Area Forecast Discussion
Issued by NWS Medford, OR
Issued by NWS Medford, OR
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542 FXUS66 KMFR 050222 AFDMFR Area Forecast Discussion National Weather Service Medford OR 722 PM PDT Thu Jul 4 2024 .DISCUSSION...Two max temperature records were broken today and one was tied. The broken records were at Medford and Mt. Shasta City, and the tied record was at Montague. More records are expected to occur as the heat wave maxes out this weekend and continues into next week. No updates were made this evening and the previous forecast discussion below remains valid. && .AVIATION...05/00Z TAFS...VFR conditions will continue through the TAF period with gusty north winds north of Cape Blanco, including North Bend this afternoon into this evening, and breezy afternoon and early evening winds at Roseburg. There`s some evidence supporting a very low chance of localized low clouds in portions of the Coquille Basin late tonight and portions of the coast, including North Bend late tonight resulting in IFR ceilings, but confidence is not high enough to include this in the TAF. Meanwhile, smoke from the Shelly Fire in western Siskiyou county could result in visibilities dropping below 6 miles this afternoon, and smoke could settle into the valleys tonight, locally lowering ceilings and visibility. -Petrucelli/BPN && .MARINE...Updated 800 PM Thursday, July 4, 2024...Winds and seas will gradually diminish through tonight as the thermal trough pushes inland and expands northward. North to northeast winds will ease some at this time, but seas and winds will remain hazardous to small craft with hazardous warning level seas lingering through this evening for the outer waters south of Cape Blanco. North winds will continue their downward trend Friday with the strongest winds over the northern outer waters, but they are expected to remain below small craft thresholds. Conditions improve further over the weekend with sub-advisory conditions likely for at least the inner waters, and there`s increasing evidence it will remain below any headlines for the outer waters as well. Strong high pressure aloft will disrupt the thermal trough pattern this weekend, keeping winds in the 10 to 15 knot range. Also the swell is expected to be low with combined seas expected to remain below any advisory levels. Looking at the start of next week. The thermal trough will likely develop again over the south Oregon coast, with north winds increasing on Monday and lasting into at least the middle of next week. Winds will be strongest south of Cape Blanco during this time. -Petrucelli && .FIRE WEATHER...Issued 230 pm Thursday July 4th 2024...Heatwave underway and main concern for this period is weather contribution to fire danger through the weekend. Initially the combination of wind and low humidity is a concern for the west side as forecasts humidities range from the upper single digits to low teens and winds range from sustained 6-12 mph. Prime area of concern for Friday afternoon and evening is the low elevation I-5 corridor from Roseburg to Grants Pass, Medford, and Ashland. More of the same condition will occur as warmer weather arrives Saturday except across a broader area. In addition to the abnormally hot and dry weather being realized in our local forecast grids, the HDW (Hot Dry Windy) index online is showing the condition as advertised by the GEFS members to fall within the top 5% of these events over the 30- year climatology from 1981-2010. In short, this is very unusual to have the area this hot, dry and (breezy) for this time of year. So, this occurring across the holiday weekend was the final consideration. Despite no lightning, there will be other potential sources of ignition. The heat will continue into the early part of next week. During that time a short wave trough is advertised to come up the northern California coast which is a pattern typically supportive of thunderstorms. Not seeing the moisture to get us too worried at this point, but also the solutions are deviating from one another quite a bit so confidence in strength, track and timing of the low is...low. Keep an ear out on this development. Stavish && .PREV DISCUSSION... /Issued 234 PM PDT Thu Jul 4 2024/ DISCUSSION...Satellite imagery is showing some smoke associated with the Shelly Fire now moving toward the northeast, which means that the thermal trough has indeed relaxed and the winds have shifted and are not as strong, easterly winds anymore. This is concurrent with the observations along the coast with Brookings seeing winds come from the ocean with cooler temperatures. Have gone ahead and cancelled the heat advisory for the Curry County coast. These observations and satellite imagery go far to indicate that the thermal trough has moved northward leaving us with an area oh high pressure which will influence our weather for the next several days. Inland, temperatures are heating up and are already 5 to 10 degrees hotter than they were this time yesterday. This is going to be part of a long-duration heatwave that begins today and will likely last through the weekend. Still, a few of the smaller details have changed somewhat and this could cause some additional impacts from the weather. The biggest change to the forecast is that winds are expected to be relatively calm today, but increase Friday through the weekend as an upper- level shortwave traverses the ridge. This will not bring any precipitation nor cloud cover, but it may reduce the potential for the hottest temperatures slated for Friday and Saturday. For example there was nearly a 50 percent chance for Medford to tie it`s all time record high of 115 on Saturday, that went with the forecast package yesterday, but this has decreased to a 40% chance today. Still, it is possible, and the weather has already shown to be difficult to nail the details -- see Brookings which saw a high temperature of 99 degrees yesterday. Regardless a plethora of Excessive Heat Warnings and Heat Advisories have been issued (and have been extended to include southern Siskiyou County). The other part of this change is less fortunate. It means that winds will likely be a touch higher. With critical humidities, this could spell issues for much of the west side as far as fire weather is concerned. Please see the fire weather discussion for more details. This heat wave and associated high pressure will be a long duration and last through the weekend and likely into early next week. The ridge of high pressure will shift eastward. This will bring southwest flow into the area which could increase humidities over time and gradually decrease temperatures. However, a few of the ensembles and the deterministic models are showing a low pressure system traverse up the California coast which, combined with the southwest flow from before could create thunderstorms for southern Oregon and northern California. The forecast does not introduce this quite yet as the NBM is indicating a <5% chance for thunderstorms late in the week, but this will need to be monitored as many times these heat waves are broken by a pattern favoring thunderstorms--which would not be welcome at this point. Keep an eye to the forecast for updates. -Schaaf && .MFR WATCHES/WARNINGS/ADVISORIES... OR...Excessive Heat Warning until 9 PM PDT Monday for ORZ023>026. Red Flag Warning from 4 PM to 8 PM PDT Friday for ORZ616- 620>623. Fire Weather Watch from Saturday afternoon through Sunday evening for ORZ616-617-620>624. Heat Advisory until 9 PM PDT Monday for ORZ029>031. CA...Excessive Heat Warning until 9 PM PDT Monday for CAZ080>082. Fire Weather Watch from Saturday afternoon through Sunday evening for CAZ280-284. Heat Advisory until 9 PM PDT Monday for CAZ083>085. PACIFIC COASTAL WATERS...Small Craft Advisory until 11 PM PDT Friday for PZZ350-356-370-376. Hazardous Seas Warning until 11 PM PDT this evening for PZZ376. && $$