Storm Prediction Center Day 1 Fire Weather Outlook

Created: Thu Oct 19 17:01:02 UTC 2017 (20171019 1700Z Day 1 FireWX shapefile | 20171019 1700Z Day 1 FireWX KML)

Day 1 Fire Weather Forecast graphic
Risk Area (sq. mi.) Area Pop. Some Larger Population Centers in Risk Area
Critical 37,760 268,845 Great Falls, MT...Casper, WY...Gillette, WY...Havre, MT...Lewistown, MT...

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   ZCZC SPCFWDDY1 ALL
   FNUS21 KWNS 191659

   Day 1 Fire Weather Outlook  
   NWS Storm Prediction Center Norman OK
   1159 AM CDT Thu Oct 19 2017

   Valid 191700Z - 201200Z

   ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF EASTERN WYOMING...
   ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF CENTRAL MONTANA...

   A critical area has been introduced for portions of central MT.
   Nearly all short-term guidance is underdone with the strength of
   surface winds per 16Z observations, and it appears likely that
   sustained winds of 20-30 mph with higher gusts will continue through
   much of the afternoon in combination with lowered RH values of
   15-20% and dry fuels to support a critical fire weather threat. No
   changes have been made to the surrounding elevated delineation
   encompassing a greater portion of central/eastern MT.

   Southerly winds of 15-20 mph are occurring across parts of
   central/southern MN within a return flow regime due to an enhanced
   surface pressure gradient between a surface low over Alberta Canada
   and high pressure centered over the eastern CONUS. Due to a prior
   frontal passage, substantial low-level moisture return is not
   expected to occur today, and RH values have already fallen generally
   into the 25-35% range as of 16Z. Further reduction in RH values into
   the 20-25% range seems likely, perhaps even lower than 20% on a
   brief/isolated basis. These meteorological conditions coupled with
   drying fine fuels owing to a relative lack of precipitation over the
   past week support the inclusion of an elevated fire weather area
   across parts of central/southern MN with this update. 

   In the lee of the Sierras, gusty downslope winds may briefly overlap
   with lowered RH values late this morning into early afternoon across
   far eastern CA/western NV. However, latest fuel guidance suggests
   fuels are only marginally receptive across this region. The short
   duration of strong/gusty winds occurring with RH values of 15-20%
   and coupled with the marginal fuels suggests the overall fire
   weather threat remains too marginal to warrant an elevated area.

   No changes have been made to the elevated/critical areas across
   parts of central/eastern WY. See the previous discussion below for
   more information.

   ..Gleason.. 10/19/2017

   .PREV DISCUSSION... /ISSUED 0209 AM CDT Thu Oct 19 2017/

   ...Synopsis...
   Cyclonic flow will continue to overspread the western CONUS today,
   as a large-scale trough amplifies over the Pacific Northwest. As
   this occurs, mid-level flow is forecast to strengthen over the
   northern Rockies in response to the approaching mid-level trough. At
   the surface, low pressure is expected to modestly deepen while
   meandering over central/eastern Alberta. Meanwhile, an associated
   trailing cold front will shift eastward from the Pacific Northwest
   into the Great Basin. 

   ...South-Central into Northeast Wyoming...
   Confidence in critical criteria being met and/or exceeded has
   increased enough for a Critical fire weather area to be introduced
   across northeast Wyoming. Southwesterly downslope pre-frontal winds
   are expected to strengthen by afternoon across the Elevated/Critical
   areas, as steep low-level lapse rates encourage efficient mixing to
   the surface of enhanced low-level flow. Furthermore, modest warming
   of a very dry low-level air mass will allow for minimum RH values to
   remain at or below 15% for several hours during the afternoon. While
   the degree of warming/drying should be relatively similar over the
   Elevated/Critical areas, the confidence in sustained wind speeds
   exceeding 20 mph is greatest over the Critical area. Whereas,
   sustained wind speeds of around 10-20 mph are expected over the
   Elevated area.

   ...Portions of Montana...
   The ongoing Elevated area was maintained, with only minor changes to
   incorporate the latest ensemble/deterministic guidance. By
   afternoon, the approach of stronger low/mid-level flow, associated
   with the aforementioned trough, coupled with relatively steep
   low-level lapse rates is expected to promote the development of
   sustained surface winds of around 15-25 mph. Additionally, warming
   of a dry air mass will allow minimum RH values to bottom out near
   15-25% in an area of receptive fuels (owing in part to the lack of
   recent precipitation and ongoing drought conditions). The primary
   limiting factor for an upgrade to Critical remains the uncertainty
   in whether critically reduced RH values will overlap with
   sufficiently strong sustained wind speeds for a long enough
   duration. If trends in guidance suggest these conditions will
   overlap on more than a brief/spotty basis, then a Critical fire
   weather area may be needed in a future update for portions of the
   area.

   ...Please see www.spc.noaa.gov/fire for graphic product...

      

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