"Translated" Seattle area forecast discussion.

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Area Forecast Discussion National Weather Service Seattle WA 333 PM PDT Wednesday Oct 22 2014 .
Synopsis: — disturbances moving around an upper trough offshore will continue through Thursday. The air mass is unstable — so there will be a chance of thunderstorms on the coast tonight and throughout the area on Thursday. Shower activity will diminish Thursday night and Friday morning. While it will remain rather cloudy Friday afternoon — a brief and weak ridge of high pressure aloft combined with low level offshore flow will give drier weather. A low pressure system developing off the Oregon coast will move across the area late Saturday or Saturday night. Active weather will continue into next week.
Short term: — satellite imagery

and radars

show the front that moved across the area early this morning is now nearly stationary from the Cascades into Northwestern Oregon. A broad and rather deep upper level trough is centered around 145w longitude. Upper level disturbances are rotating around this trough and are riding Northeastward along the front across the Pacific Northwest. The first disturbance enhanced precipitation today as it moved Northeast across the area. The GFS shows another wave now over the Oregon offshore waters shifting Northeast across the area tonight. The axis of the heaviest precipitation amounts will likely be shifted about 50 to 100 miles farther to the South and East of where the rain was seen today. Yet another disturbance — this one now seen as what appears to be a developing instant occlusion North of the front near 135w — appears that it will move across the area on Thursday

. Thunderstorm activity that was seen earlier today over the coastal waters has mainly moved into Vancouver Island — but some isolated lightning strikes can still be seen over the offshore waters. Some thunderstorm activity can be expected over the coastal waters tonight and there is a chance that a few lightning strikes will be seen along the coast and in the Western Olympic mountains. The air mass is expected to be a bit more unstable over the interior Thursday afternoon as the instant occlusion moves Northeast across the area. Lifted Index values fall to around -2.1 and capes rise to about 500 j/kg in the Seattle area 21z Thursday per the nam12

and the GFS is slightly more unstable. Showers with a chance of thunderstorms will be in the forecast for the entire area on Thursday. Showers diminish Thursday night

and come to an end Friday morning

across much of the area as a deep low develops off the Northern California and Southern Oregon offshore waters. This low appears to be developing in response to a system dropping Southeast from the bering sea as it phases somewhat with the remains of ana Northwest of hawaii

. The latest nam12 and GFS solutions show the low reaching its maximum depth at around 985 millibars off the Central Oregon coast

while the Canadian and ECMWF solutions are 5-10 millibars deeper. Offshore flow and short wave ridging aloft may bring a rather dry period — albeit cloudy — to the area from late Friday morning into early Friday evening. The low quickly becomes vertically stacked in all of the models off the Oregon coast — then it matures — moves Northeast — and gradually decays as it moves Northeast across our area Saturday evening

. Depending on the depth and track of the low — it may get windy over portions of Western Washington later Saturday into Saturday night. But with the low decaying and wind field expanding — expect the threat of high wind in the forecast area to be below 25 percent. Some model solutions — like the 12z Canadian solution — keep the track of the low South of the forecast area. This is not unreasonable given the general split flow pattern being seen over the Western U. S. Of late. Temperatures will be seasonable for this time of year and it will remain rather cloudy as we go through the next several days. Albrecht .
Long-term: — showers can be expected behind Saturday nights low pressure system on Sunday. Beyond that time — models are having a tough time with the details. The ECMWF has a storm track to the North of the area with frontal passages here through the middle of next week. The storm track on the GFS is just to the South of the area

— still a wet one for Western Washington but less windy. The Canadian solution is closer to the ECMWF. In any case the pattern will remain active. Albrecht

. Hydrology —  Flood Warning remains in effect for the Skokomish river in Mason County The Skokomish at potlatch crested around 17.2 feet at noon today. It is expected to fall below flood stage tonight and gradually recede Thursday through Friday. Wet weather is expected to continue through the upcoming week. But rainfall amounts are not expected to drive any rivers above flood stage. Albrecht
Aviation: — a slow moving cold front over the interior is expected to be East of the Cascades by 0600 utc Thursday. It now appears that the unstable air mass will remain over the coastal waters through tonight. Meanwhile — strong Southwest flow aloft will continues or continuously over the region through tonight

. The low level flow will remain Southerly. Expect areas of ceilings and visibilities in the 1-3k feet and 3-5 miles range — respectively — through tonight. However heavy precip will result in occasional IFR ceilings/vsbys. sea — ceilings have lifted into the Visual Flight Rules category but ocnly ceilings in the 2-3k feet range can be expected through part of tonight. Cigs near 2k feet may become predominant late tonight or early Thursday.

. Marine — a 1001 millibars low developed over the Oregon coastal waters this afternoon and this has slowed down the cold front over the Puget Sound region. The cold front should be East of the Cascades by late this evening. Will need to Watch for the possibility of a burst of Southerly winds near 25 knots over the waters from point grenville to cape shoalwater out to 60 nautical mile late this afternoon through this evening as the low moves off to the NE. Beyond this afternoon — numerical weather models were not in good agreement with the track — timing — and strength of the low that is expected the end of this week. Depending on which model is correct — this system could produce anywhere from high end Gale or low end storm force winds over parts of the area to inconsequential wind speeds. The forecast reflects the consensus. Thus anticipate Gale force winds over much of the waters Saturday night.
. Seattle


— WA —

 Flood Warning in effect for the Skokomish river in Mason County

Puget Sound Small Craft Advisory in effect for hazardous in effect for the coastal waters and West entrance to the Strait of Juan de fuca. Small Craft Advisory for rough bar in effect until 6 am Thursday for the Grays Harbor bar.

www. Weather. Gov/Seattle you can see an illustrated version of this forecast Discussion: at http://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
METAR interpretation http://weather.cod.edu/notes/metar.html
NOAA's official abbreviations http://weather.cod.edu/notes/abrv.html

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