Sunrise 5:52 AM   Sunset 8:20 PM Moonrise 2:33 AM   Moonset 12:37 PM

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FXUS66 KPQR 020427 AAA AFDPQR

Area Forecast Discussion...Updated National Weather Service Portland OR 924 PM PDT Wed May 1 2024

UPDATE
Made some updates this evening, mainly to the QPF and snow levels tonight into Thursday. Incoming shortwave trough is having some success latching on to deeper moisture, with total precipitable water (TPW) values near 1 inch as far east as 127W. The weak surface low appears to be developing a deformation band on its north side, which appears to be aiming for Mount Hood based on latest KRTX/KLGX Doppler Radar imagery. This will likely enhance precipitation on the north side of the low track, where precip would otherwise be lighter due to lacking orographics. With 00z HRRR 25th percentile QPF largely in the 0.50-0.75 inch range over the Marion/Linn/Lane Cascades and the above-mentioned banded precip heading for the Mount Hood area, feel the confidence is there to issue a marginal Winter Weather Advisory for our Oregon Cascades tonight through Thursday morning.
This advisory will be for elevations above 4000-4500 ft, reflecting the slightly warmer air associated with this system.

Aviation and marine sections have also been updated below. Weagle

SYNOPSIS
Another system will spread relatively light rain across the area this evening into Thursday morning, with another round of light snow for the Cascade passes. Heavier rain arrives Friday into Saturday, but do not expect any widespread hydrological concerns at this time. Cool, wet, unsettled weather likely continues through the middle of next week.

SHORT TERM
Through Saturday Night...Visible satellite shows overcast skies across most of northwest Oregon and southwest Washington this afternoon as high level cloud cover streams over the region ahead of the next system, helping to hold daytime highs down in the mid to upper 50s again across the area.
Speaking of the next system, the latest in a series of shortwave troughs is apparent west of Vancouver Island on water vapor imagery, with a warm front extending southeastward towards the Oregon coastal waters from an attendant surface low. Light rain associated with this front will spread across the area later this evening from northwest to southeast and continue overnight as the upper wave crosses overhead. QPF amounts remain rather modest with this system ranging from a half to a quarter inch across most of the area through Thursday morning, with generally less than two tenths along and north of a Hood River-Portland- Astoria line. The heaviest precipitation amounts will be focused along the central Oregon Casacdes which could see 0.75-1.00" through Thursday morning. Snow levels remain around 4000 feet, with roughly 2-4 inches of fresh snow expected at pass levels and locally higher amounts above the passes. Expect another brief dry spell Thursday afternoon into early Friday as transient high pressure builds in behind the departing system.
This should allow high temps to climb into the 60s for most inland locations on Thursday.

The more active weather arrives Friday afternoon as a much deeper trough drops out of the Gulf of Alaska and sends a stronger front across the area Friday into early Saturday.
Expect heavier rainfall to accompany this system as IVT values briefly max out around 250-400 kg/ms Friday evening, with precipitable water values around 1 inch running two standard deviations above normal by early May standards. QPF values remain on track from the previous forecast, bringing 1.00-1.50 inches through Saturday afternoon in the interior lowlands, 1.5-2.0" along the coast and in the mountains, and locally upwards of 2.5-3.0" in a few favored spots. Fortunately, the system looks to move through rather quickly with rain tapering off to showers by Saturday evening as the low dives south towards the CA border. So despite the impressive QPF amounts for this time of year, this should help to limit hydro concerns across the area as HEFS probabilistic guidance keeps the chance of even reaching action stage below 5 percent on all area rivers. That said, the system will still bear watching into the weekend given that area reservoirs are close to full and snow levels will be rising above 6000 feet. If nothing else, could certainly see some local ponding of water in prone areas from late Friday into early Saturday. /CB

LONG TERM
Sunday through Wednesday...Expect an active, cool, and showery pattern to persist into the middle of next week as WPC ensemble clusters continue to show general agreement on some semblance of upper level troughing remaining over the Pacific Northwest through Wednesday. Do not see any signals for particularly notable QPF in any one period beyond Saturday, but area rivers will likely continue to run high for this time of year as episodic bouts of rain continue across the region.
Temperatures will continue to run a bit below normal, with daytime highs struggling to get out of the 50s through the end of the period. /CB



AVIATION
The next warm front is just offshore, and is expected to properly reach the shore imminently around 07z Thu, with stronger precipitation at the southern terminals. Precipitation has already begun are most southern terminals, with northern ones soon to follow. Ceilings will begin to lower within an hour or two, with inland terminals falling to high end MVFR ceilings. KAST should remain low end VFR as the majority of rain passes to the south, but KONP sees a 70% chance of ceilings deteriorating to IFR thresholds between 7-12z Thu. Other southern terminals (KSLE, KEUG) only see around a 25% chance of dropping to IFR ceilings.

Around 14z Thu, the front pushes through, and ceilings will slowly improve back to VFR over the following few hours. Winds will be fairly light at almost all terminals throughout the TAF period, with the exception of KONP, which could see some southerly gusts up to 20kt accompanying the frontal passage. The next front looks to be shortly after the end of the current TAF period, bringing more rain and lowered cigs. /JLiu

Notes: The ASOS at KTTD is only available via the dial in option.
There is no estimated time of full repair and restoration for this location.

PDX AND APPROACHES...VFR conditions will quickly turn over to high end MVFR with the frontal passage around 07z Thu. Model guidance shows around 40% chance of MVFR cigs, but there will be frequent periods of intermittent MVFR, and high end MVFR cigs were put in the TAF as a result between 07-14Z Thu. Afterwards, conditions return to low end VFR ceilings. /JLiu

MARINE
With an incoming warm front, southerly winds will shift more easterly, and gusts continue to just barely meet Small Craft Advisory criteria until the front passes around 12z. Could see higher wind speeds through the coastal gaps and Columbia River Bar early Thursday morning but will be marginal for small craft speeds. Seas will not be impacted by the winds, and in fact could see lower wind waves due to the offshore winds.

The next impactful event arrives early Friday. This low pressure system and associated front appear to be much more robust - though there is ample time for it to change. Seas will build and winds will increase. Not seeing gale force winds, or combined seas exceeding 10 ft though. -Muessle/JLiu

PQR WATCHES/WARNINGS/ADVISORIES

OR...Winter Weather Advisory until 11 AM PDT Thursday for ORZ126>128.
WA...None.
PZ...Small Craft Advisory until 5 AM PDT Thursday for PZZ271-272.

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