Discussion

Our system grabs the NWS technical discussion each hour. This page is definitely for people with serious forecast needs, as the report is extremely technical. What it does do that other forecast products do not, however, is give you a sense of what the forecasters are thinking about and what larger weather patterns might be forming. If you’re a weather geek, you’ll find this interesting – else – “move along, nothing to see here” :)

The NWS has a glossary of many of the terms and abbreviations used in the discussion forecast on this page.

FXUS66 KMTR 030000
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
455 PM PDT THU SEP 2 2010

.DISCUSSION…AS OF 2:00 PM PDT THURSDAY…IT`S ANOTHER SUNNY
AND WARM AFTERNOON INLAND…BUT TEMPERATURES ARE BEGINNING TO
MODERATE CLOSER TO THE COAST. LATEST SATELLITE IMAGERY SHOWS SHALLOW
STRATUS DEVELOPING OVER OUR MARINE WATERS. ONE BAND OF STRATUS…
PROGRESSING NORTHWARD ALONG THE MONTEREY COUNTY COAST…IS NOW MOVING
IN TO THE NORTHERN HALF OF MONTEREY BAY…WHILE A SECOND LARGE AREA
OF STRATUS PROPAGATED IN LAST NIGHT AND THIS MORNING FROM THE
NORTHWEST. DOWNTOWN SAN FRANCISCO WARMED QUICKLY TO ITS HIGH FOR THE
DAY OF 83 DURING THE MORNING…AND HAS NOW ALREADY COOLED BACK
DOWN TO 75. THIS FORESHADOWS AN EXPECTED AREA WIDE COOLING TREND AS
WE HEAD INTO LABOR DAY WEEKEND.

TONIGHT…THE MARINE LAYER WILL GRADUALLY DEEPEN…AND STRATUS FILL
IN ALONG THE COAST AND BY MORNING EVEN EXTEND A SHORT WAYS INLAND
AROUND THE BAYS. THEN ON FRIDAY…THE COOLER MARINE AIR WILL
BEGIN TO WORK ITS WAY INLAND…WITH COOLING MOST PRONOUNCED
AROUND SF BAY ITSELF. FARTHER INLAND HOWEVER…ESPECIALLY LOCATIONS
MOST PROTECTED FROM MARINE AIR INFLUENCE…IT WILL STILL BE QUITE
WARM.

AS WE THEN HEAD INTO LABOR DAY WEEKEND…THE UPPER LEVEL RIDGE OF
HIGH PRESSURE NOW EXTENDING NORTHWESTWARD FROM THE DESERT SOUTHWEST
THROUGH NORTHERN CALIFORNIA WILL CONTINUE TO FLATTEN AND SHIFT BACK
SOUTHWARD AND INLAND AS THE NEXT UPPER LEVEL PACIFIC TROUGH BEGINS TO
APPROACH THE PACIFIC NORTHWEST. AS THIS OCCURS…THE MARINE LAYER
WILL FURTHER DEEPEN AND LOW LEVEL ONSHORE FLOW INCREASE…ALONG WITH
COOLING OF THE AIR MASS ALOFT. BY SUNDAY…TEMPERATURES ARE EXPECTED
TO BE BACK DOWN TO NEAR OR EVEN A BIT BELOW SEASONAL NORMS ACROSS THE
DISTRICT.

IN THE EXTENDED…CURRENT LONGER RANGE MODEL OUTPUT SUGGESTS SOME
SHORT WAVE RIDGE DEVELOPMENT OVER US ABOUT MONDAY…ALONG WITH
SOMEWHAT MORE OFFSHORE ORIENTED LOW LEVEL FLOW…AND THUS THE
POSSIBILITY OF SOME TEMPORARY MODERATE WARMING AND REDUCTION IN THE
MARINE STRATUS. BUT THEN RENEWED UPPER LEVEL TROUGH DEVELOPMENT
ALONG THE WEST COAST IS PROJECTED FOR TUESDAY AND WEDNESDAY AND A
RETURN TO COOLER CONDITIONS FOR US.

&&

.AVIATION…AS OF 4:55 PM PDT THURSDAY…A SOUTHERLY WIND REVERSAL
ALONG THE IMMEDIATE COASTLINE CONTINUES TO UNFOLD THIS AFTERNOON.
VISIBLE SATELLITE IMAGERY SHOWS STRATUS MOVING NORTH INTO MONTEREY
BAY AND BEGINNING TO EDGE OVER TO THE NORTHERN PART OF THE SALINAS
VALLEY. HOT INLAND TEMPS OFTEN HELP DRAW THE MARINE AIR BACK INLAND
BUT AT THE SAME TIME AN UPPER LEVEL HIGH WILL BE STRENGTHENING RIGHT
OVER THE CENTRAL COAST TONIGHT AND FRIDAY. THE MARINE LAYER MAY
FLUCTUATE A LITTLE OVER THE NEXT 12-24 HOURS…BUT TOUGH TO SAY FOR
SURE WHETHER THERE WILL BE A SHORT TERM ESTABLISHED TREND.

.VICINITY OF KSFO…HIGH CONFIDENCE VFR CONTINUES THROUGH THE EVENING
AND MOST LIKELY OVERNIGHT. WINDS ARE FROM THE WEST BUT WIND SPEEDS
WILL BE TRICKY SINCE THERE IS A STRONG GRADIENT FROM HALF MOON BAY
BUOY TO KSFO OF 2 MB AT THE MOMENT. AS PER USUAL THE WINDS HAVE
PICKED UP ACROSS SAN FRANCISCO BAY IN RESPONSE TO THE WIND REVERSAL
ALONG THE IMMEDIATE COASTLINE. THIS TENDS TO DAMPEN THE WINDS AT
KSFO…USUALLY. FOR NOW WEST WINDS 15 KNOTS GUSTING TO 19 KNOTS LOOKS
OK. VFR IS LIKELY ON FRIDAY BUT THE STRATUS LAYER MAY HAVE A MUCH
LARGER ADVANTAGE AT COMING IN EARLIER FRIDAY NIGHT.

.KSFO BRIDGE APPROACH…HIGH CONFIDENCE VFR TONIGHT AND FRIDAY.

.MRY BAY AREA TERMINALS…VFR AT THE MOMENT BUT STRATUS IS FILLING
IN ACROSS MONTEREY BAY. LIFR/VLIFR IS PROBABLE LATER THIS EVENING
AND BECOMES VERY LIKELY TO LINGER OVERNIGHT. VFR IS FORECAST TO
RETURN BY LATE FRIDAY MORNING.

&&

.MARINE…AS OF 4:45 PM PDT THURSDAY…WINDS AT ANGEL ISLAND ARE
GUSTING UP TO 30-35 KNOTS. WIND REVERSAL WILL PROBABLY KEEP GUSTY
WINDS GOING ACROSS THE BAY WATERS WELL INTO THE NIGHT. WILL AMEND SAN
FRANCISCO BAY WATERS FORECAST SHORTLY TO ADD A SMALL CRAFT ADVISORY
UNTIL 3 AM FRIDAY MORNING.

.MTR WATCHES/WARNINGS/ADVISORIES…
TNGT…SCA SFO BAY WATERS UNTIL 3 AM FRIDAY.

&&

$$

PUBLIC FORECAST: BLIER
AVIATION/MARINE: CANEPA

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