FXUS66 KEKA 052158
AFDEKA

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE EUREKA CA
200 PM PST SAT DEC 5 2009

.SYNOPSIS...COLDER AIR WILL FILTER INTO THE REGION TONIGHT AND 
SUNDAY. SHOWERS WILL DEVELOP ACROSS THE AREA BY TOMORROW AFTERNOON 
AND CONTINUE INTO TOMORROW NIGHT...POSSIBLY BRINGING SNOW LEVELS 
DOWN TO AROUND 500 FEET. HOWEVER PRECIPITATION WILL GENERALLY BE 
LIGHT. DRY WEATHER IS EXPECTED FOR TUESDAY WITH A SERIES OF WET 
STORM SYSTEMS EXPECTED FOR LATER IN THE WEEK.

&&

.DISCUSSION...DETAILS REVOLVING AROUND A SIGNIFICANT WEATHER CHANGE 
TOWARDS COLDER AND WINTRY WEATHER ARE THE MAIN FORECAST PROBLEMS.

A HIGHLY AMPLIFIED PATTERN UPSTAIRS WILL ALLOW A CONTINENTAL POLAR 
AIRMASS TO SPILL INTO THE REGION OVER THE NEXT COUPLE OF DAYS...WITH 
TEMPERATURES WELL BELOW SEASONAL NORMS. NOW FOCUSING ON THE 
IMPACTS...THE AIRMASS IS CURRENTLY VERY DRY AND UPSTREAM SOUNDINGS 
AND MODEL GUIDANCE SUGGEST IT WILL REMAIN SO OVERNIGHT. A HARD 
FREEZE IS EXPECTED FOR ALL INLAND AREAS TONIGHT...WITH TEMPERATURES 
BOTTOMING OUT IN THE LOWER TO MID 20S FOR MOST INLAND VALLEYS. ALONG 
THE COAST...THE SITUATION IS MORE BORDERLINE FOR SURE. GIVEN THE 
COLD/DRY AIR ADVECTION AND SLACKENING WINDS...DECIDED TO GO AHEAD 
AND ISSUE A HARD FREEZE WARNING OVERNIGHT...WITH A SUBSTANTIAL 
PORTION OF THE FORECAST AREA LIKELY TO BOTTOM OUT BETWEEN 27-29 JUST 
BEFORE SUNRISE.
 
NOW ONTO THE OTHER ISSUES...AS A SECONDARY IMPULSE ARRIVES TOMORROW 
A SUBTLE INCREASE IN MOISTURE IS NOTED. AGAIN NOT A LOT OF MOISTURE 
TO WORK WITH BUT ENOUGH TO CARRY POPS BEGINNING DURING THE LATE 
MORNING HOURS WITH THE BEST CHANCES NEAR THE OREGON BORDER. ANY 
PRECIPITATION WILL BE ALL LIQUID ALONG THE COAST AND UP TO AROUND 
2000 FEET BEFORE CHANGING OVER TO SNOW...BUT AMOUNTS DURING THE 
DAYLIGHT HOURS ARE LIKELY TO BE VERY MEAGER AND SCATTERED. 

THE MOST CRITICAL FORECAST TIME IS UNDOUBTEDLY THE SUNDAY 
NIGHT/EARLY MONDAY PERIOD. SNOW LEVELS ARE LIKELY TO FALL TO AROUND 
500 FEET MSL. MODELS SUGGEST THAT LOW TOPPED CONVECTION IS A 
POSSIBILITY ESPECIALLY OVER THE WATERS WHICH MAY MOVE ASHORE. THIS 
COULD POTENTIALLY DRAG A WINTRY MIX...WITH PERIODS OF SMALL HAIL 
AND/OR SNOW...DOWN TO THE BEACHES. THE NAM BUFKIT SOUNDINGS IN FACT 
DO SHOW A PERIOD OF MIXED PRECIP AT EUREKA BEFORE SUNRISE MONDAY 
MORNING BUT THIS IS OBVIOUSLY FAR FROM A GIVEN ESPECIALLY WITH THE 
SHOWERY AND SHORT DURATION PERIODS OF PRECIPITATION EXPECTED. AND IF 
SHOWERS STAY MAINLY OFFSHORE OR IF THE COLUMN MOISTURE REMAINS 
DRY...LITTLE PRECIP WILL OCCUR. MODELS SUGGEST A GREATER THREAT FOR 
ACCUMULATING WINTRY PRECIP ACROSS EXTREME SOUTHERN MENDOCINO COUNTY 
WHERE A BIT MORE MOISTURE IS WRAPPED INTO THE SYSTEM. WE WILL HAVE 
TO CAREFULLY WATCH THE UKIAH VALLEY AS SNOW LEVELS WILL BE LOW 
ENOUGH AND POTENTIALLY QPFS WILL BE HIGH ENOUGH FOR A SEVERAL HOUR 
WINDOW OF SNOWFALL DOWN TO THE VALLEY FLOOR. A WINTER WEATHER 
ADVISORY MAY BE POSTED...DEPENDING ON HOW THINGS EVOLVE...FOR BOTH 
COASTAL AREAS AND THE MENDOCINO INTERIOR FOR SUNDAY NIGHT/EARLY 
MONDAY SO STAY TUNED. IN ANY EVENT...WE'LL PROBABLY BE HARD PRESSED 
TO SEE MORE THAN A FEW INCHES OF SNOW ANYWHERE BUT TRAVEL IMPACTS 
COULD BE SIGNIFICANT AT SUCH LOW ELEVATIONS. 

THIS SYSTEM WILL DEPART MONDAY AFTERNOON...WITH PRECIPITATION 
GRADUALLY DIMINISHING ACROSS EASTERN/SOUTHERN PORTIONS OF THE 
FORECAST AREA BY THE EVENING. MAINLY DRY CONDITIONS ARE EXPECTED FOR 
TUESDAY. STILL A REASONABLE AMOUNT OF UNCERTAINTY WITH RESPECT TO 
THE FORECAST FOR MID TO LATE WEEK...AS SOLUTIONS GENERALLY AIM THE 
SOUTHERN STREAM OF THE JET INTO SOUTHERN CAL WITH A LARGE AMOUNT OF 
RAINFALL DOWN THERE. THE EURO CONTINUES TO BE THE WETTEST FOR 
US...BUT GIVEN ALL SOLUTIONS TENDING TO KEEP RELATIVELY COLD AIR IN 
PLACE...QPFS WILL PROBABLY BE MODEST WITH THE SNOW THREAT STILL 
REMAINING ACROSS THE UPPER TRINITY VALLEYS AND HIGHER TERRAIN 
ELSEWHERE. WITH THAT SAID...OPTED TO MAKE FEW CHANGES IN THE 
EXTENDED PERIODS. BURGER       

&&

.AVIATION...VFR CONDITIONS WITH A DRY AIRMASS IN PLACE WILL CONTINUE 
THROUGH THIS EVENING. LATEST MODEL GUIDANCE HINTING AT SOME PATCHY 
RADIATIONAL INDUCED FOG/HAZE/LOW STRATUS ALONG THE COAST /MAINLY 
AFFECTING ACV/ LATE TONIGHT AND EARLY SUNDAY MORNING. AN UPPER LEVEL 
LOW WILL ENTER THE REGION FROM THE NORTH SUNDAY...BRINGING SOME 
AFTERNOON INSTABILITY SHOWERS AS MUCH COOLER AIR BEGINS TO MOVE INTO 
NORTHERN CA. HENRY

&&

.MARINE...BRISK NORTHERLY WINDS WILL DIMINISH SLOWLY TONIGHT INTO 
SUNDAY MORNING AS THE SURFACE PRESSURE GRADIENT RELAXES A BIT. THESE 
WINDS COMBINED WITH A SHORTER PERIOD NORTHERLY SWELL...WILL KEEP 
SMALL CRAFT ADVISORIES FOR WIND AND HAZ SEAS IN EFFECT FOR THE SHORT 
TERM. A LARGE AND LONGER PERIOD WESTERLY SWELL FROM A STORM 
CURRENTLY IN THE GULF OF ALASKA...WITH MOVE INTO THE WATERS STARTING 
TUESDAY NIGHT. MEANWHILE...AN APPROACHING STORM SYSTEM WILL RESULT 
IN INCREASING SOUTHERLY WINDS STARTING WEDNESDAY. HENRY

&&

.EKA WATCHES/WARNINGS/ADVISORIES...

HARD FREEZE WARNING FOR THE REDWOOD COAST FROM 2 AM PST TO 9 AM PST 
SUNDAY.

SMALL CRAFT ADVISORY FOR WIND AND HAZARDOUS SEAS ALL WATERS. 

&&

$$

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