textproduct: Seattle/Tacoma

SYNOPSIS

High clouds embedded in the westerly flow aloft today and tonight. Weather system moving through Sunday. Post frontal convergence zone Sunday night with low snow levels. Dry Monday and Tuesday before the next system brings rain and locally windy conditions to the area Wednesday. Unsettled weather continuing Thursday into Friday.

SHORT TERM /TODAY THROUGH MONDAY/

Satellite imagery shows high clouds over most of the area early this morning. The cloud cover has prevented fog from forming and also kept temperatures a few degrees warmer compared to yesterday morning. Temperatures at 2 am/09z were in the upper 30s to mid 40s.

Little change in the pattern today and tonight with high clouds embedded in the flow aloft continuing to stream across the area. Highs in the lower to mid 50s. Lows tonight in the 30s.

Next system moving through Western Washington Sunday afternoon with rain out ahead of the front beginning Sunday morning. Snow levels lower to below pass levels but there isn't much moisture associated with the system. Only forecasting two to four inches of new snow for the Cascades. Front moving through late in the day. Cloud cover and rain will keep highs in the 40s, about 10 degrees below normal.

Post frontal showers Sunday night. Convergence zone settling up over the Central Sound, a little further south than normal with the northwesterly flow aloft. Snow levels down to around 500 feet early Monday morning but outside of the convergence zone shower activity drying up. Lows in the upper 20a to mid 30s. Forecast low of 32 degrees in Seattle would be only the 5th time in 82 years with a low freezing or below on March 30th. The last time Seattle had a low this cold on March 30th is 32 degrees in 1968.

Drying trend Monday with showers confined to the Cascades in the morning. Plenty of sunshine but with the cold start to the day and a cool air mass over the area highs only getting back up to near 50.

LONG TERM /MONDAY NIGHT THROUGH FRIDAY/

Another cool night Monday night/Tuesday morning. Not forecasting any records but low temperatures will be within a few degrees of the records, in the mid 20s to mid 30s.

Another dry day Tuesday. Strong system digging south out of the Gulf of Alaska will pump up a weak upper level ridge over Western Washington. Highs Tuesday in the lower to mid 50s.

Models continue to trend stronger and faster with the next system. Rain out ahead of the front could reach the coast Tuesday night. Front moving through Wednesday with rain and locally windy conditions. Snow levels around 3000 feet for another round of snow in all the passes. Advisory new snow totals, 6 inches or more, not out of the question Wednesday. Lows Tuesday night in the mid 30s to lower 40s. Highs Wednesday near 50.

Cool upper level low behind the front moving over Western Washington Wednesday night into Thursday keeping showers and snow levels below the passes in the forecast. Low weakening to an upper level trough and exiting the area Thursday night into Friday. Highs remaining a few degrees below normal, in the lower to mid 50s. Lows in the mid 30s to lower 40s.

AVIATION

Westerly flow continues over the area as zonal flow continues. A shortwave will being to move over the area late Sunday. VFR conditions are expected to prevail across the area through the TAF period. High clouds will continue to stream overhead for much of the day. Weak convergence will lower ceilings a bit over much of the northern and central Puget Sound interior, but remain VFR. Winds are mostly light and variable, with a few locations hanging on to northerly winds. A weak system will send a gentle push of onshore flow across the area after 18Z Sat, which will allow most terminals to see W/SW winds, the exception being the Puget Sound area where a push down the Strait will allow winds to switch to northerly Saturday afternoon/evening. Winds then weaken once again Saturday night into early Sunday.

KSEA...VFR conditions prevail through the period. High clouds remain overhead. Weak convergence will allow for lower ceilings to develop Saturday afternoon but remain VFR. North winds 5-10 kt will switch to SW around 20-22Z before returning to N around 01-03Z Sun and remain N/NE through the evening.

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MARINE

Northerly flow will continue to prevail cross the coastal waters with broad high pressure in place over the coastal waters. A dissipating frontal system will bring a gentle push of onshore flow this afternoon with a bit of enhancement through the Strait of Juan de Fuca, but winds will likely stay below Small Craft Advisory level there tonight (30-50% probability of exceedance). A weak and disorganized low will move across the waters on Sunday. Relatively strong high pressure will quickly build across the coastal waters behind the front on Sunday night, which will increase winds across the area. The areas with the best chance of seeing Small Craft Advisory strength winds Sunday night will be across the coastal waters as well as the West/Central Strait of Juan de Fuca (70-90% probability). Winds will ease during the day on Monday as the high moves inland. A stronger low pressure will move into the region Wednesday into Thursday, which will likely bring stronger winds and seas to the area. There is a chance (40-55%) for gale force winds to the coastal waters and the East Strait/Northern Inland Waters during this time period as well.

Seas will generally remain around 7 to 9 ft through Monday. Seas lower on Tuesday before rising up to 10 to 14 ft Wednesday into Thursday as the stronger system moves into the waters.

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HYDROLOGY

No river flooding expected in the next 7 days.

SEW WATCHES/WARNINGS/ADVISORIES

WA...None. PZ...None.