SPC Day 1 Fire Weather Outlook

By Newsroom America Feeds at 19 Mar 2017

SPC Day 1 Fire Weather Outlook
Day 1 Fire Weather Outlook NWS Storm Prediction Center Norman OK 1159 AM CDT Sun Mar 19 2017 Valid 191700Z - 201200Z ...CRITICAL FIRE WEATHER AREA FOR SOUTHEAST WY...NORTHEAST CO...NEB PANHANDLE... ...CRITICAL FIRE WEATHER AREA FOR PARTS OF EAST-CENTRAL AND NORTHEAST NM INTO THE TX PANHANDLE... ...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF THE CENTRAL FL PENINSULA... Three substantial changes have been made to the outlook: 1. A critical area has been introduced for portions of the central FL peninsula. As a very dry post-frontal airmass filters into FL, minimum RH values are expected to drop below critical thresholds in many areas, with values as low as 20% possible in the central peninsula. Meanwhile, morning soundings and recent radar-derived wind observations indicate 20-25 mph of northwesterly flow just above the surface. As the boundary layer deepens, this will support sustained winds of 15 mph with locally higher gusts, which will be sufficient for a critical fire weather threat. 2. The critical area has been expanded into portions of northeast CO. While wind speeds still look somewhat marginal, deep mixing this afternoon should allow for sufficient flow to result in a critical threat, given very warm and dry conditions. 3. The elevated area has been expanded to cover much of central into northeast KS, and more of western/northern OK. While it is currently rather moist across this area, substantial mixing and drying is possible later today as strong heating occurs, with RH possibly dropping to around 25-35%. Given quite strong southerly winds this afternoon and available dry fuels, this drying will be sufficient for an elevated fire weather threat. Elsewhere, the previous forecast reasoning still holds. See the previous discussion below for more information. ..Dean.. 03/19/2017 .PREV DISCUSSION... /ISSUED 0145 AM CDT Sun Mar 19 2017/ ...Synopsis... An amplified and progressive pattern will continue across the contiguous U.S. today as a vigorous upper trough/closed 500-mb low moves from the Mid-Atlantic into the western Atlantic. A mid-level anticyclone will remain over far northern Mexico with a flattened ridge located across the central states. A belt of strong and deep westerly flow will encompass the north-central U.S. on the southern fringe of a shortwave trough over central Canada. In the low levels, weak low pressure is forecast over the central Great Plains while a ridge of high pressure extends from the Great Lakes southward into the Gulf of Mexico. ...WY into the western half of NE and the northeast quadrant of CO... Model guidance shows a corridor of 40-50 kt 500-mb westerly flow from the northern Great Basin eastward through the NE Panhandle with a weakening in flow expected farther south over CO where the height gradient is less. Diurnal heating coincident with downslope winds will likely result in RH falling into the l0-15 percent range over southeastern WY into western NE. Model guidance suggests flow to be strongest with elevations at or above 4000 ft MSL---which will be in closer proximity to strong 700-mb flow and more susceptible to mechanical mixing of the flow to the surface in gusts. Sustained winds in the 20-25 mph range are expected and recent model runs of the HRRR imply the greatest juxtaposition of low RH/strong winds in the critical area. Surrounding the critical area, strong winds are forecast across WY (20-30 mph) but slightly higher RH will probably temper the overall fire-weather risk. Farther south in closer proximity to the Palmer Divide, a weaker gradient will likely limit sustained wind speeds to not reach critical levels but RH will likely fall below 10 percent during the afternoon. ...eastern portions of NM into the TX Panhandle and western OK and adjacent portions of KS/CO... Models continue to show a relatively small ellipsoid-shaped area of enhanced surface-700 mb flow paralleling I-40. Model forecast soundings show very steep lapse rates during the late afternoon and RH will likely fall into the upper single digits across a large part of the area. In the critical area, sustained winds around 20 mph may intermittently occur for several hours and perhaps yield a concentrated fire-weather threat compared to areas farther north and south where sustained winds are forecast to generally be in the 10-15 mph range. ...much of FL into far southeastern AL and southern GA... Northerly winds of 10-15 mph are forecast with some higher gusts possible in a post-frontal airmass. Strong heating and dry low levels will yield RH values falling into the 15-35 percent range in parts of the FL peninsula. Localized critical conditions are possible but will tend to be intermittent/spotty and may occur over interior west-central into central and the north-central portion of the FL peninsula. This forecast update has included the FL Panhandle owing to RH forecast to fall into the 20-25 percent range. An easterly component to the low-level flow near the immediate east coast will tend to limit minimum RH to be above 35 percent. ...Please see www.spc.noaa.gov/fire for graphic product... Read more



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