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Area Forecast Discussion (AFD)

Issued by San Francisco Bay Area, CA (MTR)

FXUS66 KMTR 230429

Area Forecast Discussion
National Weather Service San Francisco Bay Area
929 PM PDT Mon Apr 22 2019

.SYNOPSIS...High pressure will continue to build over the region 
resulting in well above normal temperatures through midweek. 
Conditions cool slightly late in the week as onshore flow returns 
and the ridge of high pressure weakens. 

&& of 9:29 PM PDT Monday...No significant forecast 
updates planned for this evening. Satellite shows some high clouds
spilling over the region in anti-cyclonic flow aloft associated 
with upper level high pressure. High temperatures today were warm 
with lots of upper 70s and 80s across the region with Santa Rosa 
topping out at 90 degrees. Only the immediate coast stayed cool 
with a shallow marine layer keeping Half Moon Bay at 60 with 65 
for Monterey. 

The current surface gradients still show over 8.5 mb northerly
down the coast from Arcata to SFO. This will keep the coast clear
of low clouds overnight. Offshore winds in the hills will peak 
tonight and ease on Tuesday. At first glance it would appear there
could be several degrees of warming on Tuesday but as the 
northerly gradient eases we'll likely lose some of the adiabatic 
compression. Upshot is the current forecast shows temps for 
Tuesday afternoon warming a few degrees from today and that 
forecast looks valid at this time. 

Right now we dont see any dramatic cooling trends. On Weds temps
may cool a few degrees with further cooling back to near normal by
Thursday and Friday as more distinct onshore flow returns. Will
have to be on the lookout for a southerly wind reversal along the
coast but not seeing that in the model guidance at the this time
with the more likely scenario being that stratus envelops much of
the coastal waters later Weds into Thursday morning.

We've quickly transitioned out of the wet season and into a more
typical spring pattern of gusty winds, periods of stratus and warm

The current long range forecast looks dry and seasonable this
weekend through the end of the month.


.PREV of 2:39 PM PDT Monday...Mostly sunny 
conditions prevail over the region this afternoon as the last 
patch of stratus over the Monterey Bay dissipates. This is a 
result of the building high pressure aloft and weak offshore flow 
developing over the region. Temperatures have already reached into
the lower 80s in the North Bay Valleys as warmer, drier air mixes
down to the surface. For tonight, cannot rule out a few low 
clouds returning near the Monterey Bay, yet mostly clear 
conditions are more likely region-wide. 

Much warmer conditions are forecast for Tuesday afternoon as 
widespread 80s will be common inland. Cannot rule out interior 
valleys of the North Bay, East Bay and portions of the Salinas 
Valley reaching into the lower 90s. With the weak offshore pattern 
and lack of a marine layer, 70s will be common along the coast with 
even lower 80s in locations such as Santa Cruz and Big Sur. These 
temperatures are a good 5-10 deg above average at the coast and 10 
to as much as 20 deg in the interior. With this said, heat impacts 
may reach into moderate levels during the afternoon hours across the 
interior valley locations on Tuesday. However, overall risk will be 
lower given modest cooling during the overnight hours. Folks 
sensitive to heat should plan outdoor activities during the early 
morning or late evening hours and avoid extraneous activity during 
the peak heating. 

The ridge aloft will remain the dominate feature heading into 
Wednesday with above average temperatures ongoing, especially 
inland. However, the ridge will shift eastward a bit and allow for 
weak onshore flow to return to coastal areas. Thus, look for cooling 
temperatures near the coast and to a lesser degree over inland areas 
as well. Onshore flow will continue to increase late in the week and 
result in modest cooling region-wide. Overnight/morning coastal 
clouds may even return as early as Wednesday along the coast and 
spread further inland later in the week. 

The forecast models continue to indicate a mid/upper level low will 
develop and approach the southern California coast this upcoming 
weekend. This would bring an increase in cloud cover, slightly 
cooler temperatures and potential for light precipitation over the 
southern portion of the state. While some ensemble members bring 
light QPF (around 0.01" of an inch or so) to portions of the Central 
Coast, will maintain a dry forecast at this time as widespread 
rainfall appears unlikely. Something worth watching nonetheless.


.AVIATION...As of 05:00 PM PDT Monday...for 00Z TAFs. VFR 
conditions and clear skies prevail across the region. Light to 
moderate onshore winds will gradually diminish later this evening.
Continue to expect the the San Francisco Bay Area terminals to 
remain VFR through the night and into Tuesday as the north to
south pressure gradient remains pretty strong, and the boundary 
layer air mass relatively dry. On the other hand, do believe 
ceilings will develop overnight at the Monterey Bay terminals.

Vicinity of KSFO...VFR conditions are forecast to prevail through
the night and on Tuesday. Moderately strong onshore winds 20 to 25
kt will prevail through around sunset, then progressively 

SFO Bridge Approach...Same as KSFO.

Monterey Bay Terminals...VFR conditions are expected to prevail
through the evening hours, but latest model output and 
statistical guidance indicate likelihood of ceiling development
after around 06Z. Light onshore winds will become light and 
variable by mid-evening.

&& of 09:13 PM PDT Monday...Moderate northwest winds
will prevail tonight over the coastal  waters as high pressure
remains over the eastern Pacific and low  pressure over the Desert
Southwest. Winds will subside a bit over the southern waters on
Tuesday, then increase again Tuesday night. Steep short-period
seas will persist.


     .Tngt...SCA...Pt Arena to Pt Reyes 0-10 nm
             SCA...Pt Arena to Pigeon Pt 10-60 nm
             SCA...Pt Reyes to Pigeon Pt 0-10 nm until 3 AM
             SCA...Pt Pinos to Pt Piedras Blancas 0-10 nm until 3 AM
             SCA...Pigeon Pt to Pt Piedras Blancas 10-60 nm




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