SPC Day 2 Fire Weather Outlook

By Newsroom America Feeds at 10 Aug 2017

SPC Day 2 Fire Weather Outlook
Day 2 Fire Weather Outlook NWS Storm Prediction Center Norman OK 0258 PM CDT Thu Aug 10 2017 Valid 111200Z - 121200Z ...CRITICAL FIRE WEATHER AREA FOR SCATTERED DRY THUNDERSTORMS ACROSS PARTS OF CENTRAL/EASTERN OREGON... A scattered dry thunderstorm area has been introduced along the OR Cascades and continuing into northeastern OR for Day 2/Friday. Per latest short-term guidance, a greater concentration of thunderstorms is expected across this area Friday afternoon and evening as a weak upper low and associated lift over northern CA move northeastward. While storm motions will admittedly be slow, and may allow for some wetting rainfall in the heaviest cores, the presence of very dry to record dry fuels, forecast precipitable water values generally around 0.6-0.9 inch, and abundant lightning expected to occur all suggest a scattered dry thunderstorm area is warranted. The isolated dry thunderstorm area has been expanded eastward to include more of north-central/northeastern MT. Here, at least isolated thunderstorms should develop within northwesterly mid-level flow on the eastern half of an upper ridge. Precipitable water values around 0.6-0.8 inch, enhanced mid-level flow promoting fast storm motions, and dry fuels all support the eastward expansion. Some consideration was given to a scattered dry thunderstorm area across parts of northwestern MT and vicinity, but overall convective coverage across this region remains somewhat in question as large-scale lift attendant to a southeastward-moving shortwave trough over north-central/northeastern MT only glances this region. Will therefore defer the possible introduction of a scattered dry thunderstorm area in MT to a later update. For additional information, see the previous discussion below. ..Gleason.. 08/10/2017 .PREV DISCUSSION... /ISSUED 0144 AM CDT Thu Aug 10 2017/ ...Synopsis... As a trough approaches the Pacific Northwest through the period, the downstream Rex block (in place for several days prior) will break down. This evolution will feature a northern California low further weakening and progressing east/northeast towards Idaho. Meanwhile, another shortwave trough will advance towards northern Montana, within a regime of northwesterly flow along the eastern edge of the ridge associated with the decaying block. ...Northwest US... The assortment of impulses, combined with sufficient mid-level moisture/instability, will foster convective development across much of the region Friday. Precipitable-water values will be highest near/west of the Cascades, as moisture increases ahead of the offshore trough. Therefore, primarily wet thunderstorm modes are forecast here; however, the abundance of lightning, combined with dry fuels, supports an isolated dry-thunderstorm designation. Farther east, tropospheric moisture content will be less, encouraging convection of a drier mode. While storm coverage will likely not be quite as expansive as points farther west, these drier conditions will yield at least an isolated dry-thunderstorm threat. Additionally, an upgrade to scattered/critical may be required in later updates, especially around northwest Montana where storm motions will be quicker. ...Please see www.spc.noaa.gov/fire for graphic product... Read more



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