Fire Weather Outlook Discussion
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FNUS28 KWNS 162151

Day 3-8 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
0350 PM CST Sat Dec 16 2017

Valid 181200Z - 241200Z

Portions of the Southwest will be under the influence of a continued
offshore gradient at the very beginning of the extended forecast
period (D3/Mon) and also from D6/Thu through the end of the forecast
period as high pressure lingers in portions of the Great Basin.
Around the D5/Wed and D6/Thu time frame, a powerful mid/upper jet
will dive southward along the West Coast on the western periphery of
a strong mid-level disturbance.  Downstream of this disturbance/jet,
surface cyclogenesis in the Plains will result in a developing dry
sector in New Mexico and adjacent west Texas.  Fire weather concerns
will be heightened in northern/central California and also across
portions of the southern High Plains in response to each of these
synoptic features.

...Southern California...
An offshore pressure gradient will persist at least into D3/Mon
morning across the region, although the gradient is likely to weaken
with time due to weakening high pressure in areas of Nevada and
Utah.  A few areas of gusty winds are likely to persist across the
region - particularly in terrain-favored areas - which may continue
to complicate ongoing suppression efforts for current large fires
across the region.

Latest indications are that a weak onshore flow regime may develop
across the region briefly around the D5/Wed time frame which may
result in a temporary reprieve from threatening atmospheric fire
weather conditions around that time due to slightly higher RH
values.  However, another Santa Ana event should return around
D6/Thu and may persist through the end of the period.  The overall
magnitude of this event is still unclear - although it appears that
at least elevated fire weather conditions are likely as fuels will
remain dry and antecedent precipitation chances remain extremely
low.  40% probability areas have been added during this time frame
to address the potential threat.

...Central/Northern California...
Northerly surface winds should increase substantially (especially in
terrain favored areas) in response to a couple of synoptic-scale
atmospheric features: 1) A strong cold front and attendant surface
pressure trough traversing the region, which will act to steepen the
surface pressure gradient, and 2) a powerful (75-90 kt) jet on the
west side of a vigorous mid-level trough.  Some low-level drying is
also expected, with near-critical RH values expected during the
afternoons of D5/Wed and D6/Thu.  40% areas have been added with the
expectation that minimal antecedent rainfall will occur and fuels
will remain favorable for rapid fire spread.

...D5/Wed - Southern High Plains...
Surface cyclogenesis/lee troughing will favor development of a `dry`
sector in portions of eastern New Mexico and west Texas during the
period with near-critical RH values and areas of 20+ mph westerly
winds.  Fuels in this area are expected to remain dry as any
precipitation potential remains displaced to the south and east.
Given the fire weather potential, a 40% area has been added for this

..Cook.. 12/16/2017

...Please see for graphic product...

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