"Translated" Seattle area forecast discussion.

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ttaa00 sea 012304
Area Forecast Discussion National Weather Service Seattle WA 245 PM PST Tuesday Dec 1 2009 .
Synopsis: — an upper level ridge building over the region

and a surface high over British Columbia

will produce dry North flow aloft across Western Washington through Thursday. The ridge and surface high will maintain mostly clear cool and dry weather through Thursday

— except for areas of morning fog. The ridge will break down after midweek — allowing an upper level low to move over the region Friday

through Monday. This will bring back cloudier weather with a chance of rain or showers.

.
Short term: — visible satellite imagery shows skies are pretty much clear over West WA this afternoon

. Still some small areas of clouds over the Southwest interior — but this should dissipate early this evening. With clear skies overnight — radiational cooling conditions will be excellent. North winds will slow down the fog formation — but with dew points currently in the middle to upper 30s from Puget Sound Southward — and forecast Lows expected to be colder — there will be areas of fog around Wednesday morning. Dewpoints up around Bellingham and the san Juans have already dipped into the middle 20s — so not much fog is expected there. Model trends look good through Thursday — slowly moving the upper level ridge along 130w

inland over B. C. On Thursday

— and shifting the B. C. Surface high

Southeast over the Northern rockies

. The shift to Easterly low level flow by Thursday — combined with subsidence over the area — should gradually reduce the fog coverage Thursday and Friday mornings. Mornings should be chilly with the coldest areas getting down to the middle 20s by Thursday morning. Models are in better consensus for Friday but still have important differences. Have gone with the ECMWF solution — supported by the Canadian. This solution takes the upper level shortwave trough approaching the B. C. Coast Thursday afternoon — Southeastward over West WA as a closed low by Friday afternoon. The GFS has consistently taken the low further East

which would result in a dry forecast. Will keep the chance of rain for Friday — but have nudged precipitation probabilites up a bit more in line with the ECMWF. Kam .
Long-term: — both 12z GFS and 12z ECMWF move the low slowly South over Oregon

by Sunday. Have kept a chance of rain over West WA Friday night and Saturday per the ECMWF. With the upper low over Oregon — models had Sunday/Monday dry — but the best course with the low in the vicinity for days 5 onward is to hang on to a chance of showers. Latest 18z GFS run has come in with a few changes in details during this period which supports taking the conservative approach. Both models set up cool North Northeast low level flow over the area by Sunday as the upper low moves South of WA and a strong surface high forms over B. C.

. This will allow a colder air mass to slide down over the area during the Sunday Tuesday period. GFS may be overdoing the cold air advection as usual — but have still cooled off max/min temps from Saturday on to be more in line with the pattern. Kam

. Hydrology — there is no threat of river flooding expected in the forecast area through Dececember 11th. This includes the green river. Only light precipitation is expected as an upper level low moves over the area Friday and Saturday. The upper level low may still be in the vicinity Sunday and Monday so will maintain a low chance of showers. GFS/ECMWF are showing a shift back to a wetter pattern sometime next week as Westerly flow across the Northeast Pacific undercuts the large upper level ridge along 140w. Exactly when this return to a wetter pattern happens is still uncertain — but does not necessarily mean returning to a flood pattern. Kam
.
Aviation: — dry Northwesterly flow aloft and offshore surface flow is giving largely clear skies around Puget Sound. Skies will be mostly clear

tonight and Wednesday. Patchy fog is possible late tonight and early Wednesday morning at susceptible locations — Olympia and possibly Everett. sea — should be clear tonight — with a small chance of fog in the morning but will not mention it in the taf. Winds North 8-12 knots this evening — becoming Northeast 4-8 knots overnight. Chb

. Marine — high pressure over Central British Columbia will give offshore flow today through the rest of the week. Have kept small craft advisories for the West entrance and Northern inland waters going into the evening — where winds are still pushing advisory levels. Also added Puget Sound into the advisory category as observations in the South end are near advisory levels

. Winds over all areas will diminish somewhat — at the West entrance they are likely to rise again in the morning. A very weak front is forecast to dissipate over the area on Friday. It will have little impact but could turn the Northerlies around to Southeast winds for awhile. There is some chance of arctic outflow in the North this weekend. A somewhat more likely solution is the coldest air will slip into Eastern Washington and Montana — with only moderate outflow in Western Washington. Have kept winds below 30 knots through the weekend. A little strengthening in the gradients could boost Northeast winds into the gale category at the West entrance and over the Northern inland waters this weekend. Chb

. Seattle

Watches/Warnings/Advisories

— WA — none

Puget Sound — please see www. Weather. Gov/seattle/gafd/latest_webafd.html .

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 or THIS LINK at NWS
To learn about cloud types see this article with pictures
Cloud levels: Just ad two zeros to the right to get the actual forecast cloud level in feet. So 030 is 3,000ft

Heights*:

1000 mb is near the surface (sea level - 400 ft), standard sea level pressure is 1013.25 mb at 15C°
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).
*When 500mb heights are said to be "rising to 540" it means 5400m above sea level. (height above zero geopotential meters.)
Confusingly, when discussing 850mb heights, the convention is to omit the leading 1, so that 850mb heights of 540 dam are actually 1540meters.
(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/

Alternate glossaries:
NWS official glossary -- Very complete except for idiosyncratic forecasters
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