Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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893 FXUS66 KMFR 050409 AFDMFR Area Forecast Discussion National Weather Service Medford OR 809 PM PST Wed Dec 4 2024 .UPDATE... Noteworthy item for this update includes the addition of a Dense Fog Advisory for some of the westside valleys and the coast. Satellite trends support this along with observations. The big question is where will freezing/below freezing temperatures be realized. This could create a light glaze of ice on elevated surfaces like bridges and overpasses, along with vehicles and even sidewalks and roadways. Please use extra caution tonight through the Thursday morning commute and allow for extra time given the hazardous driving conditions. The Rogue Valley and parts of the Illinois Valley are the most likely to see patchy to isolated freezing fog. -Guerrero && .PREV DISCUSSION... /Issued 354 PM PST Wed Dec 4 2024/ DISCUSSION...Satellite image shows low clouds lingering in portions of the Umpqua Basin Illinois Valley and in the Grants Pass area. The low clouds are slowly burning off, but those areas should break out late in the day before becoming socked in again early this evening. Elsewhere, it`s clear. Weak upper troughing will approach the area from the west tonight, but it will weaken as it runs into the upper ridge. Therefore precipitation will be limited to the coast, north of North Bend Thursday morning. Even then rainfall amounts should only amount to a trace to a hundreths of an inch at best. Thursday afternoon is likely to be dry. The one thing the front will do is bring more cloud cover to the area tonight into Thursday morning, with the cloud cover thickest in the Umpqua Divide. This should keep temperatures from dropping down below freezing. Farther south, in portions of the Rogue parts of the Illinois, Shasta, and Scott Valleys, the cloud cover may not be sufficient enough to keep temperatures from dropping below freezing, so we could be dealing with another round of freezing fog later Wednesday night into Thursday morning. Areas that experience freezing fog will result in low visibility along with slick driving conditions for the early morning commute, especially on bridges and any other elevated roads because of not warming from the ground below. Dry weather is likely Friday with upper ridging building into the area. The main variable will be the extent of cloud cover and will it be sufficient enough to keep low clouds and fog from forming. For now, kept it out of the forecast, but this will need to be looked at again. A stronger upper trough will approach the area Saturday, with a surface front pushing into the area. This will bring light to occasionally moderate precipitation primarily along and west of the Cascades. Snow levels Saturday morning will be above pass levels, with snow levels lowering Saturday afternoon to around 6500 feet by Saturday evening. However, by that time, precipitation will be lighter which should limit the amount of snow around Crater Lake. The higher passes should be okay with no snow accumulation during the day Saturday, but could not rule out up to an inch around Diamond Lake Saturday night. Upper troughing remain over the area Sunday with a few showers possible west of the Cascades. The shortwave moving in from the northwest withing the upper trough is not expected to have much, if any over water trajectory which typically results in little to no precipitation. There`s still good agreement among the operational, ensembles and clusters showing upper ridging building back in by the start of next week and could last into at least the middle of next week with dry weather likely. A look at the individual ECMWF ensemble members show 8 of 50 members showing any precipitation next Wednesday, and 2 out of 30 members from the GFS. In contrast the NBM is running too hot (meaning too high and too far inland with respect to pops). Given the above, the forecast in the extended through Wednesday will be less than what the NBM solutions are suggesting. After next Wednesday, the general consensus is for the weather pattern to become more active, with cool and unsettled conditions. -Petrucelli AVIATION...05/00Z TAFS...We`ll start off the evening hours with mostly clear skies, although there is some LIFR stratus lingering in the Umpqua(RBG) and Illinois Valleys this evening. The probability of LIFR visibilities and ceilings tonight is about 50 to 60 percent. The reason why it`s not higher is we`ll see some higher clouds move into the region tonight ahead of the next wave. This could inhibit fog and stratus formation. However, when the high clouds are thin, fog usually forms without a problem. The MOS bulletins are predicting fog in the Rogue Valley(MFR) later tonight. We think the fog will clear during the day on Thursday as an upper level wave moves through Oregon. MARINE...Updated 200 PM PST Wednesday, December 04, 2024...Light to moderate winds and relatively calm seas will persist into Friday. South winds will increase slightly Thursday into Thursday night. A warm front moves through Friday night with a stronger cold front following on Saturday evening. The cold front will be followed by rapidly building seas Saturday night into Sunday, with very steep hazardous seas likely. Right now, the swell on Sunday is anticipated to reach up to 17 feet at 15 seconds, which would be a long period swell. Seas gradually lower into Monday. -Smith && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Dense Fog Advisory until 1 PM PST Thursday for ORZ021>024-026. Air Stagnation Advisory until 4 AM PST Saturday for ORZ023-024- 026-029>031. CA...None. PACIFIC COASTAL WATERS...None. && $$