Fire Weather Outlook Discussion
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FNUS21 KWNS 210834
FWDDY1

DAY 1 FIRE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0334 AM CDT TUE APR 21 2015

VALID 211200Z - 221200Z

...SYNOPSIS...
DEEP CLOSED MID/UPPER LOW WILL SLOWLY DRIFT FROM THE UPPER GREAT
LAKES E/NE INTO SERN ONTARIO THROUGH THE PERIOD. A BELT OF ENHANCED
FLOW WILL EXIST ON ITS PERIPHERY...GENERALLY FROM THE NRN PLAINS TO
THE OH VALLEY/MIDWEST AND INTO NEW ENGLAND. MEANWHILE...A WEAK REX
BLOCK PATTERN ALONG THE WEST COAST WILL SLOWLY TRANSITION TO A MEAN
TROUGH...AS RIDGING ACROSS THE PAC NW PROGRESSES EWD AND A WEAK
MID/UPPER LOW PERSISTS OVER SRN CA. AT THE SFC...AN OCCLUDED LOW
WILL PERSIST OVER ERN ONTARIO/WRN QUEBEC. TO THE WEST...A COLD FRONT
WILL PUSH SOUTH ACROSS THE NRN/CNTRL PLAINS...WITH HIGH PRESSURE
BUILDING IN ITS WAKE. A BROAD AREA OF LOW PRESSURE WILL BE SITUATED
ACROSS THE INTER-MOUNTAIN WEST.

...PORTIONS OF THE MID/UPPER MO VALLEY...
WITH A CONTINUATION OF DEEP N/NWLY FLOW OVER THE REGION...WINDY
CONDITIONS WILL BE REALIZED WITH THE ONSET OF DIURNAL MIXING.
ALTHOUGH NOT AS STRONG AS THE PREVIOUS DAY...SUSTAINED WINDS OF
20-30 MPH WILL BE POSSIBLE. MOREOVER...WHILE SOME COOL-SEASON FUELS
/E.G. SHORTER GRASSES/ HAVE EXPERIENCED GREEN-UP...MANY
TALLER/WARM-SEASON FUELS REMAIN DORMANT AND PRE-CONDITIONED BY THE
WINDY/DRY DAY PRIOR TO THE PERIOD. IN TERMS OF RH VALUES...THE
N/NWLY FLOW AROUND THE WRN EDGE OF THE MID/UPPER LOW WILL CONTINUE
TO REINFORCE A DRY AIR MASS /CHARACTERIZED BY PWAT VALUES OF 0.2-0.3
IN/ OVER THE REGION. HOWEVER...DIURNAL MIXING/HEATING...ESPECIALLY
EARLIER IN THE DAY...MAY BE SLIGHTLY SUBDUED BY AN INCREASE IN
MID-LEVEL CLOUDS/MOISTURE AS A SUBTLE SHORTWAVE TROUGH /NOTED IN WV
IMAGERY OVER ERN SASKATCHEWAN AS OF 08Z/ AND ASSOCIATED FRONT CROSS
THE REGION. THEREFORE...WHILE RH VALUES MAY BRIEFLY FALL BELOW 20
PERCENT...IT SEEMS MORE LIKELY THAT WIDESPREAD MIN VALUES WILL BE IN
THE 20-25 PERCENT RANGE...WHICH IS SUPPORTED BY SSEO/SREF GUIDANCE.
THEREFORE...CONSIDERING THE RELATIVELY COOL DAYTIME TEMPS...A
CRITICAL DELINEATION WAS NOT INTRODUCED. HOWEVER...THE ELEVATED
DELINEATION WAS EXPANDED SLIGHTLY TO THE SW AND TO THE NORTH TO
ACCOUNT FOR THE LATEST OBSERVATIONAL/GUIDANCE TRENDS.

...PORTIONS OF SERN AZ/SRN NM...
AS SOME MODEST ENHANCEMENT OF MID-LEVEL FLOW OCCURS AHEAD OF THE
WEAK SRN-CA LOW...VERY DEEP DIURNAL MIXING AND RESULTANT VERTICAL
MOMENTUM TRANSFER WILL YIELD SUSTAINED SWLY WINDS AROUND 15-20 MPH.
WITH A DRY ANTECEDENT AIR MASS ESTABLISHED...RH VALUES WILL FALL
BELOW 10-15 PERCENT ACROSS MUCH OF THE DESERT SOUTHWEST. THE LACK OF
STRONGER FLOW ALOFT/LACK OF ANY ROBUST LOW-LEVEL MASS RESPONSE NEAR
THE REGION PRECLUDE THE NEED FOR A CRITICAL DELINEATION WITH THIS
FORECAST. AS SUCH...THE PREVIOUS ELEVATED DELINEATION HAS BEEN
MAINTAINED.

...CNTRL IL TO CNTRL OH...
LOCALIZED ELEVATED FIRE-WX CONDITIONS WILL BE POSSIBLE DURING THE
AFTERNOON/EARLY EVENING...AS STRONG WLY FLOW TO THE SOUTH OF THE
MAIN UPPER LOW PERSISTS OVER THE REGION. SUSTAINED WINDS OF 25-35
MPH WILL COMBINE WITH RH VALUES FALLING BELOW 30 PERCENT TO INCREASE
FIRE-WX CONCERNS. HOWEVER...LACK OF CONFIDENCE IN MIN RH VALUES
BELOW 25 PERCENT...AS WELL AS FUELS ACROSS THIS REGION BEING LESS
RECEPTIVE THAN THEY ARE OVER THE NRN PLAINS...PRECLUDES DELINEATION
AT THIS TIME.

..PICCA.. 04/21/2015

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




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