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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

                            
000
FXUS66 KMTR 232123
AFDMTR

Area Forecast Discussion
National Weather Service San Francisco Bay Area
223 PM PDT Tue Apr 23 2019

.SYNOPSIS...Well above normal temperatures today with high 
pressure and offshore winds in place. A few degrees of cooling 
possible by Wednesday for the North Bay, but no big changes in the
weather pattern. Onshore winds return by late in the week and 
into the weekend with temperatures gradually returning to seasonal
normal values.

&&

.DISCUSSION...as of 2:23 PM PDT Tuesday...Warm-to-hot day across 
the San Francisco Bay Area and Central California Coast as an 
upper level ridge axis sits over the northern half of California. 
The 12Z Oakland sounding earlier this morning resulted in 925 mb, 
850 mb, 700 mb, and 500 mb heights and temperatures at/above the 
90th percentile for this calendar day (according to the Storm 
Prediction Center's Sounding Climatology Page). The SFO-SAC 
surface pressure gradient as of 19Z was -0.3 mb. All of these 
parameters are good ingredients for producing an anomalously warm 
middle to late April afternoon. Early afternoon surface 
observations are in agreement with this thinking as temperatures 
are generally running a solid 3-8 degrees warmer than mid-day 
yesterday. By the time the afternoon wraps up, we'll see 
widespread 70s for coastal communities, and 80s to low 90s for 
interior valleys and the Santa Cruz Mountains. This equates to 
around 10-20 degrees warmer than climatological normal values.

The positively-tilted ridge axis responsible for the warm-to-hot 
temperatures is progged to slide southeastward over the next 24 
hours as the center of the upper level ridge offshore weakens 
slightly. This should result in some cooling for Wednesday 
afternoon for the North Bay while interior locations in Monterey 
and San Benito Counties may actually see some day-to-day warming 
as the ridge axis shifts. The marine layer appears that it will 
struggle to redevelop tonight, though there are hints of it 
returning sometime on Wednesday night or Thursday for the Central 
Coast.

Widespread day-to-day cooling should commence beginning Thursday 
as the ridge continues to weaken and upper level heights drop over
our region. By 00Z Friday, models place a weak upper level low 
around 31 deg N, 139 deg W (or about 1300 miles west of San 
Diego), and have it push eastward toward southern California 
through over the course of the weekend. For our area of the state,
most locations should remain dry, though parts of rural Monterey 
County have a slight chance of experiencing light rain showers. 

Model solutions begin to diverge by the beginning of next week.
The Climate Prediction Center's 6-10 and 8-14 day outlooks provide
equal chances for above and below normal temps for our part of 
the state (i.e., no clear signal of one way or the other).

&&

.AVIATION...As of 10:35 AM PDT Tuesday...VFR. Other than FEW/SCT
high clouds streaming over the northern portion of the region this
morning, VFR conditions will prevail. Forecast models do show an
increase in low level moisture and development of low stratus 
over the Monterey Bay terminals and even over the North Bay early
Wednesday morning. However, confidence of occurrence is low for 
the North Bay and moderate for the Monterey Bay terminals. 

Vicinity of KSFO...VFR. 

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...VFR. Potential for low clouds to develop
around 12 Z Wednesday. Moderate confidence.

&&

.MARINE...as of 9:36 AM PDT Tuesday...High pressure off of the 
California coast will slowly shift northward today. Winds over the
northern waters will remain moderate and gusty resulting in 
steep, short-period swell. Elsewhere, winds will be locally gusty 
at times in the afternoon and evening hours yet weaker overall.

&&

.MTR WATCHES/WARNINGS/ADVISORIES...
     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm

&&

$$

PUBLIC FORECAST: Rowe
AVIATION: RGass
MARINE: RGass

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