Scientific Forecaster Discussion

000 fxus66 ksew 231620 afdsew Area forecast discussion National Weather Service Seattle Washington 920 am PDT Tue Apr 23 2019 Update /today/...onshore flow will give mostly cloudy conditions to the area today. Radars show some very light showers near the western slopes of the Cascades this morning. These showers are expected to increase somewhat this afternoon and evening as the moist boundary layer is warmed as as inflow from the Pacific converges around the terrain of Vancouver Island, the olympic peninsula, and the Chehalis gap and gets lifted up the Cascades. Minor updates were made to today's forecast to refine cloud cover, shower chances, and precipitation amounts toward latest mesoscale model solutions. Otherwise, forecasts that show a decrease in showers and clouds tonight and dry conditions Wednesday through Thursday are on track. Albrecht && Synopsis...scattered showers will taper today as an upper trough shifts inland. High pressure aloft will bring dry weather Wednesday and Thursday. A weak upper trough will bring a slight chance of showers on Friday. A stronger and wetter trough will move through on Saturday followed by mainly dry weather Sunday and Monday. && Aviation...a few scattered showers may linger today with a weak convergence zone potentially developing between the pae to bli area. Ceilings are low this morning, mostly in the MVFR category with some spotty IFR. Gradual improvement is expected this afternoon back to VFR. Ceilings could drop back to MVFR tonight but it does seem likely there will be more clearing come Wednesday. Winds from the S/SW in the 10-15kt range with a few gusts near 20kt possible. Winds then turn to the east/NE for terminals near the south sound tonight. Ksea...MVFR cigs this morning with spotty periods of IFR possible. Cigs are expected to lift back to VFR this afternoon. Southerly winds 10-15 knots, becoming more east-northeast tonight. Borth/kovacik && Marine...onshore flow will increase across the coastal waters today, followed by a rather strong push of westerly flow down the Strait of Juan de Fuca. Have upgraded the gale watch starting at 18z to a Gale Warning for the central and eastern Strait of Juan de Fuca. Winds will likely bleed in to nearby Admiralty Inlet and northern inland waters, so have extended the small craft craft advisory to include those areas. Winds are expected to die down in the Strait on Wednesday but will need to watch northern inland waters and coastal waters for another round of Small Craft Advisory wind. Borth/kovacik && Previous discussion... /issued 237 am PDT Tue Apr 23 2019/ Synopsis...scattered showers will taper today as an upper trough shifts inland. High pressure aloft will bring dry weather Wednesday and Thursday. A weak upper trough will bring a slight chance of showers on Friday. A stronger and wetter trough will move through on Saturday followed by mainly dry weather Sunday and Monday. Short term /today through Thursday/...a broad upper trough will maintain a chance of showers today - mainly Coast, Mountains and in a loosely defined Puget Sound convergence zone this afternoon and evening. Highs will be near normal. An upper ridge will build over the area Wednesday and Thursday for dry weather with highs warming a couple degrees each day. Wednesday should be mostly sunny after areas of morning low clouds burn off. Mid and high clouds will be increasing again on Thursday as the next upper trough approaches. Schneider Long term /Friday through Monday/...a weak upper trough will cross the area on Friday. An isolated shower is possible but mostly it looks like another dry day. A stronger upper trough will drop down from the northwest on Saturday for a good chance of showers and low snow levels, at least for late April. The Saturday upper trough will shift inland on Sunday with shower chances ending. Another weak upper trough will develop over the area on Monday for a slight chance of showers again. Temperatures will be seasonable through the period. Schneider Aviation...a weak frontal boundary will continue to make eastward progress across the state this morning. This front was responsible for shower activity earlier in the day, much of which has ended. A few scattered showers may linger today with a potential convergence zone developing mainly in the pae to bli area. Ceilings are low this morning, mostly in the MVFR category with some spotty IFR. These ceilings will carry thru sunrise where then gradual improvement is expected thru the afternoon back to VFR. Ceilings could drop back to MVFR tonight but it does seem likely there will be more clearing come Wednesday. Winds from the S/SW in the 10-15kt range with a few gusts near 20kt possible. Winds then turn to the east/NE for at least terminals near the south sound tonight. Ksea...MVFR cigs this morning with spotty periods of IFR possible. Cig lift back to VFR this afternoon. Spotty showers linger in the vicinity. Winds S 10-15 with a few gusts before turning NE tonight. Kovacik Marine...a weak cold frontal boundary will continue to push through Washington state this morning. Southerly wind out ahead of the airmass boundary will shift to the west/northwest in the front's wake. Overall, light gradients will yield fairly tranquil winds across all waters through sunrise. During the morning hours following sunrise today, winds out the west/northwest behind the front will increase across the coastal waters, followed eventually by a rather strong push of westerly flow down the Strait of Juan de Fuca. Have issued a Small Craft Advisory for the central and eastern portions of the Strait beginning 18z. Winds will likely bleed in to nearby Admiralty Inlet and northern inland waters. Have opted to go Small Craft Advisory for the inlet but omitted headlines in northern inland waters, as majority of these waters should remain well below 21kts. By this evening, guidance suggests gradients increase substantially within the Strait to the 3.6-3.9 mb range with continued strong westerly flow. Nonetheless, even the most aggressive guidance suggest winds only in the upper 20 kt range. Despite this discrepancy, gales could become possible across the central and eastern Strait tonight so have issued a gale watch and will let day shift make the call. Winds finally die down in Strait for Wednesday but will need to watch northern inland waters and coastal waters for another round of Small Craft Advisory wind. Kovacik Hydrology...river flooding is not expected for the next 7 days. && Sew watches/warnings/advisories... Washington...none. Pz...Gale Warning until 3 am PDT Wednesday for central U.S. Waters Strait of Juan de Fuca-East Entrance U.S. Waters Strait of Juan de Fuca. Small Craft Advisory from 3 PM this afternoon to 3 am PDT Wednesday for northern inland waters including the San Juan Islands. Small Craft Advisory until 5 am PDT Wednesday for Admiralty Inlet.

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