Fire Weather Outlook Discussion
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FNUS21 KWNS 191558

Day 1 Fire Weather Outlook
NWS Storm Prediction Center Norman OK
1058 AM CDT Thu Apr 19 2018

Valid 191700Z - 201200Z


...Portions of the Southwest through the central High Plains...

The elevated, critical and extremely critical areas remain unchanged
from the previous forecast. The only change as been to expand the
isolated dry thunderstorm area northward to the NM/CO border. This
area will see the best chance for isolated dry thunderstorms into
the evening hours based on latest hi-res guidance. For more forecast
details, see the previous discussion below.

...Portions of Georgia to southeast Virginia...

The elevated fire weather area has been expanded northward into
southeast VA. Dry and windy conditions, similar to those across the
Carolinas, will develop during the afternoon hours behind a cold
front. RH values from 20-30 percent will align with westerly winds
around 15 mph with higher gusts. Where fuels are dry, this will
result in elevated fire weather conditions.

..Leitman.. 04/19/2018

.PREV DISCUSSION... /ISSUED 0138 AM CDT Thu Apr 19 2018/

The greatest fire weather concerns this afternoon will be tied to a
vigorous mid-level system migrating eastward across central
California and Nevada.  A strong (80-90 kt) mid-level jet will round
the base of this disturbance and overspread dry areas of the
Southwest during peak heating hours.  Immediately downstream of this
disturbance, a surface low will deepen across southern Utah.  The
aforementioned synoptic features will amplify surface flow near the
Four Corners region amidst a very dry low-level airmass.

Farther east, a relatively dry post-frontal airmass will overspread
areas of the Carolinas and Georgia, with elevated fire weather
conditions developing there during the afternoon.

...Portions of the Southwest through the central High Plains...
A broad area of southerly surface flow will develop across the
region in response to the aforementioned synoptic features and
vertical mixing processes.  20-25 mph southerly flow will become
common across the High Plains - increasing to 30-40 mph in areas of
eastern Arizona and western New Mexico nearer/beneath the mid-level
jet.  Meanwhile, a dry low-level airmass will remain in place, with
single-digit dewpoints resulting in extremely low RH across Arizona
and New Mexico northward into areas along the Utah/Colorado border.
These conditions, in conjunction with dry fuels (evidenced by
ongoing large fire activity) will promote rapid fire spread and
extreme behavior, and an extremely critical fire weather delineation
remains in place where this potential is the greatest.  Surrounding
the extremely critical delineation, winds will be somewhat weaker
(20-30 mph with higher gusts) and RH slightly higher(7-15%).  A
critical delineation remains in place in these areas.

Farther east into the central Plains, 20-25 mph surface flow will
develop from the Transpecos northward through northeastern Colorado.
 10-15% RH values will exist in portions of the Colorado Front Range
and adjacent higher elevations (around 10-15%), necessitating a
critical area there.  Farther south and east (into the New Mexico
Plains and adjacent areas of Texas), RH values will be somewhat
higher given very modest low-level moisture advection.
Nevertheless, heating/mixing will result in areas of 13-17% RH
values, with areas of locally/briefly critical fire weather possible
across the elevated area.

Lastly, lift associated with the approaching mid-level wave will
combine with gradually increasing low-level moisture across
south-central New Mexico near the Rio Grande Valley.  A few
high-based thunderstorms may develop and produce locally wetting
rainfall and downbursts.  Lightning strikes on the periphery of
heavier cores may result in fire starts given dry fuels in the
region, and erratic surface winds may complicate any fire
suppression efforts that may be ongoing.  An isolated dry thunder
area has been drawn to address this threat.

A relatively dry airmass will overspread the region this afternoon
behind a cold front entering the western Atlantic near the Gulf
Stream.  10-15 mph northwesterly surface flow will become common
behind the front, and RH values should fall into the 18-30% range
during peak heating hours as temperatures rise into the 70s F.
Despite recent rainfall over the past three days, areas of dry fine
fuels may support rapid fire spread, and an elevated fire weather
delineation has been made to address this potential.

...Please see for graphic product...

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