Area Forecast Discussion National Weather Service Seattle WA 300 PM PST Friday Feb 27 2015
Synopsis: — showers will end tonight as drier Northerly flow aloft and low level offshore flow develops. The 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: — an upper low over Northwest Oregon will shift South tonight. Showers will continue to decrease across the area this evening as the upper low pulls away. Showers should pretty much come to an end after midnight tonight as drier Northerly flow aloft and low level offshore flow develop.
A surface high moving into Southern British Columbia will result in locally breezy Northerly winds tonight and Saturday. Otherwise — Saturday should be a sunny day after some lingering early morning clouds. Sunday should be another sunny day.
Low level offshore flow will weaken and the flow aloft will back to Northwest on Wednesday as a weather system approaches from the Northwest for less wind. This weather system will drop down from the Northwest Sunday night and Monday — bringing clouds. The ECMWF shows rain all areas with this feature but the GFS just has spotty precipitation and the GEM is dry. The forecast is a blend of these models for now which means mostly cloudy with a chance of rain. Schneider
Long-term: — an upper ridge will be over the Northeast Pacific Tuesday and Wednesday — giving dry Northerly flow aloft to Western Washington. There will be some breezy North winds Tuesday as a surface high moves into Southern British Columbia — then less wind Wednesday as the high shifts Southeast.
Models show the upper ridge weakening a bit Thursday with a warm front moving over the top. This will bring some clouds to the area and perhaps a chance of rain — with the best chances coast and far North. A cold front will approach from the West on Friday. This day could wind up being dry but a chance of rain cannot be completely ruled out for now. Schneider
Hydrology — flooding is unlikely for the next 7 days.
Aviation: — a small upper level and surface low near Astoria at 2 PM PST will move South over North CA by 4 AM PST. Drier North Northeast flow surface and aloft will gradually push South over West WA tonight as an upper level ridge moves over North B. C. And a surface ridge moves over South B. C.
Rain is beginning to diminish over the North interior this afternoon while showers have developed over the Southwest interior. This has allowed a mix of cloud layers to persist over West WA. Visual Flight Rules conditions predominate over the North interior but a mix of Visual Flight Rules and IFR ceilings is still present over Puget Sound and the Southwest interior. Latest models still indicate decreasing moisture from the North across the area tonight — but probably a little slower than previously expected. The surface ridge over South B. C. Will increase North Northeast surface winds across West WA through 10 PM PST with locally windy conditions continuing through 10 AM PST — particularly over the North interior. With an upper level ridge over B. C. On Saturday and dry North Northeast flow aloft — good Visual Flight Rules conditions are expected.
SeaTac — ceilings at sea are expected to remain Visual Flight Rules — generally broken overcast cloud deck at 5000 ft. and higher through 1 AM PST — with cloud layers becoming scattered after 1 AM PST. N Northeast surface winds will remain 5-10 knots through 1 AM PST — increasing to 10-15 after 1 AM PST. The increase in surface winds will provide enough mixing to preclude fog from forming. Kam
Marine — a 1006 millibars surface low near Astoria at 2 PM PST will move South over North CA by 4 AM PST Saturday. Moderate North Northeast surface flow will develop this evening as a surface ridge moves down over Southern B. C. Behind the low. Small Craft Advisories are in effect for all waters for the North Northeast surface winds. Most areas should remain in the 15-25 range — but the North inland waters and the East entrance should be a little stronger. The Canadian mesoscale model is still the only one that shows 30-35 kt Gale winds over the North inland and East entrance from 10 PM PST 4 AM PST — so I will stick with the consensus and keep winds 30 knots or below.
Surface winds will gradually diminish Saturday as the surface ridge settles over West WA.
Models show an upper level and surface trough moving South across the area Sunday night. The WRF GFS indicated a brief period of Northerly Small Craft Advisory winds mainly over the coastal waters and through Puget Sound immediately behind this feature. Another surface ridge will move down over B. C. Monday night and Tuesday for another period of moderate East Northeast flow. Kam
Puget Sound — Small Craft Advisory all waters.
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