Seattle area forecast discussion.

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Area Forecast Discussion National Weather Service Seattle WA 945 AM PDT Fri Oct 14 2016

.SYNOPSIS...Wet windy weather will continue today as a strong low pressure system tracks northeast across Vancouver Island. The remains of a Pacific typhoon will arrive late Saturday and move through Saturday night with the potential for widespread damaging winds. It will also bring significant precipitation with a threat of flooding. Showery weather will continue next week.




.SHORT TERM...Lots of weather to talk about today and Saturday. By Sunday, things should be settling down although it will remain blustery and showery. The highlights for the next couple days:

Convection...A post-frontal unstable sheared environment has resulted in some pretty strong storms across the area early this morning. Frequent lightning, heavy rains, and hail have been reported so far. Radar has been showing some impressive rotation in a few storms as well. Things should settle down by early afternoon as the air mass becomes more stable.

Wind...A filling low will move into central Vancouver Island today at around 980 MB. This should bring spotty high wind to the coast and north interior today with wind advisories for Puget Sound.

A second storm - the remnants of a typhoon - will move onshore late Saturday. The models are having a hard time pinning down the exact track of the surface low which is the critical detail. The best estimate and mostly likely scenario is a low around 970 mb will make landfall somewhere over the far north coast late Saturday afternoon and then fill and move inland into southern British Columbia during the evening. The should give high wind to most of the area with the strongest winds Saturday evening.

Coastal Flooding...The deep low NW of Cape Flattery today is generating a 20 to 25 foot SW swell along the WA coast. This will generate high surf along the WA coast through this evening.

Computer models have converged on more of a SW-NE track for the powerful low on Saturday, although the models still have small but critical differences in the exact track. At this point it looks like the SW-NE track will spare most or all of the central and northern WA coast from large waves Saturday night. However, a slight westward change in the track could expose the central coast around Grays Harbor to large waves.

Flooding...the Skokomish river is currently flooding. A flood watch is also up for Snohomish and Whatcom counties. See the Hydrology section below for more details. Schneider

.LONG TERM...Previous discussion...More typical October weather will prevail during the extended period. An upper trough should keep the area fairly wet Monday afternoon through Tuesday. Wednesday should be the driest day, as a dirty upper ridge moves through. The south end of a system moving into British Columbia could bring more rain on Thursday. McDonnal




.AVIATION...Energetic and fast-moving upper trough will move across western Washington today, with a deep surface low passing across central or southern Vancouver Island. Another upper trough will approach during the day on Saturday, with a deep surface low approaching from the Pacific. With cold air aloft, lots of convective cells until this evening. Lots of wind energy causing organization of cells into lines with gusty winds. Quick shot of low-level onshore flow this afternoon will cause cigs to come down. Air mass will become more stable tonight, and an increasing offshore component to low-level flow will inhibit low clouds. Heavy rain returning around mid-day Saturday in advance of deep, powerful low center on Saturday evening.

KSEA...Thunderstorms and convection currently moving inland toward Puget Sound. Cells will be weakening as they approach the terminal around 18z. Lightning cannot be ruled out, but odds are too low for inclusion in TAF. Sfc winds will also pick up around 18z and persist into the afternoon, with gusts a peak gust near 40 kt possible around 21z. Brief sw wind may bring in a period of MVFR cigs later this aftn. Then a drying easterly component to low- level flow will return tonight, holding cigs up despite the prevalence of a moist air mass and rain. Haner




.MARINE...A deep 977 MB low about 200 NM NW of Cape Flattery will move NE across central Vancouver Island by Early this afternoon, then move rapidly NE over southern B.C. by late afternoon. High end gales are expected over most of the coastal and northern interior waters through this afternoon. Combined seas 15 to 25 feet are expected.

After a short lull in-between storms tonight through Saturday morning, a powerful 971 MB low is expected to move NE across the coastal waters, crossing Cape Flattery early Saturday evening. This system has a good chance of producing storm force winds over much of the coastal and inland waters. The location and strength of the winds will tied to small changes in the the track of the low, which is still changing in the computer models. Kam




.HYDROLOGY...A flood warning is in effect for the Skokomish River in Mason county. It reached flood stage just after midnight. Some of the more flood-prone rivers running off the west slopes of the Cascades are also at risk, especially the Nooksack River in Whatcom County and the Stillaguamish River in Snohomish County. A flood watch is in effect for those two counties.

Rainfall today and tonight will be less, but the system for Saturday and Saturday night could bring rainfall similar to what occurred during the past 24 hours. At this point, the Northwest River Forecast Center guidance keeps all rivers other than the Skokomish below flood stage through the weekend, but that can change quickly. Small landslides could also become a concern over the weekend. With dry antecedent conditions, we are still below the threshold for concern, but heavy rain in the lowlands Saturday and Saturday night could push some areas above. McDonnal/Schneider




.SEW WATCHES/WARNINGS/ADVISORIES... WA...Wind Advisory until 6 PM PDT this evening for Bellevue and Vicinity-Bremerton and Vicinity-Everett and Vicinity-Hood Canal Area-Seattle and Vicinity-Southwest Interior-Tacoma Area.

High Wind Watch from Saturday afternoon through late Saturday night for Admiralty Inlet Area-Bellevue and Vicinity- Bremerton and Vicinity-Cascades of Pierce and Lewis Counties-Cascades of Snohomish and King Counties-Cascades of Whatcom and Skagit Counties-Central Coast-East Puget Sound Lowlands-Eastern Strait of Juan de Fuca-Everett and Vicinity-Hood Canal Area-Lower Chehalis Valley Area-North Coast-Olympics-San Juan County-Seattle and Vicinity- Southwest Interior-Tacoma Area-Western Skagit County- Western Strait of Juan De Fuca-Western Whatcom County.

Flood Watch until 6 PM PDT this evening for Bellevue and Vicinity-Cascades of Snohomish and King Counties-Cascades of Whatcom and Skagit Counties-East Puget Sound Lowlands- Everett and Vicinity-Western Whatcom County.

High Wind Warning until 3 PM PDT this afternoon for Admiralty Inlet Area-Central Coast-North Coast-San Juan County- Western Skagit County-Western Whatcom County.

High Surf Advisory until 11 PM PDT this evening for Central Coast-North Coast.

PZ...Small Craft Advisory for rough bar until 5 PM PDT Sunday for Grays Harbor Bar.

Storm Watch from Saturday afternoon through Saturday evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 PM this afternoon to 11 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm- East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands.

Gale Warning until 5 PM PDT this afternoon for Admiralty Inlet- Coastal Waters From Cape Flattery To James Island 10 To 60 Nm-Coastal Waters From Cape Flattery To James Island Out 10 Nm-Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm-East Entrance U.S. Waters Strait Of Juan De Fuca-Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.

Storm Watch from Saturday afternoon through late Saturday night for Admiralty Inlet-Central U.S. Waters Strait Of Juan De Fuca-East Entrance U.S. Waters Strait Of Juan De Fuca- Northern Inland Waters Including The San Juan Islands-Puget Sound and Hood Canal.

Small Craft Advisory from 3 PM this afternoon to 11 PM PDT this evening for West Entrance U.S. Waters Strait Of Juan De Fuca.

Gale Warning until 3 PM PDT this afternoon for West Entrance U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory until 5 PM PDT this afternoon for Central U.S. Waters Strait Of Juan De Fuca.

Small Craft Advisory from 5 PM this afternoon to 2 AM PDT Saturday for Admiralty Inlet-Puget Sound and Hood Canal.




$$

www.weather.gov/seattle

You can see an illustrated version of this discussion at www.weather.gov/seattle/gafd/latest_webafd.html

Other regional discussions translated:  Seattle | Spokane | Portland | Pendelton | Medford
The Area Forecast Discussion is issued four times daily around 3AM, 9AM, 3PM, and 9PM.
The original form of the discussion, in all CAPS can be found at http://www.srh.noaa.gov/data/SEW/AFDSEW or With hyperlinks to Jargon http://www.wrh.noaa.gov/total_forecast/getprod.php?prod=XXXAFDSEW&wfo=sew&dict=no&version=0
Another form with hyperlinks to images referenced in the discussion can be found at: http://www.wrh.noaa.gov/sew/gafd/latest_webafd.html

A complete list of airport weather stations used for the METAR reporting system is at: http://adds.aviationweather.gov/metars/stations.txt . Regional airports weather station designations are at the bottom of this page.

For a Glossary of jargon used in these discussions see this link

NWS Glossary lookup. . You can either type in the word you are looking for in the box below or browse by letter.

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To learn about cloud types see this article with pictures

Discussion Heights*:

Under normal conditions, a 1000 mb height is near the surface (sea level - 400 ft),
standard sea level pressure is 1013.25 mb at 15C°
By looking up current pressure and temperature, we can calculate what the standard mb height levels are today.

Typical Heights* values above the 850mb level.:

Standard sea level pressure is 1013.25 mb at 15C° — also known as a standard atmosphere.
Most of the time,
1000 mb is near the surface (sea level - 400 ft) (In really deep low pressure, Sea level pressure can drop well below 990mb.)
850 mb is near 1,500 meters (5,000 ft),
700 mb is near 3,000 meters (10,000 ft),
500 mb is near 5,500 meters (18,000 ft),
300 mb is near 9,300 meters (30,000 ft).
*Note: When 500mb heights are said to be "rising to 540" it means 5400m above sea level. (height above zero geopotential meters.)
But, confusingly, when discussing 850mb heights, the convention is to omit the leading 1, so that 850mb heights of "540 dam" are actually 1540 meters above sea level.

(What committee came up with all this? I guess we have to remember that bits used to be very expensive.)
Just remember that when (constant pressure) heights rise it means that the pressure on the surface is rising too. More on heights and how they are reported: http://www.theweatherprediction.com/basic/obs/


For Cloud levels (aka ceilings) in the untranslated discussion: Just add two zeros to the right to get the actual forecast cloud level in feet. So 030 is 3,000ft.

Alternate Weather Jargon glossaries:
NWS official glossary -- Very complete except for idiosyncratic forecasters Or use above form.
Contractions only from NOAA
http://lena.jax.org/localinfo/weather/txt/glossary.html
http://www.crh.noaa.gov/dtx/afdterms.php
http://www.theweatherprediction.com/jargon/
METAR interpretation http://weather.cod.edu/notes/metar.html
NOAA's official abbreviations http://weather.cod.edu/notes/abrv.html

Acronyms
ACARS	Aeronautical Radio Communications Addressing Reporting System
VFR     Visual Flight Rules

   Numerical Forecast Models Abbreviations
CMC Canadian Meteorological Centre
ECMWF European Centre for Medium-Range Weather Forecasts
GEM Global Environment Multiscale (CMC's short-range model)
GFDL Geophysical Fluid Dynamics Laboratory's Hurricane Model
GFS Global Forecast System (formerly known as the AVN and MRF)
MM5 Penn State University/National Center for Atmospheric Research's Mesoscale Model
NAM North American Mesoscale (formerly known as the Eta)
NGM Nested Grid Model
NOGAPS Navy Operational Global Atmospheric Prediction System
RUC Rapid Update Cycle Forecast Model
SREF Short Range Ensemble Forecasts
UKMET United Kingdom Meteorological Office
					  


Washington Airports and other NWS stations

                                            elevations in meters 
                              N       W      elev 
WA ARLINGTON MUNI   KAWO    48 10N  122 10W   42 
WA BELLINGHAM       KBLI    48 48N  122 32W   50 
WA WHATCOM (BLI)    KHUH    48 57N  122 35W   26 
WA BREMERTON NTNL   KPWT    47 30N  122 45W  147 
WA BURLINGTON/MT V  KBVS    48 28N  122 25W   43 
WA CHEHALIS CENTRAL KCLS    46 41N  122 59W   54 
WA COLVILLE MUNICIP KCQV    48 32N  117 52W  572 
WA DEER PARK        KDEW    47 58N  117 26W  668 
WA EASTSOUND/ORCAS  KORS    48 42N  122 54W    8 
WA ELLENSBURG       KELN    47 02N  120 32W  519 
WA EPHRATA          KEPH    47 18N  119 31W  383 
WA EVERETT          KPAE    47 55N  122 17W  180 
WA FAIRCHILD AFB    KSKA    47 37N  117 39W  750 
WA FORT LEWIS/GRAY  KGRF    47 04N  122 34W   92 
WA FRIDAY HARBOR    KFHR    48 31N  123 02W   32 
WA HANFORD          KHMS    46 34N  119 35W  223 
WA HOQUIAM          KHQM    46 58N  123 56W    7 
WA KELSO LONGVEIW   KKLS    46 07N  122 54W    5 
WA MOSES LAKE       KMWH    47 12N  119 19W  362 
WA OAK HARBOR AIRPA K76S    48 15N  122 40W   58 
WA OLYMPIA          KOLM    46 58N  122 54W   58 
WA OMAK             KOMK    48 28N  119 31W  395 
WA PASCO            KPSC    46 16N  119 07W  121 
WA PORT ANGELES     KCLM    48 07N  123 30W   85 
WA PULLMAN/MOSCOW   KPUW    46 45N  117 07W  773 
WA PUYALLOP/THUN    KPLU    47 06N  122 17W  164 
WA QUILLAYUTE       KUIL    47 56N  124 33W   54 
WA RENTON           KRNT    47 30N  122 13W   21 
WA SEATTLE/BOEING   KBFI    47 33N  122 19W    4 
WA SEATTLE/METRO    KSEA    47 27N  122 19W  136 
WA SEATTLE/WFO      KSEW    47 27N  122 18W  130 
WA SEATTLE/ARTCC    KZSE    47 17N  122 11W   99 
WA SEATTLE/CAMANO I KATX    48 12N  122 30W  151 
WA SHELTON          KSHN    47 14N  123 08W   82 
WA SPOKANE          KOTX    47 41N  117 38W  727 
WA SPOKANE/FELTS    KSFF    47 41N  117 19W  609 
WA SPOKANE/METRO    KGEG    47 37N  117 32W  735 
WA STAMPEDE PASS    KSMP    47 17N  121 20W 1208 
WA TACOMA           KTIW    47 16N  122 35W   89 
WA TACOMA/MC CHORD  KTCM    47 07N  122 28W   98 
WA TATOOSH/VOR      KTOU    48 18N  124 38W  520 
WA TOLEDO WINLOCK M KTDO    46 28N  122 47W  113 
WA VANCOUVER        KVUO    45 37N  122 39W    8 
WA WALLA WALLA      KALW    46 06N  118 17W  363 
WA WENATCHEE        KEAT    47 24N  120 12W  377 
WA WHIDBEY IS. NAS  KNUW    48 21N  122 39W   14 
WA YAKIMA           KYKM    46 34N  120 32W  324 
WA BURLINGTON/MT V  K75S    48 28N  122 25W   43 
WA COLVILLE         K63S    48 32N  117 52W  571 
WA DEER PARK        K07S    47 58N  117 26W  668 
WA DESTRUCTION ISL          47 40N  124 31W   21 
WA PORT ANGELES CG  KNOW    48 08N  123 25W    4 
WA SMITH ISLAND             48 19N  122 10W   15 
WA PEARSON/VANCOUVR K60S    45 37N  122 39W    8 
WA WEST POINT (LS)          47 40N  122 34W    3 

BC ABBOTSFORD AIRPO CYXX    49 01N  122 22W   58 
BC AGASSIZ (AUTO)   CWZA    49 15N  121 46W   15 
BC ENTRANCE IL AUTO CWEL    49 13N  123 47W    5 
BC ESQUIMALT METOC  CWPF    48 25N  123 25W   12 
BC HOPE AIRPORT (MA CYHE    49 22N  121 28W   39 
BC HOPE SLIDE       CWKV    49 16N  121 13W  674 
BC KELP REEFS       CWZO    48 33N  123 14W    1 
BC MALAHAT (AUTOB)  CWKH    48 34N  123 34W  366 
BC MERRY ISLAND     CWMR    49 28N  123 55W    8 
BC MT SICKER RADAR  CXSI    48 51N  123 45W    1 
BC NANAIMO AIRPORT  CYCD    49 02N  123 52W   28 
BC P. MEADOWS CS AU CWMM    49 12N  122 40W    5 
BC RACE ROCKS AUTOB CWQK    48 17N  123 31W    5 
BC SAND headS (LS)  CWVF    49 06N  123 18W    1 
BC SATURNA ISL (MAP CWEZ    48 46N  123 02W    7 
BC SHERINGHAM AUTOB CWSP    48 22N  123 55W   21 
BC SQUAMISH (AUTOB) CWSK    49 46N  123 10W   60 
BC VANCOUVER (AUTOB CWHC    49 17N  123 07W    2 
BC VANCOUVER INTL A CYVR    49 10N  123 10W    2 
BC VIC. HARTLAND AU CWVV    48 31N  123 28W   49 
BC VICTORIA (AUTOB) CWLM    48 25N  123 19W   70 
BC VICTORIA HARBOUR CYWH    48 25N  123 23W   10 
BC VICTORIA INTL AR CYYJ    48 38N  123 25W   19 
BC VICTORIA UNIV    CWYJ    48 28N  123 18W   39 
BC W VANCOUVER AUTO CWWA    49 21N  123 10W  178 
BC WHITE ROCK AUTOB CWWK    49 01N  122 46W   15