Fire Weather Outlook Discussion
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FNUS21 KWNS 041508
FWDDY1

DAY 1 FIRE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
1007 AM CDT TUE AUG 04 2015

VALID 041700Z - 051200Z

ONLY MINOR CHANGES WERE MADE TO THE ELEVATED WIND/RH AREA TO EXTEND
THE AREA OF CONCERN FURTHER EAST TO THE CENTRAL WA/ID BORDER BASED
ON LATEST SURFACE OBSERVATIONS AND MODEL GUIDANCE.
OTHERWISE...PREVIOUS FORECAST REASONING REMAINS THE SAME. SEE
DISCUSSION BELOW FOR MORE DETAILS.

..LEITMAN.. 08/04/2015

.PREV DISCUSSION... /ISSUED 0341 AM CDT TUE AUG 04 2015/

...SYNOPSIS...
EARLY THIS MORNING...MOISTURE-CHANNEL IMAGERY INDICATES A SHORTWAVE
TROUGH CROSSING PARTS OF THE NRN/CNTRL ROCKIES -- TO THE S OF A
RIDGE EXTENDING NWD OVER THE CANADIAN PRAIRIE PROVINCES. THIS TROUGH
WILL CONTINUE TO TRACK EWD...WHILE AN UPSTREAM CYCLONE OVER BRITISH
COLUMBIA DEVELOPS INTO THE NWRN CONUS. AS THIS OCCURS...A MID-LEVEL
DISTURBANCE OVER THE PACIFIC WATERS WELL OFF THE COAST OF NRN CA
WILL MOVE ONSHORE TOWARD THE GREAT BASIN. A SEPARATE...MORE SUBTLE
IMPULSE LIES BETWEEN THE AFOREMENTIONED SHORTWAVE TROUGH AND THE
PACIFIC DISTURBANCE -- PRESENTLY OVER ORE -- AND WILL CONTINUE
TRACKING ENEWD. THE COMBINATION OF THESE PERTURBATIONS WILL
INFLUENCE FIRE-WEATHER CONCERNS ACROSS PARTS OF THE NWRN CONUS.
MEANWHILE...MID-LEVEL TROUGHING WILL PERSIST ACROSS PARTS OF THE
NORTHEAST...WITH RIDGING ACROSS THE SWRN CONUS.

...PORTIONS OF NRN CA/NRN NV NEWD INTO WRN MT...
WHILE THE REGION WILL BE IN THE WAKE OF THE SHORTWAVE TROUGH
PRESENTLY CROSSING THE NRN/CNTRL ROCKIES...REINFORCING ASCENT
OFFERED BY BOTH THE AFOREMENTIONED MIGRATORY OREGON IMPULSE AND THE
PACIFIC DISTURBANCE WILL SUPPORT CHANCES FOR THUNDERSTORMS THROUGH
THE PERIOD. DIURNALLY ENHANCED TERRAIN-DRIVEN CIRCULATIONS WILL ALSO
YIELD THUNDERSTORM POTENTIAL...AS THE AIR MASS DESTABILIZES DURING
THE AFTERNOON AMIDST MODEST TROPOSPHERIC MOISTURE. LIFT AHEAD OF THE
PACIFIC DISTURBANCE WILL LIKELY SUSTAIN THUNDERSTORM POTENTIAL INTO
THE OVERNIGHT HOURS TONIGHT FROM PARTS OF NRN CA...NRN NV...AND FAR
NWRN UT INTO PARTS OF SRN ORE/SRN ID.

EARLY-MORNING GPS DATA AND MONDAY-EVENING OBSERVED SOUNDINGS
HIGHLIGHT PW VALUES GENERALLY FROM 0.60 TO 0.90 INCH...WHICH ARE
FORECAST TO EXHIBIT LITTLE OVERALL CHANGE THROUGH THE D1/TUE PERIOD.
FURTHERMORE...THE PRESENCE OF 20-40 MPH OF FLOW THROUGH THE CLOUD
LAYER WILL ENCOURAGE MODEST STORM MOTIONS TO REDUCE PRECIPITATION
AMOUNTS DEPOSITED BY STORMS...WHILE DIURNAL SFC HEATING FACILITATES
DEEP MIXING AND SUB-CLOUD EVAPORATION.

A MIX OF DRY AND WET THUNDERSTORMS WILL LIKELY ENSUE...YIELDING A
POTENTIAL FOR LIGHTNING-INDUCED IGNITIONS GIVEN THE PRESENCE OF DRY
TO VERY DRY FUELS. HOWEVER...WITHOUT STRONGER LARGE-SCALE ASCENT IN
AREAS OF RELATIVELY LOWER PW...DRY-THUNDERSTORM COVERAGE IS NOT
EXPECTED TO REACH SCATTERED LEVELS...THOUGH ISOLATED DRY
THUNDERSTORMS ARE ANTICIPATED. POTENTIAL FOR LIGHTNING-INDUCED
IGNITIONS WILL EXIST ON THE PERIPHERY OF RAIN CORES. GUSTY/ERRATIC
OUTFLOW WINDS MAY ALSO ACCOMPANY THIS ACTIVITY...POTENTIALLY
INFLUENCING ANY ONGOING AND/OR NEW FIRES. SIMILAR LIGHTNING-INDUCED
IGNITION POTENTIAL MAY LAST INTO THE OVERNIGHT HOURS TONIGHT.
DESPITE HIGHER BOUNDARY-LAYER RELATIVE HUMIDITY AT NIGHT...IGNITION
POTENTIAL WILL PERSIST OWING TO THE AFOREMENTIONED FUEL DRYNESS.

...PARTS OF CNTRL/ERN WA INTO N-CNTRL ORE EWD INTO NRN ID
PANHANDLE/NWRN MT...
MODEST FLOW IN THE LOW/MID LEVELS WILL SUPPORT SWLY TO WLY SFC WINDS
AROUND 10-20 MPH...WITH DOWNSLOPE-FLOW-ENHANCED WARMING/DRYING
SUPPORTING MINIMUM RH VALUES FROM THE UPPER TEENS TO THE 20S. THE
STRONGEST OF THESE WINDS ARE EXPECTED ACROSS PARTS OF CNTRL/ERN WA
INTO N-CNTRL ORE WHERE ELEVATED DESIGNATION IS IN EFFECT...AND
BORDERLINE-CRITICAL FIRE-WEATHER CONDITIONS CANNOT BE RULED OUT ON A
BRIEF/SPOTTY BASIS NEAR THE COLUMBIA RIVER. HOWEVER...CONFIDENCE IN
ANY MORE THAN SHORT-DURATION/LOCALIZED/MARGINAL CRITICAL CONDITIONS
IS TOO LIMITED FOR CRITICAL DESIGNATION WITHOUT STRONGER LOW-LEVEL
FLOW. RELATIVELY LIGHTER WINDS ARE EXPECTED ELSEWHERE ACROSS THE
REGION OUTSIDE OF THE ELEVATED AREA PRECLUDING LARGER AREAL EXTENT
OF THE ELEVATED HIGHLIGHT...THOUGH MARGINAL/BRIEF/SPOTTY ELEVATED
FIRE-WEATHER CONDITIONS CANNOT BE RULED OUT ELSEWHERE.

...PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT...




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