Preliminary Forecasts
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FXUS02 KWNH 110623
PREEPD

PRELIMINARY EXTENDED FORECAST DISCUSSION
NWS WEATHER PREDICTION CENTER COLLEGE PARK MD
222 AM EDT FRI JUL 11 2014

VALID 12Z MON JUL 14 2014 - 12Z FRI JUL 18 2014

...OVERVIEW...
HIGHLY-AMPLIFIED PATTERN EXPECTED ACROSS NORTH AMERICA LEADING TO
WELL ABOVE NORMAL TEMPS IN THE WEST AND NORTHWEST. ON THE FLIP
SIDE...WELL BELOW-NORMAL TEMPS IN THE PLAINS AND GREAT
LAKES---WHERE DAILY LOW TEMPERATURE RECORDS FOR JULY WILL BE
TESTED.

...MODEL PREFERENCES/UNCERTAINTY ASSESSMENT...
TO PRESERVE CONTINUITY...MAINTAINED A BLEND OF THE 10/12Z
ECENS-NAEFS...THE PREVIOUS WPC GRAPHICS. FOR DAYS 3-5...WAS ABLE
TO USE ASPECTS OF THE 10/12Z GFS/ECMWF TO HANDLE THE PROGRESSION
OF THE COLD FRONT. WHERE THIS BLEND HAS SOME QUESTION
MARKS...CROPS UP DAY 6 WHEN THE COOL/DRY CANADIAN SURFACE HIGH HAS
SETTLED OVER THE MIDWEST. 10/12Z ECENS/NAEFS 12-HR POP FORECASTS
LOOK VERY MUCH LIKE CLIMO ALONG THE LOWER HALF OF THE MISSOURI
VALLEY AND THE CENTRAL GREAT LAKES STATES.

THE 10/12Z DETERMINISTIC GFS AND ECMWF LOOK VERY SIMILAR WITH
THEIR SOLUTIONS EAST OF THE DIVIDE--WITH `RELENTLESS` TROUGHING IN
EASTERN CANADA...COMBINED WITH QUASI-STATIONARY HIGH PRESSURE
RIDGING IN THE MOUNTAINS OF WESTERN CANADA AND EXTENDING INTO
NORTHEAST ALASKA AND THE GREAT BASIN. BOTH DETERMINISTIC  RUNS
CONTINUE TO POINT TO WHAT LOOKS MORE LIKE A MID-WINTER FLOW
PATTERN FOR EASTERN CANADA. IN THIS FLOW PATTERN...THE TEMPERATURE
PATTERN OVER THE LOWER 48 COULD/SHOULD BECOME ONE OF EXTREMES ON
BOTH ENDS OF THE SCALE---WITH LITTLE CHANGE BENEATH THE UPPER
RIDGE AND UPPER TROUGH.

THERE WILL BE A SUBTLE DISTURBANCE MOVING INTO THE
OREGON/WASHINGTON COAST DAY 3-4 TIME FRAME...WITH MID-LEVEL
CLOUDINESS...A DECENT MARINE PUSH AND SOME LIGHT RAINFALL
(DRIZZLE/FOG) MAY TEMPER THE HEAT FOR A DAY OR SO WEST OF THE
CASCADES. AND WITH THE GFS WAS ABOUT 3 DEGREES OF LATITUDE NORTH
VS THE ECMWF AND THE ECMWF BEING ABOUT 12 HOURS SLOWER WITH ITS
INLAND ARRIVAL...THIS ADDS MUCH MORE UNCERTAINTY THAT WIDESPREAD
WARMING WILL TAKE PLACE OVER THIS ENTIRE MEDIUM RANGE FORECAST
PERIOD. THIS CAN MEAN ALL THE DIFFERENCE BETWEEN NOCTURNAL
CONVECTION VERSUS SURFACE-BASED LIFT/OROGRAPHIC-BASED CONVECTION.
OVERALL THOUGH...THE DISTURBANCE IS RATHER SHORT-LIVED AND
BROAD-SCALE RIDGING DOES LOOK TO SPREAD WESTWARD INTO NEAR COASTAL
WATERS FROM SFO TO SEA IN THE WAKE OF THIS DISTURBANCE.

THE PRIMARY UNCERTAINTY IN THIS RATHER PERSISTENT RIDGE-TROUGH
CONFIGURATION ACROSS THE LOWER 48 IS ALONG THE NORTHERN AND
CENTRAL DIVIDE WHERE CONFLUENT FLOW---A MID-LEVEL WEST TO
NORTHWESTERLY WIND---WILL BE CARRYING RESIDUAL MONSOONAL MOISTURE
AND CONVECTIVE DEBRIS FROM THE MOUNTAINS INTO THE HIGH PLAINS. IN
PARTICULAR...THE DETERMINISTIC GUIDANCE OFFERS SEVERAL OPTIONS FOR
A CONTINUATION OF MCS-TYPE ORGANIZATION DOWNSTREAM ACROSS THE
PLAINS OF WYOMING ...COLORADO... KANSAS AND NEBRASKA AFTER DAY 5.

...SENSIBLE WEATHER HIGHLIGHTS...
LOOKING AT 10-20F ABOVE NORMAL FOR HIGHS ACROSS THE PACIFIC
NORTHWEST...NORTHERN GREAT BASIN AND CALIFORNIA. THE EXCEPTIONS
BEING ALONG THE IMMEDIATE COAST--- TUCKED BENEATH THE PERSISTENT
MARINE LAYER AND AN INTENSE LOW-LEVEL INVERSION. BENEATH THE
EASTERN NORTH AMERICAN TROUGH...5F TO 15F BELOW NORMAL FOR
LOW/HIGH TEMPERATURES IN THE PLAINS AND GREAT LAKES.

ANOTHER CANADIAN FRONTAL BOUNDARY SWEEPS ACROSS THE EASTERN THIRD
OF THE NATION...PUSHING THROUGH THE OHIO VALLEY AND LOWER THIRD OF
THE MISSOURI VALLEY DAY 3...INTO THE UPPER OHIO VALLEY AND
APPALACHIANS DAY 4...AND THROUGH THE SOUTHEAST...NORTHEAST AND
PIEDMONT ON DAY 5. THIS FRONT SHOULD BE RATHER ACTIVE WITH
SCATTERED SHOWERS AND THUNDERSTORM ACTIVITY. PLEASE REFER TO THE
SPC DAY 4-8 CONVECTIVE OUTLOOK FOR SEVERE POTENTIAL ALONG THE
FRONT.

VOJTESAK

$$





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