Area Forecast Discussion National Weather Service Seattle WA 855 PM PST Thursday Jan 29 2015
Synopsis: — an upper ridge will provide dry and mild weather through Saturday. A front will bring rain back to the area Sunday and early next week.
Short term: — an upper ridge will be over the area through Saturday night with low level offshore flow — keeping the weather dry with some night and morning fog each day. High clouds will begin to increase over the area Friday night as weak weather systems move over the top of the ridge. Highs will be above normal the next couple of days — mainly in the 50s.
A frontal system will bring a little rain to the area Sunday. Models the last few days have been waffling a bit with the strength and timing of this system but now seem to be coming into better agreement showing all areas getting a few tenths of an inch of rain during the day. Schneider
Long-term: — previous Discussion: — another Pacific frontal system will bring a round of wet weather to Western Washington on Monday. Snow levels will be lower — around 4000 feet — with a few inches of snow in the mountains. Models try to bring a weak upper level ridge to the region on Tuesday for drier weather. The ridge may flatten/weaken by midweek as more moister rolls through the Pacific Northwest. 33
Hydrology — flooding is not expected for the next 7 days.
Aviation: — a broad somewhat flat upper level ridge will remain over the Pacific Northwest tonight and Friday. A surface high centered over East WA will maintain weak low level offshore flow. The air mass remains dry and satellite imagery and observation show clear skies continuing this evening.
Good radiational cooling conditions are expected tonight. Areas of fog or low stratus will form overnight over South Puget Sound and the Southwest interior for IFR conditions. Surface winds will be weak or calm and 8 PM PST temperature dew point depressions were mostly 2f or less. Over Central Puget Sound — a little bit of North pressure gradient has kept North winds in the 3-8 knots range this evening with t/td depressions in the 3-6 degree range. The North flow should weaken overnight — but it may hold off fog formation long enough to limit the coverage to just patchy. Everett should get IFR fog as North winds will create a local upslope fog coming off of Everett harbor.
The ridge and dry air mass will keep skies mostly clear on Friday. The more persistent fog/stratus over the South part should clear by midday with patchy fog elsewhere clearing earlier.
SeaTac — good Visual Flight Rules conditions are expected tonight and Friday. Early morning IFR fog/stratus is the only issue. Weakening North winds overnight should hold off the fog formation long enough so that it only has a small chance of developing — so I will leave it out of the taf for now. Surface winds will remain North Northeast 4-7 knots through 4 AM PST then weaken to 2-4 kt. Kam
Marine — a surface ridge centered over Eastern Washington will maintain weak offshore flow through Saturday. Pressure gradients across Western Washington will remain weak — producing North to Northeast winds along the coast and through Puget Sound — and Easterly winds through the Strait.
Models have been consistent the past few runs in bringing a weak front across the area Sunday. 4 PM PST NAM and GFS both keep the surface winds over the coastal waters below 20 kt. The 4 AM PST 4km WRF GFS was just slightly stronger with a small area of 20-21 knots winds along the North Coast. Still lots of time for the models to change with 5 more main models runs to arrive before Sunday.
Models are still having trouble with the trailing front on Monday. 4 AM PST ECMWF still shows a stronger low than the other models — GFS is still weakest with an open surface trough. Even if the ECMWF is correct this system will still fall in the Small Craft Advisory range. Kam
Puget Sound — none.
You can see an illustrated version of this 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