000
FXUS66 KMTR 151557
AFDMTR

AREA FORECAST DISCUSSION
NATIONAL WEATHER SERVICE SAN FRANCISCO BAY AREA
857 AM PDT WED MAY 15 2013

...A CHANCE OF SHOWERS THURSDAY INTO FRIDAY MORNING...

.DISCUSSION...AS OF 8:55 AM PDT WEDNESDAY...FORECAST PROBLEM OF
THE DAY WILL BE SHOWER COVERAGE FOR THURSDAY INTO FRIDAY MORNING.

SHORT TERM...DESPITE A DEEP MARINE LAYER THIS MORNING THE VISIBLE
SATELLITE IMAGE IS SHOWING MOSTLY CLEAR TO PARTLY CLOUDY SKIES
AROUND THE AREA THIS MORNING. THE EXCEPTION BEING LINGERING
STRATUS AT HALFMOON BAY AND PORTIONS OF MONTEREY BAY. THESE
ISOLATED AREAS OF STRATUS SHOULD QUICKLY SCATTER OUT THIS MORNING
AS AN UPPER LEVEL BOUNDARY SLIDES ACROSS THE AREA.

CURRENTLY THE SATELLITE WATER VAPOUR IMAGE IS SHOWING A WELL
DEFINED VORT MAX APPROACHING 130W 45N. THE FORECAST MODELS HAVE
INITIALIZED WELL THIS FEATURE AND THE GENERAL SYNOPTIC PATTERN.
BOTH THE 1200Z GFS40 AND 0000Z ECMWF MOVE THIS FEATURE INTO THE
PACIFIC NORTHWEST LATER THIS AFTERNOON. BOTH MODELS THEN DEPICT A
DEEPENING TROUGH OFF OF THE COAST WHICH WILL MOVE INTO OUR
FORECAST AREA THURSDAY INTO FRIDAY. THE LATEST AMSU TPW IMAGE IS
SHOWING TPW VALUES OF 1.00 TO 1.30 INCHES ASSOCIATED WITH THIS
DEVELOPING LOW. THIS SUGGESTS THAT THERE WILL BE ENOUGH MOISTURE
WITH THIS LOW TO PRODUCE SOME SHOWERS ACROSS THE FORECAST AREA.
THE CURRENT FORECAST PACKAGE DOES REFLECT THESE SHOWERS PRIMARILY
FROM SANTA CRUZ NORTHWARD. A CROSS-SECTION ANALYSIS PERFORMED WITH
THE 1200Z NAM12 DOES SUGGEST THAT THERE WILL BE ENOUGH MOISTURE TO
SUPPORT LIGHT SHOWERS ACROSS THE CWA AS FAR SOUTH AS THE SANTA
LUCIAS. THEREFORE...I PLAN TO EXPAND SHOWER COVERAGE WITH THE
AFTERNOON FORECAST PACKAGE.


A DRYING TREND BEGINS FRIDAY AFTERNOON ACROSS THE DISTRICT AS THE
TROUGH MOVES INLAND AND HIGH PRESSURE BUILDS OVER THE EASTERN
PACIFIC. THIS DRY WEATHER WILL LEAD INTO A NICE WEEKEND WITH
MOSTLY SUNNY SKIES AND SEASONABLY WARM TEMPERATURES FORECAST.

PREVIOUS DISCUSSION...CONTINUED WARMING AND DRYING SUNDAY INTO MONDAY
WITH 850 MB TEMPS AROUND 15-16 CELSIUS ON SUNDAY...WARMING TO 18-19
CELSIUS ON MONDAY UNDER FAVORABLE NORTHERLY WIND FLOW. PATTERN
LOOKS WARM BUT NOT HOT. ECMWF THEN DROPS A COOL BUT MAINLY DRY
TROUGH DOWN THE COAST BY TUESDAY...INDUCING A DRAMATIC COOLING
TREND EVEN FOR INLAND LOCATIONS AS 850 MB TEMPS DROP BELOW 10
CELSIUS BY THE MIDDLE OF NEXT WEEK.

&&

.AVIATION...AS OF 5:00 AM PDT WEDNESDAY...ONLY PATCHY STRATUS
AROUND THE AREA TODAY. APPROACHING TROUGH HAS COOLED THE AIRMASS
ALOFT AND WEAKENED THE MARINE LAYER. SCT CLOUDS AT MOST FOR SFO
AND THE APPROACH.

VICINITY OF KSFO...VFR WITH FEW-SCT CLOUDS THROUGH 16Z.

KSFO BRIDGE APPROACH...SIMILAR TO KSFO.

MONTEREY BAY AREA TERMINALS...STRATUS IS AREAL IN COVERAGE THIS
MORNING SO THERE SHOULD BE EARLY BURNOFF. MVFR THROUGH 16Z.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .TDAY...SCA...SF BAY FROM 1 PM
             SCA...PIGEON PT TO PT PINOS 0-10 NM FROM 1 PM
             SCA...PT ARENA TO PT REYES 0-10 NM
             SCA...PT REYES TO PIGEON PT 0-10 NM
             SCA...PT PINOS TO PT PIEDRAS BLANCAS 0-10 NM
             SCA...PT ARENA TO PIGEON PT 10-60 NM
             SCA...PIGEON PT TO PT PIEDRAS BLANCAS 10-60 NM

&&

$$

PUBLIC FORECAST: LARRY
AVIATION/MARINE: W PI

VISIT US AT WWW.WEATHER.GOV/SANFRANCISCO

FOLLOW US ON FACEBOOK, TWITTER, AND YOUTUBE AT:
WWW.FACEBOOK.COM/US.NATIONALWEATHERSERVICE.SANFRANCISCOBAYAREA.GOV
WWW.TWITTER.COM/NWSBAYAREA
WWW.YOUTUBE.COM/NWSBAYAREA