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  Thursday October 19, 2017

RSS Mesoscale Discussions from Storm Prediction Center

SPC - No watches are valid as of Thu Oct 19 10:24:02 UTC 2017

No watches are valid as of Thu Oct 19 10:24:02 UTC 2017.


No Mesoscale Discussions are in effect as of Thu Oct 19 10:24:02 UTC 2017.

SPC Oct 19, 2017 Day 4-8 Severe Weather Outlook

Day 4-8 Outlook
      
Day 4-8 Outlook Image
Day 4-8 Convective Outlook  
NWS Storm Prediction Center Norman OK
0153 AM CDT Thu Oct 19 2017

Valid 221200Z - 271200Z

...DISCUSSION...
Medium-range models are in good agreement through the day3 period
then begin to diverge significantly by Sunday. Remnants of a likely
organized squall line should advance across the central/southern
Plains into portions of the lower MS Valley/upper TX Coast Sunday.
However, ECMWF/GFS/Canadian are considerably different in their
strength/placement of the upper trough by day4 and considerable
convective overturning could prove problematic in predictability of
organized convection. Thunderstorms should develop across the
undisturbed warm sector, in advance of the trough, day4-5 but too
much uncertainty exists at this time to warrant an outlook.

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SPC Day 1 Fire Weather Outlook

SPC Day 1 Fire Weather Outlook
          
Day 1 Fire Weather Outlook Image
Day 1 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0209 AM CDT Thu Oct 19 2017

Valid 191200Z - 201200Z

...CRITICAL FIRE WEATHER AREA FOR PORTIONS OF NORTHEAST WYOMING...

...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.

..Elliott.. 10/19/2017

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

Read more

SPC Day 2 Fire Weather Outlook

SPC Day 2 Fire Weather Outlook
          
Day 2 Fire Weather Outlook Image
Day 2 Fire Weather Outlook  
NWS Storm Prediction Center Norman OK
0254 AM CDT Thu Oct 19 2017

Valid 201200Z - 211200Z

...Synopsis...
A large-scale trough is forecast to move from the Pacific Northwest
into the Rockies/High Plains by the end of Day 2/Friday. As this
occurs, a mid-level speed maximum will overspread the northern
Rockies into the northern High Plains. Additionally, low pressure
over Alberta/Saskatchewan will move eastward toward Manitoba, while
a trailing cold front shifts from the Great Basin toward the
Rockies/High Plains.  

...Eastern Wyoming...
Strong/gusty southwesterly pre-frontal downslope surface winds are
forecast to develop by afternoon, as the aforementioned mid-level
speed maximum nudges into the area. A relatively deep mixed layer
will reside beneath the stronger flow, which will promote efficient
mixing, with sustained surface wind in excess of 20 mph expected.
Despite critical surface winds, the latest ensemble/deterministic
guidance continues to suggest that the degree of low-level drying
will be less than previous days -- owing in part to increasing
low-level moisture. Current indications are that minimum RH values
will remain above Critical thresholds (i.e., greater than 15%), with
minimum RH values around 15-25%. However, guidance may not be
capturing the full extent of the low-level warming/drying associated
with the downslope flow. Thus, while a Critical area was not
introduced at this time, one would be needed in future updates if
trends in guidance suggest greater low-level warming/drying.
Regardless, the strength of the low-level wind field coupled with at
least modest reductions to RH values supports maintaining the
ongoing Elevated fire weather area (with only modest adjustments).

..Elliott.. 10/19/2017

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

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