"Translated" Seattle area forecast discussion.

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Area Forecast Discussion National Weather Service Seattle WA 900 PM PST Thursday Feb 26 2015 .
Synopsis: — a low pressure system will bring rain to most of Western Washington through Friday morning before changing over to showers. A few inches of snow will fall in the mountains and possibly some of the passes. An upper ridge and offshore flow will bring sunny days and cool nights this weekend. A weak system will move through Sunday night and Monday — with dry weather again Tuesday and Wednesday.
.
Short term: — radar

shows light to moderate rain pushing into the interior of Western WA this evening as a low pressure system approaches. Cloud top brightening on Infrared satellite imagery

indicates the system is in a developing phase. Msas analysis places a 1009 millibars closed surface low off the N/Central WA coast at 04z. Models show the 500 millibars trough closing off overnight and becoming vertically aligned with a slightly deeper 1005 millibars low by 12z . This process will tend to slow the progression of the system and hold rainfall over Western WA longer. Heavier rainfall amounts of a half inch to one inch will fall within the favored deformation zone to the E/ne of the Central low circulation. High resolution models generally agree this will be from the coast through greater Puget Sound and the Southwest interior/S Cascades over the next 12 hours or so

. The North interior should have lighter rainfall amounts. Given the current satellite/radar trends — will update the forecast to call it rain rather than showers. Will also remove the thunderstorms given the precipitation is more stratiform on radar. Snow will fall in the mountains through Friday morning but the heaviest precipitation will likely be to the West of the Cascades. Snow levels will fall from about 4500 feet to 3500 feet Friday morning with a few inches of snow possible. Highest amounts up to 5 inches — just below advisory criteria — will likely occur over the Southern Cascade zone around Mt rainier. Rain transitions to showers late Friday morning or afternoon depending on how quickly the system shifts Southward. It will dry out faster across the N. Surface high pressure building over Southern B. C. Will provide increasing Northeast offshore flow later in the day into Friday night. Lower dew point air means showers will end. It also will become breezy — especially across the North interior where Fraser outflow will develop. The air mass will also be cooler and Lows will probably be in the 30s most spots Saturday morning. Dry weather and sunshine will return to Western WA over the weekend. Northeast offshore flow will hold temperatures back somewhat — but still near average in the low 50s. Exposed areas that have breezy winds will probably stay just above freezing Saturday/Sunday mornings. However — sheltered locations and the typical cold pockets will see Lows near freezing and possibly dipping into the upper 20s in a few spots. Mercer .
Long-term: — no update from previous Discussion: — a weak weather system will bring a chance of rain Sunday night through Monday night. The strength of this system has been waning in recent model runs. Tuesday through Thursday is likely to be a dry period — with a chance of rain returning Friday. Highs and Lows will be slightly below normal. Burke


. Hydrology — flooding is unlikely for the next 7 days.
.
Aviation: — a surface and upper level low along Western Vancouver island

will drop South through the coastal waters tonight

and through the Oregon waters on Friday

. The air mass around this low is moist and somewhat stable. Rain wrapping around the low

will give Marginal Visual Flight Rules ceilings and visibilities tonight into Friday morning. Conditions will dry from the North starting midday Friday as high pressure at the surface and aloft builds over British Columbia. Albrecht sea — expect 3-5 miles rain mist broken clouds at 1000 ft. to 1500 ft. overcast cloud deck at 2500 ft. through 18z Friday. Northeast wind 3-6 knots will become North 7-10 knots after 15z. Albrecht


. Marine — forecast models are showing rather good consistency and continuity this evening. A weak low West of Central Vancouver Island

will drop South through the coastal waters tonight

and the Oregon coastal waters on Friday

. Strong offshore flow will develop in the wake of the low as a 1030-1035 millibars high pressure system over British Columbia builds into the area from the North. Winds will diminish and become light on Sunday as a ridge of high pressure moves Southeast across the waters. Another round of strong North to Northeast winds are expected later Monday into Tuesday

as a 1040 millibars high builds over British Columbia — then moves by the area to the NE. Expect light wind tonight. North to Northeast wind will increase 20-25 knots along the Central and Southern outer coastal waters early Friday morning. Small Craft Advisory North to Northeast winds will spread into the remainder of the coastal waters and to all of the inland waters Friday night into Saturday. Albrecht


. Seattle

Watches/Warnings/Advisories

— WA — none.

Puget Sound Small Craft Advisory starting 15z Friday for the coastal waters from James Island to cape shoalwater 10-60 nautical mile offshore.


you can see an illustrated version of the 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
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