MON FEB 12 2018

VALID 12Z FRI FEB 16 2018 - 12Z TUE FEB 20 2018

...SIGNIFICANT TROUGH POSSIBLE FOR THE WEST NEXT WEEK...


...OVERVIEW...

MAIN DRIVERS OF THE MEDIUM RANGE FORECAST WILL BE UPPER RIDGING
NEAR THE GULF OF ALASKA AND OVER THE SOUTHEAST US AND A PERSISTENT
UPPER LOW OVER NORTHERN HUDSON BAY. THAT WILL FAVOR A RELATIVELY
STABLE LONGWAVE PATTERN WITH SYSTEMS MOVING THROUGH THE FLOW --
OUT OF THE NORTHEASTERN PACIFIC AND THROUGH THE WEST. BY NEXT
WEEK, ENSEMBLES WERE STRONGLY SHOWING INCREASING HEIGHTS IN THE
EAST AS THE UPPER HIGH EXPANDS NORTHWARD AND THE POTENTIAL FOR THE
UPSTREAM TROUGH TO DIG SMARTLY INTO CALIFORNIA AND THE INTERIOR
SOUTHWEST.


...GUIDANCE PREFERENCES...

LATEST MODELS/ENSEMBLES WERE GENERALLY CLUSTERED ENOUGH TO ALLOW
FOR A PRIMARILY DETERMINISTIC BLEND TO START (FRI/SAT FORECAST)
WITH A TREND TOWARD A MAJORITY ENSEMBLE MEAN BLEND BY NEXT TUESDAY
GIVEN THE UNCERTAINTY IN THE STRENGTH OF THE WESTERN TROUGH AND
EMBEDDED SHORTWAVES COMING OUT OF THE NORTHEASTERN PACIFIC.
NOTEWORTHY IS THE VERY GOOD AGREEMENT ON THE EASTERN RIDGING THAT
CONTINUES TO TREND STRONGER IN THE ENSEMBLES. TYPICAL VERIFICATION
SHOWS BETTER RELIABILITY FOR STRONG RIDGES RATHER THAN DEEP
TROUGHS IN THE ENSEMBLES AND THE UPPER PATTERN CONFIGURATION
CERTAINLY SUPPORTS IT.


...WEATHER HIGHLIGHTS/THREATS...

TEMPERATURES...

SURGE OF MILD TEMPERATURES AHEAD OF THE LEAD FRONTAL BOUNDARY
PUSHING THROUGH THE EAST ON FRIDAY WILL BE REPLACED BY NEAR TO
BELOW AVERAGE TEMPERATURES IN ITS WAKE FROM THE PLAINS EASTWARD.
TEMPERATURES WILL AGAIN RISE SUN/MON IN THE EAST AHEAD OF THE
WESTERN SYSTEM. TEMPERATURES MAY AGAIN RISE TO 10-20 DEGREES ABOVE
AVERAGE. FOR THE WEST, TEMPERATURES WILL GENERALLY TREND DOWNWARDS
FROM THE WEEKEND INTO NEXT MON/TUE AS THE TROUGH SINKS IN AND THE
ARCTIC FRONT TO THE NORTH SLIPS SOUTHWARD AS WELL. TEMPERATURES
WILL BE ANYWHERE FROM 5-30 DEGREES BELOW AVERAGE.

PRECIPITATION...

EXPECT A FOCUS OF PRECIPITATION ALONG THE FRONT FROM THE SOUTHERN
PLAINS EAST-NORTHEASTWARD TO THE CENTRAL APPALACHIANS LATER THIS
WEEK INTO THE WEEKEND. BY NEXT SUN-TUE, PRECIPITATION WILL EXPAND
THROUGH THE WEST, FIRST THROUGH OR/WA (WITH SNOW FOR THE COASTAL
RANGES AND CASCADES), BUT THEN ESPECIALLY THROUGH THE INTERIOR AND
PERHAPS THROUGH MUCH OF CALIFORNIA. SNOW LEVELS WILL LOWER AS
COLDER AIR WORKS IN (POSSIBLY 1500-2000 FT) ALL THE WAY TO SOME
VALLEY LOCATIONS IN NORTHERN CALIFORNIA AND OREGON/NEVADA.
PRECIPITATION COVERAGE WILL DEPEND ON THE DEPTH OF THE TROUGHING
(12Z/12 ECMWF FARTHER WEST THAN MOST MODELS/ENSEMBLES) BUT FOCUS
AS OF NOW WILL BE FROM OREGON THROUGH NEVADA INTO
UTAH/ARIZONA/COLORADO. THIS WILL INCLUDE THE COASTAL RANGES OF
WA/OR LATER THIS WEEKEND. FARTHER EAST, WITH EXPANDING RIDGING
OVER THE SOUTHEAST, THE SLOWLY MOVING COLD FRONT MAY ACT AS A
FOCUS FOR MODEST RAINFALL FROM THE LOWER MISSISSIPPI VALLEY INTO
THE OHIO AND TENNESSEE VALLEYS MON/TUE WITH SOME WINTRY WEATHER
FOR THE NORTHERN FRINGE.


FRACASSO