textproduct: Seattle/Tacoma

SYNOPSIS

High pressure aloft will briefly weaken over Western Washington today as an upper trough moves across British Columbia. Upper level ridging will rebuild into the region Sunday through Tuesday for a significant warming trend. The ridge will begin to weaken by the middle of the coming week for cooler conditions. A frontal system could bring the regions first chance of rain in more than two weeks by the end of next week.

SHORT TERM /TODAY THROUGH MONDAY/

A weak system passing well north of the area this morning has induced a decent onshore push with cooler marine air pouring inland. We'll see areas of morning low clouds getting at least part way inland and most interior locations will shave 7 to 10 degrees off their high temperatures over yesterdays readings. The cooling trend will be short-lived.

Upper level ridging will begin to rebuild into the area on Sunday. Our brief flirtation with low level onshore flow will revert to northerly Sunday afternoon then turn very weakly offshore Sunday night into early Monday as thermally induced low pressure at the surface expands northward into Western Washington once again. This will lead to a pretty good spike in high temperatures for Monday with much of the Puget Sound lowlands seeing highs in the 80s to around 90 in the Southwest Interior. Coastal high temperatures on Monday are far less certain. A number of models suggest the thermal trough will be oriented just inland from the coast. This makes the forecast from the 50th percentile NBM (near 80 at Hoquiam) used in the forecast a bit suspect. In any case, Moderate HeatRisk remains the central story for the interior lowlands on Monday.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

An upper level ridge remains over the area into Tuesday, but the low level flow will be weakly onshore. This will cool the coast, but the NBM seems to discount this reality. The thermal trough remains in place across the interior lowlands where most locations away from the water will be well into the 80s and lower 90s with widespread Moderate HeatRisk.

Upper level ridging is expected to begin to weaken as we move beyond the middle of next week. This will lead to a downward trend in temperatures. Ensembles generally agree that anomalous upper troughing will take up residence over the region by the end of next week. Though they disagree somewhat on the overall strength of the trough, the bigger story is the introduction of Western Washington's first chance at measurable precipitation in more than two weeks.

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AVIATION

VFR for the interior terminals and MVFR along the coast early this morning. While probabilities have backed off slightly, there still remains a slight chance (20-40%) the the marine stratus will bring MVFR cigs to the interior terminals between 11z-18z. Improvement to VFR this afternoon for the interior terminals. There is some uncertainty whether conditions will improve along the coast; some guidance suggests ceilings may lift for a brief period to low-end VFR in the evening (around 00z) and then quickly deteriorate after 03z to MVFR again. Latest LAMP guidance is trending more pessimistic with a 50-70% chance of MVFR cigs and slim chances of improvement to VFR in the evening. Another round of stratus is possible (30-50% chance) Sunday morning for the interior terminals after 11z. Generally SW winds today 8-15 kt, with the strongest winds along the coast. Winds ease tonight.

KSEA...VFR today with a slight chance (25-30%) of MVFR cigs between 12z-17z. Another round of MVFR possible (30% chance) Sunday morning after 12z. Southwesterly winds up to 8-12 kt through the afternoon. Winds will ease in the evening to 4-6 kt.

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MARINE

High pressure continues to weaken today as a low pressure system moves through British Columbia. Once the low pressure system pushes east of the Cascades, high pressure will quickly rebuild over area waters late this evening and will strengthen through midweek. A frontal system will approach the waters on Thursday, leading to high pressure to weaken.

A Small Craft Advisory continues this morning for elevated seas and winds. Seas and winds will gradually subside this afternoon and remain at 4-7 ft through Monday. Gusty northwesterly winds through the Strait of Georgia this morning may lead to occasional 21 kt or greater gusts over the northern interior waters. These gusts are expected from the San Juan Islands north to Point Roberts.

Moreover, with high pressure strengthening over the waters early next week, increased northerly flow over the coastal waters will bring another chance for small craft winds and seas Monday through midweek. Latest probabilities range between 45-70% for winds 21 kt or greater. Diurnal pushes through the Strait of Juan de Fuca will continue into late next week. Latest guidance suggests that the best chances for for small craft winds will be Wednesday and Thursday. On Wednesday there is a 65-85% chance for small craft winds and a slight chance (25-35%) of gales. The push on Thursday will be slightly weaker, but there is moderate to high confidence (55-70%) for small craft winds, in addition to a slight chance (15-25%) for gales.

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FIRE WEATHER

Elevated fire weather concerns on Monday and Tuesday with minimum relative humidity values dropping into the 20s in Cascade valleys. Can't rule out isolated teens as well. Fuels will continue to dry and the atmosphere may become conditionally unstable with the surface thermal trough Monday and Tuesday. Fuels are getting close to critical levels. Even without hitting critical levels needed for red flag warnings to be issued, fine fuels like grass and brush will ignite quickly with it being so dry. Lets continue to be careful out there.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...Small Craft Advisory until 11 AM PDT this morning for Coastal Waters From Cape Flattery To James Island Out 10 Nm- Coastal Waters From James Island To Point Grenville Out 10 Nm-Coastal Waters From Point Grenville To Cape Shoalwater Out 10 Nm.

Small Craft Advisory until 11 PM PDT this evening for Coastal Waters From Cape Flattery To James Island 10 To 60 Nm- Coastal Waters From James Island To Point Grenville 10 To 60 Nm-Coastal Waters From Point Grenville To Cape Shoalwater 10 To 60 Nm.