Area Forecast Discussion National Weather Service Seattle WA 330 AM PDT Friday Jul 25 2014
Synopsis: — moist Westerly flow will continue today as a weak weather system moves onto the British Columbia coast. There could be some light showers over the coast and mountains — otherwise cloudy skies will give way to partial afternoon sunshine. High pressure aloft will build over the region this weekend — bringing sunny warmer weather that should continue next week.
Short term: — wv/ir satellite imagery shows a weak short wave embedded in Westerly flow aloft moving onto the B. C. Coast and brushing Western WA. There are some middle and high level clouds associated with this system but the main affect is to maintain moist low level onshore flow. There was already plenty of moisture in the low levels from earlier today which allowed stratus to reform and expand across much of the area. The exception is the Southwest interior oddly which is mostly cloudy free so far early this morning. The forecast today indicates a cloudy start to the day — then becoming partly sunny. I reluctantly kept some low precipitation probabilities on the coast and mountains as a model output statistics blend still shows a chance of showers in these areas. Current observation do show light rain along Vancouver Island so it is possible a bit of this precipitation could skirt our area this morning. The interior lowlands should be dry outside of a few light sprinkles from the stratus layer this morning. With some sun breaking out this afternoon — Highs should reach into the low to middle 70s around Puget Sound but still in the 60s coast and Strait.
Heights slowly rise tonight but the low level flow will still be onshore. This may allow some stratus to reform over the area but it should be more patchy in nature. The four corners high builds Northward into the Northern rockies Saturday and Sunday with 500 millibars heights above 5800 maritime air mass over Western WA. This supports a dry and warming trend with Highs in the upper 70s to low 80s on Saturday — warning to the low and middle 80s Sunday under sunny skies.
Long-term: — global models continue to advertise a strong high pressure ridge dominating the interior Western U. S. Through much of next week. There is some uncertainty as to how far West the ridge will shift and this will affect where thermally induced low pressure develops. Most models runs keep the ridge axis oriented Northward over the great basin which would keep lower pressure East of the Cascades and allow for light onshore flow over Western WA. It will still be quite warm — well into the 80s — but hot temperatures into the 90s may be averted if the ridge axis remains further East. The more reliable ECMWF has varied from run to run — some putting the ridge closer to our area so a period of even warmer weather is not out of the question next week. High temperatures should be above average regardless of the exact ridge position. Mercer
Aviation: — weak upper level ridging and moderate Westerly flow aloft will persist over the region today. Low level onshore flow will strengthen somewhat during the afternoon and evening hours before relaxing late tonight.
The air mass over Western Washington has dried and become more stable overnight. Lingering low level moisture and the onshore flow has helped low clouds along the coast — Strait and through the Central interior while cloud cover over the North and Southwest interior remains spotty as of 3 AM PDT. Ceilings currently 3-5k feet most areas — expected to lower to Marginal Visual Flight Rules levels at or just after sunrise this morning. A weak upper level system moving into British Columbia this morning will keep a chance of showers and or drizzle over the coast and Olympics through this afternoon. Otherwise morning clouds will lift to Visual Flight Rules levels late morning — with clearing over much of the interior during the afternoon.
SeaTac — Visual Flight Rules ceilings expected to lower around day break to Marginal Visual Flight Rules levels near 1.5k feet — then lift by late morning and clearing during the afternoon. Light Northeast winds 4 to 6 knots will become Northwesterly by early afternoon.
Marine — onshore gradients and flow have relaxed this morning. A typical pattern of high pressure over the coastal waters and lower pressure inland will support onshore flow through early next week. Expect strongest Westerlies through the Strait — with Small Craft Advisory level winds possible at times especially during the afternoon and evening hours. The
Current forecast reflects 10 to 20 knots Westerlies this afternoon and nominal Small Craft Advisory winds during the evening hours on Saturday and Sunday. All other waters will remain 10 to 20 kts.
Puget Sound — none.
You can see an illustrated version of the forecast Discussion: at http://www.weather.gov/seattle/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.
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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