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Area Forecast Discussion (AFD)

Issued by Seattle/Tacoma, WA (SEW)

                            
000
FXUS66 KSEW 231009
AFDSEW

Area Forecast Discussion
National Weather Service Seattle WA
309 AM PDT Tue Jul 23 2019

.SYNOPSIS...An upper trough will bring clouds and a few showers 
Tuesday and Tuesday night. Weak high pressure aloft will bring dry
and warmer weather Wednesday and Thursday. A weak frontal system 
will bring another chance of showers later Friday. Dry onshore flow
will prevail next weekend. 

&&

.SHORT TERM /TODAY THROUGH THURSDAY/...An upper trough is 
approaching the region today and will move through the area tonight. 
Onshore flow continues to push stratus inland from the coast this 
morning. Most of the lowlands with the exception of parts of the 
North Interior should be covered by later this morning then low 
clouds will lift and burn off. The clouds and stronger onshore flow 
will cool highs to near or slightly below normal. Southerly flow 
aloft and some instability over the Cascades will produce a slight 
chance of thunderstorms this afternoon and evening. As the upper 
trough moves through the region, there's a chance of a few showers 
over the lowlands from about Seattle northward late this afternoon 
through early Wednesday morning. A few showers will probably linger 
over the Cascades on Wednesday. Otherwise, it looks mainly dry as 
weak high pressure aloft moves over the area. Morning clouds should 
burn off for a partly to mostly sunny afternoon. Highs will warm a 
few degrees. The drying and modest warming trend should continue 
into Thursday with a flat upper ridge over the area and high 
temperatures a few degrees above normal. 

.LONG TERM /FRIDAY THROUGH MONDAY/...Upper ridging weakens 
on Friday with another trough clipping the area Friday night. It 
might be strong enough to produce a few showers over the northern 
half of the forecast area. Clouds and a few showers could linger 
into the first part of Saturday then upper ridging rebuilds for the 
second half of the weekend with dry and warmer conditions. Much like 
the pattern of the past week or two, models flatten the ridge again 
early next week for increasing onshore flow and cooler temperatures 
but generally dry conditions.   

&&

.AVIATION...Upper level trough moving through the area late today.
Southwesterly flow aloft becoming northwesterly Wednesday morning. 
Low level onshore flow today increasing tonight behind the trough.

Stratus with ceilings below 1000 feet along the coast, moving down
the Strait of Juan de Fuca into Whidbey Island and through the
Lower Chehalis Valley into the southern portion of the Hood Canal
at 3 am/10z. Mid level clouds over the eastern portion of the
area. Stratus will continue to slowly move inland reaching the
Puget Sound area 12z-14z. The layer over the Puget Sound will be 
shallow and retreat west of the Puget Sound by late morning. 
Stratus will continue to retreat back to the coast by early 
afternoon with mid level clouds over the area. Increasing onshore 
flow tonight behind the trough will bring stratus back into the 
interior 06z-09z with ceilings in the 1000-2000 foot range. 

KSEA...Stratus reaching the terminal about 14z with ceilings 
around 1000 feet lasting until around 18z. Mid level clouds this
afternoon. Stratus returning to the terminal around 08z tonight
with ceilings 1000-2000 feet. Light and variable winds becoming
west southwesterly 4 to 8 knots this afternoon. Felton 

&&

.MARINE...Low level onshore flow today will increase behind
an upper level trough tonight with gale force winds in the Central
and Eastern Strait of Juan de Fuca. Weaker onshore flow will 
continue Wednesday and Thursday. A weak front will cross the area 
on Friday with winds becoming more southerly. Onshore flow will 
return behind the front on Saturday. Felton

&&

.HYDROLOGY...The daily hydrology discussion has ended until the
start of the next rainy season; it will only be updated as needed
until then.

&&

.SEW WATCHES/WARNINGS/ADVISORIES...
WA...None.
PZ...Small Craft Advisory from noon today to 6 PM PDT this evening 
     for East Entrance U.S. Waters Strait Of Juan De Fuca.

     Gale Warning from 6 PM this evening to 2 AM PDT Wednesday for 
     Central U.S. Waters Strait Of Juan De Fuca-East Entrance 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory until 6 PM PDT this evening for Central 
     U.S. Waters Strait Of Juan De Fuca.

     Small Craft Advisory from 6 PM this evening to 6 AM PDT 
     Wednesday for Admiralty Inlet.

&&

$$

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