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Monday, February 25, 2019

Northern Rockies Predictive Service Areas - Forecast

MARCH-APRIL-MAY-JUNE OUTLOOK                                                    Geographic Area:  Northern Rockies

Past Weather and Drought:
A cold but also fairly moist pattern took hold over the region during February, which helped to moderate incipient very dry conditions over portions of North Idaho, Southwest and Northwest Montana, and Eastern North Dakota. This cold pattern also has established and maintained solid snow cover east of the Continental Divide in the plains, with the bulk of that region now covered with a snowpack containing 1-3 inches of water equivalent. In terms of the past 90 days however, precipitation still has been somewhat below average over portions of North Idaho, Southwest Montana, and spotty areas in North Dakota. Mountain snowpacks in the western PSAs have registered substantial gains during February as well, and basin-average SWE’s are now near to slightly above-average region-wide. The latest US Drought Monitor shows that drought conditions have eased, with only areas of “Abnormally Dry” conditions persisting in North Idaho, Northwest Montana, and Northeast North Dakota.

Weather and Climate Outlook:
Weak El Niño conditions are still present according to the latest update from the NOAA Climate Prediction Center (CPC). Their long-term forecast calls for a moderation back to ENSO neutral conditions by summer. Seasonal temperature outlooks from the CPC depict above-average temperature likelihood for the entire outlook period through June in the Western PSAs, but near-average further east.  This could lead to a faster spring snowmelt in the Western PSAs. The CPC outlooks are depicting equal chances of below or above-average precipitation during the outlook period region-wide. Although the cold, moist pattern currently in place over the region will likely moderate by mid-March, mountain snowpack accumulations should persist. And so basin-average SWE’s by April 1st will likely end up being closer to long-term average values than what often occurs during weak El Niño winters.

Fuel Conditions:
Currently fuels are snow-covered across most of the Northern Rockies. When dry, warmer, windy periods return to the plains areas by mid-March, the melting snowpack moisture will help delay significant fire potential until the end of the month. With an outlook of near-average temperatures and precipitation for April in the plains, extended periods of very low fine dead fuel moistures caused by gusty chinook winds would be unlikely. If near-average temperatures and precipitation persist through the green-up months of May and June in the plains, live and dead fuel moistures would remain at near normal levels there. A slightly faster snowmelt in the western PSAs during April and May from the possibility of warmer than average temperatures would be offset by near-average precipitation, in terms of producing very low dead fuel moisture values.

Fire Season Timing/Discussion:
Typically during March and April in El Niño winters, the NRGA can see enhanced plains pre-greenup fire potential caused by more frequent and extended dry windy chinook flow periods. This is looking to be unlikely there until at least Mid-March, and the absence of drought conditions there combined with above-average precipitation for most of this region during the last 90 days will help limit significant fire potential until early April. Fire potential in the western PSAs typically is low in early spring except during dry windy periods in Southwest Montana, but these will likely not occur until at least the latter half of March, if not later. In May, through most of June, green-up conditions occur region-wide, and with the near-average precipitation outlooks then, live and dead fuel moistures should remain at near normal levels. Thus, “Normal” fire potential will be forecast for each month region-wide, March through June.