SPC Day 1 Fire Weather Outlook

DAY 1 FIRE WEATHER OUTLOOK
NWS STORM PREDICTION CENTER NORMAN OK
0353 AM CDT WED AUG 29 2012

VALID 291200Z - 301200Z

...CRITICAL FIRE WEATHER AREA FOR A LARGE PART OF MT...A SMALL PART
OF ERN ID...WRN AND PARTS OF CNTRL ND...NWRN SD...
...CRITICAL FIRE WEATHER AREA FOR MUCH OF NEB...A SMALL PART OF ERN
CO...NWRN KS...FAR SERN SD...FAR WRN IA...

...SYNOPSIS...
A MID-LEVEL TROUGH COMPOSED OF MULTIPLE SHORTWAVE IMPULSES --
EVIDENT IN EARLY-MORNING WATER VAPOR IMAGERY -- IS FORECAST TO TRACK
FROM THE PACIFIC NW ACROSS THE NRN GREAT BASIN AND NRN ROCKIES
BEFORE EVENTUALLY REACHING THE NRN PLAINS. THIS WILL AID IN THE
BREAKDOWN OF A RIDGE EXTENDING NORTH OF A BROAD WRN-CONUS
ANTICYCLONE...WHILE A ZONE OF STRONG FLOW ALOFT OVERLAYS PARTS OF
THE NWRN/N-CNTRL CONUS. IN ADDITION TO A SFC COLD FRONT ACCOMPANYING
THE WAVE...A FRONT/TROUGH WILL ALSO EXTEND OVER PARTS OF THE
NRN/CNTRL PLAINS TO THE SOUTH/SOUTHEAST OF WHICH THE SFC PRESSURE
GRADIENT WILL BE ENHANCED. ALSO OF NOTE...FOR MANY LOCATIONS OVER
THE NRN/CNTRL PLAINS...MODEL INITIALIZATION ERRORS APPEAR TO BE
SUBSTANTIALLY SMALLER FOR THE NAM MODEL COMPARED TO OTHER GUIDANCE.
THIS FORECAST CLOSELY FOLLOWS NAM MODEL AND NAM-BASED MODEL
SOLUTIONS -- E.G. NEMS-NMMB MEMBERS OF THE SREF AND 4-KM NAM OUTPUT.

...A LARGE PART OF MT...A SMALL PART OF ERN ID...WRN AND PARTS OF
CNTRL ND...NWRN SD...
SLY TO WLY WINDS...SHIFTING TO NWLY FOLLOWING THE PASSAGE OF THE
COLD FRONT...FROM 20 TO 25 MPH WITH HIGHER GUSTS ARE EXPECTED ACROSS
THE AREA. THIS WILL OCCUR AS THE MIXED-LAYER DEEPENS INTO THE
AFOREMENTIONED ZONE OF STRONGER FLOW ALOFT...AND AS AN ENHANCED
PRESSURE GRADIENT AFFECTS PARTS OF THE AREA IN ASSOCIATION WITH A
SFC LOW MOVING EWD ACROSS THE SRN CANADIAN PRAIRIES. RH VALUES ARE
EXPECTED TO FALL TO 7 TO 19 PERCENT -- LOWEST ACROSS PORTIONS OF ERN
ID -- AIDED BY DOWNSLOPE EFFECTS IN SOME AREAS. ALSO OF
NOTE...ISOLATED THUNDERSTORMS MAY OCCUR NEAR/AHEAD OF THE COLD FRONT
ACROSS CNTRL ND AMIDST THE DEEPLY MIXED BOUNDARY LAYER. WHILE
SUB-CLOUD EVAPORATIVE EFFECTS WILL LIMIT PRECIPITATION AMOUNTS...PW
VALUES AOA 0.85 INCH SHOULD PROMOTE WET-THUNDERSTORM AND MIXED
WET/DRY-THUNDERSTORM MODES AS OPPOSED TO A PURELY DRY-THUNDERSTORM
MODE. NEVERTHELESS...IGNITIONS COULD BE SUPPORTED FROM THESE
STORMS...ESPECIALLY OVER PERIPHERAL AREAS OF RAIN CORES.

...MUCH OF NEB...A SMALL PART OF ERN CO...NWRN KS...FAR SERN
SD...FAR WRN IA...
A TIGHT SFC PRESSURE GRADIENT AND A LOW-LEVEL JET MAX PERSISTING
THROUGH THE DAY ARE FORECAST TO SUPPORT SSWLY TO SWLY SFC WINDS OF
20-25 MPH WITH OCCASIONALLY HIGHER GUSTS. THESE WINDS ARE EXPECTED
TO COMBINE WITH CRITICALLY LOW RH VALUES OF 8-19 PERCENT -- LOWEST
ACROSS WRN/CNTRL PARTS OF THE CRITICAL AREA AND HIGHEST ACROSS ERN
PARTS OF THE CRITICAL AREA. THIS WILL OCCUR AS VERTICAL MIXING
INCREASES OWING TO SFC TEMPERATURES BECOMING HOT -- I.E. AROUND
95-103F. AND...WITH ONGOING DROUGHT CONDITIONS AND THE PRESENCE OF
DRY FUELS ACROSS THE AREA...CRITICAL FIRE WEATHER CONDITIONS ARE
EXPECTED.

...SURROUNDING THE CRITICAL AREAS ACROSS PORTIONS OF THE NRN/CNTRL
PLAINS...UPPER/MIDDLE MS VALLEY...NRN/CNTRL ROCKIES...NRN/CNTRL
GREAT BASIN...
IN ADVANCE OF A COLD FRONT THAT WILL CROSS PORTIONS OF THE
AREA...THE COMBINATION OF MINIMUM RH VALUES OF 10 PERCENT TO THE
LOWER 20S AND WIND SPEEDS OF 10 TO LOCALLY/BRIEFLY 20 MPH WILL YIELD
AN ELEVATED FIRE WEATHER THREAT. HOWEVER...IN THE ABSENCE OF
STRONGER DEEP-LAYER FLOW AND/OR A TIGHTER SFC PRESSURE
GRADIENT...CRITICALLY STRONG SUSTAINED WINDS ARE GENERALLY NOT
EXPECTED TO OCCUR ON ANY MORE THAN A BRIEF/SPOTTY BASIS OUTSIDE OF
THE CRITICAL AREAS. EXCEPTIONS MAY BE ACROSS NRN ND TO THE EAST OF
THE NWRN CRITICAL AREA...AND ACROSS PARTS OF IA TO THE EAST OF THE
SERN CRITICAL AREA. HOWEVER...RH VALUES ARE NOT CURRENTLY EXPECTED
TO BECOME CRITICALLY LOW IN THESE AREAS ON ANY MORE THAN A
BRIEF/SPOTTY BASIS AS THE DEPTH OF STRONGER MIXING SHOULD BE
RELATIVELY REDUCED AMIDST MODESTLY RICHER LOW-LEVEL MOISTURE.

..COHEN.. 08/29/2012

...PLEASE SEE WWW.SPC.NOAA.GOV/FIRE FOR GRAPHIC PRODUCT...
via SPC Forecast Products http://www.spc.noaa.gov/products/fire_wx/fwdy1.html