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Welcome to the Monday, August 19th fire weather briefing. My name is Jennifer Kitsmiller and
I am a meteorologist for the National Weather Service in Missoula. We have an active weather
pattern shaping up for the next week across the northern Rockies, which will lead to several
fire impacts over the next several days. So the first image I would like to show is
a current water vapor loop. In this image, the purple and blue colors represent areas
that have a lot of moisture in the mid and upper levels of the atmosphere. The orange
colors represent areas of the atmosphere that are very dry. The first feature I would like
to point out is this area of strong westerly flow associated with an upper level jet stream
which is situated along the Canadian border which I�ve circled in blue. This westerly
flow will be a player in the sensible weather for western Montana and north central Idaho
today, leading to gusty winds. You will also note the area of orange moving into central
Idaho and western Montana. This denotes very dry air moving into the area. I would also
like to draw your attention the low pressure system situated just off the California coast
line, which I�ve circled in green. This feature will act to increase the chance of
thunderstorms as early as Wednesday.
For today, as I mentioned, westerly flow aloft is expected to increase winds this afternoon.
You�ll notice blue wind barbs in this image, depicting a general west wind across western
Montana and north central Idaho. The strongest winds are expected across northwest Montana
and along the Continental Divide. I�ve highlighted these areas with a red line. Winds in these
locations could become sustained up to 20 mph with some gusts near 30 mph this afternoon.
Outside this outlined red area, winds are expected to be lighter, but could still see
gusts to 20 mph. Another concern for today is a dry airmass with low relative humidity.
The darker browns in this image represent the lower humidity values. I�ve highlighted
the locations with the expected lowest humidity in yellow, which includes southwest and west
central Montana. In these areas RHs could drop into the low teens, possibly even some
single digits across the Beaverhead Deerlodge National Forests. Elsewhere, humidity will
not be as dry, but can still expect RHs in the mid teens to low 20s percent.
Due to the expected low humidity and gusty winds, a red flag warning has been issued
for west central and southwest Montana, including the eastern portion of the Lolo National Forest
and the Beaverhead Deerlodge National Forest. Although winds will be strong across northwest
Montana, RHs are not expected to be quite as low and thus no fire weather highlights
are anticipated at this time. For Tuesday, a high pressure ridge will begin
to build back into western Montana and north central Idaho. This will allow winds to relax
and become more terrain driven. However, the airmass will remain warm and very dry. Overnight
RH recoveries on the thermal belts and ridges will be quite poor as thermal belts strengthen
under this pattern. In fact, some midslopes may only see recoveries in the upper 20-low
30% range by Tuesday and Wednesday mornings. Haines values will also be on the increase,
approaching 5s across southwest MT and north central Idaho. The low pressure system I showed
earlier will begin to creep northeastward by Wednesday, which will begin to pump mid
level moisture into the region. This means the threat for thunderstorms will return to
the forecast. Wednesday, storms are expected to be confined
to southwest Montana and the southern portions of the Clearwater/Nez Perce National Forests.
Due to the fact that the low levels of the atmosphere will still be quite dry, thunderstorms
on Wednesday are not expected to produce a lot of precipitation, meaning chances for
wetting rains are low. Gusty winds and frequent lightning will be the main concern for any
storms that develop. I�ve highlighted the areas most likely to see thunderstorms on
Wednesday in yellow here. Thursday, storms are expected to shift northward
slightly as far as the Lolo National Forest and possibly even along the high terrain of
the Continental Divide including Glacier National Park. Moisture will continue to increase during
this time frame and thus storms may begin to be a little more wet. Particularly under
thunderstorms cores. Gusty winds and frequent lightning will continue to be a concern for
any storms that develop. I�ve highlighted the areas most likely to see thunderstorms
on Thursday in yellow here. Beyond Thursday into the weekend, it does appear we will stay
in a southwest flow aloft. This means periods of thunderstorms are likely to continue though
timing exactly when and where is difficult at this time.
So in summary The next fire weather briefing is scheduled
for Thursday, August 22nd. If you have any questions between now and the next briefing,
please feel free to contact us at the National Weather Service any time.